WorldWideScience

Sample records for closed-path eddy covariance

  1. Relative humidity effects on water vapour fluxes measured with closed-path eddy-covariance systems with short sampling lines

    DEFF Research Database (Denmark)

    Fratini, Gerardo; Ibrom, Andreas; Arriga, Nicola

    2012-01-01

    It has been formerly recognised that increasing relative humidity in the sampling line of closed-path eddy-covariance systems leads to increasing attenuation of water vapour turbulent fluctuations, resulting in strong latent heat flux losses. This occurrence has been analyzed for very long (50 m...... from eddy-covariance systems featuring short (4 m) and very short (1 m) sampling lines running at the same clover field and show that relative humidity effects persist also for these setups, and should not be neglected. Starting from the work of Ibrom and co-workers, we propose a mixed method...... and correction method proposed here is deemed applicable to closed-path systems featuring a broad range of sampling lines, and indeed applicable also to passive gases as a special case. The methods described in this paper are incorporated, as processing options, in the free and open-source eddy...

  2. Comparative CO2 flux measurements by eddy covariance technique using open- and closed-path gas analysers over the equatorial Pacific Ocean

    Directory of Open Access Journals (Sweden)

    Fumiyoshi Kondo

    2012-04-01

    Full Text Available Direct comparison of air–sea CO2 fluxes by open-path eddy covariance (OPEC and closed-path eddy covariance (CPEC techniques was carried out over the equatorial Pacific Ocean. Previous studies over oceans have shown that the CO2 flux by OPEC was larger than the bulk CO2 flux using the gas transfer velocity estimated by the mass balance technique, while the CO2 flux by CPEC agreed with the bulk CO2 flux. We investigated a traditional conflict between the CO2 flux by the eddy covariance technique and the bulk CO2 flux, and whether the CO2 fluctuation attenuated using the closed-path analyser can be measured with sufficient time responses to resolve small CO2 flux over oceans. Our results showed that the closed-path analyser using a short sampling tube and a high volume air pump can be used to measure the small CO2 fluctuation over the ocean. Further, the underestimated CO2 flux by CPEC due to the attenuated fluctuation can be corrected by the bandpass covariance method; its contribution was almost identical to that of H2O flux. The CO2 flux by CPEC agreed with the total CO2 flux by OPEC with density correction; however, both of them are one order of magnitude larger than the bulk CO2 flux.

  3. Comparative CO{sub 2} flux measurements by eddy covariance technique using open- and closed-path gas analysers over the equatorial Pacific Ocean

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, Fumiyoshi (Graduate School of Natural Science and Technology, Okayama Univ., Okayama (Japan); Atmosphere and Ocean Research Inst., Univ. of Tokyo, Tokyo (Japan)), Email: fkondo@aori.u-tokyo.ac.jp; Tsukamoto, Osamu (Graduate School of Natural Science and Technology, Okayama Univ., Okayama (Japan))

    2012-04-15

    Direct comparison of airsea CO{sub 2} fluxes by open-path eddy covariance (OPEC) and closed-path eddy covariance (CPEC) techniques was carried out over the equatorial Pacific Ocean. Previous studies over oceans have shown that the CO{sub 2} flux by OPEC was larger than the bulk CO{sub 2} flux using the gas transfer velocity estimated by the mass balance technique, while the CO{sub 2} flux by CPEC agreed with the bulk CO{sub 2} flux. We investigated a traditional conflict between the CO{sub 2} flux by the eddy covariance technique and the bulk CO{sub 2} flux, and whether the CO{sub 2} fluctuation attenuated using the closed-path analyser can be measured with sufficient time responses to resolve small CO{sub 2} flux over oceans. Our results showed that the closed-path analyser using a short sampling tube and a high volume air pump can be used to measure the small CO{sub 2} fluctuation over the ocean. Further, the underestimated CO{sub 2} flux by CPEC due to the attenuated fluctuation can be corrected by the bandpass covariance method; its contribution was almost identical to that of H{sub 2}O flux. The CO{sub 2} flux by CPEC agreed with the total CO{sub 2} flux by OPEC with density correction; however, both of them are one order of magnitude larger than the bulk CO{sub 2} flux

  4. Comparing laser-based open- and closed-path gas analyzers to measure methane fluxes using the eddy covariance method

    Science.gov (United States)

    Detto, Matteo; Verfaillie, Joseph; Anderson, Frank; Xu, Liukang; Baldocchi, Dennis

    2011-01-01

    Closed- and open-path methane gas analyzers are used in eddy covariance systems to compare three potential methane emitting ecosystems in the Sacramento-San Joaquin Delta (CA, USA): a rice field, a peatland pasture and a restored wetland. The study points out similarities and differences of the systems in field experiments and data processing. The closed-path system, despite a less intrusive placement with the sonic anemometer, required more care and power. In contrast, the open-path system appears more versatile for a remote and unattended experimental site. Overall, the two systems have comparable minimum detectable limits, but synchronization between wind speed and methane data, air density corrections and spectral losses have different impacts on the computed flux covariances. For the closed-path analyzer, air density effects are less important, but the synchronization and spectral losses may represent a problem when fluxes are small or when an undersized pump is used. For the open-path analyzer air density corrections are greater, due to spectroscopy effects and the classic Webb–Pearman–Leuning correction. Comparison between the 30-min fluxes reveals good agreement in terms of magnitudes between open-path and closed-path flux systems. However, the scatter is large, as consequence of the intensive data processing which both systems require.

  5. Eddy covariance measurements with a new fast-response, enclosed-path analyzer: Spectral characteristics and cross-system comparisons

    Science.gov (United States)

    K. Novick; J. Walker; W.S. Chan; A. Schmidt; C. Sobek; J.M. Vose

    2013-01-01

    A new class of enclosed path gas analyzers suitable for eddy covariance applications combines the advantages of traditional closed-path systems (small density corrections, good performance in poor weather) and open-path systems (good spectral response, low power requirements), and permits estimates of instantaneous gas mixing ratio. Here, the extent to which these...

  6. Corrigendum to “Relative humidity effects on water vapour fluxes measured with closed-path eddy-covariance systems with short sampling lines” [Agric. Forest Meteorol. 165 (2012) 53–63

    DEFF Research Database (Denmark)

    Fratini, Gerardo; Ibrom, Andreas; Arriga, Nicola

    2012-01-01

    It has been formerly recognised that increasing relative humidity in the sampling line of closed-path eddy-covariance systems leads to increasing attenuation of water vapour turbulent fluctuations, resulting in strong latent heat flux losses. This occurrence has been analyzed for very long (50 m...... from eddy-covariance systems featuring short (4 m) and very short (1 m) sampling lines running at the same clover field and show that relative humidity effects persist also for these setups, and should not be neglected. Starting from the work of Ibrom and co-workers, we propose a mixed method...... and correction method proposed here is deemed applicable to closed-path systems featuring a broad range of sampling lines, and indeed applicable also to passive gases as a special case. The methods described in this paper are incorporated, as processing options, in the free and open-source eddy...

  7. On the use of the Webb-Pearman-Leuning theory for closed-path eddy correlation measurements

    DEFF Research Database (Denmark)

    Ibrom, Andreas; Dellwik, Ebba; Larsen, Søren Ejling

    2007-01-01

    We consider an imperfection of real closed-path eddy correlation systems-the decoupling of the water vapour and CO2 concentrations-with respect to the application of the Webb-Pearman-Leuning (WPL) theory. It is described why and how the current application of the WPL theory needs to be adapted...... into account, over-corrected the annual flux by 21%, or 31 g m(-2) yr(-1), to which the decoupling effect contributed with 7%. We suggest either converting the raw data point-by-point to mixing ratios or using the uncorrected covariances of water vapour mole fractions with the vertical wind velocity that were...

  8. Evaluation of a lower-powered analyzer and sampling system for eddy-covariance measurements of nitrous oxide fluxes

    Directory of Open Access Journals (Sweden)

    S. E. Brown

    2018-03-01

    Full Text Available Nitrous oxide (N2O fluxes measured using the eddy-covariance method capture the spatial and temporal heterogeneity of N2O emissions. Most closed-path trace-gas analyzers for eddy-covariance measurements have large-volume, multi-pass absorption cells that necessitate high flow rates for ample frequency response, thus requiring high-power sample pumps. Other sampling system components, including rain caps, filters, dryers, and tubing, can also degrade system frequency response. This field trial tested the performance of a closed-path eddy-covariance system for N2O flux measurements with improvements to use less power while maintaining the frequency response. The new system consists of a thermoelectrically cooled tunable diode laser absorption spectrometer configured to measure both N2O and carbon dioxide (CO2. The system features a relatively small, single-pass sample cell (200 mL that provides good frequency response with a lower-powered pump ( ∼  250 W. A new filterless intake removes particulates from the sample air stream with no additional mixing volume that could degrade frequency response. A single-tube dryer removes water vapour from the sample to avoid the need for density or spectroscopic corrections, while maintaining frequency response. This eddy-covariance system was collocated with a previous tunable diode laser absorption spectrometer model to compare N2O and CO2 flux measurements for two full growing seasons (May 2015 to October 2016 in a fertilized cornfield in Southern Ontario, Canada. Both spectrometers were placed outdoors at the base of the sampling tower, demonstrating ruggedness for a range of environmental conditions (minimum to maximum daily temperature range: −26.1 to 31.6 °C. The new system rarely required maintenance. An in situ frequency-response test demonstrated that the cutoff frequency of the new system was better than the old system (3.5 Hz compared to 2.30 Hz and similar to that of a closed-path

  9. Evaluation of a lower-powered analyzer and sampling system for eddy-covariance measurements of nitrous oxide fluxes

    Science.gov (United States)

    Brown, Shannon E.; Sargent, Steve; Wagner-Riddle, Claudia

    2018-03-01

    Nitrous oxide (N2O) fluxes measured using the eddy-covariance method capture the spatial and temporal heterogeneity of N2O emissions. Most closed-path trace-gas analyzers for eddy-covariance measurements have large-volume, multi-pass absorption cells that necessitate high flow rates for ample frequency response, thus requiring high-power sample pumps. Other sampling system components, including rain caps, filters, dryers, and tubing, can also degrade system frequency response. This field trial tested the performance of a closed-path eddy-covariance system for N2O flux measurements with improvements to use less power while maintaining the frequency response. The new system consists of a thermoelectrically cooled tunable diode laser absorption spectrometer configured to measure both N2O and carbon dioxide (CO2). The system features a relatively small, single-pass sample cell (200 mL) that provides good frequency response with a lower-powered pump ( ˜ 250 W). A new filterless intake removes particulates from the sample air stream with no additional mixing volume that could degrade frequency response. A single-tube dryer removes water vapour from the sample to avoid the need for density or spectroscopic corrections, while maintaining frequency response. This eddy-covariance system was collocated with a previous tunable diode laser absorption spectrometer model to compare N2O and CO2 flux measurements for two full growing seasons (May 2015 to October 2016) in a fertilized cornfield in Southern Ontario, Canada. Both spectrometers were placed outdoors at the base of the sampling tower, demonstrating ruggedness for a range of environmental conditions (minimum to maximum daily temperature range: -26.1 to 31.6 °C). The new system rarely required maintenance. An in situ frequency-response test demonstrated that the cutoff frequency of the new system was better than the old system (3.5 Hz compared to 2.30 Hz) and similar to that of a closed-path CO2 eddy-covariance system (4

  10. Influences of various calculation options on heat, water and carbon fluxes determined by open- and closed-path eddy covariance methods

    Directory of Open Access Journals (Sweden)

    Masahito Ueyama

    2012-07-01

    Full Text Available Synthesis studies using multiple-site datasets for eddy covariance potentially contain uncertainties originating from the use of different flux calculation options, because the choice of the process for calculating half-hourly fluxes from raw time series data is left to individual researchers. In this study, we quantified the uncertainties associated with different flux calculation methods at seven sites. The differences in the half-hourly fluxes were small, generally of the order less than a few percentiles, but they were substantial for the annual fluxes. After the standardisation under current recommendations in the FLUXNET communities, we estimated the uncertainties in the annual fluxes associated with the flux calculations to be 2.6±2.7 W m−2 (the mean 90% ± confidence interval for the sensible heat flux, 72±37 g C m−2 yr−1 for net ecosystem exchange (NEE, 12±6% for evapotranspiration, 12±6% for gross primary productivity and 16±10% for ecosystem respiration. The self-heating correction strongly influenced the annual carbon balance (143±93 g C m−2 yr−1, not only for cold sites but also for warm sites, but did not fully account for differences between the open- and closed-path systems (413±189 g C m−2 yr−1.

  11. New challenges and opportunities in the eddy-covariance methodology for long-term monitoring networks

    Science.gov (United States)

    Papale, Dario; Fratini, Gerardo

    2013-04-01

    Eddy-covariance is the most direct and most commonly applied methodology for measuring exchange fluxes of mass and energy between ecosystems and the atmosphere. In recent years, the number of environmental monitoring stations deploying eddy-covariance systems increased dramatically at the global level, exceeding 500 sites worldwide and covering most climatic and ecological regions. Several long-term environmental research infrastructures such as ICOS, NEON and AmeriFlux selected the eddy-covariance as a method to monitor GHG fluxes and are currently collaboratively working towards defining common measurements standards, data processing approaches, QA/QC procedures and uncertainty estimation strategies, to the aim of increasing defensibility of resulting fluxes and intra and inter-comparability of flux databases. In the meanwhile, the eddy-covariance research community keeps identifying technical and methodological flaws that, in some cases, can introduce - and can have introduced to date - significant biases in measured fluxes or increase their uncertainty. Among those, we identify three issues of presumably greater concern, namely: (1) strong underestimation of water vapour fluxes in closed-path systems, and its dependency on relative humidity; (2) flux biases induced by erroneous measurement of absolute gas concentrations; (3) and systematic errors due to underestimation of vertical wind variance in non-orthogonal anemometers. If not properly addressed, these issues can reduce the quality and reliability of the method, especially as a standard methodology in long-term monitoring networks. In this work, we review the status of the art regarding such problems, and propose new evidences based on field experiments as well as numerical simulations. Our analyses confirm the potential relevance of these issues but also hint at possible coping approaches, to minimize problems during setup design, data collection and post-field flux correction. Corrections are under

  12. A compact and stable eddy covariance set-up for methane measurements using off-axis integrated cavity output spectroscopy

    Directory of Open Access Journals (Sweden)

    D. M. D. Hendriks

    2008-01-01

    Full Text Available A Fast Methane Analyzer (FMA is assessed for its applicability in a closed path eddy covariance field set-up in a peat meadow. The FMA uses off-axis integrated cavity output spectroscopy combined with a highly specific narrow band laser for the detection of CH4 and strongly reflective mirrors to obtain a laser path length of 2–20×103 m. Statistical testing and a calibration experiment showed high precision (7.8×10−3 ppb and accuracy (<0.30% of the instrument, while no drift was observed. The instrument response time was determined to be 0.10 s. In the field set-up, the FMA is attached to a scroll pump and combined with a 3-axis ultrasonic anemometer and an open path infrared gas analyzer for measurements of carbon dioxide and water vapour. The power-spectra and co-spectra of the instruments were satisfactory for 10 Hz sampling rates.

    Due to erroneous measurements, spikes and periods of low turbulence the data series consisted for 26% of gaps. Observed CH4 fluxes consisted mainly of emission, showed a diurnal cycle, but were rather variable over. The average CH4 emission was 29.7 nmol m−2 s−1, while the typical maximum CH4 emission was approximately 80.0 nmol m−2 s−1 and the typical minimum flux was approximately 0.0 nmol m−2 s−1. The correspondence of the measurements with flux chamber measurements in the footprint was good and the observed CH4 emission rates were comparable with eddy covariance CH4 measurements in other peat areas.

    Additionally, three measurement techniques with lower sampling frequencies were simulated, which might give the possibility to measure CH4 fluxes without an external pump and save energy. Disjunct eddy covariance appeared to be the most reliable substitute for 10 Hz eddy covariance, while relaxed eddy accumulation gave

  13. LOW-POWER SOLUTION FOR EDDY COVARIANCE MEASUREMENTS OF METHANE FLUX

    Science.gov (United States)

    Anderson, T.; Burba, G. G.; Komissarov, A.; McDermitt, D. K.; Xu, L.; Zona, D.; Oechel, W. C.; Schedlbauer, J. L.; Oberbauer, S. F.; Riensche, B.; Allyn, D.

    2009-12-01

    Open-path analyzers offer a number of advantages for measuring methane fluxes, including undisturbed in-situ flux measurements, spatial integration using the Eddy Covariance approach, zero frequency response errors due to tube attenuation, confident water and thermal density terms from co-located fast measurements of water and sonic temperature, and possibility of remote and mobile solar-powered or small-generator-powered deployments due to lower power demands in the absence of a pump. The LI-7700 open-path methane analyzer is a VCSEL (vertical-cavity surface-emitting laser)-based instrument. It employs an open Herriott cell and measures levels of methane with RMS noise below 5 ppb at 10 Hz sampling in controlled laboratory conditions. The power consumption of the stand-alone LI-7700 in steady-state is about 8W, so it can be deployed in any methane-generating location of interest on a portable or mobile solar-powered tower, and it does not have to have grid power or permanent industrial generator. Eddy Covariance measurements of methane flux using the LI-7700 open-path methane analyzer were conducted in 2006-2009 in five ecosystems with contrasting weather and moisture conditions: (1) sawgrass wetland in the Florida Everglades; (2) coastal wetlands in an Arctic tundra; and (3) pacific mangroves in Mexico; (4) maize field and (5) ryegrass field in Nebraska. Methane co-spectra behaved in a manner similar to that of the co-spectra of carbon dioxide, water vapor, and air temperature, demonstrating that the LI-7700 adequately measured fluctuations in methane concentration across the whole spectrum of frequencies contributing to vertical atmospheric turbulent transport at the experimental sites. All co-spectra also closely followed the Kaimal model, and demonstrated good agreement with another methane co-spectrum obtained with a TDLS (Tunable Diode Laser Spectroscope; Unisearch Associates, Inc.) over a peatland. Overall, hourly methane fluxes ranged from near-zero at

  14. N2O fluxes over a corn field from an open-path, laser-based eddy covariance system and static chambers

    Science.gov (United States)

    Tao, L.; Pan, D.; Gelfand, I.; Abraha, M.; Moyer, R.; Poe, A.; Sun, K.; Robertson, P.; Zondlo, M. A.

    2015-12-01

    Nitrous oxide (N2O) is important greenhouse and ozone-depleting gase. Although many efforts have been paid to N2O emissions, the spatial and temporal variability of N2O emissions still subject to large uncertainty. Application of the eddy covariance method for N2O emissions research would allow continuous ecosystem level flux measurements. The caveat, however, is need for high precision and high frequency measurements in field. In this study, an open-path, quantum cascade-laser-based eddy covariance N2O sensor has been deployed nearly continuously since May 2015 over a corn field at the W.K. Kellogg Biological Station site in SW Michigan. The field precision of the N2O sensor was assessed to be 0.1 ppbv at 10 Hz, and the total consumption was ~ 40 W, allowing the system to be powered solely by solar panels. The stability of the sensor under different temperature and humidity was tested within an environmental chamber. Spectroscopic experiments and cospectra analyses were carried out to study specific corrections associated with the sensor for eddy covariance techniques, including the line broadening effect due to water vapor and high frequency flux attenuation owning to sample path averaging. Ogive analyses indicated that the high-frequency N2O flux loss due to various damping effects was comparable to those of the CO2 flux. The detection limit of flux was estimated to be 0.3 ng N s-1 m-2 with a flux averaging interval of 30 minutes. The results from the EC system were also compared with ground measurements by standard static chambers (SC). Overall, more than 150 individual chamber measurements were taken within the footprint of the EC system. We found good correlation between the EC and SC methods given the spatiotemporal differences between the two techniques (R2 = 0.75). Both methods detected increased emissions during afternoon as compared to morning and night hours. Differences between EC and SC were also studied by investigating spatial variability with a

  15. Field intercomparison of four methane gas analyzers suitable for eddy covariance flux measurements

    Science.gov (United States)

    Peltola, O.; Mammarella, I.; Haapanala, S.; Burba, G.; Vesala, T.

    2013-06-01

    Performances of four methane gas analyzers suitable for eddy covariance measurements are assessed. The assessment and comparison was performed by analyzing eddy covariance data obtained during summer 2010 (1 April to 26 October) at a pristine fen, Siikaneva, Southern Finland. High methane fluxes with pronounced seasonality have been measured at this fen. The four participating methane gas analyzers are commercially available closed-path units TGA-100A (Campbell Scientific Inc., USA), RMT-200 (Los Gatos Research, USA), G1301-f (Picarro Inc., USA) and an early prototype open-path unit Prototype-7700 (LI-COR Biosciences, USA). The RMT-200 functioned most reliably throughout the measurement campaign, during low and high flux periods. Methane fluxes from RMT-200 and G1301-f had the smallest random errors and the fluxes agree remarkably well throughout the measurement campaign. Cospectra and power spectra calculated from RMT-200 and G1301-f data agree well with corresponding temperature spectra during a high flux period. None of the gas analyzers showed statistically significant diurnal variation for methane flux. Prototype-7700 functioned only for a short period of time, over one month, in the beginning of the measurement campaign during low flux period, and thus, its overall accuracy and season-long performance were not assessed. The open-path gas analyzer is a practical choice for measurement sites in remote locations due to its low power demand, whereas for G1301-f methane measurements interference from water vapor is straightforward to correct since the instrument measures both gases simultaneously. In any case, if only the performance in this intercomparison is considered, RMT-200 performed the best and is the recommended choice if a new fast response methane gas analyzer is needed.

  16. Strong low-pass filtering effects on water vapour flux measurements with closed-path eddy correlation systems

    DEFF Research Database (Denmark)

    Ibrom, Andreas; Dellwik, Ebba; Flyvbjerg, Henrik K.

    2007-01-01

    datasets for this substantial measurement error. In contrast to earlier studies, a large number of spectra and raw data have been used in the analysis to define the low-pass filtering characteristic of the EC system. This revealed that the cut-off frequency of the closed-path EC system for water vapour......Turbulent water vapour fluxes measured with closed-path eddy correlation (EC) systems are unintentionally low-pass filtered by the system in a manner that varies with environmental conditions. Why and how is described here. So is the practical method that systematically corrects long-term flux...... concentration measurements decreases exponentially with increasing relative humidity. After correction for this unintended filtering, the fluxes are consistent with CO2 and H2O fluxes that were measured with an open-path sensor at the same time. The correction of water vapour flux measurements over a Beech...

  17. Eddy-covariance methane flux measurements over a European beech forest

    Science.gov (United States)

    Gentsch, Lydia; Siebicke, Lukas; Knohl, Alexander

    2015-04-01

    The role of forests in global methane (CH4) turnover is currently not well constrained, partially because of the lack of spatially integrative forest-scale measurements of CH4 fluxes. Soil chamber measurements imply that temperate forests generally act as CH4 sinks. Upscaling of chamber observations to the forest scale is however problematic, if the upscaling is not constrained by concurrent 'top-down' measurements, such as of the eddy-covariance type, which provide sufficient integration of spatial variations and of further potential CH4 flux components within forest ecosystems. Ongoing development of laser absorption-based optical instruments, resulting in enhanced measurement stability, precision and sampling speed, has recently improved the prospects for meaningful eddy-covariance measurements at sites with presumably low CH4 fluxes, hence prone to reach the flux detection limit. At present, we are launching eddy-covariance CH4 measurements at a long-running ICOS flux tower site (Hainich National Park, Germany), located in a semi natural, unmanaged, beech dominated forest. Eddy-covariance measurements will be conducted with a laser spectrometer for parallel CH4, H2Ov and CO2 measurements (FGGA, Los Gatos Research, USA). Independent observations of the CO2 flux by the FGGA and a standard Infrared Gas Analyser (LI-7200, LI-COR, USA) will allow to evaluate data quality of measured CH4 fluxes. Here, we want to present first results with a focus on uncertainties of the calculated CH4 fluxes with regard to instrument precision, data processing and site conditions. In future, we plan to compare eddy-covariance flux estimates to side-by-side turbulent flux observations from a novel eddy accumulation system. Furthermore, soil CH4 fluxes will be measured with four automated chambers situated within the tower footprint. Based on a previous soil chamber study at the same site, we expect the Hainich forest site to act as a CH4 sink. However, we hypothesize that our

  18. Eddy covariance methane measurements at a Ponderosa pine plantation in California

    Directory of Open Access Journals (Sweden)

    T. Röckmann

    2009-11-01

    Full Text Available Long term methane flux measurements have been mostly performed with plant or soil enclosure techniques on specific components of an ecosystem. New fast response methane analyzers make it possible to use the eddy covariance (EC technique instead. The EC technique is advantageous because it allows continuous flux measurements integrating over a larger and more representative area including the complete ecosystem, and allows fluxes to be observed as environmental conditions change naturally without disturbance. We deployed the closed-path Fast Methane analyzer (FMA from Los Gatos Research Ltd and demonstrate its performance for EC measurements at a Ponderosa pine plantation at the Blodgett Forest site in central California. The fluctuations of the CH4 concentration measured at 10 Hz appear to be small and their standard deviation is comparable to the magnitude of the signal noise (±5 ppbv. Consequently, the power spectra typically have a white noise signature at the high frequency end (a slope of +1. Nevertheless, in the frequency range important for turbulent exchange, the cospectra of CH4 compare very well with all other scalar cospectra confirming the quality of the FMA measurements are good for the EC technique. We furthermore evaluate the complications of combined open and closed-path measurements when applying the Webb-Pearman-Leuning (WPL corrections (Webb et al., 1980 and the consequences of a phase lag between the water vapor and methane signal inside the closed path system. The results of diurnal variations of CH4 concentrations and fluxes are summarized and compared to the monthly results of process-based model calculations.

  19. Eddy Covariance Measurements of Methane Flux at Remote Sites with New Low-Power Lightweight Fast Gas Analyzer

    Science.gov (United States)

    Xu, Liukang; Burba, George; Schedlbauer, Jessica; Zona, Donatella; McDermitt, Dayle K.; Anderson, Tyler; Oberbauer, Steven; Oechel, Walter; Komissarov, Anatoly; Riensche, Brad

    2010-05-01

    Majority of natural methane production happens at remote unpopulated areas in ecosystems with little or no infrastructure or easily available grid power, such as arctic and boreal wetlands, tropical mangroves, etc. Present approaches for direct measurements of CH4 fluxes rely on fast closed-path analyzers, which have to work under significantly reduced pressures, and require powerful pumps and grid power. Power and labor demands may be reasons why CH4 flux is often measured at locations with good infrastructure and grid power, and not with high CH4 production. An instrument was developed to allow Eddy Covariance measurements of CH4 flux with power consumption 30-150 times below presently available technologies. This instrument, LI-7700, uses proposed extremely low-power technology would allows placing methane Eddy Covariance stations in the middle of the source (wetland, rice paddy, forest, etc.) in the absence of the grid power. This could significantly expand the Eddy Covariance CH4 flux measurements coverage, and possibly, significantly improve the budget estimates of world CH4 emissions and budget. Various prototypes of the LI-7700 were field-tested for three seasons at the remote site in middle of Everglades National Park (Florida, USA) using solar panels, at three stationary and several mobile sites during three seasons at remote Arctic wetlands near Barrow (Alaska, USA), in the tropical mangroves near La Paz (Mexico) using portable generator, and in bare agricultural field near Mead (Nebraska, USA) during 2005 through 2010. Latest data on CH4 concentration, co-spectra and fluxes, and latest details of instrumental design are examined in this presentation. Overall, hourly methane fluxes ranged from near-zero at night to about 4 mg m-2 h-1 in midday in arctic tundra. Observed fluxes were within the ranges reported in the literature for a number of wetlands in North America, including the Everglades wetlands. Diurnal patterns were similar to those measured by

  20. Covariant path integrals on hyperbolic surfaces

    International Nuclear Information System (INIS)

    Schaefer, J.

    1997-01-01

    DeWitt close-quote s covariant formulation of path integration [B. De Witt, open-quotes Dynamical theory in curved spaces. I. A review of the classical and quantum action principles,close quotes Rev. Mod. Phys. 29, 377 endash 397 (1957)] has two practical advantages over the traditional methods of open-quotes lattice approximations;close quotes there is no ordering problem, and classical symmetries are manifestly preserved at the quantum level. Applying the spectral theorem for unbounded self-adjoint operators, we provide a rigorous proof of the convergence of certain path integrals on Riemann surfaces of constant curvature -1. The Pauli endash DeWitt curvature correction term arises, as in DeWitt close-quote s work. Introducing a Fuchsian group Γ of the first kind, and a continuous, bounded, Γ-automorphic potential V, we obtain a Feynman endash Kac formula for the automorphic Schroedinger equation on the Riemann surface Γ backslash H. We analyze the Wick rotation and prove the strong convergence of the so-called Feynman maps [K. D. Elworthy, Path Integration on Manifolds, Mathematical Aspects of Superspace, edited by Seifert, Clarke, and Rosenblum (Reidel, Boston, 1983), pp. 47 endash 90] on a dense set of states. Finally, we give a new proof of some results in C. Grosche and F. Steiner, open-quotes The path integral on the Poincare upper half plane and for Liouville quantum mechanics,close quotes Phys. Lett. A 123, 319 endash 328 (1987). copyright 1997 American Institute of Physics

  1. Eddy Covariance Measurements of the Sea-Spray Aerosol Flu

    Science.gov (United States)

    Brooks, I. M.; Norris, S. J.; Yelland, M. J.; Pascal, R. W.; Prytherch, J.

    2015-12-01

    Historically, almost all estimates of the sea-spray aerosol source flux have been inferred through various indirect methods. Direct estimates via eddy covariance have been attempted by only a handful of studies, most of which measured only the total number flux, or achieved rather coarse size segregation. Applying eddy covariance to the measurement of sea-spray fluxes is challenging: most instrumentation must be located in a laboratory space requiring long sample lines to an inlet collocated with a sonic anemometer; however, larger particles are easily lost to the walls of the sample line. Marine particle concentrations are generally low, requiring a high sample volume to achieve adequate statistics. The highly hygroscopic nature of sea salt means particles change size rapidly with fluctuations in relative humidity; this introduces an apparent bias in flux measurements if particles are sized at ambient humidity. The Compact Lightweight Aerosol Spectrometer Probe (CLASP) was developed specifically to make high rate measurements of aerosol size distributions for use in eddy covariance measurements, and the instrument and data processing and analysis techniques have been refined over the course of several projects. Here we will review some of the issues and limitations related to making eddy covariance measurements of the sea spray source flux over the open ocean, summarise some key results from the last decade, and present new results from a 3-year long ship-based measurement campaign as part of the WAGES project. Finally we will consider requirements for future progress.

  2. Quantification of surface energy fluxes from a small water body using scintillometry and eddy covariance

    DEFF Research Database (Denmark)

    McGloin, Ryan; McGowan, Hamish; McJannet, David

    2014-01-01

    Accurate quantification of evaporation from small water storages is essential for water management and planning, particularly in water-scarce regions. In order to ascertain suitable methods for direct measurement of evaporation from small water bodies, this study presents a comparison of eddy......% greater than eddy covariance measurements. We suggest possible reasons for this difference and provide recommendations for further research for improving measurements of surface energy fluxes over small water bodies using eddy covariance and scintillometry. Key Points Source areas for Eddy covariance...... and scintillometry were on the water surface Reasonable agreement was shown between the sensible heat flux measurements Scintillometer estimates of latent heat flux were greater than eddy covariance...

  3. Estimating surface fluxes using eddy covariance and numerical ogive optimization

    DEFF Research Database (Denmark)

    Sievers, J.; Papakyriakou, T.; Larsen, Søren Ejling

    2015-01-01

    Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low-frequency con......Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low...

  4. Estimating local atmosphere-surface fluxes using eddy covariance and numerical Ogive optimization

    DEFF Research Database (Denmark)

    Sievers, Jakob; Papakyriakou, Tim; Larsen, Søren

    2014-01-01

    Estimating representative surface-fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modeling efforts, low-frequency cont......Estimating representative surface-fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modeling efforts, low...

  5. Elucidating Carbon Exchange at the Regional Scale Via Airborne Eddy Covariance Flux Measurements

    Science.gov (United States)

    Hannun, R. A.; Wolfe, G. M.; Kawa, S. R.; Newman, P. A.; Hanisco, T. F.; Diskin, G. S.; DiGangi, J. P.; Nowak, J. B.; Barrick, J. D. W.; Thornhill, K. L., II; Noormets, A.; Vargas, R.; Clark, K. L.; Kustas, W. P.

    2017-12-01

    Direct flux observations from aircraft provide a unique tool for probing greenhouse gas (GHG) sources and sinks on a regional scale. Airborne eddy covariance, which relies on high-frequency, simultaneous measurements of fluctuations in concentration and vertical wind speed, is a robust method for quantifying surface-atmosphere exchange. We have assembled and flown an instrument payload onboard the NASA C-23 Sherpa aircraft capable of measuring CO2, CH4, H2O, and heat fluxes. Flights for the Carbon Airborne Flux Experiment (CARAFE) took place during September 2016 and May 2017 based out of Wallops Flight Facility, VA. Flight tracks covered a variety of ecosystems and land-use types in the Mid-Atlantic, including forests, croplands, and wetlands. Carbon fluxes are derived using eddy covariance and wavelet analysis. Our results show a strong drawdown of CO2 and near-zero CH4 emissions from crops and dry-land forest, but seasonally strong CH4 flux from wetland forest. CARAFE flux data will also be compared with observations from several flux towers along the flight path to complement the airborne measurements. We will further assess the effects of land surface type and seasonal variability in carbon exchange. Regional-scale flux observations from CARAFE supply a useful constraint for improving top-down and bottom up estimates of carbon sources and sinks.

  6. A comparison of methane emission measurements using eddy covariance and manual and automated chamber-based techniques in Tibetan Plateau alpine wetland

    International Nuclear Information System (INIS)

    Yu, Lingfei; Wang, Hao; Wang, Guangshuai; Song, Weimin; Huang, Yao; Li, Sheng-Gong; Liang, Naishen; Tang, Yanhong; He, Jin-Sheng

    2013-01-01

    Comparing of different CH 4 flux measurement techniques allows for the independent evaluation of the performance and reliability of those techniques. We compared three approaches, the traditional discrete Manual Static Chamber (MSC), Continuous Automated Chamber (CAC) and Eddy Covariance (EC) methods of measuring the CH 4 fluxes in an alpine wetland. We found a good agreement among the three methods in the seasonal CH 4 flux patterns, but the diurnal patterns from both the CAC and EC methods differed. While the diurnal CH 4 flux variation from the CAC method was positively correlated with the soil temperature, the diurnal variation from the EC method was closely correlated with the solar radiation and net CO 2 fluxes during the daytime but was correlated with the soil temperature at nighttime. The MSC method showed 25.3% and 7.6% greater CH 4 fluxes than the CAC and EC methods when measured between 09:00 h and 12:00 h, respectively. -- Highlights: •Chamber and eddy covariance methods showed similar seasonal CH 4 flux patterns. •Chamber and eddy covariance methods showed different diurnal CH 4 flux patterns. •Static chamber methods gave a higher magnitude of CH 4 flux. -- The chamber-based methods and the eddy covariance method showed similar seasonal CH 4 flux patterns, but the manual static chamber method resulted in a higher CH 4 flux measurement

  7. Eddy Covariance Method for CO2 Emission Measurements: CCS Applications, Principles, Instrumentation and Software

    Science.gov (United States)

    Burba, George; Madsen, Rod; Feese, Kristin

    2013-04-01

    The Eddy Covariance method is a micrometeorological technique for direct high-speed measurements of the transport of gases, heat, and momentum between the earth's surface and the atmosphere. Gas fluxes, emission and exchange rates are carefully characterized from single-point in-situ measurements using permanent or mobile towers, or moving platforms such as automobiles, helicopters, airplanes, etc. Since the early 1990s, this technique has been widely used by micrometeorologists across the globe for quantifying CO2 emission rates from various natural, urban and agricultural ecosystems [1,2], including areas of agricultural carbon sequestration. Presently, over 600 eddy covariance stations are in operation in over 120 countries. In the last 3-5 years, advancements in instrumentation and software have reached the point when they can be effectively used outside the area of micrometeorology, and can prove valuable for geological carbon capture and sequestration, landfill emission measurements, high-precision agriculture and other non-micrometeorological industrial and regulatory applications. In the field of geological carbon capture and sequestration, the magnitude of CO2 seepage fluxes depends on a variety of factors. Emerging projects utilize eddy covariance measurement to monitor large areas where CO2 may escape from the subsurface, to detect and quantify CO2 leakage, and to assure the efficiency of CO2 geological storage [3,4,5,6,7,8]. Although Eddy Covariance is one of the most direct and defensible ways to measure and calculate turbulent fluxes, the method is mathematically complex, and requires careful setup, execution and data processing tailor-fit to a specific site and a project. With this in mind, step-by-step instructions were created to introduce a novice to the conventional Eddy Covariance technique [9], and to assist in further understanding the method through more advanced references such as graduate-level textbooks, flux networks guidelines, journals

  8. An estimate of the terrestrial carbon budget of Russia using inventory-based, eddy covariance and inversion methods

    Directory of Open Access Journals (Sweden)

    A. J. Dolman

    2012-12-01

    Full Text Available We determine the net land to atmosphere flux of carbon in Russia, including Ukraine, Belarus and Kazakhstan, using inventory-based, eddy covariance, and inversion methods. Our high boundary estimate is −342 Tg C yr−1 from the eddy covariance method, and this is close to the upper bounds of the inventory-based Land Ecosystem Assessment and inverse models estimates. A lower boundary estimate is provided at −1350 Tg C yr−1 from the inversion models. The average of the three methods is −613.5 Tg C yr−1. The methane emission is estimated separately at 41.4 Tg C yr−1.

    These three methods agree well within their respective error bounds. There is thus good consistency between bottom-up and top-down methods. The forests of Russia primarily cause the net atmosphere to land flux (−692 Tg C yr−1 from the LEA. It remains however remarkable that the three methods provide such close estimates (−615, −662, −554 Tg C yr–1 for net biome production (NBP, given the inherent uncertainties in all of the approaches. The lack of recent forest inventories, the few eddy covariance sites and associated uncertainty with upscaling and undersampling of concentrations for the inversions are among the prime causes of the uncertainty. The dynamic global vegetation models (DGVMs suggest a much lower uptake at −91 Tg C yr−1, and we argue that this is caused by a high estimate of heterotrophic respiration compared to other methods.

  9. Measuring evapotranspiration using an eddy covariance system over the Albany Thicket of the Eastern Cape, South Africa

    Science.gov (United States)

    Gwate, O.; Mantel, Sukhmani K.; Palmer, Anthony R.; Gibson, Lesley A.

    2016-10-01

    Determining water and carbon fluxes over a vegetated surface is important in a context of global environmental changes and the fluxes help in understanding ecosystem functioning. Pursuant to this, the study measured evapotranspiration (ET) using an eddy covariance (EC) system installed over an intact example of the Albany Thicket (AT) vegetation in the Eastern Cape, South Africa. Environmental constraints to ET were also assessed by examining the response of ET to biotic and abiotic factors. The EC system comprised of an open path Infrared Gas Analyser and Sonic anemometer and an attendant weather station to measure bi-meteorological variables. Post processing of eddy covariance data was conducted using EddyPro software. Quality assessment of fluxes was also performed and rejected and missing data were filled using the method of mean diurnal variations (MDV). Much of the variation in ET was accounted for by the leaf area index (LAI, p water storage capacity of the vegetation and the possibility of vegetation accessing ground water. Most of the net radiation was consumed by sensible heat flux and this means that ET in the area is essentially water limited since abundant energy was available to drive turbulent transfers of energy. Understanding the environmental constraints to ET is crucial in predicting the ecosystem response to environmental forces such as climate change.

  10. Uncertainties in surface mass and energy flux estimates due to different eddy covariance sensors and technical set-up

    Science.gov (United States)

    Arriga, Nicola; Fratini, Gerardo; Forgione, Antonio; Tomassucci, Michele; Papale, Dario

    2010-05-01

    Eddy covariance is a well established and widely used methodology for the measurement of turbulent fluxes of mass and energy in the atmospheric boundary layer, in particular to estimate CO2/H2O and heat exchange above ecologically relevant surfaces (Aubinet 2000, Baldocchi 2003). Despite its long term application and theoretical studies, many issues are still open about the effect of different experimental set-up on final flux estimates. Open issues are the evaluation of the performances of different kind of sensors (e.g. open path vs closed path infra-red gas analysers, vertical vs horizontal mounting ultrasonic anemometers), the quantification of the impact of corresponding physical corrections to be applied to get robust flux estimates taking in account all processes concurring to the measurement (e.g. the so-called WPL term, signal attenuation due to air sampling system for closed path analyser, relative position of analyser and anemometer) and the differences between several data transmission protocols used (analogue, digital RS-232, SDM). A field experiment was designed to study these issues using several instruments among those most used within the Fluxnet community and to compare their performances under conditions supposed to be critical: rainy and cold weather conditions for open-path analysers (Burba 2008), water transport and absorption at high air relative humidity conditions for closed-path systems (Ibrom, 2007), frequency sampling limits and recorded data robustness due to different transmission protocols (RS232, SDM, USB, Ethernet) and finally the effect of the displacement between anemometer and analyser using at least two identical analysers placed at different horizontal and vertical distances from the anemometer. Aim of this experiment is to quantify the effect of several technical solutions on the final estimates of fluxes measured at a point in the space and if they represent a significant source of uncertainty for mass and energy cycle

  11. Comparison of Sensible Heat Flux from Eddy Covariance and Scintillometer over different land surface conditions

    Science.gov (United States)

    Zeweldi, D. A.; Gebremichael, M.; Summis, T.; Wang, J.; Miller, D.

    2008-12-01

    The large source of uncertainty in satellite-based evapotranspiration algorithm results from the estimation of sensible heat flux H. Traditionally eddy covariance sensors, and recently large-aperture scintillometers, have been used as ground truth to evaluate satellite-based H estimates. The two methods rely on different physical measurement principles, and represent different foot print sizes. In New Mexico, we conducted a field campaign during summer 2008 to compare H estimates obtained from the eddy covariance and scintillometer methods. During this field campaign, we installed sonic anemometers; one propeller eddy covariance (OPEC) equipped with net radiometer and soil heat flux sensors; large aperture scintillometer (LAS); and weather station consisting of wind speed, direction and radiation sensors over three different experimental areas consisting of different roughness conditions (desert, irrigated area and lake). Our results show the similarities and differences in H estimates obtained from these various methods over the different land surface conditions. Further, our results show that the H estimates obtained from the LAS agree with those obtained from the eddy covariance method when high frequency thermocouple temperature, instead of the typical weather station temperature measurements, is used in the LAS analysis.

  12. Integrating lysimeter drainage and eddy covariance flux measurements in a groundwater recharge model

    DEFF Research Database (Denmark)

    Vasquez, Vicente; Thomsen, Anton Gårde; Iversen, Bo Vangsø

    2015-01-01

    Field scale water balance is difficult to characterize because controls exerted by soils and vegetation are mostly inferred from local scale measurements with relatively small support volumes. Eddy covariance flux and lysimeters have been used to infer and evaluate field scale water balances...... because they have larger footprint areas than local soil moisture measurements.. This study quantifies heterogeneity of soil deep drainage (D) in four 12.5 m2 repacked lysimeters, compares evapotranspiration from eddy covariance (ETEC) and mass balance residuals of lysimeters (ETwbLys), and models D...

  13. The energy balance experiment EBEX-2000. Part II: Intercomparison of eddy-covariance sensors and post-field data processing methods

    OpenAIRE

    Mauder, M.; Oncley, S.P.; Vogt, R.; Weidinger, T.; Ribeiro, L.; Bernhofer, C.; Foken, T.; Kohsiek, W.; Bruin, de, H.A.R.; Liu, H.

    2007-01-01

    The eddy-covariance method is the primary way of measuring turbulent fluxes directly. Many investigators have found that these flux measurements often do not satisfy a fundamental criterion¿closure of the surface energy balance. This study investigates to what extent the eddy-covariance measurement technology can be made responsible for this deficiency, in particular the effects of instrumentation or of the post-field data processing. Therefore, current eddy-covariance sensors and several pos...

  14. Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment

    NARCIS (Netherlands)

    Peltola, O.; Hensen, A.; Helfter, C.; Belelli Marchesini, L.; Bosveld, F.C.; Bulk, van de W.C.M.; Elbers, J.A.; Haapanala, S.; Holst, J.; Laurila, T.; Lindroth, A.; Nemitz, E.; Röckmann, T.; Vermeulen, A.T.; Mammarella, I.

    2014-01-01

    The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying

  15. Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements : the InGOS inter-comparison field experiment

    NARCIS (Netherlands)

    Peltola, O.; Hensen, A.; Helfter, C.; Belelli Marchesini, L.; Bosveld, F. C.; Van Den Bulk, W. C M; Elbers, J. A.; Haapanala, S.; Holst, J.; Laurila, T.; Lindroth, A.; Nemitz, E.; Röckmann, T.; Vermeulen, A. T.; Mammarella, I.

    2014-01-01

    The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying

  16. Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment

    NARCIS (Netherlands)

    Peltola, O.; Hensen, A.; Helfter, C.; Belelli Marchesini, L.; Bosveld, F. C.; Van Den Bulk, W. C. M.; Elbers, J. A.; Haapanala, S.; Holst, J.; Laurila, T.; Lindroth, A.; Nemitz, E.; Röckmann, T.; Vermeulen, A. T.; Mammarella, I.

    2014-01-01

    The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimize the effect of varying

  17. The energy balance experiment EBEX-2000. Part II: Intercomparison of eddy-covariance sensors and post-field data processing methods

    NARCIS (Netherlands)

    Mauder, M.; Oncley, S.P.; Vogt, R.; Weidinger, T.; Ribeiro, L.; Bernhofer, C.; Foken, T.; Kohsiek, W.; Bruin, de H.A.R.; Liu, H.

    2007-01-01

    The eddy-covariance method is the primary way of measuring turbulent fluxes directly. Many investigators have found that these flux measurements often do not satisfy a fundamental criterion¿closure of the surface energy balance. This study investigates to what extent the eddy-covariance measurement

  18. Eddy covariance methane measurements at a Ponderosa pine plantation in California

    NARCIS (Netherlands)

    Smeets, C.J.P.P.; Holzinger, R.; Vigano, I.; Goldstein, A.H.; Röckmann, T.

    2009-01-01

    Long term methane flux measurements have been mostly performed with plant or soil enclosure techniques on specific components of an ecosystem. New fast response methane analyzers make it possible to use the eddy covariance (EC) technique instead. The EC technique is advantageous because it allows

  19. Large-eddy simulations of surface-induced turbulence and its implications to the interpretation of eddy-covariance measurements in heterogeneous landscapes

    Science.gov (United States)

    Bohrer, G.; Kenny, W.; Morin, T. H.

    2015-12-01

    We used the RAMS-based Forest Large Eddy Simulations (RAFLES) to evaluate the sensitivity of eddy covariance measurements to land-surface discontinuity. While the sensitivity of eddy covariance measurements to surface heterogeneity is well known, it is, in most cases, no feasible to restrict measurements only to sites where the surface include undisturbed and homogeneous land cover over vast distances around the observation tower. The common approach to handle surface heterogeneity is to use a footprint model and reject observations obtained while the source of observed signal is from a mixture of land-use types, and maintain only measurements where the signal originates mostly from the land-use type of interest. We simulated two scenarios - measurements of fluxes from a small forest-surrounded lake, and measurements near a forest edge. These are two very common scenarios where measurements are bound to be affected by heterogeneity - measurements in small lakes, will, by definition, be in some non-negligible proximity or the lake edge; forest edges are common in any forest, near the forest patch edge but also around disturbed patches and forest gaps. We identify regions where the surface heterogeneity is creating persistent updraft or downdraft. A non-zero mean vertical wind is typically neglected in eddy-covariance measurements. We find that these circulations lead to both vertical and horizontal advection that cannot be easily measured by a single eddy-covariance tower. We identify downwind effects, which are well known, but also quantify the upwind effects. We find that surface-induced circulations may affect the flux measured from a tower up to several canopy heights ahead of the discontinuity. We used the High-resolution Volatile Organic Compound Atmospheric Chemistry in Canopies (Hi-VACC) model to determine the actual measurement footprints throughout the RAFLES domain. We estimated the land-cover type distribution of the source signal at different virtual

  20. The energy balance experiment EBEX-2000. Part II: Intercomparison of eddy-covariance sensors and post-field data processing methods

    Science.gov (United States)

    Mauder, Matthias; Oncley, Steven P.; Vogt, Roland; Weidinger, Tamas; Ribeiro, Luis; Bernhofer, Christian; Foken, Thomas; Kohsiek, Wim; de Bruin, Henk A. R.; Liu, Heping

    2007-04-01

    The eddy-covariance method is the primary way of measuring turbulent fluxes directly. Many investigators have found that these flux measurements often do not satisfy a fundamental criterion—closure of the surface energy balance. This study investigates to what extent the eddy-covariance measurement technology can be made responsible for this deficiency, in particular the effects of instrumentation or of the post-field data processing. Therefore, current eddy-covariance sensors and several post-field data processing methods were compared. The differences in methodology resulted in deviations of 10% for the sensible heat flux and of 15% for the latent heat flux for an averaging time of 30 min. These disparities were mostly due to different sensor separation corrections and a linear detrending of the data. The impact of different instrumentation on the resulting heat flux estimates was significantly higher. Large deviations from the reference system of up to 50% were found for some sensor combinations. However, very good measurement quality was found for a CSAT3 sonic together with a KH20 krypton hygrometer and also for a UW sonic together with a KH20. If these systems are well calibrated and maintained, an accuracy of better than 5% can be achieved for 30-min values of sensible and latent heat flux measurements. The results from the sonic anemometers Gill Solent-HS, ATI-K, Metek USA-1, and R.M. Young 81000 showed more or less larger deviations from the reference system. The LI-COR LI-7500 open-path H2O/CO2 gas analyser in the test was one of the first serial numbers of this sensor type and had technical problems regarding direct solar radiation sensitivity and signal delay. These problems are known by the manufacturer and improvements of the sensor have since been made.

  1. Innovative CO2 Analyzer Technology for the Eddy Covariance Flux Monitor, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to build and evaluate NDIR Analyzers that can observe eddy covariance flux of CO2 from unmanned airborne platforms. For both phases, a total of four...

  2. NEON's Eddy-Covariance Storage Exchange: from Tower to Data Portal

    Science.gov (United States)

    Durden, N. P.; Luo, H.; Xu, K.; Metzger, S.; Durden, D.

    2017-12-01

    NEON's eddy-covariance storage exchange system (ECSE) consists of a suite of sensors including temperature sensors, a CO2 and H2O gas analyzer, and isotopic CO2 and H2O analyzers. NEON's ECSE was developed to provide the vertical profile measurements of temperature, CO2 and H2O concentrations, the stable isotope ratios in CO2 (δ13C) and H2O (δ18O and δ2H) in the atmosphere. The profiles of temperature and concentrations of CO2 and H2O are key to calculate storage fluxes for eddy-covariance tower sites. Storage fluxes have a strong diurnal cycle and can be large in magnitude, especially at temporal scales less than one day. However, the storage term is often neglected in flux computations. To obtian accurate eddy-covariance fluxes, the storage fluxes are calculated and incorporated into the calculations of net surface-atmosphere ecosystem exchange of heat, CO2, and H2O for each NEON tower site. Once the ECSE raw data (Level 0, or L0) is retrieved at NEON's headquarters, it is preconditioned through a sequence of unit conversion, time regularization, and plausibility tests. By utilizing NEON's eddy4R framework (Metzger et al., 2017), higher-level data products are generated including: Level 1 (L1): Measurement-level specific averages of temperature and concentrations of CO2 and H2O. Level 2 (L2): Time rate of change of temperature and concentrations of CO2 and H2O over 30 min at each measurement level along the vertical tower profile. Level 3 (L3): Time rate of change of temperature and concentrations of CO2 and H2O over 30 min (L2), spatially interpolated along the vertical tower profile. Level 4 (L4): Storage fluxes of heat, CO2, and H2O calculated from the integrated time rate of change spatially interpolated profile (L3). The L4 storage fluxes are combined with turbulent fluxes to calculate the net surface-atmosphere ecosystem exchange of heat, CO2, and H2O. Moreover, a final quality flag and uncertainty budget are produced individually for each data stream

  3. Eddy covariance carbonyl sulfide flux measurements with a quantum cascade laser absorption spectrometer

    Directory of Open Access Journals (Sweden)

    K. Gerdel

    2017-09-01

    Full Text Available The trace gas carbonyl sulfide (COS has lately received growing interest from the eddy covariance (EC community due to its potential to serve as an independent approach for constraining gross primary production and canopy stomatal conductance. Thanks to recent developments of fast-response high-precision trace gas analysers (e.g. quantum cascade laser absorption spectrometers, QCLAS, a handful of EC COS flux measurements have been published since 2013. To date, however, a thorough methodological characterisation of QCLAS with regard to the requirements of the EC technique and the necessary processing steps has not been conducted. The objective of this study is to present a detailed characterisation of the COS measurement with the Aerodyne QCLAS in the context of the EC technique and to recommend best EC processing practices for those measurements. Data were collected from May to October 2015 at a temperate mountain grassland in Tyrol, Austria. Analysis of the Allan variance of high-frequency concentration measurements revealed the occurrence of sensor drift under field conditions after an averaging time of around 50 s. We thus explored the use of two high-pass filtering approaches (linear detrending and recursive filtering as opposed to block averaging and linear interpolation of regular background measurements for covariance computation. Experimental low-pass filtering correction factors were derived from a detailed cospectral analysis. The CO2 and H2O flux measurements obtained with the QCLAS were compared with those obtained with a closed-path infrared gas analyser. Overall, our results suggest small, but systematic differences between the various high-pass filtering scenarios with regard to the fraction of data retained in the quality control and flux magnitudes. When COS and CO2 fluxes are combined in the ecosystem relative uptake rate, systematic differences between the high-pass filtering scenarios largely cancel out, suggesting that

  4. Eddy covariance carbonyl sulphide flux measurements with a quantum cascade laser absorption spectrometer.

    Science.gov (United States)

    Gerdel, Katharina; Spielmann, Felix Maximilian; Hammerle, Albin; Wohlfahrt, Georg

    2017-09-26

    The trace gas carbonyl sulphide (COS) has lately received growing interest in the eddy covariance (EC) community due to its potential to serve as an independent approach for constraining gross primary production and canopy stomatal conductance. Thanks to recent developments of fast-response high-precision trace gas analysers (e.g. quantum cascade laser absorption spectrometers (QCLAS)), a handful of EC COS flux measurements have been published since 2013. To date, however, a thorough methodological characterisation of QCLAS with regard to the requirements of the EC technique and the necessary processing steps has not been conducted. The objective of this study is to present a detailed characterization of the COS measurement with the Aerodyne QCLAS in the context of the EC technique, and to recommend best EC processing practices for those measurements. Data were collected from May to October 2015 at a temperate mountain grassland in Tyrol, Austria. Analysis of the Allan variance of high-frequency concentration measurements revealed sensor drift to occur under field conditions after an averaging time of around 50 s. We thus explored the use of two high-pass filtering approaches (linear detrending and recursive filtering) as opposed to block averaging and linear interpolation of regular background measurements for covariance computation. Experimental low-pass filtering correction factors were derived from a detailed cospectral analysis. The CO 2 and H 2 O flux measurements obtained with the QCLAS were compared against those obtained with a closed-path infrared gas analyser. Overall, our results suggest small, but systematic differences between the various high-pass filtering scenarios with regard to the fraction of data retained in the quality control and flux magnitudes. When COS and CO 2 fluxes are combined in the so-called ecosystem relative uptake rate, systematic differences between the high-pass filtering scenarios largely cancel out, suggesting that this

  5. Under-ice eddy covariance flux measurements of heat, salt, momentum, and dissolved oxygen in an artificial sea ice pool

    DEFF Research Database (Denmark)

    Else, B. G T; Rysgaard, S.; Attard, K.

    2015-01-01

    as one possible cause of the high fluxes. Momentum fluxes showed interesting correlations with ice growth and melt but were generally higher than expected. We concluded that with the exception of the conductivity sensor, the eddy covariance system worked well, and that useful information about turbulent......Turbulent exchanges under sea ice play a controlling role in ice mass balance, ice drift, biogeochemistry, and mixed layer modification. In this study, we examined the potential to measure under-ice turbulent exchanges of heat, salt, momentum, and dissolved oxygen using eddy covariance...... in an experimental sea ice facility. Over a 15-day period in January 2013, an underwater eddy covariance system was deployed in a large (500 m3) inground concrete pool, which was filled with artificial seawater and exposed to the ambient (−5 to −30 °C) atmosphere. Turbulent exchanges were measured continuously...

  6. Combining sap flow and eddy covariance approaches to derive stomatal and non-stomatal O3 fluxes in a forest stand

    International Nuclear Information System (INIS)

    Nunn, A.J.; Cieslik, S.; Metzger, U.; Wieser, G.; Matyssek, R.

    2010-01-01

    Stomatal O 3 fluxes to a mixed beech/spruce stand (Fagus sylvatica/Picea abies) in Central Europe were determined using two different approaches. The sap flow technique yielded the tree-level transpiration, whereas the eddy covariance method provided the stand-level evapotranspiration. Both data were then converted into stomatal ozone fluxes, exemplifying this novel concept for July 2007. Sap flow-based stomatal O 3 flux was 33% of the total O 3 flux, whereas derivation from evapotranspiration rates in combination with the Penman-Monteith algorithm amounted to 47%. In addition to this proportional difference, the sap flow-based assessment yielded lower levels of stomatal O 3 flux and reflected stomatal regulation rather than O 3 exposure, paralleling the daily courses of canopy conductance for water vapor and eddy covariance-based total stand-level O 3 flux. The demonstrated combination of sap flow and eddy covariance approaches supports the development of O 3 risk assessment in forests from O 3 exposure towards flux-based concepts. - Combined tree sap flow and eddy covariance-based methodologies yield stomatal O 3 flux as 33% in total stand flux.

  7. Measuring Evapotranspiration of five Alley Cropping systems in Germany using the Eddy-Covariance- and Bowen-Ratio Energy-Balance methods

    Science.gov (United States)

    Markwitz, Christian; Knohl, Alexander; Siebicke, Lukas

    2017-04-01

    The inclusion of trees into the agricultural landscape of Europe is gaining popularity as a source for energy production. Fast growing tree species such as poplar or willow are included as short rotation coppice or alley cropping systems, which consist of tree alleys interleaved by annual rotating crops or perennial grasslands. Estimating turbulent fluxes of those systems using the eddy-covariance- (ECEB) and bowen-ratio energy-balance (BREB) method is challenging due to the methods limitation to horizontally homogeneous terrain and steady state conditions. As the conditions are not fulfilled for those systems the energy-balance is commonly not fully closed, with the non-closure being site specific. An underestimation of measured heat fluxes leads to an overestimation of the latent heat fluxes inferred from the ECEB method. The aim of our study is to 1) quantify the site specific non-closure of the energy-balance and 2) characterize the performance of both methods, compared to direct eddy-covariance measurements using a high frequency infra-red gas analyzer (LI-7200, Licor Inc.). To assess continuous evapotranspiration (ET) rates on a 30-minute time scale we installed a combined ECEB and BREB system at five alley cropping and five agricultural reference sites across Germany. For time periods of four weeks we performed direct eddy covariance flux measurements for H2O and CO2 over one crop- and one grassland alley cropping- and their respective reference systems during the growing season of 2016. We found a non-closure between 21 and 26 % for all sites, considering all day- and night-time data. The residual energy was highest during the morning and lowest in the afternoon. Related to that the energy-balance ratio (EBR), i.e. the ratio between the turbulent heat fluxes and available energy, was below one in the morning hours and increased slightly during the day up to 1.8, until the EBR decreased sharply after sunset. The EBR correlated to the daily cycle of solar

  8. A comparison of optical and microwave scintillometers with eddy covariance derived surface heat fluxes

    KAUST Repository

    Yee, Mei Sun; Pauwels, Valentijn R N; Daly, Edoardo; Beringer, Jason; Rü diger, Christoph; McCabe, Matthew; Walker, Jeffrey P.

    2015-01-01

    with an eddy covariance (EC) system, two different makes of optical large aperture scintillometers (LAS) and two microwave scintillometers (MWS) with different frequencies at a pasture site in a semi-arid environment of New South Wales, Australia. We used

  9. Use of eddy-covariance methods to "calibrate" simple estimators of evapotranspiration

    Science.gov (United States)

    Sumner, David M.; Geurink, Jeffrey S.; Swancar, Amy

    2017-01-01

    Direct measurement of actual evapotranspiration (ET) provides quantification of this large component of the hydrologic budget, but typically requires long periods of record and large instrumentation and labor costs. Simple surrogate methods of estimating ET, if “calibrated” to direct measurements of ET, provide a reliable means to quantify ET. Eddy-covariance measurements of ET were made for 12 years (2004-2015) at an unimproved bahiagrass (Paspalum notatum) pasture in Florida. These measurements were compared to annual rainfall derived from rain gage data and monthly potential ET (PET) obtained from a long-term (since 1995) U.S. Geological Survey (USGS) statewide, 2-kilometer, daily PET product. The annual proportion of ET to rainfall indicates a strong correlation (r2=0.86) to annual rainfall; the ratio increases linearly with decreasing rainfall. Monthly ET rates correlated closely (r2=0.84) to the USGS PET product. The results indicate that simple surrogate methods of estimating actual ET show positive potential in the humid Florida climate given the ready availability of historical rainfall and PET.

  10. An Extensible Processing Framework for Eddy-covariance Data

    Science.gov (United States)

    Durden, D.; Fox, A. M.; Metzger, S.; Sturtevant, C.; Durden, N. P.; Luo, H.

    2016-12-01

    The evolution of large data collecting networks has not only led to an increase of available information, but also in the complexity of analyzing the observations. Timely dissemination of readily usable data products necessitates a streaming processing framework that is both automatable and flexible. Tower networks, such as ICOS, Ameriflux, and NEON, exemplify this issue by requiring large amounts of data to be processed from dispersed measurement sites. Eddy-covariance data from across the NEON network are expected to amount to 100 Gigabytes per day. The complexity of the algorithmic processing necessary to produce high-quality data products together with the continued development of new analysis techniques led to the development of a modular R-package, eddy4R. This allows algorithms provided by NEON and the larger community to be deployed in streaming processing, and to be used by community members alike. In order to control the processing environment, provide a proficient parallel processing structure, and certify dependencies are available during processing, we chose Docker as our "Development and Operations" (DevOps) platform. The Docker framework allows our processing algorithms to be developed, maintained and deployed at scale. Additionally, the eddy4R-Docker framework fosters community use and extensibility via pre-built Docker images and the Github distributed version control system. The capability to process large data sets is reliant upon efficient input and output of data, data compressibility to reduce compute resource loads, and the ability to easily package metadata. The Hierarchical Data Format (HDF5) is a file format that can meet these needs. A NEON standard HDF5 file structure and metadata attributes allow users to explore larger data sets in an intuitive "directory-like" structure adopting the NEON data product naming conventions.

  11. The Polyakov path integral over bordered surfaces 3 (The BRST extended closed string off-shell amplitudes)

    International Nuclear Information System (INIS)

    Jaskolski, Z.

    1991-05-01

    The geometrical approach to the functional integral over Faddeev-Popov ghost fields is developed and applied to construct the BRST extension of the off-shell closed string amplitudes in the constant curvature gauge. In this gauge the overlap path integral for off-shell amplitudes is evaluated. It leads to the nonlocal sewing procedure generating all off-shell amplitudes from the cubic interaction vertex. The general scheme of the reconstruction of a covariant closed string field theory from the off-shell amplitudes is discussed within the path integral framework. (author). 30 refs

  12. Turbulent fluxes by "Conditional Eddy Sampling"

    Science.gov (United States)

    Siebicke, Lukas

    2015-04-01

    for the field (one to two orders of magnitude lower compared to current closed-path laser based eddy covariance systems). Potential applications include fluxes of CO2, CH4, N2O, VOCs and other tracers. Finally we assess the flux accuracy of the Conditional Eddy Sampling (CES) approach as in our real implementation relative to alternative techniques including eddy covariance (EC) and relaxed eddy accumulation (REA). We further quantify various sources of instrument and method specific measurement errors. This comparison uses real measurements of 20 Hz turbulent time series of 3D wind velocity, sonic temperature and CO2 mixing ratio over a mixed decidious forest at the 'ICOS' flux tower site 'Hainich', Germany. Results from a simulation using real wind and CO2 timeseries from the Hainich site from 30 April to 3 November 2014 and real instrument performance suggest that the maximum flux estimates error (50% and 75% error quantiles) from Conditional Eddy Sampling (CES) relative to the true flux is 1.3% and 10%, respectively for monthly net fluxes, 1.6% and 7%, respectively for daily net fluxes and 8% and 35%, respectively for 30-minute CO2 flux estimates. Those results from CES are promising and outperform our REA estimates by about a factor of 50 assuming REA with constant b value. Results include flux time series from the EC, CES and REA approaches from 30-min to annual resolution.

  13. Forest Ecosystem respiration estimated from eddy covariance and chamber measurements under high turbulence and substantial tree mortality from bark beetles

    Science.gov (United States)

    Speckman, Heather N.; Frank, John M.; Bradford, John B.; Miles, Brianna L.; Massman, William J.; Parton, William J.; Ryan, Michael G.

    2015-01-01

    Eddy covariance nighttime fluxes are uncertain due to potential measurement biases. Many studies report eddy covariance nighttime flux lower than flux from extrapolated chamber measurements, despite corrections for low turbulence. We compared eddy covariance and chamber estimates of ecosystem respiration at the GLEES Ameriflux site over seven growing seasons under high turbulence (summer night mean friction velocity (u*) = 0.7 m s−1), during which bark beetles killed or infested 85% of the aboveground respiring biomass. Chamber-based estimates of ecosystem respiration during the growth season, developed from foliage, wood and soil CO2 efflux measurements, declined 35% after 85% of the forest basal area had been killed or impaired by bark beetles (from 7.1 ±0.22 μmol m−2 s−1 in 2005 to 4.6 ±0.16 μmol m−2 s−1 in 2011). Soil efflux remained at ~3.3 μmol m−2 s−1 throughout the mortality, while the loss of live wood and foliage and their respiration drove the decline of the chamber estimate. Eddy covariance estimates of fluxes at night remained constant over the same period, ~3.0 μmol m−2 s−1 for both 2005 (intact forest) and 2011 (85% basal area killed or impaired). Eddy covariance fluxes were lower than chamber estimates of ecosystem respiration (60% lower in 2005, and 32% in 2011), but the mean night estimates from the two techniques were correlated within a year (r2 from 0.18-0.60). The difference between the two techniques was not the result of inadequate turbulence, because the results were robust to a u* filter of > 0.7 m s−1. The decline in the average seasonal difference between the two techniques was strongly correlated with overstory leaf area (r2=0.92). The discrepancy between methods of respiration estimation should be resolved to have confidence in ecosystem carbon flux estimates.

  14. Forest ecosystem respiration estimated from eddy covariance and chamber measurements under high turbulence and substantial tree mortality from bark beetles.

    Science.gov (United States)

    Speckman, Heather N; Frank, John M; Bradford, John B; Miles, Brianna L; Massman, William J; Parton, William J; Ryan, Michael G

    2015-02-01

    Eddy covariance nighttime fluxes are uncertain due to potential measurement biases. Many studies report eddy covariance nighttime flux lower than flux from extrapolated chamber measurements, despite corrections for low turbulence. We compared eddy covariance and chamber estimates of ecosystem respiration at the GLEES Ameriflux site over seven growing seasons under high turbulence [summer night mean friction velocity (u*) = 0.7 m s(-1)], during which bark beetles killed or infested 85% of the aboveground respiring biomass. Chamber-based estimates of ecosystem respiration during the growth season, developed from foliage, wood, and soil CO2 efflux measurements, declined 35% after 85% of the forest basal area had been killed or impaired by bark beetles (from 7.1 ± 0.22 μmol m(-2) s(-1) in 2005 to 4.6 ± 0.16 μmol m(-2) s(-1) in 2011). Soil efflux remained at ~3.3 μmol m(-2) s(-1) throughout the mortality, while the loss of live wood and foliage and their respiration drove the decline of the chamber estimate. Eddy covariance estimates of fluxes at night remained constant over the same period, ~3.0 μmol m(-2) s(-1) for both 2005 (intact forest) and 2011 (85% basal area killed or impaired). Eddy covariance fluxes were lower than chamber estimates of ecosystem respiration (60% lower in 2005, and 32% in 2011), but the mean night estimates from the two techniques were correlated within a year (r(2) from 0.18 to 0.60). The difference between the two techniques was not the result of inadequate turbulence, because the results were robust to a u* filter of >0.7 m s(-1). The decline in the average seasonal difference between the two techniques was strongly correlated with overstory leaf area (r(2) = 0.92). The discrepancy between methods of respiration estimation should be resolved to have confidence in ecosystem carbon flux estimates. © 2014 John Wiley & Sons Ltd.

  15. Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment

    Science.gov (United States)

    Peltola, O.; Hensen, A.; Helfter, C.; Belelli Marchesini, L.; Bosveld, F. C.; van den Bulk, W. C. M.; Elbers, J. A.; Haapanala, S.; Holst, J.; Laurila, T.; Lindroth, A.; Nemitz, E.; Röckmann, T.; Vermeulen, A. T.; Mammarella, I.

    2014-06-01

    The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions. The moderate CH4 fluxes observed at the location, of the order of 25 nmol m-2 s-1, provided a suitable signal for testing the instruments' performance. Generally, all analysers tested were able to quantify the concentration fluctuations at the frequency range relevant for turbulent exchange and were able to deliver high-quality data. The tested cavity ringdown spectrometer (CRDS) instruments from Picarro, models G2311-f and G1301-f, were superior to other CH4 analysers with respect to instrumental noise. As an open-path instrument susceptible to the effects of rain, the LI-COR LI-7700 achieved lower data coverage and also required larger density corrections; however, the system is especially useful for remote sites that are restricted in power availability. In this study the open-path LI-7700 results were compromised due to a data acquisition problem in our data-logging setup. Some of the older closed-path analysers tested do not measure H2O concentrations alongside CH4 (i.e. FMA1 and DLT-100 by Los Gatos Research) and this complicates data processing since the required corrections for dilution and spectroscopic interactions have to be based on external information. To overcome this issue, we used H2O mole fractions measured by other gas analysers, adjusted them with different methods and then applied them to correct the CH4 fluxes. Following this procedure we estimated a bias of the order of 0.1 g (CH4) m-2 (8% of the measured mean flux) in the processed and corrected CH4 fluxes on a monthly scale due to missing H2O concentration measurements. Finally, cumulative CH4 fluxes over 14 days from three closed-path gas analysers, G2311-f (Picarro Inc

  16. Quality analysis applied on eddy covariance measurements at complex forest sites using footprint modelling

    Czech Academy of Sciences Publication Activity Database

    Rebmann, C.; Göckede, M.; Foken, T.; Aubinet, M.; Aurela, M.; Berbigier, P.; Bernhofer, C.; Buchmann, N.; Carrara, A.; Cescatti, A.; Ceulemans, R.; Clement, R.; Elbers, J. A.; Granier, A.; Grünwald, T.; Guyon, D.; Havránková, Kateřina; Heinesch, B.; Knohl, A.; Laurila, T.; Longdoz, B.; Marcolla, B.; Markkanen, T.; Miglietta, F.; Moncrieff, J.; Montagnani, L.; Moors, E.; Nardino, M.; Ourcival, J.-M.; Rambal, S.; Rannik, Ü.; Rotenberg, E.; Sedlák, Pavel; Unterhuber, G.; Vesala, T.; Yakir, D.

    2005-01-01

    Roč. 80, - (2005), s. 121-141 ISSN 0177-798X Grant - others:Carboeuroflux(XE) EVK-2-CT-1999-00032 Institutional research plan: CEZ:AV0Z30420517; CEZ:AV0Z6087904 Keywords : Eddy covariance * Quality assurance * Quality control * Footprint modelling * Heterogeneity Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.295, year: 2005

  17. Eddy Covariance Measurements of Methane Flux at a Tropical Peat Forest in Sarawak, Malaysian Borneo

    Science.gov (United States)

    Tang, Angela C. I.; Stoy, Paul C.; Hirata, Ryuichi; Musin, Kevin K.; Aeries, Edward B.; Wenceslaus, Joseph; Melling, Lulie

    2018-05-01

    Tropical biogenic sources are a likely cause of the recent increase in global atmospheric methane concentration. To improve our understanding of tropical methane sources, we used the eddy covariance technique to measure CH4 flux (FCH4) between a tropical peat forest ecosystem and the atmosphere in Malaysian Borneo over a 2-month period during the wet season. Mean daily FCH4 during the measurement period, on the order of 0.024 g C-CH4·m-2·day-1, was similar to eddy covariance FCH4 measurements from tropical rice agroecosystems and boreal fen ecosystems. A linear modeling analysis demonstrated that air temperature (Tair) was critical for modeling FCH4 before the water table breached the surface and that water table alone explained some 20% of observed FCH4 variability once standing water emerged. Future research should measure FCH4 on an annual basis from multiple tropical ecosystems to better constrain tropical biogenic methane sources.

  18. Eddy covariance measurements of sea spray particles over the Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    S. J. Norris

    2008-02-01

    Full Text Available Most estimates of sea spray aerosol source functions have used indirect means to infer the rate of production as a function of wind speed. Only recently has the technology become available to make high frequency measurements of aerosol spectra suitable for direct eddy correlation determination of the sea spray particle flux. This was accomplished in this study by combining a newly developed fast aerosol particle counter with an ultrasonic anemometer which allowed for eddy covariance measurements of size-segregated particle fluxes. The aerosol instrument is the Compact Lightweight Aerosol Spectrometer Probe (CLASP – capable of measuring 8-channel size spectra for mean radii between 0.15 and 3.5 µm at 10 Hz. The first successful measurements were made during the Waves, Air Sea Fluxes, Aerosol and Bubbles (WASFAB field campaign in October 2005 in Duck (NC, USA. The method and initial results are presented and comparisons are made with recent sea spray source functions from the literature.

  19. Using Riverboat-Mounted Eddy Covariance for Direct Measurements of Air-water Gas Exchange in Amazonia

    Science.gov (United States)

    Miller, S. D.; Freitas, H.; Read, E.; Goulden, M. L.; Rocha, H.

    2007-12-01

    Gas evasion from Amazonian rivers and lakes to the atmosphere has been estimated to play an important role in the regional budget of carbon dioxide (Richey et al., 2002) and the global budget of methane (Melack et al., 2004). These flux estimates were calculated by combining remote sensing estimates of inundation area with water-side concentration gradients and gas transfer rates (piston velocities) estimated primarily from floating chamber measurements (footprint ~1 m2). The uncertainty in these fluxes was large, attributed primarily to uncertainty in the gas exchange parameterization. Direct measurements of the gas exchange coefficient are needed to improve the parameterizations in these environments, and therefore reduce the uncertainty in fluxes. The micrometeorological technique of eddy covariance is attractive since it is a direct measurement of gas exchange that samples over a much larger area than floating chambers, and is amenable to use from a moving platform. We present eddy covariance carbon dioxide exchange measurements made using a small riverboat in rivers and lakes in the central Amazon near Santarem, Para, Brazil. Water-side carbon dioxide concentration was measured in situ, and the gas exchange coefficient was calculated. We found the piston velocity at a site on the Amazon River to be similar to existing ocean-based parameterizations, whereas the piston velocity at a site on the Tapajos River was roughly a factor 5 higher. We hypothesize that the enhanced gas exchange at the Tapajos site was due to a shallow upwind fetch. Our results demonstrate the feasibility of boat-based eddy covariance on these rivers, and also the utility of a mobile platform to investigate spatial variability of gas exchange.

  20. Towards an integrated quality control procedure for eddy-covariance data

    Science.gov (United States)

    Vitale, Domenico; Papale, Dario

    2017-04-01

    The eddy-covariance technique is nowadays the most reliable and direct way, allowing to calculate the main fluxes of Sensible and Latent Heat and of Net Ecosystem Exchange, this last being the result of the difference between the CO2 assimilated by photosynthetic activities and those released to the atmosphere through the ecosystem respiration processes. Despite the improvements in accuracy of measurement instruments and software development, the eddy-covariance technique is not suitable under non-ideal conditions respect to the instruments characteristics and the physical assumption behind the technique mainly related to the well-developed and stationary turbulence conditions. Under these conditions the calculated fluxes are not reliable and need to be flagged and discarded. In order to discover these unavoidable "bad" fluxes and build dataset with the highest quality, several tests applied both on high-frequency (10-20 Hz) raw data and on half-hourly times series have been developed in the past years. Nevertheless, there is an increasing need to develop a standardized quality control procedure suitable not only for the analysis of long-term data, but also for the near-real time data processing. In this paper, we review established quality assessment procedures and present an innovative quality control strategy with the purpose of integrating the existing consolidated procedures with robust and advanced statistical tests more suitable for the analysis of time series data. The performance of the proposed quality control strategy is evaluated both on simulated and EC data distributed by the ICOS research infrastructure. It is concluded that the proposed strategy is able to flag and exclude unrealistic fluxes while being reproducible and retaining the largest possible amount of high quality data.

  1. Covariant path integrals on hyperbolic surfaces

    Science.gov (United States)

    Schaefer, Joe

    1997-11-01

    DeWitt's covariant formulation of path integration [B. De Witt, "Dynamical theory in curved spaces. I. A review of the classical and quantum action principles," Rev. Mod. Phys. 29, 377-397 (1957)] has two practical advantages over the traditional methods of "lattice approximations;" there is no ordering problem, and classical symmetries are manifestly preserved at the quantum level. Applying the spectral theorem for unbounded self-adjoint operators, we provide a rigorous proof of the convergence of certain path integrals on Riemann surfaces of constant curvature -1. The Pauli-DeWitt curvature correction term arises, as in DeWitt's work. Introducing a Fuchsian group Γ of the first kind, and a continuous, bounded, Γ-automorphic potential V, we obtain a Feynman-Kac formula for the automorphic Schrödinger equation on the Riemann surface ΓH. We analyze the Wick rotation and prove the strong convergence of the so-called Feynman maps [K. D. Elworthy, Path Integration on Manifolds, Mathematical Aspects of Superspace, edited by Seifert, Clarke, and Rosenblum (Reidel, Boston, 1983), pp. 47-90] on a dense set of states. Finally, we give a new proof of some results in C. Grosche and F. Steiner, "The path integral on the Poincare upper half plane and for Liouville quantum mechanics," Phys. Lett. A 123, 319-328 (1987).

  2. The assessment of water vapour and carbon dioxide fluxes above arable crops - a comparison of methods

    Energy Technology Data Exchange (ETDEWEB)

    Schaaf, S.; Daemmgen, U.; Burkart, S. [Federal Agricultural Research Centre, Inst. of Agroecology, Braunschweig (Germany); Gruenhage, L. [Justus-Liebig-Univ., Inst. for Plant Ecology, Giessen (Germany)

    2005-04-01

    Vertical fluxes of water vapour and carbon dioxide obtained from gradient, eddy covariance (closed and open path systems) and chamber measurements above arable crops were compared with the directly measured energy balance and the harvested net biomass carbon. The gradient and chamber measurements were in the correct order of magnitude, whereas the closed path eddy covariance system showed unacceptably small fluxes. Correction methods based on power spectra analysis yielded increased fluxes. However, the energy balance could not be closed satisfactorily. The application of the open path system proved to be successful. The SVAT model PLATIN which had been adapted to various arable crops was able to depict the components of the energy balance adequately. Net carbon fluxes determined with the corrected closed path data sets, chamber, and SVAT model equal those of the harvested carbon. (orig.)

  3. Toward a Mexican eddy covariance network for carbon cycle science

    Science.gov (United States)

    Vargas, Rodrigo; Yépez, Enrico A.

    2011-09-01

    First Annual MexFlux Principal Investigators Meeting; Hermosillo, Sonora, Mexico, 4-8 May 2011; The carbon cycle science community has organized a global network, called FLUXNET, to measure the exchange of energy, water, and carbon dioxide (CO2) between the ecosystems and the atmosphere using the eddy covariance technique. This network has provided unprecedented information for carbon cycle science and global climate change but is mostly represented by study sites in the United States and Europe. Thus, there is an important gap in measurements and understanding of ecosystem dynamics in other regions of the world that are seeing a rapid change in land use. Researchers met under the sponsorship of Red Temática de Ecosistemas and Consejo Nacional de Ciencia y Tecnologia (CONACYT) to discuss strategies to establish a Mexican eddy covariance network (MexFlux) by identifying researchers, study sites, and scientific goals. During the meeting, attendees noted that 10 study sites have been established in Mexico with more than 30 combined years of information. Study sites span from new sites installed during 2011 to others with 9 to 6 years of measurements. Sites with the longest span measurements are located in Baja California Sur (established by Walter Oechel in 2002) and Sonora (established by Christopher Watts in 2005); both are semiarid ecosystems. MexFlux sites represent a variety of ecosystem types, including Mediterranean and sarcocaulescent shrublands in Baja California; oak woodland, subtropical shrubland, tropical dry forest, and a grassland in Sonora; tropical dry forests in Jalisco and Yucatan; a managed grassland in San Luis Potosi; and a managed pine forest in Hidalgo. Sites are maintained with an individual researcher's funds from Mexican government agencies (e.g., CONACYT) and international collaborations, but no coordinated funding exists for a long-term program.

  4. Comparison of ecosystem water flux measured with the Eddy covariance- and the direct xylem sap flux method in a mountainous forest

    Energy Technology Data Exchange (ETDEWEB)

    Stefanicki, G; Geissbuehler, P; Siegwolf, R [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1999-08-01

    The Eddy covariance technique allows to measure different components of turbulent air fluxes, including the flow of water vapour. Sap flux measurements determine directly the water flow in tree stems. We compared the water flux just above the crowns of trees in a forest by the technique of Eddy covariance and the water flux by the xylem sap flux method. These two completely different approaches showed a good qualitative correspondence. The correlation coefficient is 0.8. With an estimation of the crown diameter of the measured tree we also find a very good quantitative agreement. (author) 3 figs., 5 refs.

  5. Comparison of carbon uptake estimates from forest inventory and Eddy-Covariance for a montane rainforest in central Sulawesi

    Science.gov (United States)

    Heimsch, Florian; Kreilein, Heiner; Rauf, Abdul; Knohl, Alexander

    2016-04-01

    Rainforests in general and montane rainforests in particular have rarely been studied over longer time periods. We aim to provide baseline information of a montane tropical forest's carbon uptake over time in order to quantify possible losses through land-use change. Thus we conducted a re-inventory of 22 10-year old forest inventory plots, giving us a rare opportunity to quantify carbon uptake over such a long time period by traditional methods. We discuss shortfalls of such techniques and why our estimate of 1.5 Mg/ha/a should be considered as the lower boundary and not the mean carbon uptake per year. At the same location as the inventory, CO2 fluxes were measured with the Eddy-Covariance technique. Measurements were conducted at 48m height with an LI 7500 open-path infrared gas analyser. We will compare carbon uptake estimates from these measurements to those of the more conventional inventory method and discuss, which factors are probably responsible for differences.

  6. Ventilation of subterranean CO2 and Eddy covariance incongruities over carbonate ecosystems

    Directory of Open Access Journals (Sweden)

    F. Domingo

    2010-03-01

    Full Text Available Measurements of CO2 fluxes with Eddy Covariance (EC systems are ongoing over different ecosystems around the world, through different measuring networks, in order to assess the carbon balance of these ecosystems. In carbonate ecosystems, characterized by the presence of subterranean pores and cavities, ventilation of the CO2 accumulated in these cavities and pores can act as an extra source of CO2 exchange between the ecosystem and the atmosphere. In this work we analyse the effect of the subterranean heterogeneity of a carbonate ecosystem on measurements of CO2 fluxes by comparing measurements from two EC systems with distinct footprints. Results showed that both EC systems agreed for measurements of evapotranspiration and of CO2 in periods when respiratory and photosynthetic processes were dominant (biological periods, with a regression slope of 0.99 and 0.97, respectively. However, in periods when the main source of CO2 comes from the ventilation of subterranean pores and cavities (abiotic periods agreement is not good, with a regression slope of 0.6. Ground-penetrating radar measurements of the sub-surface confirmed the existence of high sub-surface heterogeneity that, combined with different footprints, lead to differences in the measurements of the two EC systems. These results show that measurements of CO2 fluxes with Eddy covariance systems over carbonate ecosystems must be taken carefully, as they may not be representative of the ecosystem under consideration.

  7. Nitrous oxide emissions from a beech forest floor measured by eddy covariance and soil enclosure techniques

    DEFF Research Database (Denmark)

    Pihlatie, M.; Rinne, J.; Ambus, P.

    2005-01-01

    Spring time nitrous oxide (N2O) emissions from an old beech (Fagus sylvatica L.) forest were measured with eddy covariance (EC) and chamber techniques. The aim was to obtain information on the spatial and temporal variability in N2O emissions and link the emissions to soil environmental parameters...

  8. Modeling gross primary production in semi-arid Inner Mongolia using MODIS imagery and eddy covariance data

    Science.gov (United States)

    Ranjeet John; Jiquan Chen; Asko Noormets; Xiangming Xiao; Jianye Xu; Nan Lu; Shiping Chen

    2013-01-01

    We evaluate the modelling of carbon fluxes from eddy covariance (EC) tower observations in different water-limited land-cover/land-use (LCLU) and biome types in semi-arid Inner Mongolia, China. The vegetation photosynthesis model (VPM) and modified VPM (MVPM), driven by the enhanced vegetation index (EVI) and land-surface water index (LSWI), which were derived from the...

  9. The relation between operator and path integral covariant quantizations of the Green-Schwarz superstring

    International Nuclear Information System (INIS)

    Nissimov, E.; Pacheva, S.; Solomon, S.

    1989-02-01

    By further study of the geometry of the harmonic superspace constraints, we make explicit the relation between the operator and path integral approaches to the manifestly covariant harmonic superstring. In particular we find the correct complete set of functionally independent gauge symmetries for the auxiliary variables and identify the ones corresponding to the harmonic superfield postulate in the operator formalism. Then, we deduce in a systematic way the lagrangian path integral from the well defined covariant hamiltonian formulation of the GS superstring. (authors)

  10. Covariant field theory of closed superstrings

    International Nuclear Information System (INIS)

    Siopsis, G.

    1989-01-01

    The authors construct covariant field theories of both type-II and heterotic strings. Toroidal compactification is also considered. The interaction vertices are based on Witten's vertex representing three strings interacting at the mid-point. For closed strings, the authors thus obtain a bilocal interaction

  11. Modelling carbon and water exchange of a grazed pasture in New Zealand constrained by eddy covariance measurements.

    Science.gov (United States)

    Kirschbaum, Miko U F; Rutledge, Susanna; Kuijper, Isoude A; Mudge, Paul L; Puche, Nicolas; Wall, Aaron M; Roach, Chris G; Schipper, Louis A; Campbell, David I

    2015-04-15

    We used two years of eddy covariance (EC) measurements collected over an intensively grazed dairy pasture to better understand the key drivers of changes in soil organic carbon stocks. Analysing grazing systems with EC measurements poses significant challenges as the respiration from grazing animals can result in large short-term CO2 fluxes. As paddocks are grazed only periodically, EC observations derive from a mosaic of paddocks with very different exchange rates. This violates the assumptions implicit in the use of EC methodology. To test whether these challenges could be overcome, and to develop a tool for wider scenario testing, we compared EC measurements with simulation runs with the detailed ecosystem model CenW 4.1. Simulations were run separately for 26 paddocks around the EC tower and coupled to a footprint analysis to estimate net fluxes at the EC tower. Overall, we obtained good agreement between modelled and measured fluxes, especially for the comparison of evapotranspiration rates, with model efficiency of 0.96 for weekly averaged values of the validation data. For net ecosystem productivity (NEP) comparisons, observations were omitted when cattle grazed the paddocks immediately around the tower. With those points omitted, model efficiencies for weekly averaged values of the validation data were 0.78, 0.67 and 0.54 for daytime, night-time and 24-hour NEP, respectively. While not included for model parameterisation, simulated gross primary production also agreed closely with values inferred from eddy covariance measurements (model efficiency of 0.84 for weekly averages). The study confirmed that CenW simulations could adequately model carbon and water exchange in grazed pastures. It highlighted the critical role of animal respiration for net CO2 fluxes, and showed that EC studies of grazed pastures need to consider the best approach of accounting for this important flux to avoid unbalanced accounting. Copyright © 2015. Published by Elsevier B.V.

  12. On the coupled use of sapflow and eddy covariance measurements: environmental impacts on the evapotranspiration of an heterogeneous - wild olives based - Sardinian ecosystem.

    Science.gov (United States)

    Curreli, Matteo; Corona, Roberto; Montaldo, Nicola; Oren, Ram

    2015-04-01

    Sapflow and eddy covariance techniques are attractive methods for evapotranspiration (ET) estimates. We demonstrated that in Mediterranean ecosystems, characterized by an heterogeneous spatial distribution of different plant functional types (PFT) such as grass and trees, the combined use of these techniques becomes essential for the actual ET estimates. Indeed, during the dry summers these water-limited heterogeneous ecosystems are typically characterized by a simple dual PFT system with strong-resistant woody vegetation and bare soil, since grass died. An eddy covariance - micrometeorological tower has been installed over an heterogeneous ecosystem at the Orroli site in Sardinia (Italy) from 2003. The site landscape is a mixture of Mediterranean patchy vegetation types: wild olives, different shrubs and herbaceous species, which died during the summer. Where patchy land cover leads and the surface fluxes from different cover are largely different, ET evaluation may be not robust enough and eddy covariance method hypothesis are not anymore preserved. In these conditions the sapflow measurements, performed by thermodissipation probes, provide robust estimates of the transpiration from woody vegetation. Through the coupled use of the sapflow sensor observations, a 2D footprint model of the eddy covariance tower and high resolution satellite images for the estimate of the foot print land cover map, the eddy covariance measurements can be correctly interpreted, and ET components (bare soil evaporation and woody vegetation transpiration) can be separated. Based on the Granier technique, 33 thermo-dissipation probes have been built and 6 power regulators have been assembled to provide a constant current of 3V to the sensors. The sensors have been installed at the Orroli site into 15 wild olives clumps with different characteristics in terms of tree size, exposition to wind and solar radiation and soil depth. The sap flow sensors outputs are analyzed to estimate

  13. Continuous Eddy Covariance Measurements of N2O Emissions and Controls from an Intensively Grazed Dairy Farm

    Science.gov (United States)

    Schipper, L. A.; Liang, L. L.; Wall, A.; Campbell, D.

    2017-12-01

    New Zealand's greenhouse gas (GHG) inventory is disproportionally dominated by methane and nitrous oxide which account for 54% of emissions. These GHGs are derived from pastoral agriculture that supports dairying and meat production. To date, most studies on quantifying or mitigating agricultural N2O emissions have used flux chamber measurements. Recent advances in detector technology now means that routine field-to-farm scale measurements of N2O emissions might be possible using the eddy covariance technique. In late 2016, we established an eddy covariance tower that measured N2O emissions from a dairy farm under year-round grazing. An Aerodyne quantum cascade laser (QCL) was used to measure N2O, CH4 and H2O concentration at 10 Hz and housed in a weatherproof and insulated enclosure (0.9 m ´ 1.2 m) and powered by mains power (240 VAC). The enclosure maintained a stable setpoint temperature (30±0.2°C) by using underground cooling pipes, fans and recirculating instrument heat. QCL (true 10 Hz digital) and CSAT3B sonic anemometer high frequency data are aligned using Network Time Protocol and EddyPro covariance maximisation during flux processing. Fluxes generally integrated over about 6-8 ha. Stable summertime baseline N2O fluxes (FN2O) were around 12-24 g N2O-N ha-1 d-1 (0.5-1.0 nmol N2O m-2 s-1). Grazing by cows during dry summer resulted in only modest increases in FN2O to 24-48 g N2O-N ha-1 d-1 (1.0-2.0 nmol N2O m-2 s-1). However, the first rain events after grazing resulted in large, short-lived (1-3 days) FN2O pulses reaching peaks of 144-192 g N2O-N ha-1 d-1 (6-8 nmol N2O m-2 s-1). During these elevated N2O emissions, FN2O displayed a significant diurnal signal, with peak fluxes mid-afternoon which was best explained by variation in shallow soil temperature in summer. In winter (both cooler and wetter) FN2O were not as easily explained on a daily basis but were generally greater than summer. Throughout the year, FN2O was strongly dependent on water filled

  14. Ecosystem water use efficiency of norway spruce monoculture from eddy-covariance and ecophysiological measurements

    Czech Academy of Sciences Publication Activity Database

    Pokorný, Radek; Slípková, Romana; Havránková, Kateřina; Pavelka, Marian

    2012-01-01

    Roč. 951, č. 1 (2012), s. 301-308 ISSN 0567-7572. [International Workshop On Sap Flow /8./. Volterra, 08.05.2011-12.05.2011] R&D Projects: GA MŽP(CZ) SP/2D1/70/08; GA MŽP(CZ) SP/2D1/93/07; GA MŠk(CZ) ED1.1.00/02.0073; GA MŠk(CZ) LM2010007 Institutional research plan: CEZ:AV0Z60870520 Keywords : eddy-covariance * evaporation * Picea abies * sap flow * transpiration Subject RIV: EH - Ecology, Behaviour

  15. Eddy Covariance Measurements Over a Maize Field: The Contribution of Minor Flux Terms to the Energy Balance Gap

    Science.gov (United States)

    Smidt, J.; Ingwersen, J.; Streck, T.

    2015-12-01

    The lack of energy balance closure is a long-standing problem in eddy covariance (EC) measurements. The energy balance equation is defined as Rn - G = H + λE, where Rn is net radiation, G is the ground heat flux, H is the sensible heat flux and λE is the latent heat flux. In most cases of energy imbalance, either Rn is overestimated or the ground heat and turbulent fluxes are underestimated. Multiple studies have shown that calculations, incorrect instrument installation/calibration and measurement errors alone do not entirely account for this imbalance. Rather, research is now focused on previously neglected sources of heat storage in the soil, biomass and air beneath the EC station. This project examined the potential of five "minor flux terms" - soil heat storage, biomass heat storage, energy consumption by photosynthesis, air heat storage and atmospheric moisture change, to further close the energy balance gap. Eddy covariance measurements were conducted at a maize (Zea mays) field in southwest Germany during summer 2014. Soil heat storage was measured for six weeks at 11 sites around the field footprint. Biomass and air heat storage were measured for six subsequent weeks at seven sites around the field footprint. Energy consumption by photosynthesis was calculated using the CO2 flux data. Evapotranspiration was calculated using the water balance method and then compared to the flux data processed with three post-closure methods: the sensible heat flux, the latent heat flux and the Bowen ratio post-closure methods. An energy balance closure of 66% was achieved by the EC station measurements over the entire investigation period. During the soil heat flux campaign, EC station closure was 74.1%, and the field footprint soil heat storage contributed 3.3% additional closure. During the second minor flux term measurement period, closure with the EC station data was 91%. Biomass heat storage resulted in 1.1% additional closure, the photosynthesis flux closed the gap

  16. Static Vented Chamber and Eddy Covariance Methane Flux Comparisons in Mid-South US Rice

    Science.gov (United States)

    Reba, M. L.; Fong, B.; Adviento-Borbe, A.; Runkle, B.; Suvocarev, K.; Rival, I.

    2017-12-01

    Rice cultivation contributes higher amounts of GHG emissions (CO2 and CH4) due to flooded field conditions. A comparison between eddy covariance and static vented flux chamber measurement techniques is presented. Rice GHG emissions originating from plot level chambers may not accurately describe the aggregate effects of all the soil and micrometeorological variations across a production field. Eddy covariance (EC) is a direct, integrated field measurement of field scale trace gases. Flux measurements were collected in NE Arkansas production size rice fields (16 ha, 40 ac) during the 2015 and 2016 production seasons (June-August) in continuous flood (CF) irrigation. The study objectives included quantifying the difference between chamber and EC measurements, and categorizing flux behavior to growth stage and field history. EC daily average emissions correlated with chamber measurements (R2=0.27-0.54) more than average from 09:00-12:00 which encompassed chamber measurement times (R2=0.23-0.32). Maximum methane emissions occurred in the late afternoon from 14:00-18:00 which corresponded with maximum soil heat flux and air temperature. The total emissions from the study fields ranged from 27-117 kg CH4-C ha-1 season-1. The emission profile was lower in 2015, most likely due to higher rainfall and cooler temperatures during the growing season compared to 2016. These findings improve our understanding of GHG emissions at the field scale under typical production practices and validity of chamber and EC flux measurement techniques.

  17. Monitoring gas and heat emissions at Norris Geyser Basin, Yellowstone National Park, USA based on a combined eddy covariance and Multi-GAS approach

    Science.gov (United States)

    Lewicki, J. L.; Kelly, P. J.; Bergfeld, D.; Vaughan, R. G.; Lowenstern, J. B.

    2017-11-01

    We quantified gas and heat emissions in an acid-sulfate, vapor-dominated area (0.04-km2) of Norris Geyser Basin, located just north of the 0.63 Ma Yellowstone Caldera and near an area of anomalous uplift. From 14 May to 3 October 2016, an eddy covariance system measured half-hourly CO2, H2O and sensible (H) and latent (LE) heat fluxes and a Multi-GAS instrument measured (1 Hz frequency) atmospheric H2O, CO2 and H2S volumetric mixing ratios. We also measured soil CO2 fluxes using the accumulation chamber method and temperature profiles on a grid and collected fumarole gas samples for geochemical analysis. Eddy covariance CO2 fluxes ranged from - 56 to 885 g m- 2 d- 1. Using wavelet analysis, average daily eddy covariance CO2 fluxes were locally correlated with average daily environmental parameters on several-day to monthly time scales. Estimates of CO2 emission rate from the study area ranged from 8.6 t d- 1 based on eddy covariance measurements to 9.8 t d- 1 based on accumulation chamber measurements. Eddy covariance water vapor fluxes ranged from 1178 to 24,600 g m- 2 d- 1. Nighttime H and LE were considered representative of hydrothermal heat fluxes and ranged from 4 to 183 and 38 to 504 W m- 2, respectively. The total hydrothermal heat emission rate (H + LE + radiant) estimated for the study area was 11.6 MW and LE contributed 69% of the output. The mean ± standard deviation of H2O, CO2 and H2S mixing ratios measured by the Multi-GAS system were 9.3 ± 3.1 parts per thousand, 467 ± 61 ppmv, and 0.5 ± 0.6 ppmv, respectively, and variations in the gas compositions were strongly correlated with diurnal variations in environmental parameters (wind speed and direction, atmospheric temperature). After removing ambient H2O and CO2, the observed variations in the Multi-GAS data could be explained by the mixing of relatively H2O-CO2-H2S-rich fumarole gases with CO2-rich and H2O-H2S-poor soil gases. The fumarole H2O/CO2 and CO2/H2S end member ratios (101.7 and 27

  18. Monitoring gas and heat emissions at Norris Geyser Basin, Yellowstone National Park, USA based on a combined eddy covariance and Multi-GAS approach

    Science.gov (United States)

    Lewicki, Jennifer L.; Kelly, Peter; Bergfeld, Deborah; Vaughan, R. Greg; Lowenstern, Jacob B.

    2017-01-01

    We quantified gas and heat emissions in an acid-sulfate, vapor-dominated area (0.04-km2) of Norris Geyser Basin, located just north of the 0.63 Ma Yellowstone Caldera and near an area of anomalous uplift. From 14 May to 3 October 2016, an eddy covariance system measured half-hourly CO2, H2O and sensible (H) and latent (LE) heat fluxes and a Multi-GAS instrument measured (1 Hz frequency) atmospheric H2O, CO2 and H2S volumetric mixing ratios. We also measured soil CO2 fluxes using the accumulation chamber method and temperature profiles on a grid and collected fumarole gas samples for geochemical analysis. Eddy covariance CO2 fluxes ranged from − 56 to 885 g m− 2 d− 1. Using wavelet analysis, average daily eddy covariance CO2 fluxes were locally correlated with average daily environmental parameters on several-day to monthly time scales. Estimates of CO2emission rate from the study area ranged from 8.6 t d− 1 based on eddy covariance measurements to 9.8 t d− 1 based on accumulation chamber measurements. Eddy covariance water vapor fluxes ranged from 1178 to 24,600 g m− 2 d− 1. Nighttime H and LEwere considered representative of hydrothermal heat fluxes and ranged from 4 to 183 and 38 to 504 W m− 2, respectively. The total hydrothermal heat emission rate (H + LE + radiant) estimated for the study area was 11.6 MW and LE contributed 69% of the output. The mean ± standard deviation of H2O, CO2 and H2S mixing ratios measured by the Multi-GAS system were 9.3 ± 3.1 parts per thousand, 467 ± 61 ppmv, and 0.5 ± 0.6 ppmv, respectively, and variations in the gas compositions were strongly correlated with diurnal variations in environmental parameters (wind speed and direction, atmospheric temperature). After removing ambient H2O and CO2, the observed variations in the Multi-GAS data could be explained by the mixing of relatively H2O-CO2-H2S-rich fumarole gases with CO2-rich and H2O-H2S-poor soil gases. The

  19. Monitoring ecosystem reclamation recovery using optical remote sensing: Comparison with field measurements and eddy covariance.

    Science.gov (United States)

    Chasmer, L; Baker, T; Carey, S K; Straker, J; Strilesky, S; Petrone, R

    2018-06-12

    Time series remote sensing vegetation indices derived from SPOT 5 data are compared with vegetation structure and eddy covariance flux data at 15 dry to wet reclamation and reference sites within the Oil Sands region of Alberta, Canada. This comprehensive analysis examines the linkages between indicators of ecosystem function and change trajectories observed both at the plot level and within pixels. Using SPOT imagery, we find that higher spatial resolution datasets (e.g. 10 m) improves the relationship between vegetation indices and structural measurements compared with interpolated (lower resolution) pixels. The simple ratio (SR) vegetation index performs best when compared with stem density-based indicators (R 2  = 0.65; p  0.02). Fluxes (net ecosystem production (NEP) and gross ecosystem production (GEP)) are most related to NDVI and SAVI when these are interpolated to larger 20 m × 20 m pixels (R 2  = 0.44-0.50; p  3 m 2  m -2 , making this index more appropriate for newly regenerating reclamation areas. For sites with LAI remote sensing in combination with field and eddy covariance data for monitoring and scaling of reclaimed and reference site productivity within and beyond the Oil Sands Region of western Canada. Copyright © 2018 Elsevier B.V. All rights reserved.

  20. A Comparison of Three Gap Filling Techniques for Eddy Covariance Net Carbon Fluxes in Short Vegetation Ecosystems

    Directory of Open Access Journals (Sweden)

    Xiaosong Zhao

    2015-01-01

    Full Text Available Missing data is an inevitable problem when measuring CO2, water, and energy fluxes between biosphere and atmosphere by eddy covariance systems. To find the optimum gap-filling method for short vegetations, we review three-methods mean diurnal variation (MDV, look-up tables (LUT, and nonlinear regression (NLR for estimating missing values of net ecosystem CO2 exchange (NEE in eddy covariance time series and evaluate their performance for different artificial gap scenarios based on benchmark datasets from marsh and cropland sites in China. The cumulative errors for three methods have no consistent bias trends, which ranged between −30 and +30 mgCO2 m−2 from May to October at three sites. To reduce sum bias in maximum, combined gap-filling methods were selected for short vegetation. The NLR or LUT method was selected after plant rapidly increasing in spring and before the end of plant growing, and MDV method was used to the other stage. The sum relative error (SRE of optimum method ranged between −2 and +4% for four-gap level at three sites, except for 55% gaps at soybean site, which also obviously reduced standard deviation of error.

  1. Eddy covariance measurements of greenhouse gases from a restored and rewetted raised bog ecosystem.

    Science.gov (United States)

    Lee, S. C.; Christen, A.; Black, T. A.; Johnson, M. S.; Ketler, R.; Nesic, Z.; Merkens, M.

    2015-12-01

    Wetland ecosystems play a significant role in the global carbon (C) cycle. Wetlands act as a major long-term storage of carbon by sequestrating carbon-dioxide (CO2) from the atmosphere. Meanwhile, they can emit significant amounts of methane (CH4) due to anaerobic microbial decomposition. The Burns Bog Ecological Conservancy Area (BBECA) is recognized as one of Canada's largest undeveloped natural areas retained within an urban area. Historically, it has been substantially reduced in size and degraded by peat mining and agriculture. Since 2005, the bog has been declared a conservancy area, and the restoration efforts in BBECA focus on rewetting the disturbed ecosystems to promote a transition back to a raised bog. A pilot study measured CH4, CO2 and N2O exchanges in 2014 and concluded to monitor CO2, CH4 fluxes continuously. From the perspective of greenhouse gas (GHG) emissions, CO2 sequestered in bog needs to be protected and additional CO2 and CH4 emissions due to land-cover change need to be reduced by wise management. In this study, we measured the growing-season (June-September) fluxes of CO2 and CH4 exchange using eddy covariance (EC). A floating platform with an EC system for both CO2 (closed-path) and CH4 (open-path) began operation in June 2015. During the growing-season, gross ecosystem photosynthesis (GEP) and ecosystem respiration (Re) averaged 5.87 g C m-2 day-1 and 2.02 g C m-2 day-1, respectively. The magnitude of GEP and Re were lower than in previous studies of pristine northern peatlands. The daily average CH4 emission was 0.99 (±1.14) g C m-2 day-1 and it was higher than in most previous studies. We also characterized how environmental factors affected the seasonal dynamics of these exchanges in this disturbed peatland. Our measurements showed that soil temperature and soil water content were major drivers of seasonal changes of GHG fluxes. The daily average GHG warming potential (GWP) of the emissions in the growing seasons (from CO2 and CH4

  2. Gap-filling eddy-covariance data using a complex system of neural networks

    Science.gov (United States)

    Dúbrava, Matúš; Rebok, Tomáš; Havránková, Kateřina; Pavelka, Marian

    2014-05-01

    The eddy-covariance technique measures the flux of matter and energy between various ecosystems and the atmosphere. The fluxes characterize an interaction of the ecosystems with their surroundings and provide valuable knowledge to Global Climate Change issues. Among the main assets of the method belongs the possible evaluation of the carbon balance, expressed as the Net Ecosystem carbon Exchange (NEE) parameter. However, when unfavorable micro-meteorological conditions (e.g., stable stratification and low turbulent mixing) happen, measured fluxes are inaccurate and need to be corrected and/or gap-filled. Thus, there is a long-term challenge for many research teams from the flux community to develop the most accurate gap-filling method -- many statistical as well as empirical approaches have been proposed so far (e.g., mean replacement, interpolation, extrapolation, regression analysis, methods based on plant physiology depending on meteorological variables, etc.), each of them having its strengths and weaknesses. The artificial neural networks (ANNs) -- purely empirical non-linear regression models generally able to solve any fitness approximation and pattern recognition problem -- were proven as a promising approach and one of the most precise method for gap-filling the eddy-covariance data. However, even though providing encouraging results when considering a prediction error throughout the whole dataset, they considerably fail in fitting inherently present spikes in the NEE values. This drawback results from the nature of ANNs, since their ability to fit spikes is partly in contrast with their ability to reliably approximate previously unseen data -- while the spike fitting can be improved by an increasing number of training epochs, this often leads to ANNs over-fitting and thus losing their generalization ability, resulting in higher overall prediction error. Since the proper generalization ability has greater impact on the precision of the results, current

  3. VOC emission rates over London and South East England obtained by airborne eddy covariance.

    Science.gov (United States)

    Vaughan, Adam R; Lee, James D; Shaw, Marvin D; Misztal, Pawel K; Metzger, Stefan; Vieno, Massimo; Davison, Brian; Karl, Thomas G; Carpenter, Lucy J; Lewis, Alastair C; Purvis, Ruth M; Goldstein, Allen H; Hewitt, C Nicholas

    2017-08-24

    Volatile organic compounds (VOCs) originate from a variety of sources, and play an intrinsic role in influencing air quality. Some VOCs, including benzene, are carcinogens and so directly affect human health, while others, such as isoprene, are very reactive in the atmosphere and play an important role in the formation of secondary pollutants such as ozone and particles. Here we report spatially-resolved measurements of the surface-to-atmosphere fluxes of VOCs across London and SE England made in 2013 and 2014. High-frequency 3-D wind velocities and VOC volume mixing ratios (made by proton transfer reaction - mass spectrometry) were obtained from a low-flying aircraft and used to calculate fluxes using the technique of eddy covariance. A footprint model was then used to quantify the flux contribution from the ground surface at spatial resolution of 100 m, averaged to 1 km. Measured fluxes of benzene over Greater London showed positive agreement with the UK's National Atmospheric Emissions Inventory, with the highest fluxes originating from central London. Comparison of MTBE and toluene fluxes suggest that petroleum evaporation is an important emission source of toluene in central London. Outside London, increased isoprene emissions were observed over wooded areas, at rates greater than those predicted by a UK regional application of the European Monitoring and Evaluation Programme model (EMEP4UK). This work demonstrates the applicability of the airborne eddy covariance method to the determination of anthropogenic and biogenic VOC fluxes and the possibility of validating emission inventories through measurements.

  4. Carbon fluxes of surfaces vs. ecosystems. Advantages of measuring eddy covariance and soil respiration simultaneously in dry grassland ecosystems

    Czech Academy of Sciences Publication Activity Database

    Nagy, Z.; Pintér, K.; Pavelka, Marian; Dařenová, Eva; Balogh, J.

    2011-01-01

    Roč. 8, č. 9 (2011), s. 2523-2534 ISSN 1726-4170 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0073 Institutional research plan: CEZ:AV0Z60870520 Keywords : carbon fluxes * ecosystems * grassland ecoystems * measuring eddy covariance * soil respiration Subject RIV: EH - Ecology, Behaviour Impact factor: 3.859, year: 2011

  5. NEON's eddy-covariance: interoperable flux data products, software and services for you, now

    Science.gov (United States)

    Metzger, S.; Desai, A. R.; Durden, D.; Hartmann, J.; Li, J.; Luo, H.; Durden, N. P.; Sachs, T.; Serafimovich, A.; Sturtevant, C.; Xu, K.

    2017-12-01

    Networks of eddy-covariance (EC) towers such as AmeriFlux, ICOS and NEON are vital for providing the necessary distributed observations to address interactions at the soil-vegetation-atmosphere interface. NEON, close to full operation with 47 tower sites, will represent the largest single-provider EC network globally. Its standardized observation and data processing suite is designed specifically for inter-site comparability and analysis of feedbacks across multiple spatial and temporal scales. Furthermore, NEON coordinates EC with rich contextual observations such as airborne remote sensing and in-situ sampling bouts. In January 2018 NEON enters its operational phase, and EC data products, software and services become fully available to the science community at large. These resources strive to incorporate lessons-learned through collaborations with AmeriFlux, ICOS, LTER and others, to suggest novel systemic solutions, and to synergize ongoing research efforts across science communities. Here, we present an overview of the ongoing product release, alongside efforts to integrate and collaborate with existing infrastructures, networks and communities. Near-real-time heat, water and carbon cycle observations in "basic" and "expanded", self-describing HDF5 formats become accessible from the NEON Data Portal, including an Application Program Interface. Subsequently, they are ingested into the AmeriFlux processing pipeline, together with inclusion in FLUXNET globally harmonized data releases. Software for reproducible, extensible and portable data analysis and science operations management also becomes available. This includes the eddy4R family of R-packages underlying the data product generation, together with the ability to directly participate in open development via GitHub version control and DockerHub image hosting. In addition, templates for science operations management include a web-based field maintenance application and a graphical user interface to simplify

  6. Comparison of eddy covariance and modified Bowen ratio methods for measuring gas fluxes and implications for measuring fluxes of persistent organic pollutants

    Directory of Open Access Journals (Sweden)

    D. J. Bolinius

    2016-04-01

    Full Text Available Semi-volatile persistent organic pollutants (POPs cycle between the atmosphere and terrestrial surfaces; however measuring fluxes of POPs between the atmosphere and other media is challenging. Sampling times of hours to days are required to accurately measure trace concentrations of POPs in the atmosphere, which rules out the use of eddy covariance techniques that are used to measure gas fluxes of major air pollutants. An alternative, the modified Bowen ratio (MBR method, has been used instead. In this study we used data from FLUXNET for CO2 and water vapor (H2O to compare fluxes measured by eddy covariance to fluxes measured with the MBR method using vertical concentration gradients in air derived from averaged data that simulate the long sampling times typically required to measure POPs. When concentration gradients are strong and fluxes are unidirectional, the MBR method and the eddy covariance method agree within a factor of 3 for CO2, and within a factor of 10 for H2O. To remain within the range of applicability of the MBR method, field studies should be carried out under conditions such that the direction of net flux does not change during the sampling period. If that condition is met, then the performance of the MBR method is neither strongly affected by the length of sample duration nor the use of a fixed value for the transfer coefficient.

  7. Modelling carbon fluxes of forest and grassland ecosystems in Western Europe using the CARAIB dynamic vegetation model: evaluation against eddy covariance data.

    Science.gov (United States)

    Henrot, Alexandra-Jane; François, Louis; Dury, Marie; Hambuckers, Alain; Jacquemin, Ingrid; Minet, Julien; Tychon, Bernard; Heinesch, Bernard; Horemans, Joanna; Deckmyn, Gaby

    2015-04-01

    Eddy covariance measurements are an essential resource to understand how ecosystem carbon fluxes react in response to climate change, and to help to evaluate and validate the performance of land surface and vegetation models at regional and global scale. In the framework of the MASC project (« Modelling and Assessing Surface Change impacts on Belgian and Western European climate »), vegetation dynamics and carbon fluxes of forest and grassland ecosystems simulated by the CARAIB dynamic vegetation model (Dury et al., iForest - Biogeosciences and Forestry, 4:82-99, 2011) are evaluated and validated by comparison of the model predictions with eddy covariance data. Here carbon fluxes (e.g. net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (RECO)) and evapotranspiration (ET) simulated with the CARAIB model are compared with the fluxes measured at several eddy covariance flux tower sites in Belgium and Western Europe, chosen from the FLUXNET global network (http://fluxnet.ornl.gov/). CARAIB is forced either with surface atmospheric variables derived from the global CRU climatology, or with in situ meteorological data. Several tree (e.g. Pinus sylvestris, Fagus sylvatica, Picea abies) and grass species (e.g. Poaceae, Asteraceae) are simulated, depending on the species encountered on the studied sites. The aim of our work is to assess the model ability to reproduce the daily, seasonal and interannual variablility of carbon fluxes and the carbon dynamics of forest and grassland ecosystems in Belgium and Western Europe.

  8. Continuous measurement of air-water gas exchange by underwater eddy covariance

    Science.gov (United States)

    Berg, Peter; Pace, Michael L.

    2017-12-01

    Exchange of gases, such as O2, CO2, and CH4, over the air-water interface is an important component in aquatic ecosystem studies, but exchange rates are typically measured or estimated with substantial uncertainties. This diminishes the precision of common ecosystem assessments associated with gas exchanges such as primary production, respiration, and greenhouse gas emission. Here, we used the aquatic eddy covariance technique - originally developed for benthic O2 flux measurements - right below the air-water interface (˜ 4 cm) to determine gas exchange rates and coefficients. Using an acoustic Doppler velocimeter and a fast-responding dual O2-temperature sensor mounted on a floating platform the 3-D water velocity, O2 concentration, and temperature were measured at high-speed (64 Hz). By combining these data, concurrent vertical fluxes of O2 and heat across the air-water interface were derived, and gas exchange coefficients were calculated from the former. Proof-of-concept deployments at different river sites gave standard gas exchange coefficients (k600) in the range of published values. A 40 h long deployment revealed a distinct diurnal pattern in air-water exchange of O2 that was controlled largely by physical processes (e.g., diurnal variations in air temperature and associated air-water heat fluxes) and not by biological activity (primary production and respiration). This physical control of gas exchange can be prevalent in lotic systems and adds uncertainty to assessments of biological activity that are based on measured water column O2 concentration changes. For example, in the 40 h deployment, there was near-constant river flow and insignificant winds - two main drivers of lotic gas exchange - but we found gas exchange coefficients that varied by several fold. This was presumably caused by the formation and erosion of vertical temperature-density gradients in the surface water driven by the heat flux into or out of the river that affected the turbulent

  9. Continuous measurement of air–water gas exchange by underwater eddy covariance

    Directory of Open Access Journals (Sweden)

    P. Berg

    2017-12-01

    Full Text Available Exchange of gases, such as O2, CO2, and CH4, over the air–water interface is an important component in aquatic ecosystem studies, but exchange rates are typically measured or estimated with substantial uncertainties. This diminishes the precision of common ecosystem assessments associated with gas exchanges such as primary production, respiration, and greenhouse gas emission. Here, we used the aquatic eddy covariance technique – originally developed for benthic O2 flux measurements – right below the air–water interface (∼ 4 cm to determine gas exchange rates and coefficients. Using an acoustic Doppler velocimeter and a fast-responding dual O2–temperature sensor mounted on a floating platform the 3-D water velocity, O2 concentration, and temperature were measured at high-speed (64 Hz. By combining these data, concurrent vertical fluxes of O2 and heat across the air–water interface were derived, and gas exchange coefficients were calculated from the former. Proof-of-concept deployments at different river sites gave standard gas exchange coefficients (k600 in the range of published values. A 40 h long deployment revealed a distinct diurnal pattern in air–water exchange of O2 that was controlled largely by physical processes (e.g., diurnal variations in air temperature and associated air–water heat fluxes and not by biological activity (primary production and respiration. This physical control of gas exchange can be prevalent in lotic systems and adds uncertainty to assessments of biological activity that are based on measured water column O2 concentration changes. For example, in the 40 h deployment, there was near-constant river flow and insignificant winds – two main drivers of lotic gas exchange – but we found gas exchange coefficients that varied by several fold. This was presumably caused by the formation and erosion of vertical temperature–density gradients in the surface water driven by the heat flux into or

  10. Comparison of soil CO2 fluxes by eddy-covariance and chamber methods in fallow periods of a corn-soybean rotation

    Science.gov (United States)

    Soil carbon dioxide (CO2) fluxes are typically measured by eddy-covariance (EC) or chamber (Ch) methods, but a long-term comparison has not been undertaken. This study was conducted to assess the agreement between EC and Ch techniques when measuring CO2 flux during fallow periods of a corn-soybean r...

  11. Tools and Methods for Visualization of Mesoscale Ocean Eddies

    Science.gov (United States)

    Bemis, K. G.; Liu, L.; Silver, D.; Kang, D.; Curchitser, E.

    2017-12-01

    Mesoscale ocean eddies form in the Gulf Stream and transport heat and nutrients across the ocean basin. The internal structure of these three-dimensional eddies and the kinematics with which they move are critical to a full understanding of their transport capacity. A series of visualization tools have been developed to extract, characterize, and track ocean eddies from 3D modeling results, to visually show the ocean eddy story by applying various illustrative visualization techniques, and to interactively view results stored on a server from a conventional browser. In this work, we apply a feature-based method to track instances of ocean eddies through the time steps of a high-resolution multidecadal regional ocean model and generate a series of eddy paths which reflect the life cycle of individual eddy instances. The basic method uses the Okubu-Weiss parameter to define eddy cores but could be adapted to alternative specifications of an eddy. Stored results include pixel-lists for each eddy instance, tracking metadata for eddy paths, and physical and geometric properties. In the simplest view, isosurfaces are used to display eddies along an eddy path. Individual eddies can then be selected and viewed independently or an eddy path can be viewed in the context of all eddy paths (longer than a specified duration) and the ocean basin. To tell the story of mesoscale ocean eddies, we combined illustrative visualization techniques, including visual effectiveness enhancement, focus+context, and smart visibility, with the extracted volume features to explore eddy characteristics at multiple scales from ocean basin to individual eddy. An evaluation by domain experts indicates that combining our feature-based techniques with illustrative visualization techniques provides an insight into the role eddies play in ocean circulation. A web-based GUI is under development to facilitate easy viewing of stored results. The GUI provides the user control to choose amongst available

  12. Suitability of quantum cascade laser spectroscopy for CH4 and N2O eddy covariance flux measurements

    Directory of Open Access Journals (Sweden)

    A. T. Vermeulen

    2007-08-01

    Full Text Available A quantum cascade laser spectrometer was evaluated for eddy covariance flux measurements of CH4 and N2O using three months of continuous measurements at a field site. The required criteria for eddy covariance flux measurements including continuity, sampling frequency, precision and stationarity were examined. The system operated continuously at a dairy farm on peat grassland in the Netherlands from 17 August to 6 November 2006. An automatic liquid nitrogen filling system for the infrared detector was employed to provide unattended operation of the system. The electronic sampling frequency was 10 Hz, however, the flow response time was 0.08 s, which corresponds to a bandwidth of 2 Hz. A precision of 2.9 and 0.5 ppb Hz−1/2 was obtained for CH4 and N2O, respectively. Accuracy was assured by frequent calibrations using low and high standard additions. Drifts in the system were compensated by using a 120 s running mean filter. The average CH4 and N2O exchange was 512 ngC m−2 s−1 (2.46 mg m−2 hr−1 and 52 ngN m−2 s−1 (0.29 mg m−2 hr−1. Given that 40% of the total N2O emission was due to a fertilizing event.

  13. Covariant and consistent anomalies in two dimensions in path-integral formulation

    International Nuclear Information System (INIS)

    Joglekar, S.D.; Saini, G.

    1993-01-01

    We give a definition of a one-parameter family of regularized chiral currents in a chiral non-Abelian gauge theory in two dimensions in path-integral formulation. We show that covariant and consistent currents are obtained from this family by selecting two specific values of the free parameter, and thus our regularization interpolates between these two. Our procedure uses chiral bases constructed from eigenfunctions of the same operator for ψ L and anti ψ L . Definition of integration measure and regularization is done in terms of the same Hermitian operator D α =∂+iαA. Covariant and consistent currents (and indeed the entire family) are classically conserved. Difference with previous works are explained, in particular, that an anomaly in the general basis does differ from the Jacobian contribution. (orig.)

  14. A New Tool for Automated Data Collection and Complete On-site Flux Data Processing for Eddy Covariance Measurements

    Science.gov (United States)

    Begashaw, I. G.; Kathilankal, J. C.; Li, J.; Beaty, K.; Ediger, K.; Forgione, A.; Fratini, G.; Johnson, D.; Velgersdyk, M.; Hupp, J. R.; Xu, L.; Burba, G. G.

    2014-12-01

    The eddy covariance method is widely used for direct measurements of turbulent exchange of gases and energy between the surface and atmosphere. In the past, raw data were collected first in the field and then processed back in the laboratory to achieve fully corrected publication-ready flux results. This post-processing consumed significant amount of time and resources, and precluded researchers from accessing near real-time final flux results. A new automated measurement system with novel hardware and software designs was developed, tested, and deployed starting late 2013. The major advancements with this automated flux system include: 1) Enabling logging high-frequency, three-dimensional wind speeds and multiple gas densities (CO2, H2O and CH4), low-frequency meteorological data, and site metadata simultaneously through a specially designed file format 2) Conducting fully corrected, real-time on-site flux computations using conventional as well as user-specified methods, by implementing EddyPro Software on a small low-power microprocessor 3) Providing precision clock control and coordinate information for data synchronization and inter-site data comparison by incorporating a GPS and Precision Time Protocol. Along with these innovations, a data management server application was also developed to chart fully corrected real-time fluxes to assist remote system monitoring, to send e-mail alerts, and to automate data QA/QC, transfer and archiving at individual stations or on a network level. Combination of all of these functions was designed to help save substantial amount of time and costs associated with managing a research site by eliminating the post-field data processing, reducing user errors and facilitating real-time access to fully corrected flux results. The design, functionality, and test results from this new eddy covariance measurement tool will be presented.

  15. On the estimate of the transpiration in Mediterranean heterogeneous ecosystems with the coupled use of eddy covariance and sap flow techniques.

    Science.gov (United States)

    Corona, Roberto; Curreli, Matteo; Montaldo, Nicola; Oren, Ram

    2013-04-01

    Mediterranean ecosystems are commonly heterogeneous savanna-like ecosystems, with contrasting plant functional types (PFT) competing for the water use. Mediterranean regions suffer water scarcity due to the dry climate conditions. In semi-arid regions evapotranspiration (ET) is the leading loss term of the root-zone water budget with a yearly magnitude that may be roughly equal to the precipitation. Despite the attention these ecosystems are receiving, a general lack of knowledge persists about the estimate of ET and the relationship between ET and the plant survival strategies for the different PFTs under water stress. During the dry summers these water-limited heterogeneous ecosystems are mainly characterized by a simple dual PFT-landscapes with strong-resistant woody vegetation and bare soil since grass died. In these conditions due to the low signal of the land surface fluxes captured by the sonic anemometer and gas analyzer the widely used eddy covariance may fail and its ET estimate is not robust enough. In these conditions the use of the sap flow technique may have a key role, because theoretically it provides a direct estimate of the woody vegetation transpiration. Through the coupled use of the sap flow sensor observations, a 2D foot print model of the eddy covariance tower and high resolution satellite images for the estimate of the foot print land cover map, the eddy covariance measurements can be correctly interpreted, and ET components (bare soil evaporation and woody vegetation transpiration) can be separated. The case study is at the Orroli site in Sardinia (Italy). The site landscape is a mixture of Mediterranean patchy vegetation types: trees, including wild olives and cork oaks, different shrubs and herbaceous species. An extensive field campaign started in 2004. Land-surface fluxes and CO2 fluxes are estimated by an eddy covariance technique based micrometeorological tower. Soil moisture profiles were also continuously estimated using water

  16. Evaluation of an on-line methodology for measuring volatile organic compounds (VOC) fluxes by eddy-covariance with a PTR-TOF-Qi-MS

    Science.gov (United States)

    Loubet, Benjamin; Buysse, Pauline; Lafouge, Florence; Ciuraru, Raluca; Decuq, Céline; Zurfluh, Olivier

    2017-04-01

    Field scale flux measurements of volatile organic compounds (VOC) are essential for improving our knowledge of VOC emissions from ecosystems. Many VOCs are emitted from and deposited to ecosystems. Especially less known, are crops which represent more than 50% of French terrestrial surfaces. In this study, we evaluate a new on-line methodology for measuring VOC fluxes by Eddy Covariance with a PTR-Qi-TOF-MS. Measurements were performed at the ICOS FR-GRI site over a crop using a 30 m long high flow rate sampling line and an ultrasonic anemometer. A Labview program was specially designed for acquisition and on-line covariance calculation: Whole mass spectra ( 240000 channels) were acquired on-line at 10 Hz and stored in a temporary memory. Every 5 minutes, the spectra were mass-calibrated and normalized by the primary ion peak integral at 10 Hz. The mass spectra peaks were then retrieved from the 5-min averaged spectra by withdrawing the baseline, determining the resolution and using a multiple-peak detection algorithm. In order to optimize the peak detection algorithm for the covariance, we determined the covariances as the integrals of the peaks of the vertical-air-velocity-fluctuation weighed-averaged-spectra. In other terms, we calculate , were w is the vertical component of the air velocity, Sp is the spectra, t is time, lag is the decorrelation lag time and denotes an average. The lag time was determined as the decorrelation time between w and the primary ion (at mass 21.022) which integrates the contribution of all reactions of VOC and water with the primary ion. Our algorithm was evaluated by comparing the exchange velocity of water vapor measured by an open path absorption spectroscopy instrument and the water cluster measured with the PTRQi-TOF-MS. The influence of the algorithm parameters and lag determination is discussed. This study was supported by the ADEME-CORTEA COV3ER project (http://www6.inra.fr/cov3er).

  17. Evaluation of a plot-scale methane emission model using eddy covariance observations and footprint modelling

    Directory of Open Access Journals (Sweden)

    A. Budishchev

    2014-09-01

    Full Text Available Most plot-scale methane emission models – of which many have been developed in the recent past – are validated using data collected with the closed-chamber technique. This method, however, suffers from a low spatial representativeness and a poor temporal resolution. Also, during a chamber-flux measurement the air within a chamber is separated from the ambient atmosphere, which negates the influence of wind on emissions. Additionally, some methane models are validated by upscaling fluxes based on the area-weighted averages of modelled fluxes, and by comparing those to the eddy covariance (EC flux. This technique is rather inaccurate, as the area of upscaling might be different from the EC tower footprint, therefore introducing significant mismatch. In this study, we present an approach to validate plot-scale methane models with EC observations using the footprint-weighted average method. Our results show that the fluxes obtained by the footprint-weighted average method are of the same magnitude as the EC flux. More importantly, the temporal dynamics of the EC flux on a daily timescale are also captured (r2 = 0.7. In contrast, using the area-weighted average method yielded a low (r2 = 0.14 correlation with the EC measurements. This shows that the footprint-weighted average method is preferable when validating methane emission models with EC fluxes for areas with a heterogeneous and irregular vegetation pattern.

  18. Assessing the net effect of long-term drainage on a permafrost ecosystem through year-round eddy-covariance flux measurements

    Science.gov (United States)

    Kittler, F.; Heimann, M.; Goeckede, M.; Zimov, S. A.; Zimov, N.

    2014-12-01

    Permafrost regions in the Northern high latitudes play a key role in the carbon budget of the earth system because of their massive carbon reservoir and the uncertain feedback processes with future climate change. For an improved understanding of mechanisms and drivers dominating permafrost carbon cycling, more observations in high-latitude regions are needed. Particularly the contribution of wintertime fluxes to the annual carbon budget and the impact of disturbances on biogeochemical and biogeophysical ecosystem properties, and the resulting modification of the carbon cycle, have rarely been studied to date. In summer of 2013, we established a new eddy-covariance station for continuous, year-round monitoring of carbon fluxes and their environmental drivers near Cherskii in Northeast Siberia (68.75°N, 161.33°E). Parts of the observation area have been disturbed by drainage since 2004, altering the soil water conditions in a way that is expected for degrading ice-rich permafrost under a warming climate. With two eddy-covariance towers running in parallel over the disturbed (drained) area and a reference area nearby, respectively, we can directly infer the disturbance effect on the carbon cycle budgets and the dominating biogeochemical mechanisms. This study presents findings based on 16 months of continuous eddy-covariance CO2 flux measurements (July 2013 - October 2014) for both observation areas. At both towers, we observed systematic, non-zero flux contributions outside the growing seasons that significantly altered annual CO2 budgets. A direct comparison of fluxes between the two disturbance regimes indicates a net reduction of the sink strength for CO2 in the disturbed area during the growing season, mostly caused by reduced CO2 uptake with low water levels in late summer. Moreover, shifts in soil temperatures and snow cover caused by reduced soil water levels result in lower net CO2 emissions during the winter at the drained area, which is partly

  19. Generalized Lagrangian Path Approach to Manifestly-Covariant Quantum Gravity Theory

    Directory of Open Access Journals (Sweden)

    Massimo Tessarotto

    2018-03-01

    Full Text Available A trajectory-based representation for the quantum theory of the gravitational field is formulated. This is achieved in terms of a covariant Generalized Lagrangian-Path (GLP approach which relies on a suitable statistical representation of Bohmian Lagrangian trajectories, referred to here as GLP-representation. The result is established in the framework of the manifestly-covariant quantum gravity theory (CQG-theory proposed recently and the related CQG-wave equation advancing in proper-time the quantum state associated with massive gravitons. Generally non-stationary analytical solutions for the CQG-wave equation with non-vanishing cosmological constant are determined in such a framework, which exhibit Gaussian-like probability densities that are non-dispersive in proper-time. As a remarkable outcome of the theory achieved by implementing these analytical solutions, the existence of an emergent gravity phenomenon is proven to hold. Accordingly, it is shown that a mean-field background space-time metric tensor can be expressed in terms of a suitable statistical average of stochastic fluctuations of the quantum gravitational field whose quantum-wave dynamics is described by GLP trajectories.

  20. Methane eddy covariance flux measurements from a low flying aircraft: Bridging the scale gap between local and regional emissions estimates

    Science.gov (United States)

    Sayres, D. S.; Dobosy, R.; Dumas, E. J.; Kochendorfer, J.; Wilkerson, J.; Anderson, J. G.

    2017-12-01

    The Arctic contains a large reservoir of organic matter stored in permafrost and clathrates. Varying geology and hydrology across the Arctic, even on small scales, can cause large variability in surface carbon fluxes and partitioning between methane and carbon dioxide. This makes upscaling from point source measurements such as small flux towers or chambers difficult. Ground based measurements can yield high temporal resolution and detailed information about a specific location, but due to the inaccessibility of most of the Arctic to date have only made measurements at very few sites. In August 2013, a small aircraft, flying low over the surface (5-30 m), and carrying an air turbulence probe and spectroscopic instruments to measure methane, carbon dioxide, nitrous oxide, water vapor and their isotopologues, flew over the North Slope of Alaska. During the six flights multiple comparisons were made with a ground based Eddy Covariance tower as well as three region surveys flights of fluxes over three areas each approximately 2500 km2. We present analysis using the Flux Fragment Method and surface landscape classification maps to relate the fluxes to different surface land types. We show examples of how we use the aircraft data to upscale from a eddy covariance tower and map spatial variability across different ecotopes.

  1. Observing Carbon Dioxide Fluxes on a Corn Field and a Native Savanna in the Colombian Orinoco River Region Using Eddy Covariance

    Science.gov (United States)

    Morales-Rincon, L. A.; Jimenez-Pizarro, R.; Rodríguez, N.

    2016-12-01

    The Orinoco River basin is expected to become Colombia's largest farming belt in the near future. Agriculture and land use change are the most important greenhouse gas (GHG) source in Colombia and one of the most important globally. At the same time, agriculture is one of the few economic sectors that is also able to act as a sink, e.g. through soil carbon storage. Emissions are largely determined by agricultural practices, thus practice identification and C flux monitoring are of paramount importance for mitigation alternative identification. During second semester of 2015, we measured CO2 fluxes over a commercial corn filed the Colombian Orinoco River Region using enclosed-path eddy covariance. The plot behaved as a CO2 sink during crop development. We found that inter-crop activities played a key role in defining whether the area acted as a net source or sink. Quantifying C fluxes at under local soil and meteorological conditions provides new high quality scientific information, which could be incorporated into a wider evaluation of agroindustry process, e.g. through the C footprint. We will also present ongoing carbon flux measurements in a native savanna and will discuss on the possibility of extrapolating our result to wider areas using process based models.

  2. Eddy covariance fluxes of the NO-O3-NO2 triad above the forest canopy at the ATTO Site in the Amazon Basin

    Science.gov (United States)

    Tsokankunku, Anywhere; Wolff, Stefan; Sörgel, Matthias; Berger, Martina; Zelger, Michael; Dlugi, Ralf

    2017-04-01

    Nitrogen monoxide (NO) and nitrogen dioxide (NO2) (denoted together as NOx) determine the abundance of the tropospheric oxidants OH, O3 and NO3 that regulate atmospheric self-cleaning. The three reactive trace gases NO, NO2 and O3 undergo a series of interconnected photochemical reactions and are often referred to as the NO-O3-NO2 triad. Ozone deposition is mainly controlled by stomatal uptake, thus contributes to oxidative stress for the plants. Similarly, nitrogen dioxide from above or below the canopy is deposited to leaves through stomatal uptake. NO emissions from soils contribute to above canopy O3 formation and accelerate OH recycling. Therefore, quantification of the exchange fluxes of these species between the atmosphere and the biosphere are important for atmospheric chemistry and ecosystem research as well. The eddy covariance method is state of the art for direct measurements of ecosystem fluxes of trace gases. Eddy covariance measurements of NOx in pristine environments are rare because of lack of availability of instruments with the required precision to resolve concentrations characteristic of these environments. The Amazon Tall Tower Observatory (ATTO) is located in a pristine rainforest environment in the Amazon basin about 150 km northeast of the city of Manaus. It is the ideal site for studying the biosphere-atmosphere exchange of the NO-O3-NO2 triad, being largely undisturbed by anthropogenic sources. During an intensive measurement campaign in November 2015 at the ATTO site, measurements of NO, NO2 and O3 were carried out at 42 m above ground level on the 80 m walk-up tower with a fast (5 Hz) and sensitive (radiation. Vertical concentration profile measurements of NO, NO2 and O3 were available at 8 levels on the INSTANT tower from a reactive trace gas profile system which has been operational at the site since 2012. From these measurements, we present eddy covariance fluxes of the NO-O3-NO2 triad. We relate the fluxes to the canopy

  3. Deriving Daytime Variables From the AmeriFlux Standard Eddy Covariance Data Set

    Energy Technology Data Exchange (ETDEWEB)

    van Ingen, Catharine [Berkeley Water Center. Berkeley, CA (United States); Microsoft. San Francisco, CA (United States); Agarwal, Deborah A. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Berkeley Water Center. Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); Humphrey, Marty [Univ. of Virginia, Charlottesville, VA (United States); Li, Jie [Univ. of Virginia, Charlottesville, VA (United States)

    2008-12-06

    A gap-filled, quality assessed eddy covariance dataset has recently become available for the AmeriFluxnetwork. This dataset uses standard processing and produces commonly used science variables. This shared dataset enables robust comparisons across different analyses. Of course, there are many remaining questions. One of those is how to define 'during the day' which is an important concept for many analyses. Some studies have used local time — for example 9am to 5pm; others have used thresholds on photosynthetic active radiation (PAR). A related question is how to derive quantities such as the Bowen ratio. Most studies compute the ratio of the averages of the latent heat (LE) and sensible heat (H). In this study, we use different methods of defining 'during the day' for GPP, LE, and H. We evaluate the differences between methods in two ways. First, we look at a number of statistics of GPP. Second, we look at differences in the derived Bowen ratio. Our goal is not science per se, but rather informatics in support of the science.

  4. Using eddy covariance to measure the dependence of air-sea CO2 exchange rate on friction velocity

    Science.gov (United States)

    Landwehr, Sebastian; Miller, Scott D.; Smith, Murray J.; Bell, Thomas G.; Saltzman, Eric S.; Ward, Brian

    2018-03-01

    Parameterisation of the air-sea gas transfer velocity of CO2 and other trace gases under open-ocean conditions has been a focus of air-sea interaction research and is required for accurately determining ocean carbon uptake. Ships are the most widely used platform for air-sea flux measurements but the quality of the data can be compromised by airflow distortion and sensor cross-sensitivity effects. Recent improvements in the understanding of these effects have led to enhanced corrections to the shipboard eddy covariance (EC) measurements.Here, we present a revised analysis of eddy covariance measurements of air-sea CO2 and momentum fluxes from the Southern Ocean Surface Ocean Aerosol Production (SOAP) study. We show that it is possible to significantly reduce the scatter in the EC data and achieve consistency between measurements taken on station and with the ship underway. The gas transfer velocities from the EC measurements correlate better with the EC friction velocity (u*) than with mean wind speeds derived from shipboard measurements corrected with an airflow distortion model. For the observed range of wind speeds (u10 N = 3-23 m s-1), the transfer velocities can be parameterised with a linear fit to u*. The SOAP data are compared to previous gas transfer parameterisations using u10 N computed from the EC friction velocity with the drag coefficient from the Coupled Ocean-Atmosphere Response Experiment (COARE) model version 3.5. The SOAP results are consistent with previous gas transfer studies, but at high wind speeds they do not support the sharp increase in gas transfer associated with bubble-mediated transfer predicted by physically based models.

  5. Closed-time path formalism of quantum scattering

    International Nuclear Information System (INIS)

    Manoukian, E.B.

    1988-01-01

    The closed-time path formalism of quantum mechanics, first introduced by Schwinger, is developed starting from a second-quantized formalism by using a functional calculus. An exact functional expression for the closed-time amplitude for a particle state (not just of the vacuum state)is derived from which time-dependent expectation value of observables may be written in closed functional form. In particular, this leads directly to the expression for transition probabilities for scattering theory without computing first the corresponding amplitudes. Finally it is made a comparison with the standard approach

  6. Simulating carbon and water fluxes at Arctic and boreal ecosystems in Alaska by optimizing the modified BIOME-BGC with eddy covariance data

    Science.gov (United States)

    Ueyama, M.; Kondo, M.; Ichii, K.; Iwata, H.; Euskirchen, E. S.; Zona, D.; Rocha, A. V.; Harazono, Y.; Nakai, T.; Oechel, W. C.

    2013-12-01

    To better predict carbon and water cycles in Arctic ecosystems, we modified a process-based ecosystem model, BIOME-BGC, by introducing new processes: change in active layer depth on permafrost and phenology of tundra vegetation. The modified BIOME-BGC was optimized using an optimization method. The model was constrained using gross primary productivity (GPP) and net ecosystem exchange (NEE) at 23 eddy covariance sites in Alaska, and vegetation/soil carbon from a literature survey. The model was used to simulate regional carbon and water fluxes of Alaska from 1900 to 2011. Simulated regional fluxes were validated with upscaled GPP, ecosystem respiration (RE), and NEE based on two methods: (1) a machine learning technique and (2) a top-down model. Our initial simulation suggests that the original BIOME-BGC with default ecophysiological parameters substantially underestimated GPP and RE for tundra and overestimated those fluxes for boreal forests. We will discuss how optimization using the eddy covariance data impacts the historical simulation by comparing the new version of the model with simulated results from the original BIOME-BGC with default ecophysiological parameters. This suggests that the incorporation of the active layer depth and plant phenology processes is important to include when simulating carbon and water fluxes in Arctic ecosystems.

  7. Eddy covariance flux measurements of gaseous elemental mercury using cavity ring-down spectroscopy.

    Science.gov (United States)

    Pierce, Ashley M; Moore, Christopher W; Wohlfahrt, Georg; Hörtnagl, Lukas; Kljun, Natascha; Obrist, Daniel

    2015-02-03

    A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth's surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements took place near Reno, NV, in September and October 2012 encompassing natural, low-mercury (Hg) background soils and Hg-enriched soils. During nine days of measurements with deployment of Hg-enriched soil in boxes within 60 m upwind of the EC tower, the covariance of GEM concentration and vertical wind speed was measured, showing that EC fluxes over an Hg-enriched area were detectable. During three separate days of flux measurements over background soils (without Hg-enriched soils), no covariance was detected, indicating fluxes below the detection limit. When fluxes were measurable, they strongly correlated with wind direction; the highest fluxes occurred when winds originated from the Hg-enriched area. Comparisons among the three methods showed good agreement in direction (e.g., emission or deposition) and magnitude, especially when measured fluxes originated within the Hg-enriched soil area. EC fluxes averaged 849 ng m(-2) h(-1), compared to DFC fluxes of 1105 ng m(-2) h(-1) and MBR fluxes

  8. Eddy covariance measurements with high-resolution time-of-flight aerosol mass spectrometry: a new approach to chemically resolved aerosol fluxes

    Directory of Open Access Journals (Sweden)

    D. K. Farmer

    2011-06-01

    Full Text Available Although laboratory studies show that biogenic volatile organic compounds (VOCs yield substantial secondary organic aerosol (SOA, production of biogenic SOA as indicated by upward fluxes has not been conclusively observed over forests. Further, while aerosols are known to deposit to surfaces, few techniques exist to provide chemically-resolved particle deposition fluxes. To better constrain aerosol sources and sinks, we have developed a new technique to directly measure fluxes of chemically-resolved submicron aerosols using the high-resolution time-of-flight aerosol mass spectrometer (HR-AMS in a new, fast eddy covariance mode. This approach takes advantage of the instrument's ability to quantitatively identify both organic and inorganic components, including ammonium, sulphate and nitrate, at a temporal resolution of several Hz. The new approach has been successfully deployed over a temperate ponderosa pine plantation in California during the BEARPEX-2007 campaign, providing both total and chemically resolved non-refractory (NR PM1 fluxes. Average deposition velocities for total NR-PM1 aerosol at noon were 2.05 ± 0.04 mm s−1. Using a high resolution measurement of the NH2+ and NH3+ fragments, we demonstrate the first eddy covariance flux measurements of particulate ammonium, which show a noon-time deposition velocity of 1.9 ± 0.7 mm s−1 and are dominated by deposition of ammonium sulphate.

  9. Delta-Flux: An eddy covariance network for a climate-smart Lower Mississippi Basin

    Science.gov (United States)

    Runkle, Benjamin R. K.; Rigby, James R.; Reba, Michele L.; Anapalli, Saseendran S.; Bhattacharjee, Joydeep; Krauss, Ken W.; Liang, Lu; Locke, Martin A.; Novick, Kimberly A.; Sui, Ruixiu; Suvočarev, Kosana; White, Paul M.

    2017-01-01

    Networks of remotely monitored research sites are increasingly the tool used to study regional agricultural impacts on carbon and water fluxes. However, key national networks such as the National Ecological Observatory Network and AmeriFlux lack contributions from the Lower Mississippi River Basin (LMRB), a highly productive agricultural area with opportunities for soil carbon sequestration through conservation practices. The authors describe the rationale to create the new Delta-Flux network, which will coordinate efforts to quantify carbon and water budgets at seventeen eddy covariance flux tower sites in the LMRB. The network structure will facilitate climate-smart management strategies based on production-scale and continuous measurements of carbon and water fluxes from the landscape to the atmosphere under different soil and water management conditions. The seventeen instrumented field sites are expected to monitor fluxes within the most characteristic landscapes of the target area: row-crop fields, pasture, grasslands, forests, and marshes. The network participants are committed to open collaboration and efficient regionalization of site-level findings to support sustainable agricultural and forestry management and conservation of natural resources.

  10. Combining eddy-covariance measurements and Penman-Monteith type models to estimate evapotranspiration of flooded and aerobic rice

    Science.gov (United States)

    Facchi, Arianna; Masseroni, Daniele; Gharsallah, Olfa; Gandolfi, Claudio

    2014-05-01

    Rice is of great importance both from a food supply point of view, since it represents the main food in the diet of over half the world's population, and from a water resources point of view, since it consumes almost 40% of the water amount used for irrigation. About 90% of global production takes place in Asia, while European production is quantitatively modest (about 3 million tons). However, Italy is the Europe's leading producer, with over half of total production, almost totally concentrated in a large traditional paddy rice area between the Lombardy and Piedmont regions, in the north-western part of the country. In this area, irrigation of rice is traditionally carried out by continuous flooding. The high water requirement of this irrigation regime encourages the introduction of water saving irrigation practices, as flood irrigation after sowing in dry soil and intermittent irrigation (aerobic rice). In the agricultural season 2013 an intense monitoring activity was conducted on three experimental fields located in the Padana plain (northern Italy) and characterized by different irrigation regimes (traditional flood irrigation, flood irrigation after sowing in dry soil, intermittent irrigation), with the aim of comparing the water balance terms for the three irrigation treatments. Actual evapotranspiration (ET) is one of the terms, but, unlike others water balance components, its field monitoring requires expensive instrumentation. This work explores the possibility of using only one eddy covariance system and Penman-Monteith (PM) type models for the determination of ET fluxes for the three irrigation regimes. An eddy covariance station was installed on the levee between the traditional flooded and the aerobic rice fields, to contemporaneously monitor the ET fluxes from this two treatments as a function of the wind direction. A detailed footprint analysis was conducted - through the application of three different analytical models - to determine the position

  11. Evaluating the convergence between eddy-covariance and biometric methods for assessing carbon budgets of forests

    Science.gov (United States)

    Campioli, M.; Malhi, Y.; Vicca, S.; Luyssaert, S.; Papale, D.; Peñuelas, J.; Reichstein, M.; Migliavacca, M.; Arain, M. A.; Janssens, I. A.

    2016-12-01

    The eddy-covariance (EC) micro-meteorological technique and the ecology-based biometric methods (BM) are the primary methodologies to quantify CO2 exchange between terrestrial ecosystems and the atmosphere (net ecosystem production, NEP) and its two components, ecosystem respiration and gross primary production. Here we show that EC and BM provide different estimates of NEP, but comparable ecosystem respiration and gross primary production for forest ecosystems globally. Discrepancies between methods are not related to environmental or stand variables, but are consistently more pronounced for boreal forests where carbon fluxes are smaller. BM estimates are prone to underestimation of net primary production and overestimation of leaf respiration. EC biases are not apparent across sites, suggesting the effectiveness of standard post-processing procedures. Our results increase confidence in EC, show in which conditions EC and BM estimates can be integrated, and which methodological aspects can improve the convergence between EC and BM.

  12. Representation of physiological drought at ecosystem level based on model and eddy covariance measurements

    Science.gov (United States)

    Zhang, Y.; Novick, K. A.; Song, C.; Zhang, Q.; Hwang, T.

    2017-12-01

    Drought and heat waves are expected to increase both in frequency and amplitude, exhibiting a major disturbance to global carbon and water cycles under future climate change. However, how these climate anomalies translate into physiological drought, or ecosystem moisture stress are still not clear, especially under the co-limitations from soil moisture supply and atmospheric demand for water. In this study, we characterized the ecosystem-level moisture stress in a deciduous forest in the southeastern United States using the Coupled Carbon and Water (CCW) model and in-situ eddy covariance measurements. Physiologically, vapor pressure deficit (VPD) as an atmospheric water demand indicator largely controls the openness of leaf stomata, and regulates atmospheric carbon and water exchanges during periods of hydrological stress. Here, we tested three forms of VPD-related moisture scalars, i.e. exponent (K2), hyperbola (K3), and logarithm (K4) to quantify the sensitivity of light-use efficiency to VPD along different soil moisture conditions. The sensitivity indicators of K values were calibrated based on the framework of CCW using Monte Carlo simulations on the hourly scale, in which VPD and soil water content (SWC) are largely decoupled and the full carbon and water exchanging information are held. We found that three K values show similar performances in the predictions of ecosystem-level photosynthesis and transpiration after calibration. However, all K values show consistent gradient changes along SWC, indicating that this deciduous forest is less responsive to VPD as soil moisture decreases, a phenomena of isohydricity in which plants tend to close stomata to keep the leaf water potential constant and reduce the risk of hydraulic failure. Our study suggests that accounting for such isohydric information, or spectrum of moisture stress along different soil moisture conditions in models can significantly improve our ability to predict ecosystem responses to future

  13. Challenges and benefits on long-term eddy covariance measurements over lakes

    Science.gov (United States)

    Vesala, Timo; Golub, Malgorzata; Desai, Ankur; Heiskanen, Jouni; Provenzale, Maria; Rantakari, Miitta; Ojala, Anne; Mammarella, Ivan

    2017-04-01

    Eddy Covariance (EC) data on carbon dioxide fluxes is presently available on about 30 lakes but the time series are mostly short, order of one year. Longer EC series together with chamber measurements and appropriate auxiliary data on water column allow for more accurate estimates of the aquatic component in terrestrial carbon balance and analysis of the environmental controls. We discuss on challenges for long-term EC measurements over freshwater ecosystems and demonstrate the benefits of EC data for carbon cycle studies via examples from long-term sites EC sites in Finland. We discuss on the auxiliary measurements needed and the general design of the whole measurement set-up to get representative information. We discuss on challenges related to the CO2 flux partitioning for freshwater ecosystems and introduce a new method to estimate the net primary productivity (NPP) on EC data, which is superior to more traditional methods (bottle incubations, 14C technique) with a poor temporal resolution. Finally, we collected and analyzed CO2 fluxes from 19 globally distributed lakes and reservoirs representing six climate zones. The mean flux was c. 0.3 micro mole / m2 s. We applied a simple upscaling to the direct observations and ended up to the estimate which is about half of the current emission estimate for lentic systems.

  14. Regional Scaling of Airborne Eddy Covariance Flux Observation

    Science.gov (United States)

    Sachs, T.; Serafimovich, A.; Metzger, S.; Kohnert, K.; Hartmann, J.

    2014-12-01

    The earth's surface is tightly coupled to the global climate system by the vertical exchange of energy and matter. Thus, to better understand and potentially predict changes to our climate system, it is critical to quantify the surface-atmosphere exchange of heat, water vapor, and greenhouse gases on climate-relevant spatial and temporal scales. Currently, most flux observations consist of ground-based, continuous but local measurements. These provide a good basis for temporal integration, but may not be representative of the larger regional context. This is particularly true for the Arctic, where site selection is additionally bound by logistical constraints, among others. Airborne measurements can overcome this limitation by covering distances of hundreds of kilometers over time periods of a few hours. The Airborne Measurements of Methane Fluxes (AIRMETH) campaigns are designed to quantitatively and spatially explicitly address this issue: The research aircraft POLAR 5 is used to acquire thousands of kilometers of eddy-covariance flux data. During the AIRMETH-2012 and AIRMETH-2013 campaigns we measured the turbulent exchange of energy, methane, and (in 2013) carbon dioxide over the North Slope of Alaska, USA, and the Mackenzie Delta, Canada. Here, we present the potential of environmental response functions (ERFs) for quantitatively linking flux observations to meteorological and biophysical drivers in the flux footprints. We use wavelet transforms of the original high-frequency data to improve spatial discretization of the flux observations. This also enables the quantification of continuous and biophysically relevant land cover properties in the flux footprint of each observation. A machine learning technique is then employed to extract and quantify the functional relationships between flux observations and the meteorological and biophysical drivers. The resulting ERFs are used to extrapolate fluxes over spatio-temporally explicit grids of the study area. The

  15. Eddy covariance N2O flux measurements at low flux rates: results from the InGOS campaign in a Danish willow field.

    Science.gov (United States)

    Ibrom, Andreas; Brümmer, Christian; Hensen, Arjan; van Asperen, Hella; Carter, Mette S.; Gasche, Rainer; Famulari, Daniela; Kutsch, Werner; Pilegaard, Kim; Ambus, Per

    2014-05-01

    Nitrous oxide (N2O) fluxes from soils are characterised by their high spatial and temporal variability. The fluxes depend on the availability of the substrates for nitrification and denitrification and soil physical and chemical conditions that control the metabolic microbial activity. The sporadic nature of the fluxes and their high sensitivity to alterations of the soil climate put very high demands on measurement approaches. Laser spectroscopy enables accurate and fast response detection of atmospheric N2O concentrations and is used for eddy covariance (EC) flux measurements. Alternatively N2O fluxes can be measured with chambers together with high precision analysers. Differences in the measurement approaches and system designs are expected to have a considerable influence on the accuracy of the flux estimation. This study investigates how three different eddy covariance systems perform in a situation of low N2O fluxes from a flat surface. Chamber flux measurements with differing chamber and analyser designs are used for comparison. In April 2013, the EU research infrastructure project InGOS (http://www.ingos-infrastructure.eu/) organised a campaign of N2O flux measurements in a willow plantation close to the Risø Campus of the Technical University of Denmark. The willow field was harvested in February 2013 and received mineral fertiliser equivalent to 120 kg N ha-1 before the campaign started. Three different eddy covariance systems took part in the campaign: two Aerodyne quantum cascade laser (QCL) based systems and one Los Gatos Research off-axis integrated-cavity-output spectroscopy (ICOS) system for N2O and CO. The sonic anemometers were all installed at 2 m height above the bare ground. Gill R3 type sonic anemometers were used with QCL systems and a Gil HS-50 with the ICOS system. The 10 Hz raw data were analysed with group specific softwares and procedures. The local conditions in the exceptionally cold and dry spring 2013 did not lead to large N2O flux

  16. Ingredients of the Eddy Soup: A Geometric Decomposition of Eddy-Mean Flow Interactions

    Science.gov (United States)

    Waterman, S.; Lilly, J. M.

    2014-12-01

    Understanding eddy-mean flow interactions is a long-standing problem in geophysical fluid dynamics with modern relevance to the task of representing eddy effects in coarse resolution models while preserving their dependence on the underlying dynamics of the flow field. Exploiting the recognition that the velocity covariance matrix/eddy stress tensor that describes eddy fluxes, also encodes information about eddy size, shape and orientation through its geometric representation in the form of the so-called variance ellipse, suggests a potentially fruitful way forward. Here we present a new framework that describes eddy-mean flow interactions in terms of a geometric description of the eddy motion, and illustrate it with an application to an unstable jet. Specifically we show that the eddy vorticity flux divergence F, a key dynamical quantity describing the average effect of fluctuations on the time-mean flow, may be decomposed into two components with distinct geometric interpretations: 1. variations in variance ellipse orientation; and 2. variations in the anisotropic part of the eddy kinetic energy, a function of the variance ellipse size and shape. Application of the divergence theorem shows that F integrated over a region is explained entirely by variations in these two quantities around the region's periphery. This framework has the potential to offer new insights into eddy-mean flow interactions in a number of ways. It identifies the ingredients of the eddy motion that have a mean flow forcing effect, it links eddy effects to spatial patterns of variance ellipse geometry that can suggest the mechanisms underpinning these effects, and finally it illustrates the importance of resolving eddy shape and orientation, and not just eddy size/energy, to accurately represent eddy feedback effects. These concepts will be both discussed and illustrated.

  17. Analysis of Grassland Ecosystem Physiology at Multiple Scales Using Eddy Covariance, Stable Isotope and Remote Sensing Techniques

    Science.gov (United States)

    Flanagan, L. B.; Geske, N.; Emrick, C.; Johnson, B. G.

    2006-12-01

    Grassland ecosystems typically exhibit very large annual fluctuations in above-ground biomass production and net ecosystem productivity (NEP). Eddy covariance flux measurements, plant stable isotope analyses, and canopy spectral reflectance techniques have been applied to study environmental constraints on grassland ecosystem productivity and the acclimation responses of the ecosystem at a site near Lethbridge, Alberta, Canada. We have observed substantial interannual variation in grassland productivity during 1999-2005. In addition, there was a strong correlation between peak above-ground biomass production and NEP calculated from eddy covariance measurements. Interannual variation in NEP was strongly controlled by the total amount of precipitation received during the growing season (April-August). We also observed significant positive correlations between a multivariate ENSO index and total growing season precipitation, and between the ENSO index and annual NEP values. This suggested that a significant fraction of the annual variability in grassland productivity was associated with ENSO during 1999-2005. Grassland productivity varies asymmetrically in response to changes in precipitation with increases in productivity during wet years being much more pronounced than reductions during dry years. Strong increases in plant water-use efficiency, based on carbon and oxygen stable isotope analyses, contribute to the resilience of productivity during times of drought. Within a growing season increased stomatal limitation of photosynthesis, associated with improved water-use efficiency, resulted in apparent shifts in leaf xanthophyll cycle pigments and changes to the Photochemical Reflectance Index (PRI) calculated from hyper-spectral reflectance measurements conducted at the canopy-scale. These shifts in PRI were apparent before seasonal drought caused significant reductions in leaf area index (LAI) and changes to canopy-scale "greenness" based on NDVI values. With

  18. Eddy covariance flux measurements of ammonia by high temperature chemical ionisation mass spectrometry

    Directory of Open Access Journals (Sweden)

    J. Sintermann

    2011-03-01

    Full Text Available A system for fast ammonia (NH3 measurements with chemical ionisation mass spectrometry (CIMS based on a commercial Proton Transfer Reaction-Mass Spectrometer (PTR-MS is presented. It uses electron transfer reaction as ionisation pathway and features a drift tube of polyetheretherketone (PEEK and silica-coated steel. Heating the instrumental inlet and the drift tube to 180 °C enabled an effective time resolution of ~1 s and made it possible to apply the instrument for eddy covariance (EC measurements. EC fluxes of NH3 were measured over two agricultural fields in Oensingen, Switzerland, following fertilisations with cattle slurry. Air was aspirated close to a sonic anemometer at a flow of 100 STP L min−1 and was directed through a 23 m long 1/2" PFA tube heated to 150 °C to an air-conditioned trailer where the gas was sub-sampled from the large bypass stream. This setup minimised damping of fast NH3 concentration changes between the sampling point and the actual measurement. High-frequency attenuation loss of the NH3 fluxes of 20 to 40% was quantified and corrected for using an empirical ogive method. The instrumental NH3 background signal showed a minor interference with H2O which was characterised in the laboratory. The resulting correction of the NH3 flux after slurry spreading was less than 1‰. The flux detection limit of the EC system was about 5 ng m−2 s−1 while the accuracy of individual flux measurements was estimated 16% for the high-flux regime during these experiments. The NH3 emissions after broad spreading of the slurry showed an initial maximum of 150 μg m−2 s−1 with a fast decline in the following hours.

  19. Evaluating the convergence between eddy-covariance and biometric methods for assessing carbon budgets of forests

    Science.gov (United States)

    Campioli, M.; Malhi, Y.; Vicca, S.; Luyssaert, S.; Papale, D.; Peñuelas, J.; Reichstein, M.; Migliavacca, M.; Arain, M. A.; Janssens, I. A.

    2016-01-01

    The eddy-covariance (EC) micro-meteorological technique and the ecology-based biometric methods (BM) are the primary methodologies to quantify CO2 exchange between terrestrial ecosystems and the atmosphere (net ecosystem production, NEP) and its two components, ecosystem respiration and gross primary production. Here we show that EC and BM provide different estimates of NEP, but comparable ecosystem respiration and gross primary production for forest ecosystems globally. Discrepancies between methods are not related to environmental or stand variables, but are consistently more pronounced for boreal forests where carbon fluxes are smaller. BM estimates are prone to underestimation of net primary production and overestimation of leaf respiration. EC biases are not apparent across sites, suggesting the effectiveness of standard post-processing procedures. Our results increase confidence in EC, show in which conditions EC and BM estimates can be integrated, and which methodological aspects can improve the convergence between EC and BM. PMID:27966534

  20. Wind changes above warm Agulhas Current eddies

    CSIR Research Space (South Africa)

    Rouault, M

    2016-01-01

    Full Text Available speeds above the eddies at the instantaneous scale; 20 % of cases had incomplete data due to partial global coverage by the scatterometer for one path. For cases where the wind is stronger above warm eddies, there is no relationship between the increase...

  1. Comprehensive comparison of gap filling techniques for eddy covariance net carbon fluxes

    Science.gov (United States)

    Moffat, A. M.; Papale, D.; Reichstein, M.; Hollinger, D. Y.; Richardson, A. D.; Barr, A. G.; Beckstein, C.; Braswell, B. H.; Churkina, G.; Desai, A. R.; Falge, E.; Gove, J. H.; Heimann, M.; Hui, D.; Jarvis, A. J.; Kattge, J.; Noormets, A.; Stauch, V. J.

    2007-12-01

    Review of fifteen techniques for estimating missing values of net ecosystem CO2 exchange (NEE) in eddy covariance time series and evaluation of their performance for different artificial gap scenarios based on a set of ten benchmark datasets from six forested sites in Europe. The goal of gap filling is the reproduction of the NEE time series and hence this present work focuses on estimating missing NEE values, not on editing or the removal of suspect values in these time series due to systematic errors in the measurements (e.g. nighttime flux, advection). The gap filling was examined by generating fifty secondary datasets with artificial gaps (ranging in length from single half-hours to twelve consecutive days) for each benchmark dataset and evaluating the performance with a variety of statistical metrics. The performance of the gap filling varied among sites and depended on the level of aggregation (native half- hourly time step versus daily), long gaps were more difficult to fill than short gaps, and differences among the techniques were more pronounced during the day than at night. The non-linear regression techniques (NLRs), the look-up table (LUT), marginal distribution sampling (MDS), and the semi-parametric model (SPM) generally showed good overall performance. The artificial neural network based techniques (ANNs) were generally, if only slightly, superior to the other techniques. The simple interpolation technique of mean diurnal variation (MDV) showed a moderate but consistent performance. Several sophisticated techniques, the dual unscented Kalman filter (UKF), the multiple imputation method (MIM), the terrestrial biosphere model (BETHY), but also one of the ANNs and one of the NLRs showed high biases which resulted in a low reliability of the annual sums, indicating that additional development might be needed. An uncertainty analysis comparing the estimated random error in the ten benchmark datasets with the artificial gap residuals suggested that the

  2. eddy4R 0.2.0: a DevOps model for community-extensible processing and analysis of eddy-covariance data based on R, Git, Docker, and HDF5

    Science.gov (United States)

    Metzger, Stefan; Durden, David; Sturtevant, Cove; Luo, Hongyan; Pingintha-Durden, Natchaya; Sachs, Torsten; Serafimovich, Andrei; Hartmann, Jörg; Li, Jiahong; Xu, Ke; Desai, Ankur R.

    2017-08-01

    Large differences in instrumentation, site setup, data format, and operating system stymie the adoption of a universal computational environment for processing and analyzing eddy-covariance (EC) data. This results in limited software applicability and extensibility in addition to often substantial inconsistencies in flux estimates. Addressing these concerns, this paper presents the systematic development of portable, reproducible, and extensible EC software achieved by adopting a development and systems operation (DevOps) approach. This software development model is used for the creation of the eddy4R family of EC code packages in the open-source R language for statistical computing. These packages are community developed, iterated via the Git distributed version control system, and wrapped into a portable and reproducible Docker filesystem that is independent of the underlying host operating system. The HDF5 hierarchical data format then provides a streamlined mechanism for highly compressed and fully self-documented data ingest and output. The usefulness of the DevOps approach was evaluated for three test applications. First, the resultant EC processing software was used to analyze standard flux tower data from the first EC instruments installed at a National Ecological Observatory (NEON) field site. Second, through an aircraft test application, we demonstrate the modular extensibility of eddy4R to analyze EC data from other platforms. Third, an intercomparison with commercial-grade software showed excellent agreement (R2 = 1.0 for CO2 flux). In conjunction with this study, a Docker image containing the first two eddy4R packages and an executable example workflow, as well as first NEON EC data products are released publicly. We conclude by describing the work remaining to arrive at the automated generation of science-grade EC fluxes and benefits to the science community at large. This software development model is applicable beyond EC and more generally builds

  3. eddy4R 0.2.0: a DevOps model for community-extensible processing and analysis of eddy-covariance data based on R, Git, Docker, and HDF5

    Directory of Open Access Journals (Sweden)

    S. Metzger

    2017-08-01

    Full Text Available Large differences in instrumentation, site setup, data format, and operating system stymie the adoption of a universal computational environment for processing and analyzing eddy-covariance (EC data. This results in limited software applicability and extensibility in addition to often substantial inconsistencies in flux estimates. Addressing these concerns, this paper presents the systematic development of portable, reproducible, and extensible EC software achieved by adopting a development and systems operation (DevOps approach. This software development model is used for the creation of the eddy4R family of EC code packages in the open-source R language for statistical computing. These packages are community developed, iterated via the Git distributed version control system, and wrapped into a portable and reproducible Docker filesystem that is independent of the underlying host operating system. The HDF5 hierarchical data format then provides a streamlined mechanism for highly compressed and fully self-documented data ingest and output. The usefulness of the DevOps approach was evaluated for three test applications. First, the resultant EC processing software was used to analyze standard flux tower data from the first EC instruments installed at a National Ecological Observatory (NEON field site. Second, through an aircraft test application, we demonstrate the modular extensibility of eddy4R to analyze EC data from other platforms. Third, an intercomparison with commercial-grade software showed excellent agreement (R2  =  1.0 for CO2 flux. In conjunction with this study, a Docker image containing the first two eddy4R packages and an executable example workflow, as well as first NEON EC data products are released publicly. We conclude by describing the work remaining to arrive at the automated generation of science-grade EC fluxes and benefits to the science community at large. This software development model is applicable beyond EC

  4. A new disjunct eddy-covariance system for BVOC flux measurements - validation on CO2 and H2O fluxes

    Science.gov (United States)

    Baghi, R.; Durand, P.; Jambert, C.; Jarnot, C.; Delon, C.; Serça, D.; Striebig, N.; Ferlicoq, M.; Keravec, P.

    2012-12-01

    The disjunct eddy covariance (DEC) method is an interesting alternative to the conventional eddy covariance (EC) method because it allows the estimation of turbulent fluxes of species for which fast sensors are not available. We have developed and validated a new disjunct sampling system (called MEDEE). This system is built with chemically inert materials. Air samples are taken quickly and alternately in two cylindrical reservoirs, the internal pressures of which are regulated by a moving piston. The MEDEE system was designed to be operated either on the ground or aboard an aircraft. It is also compatible with most analysers since it transfers the air samples at a regulated pressure. To validate the system, DEC and EC measurements of CO2 and latent heat fluxes were performed concurrently during a field campaign. EC fluxes were first compared to simulated DEC (SDEC) fluxes and then to actual DEC fluxes. Both the simulated and actual DEC fluxes showed a good agreement with EC fluxes in terms of correlation. The determination coefficients (R2) were 0.93 and 0.91 for DEC and SDEC latent heat fluxes, respectively. For DEC and SDEC CO2 fluxes R2 was 0.69 in both cases. The conditions of low fluxes experienced during the campaign impaired the comparison of the different techniques especially for CO2 flux measurements. Linear regression analysis showed an 14% underestimation of DEC fluxes for both CO2 and latent heat compared to EC fluxes. A first field campaign, focusing on biogenic volatile organic compound (BVOC) emissions, was carried out to measure isoprene fluxes above a downy oak (Quercus Pubescens) forest in the south-east of France. The measured standard emission rate was in the lower range of reported values in earlier studies. Further analysis will be conducted through ground-based and airborne campaigns in the coming years.

  5. Predicting deep percolation with eddy covariance under mulch drip irrigation

    Science.gov (United States)

    Ming, Guanghui; Tian, Fuqiang; Hu, Hongchang

    2016-04-01

    Water is essential for the agricultural development and ecological sustainability of the arid and semi-arid oasis with rare precipitation input and high evaporation demand. Deep percolation (DP) defined as excess irrigation water percolating below the plant root zone will reduce irrigation water use efficiency (WUE). But the DP was often ignored in mulch drip irrigation (MDI) which has reached the area of 1.6 million hectares in Xinjiang, the northwest of China. In this study DP experiments were conducted at an agricultural experiment station located within an irrigation district in the Tarim River Basin for four cotton growing periods. First it was detected the irrigation water infiltrated into the soil layers below 100cm and the groundwater level responded to the irrigation events well. Then DP below 100cm soil layers was calculated using the soil water balance method with the aid of eddy covariance (with the energy balance closure of 0.72). The negative DP (groundwater contribution to the crop-water use through capillary rising) at the seedling and harvesting stages can reach 77mm and has a good negative correlation with the groundwater level and positive correlation with potential evaporation. During the drip irrigation stage approximately 45% of the irrigation became DP and resulted in the low irrigation WUE of 0.6. The DP can be 164mm to 270mm per year which was positive linearly correlated to irrigation depth and negative linear correlated to irrigation interval. It is better to establish the irrigation schedule with small irrigation depth and given frequently to reduce deep percolation and meet crop needs.

  6. Eddy Covariance Fluxes of the NO-O3-NO2 Triad above the Forest Canopy at the ATTO Site in the Amazon Basin

    Science.gov (United States)

    Tsokankunku, A.; Wolff, S.; Berger, M.; Zelger, M.; Dlugi, R. J. W.; Andreae, M. O.; Sörgel, M.

    2017-12-01

    Nitrogen monoxide (NO) and nitrogen dioxide (NO2) (denoted together as NOx) determine the abundance of the tropospheric oxidants OH, O3 and NO3 that regulate atmospheric self-cleaning. The three reactive trace gases NO, NO2 and O3 undergo a series of interconnected photochemical reactions and are therefore often referred to as the NO-O3-NO2 triad. Ozone deposition is mainly controlled by stomatal uptake, therefore resulting in oxidative stress for the plants. Similarly, nitrogen dioxide from above or below the canopy is deposited to leaves through stomatal uptake. NO emissions from soils contribute to above canopy O3 formation and accelerate OH recycling. Therefore, quantification of the biosphere-atmosphere exchange fluxes of these species is important for atmospheric chemistry and ecosystem research. The eddy covariance method is state of the art for direct measurements of ecosystem fluxes of trace gases. Eddy covariance measurements of NOx in pristine environments are rare because of lack of availability of instruments with the required precision to resolve concentrations characteristic of these environments with the required high time resolution. The Amazon Tall Tower Observatory (ATTO) is located in a pristine rainforest environment in the Amazon basin about 150 km northeast of the city of Manaus. It is the ideal site for studying the biosphere-atmosphere exchange of the NO-O3-NO2 triad, because of the absence of nearby anthropogenic sources. During an intensive measurement campaign in November 2015 at the ATTO site, measurements of NO, NO2 and O3 were carried out at 42 m above ground level on the 80 m walk-up tower with a fast (5 Hz) and sensitive (< 30 ppt) instrument (CLD790SR2, Eco Physics) for NO and NO2 and with 10 Hz for O3 (Enviscope GmbH). Additionally, a suite of micrometeorological instruments was installed, including a profile of 3-dimensional sonic anemometers and meteorological sensors. Vertical concentration profile measurements of NO, NO2 and O

  7. Intercomparison of methods for the estimation of displacement height and roughness length from single-level eddy covariance data

    Science.gov (United States)

    Graf, Alexander; van de Boer, Anneke; Schüttemeyer, Dirk; Moene, Arnold; Vereecken, Harry

    2013-04-01

    The displacement height d and roughness length z0 are parameters of the logarithmic wind profile and as such these are characteristics of the surface, that are required in a multitude of meteorological modeling applications. Classically, both parameters are estimated from multi-level measurements of wind speed over a terrain sufficiently homogeneous to avoid footprint-induced differences between the levels. As a rule-of thumb, d of a dense, uniform crop or forest canopy is 2/3 to 3/4 of the canopy height h, and z0 about 10% of canopy height in absence of any d. However, the uncertainty of this rule-of-thumb becomes larger if the surface of interest is not "dense and uniform", in which case a site-specific determination is required again. By means of the eddy covariance method, alternative possibilities to determine z0 and d have become available. Various authors report robust results if either several levels of sonic anemometer measurements, or one such level combined with a classic wind profile is used to introduce direct knowledge on the friction velocity into the estimation procedure. At the same time, however, the eddy covariance method to measure various fluxes has superseded the profile method, leaving many current stations without a wind speed profile with enough levels sufficiently far above the canopy to enable the classic estimation of z0 and d. From single-level eddy covariance measurements at one point in time, only one parameter can be estimated, usually z0 while d is assumed to be known. Even so, results tend to scatter considerably. However, it has been pointed out, that the use of multiple points in time providing different stability conditions can enable the estimation of both parameters, if they are assumed constant over the time period regarded. These methods either rely on flux-variance similarity (Weaver 1990 and others following), or on the integrated universal function for momentum (Martano 2000 and others following). In both cases

  8. Storage flux uncertainty impact on eddy covariance net ecosystem exchange measurements

    Science.gov (United States)

    Nicolini, Giacomo; Aubinet, Marc; Feigenwinter, Christian; Heinesch, Bernard; Lindroth, Anders; Mamadou, Ossénatou; Moderow, Uta; Mölder, Meelis; Montagnani, Leonardo; Rebmann, Corinna; Papale, Dario

    2017-04-01

    Complying with several assumption and simplifications, most of the carbon budget studies based on eddy covariance (EC) measurements, quantify the net ecosystem exchange (NEE) by summing the flux obtained by EC (Fc) and the storage flux (Sc). Sc is the rate of change of CO2, within the so called control volume below the EC measurement level, given by the difference in the instantaneous profiles of concentration at the beginning and end of the EC averaging period, divided by the averaging period. While cumulating over time led to a nullification of Sc, it can be significant at short time periods. The approaches used to estimate Sc fluxes largely vary, from measurements based only on a single sampling point (usually located at the EC measurement height) to measurements based on several sampling profiles distributed within the control volume. Furthermore, the number of sampling points within each profile vary, according to their height and the ecosystem typology. It follows that measurement accuracy increases with the sampling intensity within the control volume. In this work we use the experimental dataset collected during the ADVEX campaign in which Sc flux has been measured in three similar forest sites by the use of 5 sampling profiles (towers). Our main objective is to quantify the impact of Sc measurement uncertainty on NEE estimates. Results show that different methods may produce substantially different Sc flux estimates, with problematic consequences in case high frequency (half-hourly) data are needed for the analysis. However, the uncertainty on long-term estimates may be tolerate.

  9. An eddy covariance system to characterize the atmospheric surface layer and turbulent latent heat fluxes over a debris-covered Himalayan glacier.

    Science.gov (United States)

    Litt, Maxime; Steiner, Jakob F.; Stigter, Emmy E.; Immerzeel, Walter; Shea, Joseph Michael

    2017-04-01

    Over debris-covered glaciers, water content variations in the debris layer can drive significant changes in its thermal conductivity and significantly impact melt rates. Since sublimation and evaporation are favoured in high-altitude conditions, e.g., low atmospheric pressure and high wind speeds, they are expected to strongly influence the water balance of the debris-layer. Dedicated latent heat fluxes measurements at the debris surface are essential to characterize the debris heat conductivity in order to assess underlying ice melt. Furthermore, the contribution of the turbulent fluxes in the surface energy balance over debris covered glacier remains uncertain since they are generally evaluated through similarity methods which might not be valid in complex terrain. We present the first results of a 15-day eddy-covariance experiment installed at the end of the monsoon (September-October) on a 3-m tower above the debris-covered Lirung glacier in Nepal. The tower also included measurements of the 4 radiation components. The eddy covariance measurements allowed for the characterization of the turbulence in the atmospheric surface layer, as well as the direct measurements of evaporation, sublimation and turbulent sensible heat fluxes. The experiment helps us to evaluate the contribution of turbulent fluxes to the surface energy balance over this debris-covered glacier, through a precise characterization of the overlying turbulent atmospheric surface layer. It also helps to study the role of the debris-layer water content changes through evaporation and sublimation and its feedback on heat conduction in this layer. The large observed turbulent fluxes play a significant role in the energy balance at the debris surface and significantly influence debris moisture, conductivity and subsequently underlying ice melt.

  10. Carbon balance assessment by eddy covariance method for agroecosystems with potato plants and oats & vetch mixture on sod-podzolic soils of Russia

    Science.gov (United States)

    Meshalkina, J. L.; Yaroslavtsev, A. M.; Vasenev, I. I.; Andreeva, I. V.; Tihonova, M. V.

    2018-01-01

    The carbon balance for the agroecosystems with potato plants and oats & vetch mixture on sod-podzolics soils was evaluated using the eddy covariance approach. Absorption of carbon was recorded only during the growing season; maximum values were detected for all crops in July. The number of days during the vegetation period, when the carbon stocked in the fields with potatoes and oats & vetch mixture was about the same and accounted for 53-55 days. During this period, the increase in gross primary production (GPP) is well correlated with the crop yields. The curve of the gross primary productivity is closely linked to the phases of development of plants; for potatoes, this graph differs significantly for all phases. Form of oats & vetch mixture biomass curve shown linear increases. Carbon losses were observed for all the studied agroecosystems: for fields with an oats & vetch mixture they were 254 g C m-2 y-1, while for fields with potato plants they were 307 g C m-2 y-1. Values about 250-300 g C m-2 per year may be considered as estimated values for the total carbon uptake for agroecosystems with potato plants and oats & vetch mixture on sod-podzolic soils.

  11. Central Russia agroecosystem monitoring with CO2 fluxes analysis by eddy covariance method

    Directory of Open Access Journals (Sweden)

    Joulia Meshalkina

    2015-07-01

    Full Text Available The eddy covariance (EC technique as a powerful statistics-based method of measurement and calculation the vertical turbulent fluxes of greenhouses gases within atmospheric boundary layers provides the continuous, long-term flux information integrated at the ecosystem scale. An attractive way to compare the agricultural practices influences on GHG fluxes is to divide a crop area into subplots managed in different ways. The research has been carried out in the Precision Farming Experimental Field of the Russian Timiryazev State Agricultural University (RTSAU, Moscow in 2013 under the support of RF Government grant # 11.G34.31.0079, EU grant # 603542 LUС4С (7FP and RF Ministry of education and science grant # 14-120-14-4266-ScSh. Arable Umbric Albeluvisols have around 1% of SOC, 5.4 pH (KCl and NPK medium-enhanced contents in sandy loam topsoil. The CO2 flux seasonal monitoring has been done by two eddy covariance stations located at the distance of 108 m. The LI-COR instrumental equipment was the same for the both stations. The stations differ only by current crop version: barley or vetch and oats. At both sites, diurnal patterns of NEE among different months were very similar in shape but varied slightly in amplitude. NEE values were about zero during spring time. CO2 fluxes have been intensified after crop emerging from values of 3 to 7 µmol/s∙m2 for emission, and from 5 to 20 µmol/s∙m2 for sink. Stabilization of the fluxes has come at achieving plants height of 10-12 cm. Average NEE was negative only in June and July. Maximum uptake was observed in June with average values about 8 µmol CO2 m−2 s−1. Although different kind of crops were planted on the fields A and B, GPP dynamics was quite similar for both sites: after reaching the peak values at the mid of June, GPP decreased from 4 to 0.5 g C CO2 m-2 d-1 at the end of July. The difference in crops harvesting time that was equal two weeks did not significantly influence the daily

  12. USE OF RELAXED EDDY ACCUMULATION TO MEASURE BIOSPHERE-ATMOSPHERE EXCHANGE OF ISOPRENE AND OTHER BIOLOGICAL TRACE GASES

    Science.gov (United States)

    The micrometeorological flux measurement technique known as relaxed eddy accumulation (REA) holds promise as a powerful new tool for ecologists. The more popular eddy covariance (eddy correlation) technique requires the use of sensors that can respond at fast rates (10 Hz), and t...

  13. Eddy Correlation Flux Measurement System (ECOR) Handbook

    Energy Technology Data Exchange (ETDEWEB)

    Cook, DR

    2011-01-31

    The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration.

  14. Ecosystem Phenology from Eddy-covariance Measurements: Spring Photosynthesis in a Cool Temperate Bog

    Science.gov (United States)

    Lafleur, P.; Moore, T. R.; Poon, D.; Seaquist, J.

    2005-12-01

    The onset and increase of spring photosynthetic flux of carbon dioxide is an important attribute of the carbon budget of northern ecosystems and we used eddy-covariance measurements from March to May over 5 years at the Mer Bleue ombrotrophic bog to establish the important controls. The onset of ecosystem photosynthesis (day-of-year from 86 to 101) was associated with the disappearance on the snow cover and there is evidence that photosynthesis can continue after a thin new snowfall. The growth of photosynthesis during the spring period was partially associated with light (daily photosynthetically active radiation) but primarily with temperature, with the strongest correlation being observed with peat temperature at a depth of 5 and 10 cm, except in one year in which there was a long snow cover. The vegetation comprises mosses, which are able to photosynthesize very early, evergreen shrubs, which appear dependent on soil warming, and deciduous shrubs, which leaf-out only in late spring. We observed changes in shrub leaf colour from brown to green and concomitant increases in foliar nitrogen and chlorophyll concentrations during the spring in this "evergreen" system. We analyzed MODIS images for periods of overlap of tower and satellite data and found a generally strong correlation, though the infrequent satellite measurements were unable to pick out the onset and timing of rapid growth of photosynthesis in this ecosystem.

  15. Long term measurement of lake evaporation using a pontoon mounted Eddy Covariance system

    Science.gov (United States)

    McGowan, H. A.; McGloin, R.; McJannet, D.; Burn, S.

    2011-12-01

    Accurate quantification of evaporation from water storages is essential for design of water management and allocation policy that aims to balance demands for water without compromising the sustainability of future water resources, particularly during periods of prolonged and severe drought. Precise measurement of evaporation from lakes and dams however, presents significant research challenges. These include design and installation of measurement platforms that can withstand a range of wind and wave conditions; accurate determination of the evaporation measurement footprint and the influence of changing water levels. In this paper we present results from a two year long deployment of a pontoon mounted Eddy Covariance (EC) system on a 17.2ha irrigation reservoir in southeast Queensland, Australia. The EC unit included a CSAT-3 sonic anemometer (Campbell Scientific, Utah, United States) and a Li-Cor CS7500 open-path H2O/CO2 infrared gas analyzer (LiCor, Nebraska, United States) at a height of 2.2m, a net radiometer (CNR1, Kipp & Zonen, Netherlands) at a height of 1.2m and a humidity and temperature probe (HMP45C,Vaisala, Finland) at 2.3m. The EC unit was controlled by a Campbell Scientific CR3000 data logger with flux measurements made at 10 Hz and block averaged values logged every 15 minutes. Power to the EC system was from mounted solar panels that charged deep cycle lead-acid batteries while communication was via a cellphone data link. The pontoon was fitted with a weighted central beam and gimbal ring system that allowed self-levelling of the instrumentation and minimized dynamic influences on measurements (McGowan et al 2010; Wiebe et al 2011). EC measurements were corrected for tilt errors using the double rotation method for coordinate rotation described by Wilczak et al. (2001). High and low frequency attenuation of the measured co-spectrum was corrected using Massman's (2000) method for estimating frequency response corrections, while measurements were

  16. Memristor Multiport Readout: A Closed-Form Solution for Sneak Paths

    KAUST Repository

    Zidan, Mohammed A.; Eltawil, Ahmed M.; Fahmy, Hossam A.H.; Kurdahi, Fadi; Salama, Khaled N.

    2014-01-01

    In this paper, we introduce for the first time, a closed-form solution for the memristor-based memory sneak paths without using any gating elements. The introduced technique fully eliminates the effect of sneak paths by reading the stored data using multiple access points and evaluating a simple addition/subtraction on the different readings. The new method requires fewer reading steps compared to previously reported techniques, and has a very small impact on the memory density. To verify the underlying theory, the proposed system is simulated using Synopsys HSPICE showing the ability to achieve a 100% sneak-path error-free memory. In addition, the effect of quantization bits on the system performance is studied.

  17. Memristor Multiport Readout: A Closed-Form Solution for Sneak Paths

    KAUST Repository

    Zidan, Mohammed A.

    2014-06-18

    In this paper, we introduce for the first time, a closed-form solution for the memristor-based memory sneak paths without using any gating elements. The introduced technique fully eliminates the effect of sneak paths by reading the stored data using multiple access points and evaluating a simple addition/subtraction on the different readings. The new method requires fewer reading steps compared to previously reported techniques, and has a very small impact on the memory density. To verify the underlying theory, the proposed system is simulated using Synopsys HSPICE showing the ability to achieve a 100% sneak-path error-free memory. In addition, the effect of quantization bits on the system performance is studied.

  18. Optimal determination of the parameters controlling biospheric CO{sub 2} fluxes over Europe using eddy covariance fluxes and satellite NDVI measurements

    Energy Technology Data Exchange (ETDEWEB)

    Aalto, Tuula [Finnish Meteorological Inst., Helsinki (Finland). Air Quality Research; Ciais, Philippe; Moulin, Cyril [UMR CEA-CNRS, Gif-sur-Yvette (France). Laboratoire des Sciences du Climat et de l' Environnement; Chevillard, Anne [CEA, Fontenay-aux-Roses (France). DPRE/SERGD/LEIRPA

    2004-04-01

    Ecosystem CO{sub 2} flux measurements using the eddy covariance method were compared with the biospheric CO{sub 2} exchange estimates of a regional scale atmospheric model. The model described the seasonal patterns quite well, but underestimated the amplitude of the fluxes, especially at the northern sites. Two model parameters, photosynthetic efficiency for light use and Q{sub 10} for soil respiration, were re-evaluated on a diurnal and seasonal basis using the results from flux measurements. In most cases the photosynthetic efficiency was higher than the earlier estimate. The resulting flux was very sensitive to the value of photosynthetic efficiency, while changes in Q{sub 10} did not have a significant effect.

  19. Eddy covariance measurement of the spatial heterogeneity of surface energy exchanges over Heron Reef, Great Barrier Reef, Australia

    Science.gov (United States)

    MacKellar, M.; McGowan, H. A.; Phinn, S. R.

    2011-12-01

    Coral reefs cover 2.8 to 6.0 x 105 km2 of the Earth's surface and are warm, shallow regions that are believed to contribute enhanced sensible and latent heat to the atmosphere, relative to the surrounding ocean. To predict the impact of climate variability on coral reefs and their weather and climate including cloud, winds, rainfall patterns and cyclone genesis, accurate parameterisation of air-sea energy exchanges over coral reefs is essential. This is also important for the parameterisation and validation of regional to global scale forecast models to improve prediction of tropical and sub-tropical marine and coastal weather. Eddy covariance measurements of air-sea fluxes over coral reefs are rare due to the complexities of installing instrumentation over shallow, tidal water. Consequently, measurements of radiation and turbulent flux data for coral reefs have been captured remotely (satellite data) or via single measurement sites downwind of coral reefs (e.g. terrestrial or shipboard instrumentation). The resolution of such measurements and those that have been made at single locations on reefs may not capture the spatial heterogeneity of surface-atmosphere energy exchanges due to the different geomorphic and biological zones on coral reefs. Accordingly, the heterogeneity of coral reefs with regard to substrate, benthic communities and hydrodynamic processes are not considered in the characterization of the surface radiation energy flux transfers across the water-atmosphere interface. In this paper we present a unique dataset of concurrent in situ eddy covariance measurements made on instrumented pontoons of the surface energy balance over different geomorphic zones of a coral reef (shallow reef flat, shallow and deep lagoons). Significant differences in radiation transfers and air-sea turbulent flux exchanges over the reef were highlighted, with higher Bowen ratios over the shallow reef flat. Increasing wind speed was shown to increase flux divergence between

  20. Eddy Correlation Flux Measurement System Handbook

    Energy Technology Data Exchange (ETDEWEB)

    Cook, D. R. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2016-01-01

    The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration. The instruments used are: • a fast-response, three-dimensional (3D) wind sensor (sonic anemometer) to obtain the orthogonal wind components and the speed of sound (SOS) (used to derive the air temperature) • an open-path infrared gas analyzer (IRGA) to obtain the water vapor density and the CO2 concentration, and • an open-path infrared gas analyzer (IRGA) to obtain methane density and methane flux at one SGP EF and at the NSA CF. The ECOR systems are deployed at the locations where other methods for surface flux measurements (e.g., energy balance Bowen ratio [EBBR] systems) are difficult to employ, primarily at the north edge of a field of crops. A Surface Energy Balance System (SEBS) has been installed collocated with each deployed ECOR system in SGP, NSA, Tropical Western Pacific (TWP), ARM Mobile Facility 1 (AMF1), and ARM Mobile Facility 2 (AMF2). The surface energy balance system consists of upwelling and downwelling solar and infrared radiometers within one net radiometer, a wetness sensor, and soil measurements. The SEBS measurements allow the comparison of ECOR sensible and latent heat fluxes with the energy balance determined from the SEBS and provide information on wetting of the sensors for data quality purposes. The SEBS at one SGP and one NSA site also support upwelling and downwelling PAR measurements to qualify those two locations as Ameriflux sites.

  1. Conversed, gauge-covariant colour charge in Su(n)QCD

    International Nuclear Information System (INIS)

    Selikhov, A.V.

    1988-01-01

    The definition of the integral of the group tensor and the gauge-covariant differential with respect to a distant point are given in the work. A conserved covariant charge dependence on family of paths has been contracted with the help of these notions. It has been shown that the same family of paths fixes a gauge in which the covariant and noncovariant conserved currents coicide. The gauge is characterized by representation of the vector potential via field strength tensor. The possibility of connecting the choice of the family of paths with the measurement procedure is discussed. 13 refs.; 2 figs

  2. DFT-Based Closed-form Covariance Matrix and Direct Waveforms Design for MIMO Radar to Achieve Desired Beampatterns

    KAUST Repository

    Bouchoucha, Taha

    2017-01-23

    In multiple-input multiple-out (MIMO) radar, for desired transmit beampatterns, appropriate correlated waveforms are designed. To design such waveforms, conventional MIMO radar methods use two steps. In the first step, the waveforms covariance matrix, R, is synthesized to achieve the desired beampattern. While in the second step, to realize the synthesized covariance matrix, actual waveforms are designed. Most of the existing methods use iterative algorithms to solve these constrained optimization problems. The computational complexity of these algorithms is very high, which makes them difficult to use in practice. In this paper, to achieve the desired beampattern, a low complexity discrete-Fourier-transform based closed-form covariance matrix design technique is introduced for a MIMO radar. The designed covariance matrix is then exploited to derive a novel closed-form algorithm to directly design the finite-alphabet constant-envelope waveforms for the desired beampattern. The proposed technique can be used to design waveforms for large antenna array to change the beampattern in real time. It is also shown that the number of transmitted symbols from each antenna depends on the beampattern and is less than the total number of transmit antenna elements.

  3. Inferring 222Rn soil fluxes from ambient 222Rn activity and eddy covariance measurements of CO2

    Directory of Open Access Journals (Sweden)

    S. van der Laan

    2016-11-01

    Full Text Available We present a new methodology, which we call Single Pair of Observations Technique with Eddy Covariance (SPOT-EC, to estimate regional-scale surface fluxes of 222Rn from tower-based observations of 222Rn activity concentration, CO2 mole fractions and direct CO2 flux measurements from eddy covariance. For specific events, the regional (222Rn surface flux is calculated from short-term changes in ambient (222Rn activity concentration scaled by the ratio of the mean CO2 surface flux for the specific event to the change in its observed mole fraction. The resulting 222Rn surface emissions are integrated in time (between the moment of observation and the last prior background levels and space (i.e. over the footprint of the observations. The measurement uncertainty obtained is about ±15 % for diurnal events and about ±10 % for longer-term (e.g. seasonal or annual means. The method does not provide continuous observations, but reliable daily averages can be obtained. We applied our method to in situ observations from two sites in the Netherlands: Cabauw station (CBW and Lutjewad station (LUT. For LUT, which is an intensive agricultural site, we estimated a mean 222Rn surface flux of (0.29 ± 0.02 atoms cm−2 s−1 with values  > 0.5 atoms cm−2 s−1 to the south and south-east. For CBW we estimated a mean 222Rn surface flux of (0.63 ± 0.04 atoms cm−2 s−1. The highest values were observed to the south-west, where the soil type is mainly river clay. For both stations good agreement was found between our results and those from measurements with soil chambers and two recently published 222Rn soil flux maps for Europe. At both sites, large spatial and temporal variability of 222Rn surface fluxes were observed which would be impractical to measure with a soil chamber. SPOT-EC, therefore, offers an important new tool for estimating regional-scale 222Rn surface fluxes. Practical applications furthermore include

  4. Mixing ratios and eddy covariance flux measurements of volatile organic compounds from an urban canopy (Manchester, UK

    Directory of Open Access Journals (Sweden)

    B. Langford

    2009-03-01

    Full Text Available Mixing ratios and fluxes of six selected volatile organic compounds (VOCs were measured above the city of Manchester (UK during the summer of 2006. A proton transfer reaction-mass spectrometer was used for the measurement of mixing ratios, and fluxes were calculated from these using both the disjunct and the virtual disjunct eddy covariance techniques. The two flux systems, which operated in alternate half hours, showed good agreement, with R2 values ranging between 0.74 and 0.9 for the individual analytes. On average, fluxes measured in the disjunct mode were approximately 20% lower than those measured in the virtual mode. This difference is due to both the dampening of the VOC signal by the disjunct flux sampler and carry over from one sample to the next. Correcting for these effects reduced the difference to less than 7%. Observed fluxes are thought to be largely controlled by anthropogenic sources, with vehicle emissions the major contributor. However, both evaporative and biogenic emissions may account for some of the VOCs present. Concentrations and fluxes of the oxygenated compounds were highest on average, ranging between 0.15 to 1 mg m−2 h−1; the fluxes of aromatic compounds were lower, between 0.12 to 0.28 mg m−2 h−1. The observed fluxes were up-scaled to give city wide emission estimates for each compound and the results compared to estimates made by the National Atmospheric Emission Inventory (NAEI for the same flux footprint. Fluxes of toluene and benzene compared most closely differing by approximately 50%, while in contrast the oxygenated fluxes were found to be between 3.6–6.3 times larger than the annual average predicted by the NAEI.

  5. Validation of 3D-CMCC Forest Ecosystem Model (v.5.1) against eddy covariance data for 10 European forest sites

    DEFF Research Database (Denmark)

    Collalti, A.; Marconi, S.; Ibrom, Andreas

    2016-01-01

    This study evaluates the performances of the new version (v.5.1) of 3D-CMCC Forest Ecosystem Model (FEM) in simulating gross primary productivity (GPP), against eddy covariance GPP data for 10 FLUXNET forest sites across Europe. A new carbon allocation module, coupled with new both phenological...... over Europe without a site-related calibration, the model has been deliberately parametrized with a single set of species-specific parametrizations for each forest ecosystem. The model consistently reproduces both in timing and in magnitude daily and monthly GPP variability across all sites...... sites we evaluate whether a more accurate representation of forest structural characteristics (i.e. cohorts, forest layers) and species composition can improve model results. In two of the three sites results reveal that model slightly increases its performances although, statistically speaking...

  6. QED on curved background and on manifolds with boundaries: Unitarity versus covariance

    International Nuclear Information System (INIS)

    Vassilevich, D.V.

    1994-11-01

    Some recent results show that the covariant path integral and the integral over physical degrees of freedom give contradicting results on curved background and on manifolds with boundaries. This looks like a conflict between unitarity and covariance. We argue that this effect is due to the use of non-covariant measure on the space of physical degrees of freedom. Starting with the reduced phase space path integral and using covariant measure throughout computations we recover standard path integral in the Lorentz gauge and the Moss and Poletti BRST-invariant boundary conditions. We also demonstrate by direct calculations that in the approach based on Gaussian path integral on the space of physical degrees of freedom some basic symmetries are broken. (author). 39 refs

  7. Annual cycle of methane emission from a boreal fen measured by the eddy covariance technique

    International Nuclear Information System (INIS)

    Rinne, Janne.; Pihlatie, Mari; Haapanala, Sami; Vesala, Timo; Riutta, Terhi; Tuittila, Eeva-Stiina; Aurela, Mika; Tuovinen, Juha-Pekka

    2007-01-01

    The northern wetlands are one of the major sources of methane into the atmosphere. We measured annual methane emission from a boreal minerotrophic fen, Siikaneva, by the eddy covariance method. The average wintertime emissions were below 1 mg/m 2 /h, and the summertime emissions about 3.5 mg/m 2 /h. The water table depth did have any clear effect on methane emissions. During most of the year the emission depended on the temperature of peat below the water table. However, during the high and late summer the emission was independent on peat temperature as well. No diurnal cycle of methane flux was found. The total annual emission from the Siikaneva site was 12.6 g/m 2 . The emissions of the snow free period contributed 91% to the annual emission. The emission pulse during the snow melting period was clearly detectable but of minor importance adding only less than 3% to the annual emission. Over 20% of the carbon assimilated during the year as carbon dioxide was emitted as methane. Thus methane emission is an important component of the carbon balance of the Siikaneva fen. This indicates need of taking methane into account when studying carbon balances of northern fen ecosystems

  8. Diurnal variability of CO2 flux at coastal zone of Taiwan based on eddy covariance observation

    Science.gov (United States)

    Chien, Hwa; Zhong, Yao-Zhao; Yang, Kang-Hung; Cheng, Hao-Yuan

    2018-06-01

    In this study, we employed shore-based eddy covariance systems for a continuous measurement of the coastal CO2 flux near the northwestern coast of Taiwan from 2011 to 2015. To ensure the validity of the analysis, the data was selected and filtered with a footprint model and an empirical mode decomposition method. The results indicate that the nearshore air-sea and air-land CO2 fluxes exhibited a significant diurnal variability and a substantial day-night difference. The net air-sea CO2 flux was -1.75 ± 0.98 μmol-C m-2 s-1, whereas the net air-land CO2 flux was 0.54 ± 7.35 μmol-C m-2 s-1, which indicated that in northwestern Taiwan, the coastal water acts as a sink of atmospheric CO2 but the coastal land acts as a source. The Random Forest Method was applied to hierarchize the influence of Chl-a, SST, DO, pH and U10 on air-sea CO2 fluxes. The result suggests that the strength of the diurnal air-sea CO2 flux is strongly influenced by the local wind speed.

  9. Evaluating Water and Energy Fluxes across Three Land Cover Types in a Desert Urban Environment through a Mobile Eddy Covariance Platform

    Science.gov (United States)

    Pierini, N.; Vivoni, E. R.; Schreiner-McGraw, A.; Lopez-Castrillo, I.

    2015-12-01

    The urbanization process transforms a natural landscape into a built environment with many engineered surfaces, leading to significant impacts on surface energy and water fluxes across multiple spatial and temporal scales. Nevertheless, the effects of different urban land covers on energy and water fluxes has been rarely quantified across the large varieties of construction materials, landscaping and vegetation types, and industrial, commercial and residential areas in cities. In this study, we deployed a mobile eddy covariance tower at three different locations in the Phoenix, Arizona, metropolitan area to capture a variety of urban land covers. The three locations each represent a common urban class in Phoenix: 1) a dense, xeric landscape (gravel cover and native plants with drip-irrigation systems near tall buildings); 2) a high-density urban site (asphalt-paved parking lot near a high-traffic intersection); and 3) a suburban mesic landscape (sprinkler-irrigated turf grass in a suburban neighborhood). At each site, we measured meteorological variables, including air temperature and relative humidity at three heights, precipitation and pressure, surface temperature, and soil moisture and temperature (where applicable), to complement the eddy covariance measurements of radiation, energy, carbon dioxide and water vapor fluxes. We evaluated the tower footprint at each site to characterize the contributing surface area to the flux measurements, including engineered and landscaping elements, as a function of time for each deployment. The different sites allowed us to compare how turbulent fluxes of water vapor and carbon dioxide vary for these representative urban land covers, in particular with respect to the role of precipitation events and irrigation. While the deployments covered different seasons, from winter to summer in 2015, the variety of daily conditions allowed quantification of the differential response to precipitation events during the winter, pre

  10. Disjunct eddy covariance measurements of volatile organic compound fluxes using proton transfer reaction mass spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Taipale, R.

    2011-07-01

    Volatile organic compounds (VOCs) are emitted into the atmosphere from natural and anthropogenic sources, vegetation being the dominant source on a global scale. Some of these reactive compounds are deemed major contributors or inhibitors to aerosol particle formation and growth, thus making VOC measurements essential for current climate change research. This thesis discusses ecosystem scale VOC fluxes measured above a boreal Scots pine dominated forest in southern Finland. The flux measurements were performed using the micrometeorological disjunct eddy covariance (DEC) method combined with proton transfer reaction mass spectrometry (PTR-MS), which is an online technique for measuring VOC concentrations. The measurement, calibration, and calculation procedures developed in this work proved to be well suited to long-term VOC concentration and flux measurements with PTR-MS. A new averaging approach based on running averaged covariance functions improved the determination of the lag time between wind and concentration measurements, which is a common challenge in DEC when measuring fluxes near the detection limit. The ecosystem scale emissions of methanol, acetaldehyde, and acetone were substantial. These three oxygenated VOCs made up about half of the total emissions, with the rest comprised of monoterpenes. Contrary to the traditional assumption that monoterpene emissions from Scots pine originate mainly as evaporation from specialized storage pools, the DEC measurements indicated a significant contribution from de novo biosynthesis to the ecosystem scale monoterpene emissions. This thesis offers practical guidelines for long-term DEC measurements with PTR-MS. In particular, the new averaging approach to the lag time determination seems useful in the automation of DEC flux calculations. Seasonal variation in the monoterpene biosynthesis and the detailed structure of a revised hybrid algorithm, describing both de novo and pool emissions, should be determined in

  11. Quantifying and reducing the differences in forest CO2-fluxes estimated by eddy covariance, biometric and chamber methods: A global synthesis

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xingchang; Wang, Chuankuan; Bond-Lamberty, Benjamin

    2017-12-15

    Carbon dioxide (CO2) fluxes between terrestrial ecosystems and the atmosphere are primarily measured with eddy covariance (EC), biometric, and chamber methods. However, it is unclear why the estimates of CO2-fluxes, when measured using these different methods, converge at some sites but diverge at others. We synthesized a novel global dataset of forest CO2-fluxes to evaluate the consistency between EC and biometric or chamber methods for quantifying CO2 budget in forests. The EC approach, comparing with the other two methods, tended to produce 25% higher estimate of net ecosystem production (NEP, 0.52Mg C ha-1 yr-1), mainly resulting from lower EC-estimated Re; 10% lower ecosystem respiration (Re, 1.39Mg C ha-1 yr-1); and 3% lower gross primary production (0.48 Mg C ha-1 yr-1) The discrepancies between EC and the other methods were higher at sites with complex topography and dense canopies versus those with flat topography and open canopies. Forest age also influenced the discrepancy through the change of leaf area index. The open-path EC system induced >50% of the discrepancy in NEP, presumably due to its surface heating effect. These results provided strong evidence that EC produces biased estimates of NEP and Re in forest ecosystems. A global extrapolation suggested that the discrepancies in CO2 fluxes between methods were consistent with a global underestimation of Re, and overestimation of NEP, by the EC method. Accounting for these discrepancies would substantially improve the our estimates of the terrestrial carbon budget .

  12. Eddy covariance VOC emission and deposition fluxes above grassland using PTR-TOF

    Directory of Open Access Journals (Sweden)

    T. M. Ruuskanen

    2011-01-01

    Full Text Available Eddy covariance (EC is the preferable technique for flux measurements since it is the only direct flux determination method. It requires a continuum of high time resolution measurements (e.g. 5–20 Hz. For volatile organic compounds (VOC soft ionization via proton transfer reaction has proven to be a quantitative method for real time mass spectrometry; here we use a proton transfer reaction time of flight mass spectrometer (PTR-TOF for 10 Hz EC measurements of full mass spectra up to m/z 315. The mass resolution of the PTR-TOF enabled the identification of chemical formulas and separation of oxygenated and hydrocarbon species exhibiting the same nominal mass. We determined 481 ion mass peaks from ambient air concentration above a managed, temperate mountain grassland in Neustift, Stubai Valley, Austria. During harvesting we found significant fluxes of 18 compounds distributed over 43 ions, including protonated parent compounds, as well as their isotopes and fragments and VOC-H+ – water clusters. The dominant BVOC fluxes were methanol, acetaldehyde, ethanol, hexenal and other C6 leaf wound compounds, acetone, acetic acid, monoterpenes and sequiterpenes.

    The smallest reliable fluxes we determined were less than 0.1 nmol m−2 s−1, as in the case of sesquiterpene emissions from freshly cut grass. Terpenoids, including mono- and sesquiterpenes, were also deposited to the grassland before and after the harvesting. During cutting, total VOC emission fluxes up to 200 nmolC m−2 s−1 were measured. Methanol emissions accounted for half of the emissions of oxygenated VOCs and a third of the carbon of all measured VOC emissions during harvesting.

  13. Eddy covariance observations of surface leakage during shallow subsurface CO2 releases

    Science.gov (United States)

    Lewicki, Jennifer L.; Hilley, George E.; Fischer, Marc L.; Pan, Lehua; Oldenburg, Curtis M.; Dobeck, Laura; Spangler, Lee

    2009-06-01

    We tested the ability of eddy covariance (EC) to detect, locate, and quantify surface CO2 flux leakage signals within a background ecosystem. For 10 days starting on 9 July 2007, and for 7 days starting on 3 August 2007, 0.1 (Release 1) and 0.3 (Release 2) t CO2 d-1, respectively, were released from a horizontal well ˜100 m in length and ˜2.5 m in depth located in an agricultural field in Bozeman, Montana. An EC station measured net CO2 flux (Fc) from 8 June 2006 to 4 September 2006 (mean and standard deviation = -12.4 and 28.1 g m-2 d-1, respectively) and from 28 May 2007 to 4 September 2007 (mean and standard deviation = -12.0 and 28.1 g m-2 d-1, respectively). The Release 2 leakage signal was visible in the Fc time series, whereas the Release 1 signal was difficult to detect within variability of ecosystem fluxes. To improve detection ability, we calculated residual fluxes (Fcr) by subtracting fluxes corresponding to a model for net ecosystem exchange from Fc. Fcr had reduced variability and lacked the negative bias seen in corresponding Fc distributions. Plotting the upper 90th percentile Fcr versus time enhanced the Release 2 leakage signal. However, values measured during Release 1 fell within the variability assumed to be related to unmodeled natural processes. Fcr measurements and corresponding footprint functions were inverted using a least squares approach to infer the spatial distribution of surface CO2 fluxes during Release 2. When combined with flux source area evaluation, inversion results roughly located the CO2 leak, while resolution was insufficient to quantify leakage rate.

  14. Towards physiologically meaningful water-use efficiency estimates from eddy covariance data.

    Science.gov (United States)

    Knauer, Jürgen; Zaehle, Sönke; Medlyn, Belinda E; Reichstein, Markus; Williams, Christopher A; Migliavacca, Mirco; De Kauwe, Martin G; Werner, Christiane; Keitel, Claudia; Kolari, Pasi; Limousin, Jean-Marc; Linderson, Maj-Lena

    2018-02-01

    Intrinsic water-use efficiency (iWUE) characterizes the physiological control on the simultaneous exchange of water and carbon dioxide in terrestrial ecosystems. Knowledge of iWUE is commonly gained from leaf-level gas exchange measurements, which are inevitably restricted in their spatial and temporal coverage. Flux measurements based on the eddy covariance (EC) technique can overcome these limitations, as they provide continuous and long-term records of carbon and water fluxes at the ecosystem scale. However, vegetation gas exchange parameters derived from EC data are subject to scale-dependent and method-specific uncertainties that compromise their ecophysiological interpretation as well as their comparability among ecosystems and across spatial scales. Here, we use estimates of canopy conductance and gross primary productivity (GPP) derived from EC data to calculate a measure of iWUE (G 1 , "stomatal slope") at the ecosystem level at six sites comprising tropical, Mediterranean, temperate, and boreal forests. We assess the following six mechanisms potentially causing discrepancies between leaf and ecosystem-level estimates of G 1 : (i) non-transpirational water fluxes; (ii) aerodynamic conductance; (iii) meteorological deviations between measurement height and canopy surface; (iv) energy balance non-closure; (v) uncertainties in net ecosystem exchange partitioning; and (vi) physiological within-canopy gradients. Our results demonstrate that an unclosed energy balance caused the largest uncertainties, in particular if it was associated with erroneous latent heat flux estimates. The effect of aerodynamic conductance on G 1 was sufficiently captured with a simple representation. G 1 was found to be less sensitive to meteorological deviations between canopy surface and measurement height and, given that data are appropriately filtered, to non-transpirational water fluxes. Uncertainties in the derived GPP and physiological within-canopy gradients and their

  15. Eddy covariance captures four-phase crassulacean acid metabolism (CAM) gas exchange signature in Agave.

    Science.gov (United States)

    Owen, Nick A; Choncubhair, Órlaith Ní; Males, Jamie; Del Real Laborde, José Ignacio; Rubio-Cortés, Ramón; Griffiths, Howard; Lanigan, Gary

    2016-02-01

    Mass and energy fluxes were measured over a field of Agave tequilana in Mexico using eddy covariance (EC) methodology. Data were gathered over 252 d, including the transition from wet to dry periods. Net ecosystem exchanges (FN,EC ) displayed a crassulacean acid metabolism (CAM) rhythm that alternated from CO2 sink at night to CO2 source during the day, and partitioned canopy fluxes (FA,EC ) showed a characteristic four-phase CO2 exchange pattern. Results were cross-validated against diel changes in titratable acidity, leaf-unfurling rates, energy exchange fluxes and reported biomass yields. Projected carbon balance (g C m(-2)  year(-1) , mean ± 95% confidence interval) indicated the site was a net sink of -333 ± 24, of which contributions from soil respiration were +692 ± 7, and FA,EC was -1025 ± 25. EC estimated biomass yield was 20.1 Mg (dry) ha(-1)  year(-1) . Average integrated daily FA,EC was -234 ± 5 mmol CO2  m(-2)  d(-1) and persisted almost unchanged after 70 d of drought conditions. Regression analyses were performed on the EC data to identify the best environmental predictors of FA . Results suggest that the carbon acquisition strategy of Agave offers productivity and drought resilience advantages over conventional semi-arid C3 and C4 bioenergy candidates. © 2015 John Wiley & Sons Ltd.

  16. Sound-speed structure and propagational characteristics of a cold core eddy in the Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    PrasannaKumar, S.; Babu, M.T.; Murty, T.V.R.

    reduces by about 20 m across the eddy. Simulation studies showed that the rays passing through the eddy undergoes a reduction in the path length thereby reducing the travel time. Travel time delay causEd. by the eddy is of the order of 200 milliseconds...

  17. Theoretical and practical program in the non-destructive testing by eddy currents - the first level

    International Nuclear Information System (INIS)

    Shaaban, H.I.; Addarwish, J.M.A.

    2014-11-01

    The testing using eddy currents is one of the non-destructive tests that use electromagnetic property as a basis for testing procedures, and there are many other ways to use this principle, including Remote Field Testing and the Magnetic Flux Leakage test. Eddy currents are electrical currents moving in a circular path, and took the name eddy of eddies that form when a liquid or gas is moving in a circular path because of objection obstacles to its track. They are generated in the material using a variable magnetic field. Non-destructive testing by eddy currents is a technique used for the detection of defects and interruptions in a material and it is a process that relies on the generation of small eddy currents in the material of the part to be examined, provided that this part is of an electrically conducting material. This technique and its scientific basis are explained in this book. Also the devices used in this technique and how to use these devices in details are explained. The book contains Twelve chapters: Introduction to non destructive testing - Engineering materials and its mechanical characteristics - Electrical and magnetic characteristics of engineering materials - Introduction to testing by eddy currents - Factors affecting eddy currents - Basis of electrical circuits used in eddy currents testing devices - Probes of eddy currents testing - Eddy currents testing devices (Theoretical) - Analysis of the examination results of testing by eddy currents: techniques and applications - Applications of testing by eddy currents - Eddy currents testing devices (Application) - Practical lessons for the first level in testing by eddy currents.

  18. DFT-Based Closed-form Covariance Matrix and Direct Waveforms Design for MIMO Radar to Achieve Desired Beampatterns

    KAUST Repository

    Bouchoucha, Taha; Ahmed, Sajid; Al-Naffouri, Tareq Y.; Alouini, Mohamed-Slim

    2017-01-01

    optimization problems. The computational complexity of these algorithms is very high, which makes them difficult to use in practice. In this paper, to achieve the desired beampattern, a low complexity discrete-Fourier-transform based closed-form covariance

  19. Using Eddy Covariance Sensors to Quantify Carbon Metabolism of Peatlands: A Case Study in Turkey

    Directory of Open Access Journals (Sweden)

    Can Ertekin

    2011-01-01

    Full Text Available Net ecosystem exchange (NEE of carbon dioxide (CO2 was measured in a cool temperate peatland in northwestern Turkey on a continuous basis using eddy covariance (EC sensors and multiple (non-linear regression-M(NLR-models. Our results showed that hourly NEE varied between −1.26 and 1.06 mg CO2 m−2 s−1, with a mean value of 0.11 mg CO2 m−2 s−1. Nighttime ecosystem respiration (RE was on average measured as 0.23 ± 0.09 mg CO2 m−2 s−1. Two best-fit M(NLR models estimated daytime RE as 0.64 ± 0.31 and 0.24 ± 0.05 mg CO2 m−2 s−1. Total RE as the sum of nighttime and daytime RE ranged from 0.47 to 0.87 mg CO2 m−2 s−1, thus yielding estimates of gross primary productivity (GPP at −0.35 ± 0.18 and −0.74 ± 0.43 mg CO2 m−2 s−1. Use of EC sensors and M(NLR models is one of the most direct ways to quantify turbulent CO2 exchanges among the soil, vegetation and atmosphere within the atmospheric boundary layer, as well as source and sink behaviors of ecosystems.

  20. Net ecosystem exchange and energy fluxes measured with the eddy covariance technique in a western Siberian bog

    Directory of Open Access Journals (Sweden)

    P. Alekseychik

    2017-08-01

    Full Text Available Very few studies of ecosystem–atmosphere exchange involving eddy covariance data have been conducted in Siberia, with none in the western Siberian middle taiga. This work provides the first estimates of carbon dioxide (CO2 and energy budgets in a typical bog of the western Siberian middle taiga based on May–August measurements in 2015. The footprint of measured fluxes consisted of a homogeneous mixture of tree-covered ridges and hollows with the vegetation represented by typical sedges and shrubs. Generally, the surface exchange rates resembled those of pine-covered bogs elsewhere. The surface energy balance closure approached 100 %. Net CO2 uptake was comparatively high, summing up to 202 gC m−2 for the four measurement months, while the Bowen ratio was seasonally stable at 28 %. The ecosystem turned into a net CO2 source during several front passage events in June and July. The periods of heavy rain helped keep the water table at a sustainably high level, preventing a usual drawdown in summer. However, because of the cloudy and rainy weather, the observed fluxes might rather represent the special weather conditions of 2015 than their typical magnitudes.

  1. Methane and CO2 fluxes of moving point sources - Beyond or within the limits of eddy covariance measurements

    Science.gov (United States)

    Felber, Raphael; Neftel, Albrecht; Münger, Andreas; Ammann, Christof

    2014-05-01

    The eddy covariance (EC) technique has been extensively used for CO2 and energy exchange measurements over different ecosystems. For some years, it has been also becoming widely used to investigate CH4 and N2O exchange over ecosystems including grazing systems. EC measurements represent a spatially integrated flux over an upwind area (footprint). Whereas for extended homogenous areas EC measurements work well, the animals in a grazing system are a challenge as they represent moving point sources that create inhomogeneous conditions in space and time. The main issues which have to be taken into account when applying EC flux measurements over a grazed system are: i) In the presence of animals the high time resolution concentration measurements show large spikes in the signal. These spikes may be filtered/reduced by standard quality control software in order to avoid wrong measurements. ii) Data on the position of the animals relative to the flux footprint is needed to quantify the contribution of the grazing animals to the measured flux. For one grazing season we investigated the ability of EC flux measurements to reliably quantify the contribution of the grazing animals to the CH4 and CO2 exchange over pasture systems. For this purpose, a field experiment with a herd of twenty dairy cows in a full-day rotational grazing system was carried out on the Swiss central plateau. Net CH4 and CO2 exchange of the pasture system was measured continuously by the eddy covariance technique (Sonic Anemometer HS-50, Gill Instruments Ltd; FGGA, Los Gatos Research Inc.). To quantify the contribution of the animals to the net flux, the position of the individual cows was recorded using GPS (5 s time resolution) on each animal. An existing footprint calculation tool (ART footprint tool) was adapted and CH4 emissions of the cows were calculated. CH4 emissions from cows could be used as a tracer to investigate the quality of the evaluation of the EC data, since the background exchange of

  2. Open-path, closed-path and reconstructed aerosol extinction at a rural site.

    Science.gov (United States)

    Gordon, Timothy D; Prenni, Anthony J; Renfro, James R; McClure, Ethan; Hicks, Bill; Onasch, Timothy B; Freedman, Andrew; McMeeking, Gavin R; Chen, Ping

    2018-04-09

    The Handix Scientific Open-Path Cavity Ringdown Spectrometer (OPCRDS) was deployed during summer 2016 in Great Smoky Mountains National Park (GRSM). Extinction coefficients from the relatively new OPCRDS and from a more well-established extinction instrument agreed to within 7%. Aerosol hygroscopic growth (f(RH)) was calculated from the ratio of ambient extinction measured by the OPCRDS to dry extinction measured by a closed-path extinction monitor (Aerodyne's Cavity Attenuated Phase Shift Particulate Matter Extinction Monitor, CAPS PMex). Derived hygroscopicity (RH 1995 at the same site and time of year, which is noteworthy given the decreasing trend for organics and sulfate in the eastern U.S. However, maximum f(RH) values in 1995 were less than half as large as those recorded in 2016-possibly due to nephelometer truncation losses in 1995. Two hygroscopicity parameterizations were investigated using high time resolution OPCRDS+CAPS PMex data, and the K ext model was more accurate than the γ model. Data from the two ambient optical instruments, the OPCRDS and the open-path nephelometer, generally agreed; however, significant discrepancies between ambient scattering and extinction were observed, apparently driven by a combination of hygroscopic growth effects, which tend to increase nephelometer truncation losses and decrease sensitivity to the wavelength difference between the two instruments as a function of particle size. There was not a statistically significant difference in the mean reconstructed extinction values obtained from the original and the revised IMPROVE (Interagency Monitoring of Protected Visual Environments) equations. On average IMPROVE reconstructed extinction was ~25% lower than extinction measured by the OPCRDS, which suggests that the IMPROVE equations and 24-hr aerosol data are moderately successful in estimating current haze levels at GRSM. However, this conclusion is limited by the coarse temporal resolution and the low dynamic range of

  3. Fast and accurate estimation of the covariance between pairwise maximum likelihood distances

    Directory of Open Access Journals (Sweden)

    Manuel Gil

    2014-09-01

    Full Text Available Pairwise evolutionary distances are a model-based summary statistic for a set of molecular sequences. They represent the leaf-to-leaf path lengths of the underlying phylogenetic tree. Estimates of pairwise distances with overlapping paths covary because of shared mutation events. It is desirable to take these covariance structure into account to increase precision in any process that compares or combines distances. This paper introduces a fast estimator for the covariance of two pairwise maximum likelihood distances, estimated under general Markov models. The estimator is based on a conjecture (going back to Nei & Jin, 1989 which links the covariance to path lengths. It is proven here under a simple symmetric substitution model. A simulation shows that the estimator outperforms previously published ones in terms of the mean squared error.

  4. Fast and accurate estimation of the covariance between pairwise maximum likelihood distances.

    Science.gov (United States)

    Gil, Manuel

    2014-01-01

    Pairwise evolutionary distances are a model-based summary statistic for a set of molecular sequences. They represent the leaf-to-leaf path lengths of the underlying phylogenetic tree. Estimates of pairwise distances with overlapping paths covary because of shared mutation events. It is desirable to take these covariance structure into account to increase precision in any process that compares or combines distances. This paper introduces a fast estimator for the covariance of two pairwise maximum likelihood distances, estimated under general Markov models. The estimator is based on a conjecture (going back to Nei & Jin, 1989) which links the covariance to path lengths. It is proven here under a simple symmetric substitution model. A simulation shows that the estimator outperforms previously published ones in terms of the mean squared error.

  5. Monitoring sensible heat flux over urban areas in a high-altitude city using Large Aperture Scintillometer and Eddy Covariance

    Science.gov (United States)

    Du, Junping; Timmermans, Wim J.; Ma, Yaoming; Su, Bob; Pema, Tsering

    2017-04-01

    Urbanization leads to modifications of surface energy balance which governs the momentum, heat and mass transfer between urban canopy layer and the atmosphere, thus impacts dynamic processes in the urban ABL and ultimately influence the local, regional and even global climate. It is essential to obtain accurate urban ABL observations to enhance our understanding of land-atmosphere interaction process over the urban area and help to improve the prediction ability of numerical model. However, up to now, there are rarely observations in high latitude cities. In one of the highest cities in the world, Lhasa, Eddy Covariance (EC) measurements have been ongoing since 10 August 2016 and a Large Aperture Scintillometer (LAS) started to work on 12 November 2016, in addition to a UHI network which has been running since 2012. Taking advantage of these observations, this poster will estimate and analyze the surface energy balance in the winter of 2016 in Lhasa, with an emphasis on sensible heat flux. An analytical footprint model and the radiative surface temperature retrieved from Landsat 8 will be employed to compare EC and LAS measurements.

  6. An Empirical Orthogonal Function-Based Algorithm for Estimating Terrestrial Latent Heat Flux from Eddy Covariance, Meteorological and Satellite Observations.

    Science.gov (United States)

    Feng, Fei; Li, Xianglan; Yao, Yunjun; Liang, Shunlin; Chen, Jiquan; Zhao, Xiang; Jia, Kun; Pintér, Krisztina; McCaughey, J Harry

    2016-01-01

    Accurate estimation of latent heat flux (LE) based on remote sensing data is critical in characterizing terrestrial ecosystems and modeling land surface processes. Many LE products were released during the past few decades, but their quality might not meet the requirements in terms of data consistency and estimation accuracy. Merging multiple algorithms could be an effective way to improve the quality of existing LE products. In this paper, we present a data integration method based on modified empirical orthogonal function (EOF) analysis to integrate the Moderate Resolution Imaging Spectroradiometer (MODIS) LE product (MOD16) and the Priestley-Taylor LE algorithm of Jet Propulsion Laboratory (PT-JPL) estimate. Twenty-two eddy covariance (EC) sites with LE observation were chosen to evaluate our algorithm, showing that the proposed EOF fusion method was capable of integrating the two satellite data sets with improved consistency and reduced uncertainties. Further efforts were needed to evaluate and improve the proposed algorithm at larger spatial scales and time periods, and over different land cover types.

  7. Eddy covariance observations of methane and nitrous oxide emissions. Towards more accurate estimates from ecosystems

    International Nuclear Information System (INIS)

    Kroon, P.S.

    2010-09-01

    About 30% of the increased greenhouse gas (GHG) emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are related to land use changes and agricultural activities. In order to select effective measures, knowledge is required about GHG emissions from these ecosystems and how these emissions are influenced by management and meteorological conditions. Accurate emission values are therefore needed for all three GHGs to compile the full GHG balance. However, the current annual estimates of CH4 and N2O emissions from ecosystems have significant uncertainties, even larger than 50%. The present study showed that an advanced technique, micrometeorological eddy covariance flux technique, could obtain more accurate estimates with uncertainties even smaller than 10%. The current regional and global trace gas flux estimates of CH4 and N2O are possibly seriously underestimated due to incorrect measurement procedures. Accurate measurements of both gases are really important since they could even contribute for more than two-third to the total GHG emission. For example: the total GHG emission of a dairy farm site was estimated at 16.10 3 kg ha -1 yr -1 in CO2-equivalents from which 25% and 45% was contributed by CH4 and N2O, respectively. About 60% of the CH4 emission was emitted by ditches and their bordering edges. These emissions are not yet included in the national inventory reports. We recommend including these emissions in coming reports.

  8. Eddy covariance measurements and parameterisation of traffic related particle emissions in an urban environment

    Directory of Open Access Journals (Sweden)

    E. M. Mårtensson

    2006-01-01

    Full Text Available Urban aerosol sources are important due to the health effects of particles and their potential impact on climate. Our aim has been to quantify and parameterise the urban aerosol source number flux F (particles m−2 s−1, in order to help improve how this source is represented in air quality and climate models. We applied an aerosol eddy covariance flux system 118.0 m above the city of Stockholm. This allowed us to measure the aerosol number flux for particles with diameters >11 nm. Upward source fluxes dominated completely over deposition fluxes in the collected dataset. Therefore, the measured fluxes were regarded as a good approximation of the aerosol surface sources. Upward fluxes were parameterised using a traffic activity (TA database, which is based on traffic intensity measurements. The footprint (area on the surface from which sources and sinks affect flux measurements, located at one point in space of the eddy system covered road and building construction areas, forests and residential areas, as well as roads with high traffic density and smaller streets. We found pronounced diurnal cycles in the particle flux data, which were well correlated with the diurnal cycles in traffic activities, strongly supporting the conclusion that the major part of the aerosol fluxes was due to traffic emissions. The emission factor for the fleet mix in the measurement area EFfm=1.4±0.1×1014 veh−1 km−1 was deduced. This agrees fairly well with other studies, although this study has an advantage of representing the actual effective emission from a mixed vehicle fleet. Emission from other sources, not traffic related, account for a F0=15±18×106 m−2 s−1. The urban aerosol source flux can then be written as F=EFfmTA+F0. In a second attempt to find a parameterisation, the friction velocity U* normalised with the average friction velocity has been included, F=EF . This parameterisation results in a somewhat reduced emission factor, 1.3×1014 veh

  9. Eddy covariance and biometric measurements show that a savanna ecosystem in Southwest China is a carbon sink

    Science.gov (United States)

    Fei, Xuehai; Jin, Yanqiang; Zhang, Yiping; Sha, Liqing; Liu, Yuntong; Song, Qinghai; Zhou, Wenjun; Liang, Naishen; Yu, Guirui; Zhang, Leiming; Zhou, Ruiwu; Li, Jing; Zhang, Shubin; Li, Peiguang

    2017-02-01

    Savanna ecosystems play a crucial role in the global carbon cycle. However, there is a gap in our understanding of carbon fluxes in the savanna ecosystems of Southeast Asia. In this study, the eddy covariance technique (EC) and the biometric-based method (BM) were used to determine carbon exchange in a savanna ecosystem in Southwest China. The BM-based net ecosystem production (NEP) was 0.96 tC ha-1 yr-1. The EC-based estimates of the average annual gross primary productivity (GPP), ecosystem respiration (Reco), and net ecosystem carbon exchange (NEE) were 6.84, 5.54, and -1.30 tC ha-1 yr-1, respectively, from May 2013 to December 2015, indicating that this savanna ecosystem acted as an appreciable carbon sink. The ecosystem was more efficient during the wet season than the dry season, so that it represented a small carbon sink of 0.16 tC ha-1 yr-1 in the dry season and a considerable carbon sink of 1.14 tC ha-1 yr-1 in the wet season. However, it is noteworthy that the carbon sink capacity may decline in the future under rising temperatures and decreasing rainfall. Consequently, further studies should assess how environmental factors and climate change will influence carbon-water fluxes.

  10. Ecological and Biogeochemical Impacts of Internal Waves on Mesophotic Coral Ecosystems: Testing Eddy Covariance and Isotope Approaches, Iriomote, Japan

    Science.gov (United States)

    Wyatt, A. S. J.; Miyajima, T.; Leichter, J.; Naruse, T.; Kuwae, T.; Yamamoto, S.; Satoh, N.; Nagata, T.

    2016-02-01

    -specific isotope analyses of amino acids (CSIA-AA), depth-specific radioisotope markers such as radiocarbon and iodine ratios (129I/127I), and eddy covariance experiments offers a promising path towards elucidating the functional importance of internal waves in the development and persistence of MCE at local to regional scales.

  11. Direct closed-form covariance matrix and finite alphabet constant-envelope waveforms for planar array beampatterns

    KAUST Repository

    Ahmed, Sajid

    2016-11-24

    Various examples of methods and systems are provided for direct closed-form finite alphabet constant-envelope waveforms for planar array beampatterns. In one example, a method includes defining a waveform covariance matrix based at least in part upon a two-dimensional fast Fourier transform (2D-FFT) analysis of a frequency domain matrix Hf associated with a planar array of antennas. Symbols can be encoded based upon the waveform covariance matrix and the encoded symbols can be transmitted via the planar array of antennas. In another embodiment, a system comprises an N x M planar array of antennas and transmission circuitry configured to transmit symbols via a two-dimensional waveform beampattern defined based at least in part upon a 2D-FFT analysis of a frequency domain matrix Hf associated with the planar array of antennas.

  12. Terrestrial gross carbon dioxide uptake : Global distribution and covariation with climate

    NARCIS (Netherlands)

    Beer, Christian; Reichstein, Markus; Tomelleri, Enrico; Ciais, Philippe; Jung, Martin; Carvalhais, Nuno; Rödenbeck, Christian; Arain, M. Altaf; Baldocchi, Dennis D.; Bonan, Gordon B.; Bondeau, Alberte; Cescatti, Alessandro; Lasslop, Gitta; Lindroth, Anders; Lomas, Mark; Luyssaert, Sebastiaan; Margolis, Hank; Oleson, Keith W.; Roupsard, Olivier; Veenendaal, Elmar; Viovy, Nicolas; Williams, Christopher M.; Woodward, F. Ian; Papale, Dario

    2010-01-01

    Terrestrial gross primary production (GPP) is the largest global CO 2 flux driving several ecosystem functions. We provide an observation-based estimate of this flux at 123 ± 8 petagrams of carbon per year (Pg C year-1) using eddy covariance flux data and various diagnostic models. Tropical forests

  13. Ecosystem-level water-use efficiency inferred from eddy covariance data: definitions, patterns and spatial up-scaling

    Science.gov (United States)

    Reichstein, M.; Beer, C.; Kuglitsch, F.; Papale, D.; Soussana, J. A.; Janssens, I.; Ciais, P.; Baldocchi, D.; Buchmann, N.; Verbeeck, H.; Ceulemans, R.; Moors, E.; Köstner, B.; Schulze, D.; Knohl, A.; Law, B. E.

    2007-12-01

    In this presentation we discuss ways to infer and to interpret water-use efficiency at ecosystem level (WUEe) from eddy covariance flux data and possibilities for scaling these patterns to regional and continental scale. In particular we convey the following: WUEe may be computed as a ratio of integrated fluxes or as the slope of carbon versus water fluxes offering different chances for interpretation. If computed from net ecosystem exchange and evapotranspiration on has to take of counfounding effects of respiration and soil evaporation. WUEe time-series at diurnal and seasonal scale is a valuable ecosystem physiological diagnostic for example about ecosystem-level responses to drought. Most often WUEe decreases during dry periods. The mean growing season ecosystem water-use efficiency of gross carbon uptake (WUEGPP) is highest in temperate broad-leaved deciduous forests, followed by temperate mixed forests, temperate evergreen conifers, Mediterranean broad-leaved deciduous forests, Mediterranean broad-leaved evergreen forests and Mediterranean evergreen conifers and boreal, grassland and tundra ecosystems. Water-use efficiency exhibits a temporally quite conservative relation with atmospheric water vapor pressure deficit (VPD) that is modified between sites by leaf area index (LAI) and soil quality, such that WUEe increases with LAI and soil water holding capacity which is related to texture. This property and tight coupling between carbon and water cycles is used to estimate catchment-scale water-use efficiency and primary productivity by integration of space-borne earth observation and river discharge data.

  14. Eddy covariance methane flux measurements over a grazed pasture: effect of cows as moving point sources

    Science.gov (United States)

    Felber, R.; Münger, A.; Neftel, A.; Ammann, C.

    2015-06-01

    Methane (CH4) from ruminants contributes one-third of global agricultural greenhouse gas emissions. Eddy covariance (EC) technique has been extensively used at various flux sites to investigate carbon dioxide exchange of ecosystems. Since the development of fast CH4 analyzers, the instrumentation at many flux sites has been amended for these gases. However, the application of EC over pastures is challenging due to the spatially and temporally uneven distribution of CH4 point sources induced by the grazing animals. We applied EC measurements during one grazing season over a pasture with 20 dairy cows (mean milk yield: 22.7 kg d-1) managed in a rotational grazing system. Individual cow positions were recorded by GPS trackers to attribute fluxes to animal emissions using a footprint model. Methane fluxes with cows in the footprint were up to 2 orders of magnitude higher than ecosystem fluxes without cows. Mean cow emissions of 423 ± 24 g CH4 head-1 d-1 (best estimate from this study) correspond well to animal respiration chamber measurements reported in the literature. However, a systematic effect of the distance between source and EC tower on cow emissions was found, which is attributed to the analytical footprint model used. We show that the EC method allows one to determine CH4 emissions of cows on a pasture if the data evaluation is adjusted for this purpose and if some cow distribution information is available.

  15. Eddy covariance flux measurements of biogenic VOCs during ECHO 2003 using proton transfer reaction mass spectrometry

    Directory of Open Access Journals (Sweden)

    C. Spirig

    2005-01-01

    Full Text Available Within the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. The eddy covariance (EC technique was applied since it represents the most direct flux measurement approach on the canopy scale and is, therefore, least susceptible to these non-ideal conditions. A specific flux calculation method was used to account for the sequential multi-component PTR-MS measurements and allowing an individual delay time adjustment as well as a rigorous quality control based on cospectral analysis. The validated flux results are consistent with light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average daytime emissions of 0.94 and 0.3µg m-2s-1, respectively. Emissions of methanol reached on average 0.087µg m-2s-1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK and methacrolein (MACR were also found, being two orders of magnitude lower than those of isoprene. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement.

  16. Dead Sea evaporation by eddy covariance measurements vs. aerodynamic, energy budget, Priestley-Taylor, and Penman estimates

    Science.gov (United States)

    Metzger, Jutta; Nied, Manuela; Corsmeier, Ulrich; Kleffmann, Jörg; Kottmeier, Christoph

    2018-02-01

    The Dead Sea is a terminal lake, located in an arid environment. Evaporation is the key component of the Dead Sea water budget and accounts for the main loss of water. So far, lake evaporation has been determined by indirect methods only and not measured directly. Consequently, the governing factors of evaporation are unknown. For the first time, long-term eddy covariance measurements were performed at the western Dead Sea shore for a period of 1 year by implementing a new concept for onshore lake evaporation measurements. To account for lake evaporation during offshore wind conditions, a robust and reliable multiple regression model was developed using the identified governing factors wind velocity and water vapour pressure deficit. An overall regression coefficient of 0.8 is achieved. The measurements show that the diurnal evaporation cycle is governed by three local wind systems: a lake breeze during daytime, strong downslope winds in the evening, and strong northerly along-valley flows during the night. After sunset, the strong winds cause half-hourly evaporation rates which are up to 100 % higher than during daytime. The median daily evaporation is 4.3 mm d-1 in July and 1.1 mm d-1 in December. The annual evaporation of the water surface at the measurement location was 994±88 mm a-1 from March 2014 until March 2015. Furthermore, the performance of indirect evaporation approaches was tested and compared to the measurements. The aerodynamic approach is applicable for sub-daily and multi-day calculations and attains correlation coefficients between 0.85 and 0.99. For the application of the Bowen ratio energy budget method and the Priestley-Taylor method, measurements of the heat storage term are inevitable on timescales up to 1 month. Otherwise strong seasonal biases occur. The Penman equation was adapted to calculate realistic evaporation, by using an empirically gained linear function for the heat storage term, achieving correlation coefficients between 0

  17. On the coupled use of eddy covariance, sap flow sensors and remote sensing information for Evapotranspiration estimates in a typical heterogeneous Mediterranean ecosystem.

    Science.gov (United States)

    Corona, R.; Montaldo, N.

    2017-12-01

    Mediterranean ecosystems are typically heterogeneous, with contrasting plant functional types (PFT, woody vegetation and grass) that compete for water use. Due to the complexity of these ecosystems there is still uncertainty on the estimate of the evapotranspiration (ET). Micrometerological measurements (e.g. eddy covariance method based, EC ) are widely used for ET estimate, but in heterogeneous systems one of the main assumption (surface homogeneity) is not preserved and the method may become less robust. In this sense, the coupled use of sap flow sensors for tree transpiration estimate, surface temperature sensors, remote sensing information for land surface characterization allow to estimate the ET components and the energy balances of the three main land surface components (woody vegetation, grass and bare soil), overtaking the EC method uncertainties. The experimental site of Orroli, in Sardinia (Italy), is a typical Mediterranean heterogeneous ecosystem, monitored from the University of Cagliari since 2003. With the intent to perform an intensive field campaign for the ET estimation, we verified the potentiality of coupling eddy covariance (EC) method, infrared sensors and thermal dissipation methods (i.e. sap flow technique) for tree transpiration estimate. As a first step 3 commercial sap flux sensors were installed in a wild olive clump where the skin temperature of one tree in the clump was monitored with an infrared transducer. Then, other 54 handmade sensors were installed in 14 clumps in the EC footprint. Measurements of diameter were recorded in all the clumps and the sapwood depth was derived from measurements in several trees. The field ET estimation from the 4 commercial sensors was obtained assuming 4 different relationship between the monitored sap flux and the diameter of the species in the footprint. Instead for the 54 handmade sensors a scaling procedure was applied based on the allometric relationships between sapwood area, diameter and

  18. Eddy covariance and biometric measurements show that a savanna ecosystem in Southwest China is a carbon sink

    Science.gov (United States)

    Fei, Xuehai; Jin, Yanqiang; Zhang, Yiping; Sha, Liqing; Liu, Yuntong; Song, Qinghai; Zhou, Wenjun; Liang, Naishen; Yu, Guirui; Zhang, Leiming; Zhou, Ruiwu; Li, Jing; Zhang, Shubin; Li, Peiguang

    2017-01-01

    Savanna ecosystems play a crucial role in the global carbon cycle. However, there is a gap in our understanding of carbon fluxes in the savanna ecosystems of Southeast Asia. In this study, the eddy covariance technique (EC) and the biometric-based method (BM) were used to determine carbon exchange in a savanna ecosystem in Southwest China. The BM-based net ecosystem production (NEP) was 0.96 tC ha−1 yr−1. The EC-based estimates of the average annual gross primary productivity (GPP), ecosystem respiration (Reco), and net ecosystem carbon exchange (NEE) were 6.84, 5.54, and −1.30 tC ha−1 yr−1, respectively, from May 2013 to December 2015, indicating that this savanna ecosystem acted as an appreciable carbon sink. The ecosystem was more efficient during the wet season than the dry season, so that it represented a small carbon sink of 0.16 tC ha−1 yr−1 in the dry season and a considerable carbon sink of 1.14 tC ha−1 yr−1 in the wet season. However, it is noteworthy that the carbon sink capacity may decline in the future under rising temperatures and decreasing rainfall. Consequently, further studies should assess how environmental factors and climate change will influence carbon-water fluxes. PMID:28145459

  19. Anticyclonic eddy energy and pathways in the Algerian basin (1993-2007)

    Science.gov (United States)

    Pessini, Federica; Perilli, Angelo; Olita, Antonio

    2016-04-01

    The Algero-Provençal basin plays a key role in the circulation of the entire Mediterranean Sea. Consequently, in the past its hydrodynamics has been intensively studied with infrared and colour satellite imagery, moorings, surface drifters and altimetry observations. The basin is divided into two sub-basins by the North Balearic front, a thermal front characterized by a high seasonal variability: the Provençal sub-basin in the north and the Algerian sub-basin in the south. The Algerian basin is dominated by mesoscale phenomena, especially anti-cyclonic eddies. The Algerian current becomes unstable and meanders; often giving rise to mesoscale eddies of both signs. The anti-cyclonic eddies (hereafter Algerian Eddies or AEs) can grow rapidly in horizontal and vertical extension. They can also detach from the Algerian slope and circulate for several months within the sub-basin, while the cyclonic ones quickly disappear. In spite of its limited dimensions, the Algerian sub-basin can contain as many as three long-life AEs, which can interact with each other and with sub-basin dynamics. In spite of the current body of research, a study on the tracking, energy and interaction of these long-life eddies in time and space is still lacking. In order to fill this gap, we applied the automated eddy detection and tracking method created by Penven (2005), which reveals the complex movements and dynamics of eddies in the Algerian sub-basin. The Penven algorithm combines the detection of the largest closed contours in SSH (Sea Surface Height) with a positive value of the relevant Okubo-Weiss parameter. The latter has already been successfully used in the Algerian Basin by Isern-Fontanet et al. (2003). The eddy-tracking algorithm is based on the minimization of a general distance that takes into account the difference in coordinates, radius, vorticity, mean height and amplitude between eddies of consecutive temporal steps. The code was modified and adapted in order to optimize its

  20. Eddy Covariance measurements of stable CO2 and H2O isotopologues

    Science.gov (United States)

    Braden-Behrens, Jelka; Knohl, Alexander

    2015-04-01

    The analysis of the stable isotope composition of CO2 and H2O fluxes (such as 13C, 18O and 2H in H2O and CO2) has provided valuable insights into ecosystem gas exchange. The approach builds on differences in the isotope signature of different ecosystem components that are primarily caused by the preference for or the discrimination against respective isotope species by important processes within the ecosystem (e.g. photosynthesis or leaf water diffusion). With the ongoing development of laser spectrometric methods, fast and precise measurements of isotopologue mixing ratios became possible, hence also enabling Eddy Covariance (EC) based approaches to directly measure the isotopic composition of CO2 and H2Ov net fluxes on ecosystem scale. During an eight month long measurement campaign in 2015, we plan to simultaneously measure CO2 and H2Ov isotopologue fluxes using an EC approach in a managed beech forest in Thuringia, Germany. For this purpose, we will use two different laser spectrometers for high frequency measurements of isotopic compositions: For H2Ov measurements, we will use an off axis cavity output water vapour isotope analyser (WVIA, Los Gatos Research Inc.) with 5 Hz response; and for CO2 measurements, we will use a quantum cascade laser-based system (QCLAS, Aerodyne Research Inc.) with thermoelectrically cooled detectors and up to 10 Hz measurement capability. The resulting continuous isotopologue flux measurements will be accompanied by intensive sampling campaigns on the leaf scale: Water from leaf, twig, soil and precipitation samples will be analysed in the lab using isotope ratio mass spectrometry. During data analysis we will put a focus on (i) the influence of carbon and oxygen discrimination on the isotopic signature of respective net ecosystem exchange, (ii) on the relationship between evapotranspiration and leaf water enrichment, and (iii) on the 18O exchange between carbon dioxide and water. At present, we already carried out extensive

  1. Scalar Similarity for Relaxed Eddy Accumulation Methods

    Science.gov (United States)

    Ruppert, Johannes; Thomas, Christoph; Foken, Thomas

    2006-07-01

    The relaxed eddy accumulation (REA) method allows the measurement of trace gas fluxes when no fast sensors are available for eddy covariance measurements. The flux parameterisation used in REA is based on the assumption of scalar similarity, i.e., similarity of the turbulent exchange of two scalar quantities. In this study changes in scalar similarity between carbon dioxide, sonic temperature and water vapour were assessed using scalar correlation coefficients and spectral analysis. The influence on REA measurements was assessed by simulation. The evaluation is based on observations over grassland, irrigated cotton plantation and spruce forest. Scalar similarity between carbon dioxide, sonic temperature and water vapour showed a distinct diurnal pattern and change within the day. Poor scalar similarity was found to be linked to dissimilarities in the energy contained in the low frequency part of the turbulent spectra ( definition.

  2. Perturbative method for the derivation of quantum kinetic theory based on closed-time-path formalism

    International Nuclear Information System (INIS)

    Koide, Jun

    2002-01-01

    Within the closed-time-path formalism, a perturbative method is presented, which reduces the microscopic field theory to the quantum kinetic theory. In order to make this reduction, the expectation value of a physical quantity must be calculated under the condition that the Wigner distribution function is fixed, because it is the independent dynamical variable in the quantum kinetic theory. It is shown that when a nonequilibrium Green function in the form of the generalized Kadanoff-Baym ansatz is utilized, this condition appears as a cancellation of a certain part of contributions in the diagrammatic expression of the expectation value. Together with the quantum kinetic equation, which can be derived in the closed-time-path formalism, this method provides a basis for the kinetic-theoretical description

  3. The closed time-path Green function formalism in many-body theory

    International Nuclear Information System (INIS)

    Guang-zhao Zhou; Zhao-bin Su; Bai-lin Hao; Lu Yu.

    1983-09-01

    The closed time-path Green function formalism, developed by our group during recent years, is briefly reviewed. The generating functional technique, the coupled equations for the order parameter and the elementary excitations as well as the systematic loop expansion are outlined. The applications to critical dynamics, quenched random systems, nonlinear response theory, superconductivity, laser system and quasi-one-dimensional conductors are described. The theoretical approach developed can be applied to both equilibrium and non-equilibrium many-body systems. (author)

  4. Direct determination of highly size-resolved turbulent particle fluxes with the disjunct eddy covariance method and a 12 – stage electrical low pressure impactor

    Directory of Open Access Journals (Sweden)

    A. Schmidt

    2008-12-01

    Full Text Available During summer 2007, turbulent vertical particle mass and number fluxes were measured for a period of 98 days near the city centre of Münster in north-west Germany. For this purpose, a valve controlled disjunct eddy covariance system was mounted at 65 m a.g.l. on a military radio tower. The concentration values for 11 size bins with aerodynamic diameters (D50 from 0.03 to 10 μm were measured with an electrical low pressure impactor. After comparison with other fluxes obtained from 10 Hz measurements with the classical eddy covariance method, the loss of information concerning high frequent parts of the flux could be stated as negligible. The results offer an extended insight in the turbulent atmospheric exchange of aerosol particles by highly size-resolved particle fluxes covering 11 size bins and show that the city of Münster acts as a relevant source for aerosol particles.

    Significant differences occur between the fluxes of the various particle size classes. While the total particle number flux shows a pattern which is strictly correlated to the diurnal course of the turbulence regime and the traffic intensity, the total mass flux exhibits a single minimum in the evening hours when coarse particles start to deposit.

    As a result, a mean mass deposition of about 10 mg m−2 per day was found above the urban test site, covering the aerosol size range from 40 nm to 2.0 μm. By contrast, the half-hourly total number fluxes accumulated over the lower ELPI stages range from −4.29×107 to +1.44×108 particles m−2 s−1 and are clearly dominated by the sub-micron particle fraction of the impactor stages with diameters between 40 nm and 320 nm. The averaged number fluxes of particles with diameters between 2.0 and 6.4 μm show lower turbulent dynamics during daytime and partially remarkably high negative fluxes with mean deposition velocities of 2×10−3 m

  5. Evaluating the potential of large-scale simulations to predict carbon fluxes of terrestrial ecosystems over a European Eddy Covariance network

    International Nuclear Information System (INIS)

    Balzarolo, M.; Boussetta, S.; Balsamo, G.; Beljaars, A.; Maignan, F.; Chevallier, F.; Poulter, B.

    2014-01-01

    This paper reports a comparison between large scale simulations of three different land surface models (LSMs), ORCHIDEE, ISBA-A-gs and CTESSEL, forced with the same meteorological data, and compared with the carbon fluxes measured at 32 eddy covariance (EC) flux tower sites in Europe. The results show that the three simulations have the best performance for forest sites and the poorest performance for cropland and grassland sites. In addition, the three simulations have difficulties capturing the seasonality of Mediterranean and sub-tropical biomes, characterized by dry summers. This reduced simulation performance is also reflected in deficiencies in diagnosed light-use efficiency (LUE) and vapour pressure deficit (VPD) dependencies compared to observations. Shortcomings in the forcing data may also play a role. These results indicate that more research is needed on the LUE and VPD functions for Mediterranean and sub-tropical biomes. Finally, this study highlights the importance of correctly representing phenology (i.e. leaf area evolution) and management (i.e. rotation-irrigation for cropland, and grazing-harvesting for grassland) to simulate the carbon dynamics of European ecosystems and the importance of ecosystem-level observations in model development and validation. (authors)

  6. First direct measurements of formaldehyde flux via eddy covariance: implications for missing in-canopy formaldehyde sources

    Directory of Open Access Journals (Sweden)

    J. P. DiGangi

    2011-10-01

    Full Text Available We report the first observations of formaldehyde (HCHO flux measured via eddy covariance, as well as HCHO concentrations and gradients, as observed by the Madison Fiber Laser-Induced Fluorescence Instrument during the BEACHON-ROCS 2010 campaign in a rural, Ponderosa Pine forest northwest of Colorado Springs, CO. A median noon upward flux of ~80 μg m−2 h−1 (~24 pptv m s−1 was observed with a noon range of 37 to 131 μg m−2 h−1. Enclosure experiments were performed to determine the HCHO branch (3.5 μg m-2 h−1 and soil (7.3 μg m−2 h−1 direct emission rates in the canopy. A zero-dimensional canopy box model, used to determine the apportionment of HCHO source and sink contributions to the flux, underpredicted the observed HCHO flux by a factor of 6. Simulated increases in concentrations of species similar to monoterpenes resulted in poor agreement with measurements, while simulated increases in direct HCHO emissions and/or concentrations of species similar to 2-methyl-3-buten-2-ol best improved model/measurement agreement. Given the typical diurnal variability of these BVOC emissions and direct HCHO emissions, this suggests that the source of the missing flux is a process with both a strong temperature and radiation dependence.

  7. Developmental dysplasia of the hip: A computational biomechanical model of the path of least energy for closed reduction.

    Science.gov (United States)

    Zwawi, Mohammed A; Moslehy, Faissal A; Rose, Christopher; Huayamave, Victor; Kassab, Alain J; Divo, Eduardo; Jones, Brendan J; Price, Charles T

    2017-08-01

    This study utilized a computational biomechanical model and applied the least energy path principle to investigate two pathways for closed reduction of high grade infantile hip dislocation. The principle of least energy when applied to moving the femoral head from an initial to a final position considers all possible paths that connect them and identifies the path of least resistance. Clinical reports of severe hip dysplasia have concluded that reduction of the femoral head into the acetabulum may occur by a direct pathway over the posterior rim of the acetabulum when using the Pavlik harness, or by an indirect pathway with reduction through the acetabular notch when using the modified Hoffman-Daimler method. This computational study also compared the energy requirements for both pathways. The anatomical and muscular aspects of the model were derived using a combination of MRI and OpenSim data. Results of this study indicate that the path of least energy closely approximates the indirect pathway of the modified Hoffman-Daimler method. The direct pathway over the posterior rim of the acetabulum required more energy for reduction. This biomechanical analysis confirms the clinical observations of the two pathways for closed reduction of severe hip dysplasia. The path of least energy closely approximated the modified Hoffman-Daimler method. Further study of the modified Hoffman-Daimler method for reduction of severe hip dysplasia may be warranted based on this computational biomechanical analysis. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1799-1805, 2017. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society.

  8. Occlusal contacting condition and masticatory function of 2 types of pattern that differ in the closing path of the mandibular incisal point during chewing.

    Science.gov (United States)

    Watanabe, Atsushi; Shiga, Hiroshi; Kobayashi, Yoshinori

    2011-10-01

    To clarify the difference in the state of occlusal contact and masticatory function between two patterns of masticatory movement path that differed in the closing path. Fifteen healthy subjects with Pattern I (a linear or concave opening path and a convex closing path) and Pattern II (similar opening path to that in Pattern I and a concave closing path) were selected. The state of occlusal contact on the working and balancing sides and the masticatory function (integral value of the masseter muscular activity, gape, masticatory width, cycle time, indicators representing the stability of the path and rhythm, and glucose extraction) were compared between the two patterns. The occlusal contact on the working side was about the same. For the balancing side, occlusal contact at the molar region was observed for Pattern II in most cases, whereas no occlusal contact was observed for Pattern I. The integral value of the masseter muscular activity and the glucose extraction were greater for Pattern I. The gape was not different between the two patterns. Pattern I had a wide masticatory width and a short cycle time. The values of the indicators representing the stability of the path and rhythm were smaller for Pattern I. It was suggested that Pattern I with a convex closing path had a functional difference and a superior masticatory function from Pattern II with a concave closing path, and the difference in the occlusal contact on the balancing side was related. Copyright © 2011 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.

  9. Virtual disjunct eddy covariance measurements of organic compound fluxes from a subalpine forest using proton transfer reaction mass spectrometry

    Directory of Open Access Journals (Sweden)

    T. G. Karl

    2002-01-01

    Full Text Available A `virtual' disjunct eddy covariance (vDEC device was tested with field measurements of biogenic VOC fluxes at a subalpine forest site in the Rocky Mountains of the USA. A PTR-MS instrument was used as the VOC sensor. Daily peak emission fluxes of 2-methyl-3-buten-2-ol (MBO, methanol, acetone and acetaldehyde were around 1.5, 1, 0.8 and 0.4 mg m-2 h-1, respectively. High pass filtering due to long sampling lines was investigated in laboratory experiments, and suggested that VOC losses in PTFA lines are generally governed by diffusion laws. Memory effects and surface reactions did not seem to play a dominant role. Model estimates of MBO fluxes compared well with measured fluxes. The results also suggest that latent heat and sensible heat fluxes are reasonably well correlated with VOC fluxes and could be used to predict variations in VOC emissions. The release of MBO, methanol, acetone and acetaldehyde resulted in significant change of tropospheric oxidant levels and a 10--40% increase in ozone levels, as inferred from a photochemical box model. We conclude that vDEC with a PTR-MS instrument is a versatile tool for simultaneous field analysis of multiple VOC fluxes.

  10. Quantum gravitation. The Feynman path integral approach

    International Nuclear Information System (INIS)

    Hamber, Herbert W.

    2009-01-01

    The book covers the theory of Quantum Gravitation from the point of view of Feynman path integrals. These provide a manifestly covariant approach in which fundamental quantum aspects of the theory such as radiative corrections and the renormalization group can be systematically and consistently addressed. The path integral method is suitable for both perturbative as well as non-perturbative studies, and is known to already provide a framework of choice for the theoretical investigation of non-abelian gauge theories, the basis for three of the four known fundamental forces in nature. The book thus provides a coherent outline of the present status of the theory gravity based on Feynman's formulation, with an emphasis on quantitative results. Topics are organized in such a way that the correspondence to similar methods and results in modern gauge theories becomes apparent. Covariant perturbation theory are developed using the full machinery of Feynman rules, gauge fixing, background methods and ghosts. The renormalization group for gravity and the existence of non-trivial ultraviolet fixed points are investigated, stressing a close correspondence with well understood statistical field theory models. Later the lattice formulation of gravity is presented as an essential tool towards an understanding of key features of the non-perturbative vacuum. The book ends with a discussion of contemporary issues in quantum cosmology such as scale dependent gravitational constants and quantum effects in the early universe. (orig.)

  11. Vacuum stress and closed paths in rectangles, pistons and pistols

    International Nuclear Information System (INIS)

    Fulling, S A; Kaplan, L; Kirsten, K; Liu, Z H; Milton, K A

    2009-01-01

    Rectangular cavities are solvable models that nevertheless touch on many of the controversial or mysterious aspects of the vacuum energy of quantum fields. This paper is a thorough study of the two-dimensional scalar field in a rectangle by the method of images, or closed classical (or optical) paths, which is exact in this case. For each point r and each specularly reflecting path beginning and ending at r, we provide formulae for all components of the stress tensor T μν (r), for all values of the curvature coupling constant ξ and all values of an ultraviolet cutoff parameter. Arbitrary combinations of Dirichlet and Neumann conditions on the four sides can be treated. The total energy is also investigated, path by path. These results are used in an attempt to clarify the physical reality of the repulsive (outward) force on the sides of the box predicted by calculations that neglect both boundary divergences and the exterior of the box. Previous authors have studied 'piston' geometries that avoid these problems and have found the force to be attractive. We consider a 'pistol' geometry that comes closer to the original problem of a box with a movable lid. We find again an attractive force, although its origin and detailed behavior are somewhat different from the piston case. However, the pistol (and the piston) model can be criticized for extending idealized boundary conditions into short distances where they are physically implausible. Therefore, it is of interest to see whether leaving the ultraviolet cutoff finite yields results that are more plausible. We then find that the force depends strongly on a geometrical parameter; it can be made repulsive, but only by forcing that parameter into the regime where the model is least convincing physically

  12. Eddy diffusion coefficients and their upper limits based on application of the similarity theory

    Directory of Open Access Journals (Sweden)

    M. N. Vlasov

    2015-07-01

    Full Text Available The equation for the diffusion velocity in the mesosphere and the lower thermosphere (MLT includes the terms for molecular and eddy diffusion. These terms are very similar. For the first time, we show that, by using the similarity theory, the same formula can be obtained for the eddy diffusion coefficient as the commonly used formula derived by Weinstock (1981. The latter was obtained by taking, as a basis, the integral function for diffusion derived by Taylor (1921 and the three-dimensional Kolmogorov kinetic energy spectrum. The exact identity of both formulas means that the eddy diffusion and heat transport coefficients used in the equations, both for diffusion and thermal conductivity, must meet a criterion that restricts the outer eddy scale to being much less than the scale height of the atmosphere. This requirement is the same as the requirement that the free path of molecules must be much smaller than the scale height of the atmosphere. A further result of this criterion is that the eddy diffusion coefficients Ked, inferred from measurements of energy dissipation rates, cannot exceed the maximum value of 3.2 × 106 cm2 s−1 for the maximum value of the energy dissipation rate of 2 W kg−1 measured in the mesosphere and the lower thermosphere (MLT. This means that eddy diffusion coefficients larger than the maximum value correspond to eddies with outer scales so large that it is impossible to use these coefficients in eddy diffusion and eddy heat transport equations. The application of this criterion to the different experimental data shows that some reported eddy diffusion coefficients do not meet this criterion. For example, the large values of these coefficients (1 × 107 cm2 s−1 estimated in the Turbulent Oxygen Mixing Experiment (TOMEX do not correspond to this criterion. The Ked values inferred at high latitudes by Lübken (1997 meet this criterion for summer and winter polar data, but the Ked values for summer at low latitudes

  13. Dispersion of tracers by the oceanic eddy field modelling programme

    International Nuclear Information System (INIS)

    Richards, K.J.

    1986-01-01

    A numerical model has been developed to study the dispersion of tracers by the oceanic eddy field. The study is designed to investigate the horizontal and vertical structure of the eddies and how this structure is influenced by the bottom topography. It is found that hills and valleys have a strong effect on the eddies above them. The flow close to the bottom has a tendency to be steered by the height contours. The surface and bottom flows become decorrelated and the vertical variation of the kinetic energy of the eddies is increased with higher topographic features. (author)

  14. Modeling light use efficiency in a subtropical mangrove forest equipped with CO2 eddy covariance

    Directory of Open Access Journals (Sweden)

    J. G. Barr

    2013-03-01

    Full Text Available Despite the importance of mangrove ecosystems in the global carbon budget, the relationships between environmental drivers and carbon dynamics in these forests remain poorly understood. This limited understanding is partly a result of the challenges associated with in situ flux studies. Tower-based CO2 eddy covariance (EC systems are installed in only a few mangrove forests worldwide, and the longest EC record from the Florida Everglades contains less than 9 years of observations. A primary goal of the present study was to develop a methodology to estimate canopy-scale photosynthetic light use efficiency in this forest. These tower-based observations represent a basis for associating CO2 fluxes with canopy light use properties, and thus provide the means for utilizing satellite-based reflectance data for larger scale investigations. We present a model for mangrove canopy light use efficiency utilizing the enhanced green vegetation index (EVI derived from the Moderate Resolution Imaging Spectroradiometer (MODIS that is capable of predicting changes in mangrove forest CO2 fluxes caused by a hurricane disturbance and changes in regional environmental conditions, including temperature and salinity. Model parameters are solved for in a Bayesian framework. The model structure requires estimates of ecosystem respiration (RE, and we present the first ever tower-based estimates of mangrove forest RE derived from nighttime CO2 fluxes. Our investigation is also the first to show the effects of salinity on mangrove forest CO2 uptake, which declines 5% per each 10 parts per thousand (ppt increase in salinity. Light use efficiency in this forest declines with increasing daily photosynthetic active radiation, which is an important departure from the assumption of constant light use efficiency typically applied in satellite-driven models. The model developed here provides a framework for estimating CO2 uptake by these forests from reflectance data and

  15. Cartographic modeling of heterogeneous landscape for footprint analysis of Eddy Covariance Measurements (Central Forest and Central Chernozem reserves, Russia)

    Science.gov (United States)

    Kozlov, Daniil

    2014-05-01

    The topographical, soil and vegetation maps of FLUXNET study areas are widely used for interpretation of eddy covariance measurements, for calibration of biogeochemical models and for making regional assessments of carbon balance. The poster presents methodological problems and results of ecosystem mapping using GIS, remote sensing, statistical and field methods on the example of two RusFluxNet sites in the Central Forest (33° E, 56°30'N) and Central Chernozem (36°10' E, 51°36'N) reserves. In the Central Forest reserve tacheometric measurements were used for topographical and peat surveys of bogged sphagnum spruce forest of 20-hectare area. Its common borders and its areas affected by windfall were determined. The supplies and spatial distribution of organic matter were obtained. The datasets of groundwater monitoring measurements on ten wells were compared with each other and the analysis of spatial and temporal groundwater variability was performed. The map of typical ecosystems of the reserve and its surroundings was created on the basis of analysis of multi-temporal Landsat images. In the Central Chernozem reserve the GNSS topographical survey was used for flux tower footprint mapping (22 ha). The features of microrelief predetermine development of different soils within the footprint. Close relationship between soil (73 drilling site) and terrain attributes (DEM with 2.5 m) allowed to build maps of soils and soil properties: carbon content, bulk density, upper boundary of secondary carbonates. Position for chamber-based soil respiration measurements was defined on the basis of these maps. The detailed geodetic and soil surveys of virgin lands and plowland were performed in order to estimate the effect of agrogenic processes such as dehumification, compaction and erosion on soils during the whole period of agricultural use of Central Chernozem reserve area and around. The choice of analogous soils was based on the similarity of their position within the

  16. Application of thermal-dissociation laser induced fluorescence (TD-LIF to measurement of HNO3, Σalkyl nitrates, Σperoxy nitrates, and NO2 fluxes using eddy covariance

    Directory of Open Access Journals (Sweden)

    D. K. Farmer

    2006-01-01

    Full Text Available Nitrogen exchange between the atmosphere and biosphere directly influences atmospheric composition. While much is known about mechanisms of NO and N2O emissions, instrumentation for the study of mechanisms contributing to exchange of other major nitrogen species is quite limited. Here we describe the application of a new technique, thermal dissociation-laser induced fluorescence (TD-LIF, to eddy covariance measurements of the fluxes of NO2, total peroxy acyl and peroxy nitrates, total alkyl and multifunctional alkyl nitrates, and nitric acid. The technique offers the potential for investigating mechanisms of exchange of these species at the canopy scale over timescales from days to years. Examples of flux measurements at a ponderosa pine plantation in the mid-elevation Sierra Nevada Mountains in California are reported and used to evaluate instrument performance.

  17. In situ measurements of tritium evapotranspiration (³H-ET) flux over grass and soil using the gradient and eddy covariance experimental methods and the FAO-56 model.

    Science.gov (United States)

    Connan, O; Maro, D; Hébert, D; Solier, L; Caldeira Ideas, P; Laguionie, P; St-Amant, N

    2015-10-01

    The behaviour of tritium in the environment is linked to the water cycle. We compare three methods of calculating the tritium evapotranspiration flux from grassland cover. The gradient and eddy covariance methods, together with a method based on the theoretical Penmann-Monteith model were tested in a study carried out in 2013 in an environment characterised by high levels of tritium activity. The results show that each of the three methods gave similar results. The various constraints applying to each method are discussed. The results show a tritium evapotranspiration flux of around 15 mBq m(-2) s(-1) in this environment. These results will be used to improve the entry parameters for the general models of tritium transfers in the environment. Copyright © 2015 Elsevier Ltd. All rights reserved.

  18. Fluxes of total reactive atmospheric nitrogen (ΣNr using eddy covariance above arable land

    Directory of Open Access Journals (Sweden)

    Christophe R. Flechard

    2013-02-01

    Full Text Available The amount and timing of reactive nitrogen exchange between agricultural land and the atmosphere play a key role in evaluating ecosystem productivity and in addressing atmospheric nitrogen budgets and transport. With the recent development of the Total Reactive Atmospheric Nitrogen Converter (TRANC apparatus, a methodology has been provided for continuous measurement of the sum of all airborne nitrogen containing species (ΣNr allowing for diurnal and seasonal investigations. We present ΣNr concentration and net flux data from an 11-month field campaign conducted at an arable field using the TRANC system within an eddy-covariance setup. Clear diurnal patterns of both ΣNr concentrations and fluxes with significant dependencies on atmospheric stability and stomatal regulation were observed in the growing season. TRANC data were compared with monthly-averaged concentrations and dry deposition rates of selected Nr compounds using DELTA denuders and ensemble-averages of four inferential models, respectively. Similar seasonal trends were found for Nr concentrations from DELTA and TRANC measurements with values from the latter being considerably higher than those of DELTA denuders. The variability of the difference between these two systems could be explained by seasonally changing source locations of NOx contributions to the TRANC signal. As soil and vegetation Nr emissions to the atmosphere are generally not treated by inferential (dry deposition models, TRANC data showed lower monthly deposition rates than those obtained from inferential modelling. Net ΣNr exchange was almost neutral (~0.072 kg N ha−1 at the end of the observation period. However, during most parts of the year, slight but permanent net ΣNr deposition was found. Our measurements demonstrate that fertilizer addition followed by substantial ΣNr emissions plays a crucial role in a site's annual atmospheric nitrogen budget. As long-term Nr measurements with high temporal

  19. Carbon balance of the typical grain crop rotation in Moscow region assessed by eddy covariance method

    Science.gov (United States)

    Meshalkina, Joulia; Yaroslavtsev, Alexis; Vassenev, Ivan

    2017-04-01

    Croplands could have equal or even greater net ecosystem production than several natural ecosystems (Hollinger et al., 2004), so agriculture plays a substantial role in mitigation strategies for the reduction of carbon dioxide emissions. In Central Russia, where agricultural soils carbon loses are 9 time higher than natural (forest's) soils ones (Stolbovoi, 2002), the reduction of carbon dioxide emissions in agroecosystems must be the central focus of the scientific efforts. Although the balance of the CO2 mostly attributed to management practices, limited information exists regarding the crop rotation overall as potential of C sequestration. In this study, we present data on carbon balance of the typical grain crop rotation in Moscow region followed for 4 years by measuring CO2 fluxes by paired eddy covariance stations (EC). The study was conducted at the Precision Farming Experimental Fields of the Russian Timiryazev State Agricultural University, Moscow, Russia. The experimental site has a temperate and continental climate and situated in south taiga zone with Arable Sod-Podzoluvisols (Albeluvisols Umbric). Two fields of the four-course rotation were studied in 2013-2016. Crop rotation included winter wheat (Triticum sativum L.), barley (Hordeum vulgare L.), potato crop (Solanum tuberosum L.) and cereal-legume mixture (Vicia sativa L. and Avena sativa L.). Crops sowing occurred during the period from mid-April to mid-May depending on weather conditions. Winter wheat was sown in the very beginning of September and the next year it occurred from under the snow in the phase of tillering. White mustard (Sinapis alba) was sown for green manure after harvesting winter wheat in mid of July. Barley was harvested in mid of August, potato crop was harvested in September. Cereal-legume mixture on herbage was collected depending on the weather from early July to mid-August. Carbon uptake (NEE negative values) was registered only for the fields with winter wheat and white

  20. Eddy Powell 1939 - 2003

    CERN Multimedia

    2003-01-01

    We were saddened to learn that Eddy Powell had passed away on Saturday 26 July after a long illness. Eddy had so many friends at CERN and made such a contribution to the Organisation that it is impossible that his passing goes without comment. Eddy was born in England on 4 August 1939 and, after serving his apprenticeship with the U.K. Ministry of Defence, he joined CERN in September 1965. As an electrical design draftsman with the Synchro-cyclotron Division he played an important role in the upgrades of that machine in the early 1970's, particularly on the RF systems and later on the development of the ISOLDE facility. This brought him into close contact with many of the technical support services in CERN and, unlike many of his compatriots, he acquired a remarkably good fluency in French. Always inquisitive on the physics carried out at CERN, he spent a great deal of time learning from physicists and engineers at all levels. When he felt sufficiently confident he became a CERN Guide for general public visit...

  1. Size-segregated fluxes of mineral dust from a desert area of northern China by eddy covariance

    Directory of Open Access Journals (Sweden)

    G. Fratini

    2007-06-01

    Full Text Available Mineral dust emission accounts for a substantial portion of particles present in the troposphere. It is emitted mostly from desert areas, mainly through intense storm episodes. The aim of this work was to quantify size-segregated fluxes of mineral dust particles emitted during storm events occurring in desert areas of northern China (Alashan desert, Inner Mongolia, known to act as one of the strongest sources of mineral dust particles in the Asian continent. Long-range transport of mineral dust emitted in this area is responsible for the high particle concentrations reached in densely populated areas, including the city of Beijing. Based on a theoretical analysis, an eddy covariance system was built to get size-segregated fluxes of mineral dust particles with optical diameters ranging between 0.26 and 7.00 µm. The system was optimised to measure fluxes under intense storm event conditions. It was tested in two sites located in the Chinese portion of the Gobi desert. During the field campaign, an intense wind erosion event, classified as a "weak dust storm", was recorded in one of them. Data obtained during this event indicate that particle number fluxes were dominated by the finer fraction, whereas in terms of mass, coarser particle accounted for the largest portion. It was found that during the storm event, ratios of size-segregated particle mass fluxes remained substantially constant and a simple parameterization of particle emission from total mass fluxes was possible. A strong correlation was also found between particle mass fluxes and the friction velocity. This relationship is extremely useful to investigate mechanisms of particle formation by wind erosion.

  2. Path-dependent functions

    International Nuclear Information System (INIS)

    Khrapko, R.I.

    1985-01-01

    A uniform description of various path-dependent functions is presented with the help of expansion of the type of the Taylor series. So called ''path-integrals'' and ''path-tensor'' are introduced which are systems of many-component quantities whose values are defined for arbitrary paths in coordinated region of space in such a way that they contain a complete information on the path. These constructions are considered as elementary path-dependent functions and are used instead of power monomials in the usual Taylor series. Coefficients of such an expansion are interpreted as partial derivatives dependent on the order of the differentiations or else as nonstandard cavariant derivatives called two-point derivatives. Some examples of pathdependent functions are presented.Space curvature tensor is considered whose geometrica properties are determined by the (non-transitive) translator of parallel transport of a general type. Covariant operation leading to the ''extension'' of tensor fiels is pointed out

  3. Partial covariance based functional connectivity computation using Ledoit-Wolf covariance regularization.

    Science.gov (United States)

    Brier, Matthew R; Mitra, Anish; McCarthy, John E; Ances, Beau M; Snyder, Abraham Z

    2015-11-01

    Functional connectivity refers to shared signals among brain regions and is typically assessed in a task free state. Functional connectivity commonly is quantified between signal pairs using Pearson correlation. However, resting-state fMRI is a multivariate process exhibiting a complicated covariance structure. Partial covariance assesses the unique variance shared between two brain regions excluding any widely shared variance, hence is appropriate for the analysis of multivariate fMRI datasets. However, calculation of partial covariance requires inversion of the covariance matrix, which, in most functional connectivity studies, is not invertible owing to rank deficiency. Here we apply Ledoit-Wolf shrinkage (L2 regularization) to invert the high dimensional BOLD covariance matrix. We investigate the network organization and brain-state dependence of partial covariance-based functional connectivity. Although RSNs are conventionally defined in terms of shared variance, removal of widely shared variance, surprisingly, improved the separation of RSNs in a spring embedded graphical model. This result suggests that pair-wise unique shared variance plays a heretofore unrecognized role in RSN covariance organization. In addition, application of partial correlation to fMRI data acquired in the eyes open vs. eyes closed states revealed focal changes in uniquely shared variance between the thalamus and visual cortices. This result suggests that partial correlation of resting state BOLD time series reflect functional processes in addition to structural connectivity. Copyright © 2015 Elsevier Inc. All rights reserved.

  4. Seasonal analyses of carbon dioxide and energy fluxes above an oil palm plantation using the eddy covariance method

    Science.gov (United States)

    Ibrahim, Anis; Haniff Harun, Mohd; Yusup, Yusri

    2017-04-01

    A study presents the measurements of carbon dioxide and latent and sensible heat fluxes above a mature oil palm plantation on mineral soil in Keratong, Pahang, Peninsular Malaysia. The sampling campaign was conducted over an 25-month period, from September 2013 to February 2015 and May 2016 to November 2016, using the eddy covariance method. The main aim of this work is to assess carbon dioxide and energy fluxes over this plantation at different time scales, seasonal and diurnal, and determine the effects of season and relevant meteorological parameters on the latter fluxes. Energy balance closure analyses gave a slope between latent and sensible heat fluxes and total incoming energy to be 0.69 with an R2 value of 0.86 and energy balance ratio of 0.80. The averaged net radiation was 108 W m-2. The results show that at the diurnal scale, carbon dioxide, latent and sensible heat fluxes exhibited a clear diurnal trend where carbon dioxide flux was at its minimum - 3.59 μmol m-2 s-1 in the mid-afternoon and maximum in the morning while latent and sensible behaved conversely to the carbon dioxide flux. The average carbon dioxide flux was - 0.37 μmol m-2 s-1. At the seasonal timescale, carbon dioxide fluxes did not show any apparent trend except during the Northeast Monsoon where the highest variability of the monthly means of carbon dioxide occurred.

  5. Planetary gyre, time-dependent eddies, torsional waves, and equatorial jets at the Earth's core surface

    DEFF Research Database (Denmark)

    Gillet, N.; Jault, D.; Finlay, Chris

    2015-01-01

    between the magnetic field and subdecadal nonzonal motions within the fluid outer core. Both the zonal and the more energetic nonzonal interannual motions were particularly intense close to the equator (below 10∘ latitude) between 1995 and 2010. We revise down the amplitude of the decade fluctuations......We report a calculation of time-dependent quasi-geostrophic core flows for 1940–2010. Inverting recursively for an ensemble of solutions, we evaluate the main source of uncertainties, namely, the model errors arising from interactions between unresolved core surface motions and magnetic fields....... Temporal correlations of these uncertainties are accounted for. The covariance matrix for the flow coefficients is also obtained recursively from the dispersion of an ensemble of solutions. Maps of the flow at the core surface show, upon a planetary-scale gyre, time-dependent large-scale eddies...

  6. Turbulent eddy diffusion models in exposure assessment - Determination of the eddy diffusion coefficient.

    Science.gov (United States)

    Shao, Yuan; Ramachandran, Sandhya; Arnold, Susan; Ramachandran, Gurumurthy

    2017-03-01

    The use of the turbulent eddy diffusion model and its variants in exposure assessment is limited due to the lack of knowledge regarding the isotropic eddy diffusion coefficient, D T . But some studies have suggested a possible relationship between D T and the air changes per hour (ACH) through a room. The main goal of this study was to accurately estimate D T for a range of ACH values by minimizing the difference between the concentrations measured and predicted by eddy diffusion model. We constructed an experimental chamber with a spatial concentration gradient away from the contaminant source, and conducted 27 3-hr long experiments using toluene and acetone under different air flow conditions (0.43-2.89 ACHs). An eddy diffusion model accounting for chamber boundary, general ventilation, and advection was developed. A mathematical expression for the slope based on the geometrical parameters of the ventilation system was also derived. There is a strong linear relationship between D T and ACH, providing a surrogate parameter for estimating D T in real-life settings. For the first time, a mathematical expression for the relationship between D T and ACH has been derived that also corrects for non-ideal conditions, and the calculated value of the slope between these two parameters is very close to the experimentally determined value. The values of D T obtained from the experiments are generally consistent with values reported in the literature. They are also independent of averaging time of measurements, allowing for comparison of values obtained from different measurement settings. These findings make the use of turbulent eddy diffusion models for exposure assessment in workplace/indoor environments more practical.

  7. Path integral quantization of parametrized field theory

    International Nuclear Information System (INIS)

    Varadarajan, Madhavan

    2004-01-01

    Free scalar field theory on a flat spacetime can be cast into a generally covariant form known as parametrized field theory in which the action is a functional of the scalar field as well as the embedding variables which describe arbitrary, in general curved, foliations of the flat spacetime. We construct the path integral quantization of parametrized field theory in order to analyze issues at the interface of quantum field theory and general covariance in a path integral context. We show that the measure in the Lorentzian path integral is nontrivial and is the analog of the Fradkin-Vilkovisky measure for quantum gravity. We construct Euclidean functional integrals in the generally covariant setting of parametrized field theory using key ideas of Schleich and show that our constructions imply the existence of nonstandard 'Wick rotations' of the standard free scalar field two-point function. We develop a framework to study the problem of time through computations of scalar field two-point functions. We illustrate our ideas through explicit computation for a time independent (1+1)-dimensional foliation. Although the problem of time seems to be absent in this simple example, the general case is still open. We discuss our results in the contexts of the path integral formulation of quantum gravity and the canonical quantization of parametrized field theory

  8. Carbon balance at represenative agroecosystems of Central European Russia with different crops assessed by eddy covariance method

    Science.gov (United States)

    Yaroslavtsev, Alexis; Meshalkina, Joulia; Mazirov, Ilya

    2016-04-01

    Despite the fact that in Russia cropland's soils carbon loses 9 time higher than forest's soils ones (Stolbovoi, 2002), agroecosystems were not given sufficient attention and most of the papers are devoted to forestry and natural ecosystems. Carbon balance was calculated at the Precision Farming Experimental Fields of the Russian Timiryazev State Agricultural University, Moscow, Russia, for two agroecosystems with different crops from the same crop rotation studied for 2 years. The experimental site has a temperate and continental climate and situated in south taiga zone with Arable Sod-Podzoluvisols (Albeluvisols Umbric). Vertical fluxes of carbon dioxide were measured with eddy covariance technique, statistical method to measure and calculate turbulent fluxes within atmospheric boundary layers (Burba, 2013). Crop rotation included potato, winter wheat, barley and vetch and oat mix. Two fields of the same crop rotation were studied in 2013-2014. One of the fields (A) was used in 2013 for barley planting (Hordeum vulgare L.). The field B was in 2013 used for planting together vetch (Vicia sativa L.) and oats (Avena sativa L.). Inversely oats and vetch grass mixt was sown in 2014 on field A. Winter wheat was sown on field A in the very beginning of September. On the second field (B) in 2014 winter wheat occurred from under the snow in the phase of tillering, after harvesting it in mid of July, white mustard (Sinapis alba) was sown for green manure. Carbon uptake (NEE negative values) was registered only for the field with winter wheat and white mustard; perhaps because the two crops were cultivated on the field within one growing season. Three other cases showed CO2 emission. Great difference in 82 g C m-2 per year in NEE between two fields with vetch and oat mix was related to higher difference in grass yields. NEE for barley field was positive during the whole year; considering only the growing season, NEE for barley was 100 g C m-2 lower and was negative. Closed

  9. Surface energy balance of an extensive green roof as quantified by full year eddy-covariance measurements.

    Science.gov (United States)

    Heusinger, Jannik; Weber, Stephan

    2017-01-15

    Green roofs are discussed as a promising type of green infrastructure to lower heat stress in cities. In order to enhance evaporative cooling, green roofs should ideally have similar Bowen ratio (β=sensible heat flux/latent heat flux) characteristics such as rural sites, especially during summer periods with high air temperatures. We use the eddy-covariance (EC) method to quantify the energy balance of an 8600m 2 extensive, non-irrigated green roof at the Berlin Brandenburg Airport, Germany over a full annual cycle. To understand the influence of water availability on green roof-atmosphere energy exchange, we studied dry and wet periods and looked into functional relationships between leaf area, volumetric water content (VWC) of the substrate, shortwave radiation and β. The surface energy balance was dominated by turbulent heat fluxes in comparison to conductive substrate heat fluxes. The Bowen ratio was slightly below unity on average but highly variable due to ambient meteorology and substrate water availability, i.e. β increased to 2 in the summer season. During dry periods mean daytime β was 3, which is comparable to typical values of urban instead of rural sites. In contrast, mean daytime β was 0.3 during wet periods. Following a summer wet period the green roof maximum daily evapotranspiration (ET) was 3.3mm, which is a threefold increase with respect to the mean summer ET. A multiple regression model indicated that the substrate VWC at the present site has to be >0.11m 3 m -3 during summer high insolation periods (>500Wm -2 ) in order to maintain favourable green roof energy partitioning, i.e. mid-day βurban green roofs can be significantly optimised by using sustainable irrigation approaches. Copyright © 2016 Elsevier B.V. All rights reserved.

  10. Eddy covariance fluxes of acyl peroxy nitrates (PAN, PPN and MPAN above a Ponderosa pine forest

    Directory of Open Access Journals (Sweden)

    G. M. Wolfe

    2009-01-01

    Full Text Available During the Biosphere Effects on AeRosols and Photochemistry EXperiment 2007 (BEARPEX-2007, we observed eddy covariance (EC fluxes of speciated acyl peroxy nitrates (APNs, including peroxyacetyl nitrate (PAN, peroxypropionyl nitrate (PPN and peroxymethacryloyl nitrate (MPAN, above a Ponderosa pine forest in the western Sierra Nevada. All APN fluxes are net downward during the day, with a median midday PAN exchange velocity of −0.3 cm s−1; nighttime storage-corrected APN EC fluxes are smaller than daytime fluxes but still downward. Analysis with a standard resistance model shows that loss of PAN to the canopy is not controlled by turbulent or molecular diffusion. Stomatal uptake can account for 25 to 50% of the observed downward PAN flux. Vertical gradients in the PAN thermal decomposition (TD rate explain a similar fraction of the flux, suggesting that a significant portion of the PAN flux into the forest results from chemical processes in the canopy. The remaining "unidentified" portion of the net PAN flux (~15% is ascribed to deposition or reactive uptake on non-stomatal surfaces (e.g. leaf cuticles or soil. Shifts in temperature, moisture and ecosystem activity during the summer – fall transition alter the relative contribution of stomatal uptake, non-stomatal uptake and thermochemical gradients to the net PAN flux. Daytime PAN and MPAN exchange velocities are a factor of 3 smaller than those of PPN during the first two weeks of the measurement period, consistent with strong intra-canopy chemical production of PAN and MPAN during this period. Depositional loss of APNs can be 3–21% of the gross gas-phase TD loss depending on temperature. As a source of nitrogen to the biosphere, PAN deposition represents approximately 4–19% of that due to dry deposition of nitric acid at this site.

  11. Recent developments in the path integral approach to anomalies

    International Nuclear Information System (INIS)

    Fujikawa, Kazuo.

    1986-08-01

    After a brief summary of the path integral approach to anomalous identities, some of the recent developments in this approach are discussed. The topics discussed include (i) Construction of the effective action by means of the covariant current, (ii) Gauss law constraint in anomalous gauge theories, (iii) Path integral approach to anomalies in superconformal transformations, (iv) Conformal and ghost number anomalies in string theory in analogy with the instanton calculation, (v) Covariant local Lorentz anomaly and its connection with the mathematical construction of the consistent anomaly. (author)

  12. Conformable eddy current array delivery

    Science.gov (United States)

    Summan, Rahul; Pierce, Gareth; Macleod, Charles; Mineo, Carmelo; Riise, Jonathan; Morozov, Maxim; Dobie, Gordon; Bolton, Gary; Raude, Angélique; Dalpé, Colombe; Braumann, Johannes

    2016-02-01

    The external surface of stainless steel containers used for the interim storage of nuclear material may be subject to Atmospherically Induced Stress Corrosion Cracking (AISCC). The inspection of such containers poses a significant challenge due to the large quantities involved; therefore, automating the inspection process is of considerable interest. This paper reports upon a proof-of-concept project concerning the automated NDT of a set of test containers containing artificially generated AISCCs. An Eddy current array probe with a conformable padded surface from Eddyfi was used as the NDT sensor and end effector on a KUKA KR5 arc HW robot. A kinematically valid cylindrical raster scan path was designed using the KUKA|PRC path planning software. Custom software was then written to interface measurement acquisition from the Eddyfi hardware with the motion control of the robot. Preliminary results and analysis are presented from scanning two canisters.

  13. Towards a network of Urban Forest Eddy Covariance stations: a unique case study in Naples

    Science.gov (United States)

    Guidolotti, Gabriele; Pallozzi, Emanuele; Esposito, Raffaela; Mattioni, Michele; Calfapietra, Carlo

    2015-04-01

    Urban forests are by definition integrated in highly human-made areas, and interact with different components of our cities. Thanks to those interactions, urban forests provide to people and to the urban environment a number of ecosystem services, including the absorption of CO2 and air pollutants thus influencing the local air quality. Moreover, in urban areas a relevant role is played by the photochemical pollution which is strongly influenced by the interactions between volatile organic compounds (VOC) and nitrogen oxides (NOx). In several cities, a high percentage of VOC is of biogenic origin mainly emitted from the urban trees. Despite their importance, experimental sites monitoring fluxes of trace gases fluxes in urban forest ecosystems are still scarce. Here we show the preliminary results of an innovative experimental site located in the Royal Park of Capodimonte within the city of Naples (40°51'N-14°15'E, 130 m above sea level). The site is mainly characterised by Quercus ilex with some patches of Pinus pinea and equipped with an eddy-covariance tower measuring the exchange of CO2, H2O, N2O, CH4, O3, PM, VOCs and NOx using state-of-the art instrumentations; it is running since the end of 2014 and it is part of the large infrastructural I-AMICA project. We suggest that the experience gained with research networks such as Fluxnet and ICOS should be duplicated for urban forests. This is crucial for carbon as there is now the ambition to include urban forests in the carbon stocks accounting system. This is even more important to understand the difficult interactions between anthropogenic and biogenic sources that often have negative implications for urban air quality. Urban environment can thus become an extraordinary case study and a network of such kind of stations might represent an important strategy both from the scientific and the applicative point of view.

  14. A comparison of optical and microwave scintillometers with eddy covariance derived surface heat fluxes

    KAUST Repository

    Yee, Mei Sun

    2015-11-01

    Accurate measurements of energy fluxes between land and atmosphere are important for understanding and modeling climatic patterns. Several methods are available to measure heat fluxes, and scintillometers are becoming increasingly popular because of their ability to measure sensible (. H) and latent (. LvE) heat fluxes over large spatial scales. The main motivation of this study was to test the use of different methods and technologies to derive surface heat fluxes.Measurements of H and LvE were carried out with an eddy covariance (EC) system, two different makes of optical large aperture scintillometers (LAS) and two microwave scintillometers (MWS) with different frequencies at a pasture site in a semi-arid environment of New South Wales, Australia. We used the EC measurements as a benchmark. Fluxes derived from the EC system and LAS systems agreed (R2>0.94), whereas the MWS systems measured lower H (bias ~60Wm-2) and larger LvE (bias ~65Wm-2) than EC. When the scintillometers were compared against each other, the two LASs showed good agreement of H (R2=0.98), while MWS with different frequencies and polarizations led to different results. Combination of LAS and MWS measurements (i.e., two wavelength method) resulted in performance that fell in between those estimated using either LAS or MWS alone when compared with the EC system. The cause for discrepancies between surface heat fluxes derived from the EC system and those from the MWS systems and the two-wavelength method are possibly related to inaccurate assignment of the structure parameter of temperature and humidity. Additionally, measurements from MWSs can be associated with two values of the Bowen ratio, thereby leading to uncertainties in the estimation of the fluxes. While only one solution has been considered in this study, when LvE was approximately less than 200Wm-2, the alternate solution may be more accurate. Therefore, for measurements of surface heat fluxes in a semi-arid or dry environment, the

  15. Impact of water use efficiency on eddy covariance flux partitioning using correlation structure analysis

    Science.gov (United States)

    Anderson, Ray; Skaggs, Todd; Alfieri, Joseph; Kustas, William; Wang, Dong; Ayars, James

    2016-04-01

    Partitioned land surfaces fluxes (e.g. evaporation, transpiration, photosynthesis, and ecosystem respiration) are needed as input, calibration, and validation data for numerous hydrological and land surface models. However, one of the most commonly used techniques for measuring land surface fluxes, Eddy Covariance (EC), can directly measure net, combined water and carbon fluxes (evapotranspiration and net ecosystem exchange/productivity). Analysis of the correlation structure of high frequency EC time series (hereafter flux partitioning or FP) has been proposed to directly partition net EC fluxes into their constituent components using leaf-level water use efficiency (WUE) data to separate stomatal and non-stomatal transport processes. FP has significant logistical and spatial representativeness advantages over other partitioning approaches (e.g. isotopic fluxes, sap flow, microlysimeters), but the performance of the FP algorithm is reliant on the accuracy of the intercellular CO2 (ci) concentration used to parameterize WUE for each flux averaging interval. In this study, we tested several parameterizations for ci as a function of atmospheric CO2 (ca), including (1) a constant ci/ca ratio for C3 and C4 photosynthetic pathway plants, (2) species-specific ci/ca-Vapor Pressure Deficit (VPD) relationships (quadratic and linear), and (3) generalized C3 and C4 photosynthetic pathway ci/ca-VPD relationships. We tested these ci parameterizations at three agricultural EC towers from 2011-present in C4 and C3 crops (sugarcane - Saccharum officinarum L. and peach - Prunus persica), and validated again sap-flow sensors installed at the peach site. The peach results show that the species-specific parameterizations driven FP algorithm came to convergence significantly more frequently (~20% more frequently) than the constant ci/ca ratio or generic C3-VPD relationship. The FP algorithm parameterizations with a generic VPD relationship also had slightly higher transpiration (5 Wm-2

  16. On the choice of the driving temperature for eddy-covariance carbon dioxide flux partitioning

    Directory of Open Access Journals (Sweden)

    G. Lasslop

    2012-12-01

    Full Text Available Networks that merge and harmonise eddy-covariance measurements from many different parts of the world have become an important observational resource for ecosystem science. Empirical algorithms have been developed which combine direct observations of the net ecosystem exchange of carbon dioxide with simple empirical models to disentangle photosynthetic (GPP and respiratory fluxes (Reco. The increasing use of these estimates for the analysis of climate sensitivities, model evaluation and calibration demands a thorough understanding of assumptions in the analysis process and the resulting uncertainties of the partitioned fluxes. The semi-empirical models used in flux partitioning algorithms require temperature observations as input, but as respiration takes place in many parts of an ecosystem, it is unclear which temperature input – air, surface, bole, or soil at a specific depth – should be used. This choice is a source of uncertainty and potential biases. In this study, we analysed the correlation between different temperature observations and nighttime NEE (which equals nighttime respiration across FLUXNET sites to understand the potential of the different temperature observations as input for the flux partitioning model. We found that the differences in the correlation between different temperature data streams and nighttime NEE are small and depend on the selection of sites. We investigated the effects of the choice of the temperature data by running two flux partitioning algorithms with air and soil temperature. We found the time lag (phase shift between air and soil temperatures explains the differences in the GPP and Reco estimates when using either air or soil temperatures for flux partitioning. The impact of the source of temperature data on other derived ecosystem parameters was estimated, and the strongest impact was found for the temperature sensitivity. Overall, this study suggests that the

  17. Assessing net ecosystem carbon exchange of U S terrestrial ecosystems by integrating eddy covariance flux measurements and satellite observations

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang, Qianlai [Purdue University; Law, Beverly E. [Oregon State University; Baldocchi, Dennis [University of California, Berkeley; Ma, Siyan [University of California, Berkeley; Chen, Jiquan [University of Toledo, Toledo, OH; Richardson, Andrew [Harvard University; Melillo, Jerry [Marine Biological Laboratory; Davis, Ken J. [Pennsylvania State University; Hollinger, D. [USDA Forest Service; Wharton, Sonia [University of California, Davis; Falk, Matthias [University of California, Davis; Paw, U. Kyaw Tha [University of California, Davis; Oren, Ram [Duke University; Katulk, Gabriel G. [Duke University; Noormets, Asko [North Carolina State University; Fischer, Marc [Lawrence Berkeley National Laboratory (LBNL); Verma, Shashi [University of Nebraska; Suyker, A. E. [University of Nebraska, Lincoln; Cook, David R. [Argonne National Laboratory (ANL); Sun, G. [USDA Forest Service; McNulty, Steven G. [USDA Forest Service; Wofsy, Steve [Harvard University; Bolstad, Paul V [University of Minnesota; Burns, Sean [University of Colorado, Boulder; Monson, Russell K. [University of Colorado, Boulder; Curtis, Peter [Ohio State University, The, Columbus; Drake, Bert G. [Smithsonian Environmental Research Center, Edgewater, MD; Foster, David R. [Harvard University; Gu, Lianhong [ORNL; Hadley, Julian L. [Harvard University; Litvak, Marcy [University of New Mexico, Albuquerque; Martin, Timothy A. [University of Florida, Gainesville; Matamala, Roser [Argonne National Laboratory (ANL); Meyers, Tilden [NOAA, Oak Ridge, TN; Oechel, Walter C. [San Diego State University; Schmid, H. P. [Indiana University; Scott, Russell L. [USDA ARS; Torn, Margaret S. [Lawrence Berkeley National Laboratory (LBNL)

    2011-01-01

    More accurate projections of future carbon dioxide concentrations in the atmosphere and associated climate change depend on improved scientific understanding of the terrestrial carbon cycle. Despite the consensus that U.S. terrestrial ecosystems provide a carbon sink, the size, distribution, and interannual variability of this sink remain uncertain. Here we report a terrestrial carbon sink in the conterminous U.S. at 0.63 pg C yr 1 with the majority of the sink in regions dominated by evergreen and deciduous forests and savannas. This estimate is based on our continuous estimates of net ecosystem carbon exchange (NEE) with high spatial (1 km) and temporal (8-day) resolutions derived from NEE measurements from eddy covariance flux towers and wall-to-wall satellite observations from Moderate Resolution Imaging Spectroradiometer (MODIS). We find that the U.S. terrestrial ecosystems could offset a maximum of 40% of the fossil-fuel carbon emissions. Our results show that the U.S. terrestrial carbon sink varied between 0.51 and 0.70 pg C yr 1 over the period 2001 2006. The dominant sources of interannual variation of the carbon sink included extreme climate events and disturbances. Droughts in 2002 and 2006 reduced the U.S. carbon sink by 20% relative to a normal year. Disturbances including wildfires and hurricanes reduced carbon uptake or resulted in carbon release at regional scales. Our results provide an alternative, independent, and novel constraint to the U.S. terrestrial carbon sink.

  18. Annual balances of CH4 and N2O from a managed fen meadow using eddy covariance flux measurements

    International Nuclear Information System (INIS)

    Schrier-Uijl, A.P.; Veenendaal, E.M.; Kroon, P.S.; Hensen, A.; Jonker, H.J.J.

    2010-10-01

    Annual terrestrial balances of methane (CH4) and nitrous oxide (N2O) are presented for a managed fen meadow in the Netherlands for 2006, 2007 and 2008, using eddy covariance (EC) flux measurements. Annual emissions derived from different methods are compared. The most accurate annual CH4 flux is achieved by gap filling EC fluxes with an empirical multivariate regression model, with soil temperature and mean wind velocity as driving variables. This model explains about 60% of the variability in observed daily CH4 fluxes. Annual N2O emissions can be separated into background emissions and event emissions due to fertilization. The background emission is estimated using a multivariate regression model also based on EC flux data, with soil temperature and mean wind velocity as driving variables. The event emissions are estimated using emission factors. The minimum direct emission factor is derived for six fertilization events by subtracting the background emission, and the IPCC default emission factor of 1% is used for the other events. In addition, the maximum direct emission factors are determined for the six events without subtracting the background emission. The average direct emission factor ranges from 1.2 to 2.8%, which is larger than the IPCC default value. Finally, the total terrestrial greenhouse gas balance is estimated at 16 Mg ha -1 year -1 in CO2-equivalents with contributions of 30, 25 and 45% by CO2, CH4 and N2O, respectively.

  19. Particle aggregation at the edges of anticyclonic eddies and implications for distribution of biomass

    Directory of Open Access Journals (Sweden)

    A. Samuelsen

    2012-06-01

    Full Text Available Acoustic measurements show that the biomass of zooplankton and mesopelagic fish is redistributed by mesoscale variability and that the signal extends over several hundred meters depth. The mechanisms governing this distribution are not well understood, but influences from both physical (i.e. redistribution and biological processes (i.e. nutrient transport, primary production, active swimming, etc. are likely. This study examines how hydrodynamic conditions and basic vertical swimming behavior act to distribute biomass in an anticyclonic eddy. Using an eddy-resolving 2.3 km-resolution physical ocean model as forcing for a particle-tracking module, particles representing passively floating organisms and organisms with vertical swimming behavior are released within an eddy and monitored for 20 to 30 days. The role of hydrodynamic conditions on the distribution of biomass is discussed in relation to the acoustic measurements. Particles released close to the surface tend, in agreement with the observations, to accumulate around the edge of the eddy, whereas particles released at depth gradually become distributed along the isopycnals. After a month they are displaced several hundreds meters in the vertical with the deepest particles found close to the eddy center and the shallowest close to the edge. There is no evidence of aggregation of particles along the eddy rim in the last simulation. The model results points towards a physical mechanism for aggregation at the surface, however biological processes cannot be ruled out using the current modeling tool.

  20. Form of the manifestly covariant Lagrangian

    Science.gov (United States)

    Johns, Oliver Davis

    1985-10-01

    The preferred form for the manifestly covariant Lagrangian function of a single, charged particle in a given electromagnetic field is the subject of some disagreement in the textbooks. Some authors use a ``homogeneous'' Lagrangian and others use a ``modified'' form in which the covariant Hamiltonian function is made to be nonzero. We argue in favor of the ``homogeneous'' form. We show that the covariant Lagrangian theories can be understood only if one is careful to distinguish quantities evaluated on the varied (in the sense of the calculus of variations) world lines from quantities evaluated on the unvaried world lines. By making this distinction, we are able to derive the Hamilton-Jacobi and Klein-Gordon equations from the ``homogeneous'' Lagrangian, even though the covariant Hamiltonian function is identically zero on all world lines. The derivation of the Klein-Gordon equation in particular gives Lagrangian theoretical support to the derivations found in standard quantum texts, and is also shown to be consistent with the Feynman path-integral method. We conclude that the ``homogeneous'' Lagrangian is a completely adequate basis for covariant Lagrangian theory both in classical and quantum mechanics. The article also explores the analogy with the Fermat theorem of optics, and illustrates a simple invariant notation for the Lagrangian and other four-vector equations.

  1. Inference and Biogeochemical Response of Vertical Velocities inside a Mode Water Eddy

    Science.gov (United States)

    Barceló-Llull, B.; Pallas Sanz, E.; Sangrà, P.

    2016-02-01

    With the aim to study the modulation of the biogeochemical fluxes by the ageostrophic secondary circulation in anticyclonic mesoscale eddies, a typical eddy of the Canary Eddy Corridor was interdisciplinary surveyed on September 2014 in the framework of the PUMP project. The eddy was elliptical shaped, 4 month old, 110 km diameter and 400 m depth. It was an intrathermocline type often also referred as mode water eddy type. We inferred the mesoscale vertical velocity field resolving a generalized omega equation from the 3D density and ADCP velocity fields of a five-day sampled CTD-SeaSoar regular grid centred on the eddy. The grid transects where 10 nautical miles apart. Although complex, in average, the inferred omega velocity field (hereafter w) shows a dipolar structure with downwelling velocities upstream of the propagation path (west) and upwelling velocities downstream. The w at the eddy center was zero and maximum values were located at the periphery attaining ca. 6 m day-1. Coinciding with the occurrence of the vertical velocities cells a noticeable enhancement of phytoplankton biomass was observed at the eddy periphery respect to the far field. A corresponding upward diapycnal flux of nutrients was also observed at the periphery. As minimum velocities where reached at the eddy center, lineal Ekman pumping mechanism was discarded. Minimum values of phytoplankton biomass where also observed at the eddy center. The possible mechanisms for such dipolar w cell are still being investigated, but an analysis of the generalized omega equation forcing terms suggest that it may be a combination of horizontal deformation and advection of vorticity by the ageostrophic current (related to nonlinear Ekman pumping). As expected for Trades, the wind was rather constant and uniform with a speed of ca. 5 m s-1. Diagnosed nonlinear Ekman pumping leaded also to a dipolar cell that mirrors the omega w dipolar cell.

  2. Oxygen optodes as fast sensors for eddy correlation measurements in aquatic systems

    DEFF Research Database (Denmark)

    Chipman, Lindsay; Huettel, Markus; Berg, Peter

    2012-01-01

    The aquatic eddy-correlation technique can be used to noninvasively determine the oxygen exchange across the sediment-water interface by analyzing the covariance of vertical flow velocity and oxygen concentration in a small measuring volume above the sea bed. The method requires fast sensors...... that combine the advantages of noninvasive measurements and integration of fluxes over a large footprint area, using a relatively rugged and less expensive sensor....

  3. Eddy currents in a nonperiodic vacuum vessel induced by axisymmetric plasma motion

    International Nuclear Information System (INIS)

    DeLucia, J.

    1985-12-01

    A method is described for calculating the two-dimensional trajectory of a vertically or horizontally unstable axisymmetric tokamak plasma in the presence of a resistive vacuum vessel. The vessel is not assumed to have toroidal symmetry. The plasma is represented by a current-filament loop that is free to move vertically and to change its major radius. Its position is evolved in time self-consistently with the vacuum vessel eddy currents. The plasma current, internal inductance, and poloidal beta can be specified functions of time so that eddy currents resulting from a disruption can be modeled. The vacuum vessel is represented by a set of current-filaments whose positions and orientations are chosen to model the dominant eddy current paths. Although the specific application is to TFTR, the present model is of general applicability. 7 refs., 4 figs., 2 tabs

  4. Condition Number Regularized Covariance Estimation.

    Science.gov (United States)

    Won, Joong-Ho; Lim, Johan; Kim, Seung-Jean; Rajaratnam, Bala

    2013-06-01

    Estimation of high-dimensional covariance matrices is known to be a difficult problem, has many applications, and is of current interest to the larger statistics community. In many applications including so-called the "large p small n " setting, the estimate of the covariance matrix is required to be not only invertible, but also well-conditioned. Although many regularization schemes attempt to do this, none of them address the ill-conditioning problem directly. In this paper, we propose a maximum likelihood approach, with the direct goal of obtaining a well-conditioned estimator. No sparsity assumption on either the covariance matrix or its inverse are are imposed, thus making our procedure more widely applicable. We demonstrate that the proposed regularization scheme is computationally efficient, yields a type of Steinian shrinkage estimator, and has a natural Bayesian interpretation. We investigate the theoretical properties of the regularized covariance estimator comprehensively, including its regularization path, and proceed to develop an approach that adaptively determines the level of regularization that is required. Finally, we demonstrate the performance of the regularized estimator in decision-theoretic comparisons and in the financial portfolio optimization setting. The proposed approach has desirable properties, and can serve as a competitive procedure, especially when the sample size is small and when a well-conditioned estimator is required.

  5. Automatic tracking of dynamical evolutions of oceanic mesoscale eddies with satellite observation data

    Science.gov (United States)

    Sun, Liang; Li, Qiu-Yang

    2017-04-01

    The oceanic mesoscale eddies play a major role in ocean climate system. To analyse spatiotemporal dynamics of oceanic mesoscale eddies, the Genealogical Evolution Model (GEM) based on satellite data is developed, which is an efficient logical model used to track dynamic evolution of mesoscale eddies in the ocean. It can distinguish different dynamic processes (e.g., merging and splitting) within a dynamic evolution pattern, which is difficult to accomplish using other tracking methods. To this end, a mononuclear eddy detection method was firstly developed with simple segmentation strategies, e.g. watershed algorithm. The algorithm is very fast by searching the steepest descent path. Second, the GEM uses a two-dimensional similarity vector (i.e. a pair of ratios of overlap area between two eddies to the area of each eddy) rather than a scalar to measure the similarity between eddies, which effectively solves the ''missing eddy" problem (temporarily lost eddy in tracking). Third, for tracking when an eddy splits, GEM uses both "parent" (the original eddy) and "child" (eddy split from parent) and the dynamic processes are described as birth and death of different generations. Additionally, a new look-ahead approach with selection rules effectively simplifies computation and recording. All of the computational steps are linear and do not include iteration. Given the pixel number of the target region L, the maximum number of eddies M, the number N of look-ahead time steps, and the total number of time steps T, the total computer time is O (LM(N+1)T). The tracking of each eddy is very smooth because we require that the snapshots of each eddy on adjacent days overlap one another. Although eddy splitting or merging is ubiquitous in the ocean, they have different geographic distribution in the Northern Pacific Ocean. Both the merging and splitting rates of the eddies are high, especially at the western boundary, in currents and in "eddy deserts". GEM is useful not only for

  6. Eddy current inspection of steam generator tubing plugs

    International Nuclear Information System (INIS)

    Cullen, W.K.

    1990-01-01

    In response to the issues raised regarding the integrity of nuclear steam generator tubing plugs manufactured from certain heats of Inconel 600, Westinghouse engineers have developed, qualified and implemented an eddy current inspection system for the in-place assessment of these plugs. The heart of the system is a robotic and effector which delivers an eddy current sensor through the reduced diameter of the plug expander and actuates the coil to physical contact with the expanded inside bore of the plug. Once deployed, the eddy current sensor is rotated along a helical path to produce a detailed scan of the plug surface above the final position of the expander. This testing produces an isometric display of degradation due to primary water stress corrosion cracking, on the inside surface of the plug. To date, successful inspections have been conducted at two nuclear units with two different robotic delivery systems. While designed specifically for mechanical plugs with a bottle bore cavity, the inspection system can also be used for expanded straight bore plugs. Details of the inspection system along with a discussion of qualification activities and actual field results are presented in this paper

  7. Stochastic Theory of Turbulence Mixing by Finite Eddies in the Turbulent Boundary Layer

    NARCIS (Netherlands)

    Dekker, H.; Leeuw, G. de; Maassen van den Brink, A.

    1995-01-01

    Turbulence mixing is treated by means of a novel formulation of nonlocal K-theory, involving sample paths and a stochastic hypothesis. The theory simplifies for mixing by exchange (strong-eddies) and is then applied to the boundary layer (involving scaling). This maps boundary layer turbulence onto

  8. Eddy covarianace measurements in a hyper-arid and hyper-saline mangroves ecosystem

    Science.gov (United States)

    Perri, S.; Marpu, P.; Molini, A.; Armstrong, P.

    2017-12-01

    The natural environment of mangroves provides a number of ecosystem services for improving water quality, supporting healthy fisheries, and protecting the coasts. Also, their carbon storage is larger than any other forest type. Several authors have recognized the importance of mangroves in global carbon cycles. However, energy, water and carbon exchanges between ecosystem and atmosphere are still not completely understood. Eddy covariance measurements are extremely valuable to understand the role of the unique stressors of costal ecosystems in gas exchange. In particular, periodic flooding and elevated soil pore water salinity influence land-atmosphere interactions. Despites the importance of flux measurements in mangroves forests, such in-situ observations are extremely rare. Our research team set up an eddy covariance tower in the Mangrove National Park of Abu Dhabi, UAE. The study site (24.4509° N, 54.4288° E) is located in a dwarf Avicennia marina ecosystem experiencing extremely high temperatures and salinity. CO2 and H2O exchanges are estimated and related to water level and salinity measurements. This unique dataset will shed some light on the net ecosystem exchange (NEE) of carbon dioxide, on energy fluxes and on evapotranspiration rates for a halophyte ecosystem under severe salt-stress and high temperature.

  9. Above-ground woody carbon sequestration measured from tree rings is coherent with net ecosystem productivity at five eddy-covariance sites.

    Science.gov (United States)

    Babst, Flurin; Bouriaud, Olivier; Papale, Dario; Gielen, Bert; Janssens, Ivan A; Nikinmaa, Eero; Ibrom, Andreas; Wu, Jian; Bernhofer, Christian; Köstner, Barbara; Grünwald, Thomas; Seufert, Günther; Ciais, Philippe; Frank, David

    2014-03-01

    • Attempts to combine biometric and eddy-covariance (EC) quantifications of carbon allocation to different storage pools in forests have been inconsistent and variably successful in the past. • We assessed above-ground biomass changes at five long-term EC forest stations based on tree-ring width and wood density measurements, together with multiple allometric models. Measurements were validated with site-specific biomass estimates and compared with the sum of monthly CO₂ fluxes between 1997 and 2009. • Biometric measurements and seasonal net ecosystem productivity (NEP) proved largely compatible and suggested that carbon sequestered between January and July is mainly used for volume increase, whereas that taken up between August and September supports a combination of cell wall thickening and storage. The inter-annual variability in above-ground woody carbon uptake was significantly linked with wood production at the sites, ranging between 110 and 370 g C m(-2) yr(-1) , thereby accounting for 10-25% of gross primary productivity (GPP), 15-32% of terrestrial ecosystem respiration (TER) and 25-80% of NEP. • The observed seasonal partitioning of carbon used to support different wood formation processes refines our knowledge on the dynamics and magnitude of carbon allocation in forests across the major European climatic zones. It may thus contribute, for example, to improved vegetation model parameterization and provides an enhanced framework to link tree-ring parameters with EC measurements. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.

  10. The case for increasing the statistical power of eddy covariance ecosystem studies: why, where and how?

    Science.gov (United States)

    Hill, Timothy; Chocholek, Melanie; Clement, Robert

    2017-06-01

    Eddy covariance (EC) continues to provide invaluable insights into the dynamics of Earth's surface processes. However, despite its many strengths, spatial replication of EC at the ecosystem scale is rare. High equipment costs are likely to be partially responsible. This contributes to the low sampling, and even lower replication, of ecoregions in Africa, Oceania (excluding Australia) and South America. The level of replication matters as it directly affects statistical power. While the ergodicity of turbulence and temporal replication allow an EC tower to provide statistically robust flux estimates for its footprint, these principles do not extend to larger ecosystem scales. Despite the challenge of spatially replicating EC, it is clearly of interest to be able to use EC to provide statistically robust flux estimates for larger areas. We ask: How much spatial replication of EC is required for statistical confidence in our flux estimates of an ecosystem? We provide the reader with tools to estimate the number of EC towers needed to achieve a given statistical power. We show that for a typical ecosystem, around four EC towers are needed to have 95% statistical confidence that the annual flux of an ecosystem is nonzero. Furthermore, if the true flux is small relative to instrument noise and spatial variability, the number of towers needed can rise dramatically. We discuss approaches for improving statistical power and describe one solution: an inexpensive EC system that could help by making spatial replication more affordable. However, we note that diverting limited resources from other key measurements in order to allow spatial replication may not be optimal, and a balance needs to be struck. While individual EC towers are well suited to providing fluxes from the flux footprint, we emphasize that spatial replication is essential for statistically robust fluxes if a wider ecosystem is being studied. © 2016 The Authors Global Change Biology Published by John Wiley

  11. Investigating scintillometer source areas

    Science.gov (United States)

    Perelet, A. O.; Ward, H. C.; Pardyjak, E.

    2017-12-01

    Scintillometry is an indirect ground-based method for measuring line-averaged surface heat and moisture fluxes on length scales of 0.5 - 10 km. These length scales are relevant to urban and other complex areas where setting up traditional instrumentation like eddy covariance is logistically difficult. In order to take full advantage of scintillometry, a better understanding of the flux source area is needed. The source area for a scintillometer is typically calculated as a convolution of point sources along the path. A weighting function is then applied along the path to compensate for a total signal contribution that is biased towards the center of the beam path, and decreasing near the beam ends. While this method of calculating the source area provides an estimate of the contribution of the total flux along the beam, there are still questions regarding the physical meaning of the weighted source area. These questions are addressed using data from an idealized experiment near the Salt Lake City International Airport in northern Utah, U.S.A. The site is a flat agricultural area consisting of two different land uses. This simple heterogeneity in the land use facilitates hypothesis testing related to source areas. Measurements were made with a two wavelength scintillometer system spanning 740 m along with three standard open-path infrared gas analyzer-based eddy-covariance stations along the beam path. This configuration allows for direct observations of fluxes along the beam and comparisons to the scintillometer average. The scintillometer system employed measures the refractive index structure parameter of air for two wavelengths of electromagnetic radiation, 880 μm and 1.86 cm to simultaneously estimate path-averaged heat and moisture fluxes, respectively. Meteorological structure parameters (CT2, Cq2, and CTq) as well as surface fluxes are compared for various amounts of source area overlap between eddy covariance and scintillometry. Additionally, surface

  12. Eddy covariance measurements of net C exchange in the CAM bioenergy crop, Agave tequiliana

    Science.gov (United States)

    Owen, Nick A.; Choncubhair, Órlaith Ní; Males, Jamie; del Real Laborde, José Ignacio; Rubio-Cortés, Ramón; Griffiths, Howard; Lanigan, Gary

    2016-04-01

    Bioenergy crop cultivation may focus more on low grade and marginal lands in order to avoid competition with food production for land and water resources. However, in many regions, this would require improvements in plant water-use efficiency that are beyond the physiological capacity of most C3 and C4 bioenergy crop candidates. Crassulacean acid metabolism (CAM) plants, such as Agave tequiliana, can combine high above-ground productivity with as little as 20% of the water demand of C3 and C4 crops. This is achieved through temporal separation of carboxylase activities, with stomata opening at night to allow gas exchange and minimise transpirational losses. Previous studies have employed 'bottom-up' methodologies to investigate carbon (C) accumulation and productivity in Agave, by scaling leaf-level gas exchange and titratable acidity (TA) with leaf area index or maximum productivity. We used the eddy covariance (EC) technique to quantify ecosystem-scale gas exchange over an Agave plantation in Mexico ('top-down' approach). Measurements were made over 252 days, including the transition from wet to dry periods. Results were cross-validated against diel changes in titratable acidity, leaf-unfurling rates, energy exchange fluxes and reported biomass yields. Net ecosystem exchange of CO2 displayed a CAM rhythm that alternated from a net C sink at night to a net C source during the day and partitioned canopy fluxes (gross C assimilation, FA,EC) showed a characteristic four-phase CO2 exchange pattern. The projected ecosystem C balance indicated that the site was a net sink of -333 ± 24 g C m-2 y-1, comprising cumulative soil respiration of 692 ± 7 g C m-2 y-1 and FA,EC of -1025 ± 25 g C m-2 y-1. EC-estimated biomass yield was 20.1 Mg ha-1 y-1. Average integrated daily FA,EC was -234 ± 5 mmol CO2 m-2 d-1 and persisted almost unchanged after 70 days of drought conditions. Our results suggest that the carbon acquisition strategy of drought avoidance employed by Agave

  13. Condition Number Regularized Covariance Estimation*

    Science.gov (United States)

    Won, Joong-Ho; Lim, Johan; Kim, Seung-Jean; Rajaratnam, Bala

    2012-01-01

    Estimation of high-dimensional covariance matrices is known to be a difficult problem, has many applications, and is of current interest to the larger statistics community. In many applications including so-called the “large p small n” setting, the estimate of the covariance matrix is required to be not only invertible, but also well-conditioned. Although many regularization schemes attempt to do this, none of them address the ill-conditioning problem directly. In this paper, we propose a maximum likelihood approach, with the direct goal of obtaining a well-conditioned estimator. No sparsity assumption on either the covariance matrix or its inverse are are imposed, thus making our procedure more widely applicable. We demonstrate that the proposed regularization scheme is computationally efficient, yields a type of Steinian shrinkage estimator, and has a natural Bayesian interpretation. We investigate the theoretical properties of the regularized covariance estimator comprehensively, including its regularization path, and proceed to develop an approach that adaptively determines the level of regularization that is required. Finally, we demonstrate the performance of the regularized estimator in decision-theoretic comparisons and in the financial portfolio optimization setting. The proposed approach has desirable properties, and can serve as a competitive procedure, especially when the sample size is small and when a well-conditioned estimator is required. PMID:23730197

  14. Assessment of the soil water balance by the combination of cosmic ray neutron sensing and eddy covariance technique in an irrigated citrus orchard (Marrakesh, Morocco)

    Science.gov (United States)

    Mroos, Katja; Baroni, Gabriele; Er-Raki, Salah; Francke, Till; Khabba, Said; Jarlan, Lionel; Hanich, Lahoucine; Oswald, Sascha E.

    2014-05-01

    Irrigation water requirement plays a crucial role in many agricultural areas and especially in arid and semi-arid landscapes. Improvements in the water management and the performance of the irrigation systems require a correct evaluation of the hydrological processes involved. However, some difficulties can arise due to the heterogeneity of the soil-plant system and of the irrigation scheme. To overcome these limitations, in this study, the soil water balance is analyzed by the combination of the Eddy Covariance technique (EC) and Cosmic Ray neutron Sensing (CRS). EC provides the measurement of the actual evapotranspiration over the area as it was presented in many field conditions. Moreover CRS showed to be a valuable approach to measure the root zone soil moisture integrated in a footprint of ~30 ha. In this way, the combination of the two methodologies should provide a better analysis of the soil water balance at field scale, as opposed to point observations, e.g. by TDR, evaporimeter and fluxmeter. Then, this could increase the capability to assess the irrigation efficiency and the agricultural water management. The study is conducted in a citrus orchard situated in a semi-arid region, 30 km southwest of Marrakesh (Morocco). The site is flat and planted with trees of same age growing in parallel rows with drip irrigation lines and application of fertilizer and pesticides. The original soil seems modified on the surface by the agricultural use, creating differences between trees, rows and lines. In addition, the drip irrigation creates also a spatial variability of the water flux distribution in the field, making this site an interesting area to test the methodology. Particular attention is given to the adaptation of the standard soil sampling campaign used for the calibration of the CRS and the introduction of a weighing function. Data were collected from June to December 2013, which corresponds to the high plant transpiration. Despite the intention of the

  15. Experiments with eddy currents: the eddy current brake

    International Nuclear Information System (INIS)

    Gonzalez, Manuel I

    2004-01-01

    A moderate-cost experimental setup is presented to help students to understand some qualitative and quantitative aspects of eddy currents. The setup operates like an eddy current brake, a device commonly used in heavy vehicles to dissipate kinetic energy by generating eddy currents. A set of simple experiments is proposed to measure eddy current losses and to relate them to various relevant parameters. Typical results for each of the experiments are presented, and comparisons with theoretical predictions are included. The experiments, which are devoted to first-year undergraduate students, deal also with other pedagogically relevant topics in electricity and magnetism, such as basic laws, electrical measurement techniques, the sources of the magnetic field and others

  16. Covariant extensions and the nonsymmetric unified field

    International Nuclear Information System (INIS)

    Borchsenius, K.

    1976-01-01

    The problem of generally covariant extension of Lorentz invariant field equations, by means of covariant derivatives extracted from the nonsymmetric unified field, is considered. It is shown that the contracted curvature tensor can be expressed in terms of a covariant gauge derivative which contains the gauge derivative corresponding to minimal coupling, if the universal constant p, characterizing the nonsymmetric theory, is fixed in terms of Planck's constant and the elementary quantum of charge. By this choice the spinor representation of the linear connection becomes closely related to the spinor affinity used by Infeld and Van Der Waerden (Sitzungsber. Preuss. Akad. Wiss. Phys. Math. Kl.; 9:380 (1933)) in their generally covariant formulation of Dirac's equation. (author)

  17. Covariance measurement in the presence of non-synchronous trading and market microstructure noise

    NARCIS (Netherlands)

    Griffin, J.E.; Oomen, R.C.A.

    2011-01-01

    This paper studies the problem of covariance estimation when prices are observed non-synchronously and contaminated by i.i.d. microstructure noise. We derive closed form expressions for the bias and variance of three popular covariance estimators, namely realised covariance, realised covariance plus

  18. Diurnal and Seasonal Variations of Eddy-Covariance Carbon Dioxide Fluxes Above an Urban Wetland, Partitioned by Vegetation Cover

    Science.gov (United States)

    Schafer, K. V.; Duman, T.

    2017-12-01

    The New Jersey Meadowlands are an urban brackish marsh with a long history of human activity causing disturbances and alterations. Carbon emissions were measured from two sites in the Meadowlands, a natural site and a restored site, using eddy-covariance (EC) from 2014 to 2016. At each site, the EC towers were placed at the interface of two vegetation covers, allowing capturing this aspect of the wetland's heterogeneity. Using footprint modeling and light response curves we were able to partition measured fluxes between vegetation cover types and compare CO2 fluxes from patches of invasive versus native wetland vegetation communities. We show that further separating the data into seasonal and diurnal fluxes reveals patterns in CO2 fluxes that allow determining the nature of each vegetation cover as a source or sink for CO2. Our results also show that CO2 emissions from the restored wetland are significantly higher than the natural wetland. Areas of invasive Phragmites australis at the natural site had the lowest CO2 release rates during winter. These were consistently lower in magnitude than summer daytime uptake, therefore making this part of the wetland a CO2 sink. Areas planted with native Spartina alterniflora at the restored site had the largest uptake during daytime, therefore seemingly justifying restoration activities. However, they also had the highest emission rates during summer nighttime, and therefore the daily summer net uptake was not the highest compared with other vegetation covers. Furthermore, emissions from the restored site during winter were larger compared to the natural site, indicating that restoration activities might have led to a significant increase of carbon release from the wetland. Thus, during the study period the restored wetland acted as a carbon source.

  19. Effect of vegetation on the energy balance and evapotranspiration in tallgrass prairie: a paired study with eddy covariance systems

    Science.gov (United States)

    Sun, X.; Zou, C.; Wilcox, B. P.; Stebler, E.

    2017-12-01

    Whole-year measurement with eddy covariance system was carried out over two adjoining plots with contrasting vegetation coverage in tallgrass prairie, one was treated with herbicide and mowing while the other one kept as undisturbed control. The magnitude and phase difference between soil heat storage and ground heat flux were explicitly examined for its relative weights and energy balance. Surface turbulent flux (sensible heat and latent heat) accounted for about 85% of available energy at both sites, implying that vegetation coverage didn't significantly influence the closure scenario of energy imbalance. The seasonal and daily pattern of energy partitioning were dramatically different between the contrasting sites during growing season. The treated site received slightly lower net radiation due to high albedo, had higher sensible heat, and reduced latent heat due to reduction on transpiration. Annual evapotranspiration (ET) in treated site was only accounts for about 73% of annual ET in control. Meanwhile, lower surface conductance and decoupling factor showed that vegetation removal would increase the sensibility of ET to vapor pressure deficit and soil drought. ET dynamics is controlled by leaf area and net radiation when soil moisture is high, while soil drought caused stomata closure and subdued ET during drought. Stomata closure and transpiration reduction caused decline in ET, surface conductance, and decoupling factor. Soil moisture storage served as an important reservoir to meet peak ET demand during growing season. In summary, ET was the dominant component of water balance in tallgrass prairie, and any land management alterring the albedo, soil mositure storage, or canopy phenology (e.g., NDVI) could significantly affect energy and water budgets in .

  20. Covariant quantization of Lagrangians with quadratic dependent fields and derivative couplings

    International Nuclear Information System (INIS)

    Lam, C.S.; Wang, K.

    1977-01-01

    A covariant path-integral formula is derived for Lagrangians with quadratic dependent fields and derivative couplings. It differs from the naive one by a factor which can be viewed graphically as due to the coupling with ghost fields. These path integrals can be shown to be unitary and to satisfy equations of motion if and only if this extra factor is present. Applications of this formula to gauge and other field theories are discussed

  1. Energy exchanges in a Central Business District - Interpretation of Eddy Covariance and radiation flux measurements (London UK)

    Science.gov (United States)

    Kotthaus, S.; Grimmond, S.

    2013-12-01

    all year round, even at night. QH systematically exceeds input from net all-wave radiation (Q*), probably sustained by a both storage and anthropogenic heat fluxes (QF). Model estimates suggest QF can exceed the Q* nearly all year round. The positive QH inhibits stable conditions, but the stability classification is determined predominantly by the pattern of friction velocity over the rough urban surface. Turbulent latent heat flux variations are controlled (beyond the available energy) by rainfall due to the small vegetation cover. The Bowen ratio is mostly larger than one. Analysis of the eddy covariance footprint surface controls for the different land cover types by flow patterns for measurements at the two heights suggests the spatial variations of the sensible heat flux observed are partly related to changes in surface roughness, even at the local scale. Where the source areas are most homogeneous, flow conditions are vertically consistent - even if initial morphometric parameters suggested the measurements may be below the blending height. Turbulence statistics and momentum flux patterns prove useful for the interpretation of turbulent heat exchanges observed.

  2. Eddy-kovarianční měření v agroekosystému v Křešíně u Pacova

    Czech Academy of Sciences Publication Activity Database

    Havránková, K.; Šigut, L.; Sedlák, Pavel; Pavelka, M.

    25 /45/, č. 5 (2013), s. 27-30 ISSN 1211-0337 Institutional support: RVO:68378289 Keywords : eddy-covariance * agroecosystem * wind analysis * footprint * CO2 flux Subject RIV: DG - Athmosphere Sciences, Meteorology http://www.ochrana-ovzdusi.cz/r13.htm

  3. Generally covariant Hamilton-Jacobi equation and rotated liquid sphere metrics

    International Nuclear Information System (INIS)

    Abdil'din, M.M.; Abdulgafarov, M.K.; Abishev, M.E.

    2005-01-01

    In the work Lense-Thirring problem on corrected Fock's first approximation metrics by Hamilton-Jacobi method considered. Generally covariant Hamilton-Jacobi equation had been sold by separation of variable method. Path equation of probe particle motion in rotated liquid sphere field is obtained. (author)

  4. An avenue of eddies: Quantifying the biophysical properties of mesoscale eddies in the Tasman Sea

    Science.gov (United States)

    Everett, J. D.; Baird, M. E.; Oke, P. R.; Suthers, I. M.

    2012-08-01

    The Tasman Sea is unique - characterised by a strong seasonal western boundary current that breaks down into a complicated field of mesoscale eddies almost immediately after separating from the coast. Through a 16-year analysis of Tasman Sea eddies, we identify a region along the southeast Australian coast which we name ‘Eddy Avenue’ where eddies have higher sea level anomalies, faster rotation and greater sea surface temperature and chlorophyll a anomalies. The density of cyclonic and anticyclonic eddies within Eddy Avenue is 23% and 16% higher respectively than the broader Tasman Sea. We find that Eddy Avenue cyclonic and anticyclonic eddies have more strongly differentiated biological properties than those of the broader Tasman Sea, as a result of larger anticyclonic eddies formed from Coral Sea water depressing chl. a concentrations, and for coastal cyclonic eddies due to the entrainment of nutrient-rich shelf waters. Cyclonic eddies within Eddy Avenue have almost double the chlorophyll a (0.35 mg m-3) of anticyclonic eddies (0.18 mg m-3). The average chlorophyll a concentration for cyclonic eddies is 16% higher in Eddy Avenue and 28% lower for anticyclonic eddies when compared to the Tasman Sea. With a strengthening East Australian Current, the propagation of these eddies will have significant implications for heat transport and the entrainment and connectivity of plankton and larval fish populations.

  5. Processing arctic eddy-flux data using a simple carbon-exchange model embedded in the ensemble Kalman filter.

    Science.gov (United States)

    Rastetter, Edward B; Williams, Mathew; Griffin, Kevin L; Kwiatkowski, Bonnie L; Tomasky, Gabrielle; Potosnak, Mark J; Stoy, Paul C; Shaver, Gaius R; Stieglitz, Marc; Hobbie, John E; Kling, George W

    2010-07-01

    Continuous time-series estimates of net ecosystem carbon exchange (NEE) are routinely made using eddy covariance techniques. Identifying and compensating for errors in the NEE time series can be automated using a signal processing filter like the ensemble Kalman filter (EnKF). The EnKF compares each measurement in the time series to a model prediction and updates the NEE estimate by weighting the measurement and model prediction relative to a specified measurement error estimate and an estimate of the model-prediction error that is continuously updated based on model predictions of earlier measurements in the time series. Because of the covariance among model variables, the EnKF can also update estimates of variables for which there is no direct measurement. The resulting estimates evolve through time, enabling the EnKF to be used to estimate dynamic variables like changes in leaf phenology. The evolving estimates can also serve as a means to test the embedded model and reconcile persistent deviations between observations and model predictions. We embedded a simple arctic NEE model into the EnKF and filtered data from an eddy covariance tower located in tussock tundra on the northern foothills of the Brooks Range in northern Alaska, USA. The model predicts NEE based only on leaf area, irradiance, and temperature and has been well corroborated for all the major vegetation types in the Low Arctic using chamber-based data. This is the first application of the model to eddy covariance data. We modified the EnKF by adding an adaptive noise estimator that provides a feedback between persistent model data deviations and the noise added to the ensemble of Monte Carlo simulations in the EnKF. We also ran the EnKF with both a specified leaf-area trajectory and with the EnKF sequentially recalibrating leaf-area estimates to compensate for persistent model-data deviations. When used together, adaptive noise estimation and sequential recalibration substantially improved filter

  6. Comparison of net CO2 fluxes measured with open- and closed-path infrared gas analyzers in an urban complex environment

    DEFF Research Database (Denmark)

    Järvi, L.; Mammarella, I.; Eugster, W.

    2009-01-01

    and their suitability to accurately measure CO2 exchange in such non-ideal landscape. In addition, this study examined the effect of open-path sensor heating on measured fluxes in urban terrain, and these results were compared with similar measurements made above a temperate beech forest in Denmark. The correlation...... between the two fluxes was good (R2 = 0.93) at the urban site, but during the measurement period the open-path net surface exchange (NSE) was 17% smaller than the closed-path NSE, indicating apparent additional uptake of CO2 by open-path measurements. At both sites, sensor heating corrections evidently...... improved the performance of the open-path analyzer by reducing discrepancies in NSE at the urban site to 2% and decreasing the difference in NSE from 67% to 7% at the forest site. Overall, the site-specific approach gave the best results at both sites and, if possible, it should be preferred in the sensor...

  7. Fragmentation function in non-equilibrium QCD using closed-time path integral formalism

    International Nuclear Information System (INIS)

    Nayak, Gouranga C.

    2009-01-01

    In this paper we implement the Schwinger-Keldysh closed-time path integral formalism in non-equilibrium QCD in accordance to the definition of the Collins-Soper fragmentation function. We consider a high-p T parton in QCD medium at initial time τ 0 with an arbitrary non-equilibrium (non-isotropic) distribution function f(vector (p)) fragmenting to a hadron. We formulate the parton-to-hadron fragmentation function in non-equilibrium QCD in the light-cone quantization formalism. It may be possible to include final-state interactions with the medium via a modification of the Wilson lines in this definition of the non-equilibrium fragmentation function. This may be relevant to the study of hadron production from a quark-gluon plasma at RHIC and LHC. (orig.)

  8. Component greenhouse gas fluxes and radiative balance from two deltaic marshes in Louisiana: Pairing chamber techniques and eddy covariance

    Science.gov (United States)

    Krauss, Ken W.; Holm, Guerry O.; Perez, Brian C.; McWhorter, David E.; Cormier, Nicole; Moss, Rebecca; Johnson, Darren; Neubauer, Scott C; Raynie, Richard C

    2016-01-01

    Coastal marshes take up atmospheric CO2 while emitting CO2, CH4, and N2O. This ability to sequester carbon (C) is much greater for wetlands on a per-area basis than from most ecosystems, facilitating scientific, political, and economic interest in their value as greenhouse gas sinks. However, the greenhouse gas balance of Gulf of Mexico wetlands is particularly understudied. We describe the net ecosystem exchange (NEEc) of CO2 and CH4 using eddy covariance (EC) in comparison with fluxes of CO2, CH4, and N2O using chambers from brackish and freshwater marshes in Louisiana, USA. From EC, we found that 182 g C m-2 y-1 was lost through NEEc from the brackish marsh. Of this, 11 g C m-2 y-1 resulted from net CH4 emissions and the remaining 171 g C m-2 y-1 resulted from net CO2 emissions. In contrast, -290 g C m2 y-1 was taken up through NEEc by the freshwater marsh, with 47 g C m-2 y-1 emitted as CH4 and -337 g C m-2 y-1 taken up as CO2. From chambers, we discovered that neither site had large fluxes of N2O. Sustained-flux greenhouse gas accounting metrics indicated that both marshes had a positive (warming) radiative balance, with the brackish marsh having a substantially greater warming effect than the freshwater marsh. That net respiratory emissions of CO2 and CH4 as estimated through chamber techniques were 2-4 times different from emissions estimated through EC requires additional understanding of the artifacts created by different spatial and temporal sampling footprints between techniques.

  9. Eddy current seminar

    International Nuclear Information System (INIS)

    Emson, C.R.I.

    1988-11-01

    The paper presents the fifth symposium in the series of Eddy Current Seminars, held in Abingdon, 1988. The meeting included a discussion on three-dimensional eddy current formulations, as well as thirteen contributed papers on computational electromagnetics. Of the thirteen papers, two papers on eddy currents in tokamaks were selected for INIS and indexed separately. (U.K.)

  10. Eddy dynamics over continental slopes under retrograde winds: Insights from a model inter-comparison

    Science.gov (United States)

    Wang, Yan; Stewart, Andrew L.

    2018-01-01

    Mesoscale eddies are ubiquitous in the ocean and play a key role in exchanges across continental slopes. In this study the properties of wind-driven baroclinic turbulence are investigated using eddy-resolving process simulations, focusing on the case of retrograde winds that arises around the margins of the subtropical gyres. In contrast to a flat-bottomed ocean, over steep slopes eddies develop from baroclinic instabilities are confined to the top few hundred meters. Deeper in the water column baroclinic instability and vertical momentum transfer are suppressed, so wind-input momentum is exported toward the open ocean by eddies before traversing down to the ocean bed. Close to the sloping topography, eddy energy sourced from the upper ocean is converted to potential energy, steepening isopycnals and driving bottom-trapped prograde flows. This process is associated with upgradient lateral buoyancy fluxes and downgradient isopycnal potential vorticity fluxes, and cannot be reproduced via linear stability calculations. These properties of wind-driven shelf/slope turbulence are contrasted against simulations with flat bathymetry. The key differences described above hinge on the flow close to the steep topographic slope, which may be sensitive to the model's vertical coordinate system. The simulations are therefore replicated using models that employ geopotential coordinates, terrain-following coordinates, and isopycnal coordinates. Quantitative inter-model discrepancies in the momentum and energy budgets are much more pronounced in the presence of a steep bottom slope. However, the key findings of this study are consistent across the models, suggesting that they are robust and warrant incorporation into parameterizations of eddy transfer across continental slopes.

  11. Vortex stability in a multi-layer quasi-geostrophic model: application to Mediterranean Water eddies

    Energy Technology Data Exchange (ETDEWEB)

    Carton, Xavier; Ménesguen, Claire; Meunier, Thomas [Laboratoire de Physique des Oceans, UBO/IFREMER/CNRS/IRD, Brest (France); Sokolovskiy, Mikhail [Institute of Water Problems of the RAS, Moscow (Russian Federation); Aguiar, Ana, E-mail: xcarton@univ-brest.fr [Instituto Dom Luiz, Universidade de Lisboa, Lisbon (Portugal)

    2014-12-01

    The stability of circular vortices to normal mode perturbations is studied in a multi-layer quasi-geostrophic model. The stratification is fitted on the Gulf of Cadiz where many Mediterranean Water (MW) eddies are generated. Observations of MW eddies are used to determine the parameters of the reference experiment; sensitivity tests are conducted around this basic case. The objective of the study is two-fold: (a) determine the growth rates and nonlinear evolutions of unstable perturbations for different three-dimensional (3D) velocity structures of the vortices, (b) check if the different structure of our idealized vortices, mimicking MW cyclones and anticyclones, can induce different stability properties in a model that conserves parity symmetry, and apply these results to observed MW eddies. The linear stability analysis reveals that, among many 3D distributions of velocity, the observed eddies are close to maximal stability, with instability time scales longer than 100 days (these time scales would be less than 10 days for vertically more sheared eddies). The elliptical deformation is most unstable for realistic eddies (the antisymmetric one dominates for small eddies and the triangular one for large eddies); the antisymmetric mode is stronger for cyclones than for anticyclones. Nonlinear evolutions of eddies with radii of about 30 km, and elliptically perturbed, lead to their re-organization into 3D tripoles; smaller eddies are stable and larger eddies break into 3D dipoles. Horizontally more sheared eddies are more unstable and sustain more asymmetric instabilities. In summary, few differences were found between cyclone and anticyclone stability, except for strong horizontal velocity shears. (paper)

  12. Vortex stability in a multi-layer quasi-geostrophic model: application to Mediterranean Water eddies

    International Nuclear Information System (INIS)

    Carton, Xavier; Ménesguen, Claire; Meunier, Thomas; Sokolovskiy, Mikhail; Aguiar, Ana

    2014-01-01

    The stability of circular vortices to normal mode perturbations is studied in a multi-layer quasi-geostrophic model. The stratification is fitted on the Gulf of Cadiz where many Mediterranean Water (MW) eddies are generated. Observations of MW eddies are used to determine the parameters of the reference experiment; sensitivity tests are conducted around this basic case. The objective of the study is two-fold: (a) determine the growth rates and nonlinear evolutions of unstable perturbations for different three-dimensional (3D) velocity structures of the vortices, (b) check if the different structure of our idealized vortices, mimicking MW cyclones and anticyclones, can induce different stability properties in a model that conserves parity symmetry, and apply these results to observed MW eddies. The linear stability analysis reveals that, among many 3D distributions of velocity, the observed eddies are close to maximal stability, with instability time scales longer than 100 days (these time scales would be less than 10 days for vertically more sheared eddies). The elliptical deformation is most unstable for realistic eddies (the antisymmetric one dominates for small eddies and the triangular one for large eddies); the antisymmetric mode is stronger for cyclones than for anticyclones. Nonlinear evolutions of eddies with radii of about 30 km, and elliptically perturbed, lead to their re-organization into 3D tripoles; smaller eddies are stable and larger eddies break into 3D dipoles. Horizontally more sheared eddies are more unstable and sustain more asymmetric instabilities. In summary, few differences were found between cyclone and anticyclone stability, except for strong horizontal velocity shears. (paper)

  13. Coherent states and covariant semi-spectral measures

    International Nuclear Information System (INIS)

    Scutaru, H.

    1976-01-01

    The close connection between Mackey's theory of imprimitivity systems and the so called generalized coherent states introduced by Perelomov is established. Coherent states give a covariant description of the ''localization'' of a quantum system in the phase space in a similar way as the imprimitivity systems give a covariant description of the localization of a quantum system in the configuration space. The observation that for any system of coherent states one can define a covariant semi-spectral measure made possible a rigurous formulation of this idea. A generalization of the notion of coherent states is given. Covariant semi-spectral measures associated with systems of coherent states are defined and characterized. Necessary and sufficient conditions for a unitary representation of a Lie group to be i) a subrepresentation of an induced one and ii) a representation with coherent states are given (author)

  14. Estimation of turbulence dissipation rate by Large eddy PIV method in an agitated vessel

    Directory of Open Access Journals (Sweden)

    Kysela Bohuš

    2015-01-01

    Full Text Available The distribution of turbulent kinetic energy dissipation rate is important for design of mixing apparatuses in chemical industry. Generally used experimental methods of velocity measurements for measurement in complex geometries of an agitated vessel disallow measurement in resolution of small scales close to turbulence dissipation ones. Therefore, Particle image velocity (PIV measurement method improved by large eddy Ply approach was used. Large eddy PIV method is based on modeling of smallest eddies by a sub grid scale (SGS model. This method is similar to numerical calculations using Large Eddy Simulation (LES and the same SGS models are used. In this work the basic Smagorinsky model was employed and compared with power law approximation. Time resolved PIV data were processed by Large Eddy PIV approach and the obtained results of turbulent kinetic dissipation rate were compared in selected points for several operating conditions (impeller speed, operating liquid viscosity.

  15. A reduced covariant string model for the extrinsic string

    International Nuclear Information System (INIS)

    Botelho, L.C.L.

    1989-01-01

    It is studied a reduced covariant string model for the extrinsic string by using Polyakov's path integral formalism. On the basis of this reduced model it is suggested that the extrinsic string has its critical dimension given by 13. Additionally, it is calculated in a simple way Poliakov's renormalization group law for the string rigidity coupling constants. (A.C.A.S.) [pt

  16. Cross-covariance functions for multivariate random fields based on latent dimensions

    KAUST Repository

    Apanasovich, T. V.

    2010-02-16

    The problem of constructing valid parametric cross-covariance functions is challenging. We propose a simple methodology, based on latent dimensions and existing covariance models for univariate random fields, to develop flexible, interpretable and computationally feasible classes of cross-covariance functions in closed form. We focus on spatio-temporal cross-covariance functions that can be nonseparable, asymmetric and can have different covariance structures, for instance different smoothness parameters, in each component. We discuss estimation of these models and perform a small simulation study to demonstrate our approach. We illustrate our methodology on a trivariate spatio-temporal pollution dataset from California and demonstrate that our cross-covariance performs better than other competing models. © 2010 Biometrika Trust.

  17. Mesoscale Eddies in the Northwestern Pacific Ocean: Three-Dimensional Eddy Structures and Heat/Salt Transports

    Science.gov (United States)

    Dong, Di; Brandt, Peter; Chang, Ping; Schütte, Florian; Yang, Xiaofeng; Yan, Jinhui; Zeng, Jisheng

    2017-12-01

    The region encompassing the Kuroshio Extension (KE) in the Northwestern Pacific Ocean (25°N-45°N and 130°E-180°E) is one of the most eddy-energetic regions of the global ocean. The three-dimensional structures and transports of mesoscale eddies in this region are comprehensively investigated by combined use of satellite data and Argo profiles. With the allocation of Argo profiles inside detected eddies, the spatial variations of structures of eddy temperature and salinity anomalies are analyzed. The results show that eddies predominantly have subsurface (near-surface) intensified temperature and salinity anomalies south (north) of the KE jet, which is related to different background stratifications between these regions. A new method based on eddy trajectories and the inferred three-dimensional eddy structures is proposed to estimate heat and salt transports by eddy movements in a Lagrangian framework. Spatial distributions of eddy transports are presented over the vicinity of the KE for the first time. The magnitude of eddy-induced meridional heat (freshwater volume) transport is on the order of 0.01 PW (103 m3/s). The eddy heat transport divergence results in an oceanic heat loss south and heat gain north of the KE, thereby reinforcing and counteracting the oceanic heat loss from air-sea fluxes south and north of the KE jet, respectively. It also suggests a poleward heat transport across the KE jet due to eddy propagation.

  18. On the Covariance of Moore-Penrose Inverses in Rings with Involution

    OpenAIRE

    Mahzoon, Hesam

    2014-01-01

    We consider the so-called covariance set of Moore-Penrose inverses in rings with an involution. We deduce some new results concerning covariance set. We will show that if $a$ is a regular element in a ${C}^{\\ast }$ -algebra, then the covariance set of $a$ is closed in the set of invertible elements (with relative topology) of ${C}^{\\ast }$ -algebra and is a cone in the ${C}^{\\ast }$ -algebra.

  19. Exact Covariance Thresholding into Connected Components for Large-Scale Graphical Lasso.

    Science.gov (United States)

    Mazumder, Rahul; Hastie, Trevor

    2012-03-01

    We consider the sparse inverse covariance regularization problem or graphical lasso with regularization parameter λ. Suppose the sample covariance graph formed by thresholding the entries of the sample covariance matrix at λ is decomposed into connected components. We show that the vertex-partition induced by the connected components of the thresholded sample covariance graph (at λ) is exactly equal to that induced by the connected components of the estimated concentration graph, obtained by solving the graphical lasso problem for the same λ. This characterizes a very interesting property of a path of graphical lasso solutions. Furthermore, this simple rule, when used as a wrapper around existing algorithms for the graphical lasso, leads to enormous performance gains. For a range of values of λ, our proposal splits a large graphical lasso problem into smaller tractable problems, making it possible to solve an otherwise infeasible large-scale problem. We illustrate the graceful scalability of our proposal via synthetic and real-life microarray examples.

  20. Eddie Rocket's Franchise

    OpenAIRE

    Vahter, Jenni

    2008-01-01

    Eddie Rocket's Franchise - Setting up a franchise restaurant in Helsinki. TIIVISTELMÄ: Eddie Rocket's on menestynyt amerikkalaistyylinen 1950-luvun ”diner” franchiseravintolaketju Irlannista. Ravintoloita on perustettu viimeisen 18 vuoden aikana 28 kappaletta Irlantiin ja Isoon Britanniaan sekä yksi Espanjaan. Tämän tutkimuksen tarkoitus on tutkia onko Eddie Rocket'silla potentiaalia menestyä Helsingissä, Suomessa. Tutkimuskysymystä on lähestytty toimiala-analyysin, markkinatutkimuksen j...

  1. Surface Conductance of Five Different Crops Based on 10 Years of Eddy-Covariance Measurements

    Directory of Open Access Journals (Sweden)

    Uwe Spank

    2016-06-01

    Full Text Available The Penman-Monteith (PM equation is a state-of-the-art modelling approach to simulate evapotranspiration (ET at site and local scale. However, its practical application is often restricted by the availability and quality of required parameters. One of these parameters is the canopy conductance. Long term measurements of evapotranspiration by the eddy-covariance method provide an improved data basis to determine this parameter by inverse modelling. Because this approach may also include evaporation from the soil, not only the ‘actual’ canopy conductance but the whole surface conductance (gc$g_{c}$ is addressed. Two full cycles of crop rotation with five different crop types (winter barley, winter rape seed, winter wheat, silage maize, and spring barley have been continuously monitored for 10 years. These data form the basis for this study. As estimates of gc$g_{c}$ are obtained on basis of measurements, we investigated the impact of measurements uncertainties on obtained values of gc$g_{c }$. Here, two different foci were inspected more in detail. Firstly, the effect of the energy balance closure gap (EBCG on obtained values of gc$g_{c}$ was analysed. Secondly, the common hydrological practice to use vegetation height (hc$h_{c}$ to determine the period of highest plant activity (i.e., times with maximum gc$g_{c}$ concerning CO2-exchange and transpiration was critically reviewed. The results showed that hc$h_{c}$ and gc$g_{c}$ do only agree at the beginning of the growing season but increasingly differ during the rest of the growing season. Thus, the utilisation of hc$h_{c}$ as a proxy to assess maximum gc$g_{c}$ (gc,max$g_{c,\\text{max}}$ can lead to inaccurate estimates of gc,max$g_{c,\\text{max}}$ which in turn can cause serious shortcomings in simulated ET. The light use efficiency (LUE is superior to hc$h_{c}$ as a proxy to determine periods with maximum gc$g_{c}$. Based on this proxy, crop specific estimates of gc

  2. Convex Banding of the Covariance Matrix.

    Science.gov (United States)

    Bien, Jacob; Bunea, Florentina; Xiao, Luo

    2016-01-01

    We introduce a new sparse estimator of the covariance matrix for high-dimensional models in which the variables have a known ordering. Our estimator, which is the solution to a convex optimization problem, is equivalently expressed as an estimator which tapers the sample covariance matrix by a Toeplitz, sparsely-banded, data-adaptive matrix. As a result of this adaptivity, the convex banding estimator enjoys theoretical optimality properties not attained by previous banding or tapered estimators. In particular, our convex banding estimator is minimax rate adaptive in Frobenius and operator norms, up to log factors, over commonly-studied classes of covariance matrices, and over more general classes. Furthermore, it correctly recovers the bandwidth when the true covariance is exactly banded. Our convex formulation admits a simple and efficient algorithm. Empirical studies demonstrate its practical effectiveness and illustrate that our exactly-banded estimator works well even when the true covariance matrix is only close to a banded matrix, confirming our theoretical results. Our method compares favorably with all existing methods, in terms of accuracy and speed. We illustrate the practical merits of the convex banding estimator by showing that it can be used to improve the performance of discriminant analysis for classifying sound recordings.

  3. Closed-time-path functional formalism in curved spacetime: Application to cosmological back-reaction problems

    International Nuclear Information System (INIS)

    Calzetta, E.; Hu, B.L.

    1987-01-01

    We discuss the generalization to curved spacetime of a path-integral formalism of quantum field theory based on the sum over paths first going forward in time in the presence of one external source from an in vacuum to a state defined on a hypersurface of constant time in the future, and then backwards in time in the presence of a different source to the same in vacuum. This closed-time-path formalism which generalizes the conventional method based on in-out vacuum persistence amplitudes yields real and causal effective actions, field equations, and expectation values. We apply this method to two problems in semiclassical cosmology. First we study the back reaction of particle production in a radiation-filled Bianchi type-I universe with a conformal scalar field. Unlike the in-out formalism which yields complex geometries the real and causal effective action here yields equations for real effective geometries, with more readily interpretable results. It also provides a clear identification of particle production as a dissipative process in semiclassical theories. In the second problem we calculate the vacuum expectation value of the stress-energy tensor for a nonconformal massive λphi 4 theory in a Robertson-Walker universe. This study serves to illustrate the use of Feynman diagrams and higher-loop calculations in this formalism. It also demonstrates the economy of this method in the calculation of expectation values over the mode-sum Bogolubov transformation methods ordinarily applied to matrix elements calculated in the conventional in-out approach

  4. Biogeochemical characteristics of a long-lived anticyclonic eddy in the eastern South Pacific Ocean

    Science.gov (United States)

    Cornejo D'Ottone, Marcela; Bravo, Luis; Ramos, Marcel; Pizarro, Oscar; Karstensen, Johannes; Gallegos, Mauricio; Correa-Ramirez, Marco; Silva, Nelson; Farias, Laura; Karp-Boss, Lee

    2016-05-01

    Mesoscale eddies are important, frequent, and persistent features of the circulation in the eastern South Pacific (ESP) Ocean, transporting physical, chemical and biological properties from the productive shelves to the open ocean. Some of these eddies exhibit subsurface hypoxic or suboxic conditions and may serve as important hotspots for nitrogen loss, but little is known about oxygen consumption rates and nitrogen transformation processes associated with these eddies. In the austral fall of 2011, during the Tara Oceans expedition, an intrathermocline, anticyclonic, mesoscale eddy with a suboxic ( 0.5 µM), suggesting that active denitrification occurred in this water mass. Using satellite altimetry, we were able to track the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W). Field studies conducted in Chilean shelf waters close to the time of eddy formation provided estimates of initial O2 and N2O concentrations of the ESSW source water in the eddy. By the time of its offshore sighting, concentrations of both O2 and N2O in the subsurface oxygen minimum zone (OMZ) of the eddy were lower than concentrations in surrounding water and "source water" on the shelf, indicating that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L-1 d-1 and the rate of N2O consumption was 3.92 nmol L-1 d-1. These results show that mesoscale eddies affect open-ocean biogeochemistry in the ESP not only by transporting physical and chemical properties from the coast to the ocean interior but also during advection, local biological consumption of oxygen within an eddy further generates conditions favorable to denitrification and loss of fixed nitrogen from the system.

  5. Comparison of chamber and eddy covariance-based CO2 and CH4 emission estimates in a heterogeneous grass ecosystem on peat

    International Nuclear Information System (INIS)

    Schrier-Uijl, A.P.; Berendse, F.; Veenendaal, E.M.; Kroon, P.S.; Hensen, A.; Leffelaar, P.A.

    2010-08-01

    Fluxes of methane (CH4) and carbon dioxide (CO2) estimated by empirical models based on small-scale chamber measurements were compared to large-scale eddy covariance (EC) measurements for CH4 and to a combination of EC measurements and EC-based models for CO2. The experimental area was a flat peat meadow in the Netherlands with heterogeneous source strengths for both greenhouse gases. Two scenarios were used to assess the importance of stratifying the landscape into landscape elements before up-scaling the fluxes measured by chambers to landscape scale: one took the main landscape elements into account (field, ditch edge ditch), the other took only the field into account. Non-linear regression models were used to up-scale the chamber measurements to field emission estimates. EC CO2 respiration consisted of measured night time EC fluxes and modeled day time fluxes using the Arrhenius model. EC CH4 flux estimate was based on daily averages and the remaining data gaps were filled by linear interpolation. The EC and chamber-based estimates agreed well when the three landscape elements were taken into account with 16.5% and 13.0% difference for CO2 respiration and CH4, respectively. However, both methods differed 31.0% and 55.1% for CO2 respiration and CH4 when only field emissions were taken into account when up-scaling chamber measurements to landscape scale. This emphasizes the importance of stratifying the landscape into landscape elements. The conclusion is that small-scale chamber measurements can be used to estimate fluxes of CO2 and CH4 at landscape scale if fluxes are scaled by different landscape elements.

  6. Determining Adequate Averaging Periods and Reference Coordinates for Eddy Covariance Measurements of Surface Heat and Water Vapor Fluxes over Mountainous Terrain

    Directory of Open Access Journals (Sweden)

    Yi-Ying Chen Ming-Hsu Li

    2012-01-01

    Full Text Available Two coordinate rotation approaches (double and planar-fit rotations and no rotation, in association with averaging periods of 15 - 480 min, were applied to compute surface heat and water vapor fluxes using the eddy covariance approach. Measurements were conducted in an experimental watershed, the Lien-Hua-Chih (LHC watershed, located in central Taiwan. For no rotation and double rotation approaches, an adequate averaging period of 15 or 30 min was suggested for better energy closure and small variations on energy closure fractions. For the planar-fit rotation approach, an adequate averaging period of 60 or 120 min was recommended, and a typical averaging period of 30 min is not superior to that of 60 or 120 min in terms of better energy closure and small variations on energy closure fractions. The Ogive function analysis revealed that the energy closure was improved with the increase of averaging time by capturing sensible heat fluxes at low-frequency ranges during certain midday hours at LHC site. Seasonal variations of daily energy closure fractions, high in dry season and low in wet season, were found to be associated with the surface dryness and strength of turbulent development. The mismatching of flux footprint areas among flux sensors was suggested as the cause of larger CF variations during the dry seasons as that indicated by the footprint analysis showing scattered source areas. During the wet season, the underestimation of turbulent fluxes by EC observations at the LHC site was attributed to weak turbulence developments as the source area identified by the footprint analysis was closer to the flux tower than those scattered in dry season.

  7. Detecting management and fertilization effects on the carbon balance of winter oilseed rape with manual closed chamber measurements: Can we outrange gap-filling uncertainty and spatiotemporal variability?

    Science.gov (United States)

    Huth, Vytas; Moffat, Antje Maria; Calmet, Anna; Andres, Monique; Laufer, Judit; Pehle, Natalia; Rach, Bernd; Gundlach, Laura; Augustin, Jürgen

    2017-04-01

    detect the flux differences between specific management practices - with additional chamber measurements installed close to the eddy tower as a reference linking the two techniques. In our experiment, we studied the effect of four different treatments of fertilization (mineral versus organic) and tillage (no-till versus mulch-till versus ploughing) on the NEE of rapeseed cropping for the climatic seasons 2013 to 2015. We compared the NEE of the treatments to the "background" NEE measured by the eddy covariance technique in the nearby reference field for the years 2013 and 2014. With this data, we estimated the uncertainty resulting from gap filling discontinuous chamber measurements and relate it to the observed effects of the four different treatments on the NEE. Here, we present first results on the applicability of the manual-chamber technique to derive the relatively small effects of rapeseed cropping on NEE and SC within a short period of three years of study.

  8. Covariant perturbations of Schwarzschild black holes

    International Nuclear Information System (INIS)

    Clarkson, Chris A; Barrett, Richard K

    2003-01-01

    We present a new covariant and gauge-invariant perturbation formalism for dealing with spacetimes having spherical symmetry (or some preferred spatial direction) in the background, and apply it to the case of gravitational wave propagation in a Schwarzschild black-hole spacetime. The 1 + 3 covariant approach is extended to a '1 + 1 + 2 covariant sheet' formalism by introducing a radial unit vector in addition to the timelike congruence, and decomposing all covariant quantities with respect to this. The background Schwarzschild solution is discussed and a covariant characterization is given. We give the full first-order system of linearized 1 + 1 + 2 covariant equations, and we show how, by introducing (time and spherical) harmonic functions, these may be reduced to a system of first-order ordinary differential equations and algebraic constraints for the 1 + 1 + 2 variables which may be solved straightforwardly. We show how both odd- and even-parity perturbations may be unified by the discovery of a covariant, frame- and gauge-invariant, transverse-traceless tensor describing gravitational waves, which satisfies a covariant wave equation equivalent to the Regge-Wheeler equation for both even- and odd-parity perturbations. We show how the Zerilli equation may be derived from this tensor, and derive a similar transverse-traceless tensor equation equivalent to this equation. The so-called special quasinormal modes with purely imaginary frequency emerge naturally. The significance of the degrees of freedom in the choice of the two frame vectors is discussed, and we demonstrate that, for a certain frame choice, the underlying dynamics is governed purely by the Regge-Wheeler tensor. The two transverse-traceless Weyl tensors which carry the curvature of gravitational waves are discussed, and we give the closed system of four first-order ordinary differential equations describing their propagation. Finally, we consider the extension of this work to the study of

  9. Meridional transport of salt in the global ocean from an eddy-resolving model

    Science.gov (United States)

    Treguier, A. M.; Deshayes, J.; Le Sommer, J.; Lique, C.; Madec, G.; Penduff, T.; Molines, J.-M.; Barnier, B.; Bourdalle-Badie, R.; Talandier, C.

    2014-04-01

    The meridional transport of salt is computed in a global eddy-resolving numerical model (1/12° resolution) in order to improve our understanding of the ocean salinity budget. A methodology is proposed that allows a global analysis of the salinity balance in relation to surface water fluxes, without defining a "freshwater anomaly" based on an arbitrary reference salinity. The method consists of a decomposition of the meridional transport into (i) the transport by the time-longitude-depth mean velocity, (ii) time-mean velocity recirculations and (iii) transient eddy perturbations. Water is added (rainfall and rivers) or removed (evaporation) at the ocean surface at different latitudes, which creates convergences and divergences of mass transport with maximum and minimum values close to ±1 Sv. The resulting meridional velocity effects a net transport of salt at each latitude (±30 Sv PSU), which is balanced by the time-mean recirculations and by the net effect of eddy salinity-velocity correlations. This balance ensures that the total meridional transport of salt is close to zero, a necessary condition for maintaining a quasi-stationary salinity distribution. Our model confirms that the eddy salt transport cannot be neglected: it is comparable to the transport by the time-mean recirculation (up to 15 Sv PSU) at the poleward and equatorial boundaries of the subtropical gyres. Two different mechanisms are found: eddy contributions are localized in intense currents such as the Kuroshio at the poleward boundary of the subtropical gyres, while they are distributed across the basins at the equatorward boundaries. Closer to the Equator, salinity-velocity correlations are mainly due to the seasonal cycle and large-scale perturbations such as tropical instability waves.

  10. Effect of the surface film electric resistance on eddy current detectability of surface cracks in Alloy 600 tubes

    International Nuclear Information System (INIS)

    Saario, T.; Paine, J.P.N.

    1995-01-01

    The most widely used technique for NDE of steam generator tubing is eddy current. This technique can reliably detect cracks grown in sodium hydroxide environment only at depths greater than 50% through wall. However, cracking caused by thiosulphate solutions have been detected and sized at shallower depths. The disparity has been proposed to be caused by the different electric resistance of the crack wall surface films and corrosion products in the cracks formed in different environments. This work was undertaken to clarify the role of surface film electric resistance on the disparity found in eddy current detectability of surface cracks in alloy 600 tubes. The proposed model explaining the above mentioned disparity is the following. The detectability of tightly closed cracks by the eddy current technique depends on the electric resistance of the surface films of the crack walls. The nature and resistance of the films which form on the crack walls during operation depends on the composition of the solution inside the crack and close to the crack location. During cooling down of the steam generator, because of contraction and loss of internal pressurization, the cracks are rather tightly closed so that exchange of electrolyte and thus changes in the film properties become difficult. As a result, the surface condition prevailing at high temperature is preserved. If the environment is such that the films formed on the crack walls under operating conditions have low electric resistance, eddy current technique will fail to indicate these cracks or will underestimate the size of these cracks. However, if the electric resistance of the films is high, a tightly closed crack will resemble an open crack and will be easily indicated and correctly sized by eddy current technique

  11. Bayes Factor Covariance Testing in Item Response Models.

    Science.gov (United States)

    Fox, Jean-Paul; Mulder, Joris; Sinharay, Sandip

    2017-12-01

    Two marginal one-parameter item response theory models are introduced, by integrating out the latent variable or random item parameter. It is shown that both marginal response models are multivariate (probit) models with a compound symmetry covariance structure. Several common hypotheses concerning the underlying covariance structure are evaluated using (fractional) Bayes factor tests. The support for a unidimensional factor (i.e., assumption of local independence) and differential item functioning are evaluated by testing the covariance components. The posterior distribution of common covariance components is obtained in closed form by transforming latent responses with an orthogonal (Helmert) matrix. This posterior distribution is defined as a shifted-inverse-gamma, thereby introducing a default prior and a balanced prior distribution. Based on that, an MCMC algorithm is described to estimate all model parameters and to compute (fractional) Bayes factor tests. Simulation studies are used to show that the (fractional) Bayes factor tests have good properties for testing the underlying covariance structure of binary response data. The method is illustrated with two real data studies.

  12. Cross-covariance functions for multivariate geostatistics

    KAUST Repository

    Genton, Marc G.

    2015-05-01

    Continuously indexed datasets with multiple variables have become ubiquitous in the geophysical, ecological, environmental and climate sciences, and pose substantial analysis challenges to scientists and statisticians. For many years, scientists developed models that aimed at capturing the spatial behavior for an individual process; only within the last few decades has it become commonplace to model multiple processes jointly. The key difficulty is in specifying the cross-covariance function, that is, the function responsible for the relationship between distinct variables. Indeed, these cross-covariance functions must be chosen to be consistent with marginal covariance functions in such a way that the second-order structure always yields a nonnegative definite covariance matrix. We review the main approaches to building cross-covariance models, including the linear model of coregionalization, convolution methods, the multivariate Matérn and nonstationary and space-time extensions of these among others. We additionally cover specialized constructions, including those designed for asymmetry, compact support and spherical domains, with a review of physics-constrained models. We illustrate select models on a bivariate regional climate model output example for temperature and pressure, along with a bivariate minimum and maximum temperature observational dataset; we compare models by likelihood value as well as via cross-validation co-kriging studies. The article closes with a discussion of unsolved problems. © Institute of Mathematical Statistics, 2015.

  13. Cross-covariance functions for multivariate geostatistics

    KAUST Repository

    Genton, Marc G.; Kleiber, William

    2015-01-01

    Continuously indexed datasets with multiple variables have become ubiquitous in the geophysical, ecological, environmental and climate sciences, and pose substantial analysis challenges to scientists and statisticians. For many years, scientists developed models that aimed at capturing the spatial behavior for an individual process; only within the last few decades has it become commonplace to model multiple processes jointly. The key difficulty is in specifying the cross-covariance function, that is, the function responsible for the relationship between distinct variables. Indeed, these cross-covariance functions must be chosen to be consistent with marginal covariance functions in such a way that the second-order structure always yields a nonnegative definite covariance matrix. We review the main approaches to building cross-covariance models, including the linear model of coregionalization, convolution methods, the multivariate Matérn and nonstationary and space-time extensions of these among others. We additionally cover specialized constructions, including those designed for asymmetry, compact support and spherical domains, with a review of physics-constrained models. We illustrate select models on a bivariate regional climate model output example for temperature and pressure, along with a bivariate minimum and maximum temperature observational dataset; we compare models by likelihood value as well as via cross-validation co-kriging studies. The article closes with a discussion of unsolved problems. © Institute of Mathematical Statistics, 2015.

  14. Covarient quantization of heterotic strings in supersymmetric chiral boson formulation

    International Nuclear Information System (INIS)

    Yu, F.

    1992-01-01

    This dissertation presents the covariant supersymmetric chiral boson formulation of the heterotic strings. The main feature of this formulation is the covariant quantization of the so-called leftons and rightons -- the (1,0) supersymmetric generalizations of the world-sheet chiral bosons -- that constitute basic building blocks of general heterotic-type string models. Although the (Neveu-Schwarz-Ramond or Green-Schwarz) heterotic strings provide the most realistic string models, their covariant quantization, with the widely-used Siegel formalism, has never been rigorously carried out. It is clarified in this dissertation that the covariant Siegel formalism is pathological upon quantization. As a test, a general classical covariant (NSR) heterotic string action that has the Siegel symmetry is constructed in arbitrary curved space-time coupled to (1,0) world-sheet super-gravity. In the light-cone gauge quantization, the critical dimensions are derived for such an action with leftons and rightons compactified on group manifolds G L x G R . The covariant quantization of this action does not agree with the physical results in the light-cone gauge quantization. This dissertation establishes a new formalism for the covariant quantization of heterotic strings. The desired consistent covariant path integral quantization of supersymmetric chiral bosons, and thus the general (NSR) heterotic-type strings with leftons and rightons compactified on torus circle-times d L S 1 x circle-times d R S 1 are carried out. An infinite set of auxiliary (1,0) scalar superfields is introduced to convert the second-class chiral constraint into first-class ones. The covariant gauge-fixed action has an extended BRST symmetry described by the graded algebra GL(1/1). A regularization respecting this symmetry is proposed to deal with the contributions of the infinite towers of auxiliary fields and associated ghosts

  15. Using eddy covariance of CO2, 13CO2 and CH4, continuous soil respiration measurements, and PhenoCams to constrain a process-based biogeochemical model for carbon market-funded wetland restoration

    Science.gov (United States)

    Oikawa, P. Y.; Baldocchi, D. D.; Knox, S. H.; Sturtevant, C. S.; Verfaillie, J. G.; Dronova, I.; Jenerette, D.; Poindexter, C.; Huang, Y. W.

    2015-12-01

    We use multiple data streams in a model-data fusion approach to reduce uncertainty in predicting CO2 and CH4 exchange in drained and flooded peatlands. Drained peatlands in the Sacramento-San Joaquin River Delta, California are a strong source of CO2 to the atmosphere and flooded peatlands or wetlands are a strong CO2 sink. However, wetlands are also large sources of CH4 that can offset the greenhouse gas mitigation potential of wetland restoration. Reducing uncertainty in model predictions of annual CO2 and CH4 budgets is critical for including wetland restoration in Cap-and-Trade programs. We have developed and parameterized the Peatland Ecosystem Photosynthesis, Respiration, and Methane Transport model (PEPRMT) in a drained agricultural peatland and a restored wetland. Both ecosystem respiration (Reco) and CH4 production are a function of 2 soil carbon (C) pools (i.e. recently-fixed C and soil organic C), temperature, and water table height. Photosynthesis is predicted using a light use efficiency model. To estimate parameters we use a Markov Chain Monte Carlo approach with an adaptive Metropolis-Hastings algorithm. Multiple data streams are used to constrain model parameters including eddy covariance of CO2, 13CO2 and CH4, continuous soil respiration measurements and digital photography. Digital photography is used to estimate leaf area index, an important input variable for the photosynthesis model. Soil respiration and 13CO2 fluxes allow partitioning of eddy covariance data between Reco and photosynthesis. Partitioned fluxes of CO2 with associated uncertainty are used to parametrize the Reco and photosynthesis models within PEPRMT. Overall, PEPRMT model performance is high. For example, we observe high data-model agreement between modeled and observed partitioned Reco (r2 = 0.68; slope = 1; RMSE = 0.59 g C-CO2 m-2 d-1). Model validation demonstrated the model's ability to accurately predict annual budgets of CO2 and CH4 in a wetland system (within 14% and 1

  16. Moments of inertia and the shapes of Brownian paths

    International Nuclear Information System (INIS)

    Fougere, F.; Desbois, J.

    1993-01-01

    The joint probability law of the principal moments of inertia of Brownian paths (open or closed) is computed, using constrained path integrals and Random Matrix Theory. The case of two-dimensional paths is discussed in detail. In particular, it is shown that the ratio of the average values of the largest and smallest moments is equal to 4.99 (open paths) and 3.07 (closed paths). Results of numerical simulations are also presented, which include investigation of the relationships between the moments of inertia and the arithmetic area enclosed by a path. (authors) 28 refs., 2 figs

  17. Shrunk loop theorem for the topology probabilities of closed Brownian (or Feynman) paths on the twice punctured plane

    International Nuclear Information System (INIS)

    Giraud, O; Thain, A; Hannay, J H

    2004-01-01

    The shrunk loop theorem proved here is an integral identity which facilitates the calculation of the relative probability (or probability amplitude) of any given topology that a free, closed Brownian (or Feynman) path of a given 'duration' might have on the twice punctured plane (plane with two marked points). The result is expressed as a 'scattering' series of integrals of increasing dimensionality based on the maximally shrunk version of the path. Physically, this applies in different contexts: (i) the topology probability of a closed ideal polymer chain on a plane with two impassable points, (ii) the trace of the Schroedinger Green function, and thence spectral information, in the presence of two Aharonov-Bohm fluxes and (iii) the same with two branch points of a Riemann surface instead of fluxes. Our theorem starts from the Stovicek scattering expansion for the Green function in the presence of two Aharonov-Bohm flux lines, which itself is based on the famous Sommerfeld one puncture point solution of 1896 (the one puncture case has much easier topology, just one winding number). Stovicek's expansion itself can supply the results at the expense of choosing a base point on the loop and then integrating it away. The shrunk loop theorem eliminates this extra two-dimensional integration, distilling the topology from the geometry

  18. Momentum, sensible heat and CO2 correlation coefficient variability: what can we learn from 20 years of continuous eddy covariance measurements?

    Science.gov (United States)

    Hurdebise, Quentin; Heinesch, Bernard; De Ligne, Anne; Vincke, Caroline; Aubinet, Marc

    2017-04-01

    Long-term data series of carbon dioxide and other gas exchanges between terrestrial ecosystems and atmosphere become more and more numerous. Long-term analyses of such exchanges require a good understanding of measurement conditions during the investigated period. Independently of climate drivers, measurements may indeed be influenced by measurement conditions themselves subjected to long-term variability due to vegetation growth or set-up changes. The present research refers to the Vielsalm Terrestrial Observatory (VTO) an ICOS candidate site located in a mixed forest (beech, silver fir, Douglas fir, Norway spruce) in the Belgian Ardenne. Fluxes of momentum, carbon dioxide and sensible heat have been continuously measured there by eddy covariance for more than 20 years. During this period, changes in canopy height and measurement height occurred. The correlation coefficients (for momemtum, sensible heat and CO2) and the normalized standard deviations measured for the past 20 years at the Vielsalm Terrestrial Observatory (VTO) were analysed in order to define how the fluxes, independently of climate conditions, were affected by the surrounding environment evolution, including tree growth, forest thinning and tower height change. A relationship between canopy aerodynamic distance and the momentum correlation coefficient was found which is characteristic of the roughness sublayer, and suggests that momentum transport processes were affected by z-d. In contrast, no relationship was found for sensible heat and CO2 correlation coefficients, suggesting that the z-d variability observed did not affect their turbulent transport. There were strong differences in these coefficients, however, between two wind sectors, characterized by contrasted stands (height differences, homogeneity) and different hypotheses were raised to explain it. This study highlighted the importance of taking the surrounding environment variability into account in order to ensure the spatio

  19. Eddy-kovarianční měření v agroekosystému v Křešíně u Pacova

    Czech Academy of Sciences Publication Activity Database

    Havránková, Kateřina; Šigut, Ladislav; Sedlák, Pavel; Pavelka, Marian

    2013-01-01

    Roč. 25, č. 5 (2013), s. 27-30 ISSN 1211-0337 R&D Projects: GA MŠk(CZ) EE2.4.31.0056; GA MŠk(CZ) ED1.1.00/02.0073; GA MŠk(CZ) LM2010007 Institutional support: RVO:67179843 Keywords : eddy-covariance * agroecosystem * wind analysis * footprint * CO2 flux Subject RIV: EH - Ecology, Behaviour

  20. Current distribution in parallel paths of the coils of a 50 Hz prototype dipole magnet

    International Nuclear Information System (INIS)

    Otter, A.J.

    1995-06-01

    The prototype dipole made for TRIUMF's Kaon Factory proposal used coils with 12 parallel paths to reduce eddy current losses in the conductors. The ac current distribution in these paths was non-uniform due to different self and mutual inductances. Small differences in inductance can cause large circulating currents in the parallel windings. This paper describes the measurement of the inductances and shows an attempt to predict the current distribution for two alternative connection schemes. (author). 4 refs., 8 figs

  1. Benthic Carbon Mineralization and Nutrient Turnover in a Scottish Sea Loch

    DEFF Research Database (Denmark)

    Glud, Ronnie N.; Berg, Peter; Stahl, Henrik

    2016-01-01

    Based on in situ microprofiles, chamber incubations and eddy covariance measurements, we investigated the benthic carbon mineralization and nutrient regeneration in a ~65-m-deep sedimentation basin of Loch Etive, UK. The sediment hosted a considerable amount of infauna that was dominated by the b......Based on in situ microprofiles, chamber incubations and eddy covariance measurements, we investigated the benthic carbon mineralization and nutrient regeneration in a ~65-m-deep sedimentation basin of Loch Etive, UK. The sediment hosted a considerable amount of infauna that was dominated....... The average benthic O2 exchange as derived by chamber incubations and the eddy covariance approach were similar (14.9 ± 2.5 and 13.1 ± 9.0 mmol m−2 day−1) providing confidence in the two measuring approaches. Moreover, the non-invasive eddy approach revealed a flow-dependent benthic O2 flux that was partly...... ascribed to enhanced ventilation of infauna burrows during periods of elevated flow rates. The ratio in exchange rates of ΣCO2 and O2 was close to unity, confirming that the O2 uptake was a good proxy for the benthic carbon mineralization in this setting. The infauna activity resulted in highly dynamic...

  2. Numerical study on the interactions between the Kuroshio current in the Luzon Strait and a mesoscale eddy

    Science.gov (United States)

    Kuo, Yi-Chun; Chern, Ching-Sheng; Zheng, Zhe-Wen

    2017-04-01

    The Luzon Strait (LS) connects the northwestern Pacific Ocean and the South China Sea (SCS) and is the western boundary gap for the Kuroshio current (KC). Satellite observations indicate that a cyclonic mesoscale eddy can trigger westward extension of the KC into the SCS and shed a smaller anticyclonic eddy to the west of the LS. We used a nonlinear reduced-gravity (primitive equation) model to study this phenomenon and analyzed the dynamic process. The location of the collision between the eddy and the KC could be critical for varying the circulation in the LS. The eddy's deformation rate, associated with its decaying speed, is also closely related to the location of the eddy during collision. When a cyclonic eddy moved from a region to the east of the Luzon Island toward the LS, the KC intruded into the SCS with growing negative vorticity during the collision of the eddy and KC. This tendency for negative vorticity is attributed to the beta effect and squeezing of the planetary vorticity caused by the flow divergence. As the eddy dissipated, the KC in the LS recovered its original pattern. When the collision of the eddy occurred at the center of the LS, the momentum balance of the KC loop was dominated by the inertial term, and the circulation in the LS remained in a leaping state.

  3. A numerical modeling study of the East Australian Current encircling and overwashing a warm-core eddy

    Science.gov (United States)

    MacDonald, H. S.; Roughan, M.; Baird, M. E.; Wilkin, J.

    2013-01-01

    AbstractWarm-core eddies (WCEs) often form in the meanders of Western Boundary Currents (WBCs). WCEs are frequently overwashed with less dense waters sourced from the WBC. We use the Regional Ocean Modelling System to investigate the ocean state during the overwashing of one such WCE in October 2008 in the East Australian Current (EAC). Comparisons of model outputs with satellite sea surface temperature and vertical profiles show that the model provides a realistic simulation of the eddy during the period when the EAC encircled and then overwashed the eddy. During the encircling stage, an eddy with closed circulation persisted at depth. In the surface EAC water entered from the north, encircled the eddy and exited to the east. The overwashing stage was initiated by the expulsion of cyclonic vorticity. For the following 8 days after the expulsion, waters from the EAC washed over the top of the eddy, transferring heat and anticyclonic vorticity radially-inward. After approximately one rotation period of overwashing, the eddy separated. The overwashing creates a two-layer system that forms a subsurface maximum velocity at the interface of the two layers. Analysis of water mass properties, Eulerian tracer dynamics, and Lagrangian particle tracks show that the original eddy sinks 10-50 m during the overwashing period. Overwashing has been observed in many WBCs and occurs in most WCEs in the western Tasman Sea.

  4. A Baroclinic Eddy Mixer: Supercritical Transformation of Compensated Eddies

    Science.gov (United States)

    Sutyrin, G.

    2016-02-01

    In contrast to many real-ocean rings and eddies, circular vortices with initial lower layer at rest tend to be highly unstable in idealized two-layer models, unless their radius is made small or the lower layer depth is made artificially large. Numerical simulations of unstable vortices with parameters typical for ocean eddies revealed strong deformations and pulsations of the vortex core in the two-layer setup due to development of corotating tripolar structures in the lower layer during their supercritical transformation. The addition of a middle layer with the uniform potential vorticity weakens vertical coupling between the upper and lower layer that enhances vortex stability and makes the vortex lifespan more realistic. Such a three-layer vortex model possesses smaller lower interface slope than the two-layer model that reduces the potential vorticity gradient in the lower layer and provides with less unstable configurations. While cyclonic eddies become only slightly deformed and look nearly circular when the middle layer with uniform potential vorticity is added, anticyclonic eddies tend to corotating and pulsating elongated states through potential vorticity stripping and stirring. Enhanced vortex stability in such three-layer setup has important implications for adequate representation of the energy transfer across scales.

  5. Toward a consistency cross-check of eddy covariance flux–based and biometric estimates of ecosystem carbon balance

    DEFF Research Database (Denmark)

    Luyssaert, S.; Reichstein, M.; Schulze, E.-D.

    2009-01-01

    Quantification of an ecosystem's carbon balance and its components is pivotal for understanding both ecosystem functioning and global cycling. Several methods are being applied in parallel to estimate the different components of the CO2 balance. However, different methods are subject to different...... sources of error. Therefore, it is necessary that site level component estimates are cross-checked against each other before being reported. Here we present a two-step approach for testing the accuracy and consistency of eddy covariance–based gross primary production (GPP) and ecosystem respiration (Re...

  6. An alternative path integral for quantum gravity

    Energy Technology Data Exchange (ETDEWEB)

    Krishnan, Chethan; Kumar, K.V. Pavan; Raju, Avinash [Center for High Energy Physics, Indian Institute of Science,Bangalore 560012 (India)

    2016-10-10

    We define a (semi-classical) path integral for gravity with Neumann boundary conditions in D dimensions, and show how to relate this new partition function to the usual picture of Euclidean quantum gravity. We also write down the action in ADM Hamiltonian formulation and use it to reproduce the entropy of black holes and cosmological horizons. A comparison between the (background-subtracted) covariant and Hamiltonian ways of semi-classically evaluating this path integral in flat space reproduces the generalized Smarr formula and the first law. This “Neumann ensemble” perspective on gravitational thermodynamics is parallel to the canonical (Dirichlet) ensemble of Gibbons-Hawking and the microcanonical approach of Brown-York.

  7. Eddy Effects in the General Circulation, Spanning Mean Currents, Mesoscale Eddies, and Topographic Generation, Including Submesoscale Nests

    Science.gov (United States)

    2014-09-30

    alongshore winds favoring upwelling circulation. As for the other EBUS (e.g., Humboldt, Benguela, and Canary Currents ), equatorward winds drive...Eddy Effects in the General Circulation, Spanning Mean Currents , Mesoscale Eddies, and Topographic Generation, Including Submesoscale Nests...environments OBJECTIVES The central scientific questions are how the eddies control the persistent currents by their eddy-induced momentum and buoyancy fluxes

  8. The covariant form of Maxwell equations for the fast simulation of the eddy current non destructive testing of complex specimens

    International Nuclear Information System (INIS)

    Caire, Francois

    2014-01-01

    This PhD work concerns the development of fast numerical tools, dedicated to the computation of the electromagnetic interaction between a low frequency 3D current source and a complex conductor, presenting rough interfaces and/or conductivity variations. The main application concerns the simulation of the Eddy Current nondestructive testing process applied to complex specimens. Indeed, the semi-analytical models available today are restricted to canonical geometries. The proposed method is based on the covariant form of Maxwell's equations, which translates the physical equations and relationships in a non-orthogonal coordinate system depending on the geometry of the specimen. Historically, this method (Curvilinear Coordinate Method, CCM or C-method) has been developed in the framework of optical applications, particularly for the characterization of diffraction gratings. Here, we transpose this formalism into the quasi-static regime and we extend the Second Order Vector Potential formalism, initially dedicated to orthonormal curvilinear coordinates systems, to general curvilinear coordinate systems. Thanks to this change of base, we are able to determine numerically a set of modal solutions of the source-free Maxwell equations in the new coordinate system introduced, and this allows us to represent the unknown fields as modal expansions in source-free domains. Then, the coefficients of these expansions are computed by introducing the source fields and by enforcing the boundary conditions that the total fields must verify at interfaces between the different media. In order to tackle the case of a layered conductor presenting rough interfaces, the generalized SOVP formalism is coupled with a recursive routine called the S-matrix algorithm. On the other hand, the application case of a complex shape specimen with depth-varying physical properties is treated by coupling the modal method we developed with a high-order numerical method: pseudo-spectral method. The

  9. Response of ecosystem carbon fluxes to drought events in a poplar plantation in Northern China

    Science.gov (United States)

    Jie Zhou; Zhiqiang Zhang; Ge Sun; Xianrui Fang; Tonggang Zha; Steve McNulty; Jiquan Chen; Ying Jin; Asko Noormets

    2013-01-01

    Poplar plantations are widely used for timber production and ecological restoration in northern China,a region that experiences frequent droughts and water scarcity. An open-path eddy-covariance (EC)system was used to continuously measure the carbon,water,and energy fluxes in a poplar plantation during the growing season (i.e., April–October)over the period 2006–2008...

  10. Water-use efficiency of a poplar plantation in Northern China

    Science.gov (United States)

    Jie Zhou; Zhiqiang Zhang; Ge sun; Xianrui Fang; Tonggang Zha; Jiquan Chen; Asko Noormets; Junting Guo; Steve McNulty

    2014-01-01

    The water-use efficiency (WUE) of an ecosystem—defined as the gross ecosystem production (GEP) divided by the evapotranspiration (ET)—is an important index for understanding the coupling of water and carbon and quantifying water–carbon trade-offs in forests. An open-path eddy covariance technique and a microclimate measurement system were deployed to investigate the...

  11. A Coherent vorticity preserving eddy-viscosity correction for Large-Eddy Simulation

    Science.gov (United States)

    Chapelier, J.-B.; Wasistho, B.; Scalo, C.

    2018-04-01

    This paper introduces a new approach to Large-Eddy Simulation (LES) where subgrid-scale (SGS) dissipation is applied proportionally to the degree of local spectral broadening, hence mitigated or deactivated in regions dominated by large-scale and/or laminar vortical motion. The proposed coherent-vorticity preserving (CvP) LES methodology is based on the evaluation of the ratio of the test-filtered to resolved (or grid-filtered) enstrophy, σ. Values of σ close to 1 indicate low sub-test-filter turbulent activity, justifying local deactivation of the SGS dissipation. The intensity of the SGS dissipation is progressively increased for σ activated in developed turbulence characterized by σ ≤σeq, where the value σeq is derived assuming a Kolmogorov spectrum. The proposed approach can be applied to any eddy-viscosity model, is algorithmically simple and computationally inexpensive. LES of Taylor-Green vortex breakdown demonstrates that the CvP methodology improves the performance of traditional, non-dynamic dissipative SGS models, capturing the peak of total turbulent kinetic energy dissipation during transition. Similar accuracy is obtained by adopting Germano's dynamic procedure albeit at more than twice the computational overhead. A CvP-LES of a pair of unstable periodic helical vortices is shown to predict accurately the experimentally observed growth rate using coarse resolutions. The ability of the CvP methodology to dynamically sort the coherent, large-scale motion from the smaller, broadband scales during transition is demonstrated via flow visualizations. LES of compressible channel are carried out and show a good match with a reference DNS.

  12. Grasland Stable Isotope Flux Measurements: Three Isotopomers of Carbon Dioxide Measured by QCL Spectroscopy

    Science.gov (United States)

    Zeeman, M. J.; Tuzson, B.; Eugster, W.; Werner, R. A.; Buchmann, N.; Emmenegger, L.

    2007-12-01

    To improve our understanding of greenhouse gas dynamics of managed ecosystems such as grasslands, we not only need to investigate the effects of management (e.g., grass cuts) and weather events (e.g., rainy days) on carbon dioxide fluxes, but also need to increase the time resolution of our measurements. Thus, for the first time, we assessed respiration and assimilation fluxes with high time resolution (5Hz) stable isotope measurements at an intensively managed farmland in Switzerland (Chamau, 400m ASL). Two different methods were used to quantify fluxes of carbon dioxide and associated fluxes of stable carbon isotopes: (1) the flux gradient method, and (2) the eddy covariance method. During a week long intensive measurement campaign, we (1) measured mixing ratios of carbon dioxide isotopomers (12C16O2, 12C16O18O, 13C16O2) with a Quantum Cascade Laser (QCL, Aerodyne Inc.) spectroscope and (2) collected air samples for isotope analyses (13C/12C) and (18O/16O) of carbon dioxide by Isotope Ratio Mass Spectrometry (IRMS, Finnigan) every two hours, concurrently along a height profile (z = 0.05; 0.10; 0.31; 2.15m). In the following week, the QCL setup was used for closed-path eddy covariance flux measurement of the carbon dioxide isotopomers, with the air inlet located next to an open-path Infra Red Gas Analyzers (IRGA, LiCor 7500) used simultaneously for carbon dioxide measurements. During this second week, an area of grass inside the footprint was cut and harvested after several days. The first results of in-field continuous QCL measurements of carbon dioxide mixing ratios and their stable isotopic ratios show good agreement with IRGA measurements and isotope analysis of flask samples by IRMS. Thus, QCL spectroscopy is a very promising tool for stable isotope flux investigations.

  13. Comparison of Landfill Methane Oxidation Measured Using Stable Isotope Analysis and CO2/CH4 Fluxes Measured by the Eddy Covariance Method

    Science.gov (United States)

    Xu, L.; Chanton, J.; McDermitt, D. K.; Li, J.; Green, R. B.

    2015-12-01

    Methane plays a critical role in the radiation balance and chemistry of the atmosphere. Globally, landfill methane emission contributes about 10-19% of the anthropogenic methane burden into the atmosphere. In the United States, 18% of annual anthropogenic methane emissions come from landfills, which represent the third largest source of anthropogenic methane emissions, behind enteric fermentation and natural gas and oil production. One uncertainty in estimating landfill methane emissions is the fraction of methane oxidized when methane produced under anaerobic conditions passes through the cover soil. We developed a simple stoichiometric model to estimate methane oxidation fraction when the anaerobic CO2 / CH4 production ratio is known, or can be estimated. The model predicts a linear relationship between CO2 emission rates and CH4 emission rates, where the slope depends on anaerobic CO2 / CH4 production ratio and the fraction of methane oxidized, and the intercept depends on non-methane-dependent oxidation processes. The model was tested using carbon dioxide emission rates (fluxes) and methane emission rates (fluxes) measured using the eddy covariance method over a one year period at the Turkey Run landfill in Georgia, USA. The CO2 / CH4 production ratio was estimated by measuring CO2 and CH4 concentrations in air sampled under anaerobic conditions deep inside the landfill. We also used a mass balance approach to independently estimate fractional oxidation based on stable isotope measurements (δ13C of methane) of gas samples taken from deep inside the landfill and just above the landfill surface. Results from the two independent methods agree well. The model will be described and methane oxidation will be discussed in relation to wind direction, location at the landfill, and age of the deposited refuse.

  14. A meso-network of eddy covariance towers across the Northwest Territories to assess high-latitude carbon and water budgets under increasing pressure

    Science.gov (United States)

    Hurkuck, M.; Marsh, P.; Quinton, W. L.; Humphreys, E.; Lafleur, P.; Helbig, M.; Hould Gosselin, G.; Sonnentag, O.

    2017-12-01

    Given their large areal coverage, high carbon densities, unique land surface properties, and disturbance regimes, Canada's diverse high-latitude ecosystems across its multiple Arctic, subarctic and boreal ecozones are integral components of the global and regional climate systems. In northwestern Canada, large portions of these ecozones contain permafrost, i.e., perennially cryotic ground. Here, we describe efforts towards a meso-network of nine eddy covariance towers to measure carbon, water and energy fluxes across the Northwest Territories to shed light on high-latitude carbon and water budgets and their rapidly changing biotic and abiotic controls in response to increasing natural and anthropogenic pressures. Distributed across six research sites (Trail Valley Creek, 68.7°N, 133.3°W; Havikpak Creek, 68.3°N, 133.3°W; Daring Lake, 64.8°N, 111.5°W; Smith Creek, 63.1°N, 123.2°W; Scotty Creek, 63.1°N, 123.2°W; Yellowknife, 62.5°N, 114.4°W), the meso-network spans the central portion of the extended ABoVE Study Domain, covering two ecozones (Taiga Plains, Southern Arctic) with differing permafrost regimes (sporadic, discontinuous, continuous), climatic settings (coastal, interior), and seven high-latitude ecosystem types: forested permafrost peat plateau, permafrost-free collapse-scar bog, subarctic woodland, mixed and dwarf-shrub tundra, and sedge fen. With our contribution, we report on the current status of the meso-network development and present results from various synthesis activities examining the role of climatic setting and resulting tundra carbon and water budgets, quantifying the impact of permafrost thaw and associated wetland expansion on boreal forest carbon and water budgets, and determining the relative importance of treeline advance compared to shrub proliferation on tundra carbon and water budgets.

  15. Uncertainty of long-term CO2 flux estimates due to the choice of the spectral correction method

    Science.gov (United States)

    Ibrom, Andreas; Geißler, Simon; Pilegaard, Kim

    2010-05-01

    The eddy covariance system at the Danish beech forest long-term flux observation site at Sorø has been intensively examined. Here we investigate which systematic and non-systematic effects the choice of the spectral correction method has on long-term net CO2 flux estimates and their components. Ibrom et al. (2007) gave an overview over different ways to correct for low-pass filtering of the atmospheric turbulent signal by a closed path eddy covariance system. They used degraded temperature time series for spectral correction of low-pass filtered signals. In this new study, correction for high-pass filtering was also included, which made it anyway necessary to use model co-spectra. We compared different ways of adapting different kinds of model co-spectra to the wealth of 14 years high frequency raw data. As the trees grew, the distance between the sonic anemometer and the displacement height decreased over time. The study enabled us to compare the two approaches and different variants of them to give recommendations on their use. The analysis showed that model spectra should not be derived from co-spectra between the vertical wind speed (w) and the scalars measured with the closed path system, i.e. CO2 and H20 concentrations, but instead with sonic temperature (T) w cospectra, to avoid low-pass filtering effects on the estimation of the co-spectral peak frequency (fx). This concern was already expressed earlier in the above mentioned study, but here we show the quantitative effects. The wT co-spectra did not show any height effect on fx as it was suggested in generally used parameterizations. A possible reason for this difference is that measurements, like in all forest flux sites, took place in the roughness sub-layer and not in the inertial sub-layer. At the same time the shape of the relationship between fx and the stability parameter ? differed much from that of often used parameterizations (e.g. from Horst, 1997). The shift of fx towards higher frequencies at

  16. Quantum cosmology based on discrete Feynman paths

    International Nuclear Information System (INIS)

    Chew, Geoffrey F.

    2002-01-01

    Although the rules for interpreting local quantum theory imply discretization of process, Lorentz covariance is usually regarded as precluding time quantization. Nevertheless a time-discretized quantum representation of redshifting spatially-homogeneous universe may be based on discrete-step Feynman paths carrying causal Lorentz-invariant action--paths that not only propagate the wave function but provide a phenomenologically-promising elementary-particle Hilbert-space basis. In a model under development, local path steps are at Planck scale while, at a much larger ''wave-function scale'', global steps separate successive wave-functions. Wave-function spacetime is but a tiny fraction of path spacetime. Electromagnetic and gravitational actions are ''at a distance'' in Wheeler-Feynman sense while strong (color) and weak (isospin) actions, as well as action of particle motion, are ''local'' in a sense paralleling the action of local field theory. ''Nonmaterial'' path segments and ''trivial events'' collaborate to define energy and gravity. Photons coupled to conserved electric charge enjoy privileged model status among elementary fermions and vector bosons. Although real path parameters provide no immediate meaning for ''measurement'', the phase of the complex wave function allows significance for ''information'' accumulated through ''gentle'' electromagnetic events involving charged matter and ''soft'' photons. Through its soft-photon content the wave function is an ''information reservoir''

  17. Eddy-induced cross-shelf export of high Chl-a coastal waters in the SE Bay of Biscay

    KAUST Repository

    Rubio, Anna

    2017-12-08

    Different remote sensing data were combined to characterise a winter anticyclonic eddy in the southeastern Bay of Biscay and to infer its effects on cross-shelf exchanges, in a period when typical along shelf-slope currents depict a cyclonic pattern. While the joint analysis of available satellite data (infrared, visible and altimetry) permitted the characterisation and tracking of the anticyclone properties and path, data from a coastal high-frequency radar system enabled a quantitative analysis of the surface cross-shelf transports associated with this anticyclone. The warm core anticyclone had a diameter of around 50km, maximum azimuthal velocities near 50cms−1 and a relative vorticity of up to −0.45f. The eddy generation occurred after the relaxation of a cyclonic wind-driven current regime over the shelf-slope; then, the eddy remained stationary for several weeks until it started to drift northwards along the shelf break. The surface signature of this eddy was observed by means of high-frequency radar data for 20 consecutive days, providing a unique opportunity to characterise and quantify, from a Lagrangian perspective, the associated transport and its effect on the Chl-a surface distribution. We observed the presence of mesoscale structures with similar characteristics in the area during different winters within the period 2011–2014. Our results suggest that the eddy-induced recurrent cross-shelf export is an effective mechanism for the expansion of coastal productive waters into the adjacent oligotrophic ocean basin.

  18. Large Eddy Simulation of the Diurnal Cycle in Southeast Pacific Stratocumulus

    Energy Technology Data Exchange (ETDEWEB)

    Caldwell, P; Bretherton, C

    2008-03-03

    This paper describes a series of 6 day large eddy simulations of a deep, sometimes drizzling stratocumulus-topped boundary layer based on forcings from the East Pacific Investigation of Climate (EPIC) 2001 field campaign. The base simulation was found to reproduce the observed mean boundary layer properties quite well. The diurnal cycle of liquid water path was also well captured, although good agreement appears to result partially from compensating errors in the diurnal cycles of cloud base and cloud top due to overentrainment around midday. At other times of the day, entrainment is found to be proportional to the vertically-integrated buoyancy flux. Model stratification matches observations well; turbulence profiles suggest that the boundary layer is always at least somewhat decoupled. Model drizzle appears to be too sensitive to liquid water path and subcloud evaporation appears to be too weak. Removing the diurnal cycle of subsidence had little effect on simulated cloud albedo. Simulations with changed droplet concentration and drizzle susceptibility showed large liquid water path differences at night, but differences were quite small at midday. Droplet concentration also had a significant impact on entrainment, primarily through droplet sedimentation feedback rather than through drizzle processes.

  19. Eddy current detection of spacers in the fuel channels of CANDU nuclear reactors

    International Nuclear Information System (INIS)

    Krause, T.W.; Schankula, J.; Sullivan, S.P.

    2002-01-01

    Garter Spring (GS) spacers in the fuel channels of CANDU nuclear reactors maintain separation between the hot pressure tube and surrounding moderator cooled calandria tube. Eddy current detection of the four GSs provides assurance that spacers are at or close to design positions and are performing their intended function of maintaining a non-zero gap between pressure tube and calandria tube. Pressure tube constrictions, resulting from relatively less diametral creep at end-of-fuel bundle locations, also produce large eddy current signals. Large constrictions, present in higher service pressure tubes, can produce signals that are 10 times larger than GS signals, reducing GS detectability to 30% in standard GS-detect probes. The introduction of field-focussing elements into the design of the standard GS detection eddy current probe has been used to recover the detectability of GS spacers by increasing the signal amplitude obtained from GSs relative to that from constrictions by a factor of 10. The work presented here compares laboratory, modelling and in-reactor measurements of GS and constriction signals obtained from the standard probe with that obtained from field-focussed eddy current probe designs. (author)

  20. Eddy current testing

    Energy Technology Data Exchange (ETDEWEB)

    Song, Sung Jin; Lee, Hyang Beom; Kim, Young Hwan [Soongsil Univ., Seoul (Korea, Republic of); Shin, Young Kil [Kunsan Univ., Gunsan (Korea, Republic of)

    2004-02-15

    Eddy current testing has been widely used for non destructive testing of steam generator tubes. In order to retain reliability in ECT, the following subjects were carried out in this study: numerical modeling and analysis of defects by using BC and RPC probes in SG tube, preparation of absolute coil impedance plane diagram by FEM. Signal interpretation of the eddy current signals obtained from nuclear power plants.

  1. Eddy current testing

    International Nuclear Information System (INIS)

    Song, Sung Jin; Lee, Hyang Beom; Kim, Young Hwan; Shin, Young Kil

    2004-02-01

    Eddy current testing has been widely used for non destructive testing of steam generator tubes. In order to retain reliability in ECT, the following subjects were carried out in this study: numerical modeling and analysis of defects by using BC and RPC probes in SG tube, preparation of absolute coil impedance plane diagram by FEM. Signal interpretation of the eddy current signals obtained from nuclear power plants

  2. Robust entry guidance using linear covariance-based model predictive control

    Directory of Open Access Journals (Sweden)

    Jianjun Luo

    2017-02-01

    Full Text Available For atmospheric entry vehicles, guidance design can be accomplished by solving an optimal issue using optimal control theories. However, traditional design methods generally focus on the nominal performance and do not include considerations of the robustness in the design process. This paper proposes a linear covariance-based model predictive control method for robust entry guidance design. Firstly, linear covariance analysis is employed to directly incorporate the robustness into the guidance design. The closed-loop covariance with the feedback updated control command is initially formulated to provide the expected errors of the nominal state variables in the presence of uncertainties. Then, the closed-loop covariance is innovatively used as a component of the cost function to guarantee the robustness to reduce its sensitivity to uncertainties. After that, the models predictive control is used to solve the optimal problem, and the control commands (bank angles are calculated. Finally, a series of simulations for different missions have been completed to demonstrate the high performance in precision and the robustness with respect to initial perturbations as well as uncertainties in the entry process. The 3σ confidence region results in the presence of uncertainties which show that the robustness of the guidance has been improved, and the errors of the state variables are decreased by approximately 35%.

  3. Latest on Mobile Methane Measurements with Fast Open-Path Technology: Experiences, Opportunities & Perspectives

    Science.gov (United States)

    Burba, George; Anderson, Tyler; Ediger, Kevin; von Fischer, Joseph; Gioli, Beniamino; Ham, Jay; Hupp, Jason; Kohnert, Katrin; Larmanou, Eric; Levy, Peter; Polidori, Andrea; Pikelnaya, Olga; Price, Eric; Sachs, Torsten; Serafimovich, Andrei; Zondlo, Mark; Zulueta, Rommel

    2016-04-01

    allowing eddy covariance measurements of methane flux with power consumption 30-150 times below other available technologies. The instrumentation was designed to run on solar panels or a small generator, and could be placed in the middle of the methane-producing ecosystem without a need for grid power. This significantly expanded the methane flux measurement coverage in permafrost regions, wetlands, rice fields and landfills. In the past few years, this instrumentation has been utilized increasingly more frequently outside of the traditional use at stationary flux towers. The novel approaches included measurements from various moving platforms, such as cars, aircraft, and ships. Projects included mapping of concentrations and vertical profiles, leak detection and quantification, mobile emission detection from natural gas cars, soil methane flux surveys, etc. This presentation will describe key developmental steps in the lightweight low-power high-resolution open-path technology, the instrument principles and key elements of the design, and will highlight several novel approaches where such instrumentation was used in mobile deployments in urban and natural environments.

  4. Climatic feedbacks between stationary and transient eddies

    International Nuclear Information System (INIS)

    Branscome, L.E.

    1994-01-01

    Stationary eddies make a significant contribution to poleward heat transport during Northern Hemisphere winter, equaling the transport by transient eddies. On the other hand, stationary eddy transport during the summer is negligible. The effect of topography on time-mean stationary waves and low-frequency variability has been widely studied. In contrast, little attention has been given to the climatic feedbacks associated with stationary eddies. Furthermore, the relationship between stationary and transient eddies in the context of global and regional climate is not well understood. The response of the climate system to anthropogenic forcing is likely to have some dependence on stationary wave transport and its interaction with transient eddies. Some early GCM simulations and observational analyses indicate a strong feedback between the meridional heat fluxes of stationary and transient eddies

  5. Portfolio management using realized covariances: Evidence from Brazil

    Directory of Open Access Journals (Sweden)

    João F. Caldeira

    2017-09-01

    Full Text Available It is often argued that intraday returns can be used to construct covariance estimates that are more accurate than those based on daily returns. However, it is still unclear whether high frequency data provide more precise covariance estimates in markets more contaminated from microstructure noise such as higher bid-ask spreads and lower liquidity. We address this question by investigating the benefits of using high frequency data in the Brazilian equities market to construct optimal minimum variance portfolios. We implement alternative realized covariance estimators based on intraday returns sampled at alternative frequencies and obtain their dynamic versions using a multivariate GARCH framework. Our evidence based on a high-dimensional data set suggests that realized covariance estimators performed significantly better from an economic point of view in comparison to standard estimators based on low-frequency (close-to-close data as they delivered less risky portfolios. Resumo: Argumenta-se frequentemente que retornos intradiários podem ser usados para construir estimativas de covariâncias mais precisas em relação àquelas obtidas com retornos diários. No entanto, ainda não está claro se os dados de alta freqüência fornecem estimativas de covariância mais precisas em mercados mais contaminados pelo ruído da microestrutura, como maiores spreads entre ofertas de compra e venda e baixa liquidez. Abordamos essa questão investigando os benefícios do uso de dados de alta freqüência no mercado de ações brasileiro através da construção de portfólios ótimos de variância mínima. Implementamos diversos estimadores de covariâncias realizadas com base em retornos intradiários amostrados em diferentes frequências e obtemos suas versões dinâmicas usando uma estrutura GARCH multivariada. Nossa evidência baseada em um conjunto de dados de alta dimensão sugere que os estimadores de covariâncias realizadas obtiveram um desempenho

  6. Multifrequency eddy current testing of helical tubes of steam generators

    International Nuclear Information System (INIS)

    Pigeon, M.; David, B.

    1983-06-01

    In the event of a water-sodium reaction in a steam-generator of a fast breeder reactor, it is necessary to test the tubes close to the leak to evaluate the damage. In SUPERPHENIX, the tubes are about 100m long and are coiled on a dead body. This report describes the equipment and the technic to test such tubes with multifrequency eddy current technics [fr

  7. Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

    Directory of Open Access Journals (Sweden)

    K.-M. Erkkilä

    2018-01-01

    Full Text Available Freshwaters bring a notable contribution to the global carbon budget by emitting both carbon dioxide (CO2 and methane (CH4 to the atmosphere. Global estimates of freshwater emissions traditionally use a wind-speed-based gas transfer velocity, kCC (introduced by Cole and Caraco, 1998, for calculating diffusive flux with the boundary layer method (BLM. We compared CH4 and CO2 fluxes from BLM with kCC and two other gas transfer velocities (kTE and kHE, which include the effects of water-side cooling to the gas transfer besides shear-induced turbulence, with simultaneous eddy covariance (EC and floating chamber (FC fluxes during a 16-day measurement campaign in September 2014 at Lake Kuivajärvi in Finland. The measurements included both lake stratification and water column mixing periods. Results show that BLM fluxes were mainly lower than EC, with the more recent model kTE giving the best fit with EC fluxes, whereas FC measurements resulted in higher fluxes than simultaneous EC measurements. We highly recommend using up-to-date gas transfer models, instead of kCC, for better flux estimates. BLM CO2 flux measurements had clear differences between daytime and night-time fluxes with all gas transfer models during both stratified and mixing periods, whereas EC measurements did not show a diurnal behaviour in CO2 flux. CH4 flux had higher values in daytime than night-time during lake mixing period according to EC measurements, with highest fluxes detected just before sunset. In addition, we found clear differences in daytime and night-time concentration difference between the air and surface water for both CH4 and CO2. This might lead to biased flux estimates, if only daytime values are used in BLM upscaling and flux measurements in general. FC measurements did not detect spatial variation in either CH4 or CO2 flux over Lake Kuivajärvi. EC measurements, on the other hand, did not show any spatial variation in CH4 fluxes but did show a clear difference

  8. Eddy current analysis in fusion devices

    International Nuclear Information System (INIS)

    Turner, L.R.

    1988-06-01

    In magnetic fusion devices, particularly tokamaks and reversed field pinch (RFP) experiments, time-varying magnetic fields are in intimate contact with electrically conducting components of the device. Induced currents, fields, forces, and torques result. This note reviews the analysis of eddy current effects in the following systems: Interaction of a tokamak plasma with the eddy currents in the first wall, blanket, and shield (FWBS) systems; Eddy currents in a complex but two-dimensional vacuum vessel, as in TFTR, JET, and JT-60; Eddy currents in the FWBS system of a tokamak reactor, such as NET, FER, or ITER; and Eddy currents in a RFP shell. The cited studies are chosen to be illustrative, rather than exhaustive. 42 refs

  9. Carbon Dioxide and Water Vapor Concentrations, Co-spectra and Fluxes from Latest Standardized Automated CO2/H2O Flux Systems versus Established Analyzer Models

    Science.gov (United States)

    Burba, G. G.; Kathilankal, J. C.; Begashaw, I.; Franzen, D.; Welles, J.; McDermitt, D. K.

    2017-12-01

    Spatial and temporal flux data coverage have improved significantly in recent years, due to standardization, automation and management of data collection, and better handling of the generated data. With more stations and networks, larger data streams from each station, and smaller operating budgets, modern tools are required to effectively and efficiently handle the entire process.These tools should produce standardized verifiable datasets, and provide a way to cross-share the standardized data with external collaborators to leverage available funding, and promote data analyses and publications. In 2015, new open-path and enclosed flux measurement systems1 were developed, based on established gas analyzer models2,3, with the goal of improving stability in the presence of contamination, refining temperature control and compensation, and providing more accurate gas concentration measurements. In 2017, the new open-path system was further refined to simplify hardware configuration, and to reduce power consumption and cost. Additionally, all new systems incorporate complete automated on-site flux calculations using EddyPro® Software4 run by a weatherized remotely-accessible microcomputer to provide standardized traceable data sets for fluxes and supporting variables. This presentation will describe details and results from the field tests of the new flux systems, in comparison to older models and reference instruments. References:1 Burba G., W. Miller, I. Begashaw, G. Fratini, F. Griessbaum, J. Kathilankal, L. Xu, D. Franz, E. Joseph, E. Larmanou, S. Miller, D. Papale, S. Sabbatini, T. Sachs, R. Sakai, D. McDermitt, 2017. Comparison of CO2 Concentrations, Co-spectra and Flux Measurements between Latest Standardized Automated CO2/H2O Flux Systems and Older Gas Analysers. 10th ICDC Conference, Switzerland: 21-25/08 2 Metzger, S., G. Burba, S. Burns, P. Blanken, J. Li, H. Luo, R. Zulueta, 2016. Optimization of an enclosed gas analyzer sampling system for measuring eddy

  10. Progress on Nuclear Data Covariances: AFCI-1.2 Covariance Library

    International Nuclear Information System (INIS)

    Oblozinsky, P.; Oblozinsky, P.; Mattoon, C.M.; Herman, M.; Mughabghab, S.F.; Pigni, M.T.; Talou, P.; Hale, G.M.; Kahler, A.C.; Kawano, T.; Little, R.C.; Young, P.G

    2009-01-01

    Improved neutron cross section covariances were produced for 110 materials including 12 light nuclei (coolants and moderators), 78 structural materials and fission products, and 20 actinides. Improved covariances were organized into AFCI-1.2 covariance library in 33-energy groups, from 10 -5 eV to 19.6 MeV. BNL contributed improved covariance data for the following materials: 23 Na and 55 Mn where more detailed evaluation was done; improvements in major structural materials 52 Cr, 56 Fe and 58 Ni; improved estimates for remaining structural materials and fission products; improved covariances for 14 minor actinides, and estimates of mubar covariances for 23 Na and 56 Fe. LANL contributed improved covariance data for 235 U and 239 Pu including prompt neutron fission spectra and completely new evaluation for 240 Pu. New R-matrix evaluation for 16 O including mubar covariances is under completion. BNL assembled the library and performed basic testing using improved procedures including inspection of uncertainty and correlation plots for each material. The AFCI-1.2 library was released to ANL and INL in August 2009.

  11. Covariate selection for the semiparametric additive risk model

    DEFF Research Database (Denmark)

    Martinussen, Torben; Scheike, Thomas

    2009-01-01

    This paper considers covariate selection for the additive hazards model. This model is particularly simple to study theoretically and its practical implementation has several major advantages to the similar methodology for the proportional hazards model. One complication compared...... and study their large sample properties for the situation where the number of covariates p is smaller than the number of observations. We also show that the adaptive Lasso has the oracle property. In many practical situations, it is more relevant to tackle the situation with large p compared with the number...... of observations. We do this by studying the properties of the so-called Dantzig selector in the setting of the additive risk model. Specifically, we establish a bound on how close the solution is to a true sparse signal in the case where the number of covariates is large. In a simulation study, we also compare...

  12. Mobile Measurements of Methane Using High-Speed Open-Path Technology

    Science.gov (United States)

    Burba, G. G.; Anderson, T.; Ediger, K.; von Fischer, J.; Gioli, B.; Ham, J. M.; Hupp, J. R.; Kohnert, K.; Levy, P. E.; Polidori, A.; Pikelnaya, O.; Price, E.; Sachs, T.; Serafimovich, A.; Zondlo, M. A.; Zulueta, R. C.

    2016-12-01

    Methane plays a critical role in the radiation balance, chemistry of the atmosphere, and air quality. The major anthropogenic sources of CH4 include oil and gas development sites, natural gas distribution networks, landfill emissions, and agricultural production. The majority of oil and gas and urban CH4 emission occurs via variable-rate point sources or diffused spots in topographically challenging terrains (e.g., street tunnels, elevated locations at water treatment plants, vents, etc.). Locating and measuring such CH4 emissions is challenging when using traditional micrometeorological techniques, and requires development of novel approaches. Landfill CH4 emissions traditionally assessed at monthly or longer time intervals are subject to large uncertainties because of the snapshot nature of the measurements and the barometric pumping phenomenon. The majority of agricultural and natural CH4 production occurs in areas with little infrastructure or easily available grid power (e.g., rice fields, arctic and boreal wetlands, tropical mangroves, etc.). A lightweight, high-speed, high-resolution, open-path technology was recently developed for eddy covariance measurements of CH4 flux, with power consumption 30-150 times below other available technologies. It was designed to run on solar panels or a small generator and be placed in the middle of the methane-producing ecosystem without a need for grid power. Lately, this instrumentation has been utilized increasingly more frequently outside of the traditional use on stationary flux towers. These novel approaches include measurements from various moving platforms, such as cars, aircraft, and ships. Projects included mapping of concentrations and vertical profiles, leak detection and quantification, mobile emission detection from natural gas-powered cars, soil CH4 flux surveys, etc. This presentation will describe key projects utilizing the novel lightweight low-power high-resolution open-path technology, and will highlight

  13. Mechanism of seasonal eddy kinetic energy variability in the eastern equatorial Pacific Ocean

    Science.gov (United States)

    Wang, Minyang; Du, Yan; Qiu, Bo; Cheng, Xuhua; Luo, Yiyong; Chen, Xiao; Feng, Ming

    2017-04-01

    Enhanced mesoscale eddy activities or tropical instability waves (TIWs) exist along the northern front of the cold tongue in the eastern equatorial Pacific Ocean. In this study, we investigate seasonal variability of eddy kinetic energy (EKE) over this region and its associated dynamic mechanism using a global, eddy-resolving ocean general circulation model (OGCM) simulation, the equatorial mooring data, and satellite altimeter observations. The seasonal-varying enhanced EKE signals are found to expand westward from 100°W in June to 180°W in December between 0°N and 6°N. This westward expansion in EKE is closely connected to the barotropically-baroclinically unstable zonal flows that are in thermal-wind balance with the seasonal-varying thermocline trough along 4°N. By adopting an 1½-layer reduced-gravity model, we confirm that the seasonal perturbation of the thermocline trough is dominated by the anticyclonic wind stress curl forcing, which develops due to southerly winds along 4°N from June to December.

  14. Mesoscale Eddies in the Solomon Sea

    Science.gov (United States)

    Hristova, H. G.; Kessler, W. S.; McWilliams, J. C.; Molemaker, M. J.

    2011-12-01

    Water mass transformation in the strong equatorward flows through the Solomon Sea influences the properties of the Equatorial Undercurrent and subsequent cold tongue upwelling. High eddy activity in the interior Solomon Sea seen in altimetric sea surface height (SSH) and in several models may provide a mechanism for these transformations. We investigate these effects using a mesoscale (4-km resolution) sigma-coordinate (ROMS) model of the Solomon Sea nested in a basin solution, forced by a repeating seasonal cycle, and evaluated against observational data. The model generates a vigorous upper layer eddy field; some of these are apparently shed as the New Guinea Coastal Undercurrent threads through the complex topography of the region, others are independent of the strong western boundary current. We diagnose the scales and vertical structure of the eddies in different parts of the Solomon Sea to illuminate their generation processes and propagation characteristics, and compare these to observed eddy statistics. Hypotheses tested are that the Solomon Sea mesoscale eddies are generated locally by baroclinic instability, that the eddies are shed as the South Equatorial Current passes around and through the Solomon Island chain, that eddies are generated by the New Guinea Coastal Undercurrent, or that eddies occurring outside of the Solomon Sea propagate into the Solomon Sea. These different mechanisms have different implications for the resulting mixing and property fluxes. They also provide different interpretations for SSH signals observed from satellites (e.g., that will be observed by the upcoming SWOT satellite).

  15. Understanding the relationship between vegetation phenology and productivity across key dryland ecosystem types through the integration of PhenoCam, satellite, and eddy covariance data

    Science.gov (United States)

    Yan, D.; Scott, R. L.; Moore, D. J.; Biederman, J. A.; Smith, W. K.

    2017-12-01

    Land surface phenology (LSP) - defined as remotely sensed seasonal variations in vegetation greenness - is intrinsically linked to seasonal carbon uptake, and is thus commonly used as a proxy for vegetation productivity (gross primary productivity; GPP). Yet, the relationship between LSP and GPP remains uncertain, particularly for understudied dryland ecosystems characterized by relatively large spatial and temporal variability. Here, we explored the relationship between LSP and the phenology of GPP for three dominant dryland ecosystem types, and we evaluated how these relationships change as a function of spatial and temporal scale. We focused on three long-term dryland eddy covariance flux tower sites: Walnut Gulch Lucky Hills Shrubland (WHS), Walnut Gulch Kendall Grassland (WKG), and Santa Rita Mesquite (SRM). We analyzed daily canopy-level, 16-day 30m, and 8-day 500m time series of greenness indices from PhenoCam, Landsat 7 ETM+/Landsat 8 OLI, and MODIS, respectively. We first quantified the impact of spatial scale by temporally resampling canopy-level PhenoCam, 30m Landsat, and 500m MODIS to 16-day intervals and then comparing against flux tower GPP estimates. We next quantified the impact of temporal scale by spatially resampling daily PhenoCam, 16-day Landsat, and 8-day MODIS to 500m time series and then comparing against flux tower GPP estimates. We find evidence of critical periods of decoupling between LSP and the phenology of GPP that vary according to the spatial and temporal scale, and as a function of ecosystem type. Our results provide key insight into dryland LSP and GPP dynamics that can be used in future efforts to improve ecosystem process models and satellite-based vegetation productivity algorithms.

  16. Development of Multichannel Eddy Current Testing Instrument

    International Nuclear Information System (INIS)

    Lee, Hee Jong; Cho, Chan Hee; Nam, Min Woo; Yoon, Byung Sik; Yoo, Hyun Joo

    2010-01-01

    Four main techniques of electromagnetic testing are used for commercial applications: eddy current testing, alternating current field testing, magnetic flux leakage testing and remote field testing. Eddy current testing is a nondestructive evaluation method, which makes eddy current flow on a specimen by applying driving pulse to eddy current probe coil, by using eddy current testing device, and makes the change of eddy current which is dependently caused by flaws, material characteristics, testing condition, receiving through eddy current, and analyzes material properties, flaws, status on the specimen. Application of EC instrumentation varies widely in industry from the identification of metal heat treatment to the inspection of steam generator tubing in nuclear power plants. In this study, we have designed multichannel EC instrument which can be applicable to the NDE of the tube in heat exchanger for electric power facility, chemistry, and military industry, and finally confirmed the proper function of EC instrumentation

  17. Analytical modeling and analysis of magnetic field and torque for novel axial flux eddy current couplers with PM excitation

    Science.gov (United States)

    Li, Zhao; Wang, Dazhi; Zheng, Di; Yu, Linxin

    2017-10-01

    Rotational permanent magnet eddy current couplers are promising devices for torque and speed transmission without any mechanical contact. In this study, flux-concentration disk-type permanent magnet eddy current couplers with double conductor rotor are investigated. Given the drawback of the accurate three-dimensional finite element method, this paper proposes a mixed two-dimensional analytical modeling approach. Based on this approach, the closed-form expressions of magnetic field, eddy current, electromagnetic force and torque for such devices are obtained. Finally, a three-dimensional finite element method is employed to validate the analytical results. Besides, a prototype is manufactured and tested for the torque-speed characteristic.

  18. Eddy properties in the Southern California Current System

    Science.gov (United States)

    Chenillat, Fanny; Franks, Peter J. S.; Capet, Xavier; Rivière, Pascal; Grima, Nicolas; Blanke, Bruno; Combes, Vincent

    2018-05-01

    The California Current System (CCS) is an eastern boundary upwelling system characterized by strong eddies that are often generated at the coast. These eddies contribute to intense, long-distance cross-shelf transport of upwelled water with enhanced biological activity. However, the mechanisms of formation of such coastal eddies, and more importantly their capacity to trap and transport tracers, are poorly understood. Their unpredictability and strong dynamics leave us with an incomplete picture of the physical and biological processes at work, their effects on coastal export, lateral water exchange among eddies and their surrounding waters, and how long and how far these eddies remain coherent structures. Focusing our analysis on the southern part of the CCS, we find a predominance of cyclonic eddies, with a 25-km radius and a SSH amplitude of 6 cm. They are formed near shore and travel slightly northwest offshore for 190 days at 2 km day-1. We then study one particular, representative cyclonic eddy using a combined Lagrangian and Eulerian numerical approach to characterize its kinematics. Formed near shore, this eddy trapped a core made up of 67% California Current waters and 33% California Undercurrent waters. This core was surrounded by other waters while the eddy detached from the coast, leaving the oldest waters at the eddy's core and the younger waters toward the edge. The eddy traveled several months as a coherent structure, with only limited lateral exchange within the eddy.

  19. Path Integral Formulation of Anomalous Diffusion Processes

    OpenAIRE

    Friedrich, Rudolf; Eule, Stephan

    2011-01-01

    We present the path integral formulation of a broad class of generalized diffusion processes. Employing the path integral we derive exact expressions for the path probability densities and joint probability distributions for the class of processes under consideration. We show that Continuous Time Random Walks (CTRWs) are included in our framework. A closed expression for the path probability distribution of CTRWs is found in terms of their waiting time distribution as the solution of a Dyson ...

  20. Phenotypic covariance at species' borders.

    Science.gov (United States)

    Caley, M Julian; Cripps, Edward; Game, Edward T

    2013-05-28

    Understanding the evolution of species limits is important in ecology, evolution, and conservation biology. Despite its likely importance in the evolution of these limits, little is known about phenotypic covariance in geographically marginal populations, and the degree to which it constrains, or facilitates, responses to selection. We investigated phenotypic covariance in morphological traits at species' borders by comparing phenotypic covariance matrices (P), including the degree of shared structure, the distribution of strengths of pair-wise correlations between traits, the degree of morphological integration of traits, and the ranks of matricies, between central and marginal populations of three species-pairs of coral reef fishes. Greater structural differences in P were observed between populations close to range margins and conspecific populations toward range centres, than between pairs of conspecific populations that were both more centrally located within their ranges. Approximately 80% of all pair-wise trait correlations within populations were greater in the north, but these differences were unrelated to the position of the sampled population with respect to the geographic range of the species. Neither the degree of morphological integration, nor ranks of P, indicated greater evolutionary constraint at range edges. Characteristics of P observed here provide no support for constraint contributing to the formation of these species' borders, but may instead reflect structural change in P caused by selection or drift, and their potential to evolve in the future.

  1. DeepEddy : a simple deep architecture for mesoscale oceanic eddy detection in SAR images

    NARCIS (Netherlands)

    Huang, Dongmei; Du, Yanling; He, Qi; Song, Wei; Liotta, Antonio

    2017-01-01

    Automatic detection of mesoscale oceanic eddies is in great demand to monitor their dynamics which play a significant role in ocean current circulation and marine climate change. Traditional methods of eddies detection using remotely sensed data are usually based on physical parameters, geometrics,

  2. Eddy covariance flux measurements confirm extreme CH4 emissions from a Swiss hydropower reservoir and resolve their short-term variability

    Directory of Open Access Journals (Sweden)

    S. Sobek

    2011-09-01

    Full Text Available Greenhouse gas budgets quantified via land-surface eddy covariance (EC flux sites differ significantly from those obtained via inverse modeling. A possible reason for the discrepancy between methods may be our gap in quantitative knowledge of methane (CH4 fluxes. In this study we carried out EC flux measurements during two intensive campaigns in summer 2008 to quantify methane flux from a hydropower reservoir and link its temporal variability to environmental driving forces: water temperature and pressure changes (atmospheric and due to changes in lake level. Methane fluxes were extremely high and highly variable, but consistently showed gas efflux from the lake when the wind was approaching the EC sensors across the open water, as confirmed by floating chamber flux measurements. The average flux was 3.8 ± 0.4 μg C m−2 s−1 (mean ± SE with a median of 1.4 μg C m−2 s−1, which is quite high even compared to tropical reservoirs. Floating chamber fluxes from four selected days confirmed such high fluxes with 7.4 ± 1.3 μg C m−2 s−1. Fluxes increased exponentially with increasing temperatures, but were decreasing exponentially with increasing atmospheric and/or lake level pressure. A multiple regression using lake surface temperatures (0.1 m depth, temperature at depth (10 m deep in front of the dam, atmospheric pressure, and lake level was able to explain 35.4% of the overall variance. This best fit included each variable averaged over a 9-h moving window, plus the respective short-term residuals thereof. We estimate that an annual average of 3% of the particulate organic matter (POM input via the river is sufficient to sustain these large CH4 fluxes. To compensate the global warming potential associated with the CH4 effluxes from this hydropower reservoir a 1.3 to 3.7 times larger terrestrial area with net carbon dioxide uptake is needed if a European-scale compilation of grasslands, croplands and forests is taken as reference. This

  3. Closed Paths of Light Trapped in a Closed Fermat Curve

    Science.gov (United States)

    Dana-Picard, Thierry; Naiman, Aaron

    2002-01-01

    Geometric constructions have previously been shown that can be interpreted as rays of light trapped either in polygons or in conics, by successive reflections. The same question, trapping light in closed Fermat curves, is addressed here. Numerical methods are used to study the behaviour of the reflection points of a triangle when the degree of the…

  4. Does canopy mean N concentration explain differences in light use efficiency in 14 eddy-covariance sites?

    Science.gov (United States)

    Peltoniemi, Mikko; Pulkkinen, Minna; Kolari, Pasi; Mäkelä, Annikki

    2010-05-01

    Production efficiency models aim at explaining variation of vegetation productivity with climatic input and information on vegetation cover often obtained from satellite observations. It has been acknowledged that different plant species differ in their potential to assimilate carbon dioxide per unit of PAR (i.e light use efficiency, LUE). Subsequently, some LUE-based models apply different LUE-coefficients for different plant functional types. Leaf N concentrations differ between plant species, and related differences in light saturated photosynthesis rate (A_max) have been detected. How much these differences affect the ecosystem production or LUE is more obscure. Canopies acclimate to prevailing environmental conditions, which causes variation e.g. in the proportion of leaves exposed to direct sunlight, leaf morphology, structure,orientation, and vertical N distibution. Furthermore, a fair proportion of photosynthesis occurs during cloudy days, in which case high A_max is unessential, and number of these days differs by location. We studied if canopy mean N concentration could explain differences in LUE derived for 14 forest sites using eddy-covariance measurements. The largest actual LUE was estimated for each site directly as an upper percentile of the ratio of Gross Primary Production (GPP) to absorbed PAR. Potential LUE for each site, on the other hand, was estimated by parameterising a LUE-based production efficiency model (Prelued), which accounts for daily changes in weather (temperature, VPD, PAR). In this model structure, the LUE-parameter for each site, can be interpreted as the potential LUE under optimal environmental conditions, i.e when the environment is not limiting production at all. Averages of the largest actual LUE and potential LUE were higher in deciduous sites than in conifer sites. Canopy mean N correlated weakly with both the largest actual and potential LUE, and the correlation was also significant in conifer subset in the former case

  5. EddyOne automated analysis of PWR/WWER steam generator tubes eddy current data

    International Nuclear Information System (INIS)

    Nadinic, B.; Vanjak, Z.

    2004-01-01

    INETEC Institute for Nuclear Technology developed software package called Eddy One which has option of automated analysis of bobbin coil eddy current data. During its development and on site use, many valuable lessons were learned which are described in this article. In accordance with previous, the following topics are covered: General requirements for automated analysis of bobbin coil eddy current data; Main approaches to automated analysis; Multi rule algorithms for data screening; Landmark detection algorithms as prerequisite for automated analysis (threshold algorithms and algorithms based on neural network principles); Field experience with Eddy One software; Development directions (use of artificial intelligence with self learning abilities for indication detection and sizing); Automated analysis software qualification; Conclusions. Special emphasis is given on results obtained on different types of steam generators, condensers and heat exchangers. Such results are then compared with results obtained by other automated software vendors giving clear advantage to INETEC approach. It has to be pointed out that INETEC field experience was collected also on WWER steam generators what is for now unique experience.(author)

  6. Rapid Water Transport by Long-Lasting Modon Eddy Pairs in the Southern Midlatitude Oceans

    Science.gov (United States)

    Hughes, Chris W.; Miller, Peter I.

    2017-12-01

    Water in the ocean is generally carried with the mean flow, mixed by eddies, or transported westward by coherent eddies at speeds close to the long baroclinic Rossby wave speed. Modons (dipole eddy pairs) are a theoretically predicted exception to this behavior, which can carry water to the east or west at speeds much larger than the Rossby wave speed, leading to unusual transports of heat, nutrients, and carbon. We provide the first observational evidence of such rapidly moving modons propagating over large distances. These modons are found in the midlatitude oceans around Australia, with one also seen in the South Atlantic west of the Agulhas region. They can travel at more than 10 times the Rossby wave speed of 1-2 cm s-1 and typically persist for about 6 months carrying their unusual water mass properties with them, before splitting into individual vortices, which can persist for many months longer.

  7. Beamforming using subspace estimation from a diagonally averaged sample covariance.

    Science.gov (United States)

    Quijano, Jorge E; Zurk, Lisa M

    2017-08-01

    The potential benefit of a large-aperture sonar array for high resolution target localization is often challenged by the lack of sufficient data required for adaptive beamforming. This paper introduces a Toeplitz-constrained estimator of the clairvoyant signal covariance matrix corresponding to multiple far-field targets embedded in background isotropic noise. The estimator is obtained by averaging along subdiagonals of the sample covariance matrix, followed by covariance extrapolation using the method of maximum entropy. The sample covariance is computed from limited data snapshots, a situation commonly encountered with large-aperture arrays in environments characterized by short periods of local stationarity. Eigenvectors computed from the Toeplitz-constrained covariance are used to construct signal-subspace projector matrices, which are shown to reduce background noise and improve detection of closely spaced targets when applied to subspace beamforming. Monte Carlo simulations corresponding to increasing array aperture suggest convergence of the proposed projector to the clairvoyant signal projector, thereby outperforming the classic projector obtained from the sample eigenvectors. Beamforming performance of the proposed method is analyzed using simulated data, as well as experimental data from the Shallow Water Array Performance experiment.

  8. Contributions to Large Covariance and Inverse Covariance Matrices Estimation

    OpenAIRE

    Kang, Xiaoning

    2016-01-01

    Estimation of covariance matrix and its inverse is of great importance in multivariate statistics with broad applications such as dimension reduction, portfolio optimization, linear discriminant analysis and gene expression analysis. However, accurate estimation of covariance or inverse covariance matrices is challenging due to the positive definiteness constraint and large number of parameters, especially in the high-dimensional cases. In this thesis, I develop several approaches for estimat...

  9. A comparison of the structure, properties, and water mass composition of quasi-isotropic eddies in western boundary currents in an eddy-resolving ocean model

    Science.gov (United States)

    Rykova, Tatiana; Oke, Peter R.; Griffin, David A.

    2017-06-01

    Using output from a near-global eddy-resolving ocean model, we analyse the properties and characteristics of quasi-isotropic eddies in five Western Boundary Current (WBC) regions, including the extensions of the Agulhas, East Australian Current (EAC), Brazil-Malvinas Confluence (BMC), Kuroshio and Gulf Stream regions. We assess the model eddies by comparing to satellite and in situ observations, and show that most aspects of the model's representation of eddies are realistic. We find that the mean eddies differ dramatically between these WBC regions - all with some unique and noteworthy characteristics. We find that the vertical displacement of isopycnals of Agulhas eddies is the greatest, averaging 350-450 m at depths of over 800-900 m. EAC (BMC) eddies are the least (most) barotropic, with only 50% (85-90%) of the velocity associated with the barotropic mode. Kuroshio eddies are the most stratified, resulting in small isopycnal displacement, even for strong eddies; and Gulf Stream eddies carry the most heat. Despite their differences, we explicitly show that the source waters for anticyclonic eddies are a mix of the WBC water (from the boundary current itself) and water that originates equatorward of the WBC eddy-field; and cyclonic eddies are a mix of WBC water and water that originates poleward of the WBC eddy-field.

  10. Covariant Transform

    OpenAIRE

    Kisil, Vladimir V.

    2010-01-01

    The paper develops theory of covariant transform, which is inspired by the wavelet construction. It was observed that many interesting types of wavelets (or coherent states) arise from group representations which are not square integrable or vacuum vectors which are not admissible. Covariant transform extends an applicability of the popular wavelets construction to classic examples like the Hardy space H_2, Banach spaces, covariant functional calculus and many others. Keywords: Wavelets, cohe...

  11. Using machine learning to assess covariate balance in matching studies.

    Science.gov (United States)

    Linden, Ariel; Yarnold, Paul R

    2016-12-01

    In order to assess the effectiveness of matching approaches in observational studies, investigators typically present summary statistics for each observed pre-intervention covariate, with the objective of showing that matching reduces the difference in means (or proportions) between groups to as close to zero as possible. In this paper, we introduce a new approach to distinguish between study groups based on their distributions of the covariates using a machine-learning algorithm called optimal discriminant analysis (ODA). Assessing covariate balance using ODA as compared with the conventional method has several key advantages: the ability to ascertain how individuals self-select based on optimal (maximum-accuracy) cut-points on the covariates; the application to any variable metric and number of groups; its insensitivity to skewed data or outliers; and the use of accuracy measures that can be widely applied to all analyses. Moreover, ODA accepts analytic weights, thereby extending the assessment of covariate balance to any study design where weights are used for covariate adjustment. By comparing the two approaches using empirical data, we are able to demonstrate that using measures of classification accuracy as balance diagnostics produces highly consistent results to those obtained via the conventional approach (in our matched-pairs example, ODA revealed a weak statistically significant relationship not detected by the conventional approach). Thus, investigators should consider ODA as a robust complement, or perhaps alternative, to the conventional approach for assessing covariate balance in matching studies. © 2016 John Wiley & Sons, Ltd.

  12. Conditional Eddies in Plasma Turbulence

    DEFF Research Database (Denmark)

    Johnsen, Helene; Pécseli, Hans; Trulsen, J.

    1986-01-01

    Conditional structures, or eddies, in turbulent flows are discussed with special attention to electrostatic turbulence in plasmas. The potential variation of these eddies is obtained by sampling the fluctuations only when a certain condition is satisfied in a reference point. The resulting...

  13. Evaluating the relationships between solar-induced chlorophyll fluorescence from Orbiting Carbon Observatory-2 and gross primary productivity from eddy covariance flux towers

    Science.gov (United States)

    Li, X.; Xiao, J.; He, B.

    2017-12-01

    Solar-induced chlorophyll fluorescence (SIF) opens a new perspective on the monitoring of vegetation photosynthesis from space, and has been recently used to estimate gross primary productivity (GPP). However, previous studies on SIF were mainly based on satellite observations from the Greenhouse Gases Observing Satellite (GOSAT) and Global Ozone Monitoring Experiment-2 (GOME-2), and the evaluation of these coarse-resolution SIF measurements using GPP derived from eddy covariance (EC) flux towers has been hindered by the scale mismatch between satellite and tower footprints. We use new far-red SIF observations from the Orbiting Carbon Observatory-2 (OCO-2) satellite with much finer spatial resolution and GPP data from EC flux towers from 2014 to 2016 to examine the relationship between GPP and SIF for temperate forests. The OCO-2 SIF tracked tower GPP fairly well, and had strong correlation with tower GPP at both retrieval bands (757nm and 771nm) and both instantaneous (mid-day) and daily timescales. Daily SIF at 757nm (SIF757) exhibited much stronger correlation with tower GPP compared to MODIS enhanced vegetation index (EVI) and normalized difference vegetation index (NDVI) derived from either Terra or Aqua and had a similarly strong relationship as EVI based on the bidirectional reflectance distribution function (BRDF) corrected reflectance product (Terra+Aqua). Absorbed photosynthetically active radiation (APAR) explained 85% of the variance in SIF757, while the product of APAR and two environmental scalars - fTmin and fVPD (representing minimum temperature stress and water stress) explained slightly higher variance (92%) in SIF757. This suggests that SIF mainly depends on APAR and also contains information on light use efficiency (LUE) reflecting environmental stresses and physiological or biochemical variations of vegetation. The hyperbolic model based on SIF757 estimated GPP well (R2=0.81, pmodel - the MODSI GPP algorithm. Our findings demonstrate the strong

  14. Final Scientific/Technical Report. A closed path methane and water vapor gas analyzer

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Liukang [LI-COR Inc., Lincoln, NE (United States); McDermitt, Dayle [LI-COR Inc., Lincoln, NE (United States); Anderson, Tyler [LI-COR Inc., Lincoln, NE (United States); Riensche, Brad [LI-COR Inc., Lincoln, NE (United States); Komissarov, Anatoly [LI-COR Inc., Lincoln, NE (United States); Howe, Julie [LI-COR Inc., Lincoln, NE (United States)

    2012-02-01

    Robust, economical, low-power and reliable closed-path methane (CH4), carbon dioxide (CO2), and water vapor (H2O) analyzers suitable for long-term measurements are not readily available commercially. Such analyzers are essential for quantifying the amount of CH4 and CO2 released from various ecosystems (wetlands, rice paddies, forests, etc.) and other surface contexts (e.g. landfills, animal husbandry lots, etc.), and for understanding the dynamics of the atmospheric CH4 and CO2 budget and their impact on climate change and global warming. The purpose of this project is to develop a closed-path methane, carbon dioxide gas and water vapor analyzer capable of long-term measurements in remote areas for global climate change and environmental research. The analyzer will be capable of being deployed over a wide range of ecosystems to understand methane and carbon dioxide exchange between the atmosphere and the surface. Measurements of methane and carbon dioxide exchange need to be made all year-round with limited maintenance requirements. During this Phase II effort, we successfully completed the design of the electronics, optical bench, trace gas detection method and mechanical infrastructure. We are using the technologies of two vertical cavity surface emitting lasers, a multiple-pass Herriott optical cell, wavelength modulation spectroscopy and direct absorption to measure methane, carbon dioxide, and water vapor. We also have designed the instrument application software, Field Programmable Gate Array (FPGA), along with partial completion of the embedded software. The optical bench has been tested in a lab setting with very good results. Major sources of optical noise have been identified and through design, the optical noise floor is approaching -60dB. Both laser modules can be temperature controlled to help maximize the stability of the analyzer. Additionally, a piezo electric transducer has been

  15. Estimation of net ecosystem metabolism of seagrass meadows in the coastal waters of the East Sea and Black Sea using the noninvasive eddy covariance technique

    Science.gov (United States)

    Lee, Jae Seong; Kang, Dong-Jin; Hineva, Elitsa; Slabakova, Violeta; Todorova, Valentina; Park, Jiyoung; Cho, Jin-Hyung

    2017-06-01

    We measured the community-scale metabolism of seagrass meadows in Bulgaria (Byala [BY]) and Korea (Hoopo Bay [HP]) to understand their ecosystem function in coastal waters. A noninvasive in situ eddy covariance technique was applied to estimate net O2 flux in the seagrass meadows. From the high-quality and high-resolution time series O2 data acquired over > 24 h, the O2 flux driven by turbulence was extracted at 15-min intervals. The spectrum analysis of vertical flow velocity and O2 concentration clearly showed well-developed turbulence characteristics in the inertial subrange region. The hourly averaged net O2 fluxes per day ranged from -474 to 326 mmol O2 m-2 d-1 (-19 ± 41 mmol O2 m-2 d-1) at BY and from -74 to 482 mmol O2 m-2 d-1 (31 ± 17 mmol O2 m-2 d-1) at HP. The net O2 production rapidly responded to photosynthetically available radiation (PAR) and showed a good relationship between production and irradiance (P-I curve). The hysteresis pattern of P-I relationships during daytime also suggested increasing heterotrophic respiration in the afternoon. With the flow velocity between 3.30 and 6.70 cm s-1, the community metabolism during daytime and nighttime was significantly increased by 20 times and 5 times, respectively. The local hydrodynamic characteristics may be vital to determining the efficiency of community photosynthesis. The net ecosystem metabolism at BY was estimated to be -17 mmol O2 m-2 d-1, which was assessed as heterotrophy. However, that at HP was 36 mmol O2 m-2 d-1, which suggested an autotrophic state.

  16. Transmit-receive eddy current probes

    International Nuclear Information System (INIS)

    Obrutsky, L.S.; Sullivan, S.P.; Cecco, V.S.

    1997-01-01

    In the last two decades, due to increased inspection demands, eddy current instrumentation has advanced from single-frequency, single-output instruments to multifrequency, computer-aided systems. This has significantly increased the scope of eddy current testing, but, unfortunately, it has also increased the cost and complexity of inspections. In addition, this approach has not always improved defect detectability or signal-to-noise. Most eddy current testing applications are still performed with impedance probes, which have well known limitations. However, recent research at AECL has led to improved eddy current inspections through the design and development of transmit-receive (T/R) probes. T/R eddy current probes, with laterally displaced transmit and receive coils, present a number of advantages over impedance probes. They have improved signal-to-noise ratio in the presence of variable lift-off compared to impedance probes. They have strong directional properties, permitting probe optimization for circumferential or axial crack detection, and possess good phase discrimination to surface defects. They can significantly increase the scope of eddy current testing permitting reliable detection and sizing of cracks in heat exchanger tubing as well as in welded areas of both ferritic and non-ferromagnetic components. This presentation will describe the operating principles of T/R probes with the help of computer-derived normalized voltage diagrams. We will discuss their directional properties and analyze the advantages of using single and multiple T/R probes over impedance probes for specific inspection cases. Current applications to surface and tube testing and some typical inspection results will be described. (author)

  17. Recognizing limitations in eddy current testing

    International Nuclear Information System (INIS)

    Van Drunen, G.; Cecco, V.S.

    1981-11-01

    This paper addresses known limitations and constraints in eddy current nondestructive testing. Incomplete appreciation for eddy current limitations is believed to have contributed to both under-utilization and misapplication of the technique. Neither situation need arise if known limitations are recognized. Some, such as the skin depth effect, are inherent to electromagnetic test methods and define the role of eddy current testing. Others can be overcome with available technology such as surface probes to find circumferential cracks in tubes and magnetic saturation of ferromagnetic alloys to eliminate permeability effects. The variables responsible for limitations in eddy current testing are discussed and where alternative approaches exist, these are presented. Areas with potential for further research and development are also identified

  18. Eddy current damping for magnetic levitation: downscaling from macro- to micro-levitation

    International Nuclear Information System (INIS)

    Elbuken, C; Khamesee, M B; Yavuz, M

    2006-01-01

    Magnetic levitation of miniaturized objects is investigated in this paper. A magnetic levitation setup is built to implement one-dimensional magnetic levitation motion. It was observed that as the levitated object becomes smaller, magnetic levitation suffers more from undesired vibrations. As a solution, eddy current damping is offered and implemented successfully by placing conductive plates close to the levitated object. An analytical expression for damping coefficient is derived. Experimentally, it is shown that eddy current damping can reduce the RMS positioning error to the level of more than one third of its original value for a 0.386 g object levitated in an air-gap region of 290 mm. The proposed system has the potential to be used for micro-manipulation purposes in a high motion range of 39.8 mm

  19. Eddy current damping for magnetic levitation: downscaling from macro- to micro-levitation

    Energy Technology Data Exchange (ETDEWEB)

    Elbuken, C; Khamesee, M B; Yavuz, M [Department of Mechanical and Mechatronics Engineering, University of Waterloo, Ontario (Canada)

    2006-09-21

    Magnetic levitation of miniaturized objects is investigated in this paper. A magnetic levitation setup is built to implement one-dimensional magnetic levitation motion. It was observed that as the levitated object becomes smaller, magnetic levitation suffers more from undesired vibrations. As a solution, eddy current damping is offered and implemented successfully by placing conductive plates close to the levitated object. An analytical expression for damping coefficient is derived. Experimentally, it is shown that eddy current damping can reduce the RMS positioning error to the level of more than one third of its original value for a 0.386 g object levitated in an air-gap region of 290 mm. The proposed system has the potential to be used for micro-manipulation purposes in a high motion range of 39.8 mm.

  20. Wind Forced Variability in Eddy Formation, Eddy Shedding, and the Separation of the East Australian Current

    Science.gov (United States)

    Bull, Christopher Y. S.; Kiss, Andrew E.; Jourdain, Nicolas C.; England, Matthew H.; van Sebille, Erik

    2017-12-01

    The East Australian Current (EAC), like many other subtropical western boundary currents, is believed to be penetrating further poleward in recent decades. Previous observational and model studies have used steady state dynamics to relate changes in the westerly winds to changes in the separation behavior of the EAC. As yet, little work has been undertaken on the impact of forcing variability on the EAC and Tasman Sea circulation. Here using an eddy-permitting regional ocean model, we present a suite of simulations forced by the same time-mean fields, but with different atmospheric and remote ocean variability. These eddy-permitting results demonstrate the nonlinear response of the EAC to variable, nonstationary inhomogeneous forcing. These simulations show an EAC with high intrinsic variability and stochastic eddy shedding. We show that wind stress variability on time scales shorter than 56 days leads to increases in eddy shedding rates and southward eddy propagation, producing an increased transport and southward reach of the mean EAC extension. We adopt an energetics framework that shows the EAC extension changes to be coincident with an increase in offshore, upstream eddy variance (via increased barotropic instability) and increase in subsurface mean kinetic energy along the length of the EAC. The response of EAC separation to regional variable wind stress has important implications for both past and future climate change studies.

  1. Eddies off the Queen Charlotte Islands

    Science.gov (United States)

    2002-01-01

    The bright red, green, and turquoise patches to the west of British Columbia's Queen Charlotte Islands and Alaska's Alexander Archipelago highlight the presence of biological activity in the ocean. These colors indicate high concentrations of chlorophyll, the primary pigment found in phytoplankton. Notice that there are a number of eddies visible in the Pacific Ocean in this pseudo-color scene. The eddies are formed by strong outflow currents from rivers along North America's west coast that are rich in nutrients from the springtime snowmelt running off the mountains. This nutrient-rich water helps stimulate the phytoplankton blooms within the eddies. (For more details, read Tracking Eddies that Feed the Sea.) To the west of the eddies in the water, another type of eddy-this one in the atmosphere-forms the clouds into the counterclockwise spiral characteristic of a low pressure system in the Northern Hemisphere. (Click on the image above to see it at full resolution; or click to see the scene in true-color.) The snow-covered mountains of British Columbia are visible in the upper righthand corner of the image. This scene was constructed using SeaWiFS data collected on June 13, 2002. SeaWiFS image courtesy the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  2. Are your covariates under control? How normalization can re-introduce covariate effects.

    Science.gov (United States)

    Pain, Oliver; Dudbridge, Frank; Ronald, Angelica

    2018-04-30

    Many statistical tests rely on the assumption that the residuals of a model are normally distributed. Rank-based inverse normal transformation (INT) of the dependent variable is one of the most popular approaches to satisfy the normality assumption. When covariates are included in the analysis, a common approach is to first adjust for the covariates and then normalize the residuals. This study investigated the effect of regressing covariates against the dependent variable and then applying rank-based INT to the residuals. The correlation between the dependent variable and covariates at each stage of processing was assessed. An alternative approach was tested in which rank-based INT was applied to the dependent variable before regressing covariates. Analyses based on both simulated and real data examples demonstrated that applying rank-based INT to the dependent variable residuals after regressing out covariates re-introduces a linear correlation between the dependent variable and covariates, increasing type-I errors and reducing power. On the other hand, when rank-based INT was applied prior to controlling for covariate effects, residuals were normally distributed and linearly uncorrelated with covariates. This latter approach is therefore recommended in situations were normality of the dependent variable is required.

  3. Covariance evaluation system

    International Nuclear Information System (INIS)

    Kawano, Toshihiko; Shibata, Keiichi.

    1997-09-01

    A covariance evaluation system for the evaluated nuclear data library was established. The parameter estimation method and the least squares method with a spline function are used to generate the covariance data. Uncertainties of nuclear reaction model parameters are estimated from experimental data uncertainties, then the covariance of the evaluated cross sections is calculated by means of error propagation. Computer programs ELIESE-3, EGNASH4, ECIS, and CASTHY are used. Covariances of 238 U reaction cross sections were calculated with this system. (author)

  4. Study, design and manufacture eddy current probes for industry applications

    International Nuclear Information System (INIS)

    Nguyen Phuc; Nguyen Van Thuy; Vuong Binh Duong; Do Minh Duc; Trinh Dinh Truong; Tran Trong Duc; Do Tung Khanh; Dang Quang Trung

    2016-01-01

    This study is based on the studying, designing and manufacturing of eddy current probes for industry applications. The main tasks of this study include: i) Describes the overview and classification of eddy current probes (which can be classified into three categories based on the mode of operation: absolute eddy current probe, differential eddy current probe and reflect eddy current probe); ii) Describes the three methods of probe designing and manufacturing (including experimental, analytical and numerical designs); iii) Describes the designing and manufacturing of eddy current probes for industry applications, which based on experimental and analytical methods. Based on this study, we have successfully manufactured some current probes (including absolute eddy current probe, differential eddy current probe and reflect eddy current probe) for surface and tube inspections. (author)

  5. Workshops and problems for benchmarking eddy current codes

    International Nuclear Information System (INIS)

    Turner, L.R.; Davey, K.; Ida, N.; Rodger, D.; Kameari, A.; Bossavit, A.; Emson, C.R.I.

    1988-02-01

    A series of six workshops was held to compare eddy current codes, using six benchmark problems. The problems include transient and steady-state ac magnetic fields, close and far boundary conditions, magnetic and non-magnetic materials. All the problems are based either on experiments or on geometries that can be solved analytically. The workshops and solutions to the problems are described. Results show that many different methods and formulations give satisfactory solutions, and that in many cases reduced dimensionality or coarse discretization can give acceptable results while reducing the computer time required. 13 refs., 1 tab

  6. Eddy-Kuroshio Interactions: Local and Remote Effects

    Science.gov (United States)

    Jan, Sen; Mensah, Vigan; Andres, Magdalena; Chang, Ming-Huei; Yang, Yiing Jang

    2017-12-01

    Quasi-geostrophic mesoscale eddies regularly impinge on the Kuroshio in the western North Pacific, but the processes underlying the evolution of these eddy-Kuroshio interactions have not yet been thoroughly investigated in the literature. Here this interaction is examined with results from a semi-idealized three-dimensional numerical model and observations from four pressure-sensor equipped inverted echo sounders (PIESs) in a zonal section east of Taiwan and satellite altimeters. Both the observations and numerical simulations suggest that, during the interaction of a cyclonic eddy with the Kuroshio, the circular eddy is deformed into an elliptic shape with the major axis in the northwest-southeast direction, before being dissipated; the poleward velocity and associated Kuroshio transport decrease and the sea level and pycnocline slopes across the Kuroshio weaken. In contrast, for an anticyclonic eddy during the eddy-Kuroshio interaction, variations in the velocity, sea level, and isopycnal depth are reversed; the circular eddy is also deformed to an ellipse but with the major axis parallel to the Kuroshio. The model results also demonstrate that the velocity field is modified first and consequently the SSH and isopycnal depth evolve during the interaction. Furthermore, due to the combined effect of impingement latitude and realistic topography, some eddy-Kuroshio interactions east of Taiwan are found to have remote effects, both in the Luzon Strait and on the East China Sea shelf northeast of Taiwan.Plain Language SummaryMesoscale eddies are everywhere in the ocean. These ocean swirls of either clockwise or counterclockwise spinning with diameter of about 100-300 km and rounding current speed of about 0.5 m/s, carrying energy and certain type of water mass, move westward and eventually reach the western boundary of each ocean. The evolution of these eddies and the interaction which occurs when they encounter the western boundary current, e.g. the Kuroshio in the

  7. Performance of STICS model to predict rainfed corn evapotranspiration and biomass evaluated for 6 years between 1995 and 2006 using daily aggregated eddy covariance fluxes and ancillary measurements.

    Science.gov (United States)

    Pattey, Elizabeth; Jégo, Guillaume; Bourgeois, Gaétan

    2010-05-01

    Verifying the performance of process-based crop growth models to predict evapotranspiration and crop biomass is a key component of the adaptation of agricultural crop production to climate variations. STICS, developed by INRA, was part of the models selected by Agriculture and Agri-Food Canada to be implemented for environmental assessment studies on climate variations, because of its built-in ability to assimilate biophysical descriptors such as LAI derived from satellite imagery and its open architecture. The model prediction of shoot biomass was calibrated using destructive biomass measurements over one season, by adjusting six cultivar parameters and three generic plant parameters to define two grain corn cultivars adapted to the 1000-km long Mixedwood Plains ecozone. Its performance was then evaluated using a database of 40 years-sites of corn destructive biomass and yield. In this study we evaluate the temporal response of STICS evapotranspiration and biomass accumulation predictions against estimates using daily aggregated eddy covariance fluxes. The flux tower was located in an experimental farm south of Ottawa and measurements carried out over corn fields in 1995, 1996, 1998, 2000, 2002 and 2006. Daytime and nighttime fluxes were QC/QA and gap-filled separately. Soil respiration was partitioned to calculate the corn net daily CO2 uptake, which was converted into dry biomass. Out of the six growing seasons, three (1995, 1998, 2002) had water stress periods during corn grain filling. Year 2000 was cool and wet, while 1996 had heat and rainfall distributed evenly over the season and 2006 had a wet spring. STICS can predict evapotranspiration using either crop coefficients, when wind speed and air moisture are not available, or resistance. The first approach provided higher prediction for all the years than the resistance approach and the flux measurements. The dynamic of evapotranspiration prediction of STICS was very good for the growing seasons without

  8. On the algebraic structure of covariant anomalies and covariant Schwinger terms

    International Nuclear Information System (INIS)

    Kelnhofer, G.

    1992-01-01

    A cohomological characterization of covariant anomalies and covariant Schwinger terms in an anomalous Yang-Mills theory is formulated and w ill be geometrically interpreted. The BRS and anti-BRS transformations are defined as purely differential geometric objects. Finally the covariant descent equations are formulated within this context. (author)

  9. Eddies in the Red Sea: A statistical and dynamical study

    KAUST Repository

    Zhan, Peng

    2014-06-01

    Sea level anomaly (SLA) data spanning 1992–2012 were analyzed to study the statistical properties of eddies in the Red Sea. An algorithm that identifies winding angles was employed to detect 4998 eddies propagating along 938 unique eddy tracks. Statistics suggest that eddies are generated across the entire Red Sea but that they are prevalent in certain regions. A high number of eddies is found in the central basin between 18°N and 24°N. More than 87% of the detected eddies have a radius ranging from 50 to 135 km. Both the intensity and relative vorticity scale of these eddies decrease as the eddy radii increase. The averaged eddy lifespan is approximately 6 weeks. AEs and cyclonic eddies (CEs) have different deformation features, and those with stronger intensities are less deformed and more circular. Analysis of long-lived eddies suggests that they are likely to appear in the central basin with AEs tending to move northward. In addition, their eddy kinetic energy (EKE) increases gradually throughout their lifespans. The annual cycles of CEs and AEs differ, although both exhibit significant seasonal cycles of intensity with the winter and summer peaks appearing in February and August, respectively. The seasonal cycle of EKE is negatively correlated with stratification but positively correlated with vertical shear of horizontal velocity and eddy growth rate, suggesting that the generation of baroclinic instability is responsible for the activities of eddies in the Red Sea.

  10. Eddy current system for inspection of train hollow axles

    Energy Technology Data Exchange (ETDEWEB)

    Chady, Tomasz; Psuj, Grzegorz; Sikora, Ryszard; Kowalczyk, Jacek; Spychalski, Ireneusz [Department of Electrical and Computer Engineering, Faculty of Electrical Engineering, West Pomeranian University of Technology, Szczecin (Poland)

    2014-02-18

    The structural integrity of wheelsets used in rolling stock is of great importance to the safety. In this paper, electromagnetic system with an eddy current transducer suitable for the inspection of hollow axles have been presented. The transducer was developed to detect surface braking defects having depth not smaller than 0.5 mm. Ultrasound technique can be utilized to inspect the whole axle, but it is not sufficiently sensitive to shallow defects located close to the surface. Therefore, the electromagnetic technique is proposed to detect surface breaking cracks that cannot be detected by ultrasonic technique.

  11. Eddy current manual, volume 2

    International Nuclear Information System (INIS)

    Cecco, V.S.; Van Drunen, G.; Sharp, F.L.

    1984-09-01

    This report on eddy current testing is divided into three sections: (a) Demonstration of Basic Principles, (b) Practical (Laboratory) Tests and, (c) Typical Certification Questions. It is intended to be used as a supplement to ΣEddy Current Manual, Volume 1Σ (AECL-7523) during CSNDT Foundation Level II and III courses

  12. Eddy Current Flaw Characterization Using Neural Networks

    International Nuclear Information System (INIS)

    Song, S. J.; Park, H. J.; Shin, Y. K.

    1998-01-01

    Determination of location, shape and size of a flaw from its eddy current testing signal is one of the fundamental issues in eddy current nondestructive evaluation of steam generator tubes. Here, we propose an approach to this problem; an inversion of eddy current flaw signal using neural networks trained by finite element model-based synthetic signatures. Total 216 eddy current signals from four different types of axisymmetric flaws in tubes are generated by finite element models of which the accuracy is experimentally validated. From each simulated signature, total 24 eddy current features are extracted and among them 13 features are finally selected for flaw characterization. Based on these features, probabilistic neural networks discriminate flaws into four different types according to the location and the shape, and successively back propagation neural networks determine the size parameters of the discriminated flaw

  13. Eddy-induced salinity pattern in the North Pacific

    Science.gov (United States)

    Abe, H.; Ebuchi, N.; Ueno, H.; Ishiyama, H.; Matsumura, Y.

    2017-12-01

    This research examines spatio-temporal behavior of sea surface salinity (SSS) after intense rainfall events using observed data from Aquarius. Aquarius SSS in the North Pacific reveals one notable event in which SSS is locally freshened by intense rainfall. Although SSS pattern shortly after the rainfall reflects atmospheric pattern, its final form reflects ocean dynamic structure; an anticyclonic eddy. Since this anticyclonic eddy was located at SSS front created by precipitation, this eddy stirs the water in a clockwise direction. This eddy stirring was visible for several months. It is expected horizontal transport by mesoscale eddies would play significant role in determining upper ocean salinity structure.

  14. Purely geometric path integral for spin-foams

    International Nuclear Information System (INIS)

    Shirazi, Atousa Chaharsough; Engle, Jonathan

    2014-01-01

    Spin-foams are a proposal for defining the dynamics of loop quantum gravity via path integral. In order for a path integral to be at least formally equivalent to the corresponding canonical quantization, at each point in the space of histories it is important that the integrand have not only the correct phase—a topic of recent focus in spin-foams—but also the correct modulus, usually referred to as the measure factor. The correct measure factor descends from the Liouville measure on the reduced phase space, and its calculation is a task of canonical analysis. The covariant formulation of gravity from which spin-foams are derived is the Plebanski–Holst formulation, in which the basic variables are a Lorentz connection and a Lorentz-algebra valued 2-form, called the Plebanski 2-form. However, in the final spin-foam sum, one usually sums over only spins and intertwiners, which label eigenstates of the Plebanski 2-form alone. The spin-foam sum is therefore a discretized version of a Plebanski–Holst path integral in which only the Plebanski 2-form appears, and in which the connection degrees of freedom have been integrated out. We call this a purely geometric Plebanski–Holst path integral. In prior work in which one of the authors was involved, the measure factor for the Plebanski–Holst path integral with both connection and 2-form variables was calculated. Before one discretizes this measure and incorporates it into a spin-foam sum, however, one must integrate out the connection in order to obtain the purely geometric version of the path integral. To calculate this purely geometric path integral is the principal task of the present paper, and it is done in two independent ways. Background independence of the resulting path integral is discussed in the final section, and gauge-fixing is discussed in appendix B. (paper)

  15. New signal processing methods for the evaluation of eddy current NDT data

    International Nuclear Information System (INIS)

    Anon.

    1987-01-01

    Signal processing and pattern recognition methods play a crucial role in a number of areas associated with nondestructive evaluation. Defect characterization schemes often involve mapping the signal onto an appropriate feature domain and using pattern recognition techniques for classification. In addition, signal processing methods are also used to acquire, enhance, restore, and compress data. EPRI Project RP 2673-4 is concerned with developing new signal processing and pattern recognition techniques for evaluating eddy current signals. Efforts under this project have focused on three closely related areas. The thrust has been to: (1) develop a scheme to compress eddy current signals for the purposes of storing them in a compact form, (2) develop a robust clustering algorithm capable of discarding feature vectors that fall in the gray areas between clusters, and (3) investigate the feasibility of designing and developing a digital eddyscope

  16. 76 FR 59394 - Big Eddy-Knight Transmission Project

    Science.gov (United States)

    2011-09-26

    ... DEPARTMENT OF ENERGY Bonneville Power Administration Big Eddy-Knight Transmission Project AGENCY... Eddy-Knight Transmission Project in Wasco County, Oregon and Klickitat County, Washington. Construction of the Big Eddy-Knight Transmission Project will accommodate long-term firm transmission requests...

  17. Problems and limitations of eddy current tube inspection

    International Nuclear Information System (INIS)

    Ilham Mukriz Zainal Abidin; Khairul Anuar Mohd Salleh; Mohamed Hairul Hasmoni

    2003-01-01

    Incomplete appreciation of eddy current limitations has contributed to both under-utilization and misapplication of the technique. A brief review on the physical principle of eddy current is presented. Eddy current technique in identifying inhomogeneity in tested tubes is discussed, highlighting its limitation in distinguishing between real pit type defects and other mundane anomalies. The variables responsible for limitation in eddy current tube inspection are discussed and alternative approaches, where they exist, are suggested. (Author)

  18. Observations of near-inertial kinetic energy inside mesoscale eddies.

    Science.gov (United States)

    Garcia Gomez, B. I.; Pallas Sanz, E.; Candela, J.

    2016-02-01

    The near-nertial oscillations (NIOs), generated by the wind stress on the surface mixed layer, are the inertia gravity waves with the lowest frequency and the highest kinetic energy. NIOs are important because they drive vertical mixing in the interior ocean during wave breaking events. Although the interaction between NIOs and mesoescale eddies has been reported by several authors, these studies are mostly analytical and numerical, and only few observational studies have attempted to show the differences in near-inertial kinetic energy (KEi) between anticyclonic and cyclonic eddies. In this work the spatial structure of the KEi inside the mesoscale eddies is computed using daily satellite altimetry and observations of horizontal velocity from 30 moorings equipped with acoustic Doppler current profilers in the western Gulf of Mexico. Consistent to theory, the obtained four-year KEi-composites show two times more KEi inside the anticyclonic eddies than inside the cyclonic ones. The vertical cross-sections of the KEi-composites show that the KEi is mainly located near the surface and at the edge of the cyclonic eddies (positive vorticity), whereas the KEi in anticyclonic eddies (negative vorticity) is maximum in the eddy's center and near to the base of the eddy where the NIOs become more inertial, are trapped, and amplified. A relative maximum in the upper anticyclonic eddy is also observed. The cyclonic eddies present a maximum of KEi near to the surface at 70 m, while the maximum of KEi in the anticyclonic eddies occurs between 800 and 1000 m. It is also shown the dependence between the distribution and magnitude of the KEi and the eddy's characteristics such as radius, vorticity, and amplitude.

  19. Hosotani model in closed string theory

    International Nuclear Information System (INIS)

    Shiraishi, Kiyoshi.

    1988-11-01

    Hosotani mechanism in the closed string theory with current algebra symmetry is described by the (old covariant) operator method. We compare the gauge symmetry breaking mechanism in a string theory which has SU(2) symmetry with the one in an equivalent compactified closed string theory. We also investigate the difference between Hosotani mechanism and Higgs mechanism in closed string theories by calculation of a fourpoint amplitude of 'Higgs' bosons at tree level. (author)

  20. A class of covariate-dependent spatiotemporal covariance functions

    Science.gov (United States)

    Reich, Brian J; Eidsvik, Jo; Guindani, Michele; Nail, Amy J; Schmidt, Alexandra M.

    2014-01-01

    In geostatistics, it is common to model spatially distributed phenomena through an underlying stationary and isotropic spatial process. However, these assumptions are often untenable in practice because of the influence of local effects in the correlation structure. Therefore, it has been of prolonged interest in the literature to provide flexible and effective ways to model non-stationarity in the spatial effects. Arguably, due to the local nature of the problem, we might envision that the correlation structure would be highly dependent on local characteristics of the domain of study, namely the latitude, longitude and altitude of the observation sites, as well as other locally defined covariate information. In this work, we provide a flexible and computationally feasible way for allowing the correlation structure of the underlying processes to depend on local covariate information. We discuss the properties of the induced covariance functions and discuss methods to assess its dependence on local covariate information by means of a simulation study and the analysis of data observed at ozone-monitoring stations in the Southeast United States. PMID:24772199

  1. Eddy current testing, volume 1

    International Nuclear Information System (INIS)

    Cecco, V.S.; Van Drunen, G.; Sharp, F.L.

    1981-11-01

    This training and reference manual was assembled to provide those involved in eddy current testing with both the fundamental principles of the technique as well as the knowledge to deal with often complicated test results. A non-rigorous approach is used to simplify complex physical phenomena. Emphasis is placed on proper choice of test frequency and interpretation. Defect detection and diagnosis receive particular attention. Design and construction of probes are covered extensively since probes play a key role in eddy current testing. The advantages and limitations of various probe types are discussed. Electromagnetic theory, instrumentation, test methods and signal analysis are covered. Simplified derivations of probe response to test parameters are presented to develop a basic understanding of eddy current behaviour. Eddy current signals are presented on impedance plane diagrams throughout the manual since this is the most common display on modern, general purpose instruments. The use of 'phase leg' in signal analysis is covered in detail. To supplement theory, practical examples are presented to develop proficiency in performing inspections, and to illustrate how basic principles are applied to diagnose real signals

  2. Joint inversion of 3-PG using eddy-covariance and inventory plot measurements in temperate-maritime conifer forests: Uncertainty in transient carbon-balance responses to climate change

    Science.gov (United States)

    Hember, R. A.; Kurz, W. A.; Coops, N. C.; Black, T. A.

    2010-12-01

    Temperate-maritime forests of coastal British Columbia store large amounts of carbon (C) in soil, detritus, and trees. To better understand the sensitivity of these C stocks to climate variability, simulations were conducted using a hybrid version of the model, Physiological Principles Predicting Growth (3-PG), combined with algorithms from the Carbon Budget Model of the Canadian Forest Sector - version 3 (CBM-CFS3) to account for full ecosystem C dynamics. The model was optimized based on a combination of monthly CO2 and H2O flux measurements derived from three eddy-covariance systems and multi-annual stemwood growth (Gsw) and mortality (Msw) derived from 1300 permanent sample plots by means of Markov chain Monte Carlo sampling. The calibrated model serves as an unbiased estimator of stemwood C with enhanced precision over that of strictly-empirical models, minimized reliance on local prescriptions, and the flexibility to study impacts of environmental change on regional C stocks. We report the contribution of each dataset in identifying key physiological parameters and the posterior uncertainty in predictions of net ecosystem production (NEP). The calibrated model was used to spin up pre-industrial C pools and estimate the sensitivity of regional net carbon balance to a gradient of temperature changes, λ=ΔC/ΔT, during three 62-year harvest rotations, spanning 1949-2135. Simulations suggest that regional net primary production, tree mortality, and heterotrophic respiration all began increasing, while NEP began decreasing in response to warming following the 1976 shift in northeast-Pacific climate. We quantified the uncertainty of λ and how it was mediated by initial dead C, tree mortality, precipitation change, and the time horizon in which it was calculated.

  3. New data-driven estimation of terrestrial CO2 fluxes in Asia using a standardized database of eddy covariance measurements, remote sensing data, and support vector regression

    Science.gov (United States)

    Ichii, Kazuhito; Ueyama, Masahito; Kondo, Masayuki; Saigusa, Nobuko; Kim, Joon; Alberto, Ma. Carmelita; Ardö, Jonas; Euskirchen, Eugénie S.; Kang, Minseok; Hirano, Takashi; Joiner, Joanna; Kobayashi, Hideki; Marchesini, Luca Belelli; Merbold, Lutz; Miyata, Akira; Saitoh, Taku M.; Takagi, Kentaro; Varlagin, Andrej; Bret-Harte, M. Syndonia; Kitamura, Kenzo; Kosugi, Yoshiko; Kotani, Ayumi; Kumar, Kireet; Li, Sheng-Gong; Machimura, Takashi; Matsuura, Yojiro; Mizoguchi, Yasuko; Ohta, Takeshi; Mukherjee, Sandipan; Yanagi, Yuji; Yasuda, Yukio; Zhang, Yiping; Zhao, Fenghua

    2017-04-01

    The lack of a standardized database of eddy covariance observations has been an obstacle for data-driven estimation of terrestrial CO2 fluxes in Asia. In this study, we developed such a standardized database using 54 sites from various databases by applying consistent postprocessing for data-driven estimation of gross primary productivity (GPP) and net ecosystem CO2 exchange (NEE). Data-driven estimation was conducted by using a machine learning algorithm: support vector regression (SVR), with remote sensing data for 2000 to 2015 period. Site-level evaluation of the estimated CO2 fluxes shows that although performance varies in different vegetation and climate classifications, GPP and NEE at 8 days are reproduced (e.g., r2 = 0.73 and 0.42 for 8 day GPP and NEE). Evaluation of spatially estimated GPP with Global Ozone Monitoring Experiment 2 sensor-based Sun-induced chlorophyll fluorescence shows that monthly GPP variations at subcontinental scale were reproduced by SVR (r2 = 1.00, 0.94, 0.91, and 0.89 for Siberia, East Asia, South Asia, and Southeast Asia, respectively). Evaluation of spatially estimated NEE with net atmosphere-land CO2 fluxes of Greenhouse Gases Observing Satellite (GOSAT) Level 4A product shows that monthly variations of these data were consistent in Siberia and East Asia; meanwhile, inconsistency was found in South Asia and Southeast Asia. Furthermore, differences in the land CO2 fluxes from SVR-NEE and GOSAT Level 4A were partially explained by accounting for the differences in the definition of land CO2 fluxes. These data-driven estimates can provide a new opportunity to assess CO2 fluxes in Asia and evaluate and constrain terrestrial ecosystem models.

  4. Variation in agricultural CO2 fluxes during the growing season, collected from more than ten eddy covariance towers in the Mississippi Delta Region

    Science.gov (United States)

    Runkle, B.; Suvocarev, K.; Reba, M. L.; Novick, K. A.; White, P.; Anapalli, S.; Locke, M. A.; Rigby, J.; Bhattacharjee, J.

    2016-12-01

    Agriculture is unique as an anthropogenic activity that plays both a large role in carbon and water cycling and whose management activities provide a key opportunity for responses to climate change. It is therefore especially crucial to bring field observations into the modeling community, test remote sensing products, encourage policy debate, and enable carbon offsets markets that generate revenue and fund climate-smart activities. The accurate measurement of agricultural CO2 exchange - both primary productivity and ecosystem respiration - in concert with evapotranspiration provides crucial information on agro-ecosystem functioning and improves our predictive capacity for estimating the impacts of climate change. In this study we report field measurements from more than 10 eddy covariance towers in the Lower Mississippi River Basin taken during the summer months of 2016. Many towers, some recently deployed, are being aggregated into a regional network known as Delta-Flux, which will ultimately include 15-20 towers by 2017. Set in and around the Mississippi Delta Region within Louisiana, Arkansas, and Mississippi, the network will collect flux, micrometeorological, and crop yield data in order to construct estimates of regional CO2 exchange. These time-series data are gap-filled using statistical and process-based models to generate estimates of summer CO2 flux. The tower network is comprised of sites representing widespread agriculture production, including rice, cotton, corn, soybean, and sugarcane; intensively managed pine forest; and bottomland hardwood forest. Unique experimental production practices are represented in the network and include restricted water use, bioenergy, and by-product utilization. Several towers compose multi-field sites testing innovative irrigation or management practices. Current mapping of agricultural carbon exchange - based on land cover layers and fixed crop emission factors - suggests an unconstrained carbon flux estimate in this

  5. ENDF-6 File 30: Data covariances obtained from parameter covariances and sensitivities

    International Nuclear Information System (INIS)

    Muir, D.W.

    1989-01-01

    File 30 is provided as a means of describing the covariances of tabulated cross sections, multiplicities, and energy-angle distributions that result from propagating the covariances of a set of underlying parameters (for example, the input parameters of a nuclear-model code), using an evaluator-supplied set of parameter covariances and sensitivities. Whenever nuclear data are evaluated primarily through the application of nuclear models, the covariances of the resulting data can be described very adequately, and compactly, by specifying the covariance matrix for the underlying nuclear parameters, along with a set of sensitivity coefficients giving the rate of change of each nuclear datum of interest with respect to each of the model parameters. Although motivated primarily by these applications of nuclear theory, use of File 30 is not restricted to any one particular evaluation methodology. It can be used to describe data covariances of any origin, so long as they can be formally separated into a set of parameters with specified covariances and a set of data sensitivities

  6. Local eddy current measurements in pulsed fields

    Energy Technology Data Exchange (ETDEWEB)

    Espina-Hernandez, J.H. [SEPI-Electronica, ESIME-IPN, UPALM Edif. ' Z' . Zacatenco, Mexico DF 07738 (Mexico)], E-mail: jhespina@gmail.com; Groessinger, R. [Institute of Solid State Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, A-1040 Vienna (Austria); Hallen, J.M. [Departamento de Ingenieria Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico DF 07738 (Mexico)

    2008-07-15

    This work presents new eddy current measurements in pulsed fields. A commercial point pick-up coil is used to detect the induction signal along the radius of Cu and Al samples with cylindrical shape and diameters between 5 and 35 mm. Local eddy current measurements were performed on the surface of conducting materials due to the small dimensions of the coil. A simple electrical circuit, used as a model, is proposed to describe the local eddy current effect in pulsed fields. The proposed model allows to calculate the phase shift angle between the signal proportional to eddy currents and the applied external field in a pulsed field magnetometer.

  7. Eddy current seminar, 24-26 Mar 1986

    International Nuclear Information System (INIS)

    Emson, C.R.I.

    1986-06-01

    The paper concerns the Eddy Current Seminars, held at the Rutherford Appleton Laboratory, United Kingdom, March 1986. Twenty two papers were presented on eddy current phenomena, and two of the papers are indexed separately. The first deals with a finite difference scheme for time dependent eddy currents in Tokamaks, the second is an analysis of the FELIX experiments with cantilevered beams and hollow cylinders. (UK)

  8. Brownian distance covariance

    OpenAIRE

    Székely, Gábor J.; Rizzo, Maria L.

    2010-01-01

    Distance correlation is a new class of multivariate dependence coefficients applicable to random vectors of arbitrary and not necessarily equal dimension. Distance covariance and distance correlation are analogous to product-moment covariance and correlation, but generalize and extend these classical bivariate measures of dependence. Distance correlation characterizes independence: it is zero if and only if the random vectors are independent. The notion of covariance with...

  9. Leavitt path algebras

    CERN Document Server

    Abrams, Gene; Siles Molina, Mercedes

    2017-01-01

    This book offers a comprehensive introduction by three of the leading experts in the field, collecting fundamental results and open problems in a single volume. Since Leavitt path algebras were first defined in 2005, interest in these algebras has grown substantially, with ring theorists as well as researchers working in graph C*-algebras, group theory and symbolic dynamics attracted to the topic. Providing a historical perspective on the subject, the authors review existing arguments, establish new results, and outline the major themes and ring-theoretic concepts, such as the ideal structure, Z-grading and the close link between Leavitt path algebras and graph C*-algebras. The book also presents key lines of current research, including the Algebraic Kirchberg Phillips Question, various additional classification questions, and connections to noncommutative algebraic geometry. Leavitt Path Algebras will appeal to graduate students and researchers working in the field and related areas, such as C*-algebras and...

  10. A relaxed eddy accumulation system for measuring vertical fluxes of nitrous acid

    Directory of Open Access Journals (Sweden)

    X. Ren

    2011-10-01

    Full Text Available A relaxed eddy accumulation (REA system combined with a nitrous acid (HONO analyzer was developed to measure atmospheric HONO vertical fluxes. The system consists of three major components: (1 a fast-response sonic anemometer measuring both vertical wind velocity and air temperature, (2 a fast-response controlling unit separating air motions into updraft and downdraft samplers by the sign of vertical wind velocity, and (3 a highly sensitive HONO analyzer based on aqueous long path absorption photometry that measures HONO concentrations in the updrafts and downdrafts. A dynamic velocity threshold (±0.5σw, where σw is a standard deviation of the vertical wind velocity was used for valve switching determined by the running means and standard deviations of the vertical wind velocity. Using measured temperature as a tracer and the average values from two field deployments, the flux proportionality coefficient, β, was determined to be 0.42 ± 0.02, in good agreement with the theoretical estimation. The REA system was deployed in two ground-based field studies. In the California Research at the Nexus of Air Quality and Climate Change (CalNex study in Bakersfield, California in summer 2010, measured HONO fluxes appeared to be upward during the day and were close to zero at night. The upward HONO flux was highly correlated to the product of NO2 and solar radiation. During the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX 2009 at Blodgett Forest, California in July 2009, the overall HONO fluxes were small in magnitude and were close to zero. Causes for the different HONO fluxes in the two different environments are briefly discussed.

  11. Path probabilities of continuous time random walks

    International Nuclear Information System (INIS)

    Eule, Stephan; Friedrich, Rudolf

    2014-01-01

    Employing the path integral formulation of a broad class of anomalous diffusion processes, we derive the exact relations for the path probability densities of these processes. In particular, we obtain a closed analytical solution for the path probability distribution of a Continuous Time Random Walk (CTRW) process. This solution is given in terms of its waiting time distribution and short time propagator of the corresponding random walk as a solution of a Dyson equation. Applying our analytical solution we derive generalized Feynman–Kac formulae. (paper)

  12. Detection process of defects in a tube close to an adjacent element, especially in a heat exchanger

    International Nuclear Information System (INIS)

    Holt, A.E.; Wehrmeister, A.E.; Whaley, H.L.

    1978-01-01

    On-site process for obtaining, by Foucault currents, the indication of a defect in a tube close to an adjacent element masking the indication of the defect. It is characterized by the course of a reference tube with an eddy current sensor near a similar adjacent element in order to obtain an indication of reference eddy currents of the adjacent element first mentioned, the completion of a joint crossover of the above first mentioned tube so as to obtain a composite indication of eddy currents of the defect and of the adjacent element, and the generation of the indication by eddy currents of the defect by comparing the composite indication with the reference indication [fr

  13. Eddy current manual: v.1

    International Nuclear Information System (INIS)

    Cecco, V.S.; Van Drunen, G.; Sharp, F.L.

    1983-09-01

    This training and reference manual was assembled to provide those involved in eddy current testing with both the fundamental principles of the technique as well as the knowledge to deal with often complicated test results. A non-rigorous approach is used to simplify complex physical phenomena. Emphasis is placed on proper choice of test frequency and signal interpretation. Defect detection and diagnosis receive particular attention. Design and construction of probes are covered extensively since probes play a key role in eddy current testing. The advantages and limitations of various probe types are discussed. Electromagnetic theory, instrumentation, test methods and signal analysis are covered. Simplified derivations of probe response to test parameters are presented to develop a basic understanding of eddy current behaviour. Eddy current signals are presented on impedance plane diagrams throughout the manual since this is the most common display on modern, general purpose instruments. The use of Σphase lagΣ in signal analysis is covered in detail. To supplement theory, practical examples are presented to develop proficiency in performing inspections, and to illustrate how basic principles are applied to diagnose real signals

  14. Mesoscale eddies are oases for higher trophic marine life

    KAUST Repository

    Godø , Olav R.; Samuelsen, Annette; Macaulay, Gavin J.; Patel, Ruben; Hjø llo, Solfrid Sæ tre; Horne, John; Kaartvedt, Stein; Johannessen, Johnny A.

    2012-01-01

    Mesoscale eddies stimulate biological production in the ocean, but knowledge of energy transfers to higher trophic levels within eddies remains fragmented and not quantified. Increasing the knowledge base is constrained by the inability of traditional sampling methods to adequately sample biological processes at the spatio-temporal scales at which they occur. By combining satellite and acoustic observations over spatial scales of 10 s of km horizontally and 100 s of m vertically, supported by hydrographical and biological sampling we show that anticyclonic eddies shape distribution and density of marine life from the surface to bathyal depths. Fish feed along density structures of eddies, demonstrating that eddies catalyze energy transfer across trophic levels. Eddies create attractive pelagic habitats, analogous to oases in the desert, for higher trophic level aquatic organisms through enhanced 3-D motion that accumulates and redistributes biomass, contributing to overall bioproduction in the ocean. Integrating multidisciplinary observation methodologies promoted a new understanding of biophysical interaction in mesoscale eddies. Our findings emphasize the impact of eddies on the patchiness of biomass in the sea and demonstrate that they provide rich feeding habitat for higher trophic marine life. 2012 God et al.

  15. Mesoscale eddies are oases for higher trophic marine life

    KAUST Repository

    Godø, Olav R.

    2012-01-17

    Mesoscale eddies stimulate biological production in the ocean, but knowledge of energy transfers to higher trophic levels within eddies remains fragmented and not quantified. Increasing the knowledge base is constrained by the inability of traditional sampling methods to adequately sample biological processes at the spatio-temporal scales at which they occur. By combining satellite and acoustic observations over spatial scales of 10 s of km horizontally and 100 s of m vertically, supported by hydrographical and biological sampling we show that anticyclonic eddies shape distribution and density of marine life from the surface to bathyal depths. Fish feed along density structures of eddies, demonstrating that eddies catalyze energy transfer across trophic levels. Eddies create attractive pelagic habitats, analogous to oases in the desert, for higher trophic level aquatic organisms through enhanced 3-D motion that accumulates and redistributes biomass, contributing to overall bioproduction in the ocean. Integrating multidisciplinary observation methodologies promoted a new understanding of biophysical interaction in mesoscale eddies. Our findings emphasize the impact of eddies on the patchiness of biomass in the sea and demonstrate that they provide rich feeding habitat for higher trophic marine life. 2012 God et al.

  16. Mesoscale eddies are oases for higher trophic marine life.

    Directory of Open Access Journals (Sweden)

    Olav R Godø

    Full Text Available Mesoscale eddies stimulate biological production in the ocean, but knowledge of energy transfers to higher trophic levels within eddies remains fragmented and not quantified. Increasing the knowledge base is constrained by the inability of traditional sampling methods to adequately sample biological processes at the spatio-temporal scales at which they occur. By combining satellite and acoustic observations over spatial scales of 10 s of km horizontally and 100 s of m vertically, supported by hydrographical and biological sampling we show that anticyclonic eddies shape distribution and density of marine life from the surface to bathyal depths. Fish feed along density structures of eddies, demonstrating that eddies catalyze energy transfer across trophic levels. Eddies create attractive pelagic habitats, analogous to oases in the desert, for higher trophic level aquatic organisms through enhanced 3-D motion that accumulates and redistributes biomass, contributing to overall bioproduction in the ocean. Integrating multidisciplinary observation methodologies promoted a new understanding of biophysical interaction in mesoscale eddies. Our findings emphasize the impact of eddies on the patchiness of biomass in the sea and demonstrate that they provide rich feeding habitat for higher trophic marine life.

  17. Scaling relations for eddy current phenomena

    International Nuclear Information System (INIS)

    Dodd, C.V.; Deeds, W.E.

    1975-11-01

    Formulas are given for various electromagnetic quantities for coils in the presence of conductors, with the scaling parameters factored out so that small-scale model experiments can be related to large-scale apparatus. Particular emphasis is given to such quantities as eddy current heating, forces, power, and induced magnetic fields. For axially symmetric problems, closed-form integrals are available for the vector potential and all the other quantities obtainable from it. For unsymmetrical problems, a three-dimensional relaxation program can be used to obtain the vector potential and then the derivable quantities. Data on experimental measurements are given to verify the validity of the scaling laws for forces, inductances, and impedances. Indirectly these also support the validity of the scaling of the vector potential and all of the other quantities obtained from it

  18. Covariant representations of nuclear *-algebras

    International Nuclear Information System (INIS)

    Moore, S.M.

    1978-01-01

    Extensions of the Csup(*)-algebra theory for covariant representations to nuclear *-algebra are considered. Irreducible covariant representations are essentially unique, an invariant state produces a covariant representation with stable vacuum, and the usual relation between ergodic states and covariant representations holds. There exist construction and decomposition theorems and a possible relation between derivations and covariant representations

  19. Large-eddy simulation of ethanol spray combustion using a finite-rate combustion model

    Energy Technology Data Exchange (ETDEWEB)

    Li, K.; Zhou, L.X. [Tsinghua Univ., Beijing (China). Dept. of Engineering Mechanics; Chan, C.K. [Hong Kong Polytechnic Univ. (China). Dept. of Applied Mathematics

    2013-07-01

    Large-eddy simulation of spray combustion is under its rapid development, but the combustion models are less validated by detailed experimental data. In this paper, large-eddy simulation of ethanol-air spray combustion was made using an Eulerian-Lagrangian approach, a subgrid-scale kinetic energy stress model, and a finite-rate combustion model. The simulation results are validated in detail by experiments. The LES obtained statistically averaged temperature is in agreement with the experimental results in most regions. The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map, indicating the droplets are concentrated in this shear region. The droplet sizes are found to be in the range of 20-100{mu}m. The instantaneous temperature map shows the close interaction between the coherent structures and the combustion reaction.

  20. Earth Observing System Covariance Realism

    Science.gov (United States)

    Zaidi, Waqar H.; Hejduk, Matthew D.

    2016-01-01

    The purpose of covariance realism is to properly size a primary object's covariance in order to add validity to the calculation of the probability of collision. The covariance realism technique in this paper consists of three parts: collection/calculation of definitive state estimates through orbit determination, calculation of covariance realism test statistics at each covariance propagation point, and proper assessment of those test statistics. An empirical cumulative distribution function (ECDF) Goodness-of-Fit (GOF) method is employed to determine if a covariance is properly sized by comparing the empirical distribution of Mahalanobis distance calculations to the hypothesized parent 3-DoF chi-squared distribution. To realistically size a covariance for collision probability calculations, this study uses a state noise compensation algorithm that adds process noise to the definitive epoch covariance to account for uncertainty in the force model. Process noise is added until the GOF tests pass a group significance level threshold. The results of this study indicate that when outliers attributed to persistently high or extreme levels of solar activity are removed, the aforementioned covariance realism compensation method produces a tuned covariance with up to 80 to 90% of the covariance propagation timespan passing (against a 60% minimum passing threshold) the GOF tests-a quite satisfactory and useful result.

  1. Eddy current testing with high penetration

    International Nuclear Information System (INIS)

    Becker, R.; Kroening, M.

    1999-01-01

    The low-frequency eddy current testing method is used when penetration into very deep layers is required. The achievable penetration depth is determined among other parameters by the lowest testing frequency that can be realised together with the eddy current sensor. When using inductive sensors, the measuring effect declines proportional to the lowering frequency (induction effect). Further reduction of testing frequency requires other types of sensors, as e.g. the GMR (Giant Magnetic Resistance), which achieves a constant measuring sensitivity down to the steady field. The multi-frequency eddy current testing method MFEC 3 of IZFP described here can be operated using three different scanning frequencies at a time. Two variants of eddy current probes are used in this case. Both have an inductive winding at their emitters, of the type of a measuring probe. The receiver end is either also an inductive winding, or a magnetic field-responsive resistance (GMR). (orig./CB) [de

  2. Thin film eddy current impulse deicer

    Science.gov (United States)

    Smith, Samuel O.; Zieve, Peter B.

    1990-01-01

    Two new styles of electrical impulse deicers has been developed and tested in NASA's Icing Research Tunnel. With the Eddy Current Repulsion Deicing Boot (EDB), a thin and flexible spiral coil is encapsulated between two thicknesses of elastomer. The coil, made by an industrial printed circuit board manufacturer, is bonded to the aluminum aircraft leading edge. A capacitor bank is discharged through the coil. Induced eddy currents repel the coil from the aluminum aircraft structure and shed accumulated ice. A second configuration, the Eddy Current Repulsion Deicing-Strip (EDS) uses an outer metal erosion strip fastened over the coil. Opposite flowing eddy currents repel the strip and create the impulse deicing force. The outer strip serves as a surface for the collection and shedding of ice and does not require any structural properties. The EDS is suitable for composite aircraft structures. Both systems successfully dispelled over 95 percent of the accumulated ice from airfoils over the range of the FAA icing envelope.

  3. Path integral representations on the complex sphere

    International Nuclear Information System (INIS)

    Grosche, C.

    2007-08-01

    In this paper we discuss the path integral representations for the coordinate systems on the complex sphere S 3C . The Schroedinger equation, respectively the path integral, separates in exactly 21 orthogonal coordinate systems. We enumerate these coordinate systems and we are able to present the path integral representations explicitly in the majority of the cases. In each solution the expansion into the wave-functions is stated. Also, the kernel and the corresponding Green function can be stated in closed form in terms of the invariant distance on the sphere, respectively on the hyperboloid. (orig.)

  4. Remote field eddy current testing

    International Nuclear Information System (INIS)

    Cheong, Y. M.; Jung, H. K.; Huh, H.; Lee, Y. S.; Shim, C. M.

    2001-03-01

    The state-of-art technology of the remote field eddy current, which is actively developed as an electromagnetic non-destructive testing tool for ferromagnetic tubes, is described. The historical background and recent R and D activities of remote-field eddy current technology are explained including the theoretical development of remote field eddy current, such as analytical and numerical approach, and the results of finite element analysis. The influencing factors for actual applications, such as the effect of frequency, magnetic permeability, receiving sensitivity, and difficulties of detection and classification of defects are also described. Finally, two examples of actual application, 1) the gap measurement between pressure tubes and calandria tube in CANDU reactor and, 2) the detection of defects in the ferromagnetic heat exchanger tubes, are described. The future research efforts are also included

  5. Visualization and analysis of eddies in a global ocean simulation

    Energy Technology Data Exchange (ETDEWEB)

    Williams, Sean J [Los Alamos National Laboratory; Hecht, Matthew W [Los Alamos National Laboratory; Petersen, Mark [Los Alamos National Laboratory; Strelitz, Richard [Los Alamos National Laboratory; Maltrud, Mathew E [Los Alamos National Laboratory; Ahrens, James P [Los Alamos National Laboratory; Hlawitschka, Mario [UC DAVIS; Hamann, Bernd [UC DAVIS

    2010-10-15

    Eddies at a scale of approximately one hundred kilometers have been shown to be surprisingly important to understanding large-scale transport of heat and nutrients in the ocean. Due to difficulties in observing the ocean directly, the behavior of eddies below the surface is not very well understood. To fill this gap, we employ a high-resolution simulation of the ocean developed at Los Alamos National Laboratory. Using large-scale parallel visualization and analysis tools, we produce three-dimensional images of ocean eddies, and also generate a census of eddy distribution and shape averaged over multiple simulation time steps, resulting in a world map of eddy characteristics. As expected from observational studies, our census reveals a higher concentration of eddies at the mid-latitudes than the equator. Our analysis further shows that mid-latitude eddies are thicker, within a range of 1000-2000m, while equatorial eddies are less than 100m thick.

  6. Spreading paths in partially observed social networks

    Science.gov (United States)

    Onnela, Jukka-Pekka; Christakis, Nicholas A.

    2012-03-01

    Understanding how and how far information, behaviors, or pathogens spread in social networks is an important problem, having implications for both predicting the size of epidemics, as well as for planning effective interventions. There are, however, two main challenges for inferring spreading paths in real-world networks. One is the practical difficulty of observing a dynamic process on a network, and the other is the typical constraint of only partially observing a network. Using static, structurally realistic social networks as platforms for simulations, we juxtapose three distinct paths: (1) the stochastic path taken by a simulated spreading process from source to target; (2) the topologically shortest path in the fully observed network, and hence the single most likely stochastic path, between the two nodes; and (3) the topologically shortest path in a partially observed network. In a sampled network, how closely does the partially observed shortest path (3) emulate the unobserved spreading path (1)? Although partial observation inflates the length of the shortest path, the stochastic nature of the spreading process also frequently derails the dynamic path from the shortest path. We find that the partially observed shortest path does not necessarily give an inflated estimate of the length of the process path; in fact, partial observation may, counterintuitively, make the path seem shorter than it actually is.

  7. Spreading paths in partially observed social networks.

    Science.gov (United States)

    Onnela, Jukka-Pekka; Christakis, Nicholas A

    2012-03-01

    Understanding how and how far information, behaviors, or pathogens spread in social networks is an important problem, having implications for both predicting the size of epidemics, as well as for planning effective interventions. There are, however, two main challenges for inferring spreading paths in real-world networks. One is the practical difficulty of observing a dynamic process on a network, and the other is the typical constraint of only partially observing a network. Using static, structurally realistic social networks as platforms for simulations, we juxtapose three distinct paths: (1) the stochastic path taken by a simulated spreading process from source to target; (2) the topologically shortest path in the fully observed network, and hence the single most likely stochastic path, between the two nodes; and (3) the topologically shortest path in a partially observed network. In a sampled network, how closely does the partially observed shortest path (3) emulate the unobserved spreading path (1)? Although partial observation inflates the length of the shortest path, the stochastic nature of the spreading process also frequently derails the dynamic path from the shortest path. We find that the partially observed shortest path does not necessarily give an inflated estimate of the length of the process path; in fact, partial observation may, counterintuitively, make the path seem shorter than it actually is.

  8. Eddy Current Assessment of Engineered Components Containing Nanofibers

    Science.gov (United States)

    Ko, Ray T.; Hoppe, Wally; Pierce, Jenny

    2009-03-01

    The eddy current approach has been used to assess engineered components containing nanofibers. Five specimens with different programmed defects were fabricated. A 4-point collinear probe was used to verify the electrical resistivity of each specimen. The liftoff component of the eddy current signal was used to test two extreme cases with different nano contents. Additional eddy current measurements were also used in detecting a missing nano layer simulating a manufacturing process error. The results of this assessment suggest that eddy current liftoff measurement can be a useful tool in evaluating the electrical properties of materials containing nanofibers.

  9. Some observations on interpolating gauges and non-covariant gauges

    International Nuclear Information System (INIS)

    Joglekar, Satish D.

    2003-01-01

    We discuss the viability of using interpolating gauges to define the non-covariant gauges starting from the covariant ones. We draw attention to the need for a very careful treatment of boundary condition defining term. We show that the boundary condition needed to maintain gauge invariance as the interpolating parameter θ varies, depends very sensitively on the parameter variation. We do this with a gauge used by Doust. We also consider the Lagrangian path-integrals in Minkowski space for gauges with a residual gauge-invariance. We point out the necessity of inclusion of an ε-term (even) in the formal treatments, without which one may reach incorrect conclusions. We, further, point out that the ε-term can contribute to the BRST WT-identities in a non-trivial way (even as ε → 0). We point out that these contributions lead to additional constraints on Green's function that are not normally taken into account in the BRST formalism that ignores the ε-term, and that they are characteristic of the way the singularities in propagators are handled. We argue that a prescription, in general, will require renormalization; if at all it is to be viable. (author)

  10. Pedigree-based estimation of covariance between dominance deviations and additive genetic effects in closed rabbit lines considering inbreeding and using a computationally simpler equivalent model.

    Science.gov (United States)

    Fernández, E N; Legarra, A; Martínez, R; Sánchez, J P; Baselga, M

    2017-06-01

    Inbreeding generates covariances between additive and dominance effects (breeding values and dominance deviations). In this work, we developed and applied models for estimation of dominance and additive genetic variances and their covariance, a model that we call "full dominance," from pedigree and phenotypic data. Estimates with this model such as presented here are very scarce both in livestock and in wild genetics. First, we estimated pedigree-based condensed probabilities of identity using recursion. Second, we developed an equivalent linear model in which variance components can be estimated using closed-form algorithms such as REML or Gibbs sampling and existing software. Third, we present a new method to refer the estimated variance components to meaningful parameters in a particular population, i.e., final partially inbred generations as opposed to outbred base populations. We applied these developments to three closed rabbit lines (A, V and H) selected for number of weaned at the Polytechnic University of Valencia. Pedigree and phenotypes are complete and span 43, 39 and 14 generations, respectively. Estimates of broad-sense heritability are 0.07, 0.07 and 0.05 at the base versus 0.07, 0.07 and 0.09 in the final generations. Narrow-sense heritability estimates are 0.06, 0.06 and 0.02 at the base versus 0.04, 0.04 and 0.01 at the final generations. There is also a reduction in the genotypic variance due to the negative additive-dominance correlation. Thus, the contribution of dominance variation is fairly large and increases with inbreeding and (over)compensates for the loss in additive variation. In addition, estimates of the additive-dominance correlation are -0.37, -0.31 and 0.00, in agreement with the few published estimates and theoretical considerations. © 2017 Blackwell Verlag GmbH.

  11. GEM: a dynamic tracking model for mesoscale eddies in the ocean

    Science.gov (United States)

    Li, Qiu-Yang; Sun, Liang; Lin, Sheng-Fu

    2016-12-01

    The Genealogical Evolution Model (GEM) presented here is an efficient logical model used to track dynamic evolution of mesoscale eddies in the ocean. It can distinguish between different dynamic processes (e.g., merging and splitting) within a dynamic evolution pattern, which is difficult to accomplish using other tracking methods. To this end, the GEM first uses a two-dimensional (2-D) similarity vector (i.e., a pair of ratios of overlap area between two eddies to the area of each eddy) rather than a scalar to measure the similarity between eddies, which effectively solves the "missing eddy" problem (temporarily lost eddy in tracking). Second, for tracking when an eddy splits, the GEM uses both "parent" (the original eddy) and "child" (eddy split from parent) and the dynamic processes are described as the birth and death of different generations. Additionally, a new look-ahead approach with selection rules effectively simplifies computation and recording. All of the computational steps are linear and do not include iteration. Given the pixel number of the target region L, the maximum number of eddies M, the number N of look-ahead time steps, and the total number of time steps T, the total computer time is O(LM(N + 1)T). The tracking of each eddy is very smooth because we require that the snapshots of each eddy on adjacent days overlap one another. Although eddy splitting or merging is ubiquitous in the ocean, they have different geographic distributions in the North Pacific Ocean. Both the merging and splitting rates of the eddies are high, especially at the western boundary, in currents and in "eddy deserts". The GEM is useful not only for satellite-based observational data, but also for numerical simulation outputs. It is potentially useful for studying dynamic processes in other related fields, e.g., the dynamics of cyclones in meteorology.

  12. Obituary: John Allen Eddy (1931-2009)

    Science.gov (United States)

    Gingerich, Owen

    2011-12-01

    Jack Eddy, who was born 25 March 1931 in Pawnee City in southeastern Nebraska, died after a long battle with cancer in Tucson, Arizona, on 10 June 2009. Best known for his work on the long-term instability of the sun, described in a landmark paper in Science titled "The Maunder Minimum," he also deserves recognition as one of the triumvirate who founded the Historical Astronomy Division of the AAS. His father ran a cooperative farm store where Jack worked as a teenager; his parents were of modest means and there were concerns whether he could afford college, but one of the state senators, also from Pawnee City, nominated him for the U.S. Naval Academy. A course in celestial navigation gave him a love of the sky. After graduation in 1953, he served four years on aircraft carriers in the Pacific during the Korean War and then as a navigator and operations officer on a destroyer in the Persian Gulf. In 1957, he left the Navy and entered graduate school at the University of Colorado in Boulder, where in 1962 he received a Ph.D. in astro-geophysics. His thesis, supervised by Gordon Newkirk, dealt with light scattering in the upper atmosphere, based on data from stratospheric balloon flights. He then worked as teacher and researcher at the High Altitude Observatory in Boulder. Always adventuresome and willing to explore new frontiers, on his own time Eddy examined an Amerindian stone circle in the Big Horn mountains of Wyoming, a so-called medicine wheel, concluding that there were alignments with both the solstitial sun and Aldebaran. His conjectures became a cover story on Science magazine in June of 1974. In 1971 Jack privately reproduced for his friends a small collection of his own hilarious cartoons titled "Job Opportunities for Out-of-work Astronomers," with an abstract beginning, "Contrary to popular belief, a PhD in Astronomy/Astrophysics need not be a drawback in locating work in this decade." For example, under merchandising, a used car salesman advertises

  13. Subregional characterization of mesoscale eddies across the Brazil-Malvinas Confluence

    Science.gov (United States)

    Mason, Evan; Pascual, Ananda; Gaube, Peter; Ruiz, Simón; Pelegrí, Josep L.; Delepoulle, Antoine

    2017-04-01

    Horizontal and vertical motions associated with coherent mesoscale structures, including eddies and meanders, are responsible for significant global transports of many properties, including heat and mass. Mesoscale vertical fluxes also influence upper ocean biological productivity by mediating the supply of nutrients into the euphotic layer, with potential impacts on the global carbon cycle. The Brazil-Malvinas Confluence (BMC) is a western boundary current region in the South Atlantic with intense mesoscale activity. This region has an active role in the genesis and transformation of water masses and thus is a critical component of the Atlantic meridional overturning circulation. The collision between the Malvinas and Brazil Currents over the Patagonian shelf/slope creates an energetic front that translates offshore to form a vigorous eddy field. Recent improvements in gridded altimetric sea level anomaly fields allow us to track BMC mesoscale eddies with high spatial and temporal resolutions using an automated eddy tracker. We characterize the eddies across fourteen 5° × 5° subregions. Eddy-centric composites of tracers and geostrophic currents diagnosed from a global reanalysis of surface and in situ data reveal substantial subregional heterogeneity. The in situ data are also used to compute the evolving quasi-geostrophic vertical velocity (QG-ω) associated with each instantaneous eddy instance. The QG-ω eddy composites have the expected dipole patterns of alternating upwelling/downwelling, however, the magnitude and sign of azimuthally averaged vertical velocity varies among subregions. Maximum eddy values are found near fronts and sharp topographic gradients. In comparison with regional eddy composites, subregional composites provide refined information about mesoscale eddy heterogeneity.

  14. Eddy diffusivity of quasi-neutrally-buoyant inertial particles

    Science.gov (United States)

    Martins Afonso, Marco; Muratore-Ginanneschi, Paolo; Gama, Sílvio M. A.; Mazzino, Andrea

    2018-04-01

    We investigate the large-scale transport properties of quasi-neutrally-buoyant inertial particles carried by incompressible zero-mean periodic or steady ergodic flows. We show how to compute large-scale indicators such as the inertial-particle terminal velocity and eddy diffusivity from first principles in a perturbative expansion around the limit of added-mass factor close to unity. Physically, this limit corresponds to the case where the mass density of the particles is constant and close in value to the mass density of the fluid, which is also constant. Our approach differs from the usual over-damped expansion inasmuch as we do not assume a separation of time scales between thermalization and small-scale convection effects. For a general flow in the class of incompressible zero-mean periodic velocity fields, we derive closed-form cell equations for the auxiliary quantities determining the terminal velocity and effective diffusivity. In the special case of parallel flows these equations admit explicit analytic solution. We use parallel flows to show that our approach sheds light onto the behavior of terminal velocity and effective diffusivity for Stokes numbers of the order of unity.

  15. Annual CO2 budget and seasonal CO2 exchange signals at a high Arctic permafrost site on Spitsbergen, Svalbard archipelago

    DEFF Research Database (Denmark)

    Luërs, J.; Westermann, Signe; Piel, K.

    2014-01-01

    -lasting snow cover, and several months of darkness. This study presents a complete annual cycle of the CO2 net ecosystem exchange (NEE) dynamics for a high Arctic tundra area at the west coast of Svalbard based on eddy covariance flux measurements. The annual cumulative CO2 budget is close to 0 g C m-2 yr-1...

  16. High atmospheric demand for water can limit forest carbon uptake and transpiration as severely as dry soil

    Science.gov (United States)

    Benjamin N. Sulman; Daniel Tyler Roman; Koong Yi; Lixin Wang; Richard P. Phillips; Kimberly A. Novick

    2016-01-01

    When stressed by low soil water content (SWC) or high vapor pressure deficit (VPD), plants close stomata, reducing transpiration and photosynthesis. However, it has historically been difficult to disentangle the magnitudes of VPD compared to SWC limitations on ecosystem-scale fluxes. We used a 13 year record of eddy covariance measurements from a forest in south...

  17. EDDY - a FORTRAN program to extract significant features from eddy-current test data - the basis of the CANSCAN system

    International Nuclear Information System (INIS)

    Jarvis, R.G.; Cranston, R.J.

    1982-09-01

    The FORTRAN program EDDY is designed to analyse data: from eddy-current scans of steam generator tubes. It is written in modular form, for future development, and it uses signal-recognition techniques that the authors developed in the profilometry of irradiated fuel elements. During a scan, significant signals are detected and extracted for immediate attention or more detailed analysis later. A version of the program was used in the CANSCAN system 'for automated eddy-current in-service inspection of nuclear steam generator tubing'

  18. Inverse modeling of the terrestrial carbon flux in China with flux covariance among inverted regions

    Science.gov (United States)

    Wang, H.; Jiang, F.; Chen, J. M.; Ju, W.; Wang, H.

    2011-12-01

    Quantitative understanding of the role of ocean and terrestrial biosphere in the global carbon cycle, their response and feedback to climate change is required for the future projection of the global climate. China has the largest amount of anthropogenic CO2 emission, diverse terrestrial ecosystems and an unprecedented rate of urbanization. Thus information on spatial and temporal distributions of the terrestrial carbon flux in China is of great importance in understanding the global carbon cycle. We developed a nested inversion with focus in China. Based on Transcom 22 regions for the globe, we divide China and its neighboring countries into 17 regions, making 39 regions in total for the globe. A Bayesian synthesis inversion is made to estimate the terrestrial carbon flux based on GlobalView CO2 data. In the inversion, GEOS-Chem is used as the transport model to develop the transport matrix. A terrestrial ecosystem model named BEPS is used to produce the prior surface flux to constrain the inversion. However, the sparseness of available observation stations in Asia poses a challenge to the inversion for the 17 small regions. To obtain additional constraint on the inversion, a prior flux covariance matrix is constructed using the BEPS model through analyzing the correlation in the net carbon flux among regions under variable climate conditions. The use of the covariance among different regions in the inversion effectively extends the information content of CO2 observations to more regions. The carbon flux over the 39 land and ocean regions are inverted for the period from 2004 to 2009. In order to investigate the impact of introducing the covariance matrix with non-zero off-diagonal values to the inversion, the inverted terrestrial carbon flux over China is evaluated against ChinaFlux eddy-covariance observations after applying an upscaling methodology.

  19. Covariant field equations in supergravity

    Energy Technology Data Exchange (ETDEWEB)

    Vanhecke, Bram [KU Leuven, Institute for Theoretical Physics, Leuven (Belgium); Ghent University, Faculty of Physics, Gent (Belgium); Proeyen, Antoine van [KU Leuven, Institute for Theoretical Physics, Leuven (Belgium)

    2017-12-15

    Covariance is a useful property for handling supergravity theories. In this paper, we prove a covariance property of supergravity field equations: under reasonable conditions, field equations of supergravity are covariant modulo other field equations. We prove that for any supergravity there exist such covariant equations of motion, other than the regular equations of motion, that are equivalent to the latter. The relations that we find between field equations and their covariant form can be used to obtain multiplets of field equations. In practice, the covariant field equations are easily found by simply covariantizing the ordinary field equations. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Covariant field equations in supergravity

    International Nuclear Information System (INIS)

    Vanhecke, Bram; Proeyen, Antoine van

    2017-01-01

    Covariance is a useful property for handling supergravity theories. In this paper, we prove a covariance property of supergravity field equations: under reasonable conditions, field equations of supergravity are covariant modulo other field equations. We prove that for any supergravity there exist such covariant equations of motion, other than the regular equations of motion, that are equivalent to the latter. The relations that we find between field equations and their covariant form can be used to obtain multiplets of field equations. In practice, the covariant field equations are easily found by simply covariantizing the ordinary field equations. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Cyclonic entrainment of preconditioned shelf waters into a frontal eddy

    Science.gov (United States)

    Everett, J. D.; Macdonald, H.; Baird, M. E.; Humphries, J.; Roughan, M.; Suthers, I. M.

    2015-02-01

    The volume transport of nutrient-rich continental shelf water into a cyclonic frontal eddy (entrainment) was examined from satellite observations, a Slocum glider and numerical simulation outputs. Within the frontal eddy, parcels of water with temperature/salinity signatures of the continental shelf (18-19°C and >35.5, respectively) were recorded. The distribution of patches of shelf water observed within the eddy was consistent with the spiral pattern shown within the numerical simulations. A numerical dye tracer experiment showed that the surface waters (≤50 m depth) of the frontal eddy are almost entirely (≥95%) shelf waters. Particle tracking experiments showed that water was drawn into the eddy from over 4° of latitude (30-34.5°S). Consistent with the glider observations, the modeled particles entrained into the eddy sunk relative to their initial position. Particles released south of 33°S, where the waters are cooler and denser, sunk 34 m deeper than their release position. Distance to the shelf was a critical factor in determining the volume of shelf water entrained into the eddy. Entrainment reduced to 0.23 Sv when the eddy was furthest from the shelf, compared to 0.61 Sv when the eddy was within 10 km of the shelf. From a biological perspective, quantifying the entrainment of shelf water into frontal eddies is important, as it is thought to play a significant role in providing an offshore nursery habitat for coastally spawned larval fish.

  2. Path integral representations on the complex sphere

    Energy Technology Data Exchange (ETDEWEB)

    Grosche, C. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik

    2007-08-15

    In this paper we discuss the path integral representations for the coordinate systems on the complex sphere S{sub 3C}. The Schroedinger equation, respectively the path integral, separates in exactly 21 orthogonal coordinate systems. We enumerate these coordinate systems and we are able to present the path integral representations explicitly in the majority of the cases. In each solution the expansion into the wave-functions is stated. Also, the kernel and the corresponding Green function can be stated in closed form in terms of the invariant distance on the sphere, respectively on the hyperboloid. (orig.)

  3. Eddy currents in pulsed field measurements

    International Nuclear Information System (INIS)

    Kuepferling, M.; Groessinger, R.; Wimmer, A.; Taraba, M.; Scholz, W.

    2002-01-01

    Full text: One problem of pulsed field magnetometry is an error in magnetization, which appears in measurements of conducting samples. This error is due to eddy currents induced by a time varying field. To allow predictions how eddy currents exert influence on the hysteresis loop, systematic experimental and theoretical studies of pulsed field measurements of metallic samples were performed. The theoretical studies include analytical calculations as well as numerical ones using a 2D finite element software. In the measurements three physical parameters have been varied: i) the conductivity of the sample by using two different materials, in this case technical Cu and Al ii) size and shape of the sample by using cylinders, spheres and cuboids iii) the pulse duration of the external field by changing the capacitor battery from 8mF ( =9.1ms) to 24mF ( =15.7ms). The time dependence of the external field corresponds with a pulsed damped harmonic oscillation with a maximum value of 5.2T. The samples were studied in the as cast state (after machining) as well as after heat treatment. Theoretical calculations showed not only good agreement with the absolute values of the measured eddy current m agnetization , they also gave an explanation of the shape of the eddy current hysteresis and the dependence of the eddy current 'magnetization' on parameters as pulse duration of the external field and conductivity of the sample. (author)

  4. Mesoscale Eddies Control the Timing of Spring Phytoplankton Blooms: A Case Study in the Japan Sea

    Science.gov (United States)

    Maúre, E. R.; Ishizaka, J.; Sukigara, C.; Mino, Y.; Aiki, H.; Matsuno, T.; Tomita, H.; Goes, J. I.; Gomes, H. R.

    2017-11-01

    Satellite Chlorophyll a (CHL) data were used to investigate the influence of mesoscale anticyclonic eddies (AEs) and cyclonic eddies (CEs) on the timing of spring phytoplankton bloom initiation around the Yamato Basin (133-139°E and 35-39.5°N) in the Japan Sea, for the period 2002-2011. The results showed significant differences between AEs and CEs in the timing and initiation mechanism of the spring phytoplankton bloom. Blooms were initiated earlier in CEs which were characterized by shallow mixed-layer depths (mixed-layer depth. Conversely, blooms appeared in the AEs despite deeper mixed-layer depth (> 100 m) but close to the commencement of positive Q0. This suggests that the relaxation of turbulent mixing is crucial for the bloom initiation in AEs.

  5. A special covariance structure for random coefficient models with both between and within covariates

    International Nuclear Information System (INIS)

    Riedel, K.S.

    1990-07-01

    We review random coefficient (RC) models in linear regression and propose a bias correction to the maximum likelihood (ML) estimator. Asymmptotic expansion of the ML equations are given when the between individual variance is much larger or smaller than the variance from within individual fluctuations. The standard model assumes all but one covariate varies within each individual, (we denote the within covariates by vector χ 1 ). We consider random coefficient models where some of the covariates do not vary in any single individual (we denote the between covariates by vector χ 0 ). The regression coefficients, vector β k , can only be estimated in the subspace X k of X. Thus the number of individuals necessary to estimate vector β and the covariance matrix Δ of vector β increases significantly in the presence of more than one between covariate. When the number of individuals is sufficient to estimate vector β but not the entire matrix Δ , additional assumptions must be imposed on the structure of Δ. A simple reduced model is that the between component of vector β is fixed and only the within component varies randomly. This model fails because it is not invariant under linear coordinate transformations and it can significantly overestimate the variance of new observations. We propose a covariance structure for Δ without these difficulties by first projecting the within covariates onto the space perpendicular to be between covariates. (orig.)

  6. Measuring Methane from Cars, Ships, Airplanes, Helicopters and Drones Using High-Speed Open-Path Technology

    Science.gov (United States)

    Burba, George; Anderson, Tyler; Biraud, Sebastien; Caulton, Dana; von Fischer, Joe; Gioli, Beniamino; Hanson, Chad; Ham, Jay; Kohnert, Katrin; Larmanou, Eric; Levy, Peter; Polidori, Andrea; Pikelnaya, Olga; Sachs, Torsten; Serafimovich, Andrei; Zaldei, Alessandro; Zondlo, Mark; Zulueta, Rommel

    2017-04-01

    Methane plays a critical role in the radiation balance, chemistry of the atmosphere, and air quality. The major anthropogenic sources of methane include oil and gas development sites, natural gas distribution networks, landfill emissions, and agricultural production. The majority of oil and gas and urban methane emission occurs via variable-rate point sources or diffused spots in topographically challenging terrains (e.g., street tunnels, elevated locations at water treatment plants, vents, etc.). Locating and measuring such methane emissions is challenging when using traditional micrometeorological techniques, and requires development of novel approaches. Landfill methane emissions traditionally assessed at monthly or longer time intervals are subject to large uncertainties because of the snapshot nature of the measurements and the barometric pumping phenomenon. The majority of agricultural and natural methane production occurs in areas with little infrastructure or easily available grid power (e.g., rice fields, arctic and boreal wetlands, tropical mangroves, etc.). A lightweight, high-speed, high-resolution, open-path technology was recently developed for eddy covariance measurements of methane flux, with power consumption 30-150 times below other available technologies. It was designed to run on solar panels or a small generator and be placed in the middle of the methane-producing ecosystem without a need for grid power. Lately, this instrumentation has been utilized increasingly more frequently outside of the traditional use on stationary flux towers. These novel approaches include measurements from various moving platforms, such as cars, aircraft, and ships. Projects included mapping of concentrations and vertical profiles, leak detection and quantification, mobile emission detection from natural gas-powered cars, soil methane flux surveys, etc. This presentation will describe the latest state of the key projects utilizing the novel lightweight low-power high

  7. IEDA [Intelligent Eddy Current Data Analysis] helps make sense of eddy current data [steam generators

    International Nuclear Information System (INIS)

    Clark, R.

    1989-01-01

    The increasing sophistication of eddy current signal interpretation in steam generator tubing has improved capabilities, but has also made the process of analysis more complex and time consuming. Westinghouse has developed an intelligent computerised tool - the IEDA (Intelligent Eddy Current Data Analysis) system, to lighten the load on analysts. Since 1985, 44 plants have been inspected with IEDA, representing over 400,000 tubes. The system has provided a repeatability and a consistency not achieved by human operators. (U.K.)

  8. The role of eddy transports in climate change

    International Nuclear Information System (INIS)

    Stone, P.H.

    1994-01-01

    Large-scale atmospheric eddies are the dominant transport mechanisms in mid and high latitudes. Thus, climate models must simulate these eddies, their effects, and their feedbacks accurately. Getting the feedbacks right is particularly important since it is the feedbacks which affect climate sensitivity. Observational studies of these feedbacks are hindered by the lack of actual climate changes for which good data is available, and by the lack of data on vertical heat fluxes. General circulation model (GCM) studies are hindered by errors in GCM simulations of transports in the current climate; the dependence of GCM results on uncertain subgrid scale parameterizations; and large computational requirements. A more promising approach for learning about eddy feedbacks and how they can be modelled is process model studies. So far these studies have only looked at the feedback between eddy sensible heat fluxes arising from baroclinic instability and the temperature structure. The results indicate that there is a very strong negative feedback between eddy fluxes and temperature structure, both meridional and vertical, with the fluxes themselves being sensitive to small changes in temperature structure. These studies need to be extended to higher vertical resolution, and to include the effects of moisture, stationary eddies, and coupling to the oceans

  9. Properties, Mechanisms and Predictability of Eddies in the Red Sea

    KAUST Repository

    Zhan, Peng

    2018-04-01

    Eddies are one of the key features of the Red Sea circulation. They are not only crucial for energy conversion among dynamics at different scales, but also for materials transport across the basin. This thesis focuses on studying the characteristics of Red Sea eddies, including their temporal and spatial properties, their energy budget, the mechanisms of their evolution, and their predictability. Remote sensing data, in-situ observations, the oceanic general circulation model, and data assimilation techniques were employed in this thesis. The eddies in the Red Sea were first identified using altimeter data by applying an improved winding-angle method, based on which the statistical properties of those eddies were derived. The results suggested that eddies occur more frequently in the central basin of the Red Sea and exhibit a significant seasonal variation. The mechanisms of the eddies’ evolution, particularly the eddy kinetic energy budget, were then investigated based on the outputs of a long-term eddy resolving numerical model configured for the Red Sea with realistic forcing. Examination of the energy budget revealed that the eddies acquire the vast majority of kinetic energy through conversion of eddy available potential energy via baroclinic instability, which is intensified during winter. The possible factors modulating the behavior of the several observed eddies in the Red Sea were then revealed by conducting a sensitivity analysis using the adjoint model. These eddies were found to exhibit different sensitivities to external forcings, suggesting different mechanisms for their evolution. This is the first known adjoint sensitivity study on specific eddy events in the Red Sea and was hitherto not previously appreciated. The last chapter examines the predictability of Red Sea eddies using an ensemble-based forecasting and assimilation system. The forecast sea surface height was used to evaluate the overall performance of the short-term eddy

  10. Covariant w∞ gravity

    NARCIS (Netherlands)

    Bergshoeff, E.; Pope, C.N.; Stelle, K.S.

    1990-01-01

    We discuss the notion of higher-spin covariance in w∞ gravity. We show how a recently proposed covariant w∞ gravity action can be obtained from non-chiral w∞ gravity by making field redefinitions that introduce new gauge-field components with corresponding new gauge transformations.

  11. Cyclonic eddies identified in the Cape Basin of the South Atlantic Ocean

    Science.gov (United States)

    Hall, C.; Lutjeharms, J. R. E.

    2011-03-01

    Inter-ocean exchange south of Africa takes place largely through the movement of Agulhas Rings into the Cape Basin. Recent observations have shown that the highly energetic flow field in this basin consists of anti-cyclonic rings as well as cyclonic eddies. Very little is known of the characteristics of the cyclonic eddies. Using altimetric data, this study determines the location, frequency and seasonality of these cyclonic eddies their size, trajectories, life spans and their association with Agulhas Rings. Cyclonic eddies were seen to split, merge and link with other cyclonic eddies, where splitting events created child cyclonic eddies. The 105 parent and 157 child cyclonic eddies identified over a decade show that on average 11 parent and 17 child cyclonic eddies appear annually in AVISO merged absolute dynamic topography data along the continental slope. Thirty-two percent follow an overall west south-westward direction, with 27% going west north-westward. Average translocation speeds are 2.2 ± 0.1 km/day for parent and 3.0 ± 0.2 km/day for child cyclonic eddies. Parent cyclonic eddy lifespan averaged 250 ± 18 days; whereas child cyclonic eddies survived for only 118 ± 11 days. A significant difference in lifespan for parent and child cyclonic eddies identified in the north and south region of the study area was detected. Seventy-seven percent of the northern and 93% of the southern cyclonic eddies were first detected directly adjacent to passing Agulhas Rings, suggesting a vital interaction between these mesoscale eddies within the region. Topographical features appeared to affect the behaviour and lifespan of these deep cyclonic eddies.

  12. Path integral for gauge theories with fermions

    International Nuclear Information System (INIS)

    Fujikawa, K.

    1980-01-01

    The Atiyah-Singer index theorem indicates that a naive unitary transformation of basis vectors for fermions interacting with gauge fields is not allowed in general. On the basis of this observation, it was previously shown that the path-integral measure of a gauge-invariant fermion theory is transformed nontrivially under the chiral transformation, and thus leads to a simple derivation of ''anomalous'' chiral Ward-Takahashi identities. We here clarify some of the technical aspects associated with the discussion. It is shown that the Jacobian factor in the path-integral measure, which corresponds to the Adler-Bell-Jackiw anomaly, is independent of any smooth regularization procedure of large eigenvalues of D in Euclidean theory; this property holds in any even-dimensional space-time and also for the gravitational anomaly. The appearance of the anomaly and its connection with the index theorem are thus related to the fact that the primary importance is attached to the Lorentz-covariant ''energy'' operator D and that D and γ 5 do not commute. The abnormal behavior of the path-integral measure at the zero-frequency sector in the presence of instantons and its connection with spontaneous symmetry breaking is also clarified. We comment on several other problems associated with the anomaly and on the Pauli-Villars regularization method

  13. Cox regression with missing covariate data using a modified partial likelihood method

    DEFF Research Database (Denmark)

    Martinussen, Torben; Holst, Klaus K.; Scheike, Thomas H.

    2016-01-01

    Missing covariate values is a common problem in survival analysis. In this paper we propose a novel method for the Cox regression model that is close to maximum likelihood but avoids the use of the EM-algorithm. It exploits that the observed hazard function is multiplicative in the baseline hazard...

  14. Evaluation and processing of covariance data

    International Nuclear Information System (INIS)

    Wagner, M.

    1993-01-01

    These proceedings of a specialists'meeting on evaluation and processing of covariance data is divided into 4 parts bearing on: part 1- Needs for evaluated covariance data (2 Papers), part 2- generation of covariance data (15 Papers), part 3- Processing of covariance files (2 Papers), part 4-Experience in the use of evaluated covariance data (2 Papers)

  15. Eddy Current Sensing of Torque in Rotating Shafts

    Science.gov (United States)

    Varonis, Orestes J.; Ida, Nathan

    2013-12-01

    The noncontact torque sensing in machine shafts is addressed based on the stress induced in a press-fitted magnetoelastic sleeve on the shaft and eddy current sensing of the changes of electrical conductivity and magnetic permeability due to the presence of stress. The eddy current probe uses dual drive, dual sensing coils whose purpose is increased sensitivity to torque and decreased sensitivity to variations in distance between probe and shaft (liftoff). A mechanism of keeping the distance constant is also employed. Both the probe and the magnetoelastic sleeve are evaluated for performance using a standard eddy current instrument. An eddy current instrument is also used to drive the coils and analyze the torque data. The method and sensor described are general and adaptable to a variety of applications. The sensor is suitable for static and rotating shafts, is independent of shaft diameter and operational over a large range of torques. The torque sensor uses a differential eddy current measurement resulting in cancellation of common mode effects including temperature and vibrations.

  16. Mesoscale eddies in the Subantarctic Front-Southwest Atlantic

    Directory of Open Access Journals (Sweden)

    Pablo D. Glorioso

    2005-12-01

    Full Text Available Satellite and ship observations in the southern southwest Atlantic (SSWA reveal an intense eddy field and highlight the potential for using continuous real-time satellite altimetry to detect and monitor mesoscale phenomena with a view to understanding the regional circulation. The examples presented suggest that mesoscale eddies are a dominant feature of the circulation and play a fundamental role in the transport of properties along and across the Antarctic Circumpolar Current (ACC. The main ocean current in the SSWA, the Falkland-Malvinas Current (FMC, exhibits numerous embedded eddies south of 50°S which may contribute to the patchiness, transport and mixing of passive scalars by this strong, turbulent current. Large eddies associated with meanders are observed in the ACC fronts, some of them remaining stationary for long periods. Two particular cases are examined using a satellite altimeter in combination with in situ observations, suggesting that cross-frontal eddy transport and strong meandering occur where the ACC flow intensifies along the sub-Antarctic Front (SAF and the Southern ACC Front (SACCF.

  17. Covariance data processing code. ERRORJ

    International Nuclear Information System (INIS)

    Kosako, Kazuaki

    2001-01-01

    The covariance data processing code, ERRORJ, was developed to process the covariance data of JENDL-3.2. ERRORJ has the processing functions of covariance data for cross sections including resonance parameters, angular distribution and energy distribution. (author)

  18. Chambers versus Relaxed Eddy Accumulation: an intercomparison study of two methods for short-term measurements of biogenic CO2 fluxes

    Science.gov (United States)

    Jasek, Alina; Zimnoch, Miroslaw; Gorczyca, Zbigniew; Chmura, Lukasz; Necki, Jaroslaw

    2014-05-01

    The presented work is a part of comprehensive study aimed at thorough characterization of carbon cycle in the urban environment of Krakow, southern Poland. In the framework of this study two independent methods were employed to quantify biogenic CO2 flux in the city: (i) closed chambers, and (ii) Relaxed Eddy Accumulation (REA). The results of a three-day intensive intercomparison campaign performed in July 2013 and utilizing both measurement methods are reported here. The chamber method is a widely used approach for measurements of gas exchange between the soil and the atmosphere. The system implemented in this study consisted of a single chamber operating in a closed-dynamic mode, combined with Vaisala CarboCAP infrared CO2 sensor in a mobile setup. An alternative flux measurement method, covering larger area is represented by REA, which is a modification of the eddy covariance method. It consists of a 3D anemometer (Gill Windmaster Pro) and the system collecting updraft and downdraft samples to 5-litre Tedlar bags. The CO2 mixing ratios in the collected samples are measured by Picarro G2101i analyzer. The setup consists of two sets of bags so that the sampling can be performed continuously with 15-min temporal resolution. A 48-hectares open meadow located close the city center was chosen as a test site for comparison of the two methods of CO2 flux measurements outlined above. In the middle of the meadow a 3-metre high tripod was installed with the anemometer and REA inlet system. For a period of 46 hours the system was measuring net CO2 flux from the surrounding area. A meteorological conditions and intensity of photosynthetically active radiation (PAR) were also recorded. In the same time, CO2 flux from several points around the REA inlet was measured with the chamber system, resulting in 93 values for both respiration and net CO2 flux. Chamber results show rather homogenous distribution of the soil CO2 flux (the mean value equal to 40.9 ± 2.2 mmol/m2h), with

  19. Sea Surface Height Variability and Eddy Statistical Properties in the Red Sea

    KAUST Repository

    Zhan, Peng

    2013-05-01

    Satellite sea surface height (SSH) data over 1992-2012 are analyzed to study the spatial and temporal variability of sea level in the Red Sea. Empirical orthogonal functions (EOF) analysis suggests the remarkable seasonality of SSH in the Red Sea, and a significant correlation is found between SSH variation and seasonal wind cycle. A winding-angle based eddy identification algorithm is employed to derive the mesoscale eddy information from SSH data. Totally more than 5500 eddies are detected, belonging to 2583 eddy tracks. Statistics suggest that eddies generate over the entire Red Sea, with two regions in the central basin of high eddy frequency. 76% of the detected eddies have a radius ranging from 40km to 100km, of which both intensity and absolute vorticity decrease with eddy radius. The average eddy lifespan is about 5 weeks, and eddies with longer lifespan tend to have larger radius but less intensity. Different deformation rate exists between anticyclonic eddies (AEs) and cyclonic eddies (CEs), those eddies with higher intensity appear to be less deformed and more circular. Inspection of the 84 long-lived eddies suggests the AEs tend to move a little more northward than CEs. AE generation during summer is obviously lower than that during other seasons, while CE generation is higher during spring and summer. Other features of AEs and CEs are similar with both vorticity and intensity reaching the summer peaks in August and winter peaks in January. Inter-annual variability reveals that the eddies in the Red Sea are isolated from the global event. The eddy property tendencies are different from the south and north basin, both of which exhibit a two-year cycle. Showing a correlation coefficient of -0.91, Brunt–Väisälä frequency is negatively correlated with eddy kinetic energy (EKE), which results from AE activities in the high eddy frequency region. Climatological vertical velocity shear variation is identical with EKE except in the autumn, suggesting the

  20. Solitonlike solutions in loop current eddies

    Science.gov (United States)

    Nakamoto, Shoichiro

    1989-01-01

    The application of the nonlinear quasi-geostrophic equations to an isolated eddy in the western continental slope region in the Gulf of Mexico is examined for a two-layer ocean model with bottom topography. In the linear limit, solutions are topographic nondispersive waves. Form-preserving solutions, or solitons, have been found. The solution is shown to be a limiting form for a nonlinear dispersive system propagating northward along the topographic waveguide in the western continental slope region in the Gulf of Mexico. Using satellite-tracked drifter data, a linear relationship is found between the amplitude of the deduced stream function of the eddy and its observed translational velocity over the continental slope, which supports the hypothesis that some mesoscale eddies interacting with the continental slope behave as solitons.

  1. Lateral resolution of eddy current imaging

    International Nuclear Information System (INIS)

    Hassan, W.; Blodgett, M.; Nagy, P.B.

    2002-01-01

    Analytical, finite element simulation, and experimental methods were used to investigate the lateral resolution of eddy current microscopy. It was found that the lateral resolution of eddy current imaging is ultimately limited by the probe-coil geometry and dimensions, but both the inspection frequency and the phase angle can be used to optimize the resolution, to some degree, at the expense of sensitivity. Electric anisotropy exhibited by noncubic crystallographic classes of materials such as titanium alloys can play a very similar role in electromagnetic materials characterization of polycrystalline metals to that of elastic anisotropy in ultrasonic materials characterization. Our results demonstrate that eddy current microscopy can be enhanced via a high-resolution, small diameter probe-coil which delivers a unique materials characterization tool well suited for the evaluation of Ti alloys

  2. Recent Ship, Satellite and Autonomous Observations of Southern Ocean Eddies

    Science.gov (United States)

    Strutton, P. G.; Moreau, S.; Llort, J.; Phillips, H. E.; Patel, R.; Della Penna, A.; Langlais, C.; Lenton, A.; Matear, R.; Dawson, H.; Boyd, P. W.

    2016-12-01

    The Southern Ocean is the area of greatest uncertainty regarding the exchange of CO2 between the ocean and atmosphere. It is also a region of abundant energetic eddies that significantly impact circulation and biogeochemistry. In the Indian sector of the Southern Ocean, cyclonic eddies are unusual in that they are upwelling favorable, as for cyclonic eddies elsewhere, but during summer they are low in silicate and phytoplankton biomass. The reverse is true for anticyclonic eddies in that they have counter-intuitive positive chlorophyll anomalies in summer. Similar but less obvious patterns occur in the Pacific and Atlantic sectors. Using ship, satellite and autonomous observations in the region south of Australia, the physical and biogeochemical signatures of both types of eddies were documented in 2016. A cyclonic eddy that lived for seven weeks exhibited doming isopycnals indicative of upwelling. However, low surface silicate and chlorophyll concentrations appeared to be characteristic of surface waters to the south where the eddy formed. Higher chlorophyll was confined to filaments at the eddy edge. Surface nitrate and phosphate concentrations were more than sufficient for a bloom of non-siliceous phytoplankton to occur. Acoustic observations from a high resolution TRIAXUS transect through the eddy documented high zooplankton biomass in the upper 150m. It is hypothesized that a non-diatom bloom was prevented by grazing pressure, but light may have also been an important limiting resource in late summer (April). Two SOCCOM floats that were deployed in the eddy field continued to monitor the physics, nitrate and bio-optics through the transition to winter. These observations across complementary platforms have identified and then explained the reason for these unexpected biological anomalies in an energetic and globally important region of the global ocean. Understanding the role of eddies in this region will be critical to the representation of mesoscale

  3. Properties and pathways of Mediterranean water eddies in the Atlantic

    Science.gov (United States)

    Bashmachnikov, I.; Neves, F.; Calheiros, T.; Carton, X.

    2015-09-01

    Data from ship vertical casts (NODC data-set), ARGO profiling floats (Coriolis data-set) and RAFOS-type neutral density floats (WOCE data-set) are used to study characteristics of meddies in the Northeast Atlantic. In total 241 Mediterranean water eddies (meddies) and 236 parts of float trajectories within meddies are selected for detailed analysis. The results suggest that the meddy generation rate at the southern and southwestern Iberian Peninsula (Portimao Canyon, cap St. Vincent, Estremadura Promontory, Gorringe Bank) is 3 times that at the northwestern Iberian Peninsula (Porto-Aveiro Canyons, Cape Finisterre and Galicia Bank). Meddies generated south of Estremadura Promontory (the southern meddies), as compared to those generated north of it (the northern meddies), have smaller radii, smaller vertical extension, higher aspect ratio, higher Rossby number and higher stability (stronger potential vorticity anomaly). These latter properties result from the southern meddies higher relative vorticity and stronger buoyancy frequency anomaly. Away from the generation regions, meddy drift concentrates along four main paths: three quasi-zonal paths (Northern, Central, Southern) and a path following the African coast (Coastal). The quasi-zonal paths are aligned to the isolines of the ambient potential vorticity field. Several cross-path exchanges, identified in this work, are aligned to topographic rises. Northward translation of the northern meddies within the North Atlantic Current to the subpolar gyre is detected. Within the first 600 km from the coast, meddy merger is proved to be a common event. This explains the observed difference in radii between the newly generated meddies and those away from the Iberian margin. The decay of the southern meddies proceeds mainly via the loss of their skirts and does not affect meddy cores until the latest stages. The decay of the northern meddies goes in parallel with the decay of their cores. In average meddy decay is achieved

  4. A theoretical analysis of the response of an air-cored eddy current coil for remote oxide thickness measurements on reactor components

    International Nuclear Information System (INIS)

    Wilson, R.

    1979-10-01

    It is shown how the impedance of an air-cored eddy current coil in close proximity to an oxidised steel component may be calculated. Representative values were selected for the oxide thickness, lift off, operating frequency, conductivities and permeabilities of the oxide coating and steel base. The values of these parameters in the calculations were allowed to vary between suitable limits to quantify the effect of each one on coil impedance. The results of the calculations are used to determine the most suitable conditions for the measurement of oxide thickness on steel components using an air-cored eddy current probe. (author)

  5. Workshops and problems for benchmarking eddy current codes

    Energy Technology Data Exchange (ETDEWEB)

    Turner, L.R.; Davey, K.; Ida, N.; Rodger, D.; Kameari, A.; Bossavit, A.; Emson, C.R.I.

    1988-08-01

    A series of six workshops was held in 1986 and 1987 to compare eddy current codes, using six benchmark problems. The problems included transient and steady-state ac magnetic fields, close and far boundary conditions, magnetic and non-magnetic materials. All the problems were based either on experiments or on geometries that can be solved analytically. The workshops and solutions to the problems are described. Results show that many different methods and formulations give satisfactory solutions, and that in many cases reduced dimensionality or coarse discretization can give acceptable results while reducing the computer time required. A second two-year series of TEAM (Testing Electromagnetic Analysis Methods) workshops, using six more problems, is underway. 12 refs., 15 figs., 4 tabs.

  6. Workshops and problems for benchmarking eddy current codes

    International Nuclear Information System (INIS)

    Turner, L.R.; Davey, K.; Ida, N.; Rodger, D.; Kameari, A.; Bossavit, A.; Emson, C.R.I.

    1988-08-01

    A series of six workshops was held in 1986 and 1987 to compare eddy current codes, using six benchmark problems. The problems included transient and steady-state ac magnetic fields, close and far boundary conditions, magnetic and non-magnetic materials. All the problems were based either on experiments or on geometries that can be solved analytically. The workshops and solutions to the problems are described. Results show that many different methods and formulations give satisfactory solutions, and that in many cases reduced dimensionality or coarse discretization can give acceptable results while reducing the computer time required. A second two-year series of TEAM (Testing Electromagnetic Analysis Methods) workshops, using six more problems, is underway. 12 refs., 15 figs., 4 tabs

  7. Development of eddy current sensor for detecting defect on ferromagnetic material

    International Nuclear Information System (INIS)

    Choi, Duck Su; Lee, Hyang Beom

    2002-01-01

    In this paper, the eddy current sensor is developed for observing the ability of detecting defect on ferromagnetic material with variation of frequency and velocity. In order to research the characteristics on eddy current sensor. The circuit which is designed for processing detected voltage is developed and differential frequency is used for eddy current sensor to detect defect with variation of frequency. The ability of eddy current sensor to detect defects is studied with variation of velocity adjusted by rotating the circular plate. This study shows that the ability of eddy current sensor for detecting defect is increased and decreased by frequency. This fact means that the sensor has its best ability at a certain frequency. And the ability of eddy current sensor by velocity is decreased by increased velocity. Therefore, the eddy current sensor has to be developed with consideration of its operation velocity and frequency.

  8. Closed description of arbitrariness in resolving quantum master equation

    Energy Technology Data Exchange (ETDEWEB)

    Batalin, Igor A., E-mail: batalin@lpi.ru [P.N. Lebedev Physical Institute, Leninsky Prospect 53, 119 991 Moscow (Russian Federation); Tomsk State Pedagogical University, Kievskaya St. 60, 634061 Tomsk (Russian Federation); Lavrov, Peter M., E-mail: lavrov@tspu.edu.ru [Tomsk State Pedagogical University, Kievskaya St. 60, 634061 Tomsk (Russian Federation); National Research Tomsk State University, Lenin Av. 36, 634050 Tomsk (Russian Federation)

    2016-07-10

    In the most general case of the Delta exact operator valued generators constructed of an arbitrary Fermion operator, we present a closed solution for the transformed master action in terms of the original master action in the closed form of the corresponding path integral. We show in detail how that path integral reduces to the known result in the case of being the Delta exact generators constructed of an arbitrary Fermion function.

  9. The formation of a subsurface anticyclonic eddy in the Peru-Chile Undercurrent and its impact on the near-coastal salinity, oxygen, and nutrient distributions

    Science.gov (United States)

    Thomsen, Soeren; Kanzow, Torsten; Krahmann, Gerd; Greatbatch, Richard J.; Dengler, Marcus; Lavik, Gaute

    2016-01-01

    The formation of a subsurface anticyclonic eddy in the Peru-Chile Undercurrent (PCUC) in January and February 2013 is investigated using a multiplatform four-dimensional observational approach. Research vessel, multiple glider, and mooring-based measurements were conducted in the Peruvian upwelling regime near 12°30'S. The data set consists of >10,000 glider profiles and repeated vessel-based hydrography and velocity transects. It allows a detailed description of the eddy formation and its impact on the near-coastal salinity, oxygen, and nutrient distributions. In early January, a strong PCUC with maximum poleward velocities of ˜0.25 m/s at 100-200 m depth was observed. Starting on 20 January, a subsurface anticyclonic eddy developed in the PCUC downstream of a topographic bend, suggesting flow separation as the eddy formation mechanism. The eddy core waters exhibited oxygen concentration of deficit of ˜17 μmol/L, and potential vorticity close to zero, which seemed to originate from the bottom boundary layer of the continental slope. The eddy-induced across-shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean. Small-scale salinity and oxygen structures were formed by along-isopycnal stirring, and indications of eddy-driven oxygen ventilation of the upper oxygen minimum zone were observed. It is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off Peru.

  10. Using Individualized Brain Network for Analyzing Structural Covariance of the Cerebral Cortex in Alzheimer's Patients.

    Science.gov (United States)

    Kim, Hee-Jong; Shin, Jeong-Hyeon; Han, Cheol E; Kim, Hee Jin; Na, Duk L; Seo, Sang Won; Seong, Joon-Kyung

    2016-01-01

    Cortical thinning patterns in Alzheimer's disease (AD) have been widely reported through conventional regional analysis. In addition, the coordinated variance of cortical thickness in different brain regions has been investigated both at the individual and group network levels. In this study, we aim to investigate network architectural characteristics of a structural covariance network (SCN) in AD, and further to show that the structural covariance connectivity becomes disorganized across the brain regions in AD, while the normal control (NC) subjects maintain more clustered and consistent coordination in cortical atrophy variations. We generated SCNs directly from T1-weighted MR images of individual patients using surface-based cortical thickness data, with structural connectivity defined as similarity in cortical thickness within different brain regions. Individual SCNs were constructed using morphometric data from the Samsung Medical Center (SMC) dataset. The structural covariance connectivity showed higher clustering than randomly generated networks, as well as similar minimum path lengths, indicating that the SCNs are "small world." There were significant difference between NC and AD group in characteristic path lengths (z = -2.97, p < 0.01) and small-worldness values (z = 4.05, p < 0.01). Clustering coefficients in AD was smaller than that of NC but there was no significant difference (z = 1.81, not significant). We further observed that the AD patients had significantly disrupted structural connectivity. We also show that the coordinated variance of cortical thickness is distributed more randomly from one region to other regions in AD patients when compared to NC subjects. Our proposed SCN may provide surface-based measures for understanding interaction between two brain regions with co-atrophy of the cerebral cortex due to normal aging or AD. We applied our method to the AD Neuroimaging Initiative (ADNI) data to show consistency in results with the SMC

  11. Covariance Bell inequalities

    Science.gov (United States)

    Pozsgay, Victor; Hirsch, Flavien; Branciard, Cyril; Brunner, Nicolas

    2017-12-01

    We introduce Bell inequalities based on covariance, one of the most common measures of correlation. Explicit examples are discussed, and violations in quantum theory are demonstrated. A crucial feature of these covariance Bell inequalities is their nonlinearity; this has nontrivial consequences for the derivation of their local bound, which is not reached by deterministic local correlations. For our simplest inequality, we derive analytically tight bounds for both local and quantum correlations. An interesting application of covariance Bell inequalities is that they can act as "shared randomness witnesses": specifically, the value of the Bell expression gives device-independent lower bounds on both the dimension and the entropy of the shared random variable in a local model.

  12. Distance covariance for stochastic processes

    DEFF Research Database (Denmark)

    Matsui, Muneya; Mikosch, Thomas Valentin; Samorodnitsky, Gennady

    2017-01-01

    The distance covariance of two random vectors is a measure of their dependence. The empirical distance covariance and correlation can be used as statistical tools for testing whether two random vectors are independent. We propose an analog of the distance covariance for two stochastic processes...

  13. Eddy-induced Sea Surface Salinity changes in the tropical Pacific

    Science.gov (United States)

    Delcroix, T. C.; Chaigneau, A.; Soviadan, D.; Boutin, J.

    2017-12-01

    We analyse the Sea Surface Salinity (SSS) signature of westward propagating mesoscale eddies in the tropical Pacific by collocating 5 years (2010-2015) of SMOS (Soil Moisture and Ocean Salinity) SSS and altimetry-derived sea level anomalies. The main characteristics of mesoscale eddies are first identified in SLA maps. Composite analyses in the Central and Eastern ITCZ regions then reveal regionally dependent impacts with opposite SSS anomalies for the cyclonic and anticyclonic eddies. In the Central region (where we have the largest meridional SSS gradient), we found dipole-like SSS changes with maximum anomalies on the leading edge of the eddy. In the Eastern region (where we have the largest near-surface vertical salinity gradient) we found monopole-like SSS changes with maximum anomalies in the eddy centre. These dipole/monopole patterns and the rotational sense of eddies suggest the dominant role of horizontal and vertical advection in the Central and Eastern ITCZ regions, respectively.

  14. Eddy energy sources and flux in the Red Sea

    KAUST Repository

    Zhan, Peng

    2015-04-01

    In the Red Sea, eddies are reported to be one of the key features of hydrodynamics in the basin. They play a significant role in converting the energy among the large-scale circulation, the available potential energy (APE) and the eddy kinetic energy (EKE). Not only do eddies affect the horizontal circulation, deep-water formation and overturning circulation in the basin, but they also have a strong impact on the marine ecosystem by efficiently transporting heat, nutrients and carbon across the basin and by pumping the nutrient-enriched subsurface water to sustain the primary production. Previous observations and modeling work suggest that the Red Sea is rich of eddy activities. In this study, the eddy energy sources and sinks have been studied based on a high-resolution MITgcm. We have also investigated the possible mechanisms of eddy generation in the Red Sea. Eddies with high EKE are found more likely to appear in the central and northern Red Sea, with a significant seasonal variability. They are more inclined to occur during winter when they acquire their energy mainly from the conversion of APE. In winter, the central and especially the northern Red Sea are subject to important heat loss and extensive evaporation. The resultant densified upper-layer water tends to sink and release the APE through baroclinic instability, which is about one order larger than the barotropic instability contribution and is the largest source term for the EKE in the Red Sea. As a consequence, the eddy energy is confined to the upper layer but with a slope deepening from south to north. In summer, the positive surface heat flux helps maintain the stratification and impedes the gain of APE. The EKE is, therefore, much lower than that in winter despite a higher wind power input. Unlike many other seas, the wind energy is not the main source of energy to the eddies in the Red Sea.

  15. Quantization of the Yang-Mills field and Mandelstam's theory in gauge-independent path-dependent formalism

    International Nuclear Information System (INIS)

    Naito, S.

    1976-01-01

    We derive commutation relations (CR's) between gauge-invariant quantities in the Yang-Mills field theory by applying the Peierls method. The CR's obtained are different from those given by Mandelstam in his gauge-independent, path-dependent formalism. However, our CR's are shown to give a consistently quantized field theory, while his CR's do not. In fact, there exist systematic errors in Mandelstam's treatment of the covariant Green's functions. On the other hand, if we correctly treat covariant Green's functions guided by his procedure, our CR's are shown to lead to the same Feynman rules for the Yang-Mills field as prescribed by Feynman, DeWitt, Faddeev and Popov, and Mandelstam

  16. Covariance Manipulation for Conjunction Assessment

    Science.gov (United States)

    Hejduk, M. D.

    2016-01-01

    The manipulation of space object covariances to try to provide additional or improved information to conjunction risk assessment is not an uncommon practice. Types of manipulation include fabricating a covariance when it is missing or unreliable to force the probability of collision (Pc) to a maximum value ('PcMax'), scaling a covariance to try to improve its realism or see the effect of covariance volatility on the calculated Pc, and constructing the equivalent of an epoch covariance at a convenient future point in the event ('covariance forecasting'). In bringing these methods to bear for Conjunction Assessment (CA) operations, however, some do not remain fully consistent with best practices for conducting risk management, some seem to be of relatively low utility, and some require additional information before they can contribute fully to risk analysis. This study describes some basic principles of modern risk management (following the Kaplan construct) and then examines the PcMax and covariance forecasting paradigms for alignment with these principles; it then further examines the expected utility of these methods in the modern CA framework. Both paradigms are found to be not without utility, but only in situations that are somewhat carefully circumscribed.

  17. Internal and forced eddy variability in the Labrador Sea

    Science.gov (United States)

    Bracco, A.; Luo, H.; Zhong, Y.; Lilly, J.

    2009-04-01

    Water mass transformation in the Labrador Sea, widely believed to be one of the key regions in the Atlantic Meridional Overturning Circulation (AMOC), now appears to be strongly impacted by vortex dynamics of the unstable boundary current. Large interannual variations in both eddy shedding and buoyancy transport from the boundary current have been observed but not explained, and are apparently sensitive to the state of the inflowing current. Heat and salinity fluxes associated with the eddies drive ventilation changes not accounted for by changes in local surface forcing, particularly during occasional years of extreme eddy activity, and constitute a predominant source of "internal" oceanic variability. The nature of this variable eddy-driven restratification is one of the outstanding questions along the northern transformation pathway. Here we investigate the eddy generation mechanism and the associated buoyancy fluxes by combining realistic and idealized numerical modeling, data analysis, and theory. Theory, supported by idealized experiments, provides criteria to test hypotheses as to the vortex formation process (by baroclinic instability linked to the bottom topography). Ensembles of numerical experiments with a high-resolution regional model (ROMS) allow for quantifying the sensitivity of eddy generation and property transport to variations in local and external forcing parameters. For the first time, we reproduce with a numerical simulation the observed interannual variability in the eddy kinetic energy in the convective region of the Labrador Basin and along the West Greenland Current.

  18. Vessel eddy current characteristics in SST-1 tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Jana, Subrata; Pradhan, Subrata, E-mail: pradhan@ipr.res.in; Dhongde, Jasraj; Masand, Harish

    2016-11-15

    Highlights: • Eddy current distribution in the SST-1 vacuum vessel. • Circuit model analysis of eddy current. • A comparison of the field lines with and without the plasma column in identical conditions. • The influence of eddy current in magnetic NULL dynamics. - Abstract: Eddy current distribution in the vacuum vessel of the Steady state superconducting (SST-1) tokamak has been determined from the experimental data obtained using an array of internal voltage loops (flux loop) installed inside the vacuum vessel. A simple circuit model has been employed. The model takes into account the geometric and constructional features of SST-1 vacuum vessel. SST-1 vacuum vessel is a modified ‘D’ shaped vessel having major axis of 1.285 m and minor axis of 0.81 m and has been manufactured from non-magnetic stainless steel. The Plasma facing components installed inside the vacuum vessel are graphite blocks mounted on Copper Chromium Zirconium (CuCrZr) heat sink plates on inconel supports. During discharge of the central solenoid, eddy currents get generated in the vacuum vessel and passive supports on it. These eddy currents influence the early magnetic NULL dynamics and plasma break-down and start-up characteristics. The computed results obtained from the model have been benchmarked against experimental data obtained in large number of SST-1 plasma shots. The results are in good agreement. Once bench marked, the calculated eddy current based on flux loop signal and circuit equation model has been extended to the reconstruction of the overall B- field contours of SST-1 tokamak in the vessel region. A comparison of the field lines with and without the plasma column in identical conditions of the central solenoid and equilibrium field profiles has also been done with an aim to quantify the diagnostics responses in vacuum shots.

  19. Flexible eddy current coil arrays

    International Nuclear Information System (INIS)

    Krampfner, Y.; Johnson, D.P.

    1987-01-01

    A novel approach was devised to overcome certain limitations of conventional eddy current testing. The typical single-element hand-wound probe was replaced with a two dimensional array of spirally wound probe elements deposited on a thin, flexible polyimide substrate. This provides full and reliable coverage of the test area and eliminates the need for scanning. The flexible substrate construction of the array allows the probes to conform to irregular part geometries, such as turbine blades and tubing, thereby eliminating the need for specialized probes for each geometry. Additionally, the batch manufacturing process of the array can yield highly uniform and reproducible coil geometries. The array is driven by a portable computer-based eddy current instrument, smartEDDY/sup TM/, capable of two-frequency operation, and offers a great deal of versatility and flexibility due to its software-based architecture. The array is coupled to the instrument via an 80-switch multiplexer that can be configured to address up to 1600 probes. The individual array elements may be addressed in any desired sequence, as defined by the software

  20. Path integral solution of the Dirichlet problem

    International Nuclear Information System (INIS)

    LaChapelle, J.

    1997-01-01

    A scheme for functional integration developed by Cartier/DeWitt-Morette is first reviewed and then employed to construct the path integral representation for the solution of the Dirichlet problem in terms of first exit time. The path integral solution is then applied to calculate the fixed-energy point-to-point transition amplitude both in configuration and phase space. The path integral solution can also be derived using physical principles based on Feynman close-quote s original reasoning. We check that the Fourier transform in energy of the fixed-energy point-to-point transition amplitude gives the well known time-dependent transition amplitude, and calculate the WKB approximation. copyright 1997 Academic Press, Inc

  1. Net primary productivity, allocation pattern and carbon use efficiency in an apple orchard assessed by integrating eddy covariance, biometric and continuous soil chamber measurements

    Directory of Open Access Journals (Sweden)

    D. Zanotelli

    2013-05-01

    Full Text Available Carbon use efficiency (CUE, the ratio of net primary production (NPP over gross primary production (GPP, is a functional parameter that could possibly link the current increasingly accurate global GPP estimates with those of net ecosystem exchange, for which global predictors are still unavailable. Nevertheless, CUE estimates are actually available for only a few ecosystem types, while information regarding agro-ecosystems is scarce, in spite of the simplified spatial structure of these ecosystems that facilitates studies on allocation patterns and temporal growth dynamics. We combined three largely deployed methods, eddy covariance, soil respiration and biometric measurements, to assess monthly values of CUE, NPP and allocation patterns in different plant organs in an apple orchard during a complete year (2010. We applied a measurement protocol optimized for quantifying monthly values of carbon fluxes in this ecosystem type, which allows for a cross check between estimates obtained from different methods. We also attributed NPP components to standing biomass increments, detritus cycle feeding and lateral exports. We found that in the apple orchard, both net ecosystem production and gross primary production on a yearly basis, 380 ± 30 g C m−2 and 1263 ± 189 g C m−2 respectively, were of a magnitude comparable to those of natural forests growing in similar climate conditions. The largest differences with respect to forests are in the allocation pattern and in the fate of produced biomass. The carbon sequestered from the atmosphere was largely allocated to production of fruit: 49% of annual NPP was taken away from the ecosystem through apple production. Organic material (leaves, fine root litter, pruned wood and early fruit falls contributing to the detritus cycle was 46% of the NPP. Only 5% was attributable to standing biomass increment, while this NPP component is generally the largest in forests. The CUE, with an annual average of 0.71

  2. Net primary productivity, allocation pattern and carbon use efficiency in an apple orchard assessed by integrating eddy-covariance, biometric and continuous soil chamber measurements

    Science.gov (United States)

    Zanotelli, D.; Montagnani, L.; Manca, G.; Tagliavini, M.

    2012-10-01

    Carbon use efficiency (CUE) is a functional parameter that could possibly link the current increasingly accurate global estimates of gross primary production with those of net ecosystem exchange, for which global predictors are still unavailable. Nevertheless, CUE estimates are actually available for only a few ecosystem types, while information regarding agro-ecosystems is scarce, in spite of the simplified spatial structure of these ecosystems that facilitates studies on allocation patterns and temporal growth dynamics. We combined three largely deployed methods, eddy covariance, soil respiration and biometric measurements, to assess monthly values of CUE, net primary production (NPP) and allocation patterns in different plant organs in an apple orchard during a complete year (2010). We applied a~measurement protocol optimized for quantifying monthly values of carbon fluxes in this ecosystem type, which allows for a cross-check between estimates obtained from different methods. We also attributed NPP components to standing biomass increments, detritus cycle feeding and lateral exports. We found that in the apple orchard both net ecosystem production and gross primary production on yearly basis, 380 ± 30 g C m-2 and 1263 ± 189 g C m-2 respectively, were of a magnitude comparable to those of natural forests growing in similar climate conditions. The largest differences with respect to forests are in the allocation pattern and in the fate of produced biomass. The carbon sequestered from the atmosphere was largely allocated to production of fruits: 49% of annual NPP was taken away from the ecosystem through apple production. Organic material (leaves, fine root litter, pruned wood and early fruit falls) contributing to the detritus cycle was 46% of the NPP. Only 5% was attributable to standing biomass increment, while this NPP component is generally the largest in forests. The CUE, with an annual average of 0.71 ± 0.09, was higher than the previously suggested

  3. Net primary productivity, allocation pattern and carbon use efficiency in an apple orchard assessed by integrating eddy covariance, biometric and continuous soil chamber measurements

    Science.gov (United States)

    Zanotelli, D.; Montagnani, L.; Manca, G.; Tagliavini, M.

    2013-05-01

    Carbon use efficiency (CUE), the ratio of net primary production (NPP) over gross primary production (GPP), is a functional parameter that could possibly link the current increasingly accurate global GPP estimates with those of net ecosystem exchange, for which global predictors are still unavailable. Nevertheless, CUE estimates are actually available for only a few ecosystem types, while information regarding agro-ecosystems is scarce, in spite of the simplified spatial structure of these ecosystems that facilitates studies on allocation patterns and temporal growth dynamics. We combined three largely deployed methods, eddy covariance, soil respiration and biometric measurements, to assess monthly values of CUE, NPP and allocation patterns in different plant organs in an apple orchard during a complete year (2010). We applied a measurement protocol optimized for quantifying monthly values of carbon fluxes in this ecosystem type, which allows for a cross check between estimates obtained from different methods. We also attributed NPP components to standing biomass increments, detritus cycle feeding and lateral exports. We found that in the apple orchard, both net ecosystem production and gross primary production on a yearly basis, 380 ± 30 g C m-2 and 1263 ± 189 g C m-2 respectively, were of a magnitude comparable to those of natural forests growing in similar climate conditions. The largest differences with respect to forests are in the allocation pattern and in the fate of produced biomass. The carbon sequestered from the atmosphere was largely allocated to production of fruit: 49% of annual NPP was taken away from the ecosystem through apple production. Organic material (leaves, fine root litter, pruned wood and early fruit falls) contributing to the detritus cycle was 46% of the NPP. Only 5% was attributable to standing biomass increment, while this NPP component is generally the largest in forests. The CUE, with an annual average of 0.71 ± 0.12, was higher

  4. FELIX experiments and computational needs for eddy current analysis of fusion reactors

    International Nuclear Information System (INIS)

    Turner, L.R.

    1984-01-01

    In a fusion reactor, changing magnetic fields are closely coupled to the electrically-conducting metal structure. This coupling is particularly pronounced in a tokamak reactor in which magnetic fields are used to confine, stabilize, drive, and heat the plasma. Electromagnetic effects in future fusion reactors will have far-reaching implications in the configuration, operation, and maintenance of the reactors. This paper describes the impact of eddy-current effects on future reactors, the requirements of computer codes for analyzing those effects, and the FELIX experiments which will provide needed data for code validation

  5. Oceanic eddies in synthetic aperture radar images

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    determining mechanism of eddy formation in this case is the vorticity (shear) of the currents or devi- ation of one current by another. Figure 10 shows the ERS-1 SAR image with a couple of cyclonic eddies that is supposedly located in the area of confluence of oppositely directed currents in the central part of the Japan Sea.

  6. Accelerating Sequential Gaussian Simulation with a constant path

    Science.gov (United States)

    Nussbaumer, Raphaël; Mariethoz, Grégoire; Gravey, Mathieu; Gloaguen, Erwan; Holliger, Klaus

    2018-03-01

    Sequential Gaussian Simulation (SGS) is a stochastic simulation technique commonly employed for generating realizations of Gaussian random fields. Arguably, the main limitation of this technique is the high computational cost associated with determining the kriging weights. This problem is compounded by the fact that often many realizations are required to allow for an adequate uncertainty assessment. A seemingly simple way to address this problem is to keep the same simulation path for all realizations. This results in identical neighbourhood configurations and hence the kriging weights only need to be determined once and can then be re-used in all subsequent realizations. This approach is generally not recommended because it is expected to result in correlation between the realizations. Here, we challenge this common preconception and make the case for the use of a constant path approach in SGS by systematically evaluating the associated benefits and limitations. We present a detailed implementation, particularly regarding parallelization and memory requirements. Extensive numerical tests demonstrate that using a constant path allows for substantial computational gains with very limited loss of simulation accuracy. This is especially the case for a constant multi-grid path. The computational savings can be used to increase the neighbourhood size, thus allowing for a better reproduction of the spatial statistics. The outcome of this study is a recommendation for an optimal implementation of SGS that maximizes accurate reproduction of the covariance structure as well as computational efficiency.

  7. Phase-space path-integral calculation of the Wigner function

    International Nuclear Information System (INIS)

    Samson, J H

    2003-01-01

    The Wigner function W(q, p) is formulated as a phase-space path integral, whereby its sign oscillations can be seen to follow from interference between the geometrical phases of the paths. The approach has similarities to the path-centroid method in the configuration-space path integral. Paths can be classified by the midpoint of their ends; short paths where the midpoint is close to (q, p) and which lie in regions of low energy (low P function of the Hamiltonian) will dominate, and the enclosed area will determine the sign of the Wigner function. As a demonstration, the method is applied to a sequence of density matrices interpolating between a Poissonian number distribution and a number state, each member of which can be represented exactly by a discretized path integral with a finite number of vertices. Saddle-point evaluation of these integrals recovers (up to a constant factor) the WKB approximation to the Wigner function of a number state

  8. Large eddy simulation of spanwise rotating turbulent channel flow with dynamic variants of eddy viscosity model

    Science.gov (United States)

    Jiang, Zhou; Xia, Zhenhua; Shi, Yipeng; Chen, Shiyi

    2018-04-01

    A fully developed spanwise rotating turbulent channel flow has been numerically investigated utilizing large-eddy simulation. Our focus is to assess the performances of the dynamic variants of eddy viscosity models, including dynamic Vreman's model (DVM), dynamic wall adapting local eddy viscosity (DWALE) model, dynamic σ (Dσ ) model, and the dynamic volumetric strain-stretching (DVSS) model, in this canonical flow. The results with dynamic Smagorinsky model (DSM) and direct numerical simulations (DNS) are used as references. Our results show that the DVM has a wrong asymptotic behavior in the near wall region, while the other three models can correctly predict it. In the high rotation case, the DWALE can get reliable mean velocity profile, but the turbulence intensities in the wall-normal and spanwise directions show clear deviations from DNS data. DVSS exhibits poor predictions on both the mean velocity profile and turbulence intensities. In all three cases, Dσ performs the best.

  9. Eddy currents in accelerator magnets

    CERN Document Server

    Moritz, G

    2010-01-01

    This paper covers the main eddy current effects in accelerator magnets - field modification (time delay and field quality) and resistive power losses. In the first part, starting from the Maxwell equations, a basic understanding of the processes is given and explained with examples of simple geometry and time behaviour. Useful formulas are derived for an analytic estimate of the size of the effects. In the second part the effects in real magnets are analysed and described in comparison with numerical and measured results. Finally, based on the previous parts, design recommendations are given regarding how to minimize eddy current effects.

  10. Masticatory path pattern during mastication of chewing gum with regard to gender difference.

    Science.gov (United States)

    Kobayashi, Yoshinori; Shiga, Hiroshi; Arakawa, Ichiro; Yokoyama, Masaoki; Nakajima, Kunihisa

    2009-01-01

    To clarify the masticatory path patterns of the mandibular incisal point during mastication of softened chewing gum with regard to gender difference. One hundred healthy subjects (50 males and 50 females) were asked to chew softened chewing gum on one side at a time (right side and left side) and the movement of the mandibular incisal point was recorded using MKG K6I. After a catalog of path patterns was made, the movement path was classified into one of the pattern groups, and then the frequency of each pattern was investigated. A catalog of path patterns consisting of the three types of opening path (op1, linear or concave path; op2, path toward the chewing side after toward the non-working side; op3, convex path) and two types of closing path (cl1, convex path; cl2, concave path) was made. The movement path was classified into one of seven patterns, with six patterns being from the catalog and a final extra pattern in which the opening and closing paths crossed. The most common pattern among the subjects was Pattern I, followed by Patterns III, II, IV, V, VII, and VI, in that order. The majority of cases, 149 (74.5%) of 200 cases, showed either Pattern I (op1 and cl1) or Pattern III (op2 and cl1). There was no significant difference between the two genders in the frequency of each pattern. The movement path could be classified into seven patterns and no gender-related difference was found in the frequency of each pattern.

  11. Magnetic Diagnostics for Equilibrium Reconstructions in the Presence of Nonaxisymmetric Eddy Current Distributions in Tokamaks

    International Nuclear Information System (INIS)

    Kaita, R.; Kozub, T.; Logan, N.; Majeski, R.; Menard, J.; Zakharov, L.

    2010-01-01

    The lithium tokamak experiment (LTX) is a modest-sized spherical tokamak (R 0 = 0.4 m and a = 0.26 m) designed to investigate the low-recycling lithium wall operating regime for magnetically confined plasmas. LTX will reach this regime through a lithium-coated shell internal to the vacuum vessel, conformal to the plasma last-closed-flux surface, and heated to 300-400 C. This structure is highly conductive and not axisymmetric. The three-dimensional nature of the shell causes the eddy currents and magnetic fields to be three-dimensional as well. In order to analyze the plasma equilibrium in the presence of three-dimensional eddy currents, an extensive array of unique magnetic diagnostics has been implemented. Sensors are designed to survive high temperatures and incidental contact with lithium and provide data on toroidal asymmetries as well as full coverage of the poloidal cross-section. The magnetic array has been utilized to determine the effects of nonaxisymmetric eddy currents and to model the start-up phase of LTX. Measurements from the magnetic array, coupled with two-dimensional field component modeling, have allowed a suitable field null and initial plasma current to be produced. For full magnetic reconstructions, a three-dimensional electromagnetic model of the vacuum vessel and shell is under development.

  12. Benchmarking the mesoscale variability in global ocean eddy-permitting numerical systems

    Science.gov (United States)

    Cipollone, Andrea; Masina, Simona; Storto, Andrea; Iovino, Doroteaciro

    2017-10-01

    The role of data assimilation procedures on representing ocean mesoscale variability is assessed by applying eddy statistics to a state-of-the-art global ocean reanalysis (C-GLORS), a free global ocean simulation (performed with the NEMO system) and an observation-based dataset (ARMOR3D) used as an independent benchmark. Numerical results are computed on a 1/4 ∘ horizontal grid (ORCA025) and share the same resolution with ARMOR3D dataset. This "eddy-permitting" resolution is sufficient to allow ocean eddies to form. Further to assessing the eddy statistics from three different datasets, a global three-dimensional eddy detection system is implemented in order to bypass the need of regional-dependent definition of thresholds, typical of commonly adopted eddy detection algorithms. It thus provides full three-dimensional eddy statistics segmenting vertical profiles from local rotational velocities. This criterion is crucial for discerning real eddies from transient surface noise that inevitably affects any two-dimensional algorithm. Data assimilation enhances and corrects mesoscale variability on a wide range of features that cannot be well reproduced otherwise. The free simulation fairly reproduces eddies emerging from western boundary currents and deep baroclinic instabilities, while underestimates shallower vortexes that populate the full basin. The ocean reanalysis recovers most of the missing turbulence, shown by satellite products , that is not generated by the model itself and consistently projects surface variability deep into the water column. The comparison with the statistically reconstructed vertical profiles from ARMOR3D show that ocean data assimilation is able to embed variability into the model dynamics, constraining eddies with in situ and altimetry observation and generating them consistently with local environment.

  13. Observation of baroclinic eddies southeast of Okinawa Island

    Institute of Scientific and Technical Information of China (English)

    PARK; Jae-Hun

    2008-01-01

    In the region southeast of Okinawa, during May to July 2001, a cyclonic and an anticyclonic eddy were observed from combined measurements of hydrocasts, an upward-looking moored acoustic Doppler current profiler (MADCP), pressure-recording inverted echo sounders (PIESs), satellite altimetry, and a coastal tide gauge. The hydrographic data showed that the lowest/highest temperature (T) and salinity (S) anomalies from a 13-year mean for the same season were respectively -3.0/+2.5℃ and -0.20/+0.15 psu at 380/500 dbar for the cyclonic/anticyclonic eddies. From the PIES data, using a gravest empirical mode method, we estimated time-varying surface dynamic height (D) anomaly referred to 2000 dbar changing from -20 to 30 cm, and time-varying T and S anomalies at 500 dbar ranging through about ±2 ℃ and ±0.2 psu, respectively. The passage of the eddies caused variations of both satellite-measured sea surface height anomaly (SSHA) and tide-gauge-measured sea level anomaly to change from about –20 to 30 cm, consistent with the D anomaly from the PIESs. Bottom pressure sensors measured no variation related to these eddy activities, which indicated that the two eddies were dominated by baro-clinicity. Time series of SSHA map confirmed that the two eddies, originating from the North Pacific Subtropical Countercurrent region near 20°―30°N and 150°―160°E, traveled about 3000 km for about 18 months with mean westward propagation speed of about 6 cm/s, before arriving at the region southeast of Okinawa Island.

  14. Detached Eddy Simulation of Flap Side-Edge Flow

    Science.gov (United States)

    Balakrishnan, Shankar K.; Shariff, Karim R.

    2016-01-01

    Detached Eddy Simulation (DES) of flap side-edge flow was performed with a wing and half-span flap configuration used in previous experimental and numerical studies. The focus of the study is the unsteady flow features responsible for the production of far-field noise. The simulation was performed at a Reynolds number (based on the main wing chord) of 3.7 million. Reynolds Averaged Navier-Stokes (RANS) simulations were performed as a precursor to the DES. The results of these precursor simulations match previous experimental and RANS results closely. Although the present DES simulations have not reached statistical stationary yet, some unsteady features of the developing flap side-edge flowfield are presented. In the final paper it is expected that statistically stationary results will be presented including comparisons of surface pressure spectra with experimental data.

  15. Analysis of Known Linear Distributed Average Consensus Algorithms on Cycles and Paths

    Directory of Open Access Journals (Sweden)

    Jesús Gutiérrez-Gutiérrez

    2018-03-01

    Full Text Available In this paper, we compare six known linear distributed average consensus algorithms on a sensor network in terms of convergence time (and therefore, in terms of the number of transmissions required. The selected network topologies for the analysis (comparison are the cycle and the path. Specifically, in the present paper, we compute closed-form expressions for the convergence time of four known deterministic algorithms and closed-form bounds for the convergence time of two known randomized algorithms on cycles and paths. Moreover, we also compute a closed-form expression for the convergence time of the fastest deterministic algorithm considered on grids.

  16. Study on classical and excess eddy currents losses of Terfenol-D

    Energy Technology Data Exchange (ETDEWEB)

    Talebian, Soheil; Hojjat, Yousef [Department of Mechanical Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Ghodsi, Mojtaba [Department of Mechanical and Industrial Engineering, Sultan Qaboos University, Muscat (Oman); Karafi, Mohammad Reza [Department of Mechanical Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of)

    2015-08-15

    In the present paper, classical and excess eddy currents losses of Terfenol-D are studied and effects of magnetic field frequency, peak of magnetic flux density and diameter of Terfenol-D on the eddy currents losses are investigated. To provide reliable data for the purpose of the paper, an experimental laboratory is fabricated and used to obtain major and minor hysteresis loops of Terfenol-D at different frequencies. In theoretical study, initially an analytical model based on uniform distribution of magnetic flux is developed which yields to calculation of classical eddy currents losses. Then, another eddy currents model based on non-uniform distribution of magnetic flux and nonlinear diffusion of electromagnetic fields is presented. The difference between output values of the two models is identified as excess eddy currents losses. Obtained results show that the values of excess losses are generally larger than classical losses and applying just classical model leads to wrong calculation of actual value of eddy currents losses. For the results obtained from two above models, empirical models with respect to the magnetic field frequency and the peak value of magnetic flux density are achieved which can predict the eddy currents losses precisely. To validate the empirical relations, experiments are repeated at a new frequency and values of power losses calculated from analytical equations are compared with the predicted values of the empirical models. The results point towards possibility to use the obtained empirical relations in order to calculate the classical and excess eddy currents losses of Terfenol-D at the frequencies below 200 Hz and different values of magnetic flux density. - Highlights: • Classical eddy currents loss of Terfenol-D is studied using Maxwell's laws. • Excess eddy currents loss of Terfenol-D is studied using Mayergoyz nonlinear model. • Effects of Terfenol-D geometry on the eddy currents losses are investigated. • Power

  17. Poincare covariance and κ-Minkowski spacetime

    International Nuclear Information System (INIS)

    Dabrowski, Ludwik; Piacitelli, Gherardo

    2011-01-01

    A fully Poincare covariant model is constructed as an extension of the κ-Minkowski spacetime. Covariance is implemented by a unitary representation of the Poincare group, and thus complies with the original Wigner approach to quantum symmetries. This provides yet another example (besides the DFR model), where Poincare covariance is realised a la Wigner in the presence of two characteristic dimensionful parameters: the light speed and the Planck length. In other words, a Doubly Special Relativity (DSR) framework may well be realised without deforming the meaning of 'Poincare covariance'. -- Highlights: → We construct a 4d model of noncommuting coordinates (quantum spacetime). → The coordinates are fully covariant under the undeformed Poincare group. → Covariance a la Wigner holds in presence of two dimensionful parameters. → Hence we are not forced to deform covariance (e.g. as quantum groups). → The underlying κ-Minkowski model is unphysical; covariantisation does not cure this.

  18. Abnormalities in Structural Covariance of Cortical Gyrification in Parkinson's Disease.

    Science.gov (United States)

    Xu, Jinping; Zhang, Jiuquan; Zhang, Jinlei; Wang, Yue; Zhang, Yanling; Wang, Jian; Li, Guanglin; Hu, Qingmao; Zhang, Yuanchao

    2017-01-01

    Although abnormal cortical morphology and connectivity between brain regions (structural covariance) have been reported in Parkinson's disease (PD), the topological organizations of large-scale structural brain networks are still poorly understood. In this study, we investigated large-scale structural brain networks in a sample of 37 PD patients and 34 healthy controls (HC) by assessing the structural covariance of cortical gyrification with local gyrification index (lGI). We demonstrated prominent small-world properties of the structural brain networks for both groups. Compared with the HC group, PD patients showed significantly increased integrated characteristic path length and integrated clustering coefficient, as well as decreased integrated global efficiency in structural brain networks. Distinct distributions of hub regions were identified between the two groups, showing more hub regions in the frontal cortex in PD patients. Moreover, the modular analyses revealed significantly decreased integrated regional efficiency in lateral Fronto-Insula-Temporal module, and increased integrated regional efficiency in Parieto-Temporal module in the PD group as compared to the HC group. In summary, our study demonstrated altered topological properties of structural networks at a global, regional and modular level in PD patients. These findings suggests that the structural networks of PD patients have a suboptimal topological organization, resulting in less effective integration of information between brain regions.

  19. Forces in Motzkin paths in a wedge

    International Nuclear Information System (INIS)

    Janse van Rensburg, E J

    2006-01-01

    Entropic forces in models of Motzkin paths in a wedge geometry are considered as models of forces in polymers in confined geometries. A Motzkin path in the square lattice is a path from the origin to a point in the line Y = X while it never visits sites below this line, and it is constrained to give unit length steps only in the north and east directions and steps of length √2 in the north-east direction. Motzkin path models may be generalized to ensembles of NE-oriented paths above the line Y = rX, where r > 0 is an irrational number. These are paths giving east, north and north-east steps from the origin in the square lattice, and confined to the r-wedge formed by the Y-axis and the line Y = rX. The generating function g r of these paths is not known, but if r > 1, then I determine its radius of convergence to be t r = min (r-1)/r≤y≤r/(r+1) [y y (1-r(1-y)) 1-r(1-y) (r(1-y)-y) r(1-y)-y ] and if r is an element of (0, 1), then t r = 1/3. The entropic force the path exerts on the line Y rX may be computed from this. An asymptotic expression for the force for large values of r is given by F(r) = log(2r)/r 2 - (1+2log(2r))/2r 3 + O (log(2r)/r 4 ). In terms of the vertex angle α of the r-wedge, the moment of the force about the origin has leading terms F(α) log(2/α) - (α/2)(1+2log(2/α)) + O(α 2 log(2/α)) as α → 0 + and F(α) = 0 if α is element of [π/4, π/2]. Moreover, numerical integration of the force shows that the total work done by closing the wedge is 1.085 07... lattice units. An alternative ensemble of NE-oriented paths may be defined by slightly changing the generating function g r . In this model, it is possible to determine closed-form expressions for the limiting free energy and the force. The leading term in an asymptotic expansions for this force agrees with the leading term in the asymptotic expansion of the above model, and the subleading term only differs by a factor of 2

  20. Surprisingly low frequency attenuation effects in long tubes when measuring turbulent fluxes at tall towers

    DEFF Research Database (Denmark)

    Ibrom, Andreas; Brændholt, Andreas; Pilegaard, Kim

    2016-01-01

    The eddy covariance technique relies on the fast and accurate measurement of gas concentration fluctuations. While for some gasses robust and compact sensors are available, measurement of, e.g., non CO2 greenhouse gas fluxes is often performed with sensitive equipment that cannot be run on a tower...... without massively disturbing the wind field. To measure CO and N2O fluxes, we installed an eddy covariance system at a 125 m mast, where the gas analyser was kept in a laboratory close to the tower and the sampling was performed using a 150 m long tube with a gas intake at 96 m height. We investigated...... by reducing both the water vapour dilution correction and the cross sensitivity effects on the N2O and CO flux measurements. Here we present the set-up of the concentration step change experiment and its results and compare them with recently developed theories for the behaviour of gases in turbulent tube...

  1. The exchange of energy, water and carbon dioxide between wet arctic tundra and the atmosphere at the Lena River Delta, Northern Siberia

    Energy Technology Data Exchange (ETDEWEB)

    Kutzbach, L.

    2006-07-01

    The ecosystem-scale exchange fluxes of energy, water and carbon dioxide between wet arctic tundra and the atmosphere were investigated by the micrometeorological eddy covariance method. The investigation site was the centre of the Lena River Delta in Northern Siberia characterised by a polar and distinctly continental climate, very cold and ice-rich permafrost and its position at the interface between the Eurasian continent and the Arctic Ocean. The measurements were performed on the surface of a Holocene river terrace characterised by wet polygonal tundra. The soils at the site are characterised by high organic matter content, low nutrient availability and pronounced water logging. The vegetation is dominated by sedges and mosses. The fluctuations of the H{sub 2}O and CO{sub 2} concentrations were measured with a closed-path infrared gas analyser. The fast-response eddy covariance measurements were supplemented by a set of slow-response meteorological and soil-meteorological measurements. The combined datasets of the two campaigns 2003 and 2004 were used to characterise the seasonal course of the energy, water and CO{sub 2} fluxes and the underlying processes for the synthetic measurement period May 28..October 21 2004/2003 including the period of snow and soil thawing as well as the beginning of refreezing. The synthetic measurement period 2004/2003 was characterised by a long snow ablation period and a late start of the growing season. On the other hand, the growing season ended also late due to high temperatures and snow-free conditions in September. The cumulative summer energy partitioning was characterised by low net radiation, large ground heat flux, low latent heat flux and very low sensible heat flux compared to other tundra sites. These findings point out the major importance of the very cold permafrost for the summer energy budget of the tundra in Northern Siberia. (orig./SR)

  2. Eddy current inspection of tubing

    International Nuclear Information System (INIS)

    Bauza, J. L. R.; Herrero, J.; Diaz, J.

    1966-01-01

    The Experimental research work carried out to develop a Eddy current testing equipment is described. Search coils with ferrite or air cores were used and the obtained results are discussed. Valuable information was gained from a improved channel in which a direct measure of the defect and the reference signal phase difference is obtained. Artificial defect used to evaluate resolution and sensitivity were produced by electro-machining and mechanical means. Finned SAP tubing was tested in a routine basis with the described equipment and the results plotted. Basic and theoretical considerations on the Eddy current testing technique are given in the last section of this report. (Author)

  3. Signal processing of eddy current three-dimensional maps

    International Nuclear Information System (INIS)

    Birac, C.; David, D.; Lamant, D.

    1987-01-01

    Digital processing of eddy current three-dimensional maps improves accuracy of detection: flattening, filtering, computing deconvolution, mapping new variables,.., give new possibilities for difficult test problems. With simulation of defects, probes, probe travels, it is now possible to compute new eddy current processes, without machining defects or building probes

  4. Covariant currents in N=2 super-Liouville theory

    International Nuclear Information System (INIS)

    Gomis, J.; Suzuki, Hiroshi

    1993-01-01

    Based on a path-integral prescription for anomaly calculation, we analyze an effective theory of the two-dimensional N=2 supergravity, i.e. N=2 super-Liouville theory. We calculate the anomalies associated with the BRST supercurrent and the ghost-number supercurrent. From those expressions of anomalies, we construct covariant BRST and ghost-number supercurrents in the effective theory. We then show that the (super-)coordinate BRST current algebra forms a superfield extension of the topological conformal algebra for an arbitrary type of conformal matter or, in terms of the string theory, for an arbitrary number of space-time dimensions. This fact is in great contrast with N=0 and N=1 (super-)Liouville theory, where the topological algebra singles out a particular value of dimensions. Our observation suggests a topological nature of the two-dimensional N=2 supergravity as a quantum theory. (orig.)

  5. Modeling Covariance Breakdowns in Multivariate GARCH

    OpenAIRE

    Jin, Xin; Maheu, John M

    2014-01-01

    This paper proposes a flexible way of modeling dynamic heterogeneous covariance breakdowns in multivariate GARCH (MGARCH) models. During periods of normal market activity, volatility dynamics are governed by an MGARCH specification. A covariance breakdown is any significant temporary deviation of the conditional covariance matrix from its implied MGARCH dynamics. This is captured through a flexible stochastic component that allows for changes in the conditional variances, covariances and impl...

  6. Econometric analysis of realised covariation: high frequency covariance, regression and correlation in financial economics

    OpenAIRE

    Ole E. Barndorff-Nielsen; Neil Shephard

    2002-01-01

    This paper analyses multivariate high frequency financial data using realised covariation. We provide a new asymptotic distribution theory for standard methods such as regression, correlation analysis and covariance. It will be based on a fixed interval of time (e.g. a day or week), allowing the number of high frequency returns during this period to go to infinity. Our analysis allows us to study how high frequency correlations, regressions and covariances change through time. In particular w...

  7. A Min-max Relation for Monotone Path Systems in Simple Regions

    DEFF Research Database (Denmark)

    Cameron, Kathleen

    1996-01-01

    A monotone path system (MPS) is a finite set of pairwise disjointpaths (polygonal arcs) in the plane such that every horizontal line intersectseach of the paths in at most one point. We consider a simple polygon in thexy-plane which bounds the simple polygonal (closed) region D. Let T and B betwo...

  8. Modified multiblock partial least squares path modeling algorithm with backpropagation neural networks approach

    Science.gov (United States)

    Yuniarto, Budi; Kurniawan, Robert

    2017-03-01

    PLS Path Modeling (PLS-PM) is different from covariance based SEM, where PLS-PM use an approach based on variance or component, therefore, PLS-PM is also known as a component based SEM. Multiblock Partial Least Squares (MBPLS) is a method in PLS regression which can be used in PLS Path Modeling which known as Multiblock PLS Path Modeling (MBPLS-PM). This method uses an iterative procedure in its algorithm. This research aims to modify MBPLS-PM with Back Propagation Neural Network approach. The result is MBPLS-PM algorithm can be modified using the Back Propagation Neural Network approach to replace the iterative process in backward and forward step to get the matrix t and the matrix u in the algorithm. By modifying the MBPLS-PM algorithm using Back Propagation Neural Network approach, the model parameters obtained are relatively not significantly different compared to model parameters obtained by original MBPLS-PM algorithm.

  9. ISSUES IN NEUTRON CROSS SECTION COVARIANCES

    Energy Technology Data Exchange (ETDEWEB)

    Mattoon, C.M.; Oblozinsky,P.

    2010-04-30

    We review neutron cross section covariances in both the resonance and fast neutron regions with the goal to identify existing issues in evaluation methods and their impact on covariances. We also outline ideas for suitable covariance quality assurance procedures.We show that the topic of covariance data remains controversial, the evaluation methodologies are not fully established and covariances produced by different approaches have unacceptable spread. The main controversy is in very low uncertainties generated by rigorous evaluation methods and much larger uncertainties based on simple estimates from experimental data. Since the evaluators tend to trust the former, while the users tend to trust the latter, this controversy has considerable practical implications. Dedicated effort is needed to arrive at covariance evaluation methods that would resolve this issue and produce results accepted internationally both by evaluators and users.

  10. Statistical Characteristics of Mesoscale Eddies in the North Pacific Derived from Satellite Altimetry

    Directory of Open Access Journals (Sweden)

    Yu-Hsin Cheng

    2014-06-01

    Full Text Available The sea level anomaly data derived from satellite altimetry are analyzed to investigate statistical characteristics of mesoscale eddies in the North Pacific. Eddies are detected by a free-threshold eddy identification algorithm. The results show that the distributions of size, amplitude, propagation speed, and eddy kinetic energy of eddy follow the Rayleigh distribution. The most active regions of eddies are the Kuroshio Extension region, the Subtropical Counter Current zone, and the Northeastern Tropical Pacific region. By contrast, eddies are seldom observed around the center of the eastern part of the North Pacific Subarctic Gyre. The propagation speed and kinetic energy of cyclonic and anticyclonic eddies are almost the same, but anticyclonic eddies possess greater lifespans, sizes, and amplitudes than those of cyclonic eddies. Most eddies in the North Pacific propagate westward except in the Oyashio region. Around the northeastern tropical Pacific and the California currents, cyclonic and anticyclonic eddies propagate westward with slightly equatorward (197° average azimuth relative to east and poleward (165° deflection, respectively. This implies that the background current may play an important role in formation of the eddy pathway patterns.

  11. Closed form fourier-based transmit beamforming for MIMO radar

    KAUST Repository

    Lipor, John J.

    2014-05-01

    In multiple-input multiple-output (MIMO) radar setting, it is often desirable to design correlated waveforms such that power is transmitted only to a given set of locations, a process known as beampattern design. To design desired beam-pattern, current research uses iterative algorithms, first to synthesize the waveform covariance matrix, R, then to design the actual waveforms to realize R. In contrast to this, we present a closed form method to design R that exploits discrete Fourier transform and Toeplitz matrix. The resulting covariance matrix fulfills the practical constraints and performance is similar to that of iterative methods. Next, we present a radar architecture for the desired beampattern that does not require the synthesis of covariance matrix nor the design of correlated waveforms. © 2014 IEEE.

  12. The eddy kinetic energy budget in the Red Sea

    KAUST Repository

    Zhan, Peng; Subramanian, Aneesh C.; Yao, Fengchao; Kartadikaria, Aditya R.; Guo, Daquan; Hoteit, Ibrahim

    2016-01-01

    The budget of eddy kinetic energy (EKE) in the Red Sea, including the sources, redistributions and sink, is examined using a high-resolution eddy-resolving ocean circulation model. A pronounced seasonally varying EKE is identified, with its maximum

  13. Eddy current standards - Cracks versus notches

    Science.gov (United States)

    Hagemaier, D. J.; Collingwood, M. R.; Nguyen, K. H.

    1992-10-01

    Eddy current tests aimed at evaluating cracks and electron-discharge machined (EDM) notches in 7075-T6 aluminum specimens are described. A comparison of the shape and amplitude of recordings made from both transverse and longitudinal scans of small EDM notches and fatigue cracks showd almost identical results. The signal amplitude and phase angle increased with an increase of EDM notch and crak size. It is concluded that equivalent eddy current results obtained from similar-size surface cracks and notches in aluminum can be used to establish a desired sensitivity level for inspection.

  14. Eddy correlation measurements of oxygen uptake in deep ocean sediments

    DEFF Research Database (Denmark)

    Berg, P.; Glud, Ronnie Nøhr; Hume, A.

    2010-01-01

    .62 +/- 0.23 (SE, n = 7), 1.65 +/- 0.33 (n = 2), and 1.43 +/- 0.15 (n = 25) mmol m(-2) d(-1). The very good agreement between the eddy correlation flux and the chamber flux serves as a new, important validation of the eddy correlation technique. It demonstrates that the eddy correlation instrumentation......Abstract: We present and compare small sediment-water fluxes of O-2 determined with the eddy correlation technique, with in situ chambers, and from vertical sediment microprofiles at a 1450 m deep-ocean site in Sagami Bay, Japan. The average O-2 uptake for the three approaches, respectively, was 1...... available today is precise and can resolve accurately even very small benthic O-2 fluxes. The correlated fluctuations in vertical velocity and O-2 concentration that give the eddy flux had average values of 0.074 cm s(-1) and 0.049 mu M. The latter represents only 0.08% of the 59 mu M mean O-2 concentration...

  15. Eddy current testing probe with dual half-cylindrical coils

    Science.gov (United States)

    Bae, Byung-Hoon; Choi, Jung-Mi; Kim, Soo-Yong

    2000-02-01

    We have developed a new eddy current probe composed of a dual half-cylindrical (2HC) coil as an exciting coil and a sensing coil that is placed in the small gap of the 2HC coil. The 2HC coil induces a linear eddy current on the narrow region within the target medium. The magnitude of eddy current has a maximum peak with the narrow width, underneath the center of the exciting 2HC coil. Because of the linear eddy current, the probe can be used to detect not only the existence of a crack but also its direction in conducting materials. Using specimen with a machined crack, and varying the exciting frequency from 0.5 to 100 kHz, we investigated the relationships between the direction of crack and the output voltage of the sensing coil.

  16. Covariance Partition Priors: A Bayesian Approach to Simultaneous Covariance Estimation for Longitudinal Data.

    Science.gov (United States)

    Gaskins, J T; Daniels, M J

    2016-01-02

    The estimation of the covariance matrix is a key concern in the analysis of longitudinal data. When data consists of multiple groups, it is often assumed the covariance matrices are either equal across groups or are completely distinct. We seek methodology to allow borrowing of strength across potentially similar groups to improve estimation. To that end, we introduce a covariance partition prior which proposes a partition of the groups at each measurement time. Groups in the same set of the partition share dependence parameters for the distribution of the current measurement given the preceding ones, and the sequence of partitions is modeled as a Markov chain to encourage similar structure at nearby measurement times. This approach additionally encourages a lower-dimensional structure of the covariance matrices by shrinking the parameters of the Cholesky decomposition toward zero. We demonstrate the performance of our model through two simulation studies and the analysis of data from a depression study. This article includes Supplementary Material available online.

  17. Eddy current analysis by the finite element circuit method

    International Nuclear Information System (INIS)

    Kameari, A.; Suzuki, Y.

    1977-01-01

    The analysis of the transient eddy current in the conductors by ''Finite Element Circuit Method'' is developed. This method can be easily applied to various geometrical shapes of thin conductors. The eddy currents on the vacuum vessel and the upper and lower support plates of JT-60 machine (which is now being constructed by Japan Atomic Energy Research Institute) are calculated by this method. The magnetic field induced by the eddy current is estimated in the domain occupied by the plasma. And the force exerted to the vacuum vessel is also estimated

  18. Covariant diagrams for one-loop matching

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zhengkang [Michigan Center for Theoretical Physics (MCTP), University of Michigan,450 Church Street, Ann Arbor, MI 48109 (United States); Deutsches Elektronen-Synchrotron (DESY),Notkestraße 85, 22607 Hamburg (Germany)

    2017-05-30

    We present a diagrammatic formulation of recently-revived covariant functional approaches to one-loop matching from an ultraviolet (UV) theory to a low-energy effective field theory. Various terms following from a covariant derivative expansion (CDE) are represented by diagrams which, unlike conventional Feynman diagrams, involve gauge-covariant quantities and are thus dubbed “covariant diagrams.” The use of covariant diagrams helps organize and simplify one-loop matching calculations, which we illustrate with examples. Of particular interest is the derivation of UV model-independent universal results, which reduce matching calculations of specific UV models to applications of master formulas. We show how such derivation can be done in a more concise manner than the previous literature, and discuss how additional structures that are not directly captured by existing universal results, including mixed heavy-light loops, open covariant derivatives, and mixed statistics, can be easily accounted for.

  19. Covariant diagrams for one-loop matching

    International Nuclear Information System (INIS)

    Zhang, Zhengkang

    2017-01-01

    We present a diagrammatic formulation of recently-revived covariant functional approaches to one-loop matching from an ultraviolet (UV) theory to a low-energy effective field theory. Various terms following from a covariant derivative expansion (CDE) are represented by diagrams which, unlike conventional Feynman diagrams, involve gauge-covariant quantities and are thus dubbed “covariant diagrams.” The use of covariant diagrams helps organize and simplify one-loop matching calculations, which we illustrate with examples. Of particular interest is the derivation of UV model-independent universal results, which reduce matching calculations of specific UV models to applications of master formulas. We show how such derivation can be done in a more concise manner than the previous literature, and discuss how additional structures that are not directly captured by existing universal results, including mixed heavy-light loops, open covariant derivatives, and mixed statistics, can be easily accounted for.

  20. High resolution eddy current microscopy

    Science.gov (United States)

    Lantz, M. A.; Jarvis, S. P.; Tokumoto, H.

    2001-01-01

    We describe a sensitive scanning force microscope based technique for measuring local variations in resistivity by monitoring changes in the eddy current induced damping of a cantilever with a magnetic tip oscillating above a conducting sample. To achieve a high sensitivity, we used a cantilever with an FeNdBLa particle mounted on the tip. Resistivity measurements are demonstrated on a silicon test structure with a staircase doping profile. Regions with resistivities of 0.0013, 0.0041, and 0.022 Ω cm are clearly resolved with a lateral resolution of approximately 180 nm. For this range of resistivities, the eddy current induced damping is found to depend linearly on the sample resistivity.

  1. Large eddy simulation of flows in industrial compressors: a path from 2015 to 2035

    Science.gov (United States)

    Gourdain, N.; Sicot, F.; Duchaine, F.; Gicquel, L.

    2014-01-01

    A better understanding of turbulent unsteady flows is a necessary step towards a breakthrough in the design of modern compressors. Owing to high Reynolds numbers and very complex geometry, the flow that develops in such industrial machines is extremely hard to predict. At this time, the most popular method to simulate these flows is still based on a Reynolds-averaged Navier–Stokes approach. However, there is some evidence that this formalism is not accurate for these components, especially when a description of time-dependent turbulent flows is desired. With the increase in computing power, large eddy simulation (LES) emerges as a promising technique to improve both knowledge of complex physics and reliability of flow solver predictions. The objective of the paper is thus to give an overview of the current status of LES for industrial compressor flows as well as to propose future research axes regarding the use of LES for compressor design. While the use of wall-resolved LES for industrial multistage compressors at realistic Reynolds number should not be ready before 2035, some possibilities exist to reduce the cost of LES, such as wall modelling and the adaptation of the phase-lag condition. This paper also points out the necessity to combine LES to techniques able to tackle complex geometries. Indeed LES alone, i.e. without prior knowledge of such flows for grid construction or the prohibitive yet ideal use of fully homogeneous meshes to predict compressor flows, is quite limited today. PMID:25024422

  2. Fast Computing for Distance Covariance

    OpenAIRE

    Huo, Xiaoming; Szekely, Gabor J.

    2014-01-01

    Distance covariance and distance correlation have been widely adopted in measuring dependence of a pair of random variables or random vectors. If the computation of distance covariance and distance correlation is implemented directly accordingly to its definition then its computational complexity is O($n^2$) which is a disadvantage compared to other faster methods. In this paper we show that the computation of distance covariance and distance correlation of real valued random variables can be...

  3. On estimating cosmology-dependent covariance matrices

    International Nuclear Information System (INIS)

    Morrison, Christopher B.; Schneider, Michael D.

    2013-01-01

    We describe a statistical model to estimate the covariance matrix of matter tracer two-point correlation functions with cosmological simulations. Assuming a fixed number of cosmological simulation runs, we describe how to build a 'statistical emulator' of the two-point function covariance over a specified range of input cosmological parameters. Because the simulation runs with different cosmological models help to constrain the form of the covariance, we predict that the cosmology-dependent covariance may be estimated with a comparable number of simulations as would be needed to estimate the covariance for fixed cosmology. Our framework is a necessary first step in planning a simulations campaign for analyzing the next generation of cosmological surveys

  4. Improved initial guess for minimum energy path calculations

    International Nuclear Information System (INIS)

    Smidstrup, Søren; Pedersen, Andreas; Stokbro, Kurt; Jónsson, Hannes

    2014-01-01

    A method is presented for generating a good initial guess of a transition path between given initial and final states of a system without evaluation of the energy. An objective function surface is constructed using an interpolation of pairwise distances at each discretization point along the path and the nudged elastic band method then used to find an optimal path on this image dependent pair potential (IDPP) surface. This provides an initial path for the more computationally intensive calculations of a minimum energy path on an energy surface obtained, for example, by ab initio or density functional theory. The optimal path on the IDPP surface is significantly closer to a minimum energy path than a linear interpolation of the Cartesian coordinates and, therefore, reduces the number of iterations needed to reach convergence and averts divergence in the electronic structure calculations when atoms are brought too close to each other in the initial path. The method is illustrated with three examples: (1) rotation of a methyl group in an ethane molecule, (2) an exchange of atoms in an island on a crystal surface, and (3) an exchange of two Si-atoms in amorphous silicon. In all three cases, the computational effort in finding the minimum energy path with DFT was reduced by a factor ranging from 50% to an order of magnitude by using an IDPP path as the initial path. The time required for parallel computations was reduced even more because of load imbalance when linear interpolation of Cartesian coordinates was used

  5. ERRORJ. Covariance processing code. Version 2.2

    International Nuclear Information System (INIS)

    Chiba, Go

    2004-07-01

    ERRORJ is the covariance processing code that can produce covariance data of multi-group cross sections, which are essential for uncertainty analyses of nuclear parameters, such as neutron multiplication factor. The ERRORJ code can process the covariance data of cross sections including resonance parameters, angular and energy distributions of secondary neutrons. Those covariance data cannot be processed by the other covariance processing codes. ERRORJ has been modified and the version 2.2 has been developed. This document describes the modifications and how to use. The main topics of the modifications are as follows. Non-diagonal elements of covariance matrices are calculated in the resonance energy region. Option for high-speed calculation is implemented. Perturbation amount is optimized in a sensitivity calculation. Effect of the resonance self-shielding on covariance of multi-group cross section can be considered. It is possible to read a compact covariance format proposed by N.M. Larson. (author)

  6. Time evolution of the eddy viscosity in two-dimensional navier-stokes flow

    Science.gov (United States)

    Chaves; Gama

    2000-02-01

    The time evolution of the eddy viscosity associated with an unforced two-dimensional incompressible Navier-Stokes flow is analyzed by direct numerical simulation. The initial condition is such that the eddy viscosity is isotropic and negative. It is shown by concrete examples that the Navier-Stokes dynamics stabilizes negative eddy viscosity effects. In other words, this dynamics moves monotonically the initial negative eddy viscosity to positive values before relaxation due to viscous term occurs.

  7. Eddy current inspection on heat exchanger tubes - problems and limitations

    International Nuclear Information System (INIS)

    Ilham Mukriz; Zainal Abidin Mohamed; Hairul Hasmoni Khairul Anuar; Mohd Salleh; Mahmood Dollah

    2005-01-01

    This paper focus on problems associated to eddy current inspection of heat exchanger tubes. A brief review on heat exchanger design and operation is presented. Eddy current technique in identifying inhomogeneity in tested tubes is discussed, highlighting its limitation in distinguishing between real pit type defects and other mundane anomalies. The limitation of the eddy current probe and equipment pertinent to the inspection are identified and areas of improvement are discussed. (Author)

  8. On the Likely Utility of Hybrid Weights Optimized for Variances in Hybrid Error Covariance Models

    Science.gov (United States)

    Satterfield, E.; Hodyss, D.; Kuhl, D.; Bishop, C. H.

    2017-12-01

    Because of imperfections in ensemble data assimilation schemes, one cannot assume that the ensemble covariance is equal to the true error covariance of a forecast. Previous work demonstrated how information about the distribution of true error variances given an ensemble sample variance can be revealed from an archive of (observation-minus-forecast, ensemble-variance) data pairs. Here, we derive a simple and intuitively compelling formula to obtain the mean of this distribution of true error variances given an ensemble sample variance from (observation-minus-forecast, ensemble-variance) data pairs produced by a single run of a data assimilation system. This formula takes the form of a Hybrid weighted average of the climatological forecast error variance and the ensemble sample variance. Here, we test the extent to which these readily obtainable weights can be used to rapidly optimize the covariance weights used in Hybrid data assimilation systems that employ weighted averages of static covariance models and flow-dependent ensemble based covariance models. Univariate data assimilation and multi-variate cycling ensemble data assimilation are considered. In both cases, it is found that our computationally efficient formula gives Hybrid weights that closely approximate the optimal weights found through the simple but computationally expensive process of testing every plausible combination of weights.

  9. Automatic analysis of signals during Eddy currents controls

    International Nuclear Information System (INIS)

    Chiron, D.

    1983-06-01

    A method and the corresponding instrument have been developed for automatic analysis of Eddy currents testing signals. This apparatus enables at the same time the analysis, every 2 milliseconds, of two signals at two different frequencies. It can be used either on line with an Eddy Current testing instrument or with a magnetic tape recorder [fr

  10. Perils of parsimony: properties of reduced-rank estimates of genetic covariance matrices.

    Science.gov (United States)

    Meyer, Karin; Kirkpatrick, Mark

    2008-10-01

    Eigenvalues and eigenvectors of covariance matrices are important statistics for multivariate problems in many applications, including quantitative genetics. Estimates of these quantities are subject to different types of bias. This article reviews and extends the existing theory on these biases, considering a balanced one-way classification and restricted maximum-likelihood estimation. Biases are due to the spread of sample roots and arise from ignoring selected principal components when imposing constraints on the parameter space, to ensure positive semidefinite estimates or to estimate covariance matrices of chosen, reduced rank. In addition, it is shown that reduced-rank estimators that consider only the leading eigenvalues and -vectors of the "between-group" covariance matrix may be biased due to selecting the wrong subset of principal components. In a genetic context, with groups representing families, this bias is inverse proportional to the degree of genetic relationship among family members, but is independent of sample size. Theoretical results are supplemented by a simulation study, demonstrating close agreement between predicted and observed bias for large samples. It is emphasized that the rank of the genetic covariance matrix should be chosen sufficiently large to accommodate all important genetic principal components, even though, paradoxically, this may require including a number of components with negligible eigenvalues. A strategy for rank selection in practical analyses is outlined.

  11. The South China Sea Mesoscale Eddy Experiment (S-MEE) and Its Primary Findings

    Science.gov (United States)

    Zhang, Z.; Tian, J.; Zhao, W.; Qiu, B.

    2016-02-01

    South China Sea (SCS), the largest marginal sea in the northwestern Pacific, have strong eddy activities as revealed by both satellite and in situ observations. The 3D structures of the SCS mesoscale eddies and their lifecycles, including the generation and dissipation processes, are, however, still not well understood at present because of the lack of well-designed field observations. In order to address the above two scientific issues (3D structure and lifecycle of SCS mesoscale eddies), the SCS Mesoscale Eddy Experiment (S-MEE for short) was designed and conducted in the period from October 2013 to June 2014. As part of S-MEE, two bottom-anchored subsurface mooring arrays with one consisting of 10 moorings and the other 7 moorings, were deployed along the historical pathway of the mesoscale eddies in the northern SCS. All the moorings were equipped with ADCPs, RCMs, CTDs and temperature chains to make continues measurements of horizontal current velocity and temperature/salinity in the whole water column. During the S-MEE, a total of 5 distinct mesoscale eddies were observed to cross the mooring arrays, among which one anticyclonic and cyclonic eddy pair was fully captured by the mooring arrays. In addition to moored observations, we also conducted two transects across the center of the anticyclonic eddy and made high-resolution hydrographic and turbulent mixing measurements. Based on the data collected by the S-MEE and concurrent satellite-derived observations, we constructed the full-depth 3D structure of the eddy pair and analyzed its generation and dissipation mechanisms. We found that the eddies extend from the surface to the sea bottom and display prominent tilted structures in the vertical. By conducting an eddy energy budget analysis, we further identified that generation of submesoscale motions constitutes the dominant mechanism for the oceanic eddy dissipation.

  12. An eddy viscosity model for flow in a tube bundle

    International Nuclear Information System (INIS)

    Soussan, D.; Grandotto, M.

    1998-01-01

    The work described in this paper is part of the development of GENEPI a 3-dimensional finite element code, designed for the thermalhydraulic analysis of steam generators. It focuses on the implementation of two-phase flow turbulence-induced viscosity in a tube bundle. The GENEPI code, as other industrial codes, uses the eddy viscosity concept introduced by Boussinesq for single phase flow. The concept assumes that the turbulent momentum transfer is similar to the viscous shear stresses. Eddy viscosity formulation is reasonably well known for single phase flows, especially in simple geometries (i.e., in smooth tube, around a single body, or behind a row of bars/tubes), but there exists very little information on it for two-phase flows. An analogy between single and two-phases is used to set up a model for eddy viscosity. The eddy viscosity model examined in this paper is used for a tube bundle geometry and, therefore, is extended to include anisotropy to the classic model. Each of the main flow directions (cross flow inline, cross flow staggered, and parallel flows) gives rise to a specific eddy viscosity formula. The results from a parametric study indicate that the eddy viscosity in the staggered flow is roughly 1.5 times as large as that for the inline cross flow, 60 times as large as that for the parallel flow, and 105 as large as that for the molecular viscosity. Then, the different terms are combined with each other to result in a global eddy viscosity model for a steam generator tube bundle flow. (author)

  13. Covariance matrix estimation for stationary time series

    OpenAIRE

    Xiao, Han; Wu, Wei Biao

    2011-01-01

    We obtain a sharp convergence rate for banded covariance matrix estimates of stationary processes. A precise order of magnitude is derived for spectral radius of sample covariance matrices. We also consider a thresholded covariance matrix estimator that can better characterize sparsity if the true covariance matrix is sparse. As our main tool, we implement Toeplitz [Math. Ann. 70 (1911) 351–376] idea and relate eigenvalues of covariance matrices to the spectral densities or Fourier transforms...

  14. Eddy energy sources and flux in the Red Sea

    KAUST Repository

    Zhan, Peng; Subramanian, Aneesh C.; Kartadikaria, Aditya R.; Hoteit, Ibrahim

    2015-01-01

    the basin and by pumping the nutrient-enriched subsurface water to sustain the primary production. Previous observations and modeling work suggest that the Red Sea is rich of eddy activities. In this study, the eddy energy sources and sinks have been studied

  15. General Galilei Covariant Gaussian Maps

    Science.gov (United States)

    Gasbarri, Giulio; Toroš, Marko; Bassi, Angelo

    2017-09-01

    We characterize general non-Markovian Gaussian maps which are covariant under Galilean transformations. In particular, we consider translational and Galilean covariant maps and show that they reduce to the known Holevo result in the Markovian limit. We apply the results to discuss measures of macroscopicity based on classicalization maps, specifically addressing dissipation, Galilean covariance and non-Markovianity. We further suggest a possible generalization of the macroscopicity measure defined by Nimmrichter and Hornberger [Phys. Rev. Lett. 110, 16 (2013)].

  16. Covariance of random stock prices in the Stochastic Dividend Discount Model

    OpenAIRE

    Agosto, Arianna; Mainini, Alessandra; Moretto, Enrico

    2016-01-01

    Dividend discount models have been developed in a deterministic setting. Some authors (Hurley and Johnson, 1994 and 1998; Yao, 1997) have introduced randomness in terms of stochastic growth rates, delivering closed-form expressions for the expected value of stock prices. This paper extends such previous results by determining a formula for the covariance between random stock prices when the dividends' rates of growth are correlated. The formula is eventually applied to real market data.

  17. Competing risks and time-dependent covariates

    DEFF Research Database (Denmark)

    Cortese, Giuliana; Andersen, Per K

    2010-01-01

    Time-dependent covariates are frequently encountered in regression analysis for event history data and competing risks. They are often essential predictors, which cannot be substituted by time-fixed covariates. This study briefly recalls the different types of time-dependent covariates......, as classified by Kalbfleisch and Prentice [The Statistical Analysis of Failure Time Data, Wiley, New York, 2002] with the intent of clarifying their role and emphasizing the limitations in standard survival models and in the competing risks setting. If random (internal) time-dependent covariates...

  18. Activities of covariance utilization working group

    International Nuclear Information System (INIS)

    Tsujimoto, Kazufumi

    2013-01-01

    During the past decade, there has been a interest in the calculational uncertainties induced by nuclear data uncertainties in the neutronics design of advanced nuclear system. The covariance nuclear data is absolutely essential for the uncertainty analysis. In the latest version of JENDL, JENDL-4.0, the covariance data for many nuclides, especially actinide nuclides, was substantialy enhanced. The growing interest in the uncertainty analysis and the covariance data has led to the organisation of the working group for covariance utilization under the JENDL committee. (author)

  19. Sizing Performance of the Newly Developed Eddy Current System

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Chan Hee; Lee, Hee Jong; Yoo, Hyun Ju; Moon, Gyoon Young; Lee, Tae Hoon [Korea Hydro and Nuclear Power Co., Ltd., Daejeon (Korea, Republic of)

    2013-10-15

    This paper describes the comparison results of sizing performance for two systems. The KHNP developed a new eddy current testing system for the inspection of steam generator tubing in domestic nuclear power plants. The equivalency assessment of the newly developed system with the EPRI-qualified system was already carried out. In this paper, the comparisons of depth-sizing performance for the artificial flaws between two systems were performed. The results show that the newly developed system is in good agreement with the qualified system. Therefore, it is expected that the newly developed eddy current system can be used for the inspection of steam generator tubing in nuclear power plants. There are some non-destructive examination (NDE) methods for the inspection of components in nuclear power plants, such as ultrasonic, radiographic, eddy current testing, etc. The eddy current testing is widely used for the inspection of steam generator (SG) tubing because it offers a relatively low cost approach for high speed, large scale testing of metallic materials in high pressure and temperature engineering systems. The Korea Hydro and Nuclear Power Co., Ltd. (KHNP) developed an eddy current testing system for the inspection of steam generator tubing in nuclear power plants. This system includes not only hardware but software such as the frequency generator and data acquisition-analysis program. The foreign eddy current system developed by ZETEC is currently used for the inspection of steam generator tubing in domestic nuclear power plants. The equivalency assessment between two systems was already carried out in accordance with the EPRI steam generator examination guidelines.

  20. Dissipative inertial transport patterns near coherent Lagrangian eddies in the ocean.

    Science.gov (United States)

    Beron-Vera, Francisco J; Olascoaga, María J; Haller, George; Farazmand, Mohammad; Triñanes, Joaquín; Wang, Yan

    2015-08-01

    Recent developments in dynamical systems theory have revealed long-lived and coherent Lagrangian (i.e., material) eddies in incompressible, satellite-derived surface ocean velocity fields. Paradoxically, observed drifting buoys and floating matter tend to create dissipative-looking patterns near oceanic eddies, which appear to be inconsistent with the conservative fluid particle patterns created by coherent Lagrangian eddies. Here, we show that inclusion of inertial effects (i.e., those produced by the buoyancy and size finiteness of an object) in a rotating two-dimensional incompressible flow context resolves this paradox. Specifically, we obtain that anticyclonic coherent Lagrangian eddies attract (repel) negatively (positively) buoyant finite-size particles, while cyclonic coherent Lagrangian eddies attract (repel) positively (negatively) buoyant finite-size particles. We show how these results explain dissipative-looking satellite-tracked surface drifter and subsurface float trajectories, as well as satellite-derived Sargassum distributions.