WorldWideScience

Sample records for eddy covariance observations

  1. 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

  2. Towards the spatial rectification of tower-based eddy-covariance flux observations

    Science.gov (United States)

    Xu, K.; Metzger, S.; Kljun, N.; Taylor, J. R.; Desai, A. R.

    2014-12-01

    Eddy-covariance (EC) observations of ecologically relevant trace gas and energy fluxes are too sparse spatially for direct assimilation into gridded earth system models (ESMs). The spatial coverage of a tower EC measurement may represent less than 1% of a grid cell resolved by ESMs. For advancing ecological inference it is hence desirable to improve the spatial representativeness of EC measurements. The objectives of this study are (i) to map the spatio-temporally variable flux field around tower EC measurements, and (ii) to quantify spatial representativeness when surrogating the flux over an ESM grid cell with EC observations that source a spatio-temporally variable patch of surface close to the tower. The present study employs environmental response functions (ERFs) for this purpose. The underlying principle is to extract the relationship between biophysical drivers and ecological responses from measurements in the time-domain under varying environmental conditions. The resulting ERF can then be used for projecting the fluxes into target areas. Based on the probability density functions of resulting flux grids, the representativeness of tower measurements is quantified. We apply ERF to EC measurements from July and August 2011 at the AmeriFlux Park Falls tall tower, Wisconsin, U.S.A. With the ERF procedure, the spatial coverage can be increased to >70% for target areas around the tower of 400 km2. From this we determine that 85% and 24% of the tower flux observations can capture the mean turbulent flux and its variability over a 900 km2 target area, respectively, at 5% significance and 80% representativeness level. Lastly, we determine an uncertainty budget for this methodology. Our companion presentation "Assessing and correcting spatial representativeness of tower eddy-covariance flux measurements" shows the applicability of the ERF procedure to provide consistent flux time series for target regions under different climatic and ecological environments.

  3. Energy budget closure observed in paired Eddy Covariance towers with increased and continuous daily turbulence

    Science.gov (United States)

    The lack of energy closure has been a longstanding issue with Eddy Covariance (EC). Multiple mechanisms have been proposed to explain the discrepancies in energy balance including diurnal energy storage changes, advection of energy, and larger scale turbulent processes that cannot be resolved by fi...

  4. 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.

  5. Bayesian multimodel estimation of global terrestrial latent heat flux from eddy covariance, meteorological, and satellite observations

    Science.gov (United States)

    Yao, Yunjun; Liang, Shunlin; Li, Xianglan; Hong, Yang; Fisher, Joshua B.; Zhang, Nannan; Chen, Jiquan; Cheng, Jie; Zhao, Shaohua; Zhang, Xiaotong; Jiang, Bo; Sun, Liang; Jia, Kun; Wang, Kaicun; Chen, Yang; Mu, Qiaozhen; Feng, Fei

    2014-04-01

    Accurate estimation of the satellite-based global terrestrial latent heat flux (LE) at high spatial and temporal scales remains a major challenge. In this study, we introduce a Bayesian model averaging (BMA) method to improve satellite-based global terrestrial LE estimation by merging five process-based algorithms. These are the Moderate Resolution Imaging Spectroradiometer (MODIS) LE product algorithm, the revised remote-sensing-based Penman-Monteith LE algorithm, the Priestley-Taylor-based LE algorithm, the modified satellite-based Priestley-Taylor LE algorithm, and the semi-empirical Penman LE algorithm. We validated the BMA method using data for 2000-2009 and by comparison with a simple model averaging (SA) method and five process-based algorithms. Validation data were collected for 240 globally distributed eddy covariance tower sites provided by FLUXNET projects. The validation results demonstrate that the five process-based algorithms used have variable uncertainty and the BMA method enhances the daily LE estimates, with smaller root mean square errors (RMSEs) than the SA method and the individual algorithms driven by tower-specific meteorology and Modern Era Retrospective Analysis for Research and Applications (MERRA) meteorological data provided by the NASA Global Modeling and Assimilation Office (GMAO), respectively. The average RMSE for the BMA method driven by daily tower-specific meteorology decreased by more than 5 W/m2 for crop and grass sites, and by more than 6 W/m2 for forest, shrub, and savanna sites. The average coefficients of determination (R2) increased by approximately 0.05 for most sites. To test the BMA method for regional mapping, we applied it for MODIS data and GMAO-MERRA meteorology to map annual global terrestrial LE averaged over 2001-2004 for spatial resolution of 0.05°. The BMA method provides a basis for generating a long-term global terrestrial LE product for characterizing global energy, hydrological, and carbon cycles.

  6. Global validation of a process-based model on vegetation gross primary production using eddy covariance observations.

    Science.gov (United States)

    Liu, Dan; Cai, Wenwen; Xia, Jiangzhou; Dong, Wenjie; Zhou, Guangsheng; Chen, Yang; Zhang, Haicheng; Yuan, Wenping

    2014-01-01

    Gross Primary Production (GPP) is the largest flux in the global carbon cycle. However, large uncertainties in current global estimations persist. In this study, we examined the performance of a process-based model (Integrated BIosphere Simulator, IBIS) at 62 eddy covariance sites around the world. Our results indicated that the IBIS model explained 60% of the observed variation in daily GPP at all validation sites. Comparison with a satellite-based vegetation model (Eddy Covariance-Light Use Efficiency, EC-LUE) revealed that the IBIS simulations yielded comparable GPP results as the EC-LUE model. Global mean GPP estimated by the IBIS model was 107.50±1.37 Pg C year(-1) (mean value ± standard deviation) across the vegetated area for the period 2000-2006, consistent with the results of the EC-LUE model (109.39±1.48 Pg C year(-1)). To evaluate the uncertainty introduced by the parameter Vcmax, which represents the maximum photosynthetic capacity, we inversed Vcmax using Markov Chain-Monte Carlo (MCMC) procedures. Using the inversed Vcmax values, the simulated global GPP increased by 16.5 Pg C year(-1), indicating that IBIS model is sensitive to Vcmax, and large uncertainty exists in model parameterization.

  7. Global validation of a process-based model on vegetation gross primary production using eddy covariance observations.

    Directory of Open Access Journals (Sweden)

    Dan Liu

    Full Text Available Gross Primary Production (GPP is the largest flux in the global carbon cycle. However, large uncertainties in current global estimations persist. In this study, we examined the performance of a process-based model (Integrated BIosphere Simulator, IBIS at 62 eddy covariance sites around the world. Our results indicated that the IBIS model explained 60% of the observed variation in daily GPP at all validation sites. Comparison with a satellite-based vegetation model (Eddy Covariance-Light Use Efficiency, EC-LUE revealed that the IBIS simulations yielded comparable GPP results as the EC-LUE model. Global mean GPP estimated by the IBIS model was 107.50±1.37 Pg C year(-1 (mean value ± standard deviation across the vegetated area for the period 2000-2006, consistent with the results of the EC-LUE model (109.39±1.48 Pg C year(-1. To evaluate the uncertainty introduced by the parameter Vcmax, which represents the maximum photosynthetic capacity, we inversed Vcmax using Markov Chain-Monte Carlo (MCMC procedures. Using the inversed Vcmax values, the simulated global GPP increased by 16.5 Pg C year(-1, indicating that IBIS model is sensitive to Vcmax, and large uncertainty exists in model parameterization.

  8. Linking plat traits at ecosystem scale to ecosystem functions as observed by eddy covariance measurements

    Science.gov (United States)

    Sadat Musavi, Talie; Kattge, Jens; Mahecha, Miguel; Reichstein, Markus; Van de Weg, Marjan; Van Bodegom, Peter; Bahn, Michael

    2013-04-01

    In this study we analyze the correlation structure among plant traits, ecosystem functional properties, characteristics of climate, soil and vegetation at 253 FLUXNET sites. This correlation structure may provide a basis for assessing vegetation functioning and its vulnerability under climate change. Until now, analyses of the FLUXNET dataset have shown that much of the observed spatial and temporal variation of ecosystem fluxes can be explained and scaled by information on soil, climate and vegetation structure, without considering the variation in the functional characteristics of the vegetation occurring at the FLUXNET sites. Instead, these studies have used plant functional types (PFT) as a parameter representing the vegetation influence on fluxes. However, provided the variability in traits that exists within an individual PFT at different sites, we analyze in this study how traits additionally influence ecosystem functional properties. We use community mean trait values to understand how vegetation characteristics relate to ecosystem functional properties, like maximum GPP at light saturation, or photosynthetic water use efficiency. These functional properties are derived from the combination of ecosystem level flux observation and information of spatial meteorology and vegetation remote sensing covariates. In addition, we investigate whether vegetation characteristics have an influence on ecosystem fluxes when combined with climate and soil information. So far analyses of this kind were impossible due to a lack of plant trait information. But the plant trait dataset TRY has been growing for years and in combination with novel methods in machine learning. We now have the opportunity to predict plant trait values for individual sites. We will present first results focusing on the relationship of ecosystem functional properties to leaf traits like specific leaf area and leaf carbon, nitrogen and phosphorus concentration scaled to canopy level.

  9. Growing season methane emissions from a permafrost peatland of northeast China: Observations using open-path eddy covariance method

    Science.gov (United States)

    Yu, Xueyang; Song, Changchun; Sun, Li; Wang, Xianwei; Shi, Fuxi; Cui, Qian; Tan, Wenwen

    2017-03-01

    The mid-high latitude permafrost peatlands in the Northern Hemisphere is a major natural source of methane (CH4) to the atmosphere. Ecosystem scale CH4 emissions from a typical permafrost peatland in the Great Hing'an Mountains were observed during the growing season of 2014 and 2015 using the open-path eddy covariance method. Relevant environmental factors such as temperature and precipitation were also collected. There was a clear diurnal variation in methane emissions in the second half of each growing season, with significantly higher emission rates in the wet sector of study area. The daily CH4 exchange ranged from 1.8 mg CH4 m-2 d-1 to 40.2 mg CH4 m-2 d-1 in 2014 and ranged from -3.9 to 15.0 mg CH4 m-2 d-1 in 2015. There were no peaks of CH4 fluxes during the spring thawing period. However, large peaks of CH4 emission were found in the second half of both growing seasons. The CH4 emission after Jul 25th accounted for 77.9% of total growing season emission in 2014 and 85.9% in 2015. The total CH4 emission during the growing season of 2014 and 2015 was approximately 1.52 g CH4 m-2 and 0.71 g CH4 m-2, respectively. CH4 fluxes during the growing seasons were significantly correlated with thawing depth (R2 = 0.71, P emissions in permafrost peatlands. Our multiyear observations indicate that the time-lagged volume of precipitation during the growing season is a key factor in interpreting locally inter-annual variations in CH4 emissions. Our results suggested that the low temperature in the deep soil layers effectively restricts methane production and emission rates; these conditions may create significant positive feedback under global climate change.

  10. Towards global empirical upscaling of FLUXNET eddy covariance observations: validation of a model tree ensemble approach using a biosphere model

    Directory of Open Access Journals (Sweden)

    M. Jung

    2009-10-01

    Full Text Available Global, spatially and temporally explicit estimates of carbon and water fluxes derived from empirical up-scaling eddy covariance measurements would constitute a new and possibly powerful data stream to study the variability of the global terrestrial carbon and water cycle. This paper introduces and validates a machine learning approach dedicated to the upscaling of observations from the current global network of eddy covariance towers (FLUXNET. We present a new model TRee Induction ALgorithm (TRIAL that performs hierarchical stratification of the data set into units where particular multiple regressions for a target variable hold. We propose an ensemble approach (Evolving tRees with RandOm gRowth, ERROR where the base learning algorithm is perturbed in order to gain a diverse sequence of different model trees which evolves over time.

    We evaluate the efficiency of the model tree ensemble (MTE approach using an artificial data set derived from the Lund-Potsdam-Jena managed Land (LPJmL biosphere model. We aim at reproducing global monthly gross primary production as simulated by LPJmL from 1998–2005 using only locations and months where high quality FLUXNET data exist for the training of the model trees. The model trees are trained with the LPJmL land cover and meteorological input data, climate data, and the fraction of absorbed photosynthetic active radiation simulated by LPJmL. Given that we know the "true result" in the form of global LPJmL simulations we can effectively study the performance of the MTE upscaling and associated problems of extrapolation capacity.

    We show that MTE is able to explain 92% of the variability of the global LPJmL GPP simulations. The mean spatial pattern and the seasonal variability of GPP that constitute the largest sources of variance are very well reproduced (96% and 94% of variance explained respectively while the monthly interannual anomalies which occupy much less variance are less well

  11. Eddy covariance based methane flux in Sundarbans mangroves, India

    Indian Academy of Sciences (India)

    Eddy covariance based methane flux in Sundarbans mangroves, India ... Eddy covariance; mangrove forests; methane flux; Sundarbans. ... In order to quantify the methane flux in mangroves, an eddy covariance flux tower was recently erected in the largest unpolluted and undisturbed mangrove ecosystem in Sundarbans ...

  12. Impacts of Diffuse Radiation on Light Use Efficiency across Terrestrial Ecosystems Based on Eddy Covariance Observation in China

    Science.gov (United States)

    Huang, Kun; Wang, Shaoqiang; Zhou, Lei; Wang, Huimin; Zhang, Junhui; Yan, Junhua; Zhao, Liang; Wang, Yanfen; Shi, Peili

    2014-01-01

    Ecosystem light use efficiency (LUE) is a key factor of production models for gross primary production (GPP) predictions. Previous studies revealed that ecosystem LUE could be significantly enhanced by an increase on diffuse radiation. Under large spatial heterogeneity and increasing annual diffuse radiation in China, eddy covariance flux data at 6 sites across different ecosystems from 2003 to 2007 were used to investigate the impacts of diffuse radiation indicated by the cloudiness index (CI) on ecosystem LUE in grassland and forest ecosystems. Our results showed that the ecosystem LUE at the six sites was significantly correlated with the cloudiness variation (0.24≤R2≤0.85), especially at the Changbaishan temperate forest ecosystem (R2 = 0.85). Meanwhile, the CI values appeared more frequently between 0.8 and 1.0 in two subtropical forest ecosystems (Qianyanzhou and Dinghushan) and were much larger than those in temperate ecosystems. Besides, cloudiness thresholds which were favorable for enhancing ecosystem carbon sequestration existed at the three forest sites, respectively. Our research confirmed that the ecosystem LUE at the six sites in China was positively responsive to the diffuse radiation, and the cloudiness index could be used as an environmental regulator for LUE modeling in regional GPP prediction. PMID:25393629

  13. Isoprene flux measurements using eddy covariance and disjunct eddy accumulation

    Science.gov (United States)

    Pressley, S. N.; Lamb, B.; Westberg, H.; Allwine, G.; Turnipseed, A.; Guenther, A.

    2005-12-01

    Quantifying biogenic hydrocarbon (BHC) emissions is important for understanding the role they play in tropospheric chemistry. Isoprene is a very reactive compound that affects the oxidative capacity of the atmosphere, which in turn determines the lifetime of numerous atmospheric constituents such as methane (CH4) and CO. The oxidation of isoprene leads to the production of peroxy radicals (RO2), which may lead to the formation of organic acids, or depending on the level of nitric oxides present, to either production or consumption of tropospheric O3. BHC emissions, in particular isoprene, are predominantly driven by increases in temperature and solar radiation, and there can be significant variations in emissions from one hour to the next, and between days. To better understand the natural variability of isoprene emissions, eddy covariance isoprene flux measurements are being collected on a long-term basis. This long-term dataset, spanning from 1999-2005, provides a unique tool for validating biogenic emission inventories that are used as input into regional photochemical models. This long-term dataset will be presented and compared to the biogenic emission inventory system (BEIS3) model estimates. Using isoprene as a compound of interest, the micrometeorological technique of disjunct eddy accumulation (DEA) was tested side-by-side with the direct eddy covariance (EC) technique. One week of DEA and EC hourly flux measurements will be presented, confirming the use of DEA to measure fluxes of other atmospheric compounds that, to date, has not been attainable.

  14. Methane fluxes above the Hainich forest by True Eddy Accumulation and Eddy Covariance

    Science.gov (United States)

    Siebicke, Lukas; Gentsch, Lydia; Knohl, Alexander

    2016-04-01

    Understanding the role of forests for the global methane cycle requires quantifying vegetation-atmosphere exchange of methane, however observations of turbulent methane fluxes remain scarce. Here we measured turbulent fluxes of methane (CH4) above a beech-dominated old-growth forest in the Hainich National Park, Germany, and validated three different measurement approaches: True Eddy Accumulation (TEA, closed-path laser spectroscopy), and eddy covariance (EC, open-path and closed-path laser spectroscopy, respectively). The Hainich flux tower is a long-term Fluxnet and ICOS site with turbulent fluxes and ecosystem observations spanning more than 15 years. The current study is likely the first application of True Eddy Accumulation (TEA) for the measurement of turbulent exchange of methane and one of the very few studies comparing open-path and closed-path eddy covariance (EC) setups side-by-side. We observed uptake of methane by the forest during the day (a methane sink with a maximum rate of 0.03 μmol m-2 s-1 at noon) and no or small fluxes of methane from the forest to the atmosphere at night (a methane source of typically less than 0.01 μmol m-2 s-1) based on continuous True Eddy Accumulation measurements in September 2015. First results comparing TEA to EC CO2 fluxes suggest that True Eddy Accumulation is a valid option for turbulent flux quantifications using slow response gas analysers (here CRDS laser spectroscopy, other potential techniques include mass spectroscopy). The TEA system was one order of magnitude more energy efficient compared to closed-path eddy covariance. The open-path eddy covariance setup required the least amount of user interaction but is often constrained by low signal-to-noise ratios obtained when measuring methane fluxes over forests. Closed-path eddy covariance showed good signal-to-noise ratios in the lab, however in the field it required significant amounts of user intervention in addition to a high power consumption. We conclude

  15. Recurrence Analysis of Eddy Covariance Fluxes

    Science.gov (United States)

    Lange, Holger; Flach, Milan; Foken, Thomas; Hauhs, Michael

    2015-04-01

    The eddy covariance (EC) method is one key method to quantify fluxes in biogeochemical cycles in general, and carbon and energy transport across the vegetation-atmosphere boundary layer in particular. EC data from the worldwide net of flux towers (Fluxnet) have also been used to validate biogeochemical models. The high resolution data are usually obtained at 20 Hz sampling rate but are affected by missing values and other restrictions. In this contribution, we investigate the nonlinear dynamics of EC fluxes using Recurrence Analysis (RA). High resolution data from the site DE-Bay (Waldstein-Weidenbrunnen) and fluxes calculated at half-hourly resolution from eight locations (part of the La Thuile dataset) provide a set of very long time series to analyze. After careful quality assessment and Fluxnet standard gapfilling pretreatment, we calculate properties and indicators of the recurrent structure based both on Recurrence Plots as well as Recurrence Networks. Time series of RA measures obtained from windows moving along the time axis are presented. Their interpretation is guided by three different questions: (1) Is RA able to discern periods where the (atmospheric) conditions are particularly suitable to obtain reliable EC fluxes? (2) Is RA capable to detect dynamical transitions (different behavior) beyond those obvious from visual inspection? (3) Does RA contribute to an understanding of the nonlinear synchronization between EC fluxes and atmospheric parameters, which is crucial for both improving carbon flux models as well for reliable interpolation of gaps? (4) Is RA able to recommend an optimal time resolution for measuring EC data and for analyzing EC fluxes? (5) Is it possible to detect non-trivial periodicities with a global RA? We will demonstrate that the answers to all five questions is affirmative, and that RA provides insights into EC dynamics not easily obtained otherwise.

  16. Disjunct eddy covariance technique for trace gas flux measurements

    Science.gov (United States)

    Rinne, H. J. I.; Guenther, A. B.; Warneke, C.; de Gouw, J. A.; Luxembourg, S. L.

    A new approach for eddy covariance flux measurements is developed and applied for trace gas fluxes in the atmospheric surface layer. In disjunct eddy covariance technique, quick samples with a relatively long time interval between them are taken instead of continuously sampling air. This subset of the time series together with vertical wind velocity data at corresponding sampling times can be correlated to give a flux. The disjunct eddy sampling gives more time to analyze the trace gas concentrations and thus makes eddy covariance measurements possible using slower sensors. In this study a proton-transfer-reaction mass spectrometer with response time of about 1 second was used with a disjunct eddy sampler to measure fluxes of volatile organic compounds from an alfalfa field. The measured day-time maximum methanol fluxes ranged from 1 mg m-2 h-1 from uncut alfalfa to 8 mg m-2 h-1 from freshly cut alfalfa. Night-time fluxes were around zero.

  17. Innovative CO2 Analyzer Technology for the Eddy Covariance Flux Monitor Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to build and evaluate NDIR Analyzers that can be used to observe Eddy Covariance Flux and Absolute Dry Mole Fraction of CO2 from stationary and airborne...

  18. Eddy covariance based methane flux in Sundarbans mangroves, India

    Indian Academy of Sciences (India)

    West Bengal Forest Department, Salt Lake, Kolkata 700 098, India. ∗. Corresponding author. e-mail: surajking123@gmail.com ... Eddy covariance; mangrove forests; methane flux; Sundarbans. J. Earth Syst. Sci. 123, No. 5, July 2014, pp. 1089–1096 .... terrestrial biomes in India. The main objective of this paper is to present.

  19. 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.

  20. 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.

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

    NARCIS (Netherlands)

    Laan, van der Sander; Manohar, Swagath; Vermeulen, Alex; Bosveld, Fred; Meijer, Harro; Manning, Andrew; Molen, van der Michiel; Laan-Luijkx, van der Ingrid

    2016-01-01

    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

  2. Weighted mean method for eddy covariance flux measurement

    Science.gov (United States)

    Kim, W.; Cho, J.; Seo, H.; Oki, T.

    2013-12-01

    The study to monitor the exchange of energy, water vapor and carbon dioxide between the atmosphere and terrestrial ecosystem has been carried out with eddy covariance method throughout the world. The monitored exchange quantity, named flux F , is conventionally determined by a mean of 1 hr or 30 min interval because no technique have been fortified to directly measure a momentary F itself at an instant of time. Therefore, the posterior analysis with this sampling should be paid attention to those spatial or temporal averaging and summation in the consideration of the sampling uncertainty. In particular, the averaging calcurated by arithmetic mean Fa might be inappropriate because the sample F used in this averaging has nonidentical inherent quality within one another according to different micrometeorological and ecophysiological conditions while those are observed under the same instruments. To overcome this issue, we propose the weighted mean Fw using a relative sampling error estimated by a sampling F and its error, and introduce Fw performance tested with EC measurements for 3 years at tangerine orchard.

  3. A True Eddy Accumulation - Eddy Covariance hybrid for measurements of turbulent trace gas fluxes

    Science.gov (United States)

    Siebicke, Lukas

    2016-04-01

    Eddy covariance (EC) is state-of-the-art in directly and continuously measuring turbulent fluxes of carbon dioxide and water vapor. However, low signal-to-noise ratios, high flow rates and missing or complex gas analyzers limit it's application to few scalars. True eddy accumulation, based on conditional sampling ideas by Desjardins in 1972, requires no fast response analyzers and is therefore potentially applicable to a wider range of scalars. Recently we showed possibly the first successful implementation of True Eddy Accumulation (TEA) measuring net ecosystem exchange of carbon dioxide of a grassland. However, most accumulation systems share the complexity of having to store discrete air samples in physical containers representing entire flux averaging intervals. The current study investigates merging principles of eddy accumulation and eddy covariance, which we here refer to as "true eddy accumulation in transient mode" (TEA-TM). This direct flux method TEA-TM combines true eddy accumulation with continuous sampling. The TEA-TM setup is simpler than discrete accumulation methods while avoiding the need for fast response gas analyzers and high flow rates required for EC. We implemented the proposed TEA-TM method and measured fluxes of carbon dioxide (CO2), methane (CH4) and water vapor (H2O) above a mixed beech forest at the Hainich Fluxnet and ICOS site, Germany, using a G2301 laser spectrometer (Picarro Inc., USA). We further simulated a TEA-TM sampling system using measured high frequency CO2 time series from an open-path gas analyzer. We operated TEA-TM side-by-side with open-, enclosed- and closed-path EC flux systems for CO2, H2O and CH4 (LI-7500, LI-7200, LI-6262, LI-7700, Licor, USA, and FGGA LGR, USA). First results show that TEA-TM CO2 fluxes were similar to EC fluxes. Remaining differences were similar to those between the three eddy covariance setups (open-, enclosed- and closed-path gas analyzers). Measured TEA-TM CO2 fluxes from our physical

  4. 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

    and technical papers. A free open-source software package with a user-friendly interface was developed accordingly for computing final fully corrected CO2 emission numbers [10]. The presentation covers highlights of the eddy covariance method, its application to geological carbon sequestration, key requirements, instrumentation and software, and reviews educational resources particularly useful for carbon sequestration research. References: [1] Aubinet, M., T. Vesala, and D. Papale (Eds.), 2012. Eddy Covariance: A Practical Guide to Measurement and Data Analysis. Springer-Verlag, 442 pp. [2] Foken T., 2008. Micrometeorology. Springer-Verlag, 308 pp. [4] Finley, R., 2009. An Assessment of Geological Carbon Sequestration in the Illinois Basin Overview of the Decatur-Illinois Basin Site. MGSC, http://www.istc.illinois.edu/info/govs_awards_docs/2009-GSA-1100-Finley.pdf [5] Liu, G. (Ed.), 2012. Greenhouse Gases: Capturing, Utilization and Reduction. Intech, 338 pp. [6] LI-COR Biosciences, 2011. Surface Monitoring for Geologic Carbon Sequestration Monitoring: Methods, Instrumentation, and Case Studies. LI-COR Biosciences, Pub. 980-11916, 15 pp. [7] Benson, S., 2006. Monitoring carbon dioxide sequestration in deep geological formations for inventory verification and carbon credits, SPE-102833, Presentation [8] Lewicki, J., G. Hilley, M. Fischer, L. Pan, C. Olden-burg, C. Dobeck, and L. Spangler, 2009.Eddy covariance observations of leakage during shallow subsurface CO2 releases. Journal of Geophys Res, 114: D12302 [9] Burba, G., 2013. Eddy Covariance Method for Scientific, Industrial, Agricultural and Regulatory Applications. LI-COR Biosciences, 328 pp. [10] LI-COR Biosciences, 2012. EddyPro 4.0: Help and User's Guide. Lincoln, NE, 208 pp.

  5. 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.

  6. 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

  7. Soil Respiration in Eddy Covariance Footprints using Forced Diffusion

    Science.gov (United States)

    Nickerson, N.; Gabriel, C. E.; Creelman, C.

    2016-12-01

    Eddy covariance (EC) has been widely used across the globe for more than 20 years, offering researchers invaluable measurements of parameters including Net Ecosystem Exchange and ecosystem respiration. However, research suggests that EC assumptions and technical obstacles can cause biased gas exchange estimates. Measurements of soil respiration (RS) at the ground level may help alleviate these biases; for example, by allowing researchers to reconcile nocturnal EC flux data with RS or by providing a means to inform gap-filling models. RS measurements have been used sparingly alongside EC towers because of the large cost required to scale chamber systems to the EC footprint and data integration and processing burdens. Here we present the Forced Diffusion (FD) method for the measurement of RS at EC sites. The FD method allows for inexpensive and autonomous measurements, providing a scalable approach to matching the EC footprint compared to other RS systems. A pilot study at the Howland Forest AmeriFlux site was carried out from July 15, 2016 to Dec., 2016 using EC, custom-made automated chambers, and FD chambers in tandem. These results emphasize how RS measurements, like those from the eosFD, can identify decoupling of above and below canopy air masses and assist in informing and parameterizing gap-filling techniques. Uncertainty in nocturnal EC fluxes has been extensively characterized at Howland Forest with EC measurements spanning more than 20 years. Similarly, long term automated measurements of RS are also made at Howland, and have already been used to inform EC gap-filling models, making Howland the ideal site for such a study. This study has been designed to reproduce previous findings from Howland using the FD approach, aiming to demonstrate that the measurements taken using the eosFD correlate well with the existing chamber systems and can be used with equal efficacy to inform gap filling models or for other other eddy covariance QA/QC procedures, including

  8. A gap-filling model for eddy covariance CO2 flux: Estimating carbon assimilated by a subtropical evergreen broad-leaved forest at the Lien-Hua-Chih flux observation site

    Science.gov (United States)

    Lan, C. Y.; Li, M. H.; Chen, Y. Y.

    2016-12-01

    Appropriate estimations of gaps appeared in eddy covariance (EC) flux observations are critical to the reliability of long-term EC applications. In this study we present a semi-parametric multivariate gap-filling model for tower-based measurement of CO2 flux. The raw EC data passing QC/QA was separated into two groups, clear sky, having net radiation greater than 50 W/m2, and nighttime/cloudy. For the clear sky conditions, the principle component analysis (PCA) was used to resolve the multicollinearity relationships among various environmental variables, including net radiation, wind speed, vapor pressure deficit, soil moisture deficit, leaf area index, and soil temperature, in association with CO2 assimilated by forest. After the principal domains were determined by the PCA, the relationships between CO2 fluxes and selected PCs (key factors) were built up by nonlinear interpolations to estimate the gap-filled CO2 flux. In view of limited photosynthesis at nighttime/cloudy conditions, respiration rate of the forest ecosystem was estimated by the Lloyd-Tylor equation. Artificial gaps were randomly selected to exam the applicability of our PCA approach. Based on tower-based measurement of CO2 flux at the Lien-Hua-Chih site, a total of 5.8 ton-C/ha/yr was assimilated in 2012.

  9. Eddy covariance fluxes and vertical concentration gradient measurements of NO and NO2 over a ponderosa pine ecosystem: observational evidence for within canopy removal of NOx

    Science.gov (United States)

    Min, K.-E.; Pusede, S. E.; Browne, E. C.; LaFranchi, B. W.; Wooldridge, P. J.; Cohen, R. C.

    2013-05-01

    Exchange of NOx (NO+NO2) between the atmosphere and biosphere is important for air quality, climate change, and ecosystem nutrient dynamics. There are few direct ecosystem scale measurements of the direction and rate of atmosphere-biosphere exchange of NOx. As a result, a complete description of the processes affecting NOx following emission from soils and/or plants as they transit from within the plant/forest canopy to the free atmosphere remains poorly constrained and debated. Here, we describe measurements of NO and NO2 fluxes and vertical concentration gradients made during the Biosphere Effects on AeRosols and Photochemistry EXperiment 2009. In general, during daytime we observe upward fluxes of NO and NO2 with counter-gradient fluxes of NO. We find that NOx fluxes from the forest canopy are smaller than calculated using observed flux-gradient relationships for conserved tracers and also smaller than measured soil NO emissions. We interpret these differences as evidence for the existence of a "canopy reduction factor". We suggest that at this site it is primarily due to chemistry converting NOx to higher nitrogen oxides within the forest canopy.

  10. 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.

  11. What can we learn about ammonia fluxes from open-path eddy covariance measurements?

    Science.gov (United States)

    Pan, D.; Zondlo, M. A.; Benedict, K. B.; Schichtel, B. A.; Ham, J. M.; Shonkwiler, K. B.; Collett, J. L., Jr.

    2016-12-01

    Ammonia (NH3) is an important component of bio-atmospheric N cycle with implications of regional air quality, human and ecosystem health degradation, and global climate change. NH3 fluxes have high spatiotemporal variability controlled by several factors, such as atmospheric NH3 concentration, meteorological conditions, and compensation point of underlying surfaces. Quantifying NH3 fluxes is further complicated by severe measurement challenges including adsorption to instrument surfaces, low mole fractions, and gas-particle phase partitioning. To overcome these challenges, we have developed an open-path, eddy covariance NH3 instrument that minimizes these sampling issues. Eddy covariance measurements in 2015 and 2016 in the Rocky Mountain National Park (RMNP), Colorado showed the capabilities of the system to measure fluxes in clean and moderate-polluted regions. Interesting patterns of NH3 fluxes and NH3 concentration variations were observed, such as deposition of NH3 associated plumes from urban and agricultural areas and reemission of a similar magnitude when clean free-tropospheric air passing the site. Observed downward fluxes during midnight and upward fluxes in early morning also indicated NH3 fluxes related to dew formation and evaporation events. More details about these patterns and their relationships with ambient temperature, relative humidity, and other fluxes will be presented. These measurements also provided an opportunity to evaluate our current understanding of transport and deposition of NH3. Micrometeorological method, backward trajectory model, and bidirectional NH3 flux model were used to analyze observed variability of NH3 concentrations and fluxes. Implications of these results and how eddy covariance measurements combined with other measurements may provide insights to better quantify NH3 fluxes will be discussed.

  12. 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...

  13. Eddy Covariance flux measurements over an ice/snow covered lake in Finland

    Science.gov (United States)

    Potes, Miguel; Salgado, Rui; Provenzale, Maria; Mammarella, Ivan

    2017-04-01

    The inland water bodies play an important role in the regional heat and mass transfer with the atmosphere. As lakes cover an area of 4.2 million km2, representing an area of more than 3% of Earth continental surface, an increasing concern in estimation of heat and greenhouse gases exchanges between inland water bodies and the atmosphere has been developed in the last years. The eddy covariance (EC) method is the worldwide most common technique used to assess turbulent fluxes over all types of surface. In the framework of two Short Term Scientific Mission of the COST action "A European network for a harmonized monitoring of snow for the benefit of climate change scenarios, hydrology and numerical weather prediction" (ES1404), it was feasible to have parallel EC measurements with two identical equipment over a boreal lake. In this communication the results are related to the period comprised between November 2015 and May 2016, including freezing and ice-free periods. Observed near surface fluxes of momentum, heat and mass (H2O and CO2) were obtained with a new eddy covariance system (EC), Campbell Scientific's IRGASON Integrated Open-Path CO2/H2O Gas Analyzer and 3D Sonic Anemometer, over lake Vanajavesi in Finland. The measurement site is located in a tip of narrow peninsula on the lake (61.133935°N; 24.259119°E), offering very good conditions for eddy covariance flux measurements. The EC system was installed at 2.5m height above the lake surface and was oriented against the prevailing wind direction in the site.

  14. 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.

  15. Can defensible estimates of canopy proximity be obtained based on single point eddy covariance measurements?

    Science.gov (United States)

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

    2017-04-01

    Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements above growing and heterogeneous ecosystems. It requires characterizing the surrounding environment. One way to achieve this is to analyse the canopy aerodynamic distance, which is the difference between measurement height (z) and displacement height (d). In this study, twenty years of eddy covariance measurements from the Vielsalm Terrestrial Observatory, a site located in a mixed temperate forest, were used. Canopy aerodynamic distance (z-d) estimates were obtained using two micrometeorological methods: the first one, which is original so far as we know, was based on analysing sensible heat cospectra; the second one was derived from the wind speed profile equation. Canopy height estimates based on inventories were used to validate both methods. The micrometeorological methods allowed the z-d variations due to changes in canopy or measurement height to be detected. In addition, the results obtained using the two methods were well correlated, spatially and temporally, with the z-d derived from canopy height measurements. The micrometeorological approaches used could therefore be a promising tool for investigating z-d variability at a high directional and temporal resolution. Questions remain, however, particularly with regard to the variability observed that cannot be explained by canopy or measurement height variation. Forest management practices and the non-fulfilment of similarity relationships were suspected to be the main explanatory factors.

  16. True eddy accumulation and eddy covariance methods and instruments intercomparison for fluxes of CO2, CH4 and H2O above the Hainich Forest

    Science.gov (United States)

    Siebicke, Lukas

    2017-04-01

    The eddy covariance (EC) method is state-of-the-art in directly measuring vegetation-atmosphere exchange of CO2 and H2O at ecosystem scale. However, the EC method is currently limited to a small number of atmospheric tracers by the lack of suitable fast-response analyzers or poor signal-to-noise ratios. High resource and power demands may further restrict the number of spatial sampling points. True eddy accumulation (TEA) is an alternative method for direct and continuous flux observations. Key advantages are the applicability to a wider range of air constituents such as greenhouse gases, isotopes, volatile organic compounds and aerosols using slow-response analyzers. In contrast to relaxed eddy accumulation (REA), true eddy accumulation (Desjardins, 1977) has the advantage of being a direct method which does not require proxies. True Eddy Accumulation has the potential to overcome above mentioned limitations of eddy covariance but has hardly ever been successfully demonstrated in practice in the past. This study presents flux measurements using an innovative approach to true eddy accumulation by directly, continuously and automatically measuring trace gas fluxes using a flow-through system. We merge high-frequency flux contributions from TEA with low-frequency covariances from the same sensors. We show flux measurements of CO2, CH4 and H2O by TEA and EC above an old-growth forest at the ICOS flux tower site "Hainich" (DE-Hai). We compare and evaluate the performance of the two direct turbulent flux measurement methods eddy covariance and true eddy accumulation using side-by-side trace gas flux observations. We further compare performance of seven instrument complexes, i.e. combinations of sonic anemometers and trace gas analyzers. We compare gas analyzers types of open-path, enclosed-path and closed-path design. We further differentiate data from two gas analysis technologies: infrared gas analysis (IRGA) and laser spectrometry (open path and CRDS closed

  17. 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...

  18. Studying the spatial variability of methane flux with five eddy covariance towers of varying height

    NARCIS (Netherlands)

    Peltola, O.; Hensen, A.; Marchesini, L. Belelli; Helfter, C.; Bosveld, F. C.; van den Bulk, W. C. M.; Haapanala, S.; van Huissteden, J.; Laurila, T.; Lindroth, A.; Nemitz, E.; Roeckmann, Thomas|info:eu-repo/dai/nl/304838233; Vermeulen, A. T.; Mammarella, I.

    2015-01-01

    In this study, the spatial representativeness of eddy covariance (EC) methane (CH4) measurements was examined by comparing parallel CH4 fluxes from three short (6 m) towers separated by a few kilometres and from two higher levels (20 m and 60 m) at one location. The measurement campaign was held on

  19. Evapotranspiration components determined by stable isotope, sap flow and eddy covariance techniques

    NARCIS (Netherlands)

    Williams, D.G.; Cable, W.; Hultine, K.; Hoedjes, J.C.B.; Yepez, E.A.; Simonneaux, V.; Er-Raki, S.; Boulet, G.; Debruin, H.A.R.; Chehbouni, A.; Hartogensis, O.K.; Timouk, F.

    2004-01-01

    Understanding and modeling water exchange in and and semiarid ecosystems is complicated by the very heterogeneous distribution of vegetation and moisture inputs, and the difficulty of measuring and validating component fluxes at a common scale. We combined eddy covariance (EC), sap flow, and stable

  20. Semiempirical modeling of abiotic and biotic factors controlling ecosystem respiration across eddy covariance sites

    NARCIS (Netherlands)

    Migliavacca, M.; Reichstein, M.; Richardson, A.D.; Colombo, R.; Sutton, M.A.; Lasslop, G.; Tomelleri, E.; Wohlfahrt, G.; Carvalhais, N.; Molen, van der M.K.

    2011-01-01

    In this study we examined ecosystem respiration (RECO) data from 104 sites belonging to FLUXNET, the global network of eddy covariance flux measurements. The goal was to identify the main factors involved in the variability of RECO: temporally and between sites as affected by climate, vegetation

  1. Uncertainty in eddy covariance flux estimates resulting from spectral attenuation [Chapter 4

    Science.gov (United States)

    W. J. Massman; R. Clement

    2004-01-01

    Surface exchange fluxes measured by eddy covariance tend to be underestimated as a result of limitations in sensor design, signal processing methods, and finite flux-averaging periods. But, careful system design, modern instrumentation, and appropriate data processing algorithms can minimize these losses, which, if not too large, can be estimated and corrected using...

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

    NARCIS (Netherlands)

    Smeets, C.J.P.P.|info:eu-repo/dai/nl/191522236; Holzinger, R.|info:eu-repo/dai/nl/337989338; Vigano, I.|info:eu-repo/dai/nl/304831956; Goldstein, A.H.; Röckmann, T.|info:eu-repo/dai/nl/304838233

    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

  3. High-quality eddy-covariance CO2 budgets under cold climate conditions

    Science.gov (United States)

    Kittler, Fanny; Eugster, Werner; Foken, Thomas; Heimann, Martin; Kolle, Olaf; Göckede, Mathias

    2017-08-01

    This study aimed at quantifying potential negative effects of instrument heating to improve eddy-covariance flux data quality in cold environments. Our overarching objective was to minimize heating-related bias in annual CO2 budgets from an Arctic permafrost system. We used continuous eddy-covariance measurements covering three full years within an Arctic permafrost ecosystem with parallel sonic anemometers operation with activated heating and without heating as well as parallel operation of open- and closed-path gas analyzers, the latter serving as a reference. Our results demonstrate that the sonic anemometer heating has a direct effect on temperature measurements while the turbulent wind field is not affected. As a consequence, fluxes of sensible heat are increased by an average 5 W m-2 with activated heating, while no direct effect on other scalar fluxes was observed. However, the biased measurements in sensible heat fluxes can have an indirect effect on the CO2 fluxes in case they are used as input for a density-flux WPL correction of an open-path gas analyzer. Evaluating the self-heating effect of the open-path gas analyzer by comparing CO2 flux measurements between open- and closed-path gas analyzers, we found systematically higher CO2 uptake recorded with the open-path sensor, leading to a cumulative annual offset of 96 gC m-2, which was not only the result of the cold winter season but also due to substantial self-heating effects during summer. With an inclined sensor mounting, only a fraction of the self-heating correction for vertically mounted instruments is required.

  4. Earth Observing System Covariance Realism Updates

    Science.gov (United States)

    Ojeda Romero, Juan A.; Miguel, Fred

    2017-01-01

    This presentation will be given at the International Earth Science Constellation Mission Operations Working Group meetings June 13-15, 2017 to discuss the Earth Observing System Covariance Realism updates.

  5. Assessing and correcting spatial representativeness of tower eddy-covariance flux measurements

    Science.gov (United States)

    Metzger, S.; Xu, K.; Desai, A. R.; Taylor, J. R.; Kljun, N.; Blanken, P.; Burns, S. P.; Scott, R. L.

    2014-12-01

    Estimating the landscape-scale exchange of ecologically relevant trace gas and energy fluxes from tower eddy-covariance (EC) measurements is often complicated by surface heterogeneity. For example, a tower EC measurement may represent less than 1% of a grid cell resolved by mechanistic models (order 100-1000 km2). In particular for data assimilation or comparison with large-scale observations, it is hence critical to assess and correct the spatial representativeness of tower EC measurements. We present a procedure that determines from a single EC tower the spatio-temporally explicit flux field of its surrounding. The underlying principle is to extract the relationship between biophysical drivers and ecological responses from measurements under varying environmental conditions. For this purpose, high-frequency EC flux processing and source area calculations (≈60 h-1) are combined with remote sensing retrievals of land surface properties and subsequent machine learning. Methodological details are provided in our companion presentation "Towards the spatial rectification of tower-based eddy-covariance flux observations". We apply the procedure to one year of data from each of four AmeriFlux sites under different climate and ecological environments: Lost Creek shrub fen wetland, Niwot Ridge subalpine conifer, Park Falls mixed forest, and Santa Rita mesquite savanna. We find that heat fluxes from the Park Falls 122-m-high EC measurement and from a surrounding 100 km2 target area differ up to 100 W m-2, or 65%. Moreover, 85% and 24% of the EC flux observations are adequate surrogates of the mean surface-atmosphere exchange and its spatial variability across a 900 km2 target area, respectively, at 5% significance and 80% representativeness levels. Alternatively, the resulting flux grids can be summarized as probability density functions, and used to inform mechanistic models directly with the mean flux value and its spatial variability across a model grid cell. Lastly

  6. 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

  7. A Comparison of GHG Flux Measurements by Relaxed Eddy Accumulation and Eddy Covariance Methods Using FTIR and QCL Analyzers

    Science.gov (United States)

    Vermeulen, A. T.; Laborde, M.; Hensen, A.; van den Bulk, P.; Famulari, D.; Griffith, D. W.; Nemitz, E.

    2013-12-01

    In this presentation results obtained with a novel system for Relaxed Eddy Accumulation (REA) measurements using an Ecotech Spectronus FTIR analyzer (Griffth et al, 2012) will be compared to eddy covariance fluxes using an Aerodyne QCL and a Licor 6262 NDIR analyzer. The REA FTIR system can be easily combined with other standard (e.g. NDIR) analyzers suited for eddy covariance measurements to allow for scaling of the obtained up/down concentration differences with the directly measured fluxes. Furthermore the FTIR system allows for on-line simultaneous high precision concentration measurement of a large number of different gases and even isotope composition, next to the measurement of CO2, CH4 and N2O mixing ratios. The final design goal for the REA FTIR system is an attractive fully automated, low maintenance system for long-term monitoring of Greenhouse Gas fluxes at the hourly time scale and a spatial scale of about 1 km2. During a campaign of four weeks in June 2013 (in the framework of the InGOS EU project) at a grazed grassland site at Easter Bush, Scotland (UK), simultaneous surface flux measurements of N2O and additionally CO2 and CH4 have been performed using our systems and a number of setups from other groups.. Weather conditions during the campaign were excellent and after the application of fertilizer at the field and some rainfall the increased emission of N2O was detected clearly by all systems. Both the eddy covariance and REA methods performed well during the campaign and the measured fluxes compare satisfactorily. In general the resulting fluxes from the FTIR system are lower then the QCL based results. Reasons for these deviations will be discussed together with implications of the results for the design of future REA measurements using the FTIR system. Griffith, D.W.T., N.M. Deutscher, C.G.R. Caldow, G. Kettlewell, M. Riggenbach and S. Hammer, A Fourier transform infrared trace gas analyser for atmospheric applications. Atmospheric Measurement

  8. 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......-frequency contributions to vertical turbulent surface fluxes. For high flux-rates (|Sensible heat flux|> 40 Wm^(-2), |latent heat flux|>10 Wm^(-2) and |CO_2 flux|>170 mmol m^(-2) d^(-1)) we found that the average relative difference between fluxes estimated by Ogive optimization and the conventional method was low (5...

  9. Evaluation of MODIS gross primary productivity for Africa using eddy covariance data

    CSIR Research Space (South Africa)

    Sjöström, M

    2013-04-01

    Full Text Available et al. 2001; Nicholson 2000, 2001; Williams et al. 2007; Williams et al. 2008) compared to North America, Europe and Asia owing to the sparse network of climate stations, eddy covariance stations, and long term ecological research sites. Line 93...: You could consider citing Schwalm CR, Williams CA, Schaefer K (2011) "Carbon consequences of global hydrologic change, 1948-2009", Journal of Geophysical Research - Biogeosciences, 116, G03042, doi:10.1029/2011JG001674. The paper assessed trends...

  10. Eddy Covariance measurements of stable isotopes (δD and δ18O) in water vapor

    Science.gov (United States)

    Braden-Behrens, Jelka; Knohl, Alexander

    2017-04-01

    Stable isotopes are a promising tool to enhance our understanding of ecosystem gas exchanges. Studying 18O and 2H in water vapour (H2Ov) can e.g. help partitioning evapotranspiration into its components. With recent developments in laser spectroscopy direct Eddy Covariance (EC) measurements for investigating fluxes of stable isotopologues became feasible. So far very few case studies have applied the EC method to measure stable isotopes in water vapor. We continuously measure fluxes of water vapor isotopologues with the EC method in a managed beech forest in Thuringia, Germany, since autumn 2015 using the following setup: An off-axis integrated cavity output water vapor isotope analyzer (WVIA, Los Gatos Research. Inc, USA) measures the water vapour concentration and its isotopic composition (δD and δ18O). The instrument, that was optimized for high flow rates (app. 4slpm) to generate high frequency (2Hz) measurements, showed sufficient precision with Allan Deviations of app. 0.12 ‰ for δD and 0.06 ‰ for δ18O for averaging periods of 100s. The instrument was calibrated hourly using a high-flow optimized version of the water vapor isotope standard source (WVISS, Los Gatos Research. Inc, USA) that provides water vapor with known isotopic composition for a large range of different concentrations. Our calibration scheme includes a near continuous concentration range calibration instead of a simple 2 or 3-point calibration to face the analyzers strong concentration dependency within a range of app. 6 000 to 16 000 ppm in winter and app. 8 000 to 23 000 ppm in summer. In the used setup, the high-flow and high-frequency optimized water vapor isotope analyzer (WVIA) showed suitable characteristics (Allan deviation and spectral energy distribution) to perform Eddy covariance measurements of stable isotopes in H2Ov. Thus, this novel instrument for EC measurements of water vapor isotopologues provides a new opportunity for studying the hydrological cycle in long

  11. Observed Score Linear Equating with Covariates

    Science.gov (United States)

    Branberg, Kenny; Wiberg, Marie

    2011-01-01

    This paper examined observed score linear equating in two different data collection designs, the equivalent groups design and the nonequivalent groups design, when information from covariates (i.e., background variables correlated with the test scores) was included. The main purpose of the study was to examine the effect (i.e., bias, variance, and…

  12. 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.

  13. Eddy Covariance Measurements of Methane Emissions from a Dairy Farm Waste Lagoon

    Science.gov (United States)

    Sokol, A. B.; Lauvaux, T.; Richardson, S.; Hlywiak, J.; Davis, K. J.; Hristov, A. N.

    2016-12-01

    Livestock manure management in dairy operations is a known source of methane (CH4), a potent greenhouse gas. Anaerobic waste lagoons are a common manure management technique; thus, their associated CH4 emissions are relevant to national greenhouse gas inventories and local air quality. Our objective was to characterize the variability of summertime CH4 emissions from a lagoon at a dairy facility in central Pennsylvania. Continuous flux measurements were taken over two weeks in July using the eddy covariance method, which uses high-frequency gas concentration and three-dimensional wind speed measurements to calculate turbulent fluxes from a source area. After data filtration based on turbulence characteristics and source area, the average CH4 flux density from the lagoon was estimated to be 99 μmol m-2 s-1. This implies daily lagoon emissions of 881 kg CH4, corresponding to an average emission rate of 340 g CH4 per cow per day. We observed no apparent relationship between emissions and air temperature or relative humidity, though an extended measurement period is needed to better quantify the relationship that is expected to exist between air and/or slurry temperature and CH4 flux. Our measured per-area emission rate is toward the high end of the range of estimates found in the literature. These results contribute to greenhouse gas inventory development and could have important implications for emission mitigation strategies.

  14. Field intercomparison of two optical analyzers for CH4 eddy covariance flux measurements

    Directory of Open Access Journals (Sweden)

    L. Emmenegger

    2010-11-01

    Full Text Available Fast response optical analyzers based on laser absorption spectroscopy are the preferred tools to measure field-scale mixing ratios and fluxes of a range of trace gases. Several state-of-the-art instruments have become commercially available and are gaining in popularity. This paper aims for a critical field evaluation and intercomparison of two compact, cryogen-free and fast response instruments: a quantum cascade laser based absorption spectrometer from Aerodyne Research, Inc., and an off-axis integrated cavity output spectrometer from Los Gatos Research, Inc. In this paper, both analyzers are characterized with respect to precision, accuracy, response time and also their sensitivity to water vapour. The instruments were tested in a field campaign to assess their behaviour under various meteorological conditions. The instrument's suitability for eddy covariance flux measurements was evaluated by applying an artificial flux of CH4 generated above a managed grassland with otherwise very low methane exchange. This allowed an independent verification of the flux measurements accuracy, including the overall eddy covariance setup and data treatment. The retrieved fluxes were in good agreement with the known artificial emission flux, which is more than satisfactory, given that the analyzers were attached to separate sonic anemometers placed on individual eddy towers with different data acquisition systems but similar data treatment that are specific to the best practice used by the involved research teams.

  15. Minimal covariant observables identifying all pure states

    Energy Technology Data Exchange (ETDEWEB)

    Carmeli, Claudio, E-mail: claudio.carmeli@gmail.com [D.I.M.E., Università di Genova, Via Cadorna 2, I-17100 Savona (Italy); I.N.F.N., Sezione di Genova, Via Dodecaneso 33, I-16146 Genova (Italy); Heinosaari, Teiko, E-mail: teiko.heinosaari@utu.fi [Turku Centre for Quantum Physics, Department of Physics and Astronomy, University of Turku (Finland); Toigo, Alessandro, E-mail: alessandro.toigo@polimi.it [Dipartimento di Matematica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); I.N.F.N., Sezione di Milano, Via Celoria 16, I-20133 Milano (Italy)

    2013-09-02

    It has been recently shown by Heinosaari, Mazzarella and Wolf (2013) [1] that an observable that identifies all pure states of a d-dimensional quantum system has minimally 4d−4 outcomes or slightly less (the exact number depending on d). However, no simple construction of this type of minimal observable is known. We investigate covariant observables that identify all pure states and have minimal number of outcomes. It is shown that the existence of this kind of observables depends on the dimension of the Hilbert space.

  16. Constraining a global ecosystem model with multi-site eddy-covariance data

    Directory of Open Access Journals (Sweden)

    S. Kuppel

    2012-10-01

    Full Text Available Assimilation of in situ and satellite data in mechanistic terrestrial ecosystem models helps to constrain critical model parameters and reduce uncertainties in the simulated energy, water and carbon fluxes. So far the assimilation of eddy covariance measurements from flux-tower sites has been conducted mostly for individual sites ("single-site" optimization. Here we develop a variational data assimilation system to optimize 21 parameters of the ORCHIDEE biogeochemical model, using net CO2 flux (NEE and latent heat flux (LE measurements from 12 temperate deciduous broadleaf forest sites. We assess the potential of the model to simulate, with a single set of inverted parameters, the carbon and water fluxes at these 12 sites. We compare the fluxes obtained from this "multi-site" (MS optimization to those of the prior model, and of the "single-site" (SS optimizations. The model-data fit analysis shows that the MS approach decreases the daily root-mean-square difference (RMS to observed data by 22%, which is close to the SS optimizations (25% on average. We also show that the MS approach distinctively improves the simulation of the ecosystem respiration (Reco, and to a lesser extent the gross primary productivity (GPP, although we only assimilated net CO2 flux. A process-oriented parameter analysis indicates that the MS inversion system finds a unique combination of parameters which is not the simple average of the different SS sets of parameters. Finally, in an attempt to validate the optimized model against independent data, we observe that global-scale simulations with MS optimized parameters show an enhanced phase agreement between modeled leaf area index (LAI and satellite-based observations of normalized difference vegetation index (NDVI.

  17. Technical note: Time lag correction of aquatic eddy covariance data measured in the presence of waves

    Science.gov (United States)

    Berg, P.; Reimers, C. E.; Rosman, J. H.; Huettel, M.; Delgard, M. L.; Reidenbach, M. A.; Özkan-Haller, H. T.

    2015-11-01

    Extracting benthic oxygen fluxes from eddy covariance time series measured in the presence of surface gravity waves requires careful consideration of the temporal alignment of the vertical velocity and the oxygen concentration. Using a model based on linear wave theory and measured eddy covariance data, we show that a substantial error in flux can arise if these two variables are not aligned correctly in time. We refer to this error in flux as the time lag bias. In one example, produced with the wave model, we found that an offset of 0.25 s between the oxygen and the velocity data produced a 2-fold overestimation of the flux. In another example, relying on nighttime data measured over a seagrass meadow, a similar offset reversed the flux from an uptake of -50 mmol m-2 d-1 to a release of 40 mmol m-2 d-1. The bias is most acute for data measured at shallow-water sites with short-period waves and low current velocities. At moderate or higher current velocities (> 5-10 cm s-1), the bias is usually insignificant. The widely used traditional time shift correction for data measured in unidirectional flows, where the maximum numerical flux is sought, should not be applied in the presence of waves because it tends to maximize the time lag bias or give unrealistic flux estimates. Based on wave model predictions and measured data, we propose a new time lag correction that minimizes the time lag bias. The correction requires that the time series of both vertical velocity and oxygen concentration contain a clear periodic wave signal. Because wave motions are often evident in eddy covariance data measured at shallow-water sites, we encourage more work on identifying new time lag corrections.

  18. 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

  19. 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.

  20. Evaluation of the Latest MODIS GPP Products across Multiple Biomes Using Global Eddy Covariance Flux Data

    Directory of Open Access Journals (Sweden)

    Lunche Wang

    2017-04-01

    Full Text Available The latest MODIS GPP (gross primary productivity product, MOD17A2H, has great advantages over the previous version, MOD17A2, because the resolution increased from 1000 m to 500 m. In this study, MOD17A2H GPP was assessed using the latest eddy covariance (EC flux data (FLUXNET2015 Dataset at eighteen sites in six ecosystems across the globe. The sensitivity of MOD17A2H GPP to the meteorology dataset and the fractional photosynthetically- active radiation (FPAR product was explored by introducing site meteorology observations and improved Global Land Surface Satellite (GLASS Leaf Area Index (LAI products. The results showed that MOD17A2H GPP underestimated flux-derived GPP at most sites. Its performance in estimating annual GPP was poor (R2 = 0.62 and even worse over eight days (R2 = 0.52. For the MOD17A2H algorithm, replacing the reanalysis meteorological datasets with the site meteorological measurements failed to improve the estimation accuracies. However, great improvements in estimating the site-based GPP were gained by replacing MODIS FPAR with GLASS FPAR. This indicated that in the existing MOD17A2H product, the errors were originated more from FPAR than the meteorological data. We further examined the potential error contributions from land cover classification and maximum light use efficiency (εmax. It was found that the current land cover classification scheme exhibited frequent misclassification errors. Moreover, the εmax value assigned in MOD17A2H was much smaller than the inferred εmax value. Therefore, the qualities of FPAR and land cover classification datasets should be upgraded, and the εmax value needs to be adjusted to provide more accurate GPP estimates using MOD17A2H for global ecosystems.

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

    Science.gov (United States)

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

    2009-11-01

    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 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.

  2. 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

  3. N2O eddy covariance fluxes: From field measurements to flux calculation

    Science.gov (United States)

    Lognoul, Margaux; Debacq, Alain; Heinesch, Bernard; Aubinet, Marc

    2017-04-01

    From March to October 2016, we performed eddy covariance measurements in a sugar beet crop at the Lonzée Terrestrial Observatory (LTO, candidate ICOS site) in Belgium. N2O and H2O atmospheric concentrations were measured at 10 Hz using a quantum-cascade laser spectrometer (Aerodyne Research, Inc.) and combined to wind speed 3D components measured with a sonic anemometer (Gill HS-50). Flux computation was carried out using the EddyPro Software (LI-COR) with a focus on adaptations needed for tracers like N2O. Data filtering and quality control were performed according to Vickers and Mahrt (1997) and Mauder and Foken (2004). The flags were adapted to N2O time series. In this presentation, different computation steps will be presented. More specifically: 1) Considering that a large proportion of N2O fluxes are small (within ± 0.5 nmol m-2 s-1), the classical stationarity test might lead to excessive data filtering and in such case, some searchers have chosen to use the running mean (RM) as a detrend method over block averaging (BA) and to filter data otherwise. For our dataset, BA mean fluxes combined to the stationarity test did not significantly differ from RM fluxes when the averaging window was 300s or larger, but were significantly larger otherwise, suggesting that significant eddies occurred at the 5-min timescale and that they were not accounted for with a shorter averaging window. 2) The determination of time-lag in the case of N2O fluxes can become tricky for two reasons : (1) the signal amplitude can differ from one time period to the next, making it difficult to use the method of covariance maximization and (2) an additional clock drift can appear if the spectrometer is not logging on the same computer than the anemometer. In our case, the N2O signal was strong enough to solve both problems and to perform time-lag compensation according to the covariance maximization, with a default value equal to the mode of the lag distribution. The automatic time

  4. Potential and Limitations of an Electrical Low Pressure Impactor in Disjunct Eddy Covariance Aerosol Flux Measurements

    Science.gov (United States)

    Held, A.; Niessner, R.; Bosveld, F.; Klemm, O.

    2006-12-01

    A micrometeorological application of an electrical low pressure impactor (ELPI) is proposed for the measurement of size-resolved particle fluxes between the surface and the atmosphere. This extends flux measurement capabilities to cover submicron particles in several size classes simultaneously. The disjunct eddy covariance system combines a sonic anemometer, an ELPI and a valve-controlled particle sampling unit. Depending on the valve setting, ambient air or filtered particle-free air is sampled and introduced into the impactor. For disjunct eddy covariance measurements, ambient air is sampled only during a very short sampling interval (~ 0.1 s) in measurement intervals of several seconds. The integrated ELPI signal is representative for the particle size distribution during the short sampling interval. This information may be correlated with fast measurements of the vertical wind speed to obtain turbulent fluxes of submicron particles simultaneously in several size classes. A prototype system has been tested in lab and field experiments in order to evaluate the technical limitations of this approach. Tests show that different valve switch cycles do not affect the concentration measurements. However, longitudinal diffusion processes within the sampling lines lead to signal dilatation. In addition, reliable measurements require a minimum number of charged particles impacting on each stage. This leads to the exclusion of some size bins in typical field applications. Nevertheless, the system showed its potential for size-resolved flux measurements under favorable conditions. Travel support by the ACCENT Access to Infrastructures program is gratefully acknowledged.

  5. Eddy-covariance flux errors due to biases in gas concentration measurements: origins, quantification and correction

    Science.gov (United States)

    Fratini, G.; McDermitt, D. K.; Papale, D.

    2013-08-01

    Errors in gas concentration measurements by infrared gas analysers can occur during eddy-covariance campaigns, associated with actual or apparent instrumental drifts or to biases due to thermal expansion, dirt contamination, aging of components or errors in field operations. If occurring on long time scales (hours to days), these errors are normally ignored during flux computation, under the assumption that errors in mean gas concentrations do not affect the estimation of turbulent fluctuations and, hence, of covariances. By analysing instrument theory of operation, and using numerical simulations and field data, we show that this is not the case for instruments with curvilinear calibrations; we further show that if not appropriately accounted for, concentration biases can lead to roughly proportional systematic flux errors, where the fractional errors in fluxes are about 30-40% the fractional errors in concentrations. We quantify these errors and characterize their dependency on main determinants. We then propose a correction procedure that largely - potentially completely - eliminates these errors. The correction, to be applied during flux computation, is based on knowledge of instrument calibration curves and on field or laboratory calibration data. Finally, we demonstrate the occurrence of such errors and validate the correction procedure by means of a field experiment, and accordingly provide recommendations for in situ operations. The correction described in this paper will soon be available in the EddyPro software (licor.com/eddypro"target="_blank">www.licor.com/eddypro).

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

    Science.gov (United States)

    Lasslop, G.; Migliavacca, M.; Bohrer, G.; Reichstein, M.; Bahn, M.; Ibrom, A.; Jacobs, C.; Kolari, P.; Papale, D.; Vesala, T.; Wohlfahrt, G.; Cescatti, A.

    2012-12-01

    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 choice between soil or air temperature must be made on site

  7. 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

  8. Observed eddy dissipation in the Agulhas Current

    CSIR Research Space (South Africa)

    Braby, L

    2016-08-01

    Full Text Available Channel and south of Madagascar dissipate as they approach the Agulhas Current. By tracking the offshore position of the current core and its velocity at 30°S in relation to eddies, it is demonstrated that eddy dissipation occurs through a transfer...

  9. 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

  10. 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...... the first week of May when the trees were leafing and the soil moisture content was at its highest. If chamber techniques are used to estimate ecosystem level N2O emissions from forest soils, placement of the chambers should be considered carefully to cover the spatial variability in the soil N2O emissions....... Mean N2O fluxes over the five week measurement period were 5.6 +/- 1.1, 10 +/- 1 and 16 +/- 11 mu g N m(-2) h(-1) from EC, automatic chamber and manual chambers, respectively. High temporal variability characterized the EC fluxes in the trunk-space. To reduce this variability, resulting mostly from...

  11. Eddy covariance flux measurements of ozone: Three stations side-by-side

    Science.gov (United States)

    Song, G.; Voß, L.; Falge, E.; Mayer, J.-C.; Moravek, A.; Trebs, I.; Bruse, M.; Zhu, Z.; Andreae, M. O.; Meixner, F. X.

    2012-04-01

    Since about two decades, fast response ozone analyzers, based on gas-phase chemiluminescence ("Güsten type"), became more and more available and emerged to be operational in atmosphere-biosphere exchange studies using the eddy-covariance technique. While there are first preliminary reports about measurements of the vertical profile of ozone fluxes in forest canopies (addressing the question of vertical flux divergence), measurements by ozone flux stations distributed in a horizontally arranged array (addressing questions of horizontal divergence and/or footprint) might be feasible. For all these measurements, the precision of ozone flux stations is of particular interest, because it defines the vertical/horizontal resolution of expected flux divergence. As a first step in this direction, we performed a 9 week, side-by-side experiment of three ozone flux stations on a small airfield in Mainz-Finthen/Germany (49.969° N, 8.148° E, 227 m a.s.l.) in late summer/autumn 2011. Turbulent fluctuations of ozone concentration (in arbitrary units) have been measured by three identical gas-phase chemiluminescence anaylzers (enviscope GmbH/ Germany) with a sampling frequency of 20 Hz. Absolute ozone concentrations have been monitored by three slow-response UV-absorption based analyzers (model 205, 2BTechnologies/U.S.A.; model 49i, ThermoInstruments/U.S.A.) every 2 and 10 seconds, respectively. Three 3D sonic anemometers (model USA-1, METEK/Germany; model CSAT3, Campbell Scientific/U.K.) have been applied to obtain fluctuations of 3D wind vectors and temperature (20Hz). All fast response sensors were mounted at 3 m above ground, the three flux stations have been aligned in cross-wind direction in a distance of about 5.5 m to each other. Sensor separation (3D anemometer - ozone intake) was 0.3 m, the length of ozone intake tubes were about 3 m. Ozone monitors have routinely been calibrated every 15 days. For the calculation of turbulent fluxes of ozone, momentum, and sensible

  12. 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

  13. Emissions of Greenhouse Gases from Urban Xi'an, China - Direct Measurements by Eddy Covariance

    Science.gov (United States)

    VanReken, T. M.; Mwaniki, G. R.; VanderSchelden, G.; O'Keeffe, P.; Waldo, S.; Erickson, M. H.; Lamb, B. K.; Jobson, B. T.; Tie, X.; Cao, J.

    2012-12-01

    Throughout the world and especially in Asia, rapid urbanization is resulting in an increasing number of very large cities. In these areas, the rate of development can outpace the perceived need for environmental regulation, and frequently there are inadequate resources available to monitor pollution or enforce compliance with those environmental regulations that do exist. These limitations obviously impact air quality on a local scale, but cities also have significant environmental impacts on regional and even global scales. In order to understand and mitigate these impacts on the surrounding environment, it is first necessary to robustly characterize the pollutant emissions themselves. This can be a significant challenge. Major discrepancies arise when comparing emissions inventories based on bottom-up compilations of source types, number, and activity levels to estimates inferred from satellite observations and other large-scale techniques. Direct measurements of neighborhood-scale emission fluxes via micrometeorological approaches provide a means to resolve these differences. Such measurements can be used to quantify the integrated vertical exchange for a wide variety of greenhouse gases and other pollutants, typically with spatial footprints of tens of square kilometers and with temporal resolutions of ~30 minutes. Here we present the results of an urban flux study conducted in Xi'an, China in August 2011. For the study a 23 m tower was erected atop the ~100 m tall administration building at Xi'an Jiaotong University. From the tower, we employed an eddy covariance approach to measure concentrations and fluxes of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and carbon monoxide (CO). Here we present an analysis of the air-surface exchange of these gases. Results indicate that while our study site in Xi'an was a net source of these species, the greenhouse gas fluxes were significantly smaller than at other sites around the world and exhibited a

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

    Directory of Open Access Journals (Sweden)

    O. Peltola

    2013-06-01

    Full Text Available 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.

  15. Soil Respiration in Eddy Covariance Footprints: A Critical Look at Researcher Needs

    Science.gov (United States)

    Gabriel, Carrie-Ellen; Nickerson, Nick; Creelman, Chance

    2017-04-01

    Eddy covariance (EC) systems have been widely used across the globe for more than 20 years, offering researchers invaluable measurements of parameters including Net Ecosystem Exchange and ecosystem respiration. However, recent research suggests that EC assumptions and technical obstacles may cause biased gas exchange estimates. Measurements of soil respiration (RS) at the ground level may help alleviate these biases; for example, by allowing researchers to reconcile nocturnal EC flux data with soil respiration or by providing a means to inform gap-filling models. RS measurements have been used sparingly alongside EC towers because of the large cost required to scale chamber systems to the EC footprint, as well as data integration and processing burdens. Here we present how the Forced Diffusion (FD) method is ideal for the measurement of RS at EC sites. The FD method allows for inexpensive and autonomous measurements, providing a scalable approach to matching the EC footprint compared to other RS systems. Here, we briefly present the methodology and results from a pilot study at the Howland Forest AmeriFlux site (Maine), carried out during the summer and fall of 2016, measuring soil respiration using the FD chamber technique. The emphasis of the remainder of the research is on gathering, interpreting and actualizing feedback from soil scientists and eddy covariance researchers and technicians on aspects of the FD methodology, deployment style, integration with existing infrastructure and data quality. Our goal is to eventually provide a framework for "ideal soil respiration measurements" that can be used by researchers, engineers and companies to develop functional and reliable soil respiration data sets that are easily coupled with data measured by EC users, and larger EC networks such as AmeriFlux and EuroFlux.

  16. Field intercomparison of four methane gas analysers suitable for eddy covariance flux measurements

    Science.gov (United States)

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

    2012-12-01

    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 analysers 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 long-term performance were not assessed. Prototype-7700 is a practical choice for measurement sites in remote locations due to its low power demand, however 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 analyser is needed.

  17. 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.

  18. Methane fluxes measured by eddy covariance and static chamber techniques at a temperate forest in central ontario, Canada

    Science.gov (United States)

    Wang, J. M.; Murphy, J. G.; Geddes, J. A.; Winsborough, C. L.; Basiliko, N.; Thomas, S. C.

    2012-12-01

    Methane flux measurements were carried out at a temperate forest (Haliburton Forest and Wildlife Reserve) in central Ontario (45°17´11´´ N, 78°32´19´´ W) from June-October, 2011. Continuous measurements were made by an off-axis integrated cavity output spectrometer Fast Greenhouse Gas Analyzer (FGGA) from Los Gatos Research Inc. that measures methane (CH4) at 10 Hz sampling rates. Fluxes were calculated from the gas measurements in conjunction with wind data collected by a 3-D sonic anemometer using the eddy covariance (EC) method. Observed methane fluxes showed net uptake of CH4 over the measurement period with an average uptake flux (± standard deviation of the mean) of -2.7 ± 0.13 nmol m-2 s-1. Methane fluxes showed a seasonal progression with average rates of uptake increasing from June through September and remaining high in October. This pattern was consistent with a decreasing trend in soil moisture content at the monthly time scale. On the diurnal timescale, there was evidence of increased uptake during the day, when the mid-canopy wind speed was at a maximum. These patterns suggest that substrate supply of CH4 and oxygen to methanotrophs, and in certain cases hypoxic soil conditions supporting methanogenesis in low-slope areas, drive the observed variability in fluxes. A network of soil static chambers used at the tower site showed close agreement with the eddy covariance flux measurements. This suggests that soil-level microbial processes, and not abiological leaf-level CH4 production, drive overall CH4 dynamics in temperate forest ecosystems such as Haliburton Forest.

  19. 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

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

    NARCIS (Netherlands)

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

    2010-01-01

    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

  1. Effects of different eddy covariance correction schemes on energy balance closure and comparisons with the modified Bowen ratio system

    Science.gov (United States)

    Adam Wolf; Nick Saliendra; Kanat Akshalov; Douglas A. Johnson; Emilio Laca

    2008-01-01

    Eddy covariance (EC) and modified Bowen ratio (MBR) systems have been shown to yield subtly different estimates of sensible heat (H), latent heat (LE), and CO2 fluxes (Fc). Our study analyzed the discrepancies between these two systems by first considering the role of the data processing algorithm used to estimate fluxes using EC and later...

  2. 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

  3. Use of change-point detection for friction-velocity threshold evaluation in eddy-covariance studies

    Science.gov (United States)

    A.G. Barr; A.D. Richardson; D.Y. Hollinger; D. Papale; M.A. Arain; T.A. Black; G. Bohrer; D. Dragoni; M.L. Fischer; L. Gu; B.E. Law; H.A. Margolis; J.H. McCaughey; J.W. Munger; W. Oechel; K. Schaeffer

    2013-01-01

    The eddy-covariance method often underestimates fluxes under stable, low-wind conditions at night when turbulence is not well developed. The most common approach to resolve the problem of nighttime flux underestimation is to identify and remove the deficit periods using friction-velocity (u∗) threshold filters (u∗

  4. Primary Marine Aerosol Emissions: Size Resolved Eddy Covariance Measurements with Estimates of the Sea Salt and Organic Carbon Fractions

    NARCIS (Netherlands)

    Nilsson, E.D.; Martensson, E.M.; Ekeren, J.S. van; Leeuw, G. de; Moerman, M.M.; O'Dowd, C.

    2007-01-01

    Primary marine aerosol fluxes were measured using eddy covariance (EC), a condensation particle counter (CPC) and an optical particle counter (OPC) with a heated inlet. The later was used to discriminate between sea salt and total aerosol. Measurements were made from the 25m tower at the research

  5. 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)...

  6. Arctic regional methane fluxes by ecotope as derived using eddy covariance from a low-flying aircraft

    Directory of Open Access Journals (Sweden)

    D. S. Sayres

    2017-07-01

    Full Text Available The Arctic terrestrial and sub-sea permafrost region contains approximately 30 % of the global carbon stock, and therefore understanding Arctic methane emissions and how they might change with a changing climate is important for quantifying the global methane budget and understanding its growth in the atmosphere. Here we present measurements from a new in situ flux observation system designed for use on a small, low-flying aircraft that was deployed over the North Slope of Alaska during August 2013. The system combines a small methane instrument based on integrated cavity output spectroscopy (ICOS with an air turbulence probe to calculate methane fluxes based on eddy covariance. We group surface fluxes by land class using a map based on LandSat Thematic Mapper (TM data with 30 m resolution. We find that wet sedge areas dominate the methane fluxes with a mean flux of 2.1 µg m−2 s−1 during the first part of August. Methane emissions from the Sagavanirktok River have the second highest at almost 1 µg m−2 s−1. During the second half of August, after soil temperatures had cooled by 7 °C, methane emissions fell to between 0 and 0.5 µg m−2 s−1 for all areas measured. We compare the aircraft measurements with an eddy covariance flux tower located in a wet sedge area and show that the two measurements agree quantitatively when the footprints of both overlap. However, fluxes from sedge vary at times by a factor of 2 or more even within a few kilometers of the tower demonstrating the importance of making regional measurements to map out methane emissions spatial heterogeneity. Aircraft measurements of surface flux can play an important role in bridging the gap between ground-based measurements and regional measurements from remote sensing instruments and models.

  7. Arctic regional methane fluxes by ecotope as derived using eddy covariance from a low-flying aircraft

    Science.gov (United States)

    Sayres, David S.; Dobosy, Ronald; Healy, Claire; Dumas, Edward; Kochendorfer, John; Munster, Jason; Wilkerson, Jordan; Baker, Bruce; Anderson, James G.

    2017-07-01

    The Arctic terrestrial and sub-sea permafrost region contains approximately 30 % of the global carbon stock, and therefore understanding Arctic methane emissions and how they might change with a changing climate is important for quantifying the global methane budget and understanding its growth in the atmosphere. Here we present measurements from a new in situ flux observation system designed for use on a small, low-flying aircraft that was deployed over the North Slope of Alaska during August 2013. The system combines a small methane instrument based on integrated cavity output spectroscopy (ICOS) with an air turbulence probe to calculate methane fluxes based on eddy covariance. We group surface fluxes by land class using a map based on LandSat Thematic Mapper (TM) data with 30 m resolution. We find that wet sedge areas dominate the methane fluxes with a mean flux of 2.1 µg m-2 s-1 during the first part of August. Methane emissions from the Sagavanirktok River have the second highest at almost 1 µg m-2 s-1. During the second half of August, after soil temperatures had cooled by 7 °C, methane emissions fell to between 0 and 0.5 µg m-2 s-1 for all areas measured. We compare the aircraft measurements with an eddy covariance flux tower located in a wet sedge area and show that the two measurements agree quantitatively when the footprints of both overlap. However, fluxes from sedge vary at times by a factor of 2 or more even within a few kilometers of the tower demonstrating the importance of making regional measurements to map out methane emissions spatial heterogeneity. Aircraft measurements of surface flux can play an important role in bridging the gap between ground-based measurements and regional measurements from remote sensing instruments and models.

  8. A study of the surface roughness lengths of a high-altitude topical glacier using profile and eddy covariance measurements

    Science.gov (United States)

    Sicart, J.; Litt, M.

    2012-12-01

    The turbulent fluxes remain poorly understood on tropical glaciers. Studies based on the bulk method have shown that sublimation can be high during the dry season, reducing the energy available for melting. However, uncertainties on the bulk method are large, especially when katabatic flows cause a wind speed maximum at low height. Wind and temperature data from an 8-level 6-m mast positioned at 5060 m asl in the ablation area of the Zongo Glacier, Bolivia (16°S), were collected during a one-month period in the dry season of 2007. Concomitant measurements of radiation fluxes and eddy covariance turbulent fluxes were conducted. The surface roughness lengths for temperature and momentum were calculated using the profile and the eddy covariance methods at the hourly time scale. The measurement period was characterized by low synoptic forcing conditions and katabatic wind prevailed at night and most of the day. Katabatic flows were often associated with a wind speed maximum at a height of about 2-3 m and with a strong temperature inversion. Near-neutral profiles were selected to avoid the presence of the katabatic wind speed maximum. Results indicate z0 values of about 3 mm and zT values of about 0.2 mm, in rough agreement with terrain observations. However the scatter in the zT values is large indicating large random errors. The relation between the ratio zT/z0 and the roughness Reynolds number is in rough agreement with the surface renewal model. However, this relation turns out to be mostly due to spurious self-correlation because of the shared variable z0 in zT/z0 and Re*. Finally, the random and systematic errors on the roughness lengths derived from the profile measurements were briefly investigated. The results emphasize the need of accurate measurements of the sensor heights to obtain unbiased roughness lengths.

  9. A study of the surface roughness lengths of a high-altitude tropical glacier using profile and eddy covariance measurements

    Science.gov (United States)

    Sicart, Jean-Emmanuel; Litt, Maxime; Ben Tahar, Vanessa

    2013-04-01

    The turbulent fluxes remain poorly understood on tropical glaciers. Studies based on the bulk method have shown that sublimation can be high during the dry season, reducing the energy available for melting. However, uncertainties on the bulk method are large, especially when katabatic flows cause a wind speed maximum at low height. Wind and temperature data from an 8-level 6-m mast positioned at 5060 m a.s.l. in the ablation area of the Zongo Glacier, Bolivia (16°S), were collected during a one-month period in the dry season of 2007. Concomitant measurements of radiation fluxes and eddy covariance turbulent fluxes were conducted. The surface roughness lengths for temperature (zT) and momentum (z0) were calculated using the profile and the eddy covariance methods at the hourly timescale. The measurement period was characterized by low synoptic forcing conditions and katabatic wind prevailed at night and most of the day. Katabatic flows were often associated with a wind speed maximum at a height of about 2-3 m and with a strong temperature inversion. Near-neutral profiles were selected to avoid the presence of the katabatic wind speed maximum. Results indicate z0 values of about 3 mm and zT values of about 0.2 mm, in rough agreement with terrain observations. However the scatter in the zT values is large indicating large random errors. The relation between the ratio zT/z0 and the roughness Reynolds number (Re*) is in rough agreement with the surface renewal model. However, this relation turns out to be mostly due to spurious self-correlation because of the shared variable z0 in zT/z0 and Re*. Finally, the random and systematic errors on the roughness lengths derived from the profile measurements were briefly investigated. The results emphasize the need of accurate measurements of the sensor heights to obtain unbiased roughness lengths.

  10. 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.

  11. Earth Observation System Flight Dynamics System Covariance Realism

    Science.gov (United States)

    Zaidi, Waqar H.; Tracewell, David

    2016-01-01

    This presentation applies a covariance realism technique to the National Aeronautics and Space Administration (NASA) Earth Observation System (EOS) Aqua and Aura spacecraft based on inferential statistics. The technique 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.

  12. 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

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

    Science.gov (United States)

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

    2017-09-01

    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 this relative metric

  14. 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.

  15. FluxPro: Real time monitoring and simulation system for eddy covariance flux measurement

    Science.gov (United States)

    Kim, W.; Seo, H.; Mano, M.; Ono, K.; Miyata, A.; Yokozawa, M.

    2010-12-01

    To cope with unusual weather changes on crop cultivation in a field level, prompt and precise monitoring of photosynthesis and evapotranspiration, and those fast and reliable forecasting are indispensable. So we have developed FluxPro which is simultaneous operating system of the monitoring and the forecasting. The monitoring subsystem provides vapor and CO2 fluxes with uncertainty to understand the live condition of photosynthesis and evapotranspiration by open-path eddy covariance flux measurement (EC) system and self-developed EC tolerance analysis scheme. The forecasting subsystem serves the predicted fluxes with anomaly based on model parameter assimilation to estimate the hourly or daily water consumption and carbon assimilation during a week by multi-simulation package consisting of various models from simple to complicate. FluxPro is helpful not only to detect a critical condition of growing crop in terms of photosynthesis and evapotranspiration but also to decide time and amount of launching control for keeping those optimization condition when an unusual weather event is arisen. In our presentation, we will demonstrate the FluxPro operated at tangerine orchard in Jeju, Korea.

  16. Delta-Flux: An Eddy Covariance Network for a Climate-Smart Lower Mississippi Basin

    Directory of Open Access Journals (Sweden)

    Benjamin R. K. Runkle

    2017-02-01

    Full Text Available 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.

  17. 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.

  18. 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.

  19. Development of an Eddy Covariance System for Air-Sea Carbon Dioxide Exchange

    Science.gov (United States)

    Miller, S. D.; Marandino, C. A.; McCormick, C.; Saltzman, E. S.

    2006-12-01

    We are developing a ship-based system to measure the air-sea pCO2 gradient and air-sea turbulent flux of CO2 over the ocean. The eddy covariance flux system uses off-the-shelf instruments to measure the turbulent wind vector (Campbell Scientific CSAT3 sonic anemometer), platform motion (Systron Donner Motion Pak II), and carbon dioxide molar density (LiCor 7000 Infrared Gas Analyzer). Two major sources of uncertainty in calculated fluxes are the effect of water vapor fluctuations on air density fluctuations (the WPL effect, Webb, Pearman and Leuning. 1980), and a spurious CO2 signal due to the sensitivity of the gas analyzer to platform motion (McGillis et al., 1998). Two flux systems were deployed side-by-side on a cruise from Manzanillo, Mexico to Puntas Arenas, Chile, in January 2006. Results from the cruise are presented, with a focus on our attempts to reduce biases in the calculated air-sea CO2 flux due to the WPL effect and the motion sensitivity of the gas analyzer.

  20. 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.

  1. Urban eddy covariance measurements reveal significant missing NOx emissions in Central Europe.

    Science.gov (United States)

    Karl, T; Graus, M; Striednig, M; Lamprecht, C; Hammerle, A; Wohlfahrt, G; Held, A; von der Heyden, L; Deventer, M J; Krismer, A; Haun, C; Feichter, R; Lee, J

    2017-05-30

    Nitrogen oxide (NOx) pollution is emerging as a primary environmental concern across Europe. While some large European metropolitan areas are already in breach of EU safety limits for NO2, this phenomenon does not seem to be only restricted to large industrialized areas anymore. Many smaller scale populated agglomerations including their surrounding rural areas are seeing frequent NO2 concentration violations. The question of a quantitative understanding of different NOx emission sources is therefore of immanent relevance for climate and air chemistry models as well as air pollution management and health. Here we report simultaneous eddy covariance flux measurements of NOx, CO2, CO and non methane volatile organic compound tracers in a city that might be considered representative for Central Europe and the greater Alpine region. Our data show that NOx fluxes are largely at variance with modelled emission projections, suggesting an appreciable underestimation of the traffic related atmospheric NOx input in Europe, comparable to the weekend-weekday effect, which locally changes ozone production rates by 40%.

  2. 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

  3. 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

  4. 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 ice grew from 5 to 25 cm thick. Heat, momentum, and dissolved oxygen fluxes were all successfully derived. Quantification of salt fluxes was unsuccessful due to noise in the conductivity sensor, a problem which appears to be resolved in a subsequent version of the instrument. Heat fluxes during...... 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...

  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. Eddies

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The maximum potential area of eddy bars (MPAEB) represents the cumulative area of the eddy occupied by sand at different times within the photographic record...

  7. Surface-atmosphere exchange of ammonia over peatland using QCL-based eddy-covariance measurements and inferential modeling

    Science.gov (United States)

    Zöll, Undine; Brümmer, Christian; Schrader, Frederik; Ammann, Christof; Ibrom, Andreas; Flechard, Christophe R.; Nelson, David D.; Zahniser, Mark; Kutsch, Werner L.

    2016-09-01

    Recent advances in laser spectrometry offer new opportunities to investigate ecosystem-atmosphere exchange of environmentally relevant trace gases. In this study, we demonstrate the applicability of a quantum cascade laser (QCL) absorption spectrometer to continuously measure ammonia concentrations at high time resolution and thus to quantify the net exchange between a seminatural peatland ecosystem and the atmosphere based on the eddy-covariance approach. Changing diurnal patterns of both ammonia concentration and fluxes were found during different periods of the campaign. We observed a clear tipping point in early spring with decreasing ammonia deposition velocities and increasingly bidirectional fluxes that occurred after the switch from dormant vegetation to CO2 uptake but was triggered by a significant weather change. While several biophysical parameters such as temperature, radiation, and surface wetness were identified to partially regulate ammonia exchange at the site, the seasonal concentration pattern was clearly dominated by agricultural practices in the surrounding area. Comparing the results of a compensation point model with our measurement-based flux estimates showed considerable differences in some periods of the campaign due to overestimation of non-stomatal resistances caused by low acid ratios. The total cumulative campaign exchange of ammonia after 9 weeks, however, differed only in a 6 % deviation with 911 and 857 g NH3-N ha-1 deposition being found by measurements and modeling, respectively. Extrapolating our findings to an entire year, ammonia deposition was lower than reported by Hurkuck et al. (2014) for the same site in previous years using denuder systems. This was likely due to a better representation of the emission component in the net signal of eddy-covariance fluxes as well as better adapted site-specific parameters in the model. Our study not only stresses the importance of high-quality measurements for studying and assessing land

  8. Surface–atmosphere exchange of ammonia over peatland using QCL-based eddy-covariance measurements and inferential modeling

    Directory of Open Access Journals (Sweden)

    U. Zöll

    2016-09-01

    Full Text Available Recent advances in laser spectrometry offer new opportunities to investigate ecosystem–atmosphere exchange of environmentally relevant trace gases. In this study, we demonstrate the applicability of a quantum cascade laser (QCL absorption spectrometer to continuously measure ammonia concentrations at high time resolution and thus to quantify the net exchange between a seminatural peatland ecosystem and the atmosphere based on the eddy-covariance approach. Changing diurnal patterns of both ammonia concentration and fluxes were found during different periods of the campaign. We observed a clear tipping point in early spring with decreasing ammonia deposition velocities and increasingly bidirectional fluxes that occurred after the switch from dormant vegetation to CO2 uptake but was triggered by a significant weather change. While several biophysical parameters such as temperature, radiation, and surface wetness were identified to partially regulate ammonia exchange at the site, the seasonal concentration pattern was clearly dominated by agricultural practices in the surrounding area. Comparing the results of a compensation point model with our measurement-based flux estimates showed considerable differences in some periods of the campaign due to overestimation of non-stomatal resistances caused by low acid ratios. The total cumulative campaign exchange of ammonia after 9 weeks, however, differed only in a 6 % deviation with 911 and 857 g NH3-N ha−1 deposition being found by measurements and modeling, respectively. Extrapolating our findings to an entire year, ammonia deposition was lower than reported by Hurkuck et al. (2014 for the same site in previous years using denuder systems. This was likely due to a better representation of the emission component in the net signal of eddy-covariance fluxes as well as better adapted site-specific parameters in the model. Our study not only stresses the importance of high-quality measurements

  9. 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

  10. Towards a standardized processing of Net Ecosystem Exchange measured with eddy covariance technique: algorithms and uncertainty estimation

    Directory of Open Access Journals (Sweden)

    D. Papale

    2006-01-01

    Full Text Available Eddy covariance technique to measure CO2, water and energy fluxes between biosphere and atmosphere is widely spread and used in various regional networks. Currently more than 250 eddy covariance sites are active around the world measuring carbon exchange at high temporal resolution for different biomes and climatic conditions. In this paper a new standardized set of corrections is introduced and the uncertainties associated with these corrections are assessed for eight different forest sites in Europe with a total of 12 yearly datasets. The uncertainties introduced on the two components GPP (Gross Primary Production and TER (Terrestrial Ecosystem Respiration are also discussed and a quantitative analysis presented. Through a factorial analysis we find that generally, uncertainties by different corrections are additive without interactions and that the heuristic u*-correction introduces the largest uncertainty. The results show that a standardized data processing is needed for an effective comparison across biomes and for underpinning inter-annual variability. The methodology presented in this paper has also been integrated in the European database of the eddy covariance measurements.

  11. Empirical Performance of Covariates in Education Observational Studies

    Science.gov (United States)

    Wong, Vivian C.; Valentine, Jeffrey C.; Miller-Bains, Kate

    2017-01-01

    This article summarizes results from 12 empirical evaluations of observational methods in education contexts. We look at the performance of three common covariate-types in observational studies where the outcome is a standardized reading or math test. They are: pretest measures, local geographic matching, and rich covariate sets with a strong…

  12. Short-term eddy-covariance measurements of CO2 fluxes at Itaipu Lake, Brazil

    Science.gov (United States)

    Dias, N. L.; Crivellaro, B. L.; Armani, F. S.; Chor, T. L.; Gobbi, M. F.; Santos, A. L.; Lemma/UFPR Scientific Team

    2013-05-01

    We describe a 5-day campaign of eddy-covariance measurements at Itaipu Lake, in Southern Brazil and estimates of CO2 fluxes over crops in the same region with a SVAT model. Itaipu Lake was formed from the damming of Paraná River at the border between Brazil and Paraguay close to Foz do Iguaçu (BR) and Ciudad del Leste (PY); Itaipu dam is jointly operated by both countries. The measurements were made on the Brazilian side, at a very small island (Lat: -25o 03'25.72" Long -54o 24'33.67" : Altitude: 220 m ASL) located approximately 420 m away from the left (Brazilian) bank. The fetch to the ragged countour of the lake is rather large in the North-South direction: 2891 m to the North, and 1817 m to the South. Eddy covariance instrumentation mounted on a short tower consisted of a Li-Cor LI7500 open-path gas analyzer measuring CO2 and H2O concentrations; 4 Campbell FW3 fine-wire thermocouples and a Campbell CSAT-3 three-dimensional sonic anemometer, and were made at 3.76 m above the tower base, which remained at 2.8 m above the water level during the campaign. Mean concentrations of CO2 with Vaisala GM343 sensors were made at the tower, at 1.77 and 3.66 m above the tower base. The sensors were intercompared before the field experiment. The measurements reported here took place from 00:00 hrs Local Time of Dec 8th 2012 to 00:00 hrs of Dec 13 8th 2012. During most of the time there was fair weather, and the wind came predominantly from the North or North-East, with very favorable fetches. Standard data processing included coordinate rotation, linear detrending, despiking and density corrections. Peak positive and negative CO2 fluxes were -0.016 and +0.013 mmol/m2/s, respectively, with a mean value over the 5-day period of -0.14 mmol/m2/s. This may be compared to CO2 flux estimates using a SVAT model over soy, which yielded peak daytime values of 0.027 mmol/m2/s. These values should be interpreted as local both in time and space (i.e. neither representative of the whole

  13. Estimation of gross primary production of irrigated maize using Landsat-8 imagery and Eddy Covariance data.

    Science.gov (United States)

    Madugundu, Rangaswamy; Al-Gaadi, Khalid A; Tola, ElKamil; Kayad, Ahmed G; Jha, Chandra Sekhar

    2017-02-01

    A study was conducted to understand the potential of Landsat-8 in the estimation of gross primary production (GPP) and to quantify the productivity of maize crop cultivated under hyper-arid conditions of Saudi Arabia. The GPP of maize crop was estimated by using the Vegetation Photosynthesis Model (VPM) utilizing remote sensing data from Landsat-8 reflectance (GPPVPM) as well as the meteorological data provided by Eddy Covariance (EC) system (GPPEC), for the period from August to November 2015. Results revealed that the cumulative GPPEC for the entire growth period of maize crop was 1871 g C m(-2). However, the cumulative GPP determined as a function of the enhanced vegetation index - EVI (GPPEVI) was 1979 g C m(-2), and that determined as a function of the normalized difference vegetation index - NDVI (GPPNDVI) was 1754 g C m(-2). These results indicated that the GPPEVI was significantly higher than the GPPEC (R(2) = 0.96, P = 0.0241 and RMSE = 12.6%). While, the GPPNDVI was significantly lower than the GPPEC (R(2) = 0.93, P = 0.0384 and RMSE = 19.7%). However, the recorded relative error between the GPPEC and both the GPPEVI and the GPPNDVI was -6.22% and 5.76%, respectively. These results demonstrated the potential of the landsat-8 driven VPM model for the estimation of GPP, which is relevant to the productivity and carbon fluxes.

  14. Benthic oxygen flux in permeable sediments of the German Bight calculated with the eddy covariance technique

    Science.gov (United States)

    Koopmans, Dirk; Ahmerkamp, Soeren; Holtappels, Moritz

    2017-04-01

    Permeable sediments in coastal zones are highly biologically active, contributing to tight recycling of carbon and nutrients between sediments and overlying water. A growing body of literature demonstrates that oxygen flux in these sediments responds dynamically to changes in current velocities and turbulent kinetic energy. As currents interact with bedforms, pressure gradients are created that drive exchange across the sediment-water interface, displacing oxygen-depleted porewaters into surface waters. We used the eddy covariance technique to quantify oxygen flux at three stations in the German Bight. Station 1 (24 m depth) was composed of medium sands with 1-2 cm bedforms and approximately 100 polychaete worms per square meter. Station 2 (24 m depth) was composed of coarse sands with 3-5 cm bedforms and few worms. Station 3 (38 m depth) and was similar to Station 1 but with intermediate worm densities. In each of the sands advection appeared to drive the displacement of hypoxic or anoxic porewater into surface waters, generating net oxygen consumption. The correspondence between the water velocity and oxygen flux was high, with oscillations in tidal currents yielding similar oscillations in benthic oxygen consumption. The tidal current was very similar across sites (mean of 16.5 - 18 cm s-1 measured 30 cm off of the bed). Oxygen consumption was greatest (45 ± 15 mmol m-2 d-1) in Station 1, the medium-grained shallow site with high polychaete worm densities. It was close to equivalent at the other two sites (27 ± 12 mmol m-2 d-1 and 28 ± 10 mmol m-2 d 1). The implications for scaling these rates up will be examined.

  15. 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.

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

    Science.gov (United States)

    Ruuskanen, T. M.; Müller, M.; Schnitzhofer, R.; Karl, T.; Graus, M.; Bamberger, I.; Hörtnagl, L.; Brilli, F.; Wohlfahrt, G.; Hansel, A.

    2013-01-01

    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. PMID:24348524

  17. Evaluation of MODIS Gross Primary Production across Multiple Biomes in China Using Eddy Covariance Flux Data

    Directory of Open Access Journals (Sweden)

    Hongji Zhu

    2016-05-01

    Full Text Available MOD17A2 provides near real-time estimates of gross primary production (GPP globally. In this study, MOD17A2 GPP was evaluated using eddy covariance (EC flux measurements at eight sites in five various biome types across China. The sensitivity of MOD17A2 to meteorological data and leaf area index/fractional photosynthetically active radiation (LAI/FPAR products were examined by introducing site meteorological measurements and improved Global Land Surface Satellite (GLASS LAI products. We also assessed the potential error contributions from land cover and maximum light use efficiency (εmax. The results showed that MOD17A2 agreed well with flux measurements of annual GPP (R2 = 0.76 when all biome types were considered as a whole. However, MOD17A2 was ineffective for estimating annual GPP at mixed forests, evergreen needleleaf forests and croplands, respectively. Moreover, MOD17A2 underestimated flux derived GPP during the summer (R2 = 0.46. It was found that the meteorological data used in MOD17A2 failed to properly estimate the site measured vapor pressure deficits (VPD (R2 = 0.31. Replacing the existing LAI/FPAR data with GLASS LAI products reduced MOD17A2 GPP uncertainties. Though land cover presented the fewest errors, εmax prescribed in MOD17A2 were much lower than inferred εmax calculated from flux data. Thus, the qualities of meteorological data and LAI/FPAR products need to be improved, and εmax should be adjusted to provide better GPP estimates using MOD17A2 for Chinese ecosystems.

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

    Science.gov (United States)

    Gerdel, Katharina; Spielmann, Felix M.; Hammerle, Albin; Wohlfahrt, Georg

    2016-04-01

    Carbonyl sulfide (COS) is the most abundant sulfur containing trace gas present in the troposphere at concentrations of around 500 ppt. Recent interest in COS by the ecosystem-physiological community has been sparked by the fact that COS co-diffuses into plant leaves pretty much the same way as carbon dioxide (CO2) does, but in contrast to CO2, COS is not known to be emitted by plants. Thus uptake of COS by vegetation has the potential to be used as a tracer for canopy gross photosynthesis, which cannot be measured directly, however represents a key term in the global carbon cycle. Since a few years, quantum cascade laser absorption spectrometers (QCLAS) are commercially available with the precision, sensitivity and time response suitable for eddy covariance (EC) flux measurements. While there exist a handful of published reports on EC flux measurements in the recent literature, no rigorous investigation of the applicability of QCLAS for EC COS flux measurements has been carried out so far, nor have been EC processing and QA/QC steps developed for carbon dioxide and water vapor flux measurements within FLUXNET been assessed for COS. The aim of this study is to close this knowledge gap, to discuss critical steps in the post-processing chain of COS EC flux measurements and to devise best-practice guidelines for COS EC flux data processing. To this end we collected EC COS (and CO2, H2O and CO) flux measurements above a temperate mountain grassland in Austria over the vegetation period 2015 with a commercially available QCLAS. We discuss various aspects of EC data post-processing, in particular issues with the time-lag estimation between sonic anemometer and QCLAS signals and QCLAS time series detrending, as well as QA/QC, in particular flux detection limits, random flux uncertainty, the interaction of various processing steps with common EC QA/QC filters (e.g. detrending and stationarity tests), u*-filtering, etc.

  19. Estimation of gross primary production of irrigated maize using Landsat-8 imagery and Eddy Covariance data

    Directory of Open Access Journals (Sweden)

    Rangaswamy Madugundu

    2017-02-01

    Full Text Available A study was conducted to understand the potential of Landsat-8 in the estimation of gross primary production (GPP and to quantify the productivity of maize crop cultivated under hyper-arid conditions of Saudi Arabia. The GPP of maize crop was estimated by using the Vegetation Photosynthesis Model (VPM utilizing remote sensing data from Landsat-8 reflectance (GPPVPM as well as the meteorological data provided by Eddy Covariance (EC system (GPPEC, for the period from August to November 2015. Results revealed that the cumulative GPPEC for the entire growth period of maize crop was 1871 g C m−2. However, the cumulative GPP determined as a function of the enhanced vegetation index – EVI (GPPEVI was 1979 g C m−2, and that determined as a function of the normalized difference vegetation index – NDVI (GPPNDVI was 1754 g C m−2. These results indicated that the GPPEVI was significantly higher than the GPPEC (R2 = 0.96, P = 0.0241 and RMSE = 12.6%. While, the GPPNDVI was significantly lower than the GPPEC (R2 = 0.93, P = 0.0384 and RMSE = 19.7%. However, the recorded relative error between the GPPEC and both the GPPEVI and the GPPNDVI was −6.22% and 5.76%, respectively. These results demonstrated the potential of the landsat-8 driven VPM model for the estimation of GPP, which is relevant to the productivity and carbon fluxes.

  20. Intercomparison of eight state-of-the-art eddy covariance methane gas analysers

    Science.gov (United States)

    Peltola, Olli; Hensen, Arjan; Helfter, Carole; Belelli Marchesini, Luca; Mammarella, Ivan; Haapanala, Sami; Holst, Jutta; Elbers, Jan; Bosveld, Fred; van den Bulk, Pim; Röckmann, Thomas; Lindroth, Anders; Laurila, Tuomas; Vermeulen, Alex; Nemitz, Eiko

    2013-04-01

    During the last decade several gas analysers became available that are capable of measuring methane concentration with high sampling frequency needed for eddy covariance measurements. These new gas analysers require less maintenance compared with the models used in the 1990's and they give more reliable estimates for the ecosystem scale methane fluxes. However, with different instrument types available now, their performance should be crosscompared and validated. A gas analyser intercomparison campaign was held at Cabauw measurement station in the Netherlands between 6th and 27th of June, 2012. The campaign was organized within the InGOS FP7 project. Cabauw is well-established site with a long history in greenhouse gas monitoring and the surrounding landscape is a considerable source of methane. In total eight methane gas analysers manufactured by Picarro Inc., Los Gatos Research, Aerodyne Research Inc. and LI-COR Inc. were used in the experiment. Tentative results show relatively good agreement between the eight methane flux estimates and they also agree with previous studies done at the site. Magnitude and variation of the flux estimates are similar. Cumulative methane emissions calculated from not gapfilled data during a 10 day episode agree within 10 %, values ranging from 190 mg(CH4) m-2 to 210 mg(CH4) m-2. Comparison of random errors of the measured methane fluxes did not reveal any big differences between the instruments. Some of the gas analysers measuring methane were also capable of measuring water vapour at the same time. This is a big asset during data processing, since effect of water vapour on methane concentration measurement can then be easily corrected without need of additional water vapour measurement. The presentation will discuss the intercomparison campaign setup, instrument performance and will provide recommendations for CH4-EC measurements.

  1. 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.

  2. 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.

  3. Experimental evaluation of water vapour cross-sensitivity for accurate eddy covariance measurement of CO2 flux using open-path CO2/H2O gas analysers

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    Fumiyoshi Kondo

    2014-10-01

    Full Text Available Non-dispersive infrared CO2/H2O gas analysers produce erroneous CO2 outputs when CO2 is measured in humid air, unless a correction for water vapour cross-sensitivity is applied. Spectroscopic cross-sensitivities arising from direct absorption interference and from the pressure broadening effect are significant in CO2 flux measurements by the eddy covariance technique using open-path gas analysers over the ocean, as opposed to land-surface measurements, where CO2 fluxes are orders of magnitude larger. In this study, a widely used analyser with manufacturer-determined correction coefficients for both cross-sensitivities was tested by laboratory experiments. Our results showed that the correction coefficient for direct absorption interference was not optimised to calculate CO2 flux accurately, and that the correction coefficient for the pressure broadening caused overestimation of the CO2 mixing ratio flux in the same direction as the water vapour flux. Overestimations of open-path eddy covariance measurements of upward CO2 fluxes in previous ocean observations probably resulted from inaccuracies in both of these correction coefficients. We also found that slight changes in spectroscopic cross-sensitivities due to contamination of the analyser's optical windows by sea salt caused a low bias in CO2 outputs with increasing H2O; however, this contamination effect was not always observed in repeated tests under different contamination conditions. We suggest that previously proposed methods for correcting the effect of optical window contamination is of limited value and that measurement of small CO2 fluxes by the open-path eddy covariance technique over the ocean should be performed after confirming the spectroscopic cross-sensitivity and ensuring that the optical windows are as clean as possible.

  4. Apparent drifts of IRGA measurements due to optical path contamination and their effects on eddy-covariance fluxes

    Science.gov (United States)

    McDermitt, D. K.; Fratini, G.; Papale, D.

    2013-12-01

    Apparent instrumental biases can cause errors in gas concentration measurements by infrared gas analysers (IRGAs) used in eddy-covariance flux measurements. Such biases most often result from deposition of atmospheric pollutants, such as aerosols, pollen, or particulate matter on surfaces in the optical path, which in some cases, can cause differential signal attenuation in the sample and reference channels of the gas analyser. We refer to such biases as apparent, to stress that they are not the result of an intrinsic loss of instrumental metric performance, but rather of incidental and avoidable deployment artefacts. Nonetheless, due to the curvilinear nature of IRGAs calibration curves, they can cause errors in eddy-covariance fluxes, resulting from reduced accuracy of the gas concentration measurement. In this work we describe the phenomenological and mathematical foundations of these concentration biases, also showing how measurements from different IRGA typologies are affected as a result. By means of numerical simulations, we find that concentration biases can lead to roughly proportional systematic flux errors, where the fractional errors in fluxes are roughly 30-40% the fractional errors in concentrations. We also propose a correction procedure and provide recommendations for field deployment and operation, to minimize or completely eliminate such errors. The correction procedure will soon be available in the EddyPro software (www.licor.com/eddypro).

  5. Eddy Covariance Flux Measurements of Pollutant Gases in the Mexico City Urban Area: a Useful Technique to Evaluate Emissions inventories

    Science.gov (United States)

    Velasco, E.; Grivicke, R.; Pressley, S.; Allwine, G.; Jobson, T.; Westberg, H.; Lamb, B.; Ramos, R.; Molina, L.

    2007-12-01

    Direct measurements of emissions of pollutant gases that include all major and minor emissions sources in urban areas are a missing requirement to improve and evaluate emissions inventories. The quality of an urban emissions inventory relies on the accuracy of the information of anthropogenic activities, which in many cases is not available, in particular in urban areas of developing countries. As part of the MCMA-2003 field campaign, we demonstrated the feasibility of using eddy covariance (EC) techniques coupled with fast-response sensors to measure fluxes of volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City. Those flux measurements demonstrated to be also a valuable tool to evaluate the emissions inventory used for air quality modeling. With the objective to confirm the representativeness of the 2003 flux measurements in terms of magnitude, composition and diurnal distribution, as well to evaluate the most recent emissions inventory, a second flux system was deployed in a different district of Mexico City during the 2006 MILAGRO field campaign. This system was located in a busy district surrounded by congested avenues close to the center of the city. In 2003 and 2006 fluxes of olefins and CO2 were measured by the EC technique using a Fast Isoprene Sensor calibrated with a propylene standard and an open path Infrared Gas Analyzer (IRGA), respectively. Fluxes of aromatic and oxygenated VOCs were analyzed by Proton Transfer Reaction-Mass Spectroscopy (PTR-MS) and the disjunct eddy covariance (DEC) technique. In 2006 the number of VOCs was extended using a disjunct eddy accumulation (DEA) system. This system collected whole air samples as function of the direction of the vertical wind component, and the samples were analyzed on site by gas chromatography / flame ionization detection (GC-FID). In both studies we found that the urban surface is a net source of CO2 and VOCs. The diurnal patterns were similar, but the 2006 fluxes

  6. 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

  7. 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

  8. 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

  9. Forest Surface Energy Balance and Evapotranspiration Estimated From Four Eddy Covariance Towers

    Science.gov (United States)

    Rabbani, G. A.; Adam, J. C.; Elliot, W. J.; Liu, H.

    2016-12-01

    Evapotranspiration (ET), which refers to the combined effect of surface water evaporation and plant transpiration, is one of the vital elements of the global water balance. It is also an important process for plants, providing water, nutrient, and cooling needs, and helping to regulate carbon dioxide entry through open/closure of the plant's stomata. Quantifying ET in forested environments is an ongoing research area. Complex physiological responses with climatic variation, combined with difficulty in making wide-spread measurements, makes ET one of the least understood components of a forest water balance. The objective of this study is to estimate ET and energy balance closure by using flux net data from eddy covariance towers. ET is estimated for different forest types with multiple age classes during the years of 2011, 2012 and 2013. We studied two coniferous forests (F1, F2), one deciduous forest (F3) and one mixed forest (F4) in Washington, Wyoming, Wisconsin and New Jersey, respectively. Label 2 (Data checked and formatted by Carbon Dioxide Information Analysis Center) gap filled flux data were collected from the AmeriFlux database (ameriflux.ornl.gov). Discrepancies between turbulent fluxes and available energy are investigated. Among the studied forests, the highest and lowest average monthly ET are exhibited by the mixed forest (F4) and coniferous forest (F1) in 2012 which are 2,692 and 633 mm/month, respectively. Difference in average monthly ET can be an implication of substantial age difference between these two types of forest. The regression analysis showed significant correlation between turbulent fluxes and available energy (R2=0.91) for mixed forest where the discrepancy varied from 5-11%. Conversely, for coniferous and deciduous forests, the discrepancy varied from 46-49% and 28%, respectively, with almost similar correlation between the fluxes (0.86 and 0.84, respectively). This study will facilitate an improved understanding of how forest type

  10. 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.

  11. 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

  12. 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

  13. Chemically-resolved aerosol eddy covariance flux measurements in urban Mexico City during MILAGRO 2006

    Directory of Open Access Journals (Sweden)

    R. Zalakeviciute

    2012-08-01

    Full Text Available As part of the MILAGRO 2006 field campaign, the exchange of atmospheric aerosols with the urban landscape was measured from a tall tower erected in a heavily populated neighborhood of Mexico City. Urban submicron aerosol fluxes were measured using an eddy covariance method with a quadrupole aerosol mass spectrometer during a two week period in March, 2006. Nitrate and ammonium aerosol concentrations were elevated at this location near the city center compared to measurements at other urban sites. Significant downward fluxes of nitrate aerosol, averaging −0.2 μg m−2 s−1, were measured during daytime. The urban surface was not a significant source of sulfate aerosols. The measurements also showed that primary organic aerosol fluxes, approximated by hydrocarbon-like organic aerosols (HOA, displayed diurnal patterns similar to CO2 fluxes and anthropogenic urban activities. Overall, 47% of submicron organic aerosol emissions were HOA, 35% were oxygenated (OOA and 18% were associated with biomass burning (BBOA. Organic aerosol fluxes were bi-directional, but on average HOA fluxes were 0.1 μg m−2 s−1, OOA fluxes were −0.03 μg m−2 s−1, and BBOA fluxes were −0.03 μg m−2 s−1. After accounting for size differences (PM1 vs PM2.5 and using an estimate of the black carbon component, comparison of the flux measurements with the 2006 gridded emissions inventory of Mexico City, showed that the daily-averaged total PM emission rates were essentially identical for the emission inventory and the flux measurements. However, the emission inventory included dust and metal particulate contributions, which were not included in the flux measurements. As a result, it appears that the inventory underestimates overall PM emissions for this location.

  14. Evaluation of Density Corrections to Methane Fluxes Measured by Open-Path Eddy Covariance over Contrasting Landscapes

    Science.gov (United States)

    Chamberlain, Samuel D.; Verfaillie, Joseph; Eichelmann, Elke; Hemes, Kyle S.; Baldocchi, Dennis D.

    2017-06-01

    Corrections accounting for air density fluctuations due to heat and water vapour fluxes must be applied to the measurement of eddy-covariance fluxes when using open-path sensors. Experimental tests and ecosystem observations have demonstrated the important role density corrections play in accurately quantifying carbon dioxide (CO2) fluxes, but less attention has been paid to evaluating these corrections for methane (CH4) fluxes. We measured CH4 fluxes with open-path sensors over a suite of sites with contrasting CH4 emissions and energy partitioning, including a pavement airfield, two negligible-flux ecosystems (drained alfalfa and pasture), and two high-flux ecosystems (flooded wetland and rice). We found that density corrections successfully re-zeroed fluxes in negligible-flux sites; however, slight overcorrection was observed above pavement. The primary impact of density corrections varied over negligible- and high-flux ecosystems. For negligible-flux sites, corrections led to greater than 100% adjustment in daily budgets, while these adjustments were only 3-10% in high-flux ecosystems. The primary impact to high-flux ecosystems was a change in flux diel patterns, which may affect the evaluation of relationships between biophysical drivers and fluxes if correction bias exists. Additionally, accounting for density effects to high-frequency CH4 fluctuations led to large differences in observed CH4 flux cospectra above negligible-flux sites, demonstrating that similar adjustments should be made before interpreting CH4 cospectra for comparable ecosystems. These results give us confidence in CH4 fluxes measured by open-path sensors, and demonstrate that density corrections play an important role in adjusting flux budgets and diel patterns across a range of ecosystems.

  15. Evaluation of Density Corrections to Methane Fluxes Measured by Open-Path Eddy Covariance over Contrasting Landscapes

    Science.gov (United States)

    Chamberlain, Samuel D.; Verfaillie, Joseph; Eichelmann, Elke; Hemes, Kyle S.; Baldocchi, Dennis D.

    2017-11-01

    Corrections accounting for air density fluctuations due to heat and water vapour fluxes must be applied to the measurement of eddy-covariance fluxes when using open-path sensors. Experimental tests and ecosystem observations have demonstrated the important role density corrections play in accurately quantifying carbon dioxide (CO2) fluxes, but less attention has been paid to evaluating these corrections for methane (CH4) fluxes. We measured CH4 fluxes with open-path sensors over a suite of sites with contrasting CH4 emissions and energy partitioning, including a pavement airfield, two negligible-flux ecosystems (drained alfalfa and pasture), and two high-flux ecosystems (flooded wetland and rice). We found that density corrections successfully re-zeroed fluxes in negligible-flux sites; however, slight overcorrection was observed above pavement. The primary impact of density corrections varied over negligible- and high-flux ecosystems. For negligible-flux sites, corrections led to greater than 100% adjustment in daily budgets, while these adjustments were only 3-10% in high-flux ecosystems. The primary impact to high-flux ecosystems was a change in flux diel patterns, which may affect the evaluation of relationships between biophysical drivers and fluxes if correction bias exists. Additionally, accounting for density effects to high-frequency CH4 fluctuations led to large differences in observed CH4 flux cospectra above negligible-flux sites, demonstrating that similar adjustments should be made before interpreting CH4 cospectra for comparable ecosystems. These results give us confidence in CH4 fluxes measured by open-path sensors, and demonstrate that density corrections play an important role in adjusting flux budgets and diel patterns across a range of ecosystems.

  16. Carbon and Nitrous Oxide Exchange from a Bioenergy Crop Cultivation on a Mineral Soil Measured with Eddy Covariance Method

    Science.gov (United States)

    Lind, S.; Shurpali, N.; Martikainen, P. J.

    2009-12-01

    Increased concentration of greenhouse gases (GHG; CO2, CH4, N2O) in the atmosphere have been linked to anthropogenic activities. Energy production based on fossil fuels is the main sources of CO2 to the atmosphere. Strategies to reduce CO2 emissions include use of bioenergy crops as energy source. To evaluate the real atmospheric value of bioenergy, knowledge on CO2 and N2O balances of ecosystems under bioenergy crop cultivation is needed. Reed canary grass (RCG, Phalaris arundinaceae L.) is increasingly being used as a bioenergy crop in the Nordic countries. It grows well in northern Europe as it tolerates flooding, requires short growing season and thrives well under low temperatures. Currently RCG is cultivated on an area of about 19000 ha in Finland and it is the highest yielding grass grown for energy purpose in Finland. The long rotation period (about ten years) of RCG cultivation without tilling favors carbon allocation into soil. First results from RCG cultivations on peat soil show that it is a promising land use option on such soils favoring soil carbon sequestration with low N2O emissions (Hyvönen et al. 2009; Shurpali et al. 2009). In order to devise a sound bioenergy policy based on this grass, studies on soils with variable characteristics under different climatic and hydrological regimes is urgently needed. Micrometeorological eddy covariance technique is suitable to study GHG fluxes at an ecosystem level (Baldocchi 2003). It is useful for continuous, direct and long-term measurements. Eddy covariance technique has been successfully used for measuring CO2 exchange in various ecosystems. The eddy covariance technique has also been used to measure N2O emissions (Denmead 2008). Aims of this study are to quantify the CO2 and N2O exchange of RCG cultivation on a mineral soil employing eddy covariance technique and to identify the key factors controlling the gas exchange. The study site on mineral soil is located in Eastern Finland. RCG was sown in spring

  17. Evaluating Spatiotemporal Differences in Methane Fluxes on the North Slope of Alaska via Eddy Covariance Footprint Modelling

    Science.gov (United States)

    Reuss-Schmidt, K.; Zona, D.

    2016-12-01

    Arctic permafrost soils store 1300-1370 Pg of organic carbon, twice the current atmospheric stock. This region is warming at approximately 1°C per decade, and permafrost soils could lose 381-616 Pg C by 2300, with a large portion potentially being released as the potent greenhouse gas methane (CH4). Despite intensive investigation, uncertainty estimates of CH4 emissions have significantly increased since the first estimates in 1974. Two main difficulties in creating a baseline flux estimate is the region's remote nature and the high spatiotemporal variability in methane fluxes. This project examines fluxes from three eddy covariance sites in Barrow, Alaska by applying the Kormann and Meixner (2001) footprint model to investigate the spatio-temporal variability in fluxes across the arctic polygonal tundra throughout the year. A LiDAR digital elevation model collected by NGEE Artic at a very fine resolution (0.25m) and WorldView2 data have been used to give quantitative metrics for vegetation and microtopographic differences over these three sites. Preliminary results show significant differences (p-value footprints that could bias flux estimates by 20%. Furthermore, the pattern of footprint variability shows divergent spatial patterns between summer and winter fluxes. The largest mean summer fluxes were observed in a low lying sedge-dominated drained lake basin (7.74 mg CH4 m-2 day-1) with the less degraded, more polygonal area having an average flux of (5.82 mg CH4 m-2 day-1). In the winter "zero curtain" period, the pattern reversed with higher fluxes coming from the polygonal area (3.58 mg CH4 m-2 day-1) and slightly lower fluxes (3.35 mg CH4 m-2 day-1) observed from the lake basin. This highlights that flux drivers differ by season and that these dynamics should be considered for estimating annual and regional fluxes.

  18. Extreme Covariant Observables for Type I Symmetry Groups

    Science.gov (United States)

    Holevo, Alexander S.; Pellonpää, Juha-Pekka

    2009-06-01

    The structure of covariant observables—normalized positive operator measures (POMs)—is studied in the case of a type I symmetry group. Such measures are completely determined by kernels which are measurable fields of positive semidefinite sesquilinear forms. We produce the minimal Kolmogorov decompositions for the kernels and determine those which correspond to the extreme covariant observables. Illustrative examples of the extremals in the case of the Abelian symmetry group are given.

  19. Eddy-covariance isofluxes of carbon dioxide measured over an urban surface in Vancouver, Canada

    Science.gov (United States)

    Christen, A.; Black, T. A.; Ketler, R.; Nesic, Z.; Semmens, C.

    2016-12-01

    Stable isotope ratios of carbon dioxide (CO2), in particular δ13C, separate between combustion of gasoline (δ13C = -27.3‰), diesel (δ13C = -28.8‰) and natural gas (δ13C = -41.6‰). For example 'Keeling plots' of δ13C have been used to partition the enhanced urban CO2 using simultaneous background data. We propose an alternative approach to directly characterize and partition urban emissions at fine temporal and spatial scales by measuring isofluxes using the eddy-covariance (EC) approach. EC fluxes of 12CO2 and 13CO2 were measured continuously on a 30m-tall tower located in Vancouver, Canada (Fluxnet ID "Ca-VSu) between March and July 2016. The tower is located near an intersection of arterial roads in a residential area characterized by building emissions from natural gas furnaces. The goal is (1) to determine δ13C of the urban emission mix at any given time, and (2) to use this information to partition total measured CO2 fluxes into combustion of natural gas and the mix of gasoline+diesel (g+d, assuming an a priori ratio). Respiratory fluxes have been shown to be small and are neglected. Fluxes were measured using a sonic anemometer (CSAT-3, CSI) and a tuneable diode laser absorption spectroscopy (TDLAS) system scanning absorption lines at 2308.171 (13CO2) and 2308.225 cm-1 (12CO2) at 10 Hz (TGA200, CSI). Every 10 minutes, the TDLAS was calibrated against three tanks, referenced against NOAA-ESRL/INSTAAR, UoC standards. Isoflux ratios (F13C) were calculated as F13C = 1000 [(w'13CO2' / w'12CO2') / RVPD-CO2) - 1]. The average measured F13C was -32.67‰, which corresponds to a mixture of 32% natural gas and 68% g+d. This matches well against a top-down inventory for the City of Vancouver, which estimates 36% natural gas and 64% g+d. Fluxes were correlated with traffic counts, with higher fluxes during daytime. F13C increased with increasing flux strength because the highest emissions originated from traffic intersections (g+d). F13C was higher during

  20. The effect of agricultural structures on the quality of eddy covariance flux data

    Science.gov (United States)

    Tanny, Josef; Achiman, Ori; Mekhmandarov, Yonatan; Pirkner, Moran

    2015-04-01

    The Eddy Covariance (EC) is a common method to directly measure whole canopy turbulent fluxes of scalars like water vapor, air temperature and CO2. The method was originally developed to measure fluxes from canopies in the open; however, in recent years it was also shown to be valid for flux measurements of agricultural crops cultivated inside structures covered by porous screens, i.e., screenhouses. To reliably measure turbulent fluxes by the EC technique, several air flow conditions should prevail. The purpose of this study was to examine two criteria, commonly used to assess the suitability of turbulent flow conditions for EC measurements in open fields, for flux measurements in different types of agricultural screenhouses and greenhouses. The two tests are the "Integral Turbulence Characteristics" (ITC), which indicates on the development of the turbulent flow, and the "Steady State" (SS), which examines the variation in time of flow statistics during the averaging period. For both tests data was classified according to their suitability for flux measurements. The research was conducted in 3 types of agricultural structures with 3 different plants: (S1) A banana screenhouse, 5.5 m in height, covered by an 8% shade net; (S2) A pepper screenhouse, 3.7 m in height, covered by an insect-proof, 50 mesh net; (S3) A 12-span naturally ventilated tomato greenhouse with a 6 m height arched gable, equipped with an insect-proof 50 mesh net on the sidewalls, and impermeable plastic cover on the roof. In each structure an EC system was installed between the top of the canopy and the roof, in a position that provided sufficient fetch for the prevailing wind, for a measurement period of at least 20 days. Mean fluxes were calculated over half-hourly time intervals. In the present study the ITC test was applied in two different approaches: (i) according to the commonly used literature model which prevails for turbulent flow in open fields (ITC1), and (ii) according to a new

  1. Eddy turbulence parameters inferred from radar observations at Jicamarca

    Directory of Open Access Journals (Sweden)

    M. N. Vlasov

    2007-03-01

    Full Text Available Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007. In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1×103 m2/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007 is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density.

  2. Eddy turbulence parameters inferred from radar observations at Jicamarca

    Directory of Open Access Journals (Sweden)

    M. N. Vlasov

    2007-03-01

    Full Text Available Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007. In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1×103 m2/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007 is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density.

  3. Biophysical controls of carbon flows in three successional Douglas-fir stands on eddy-covariance measurements

    Energy Technology Data Exchange (ETDEWEB)

    Chen, J. [Toledo Univ., Earth, Ecological and Environmental Sience, Toledo, OH (United States); Falk, M.; Paw U, K. T.; Ustin, S. L. [California Univ., Dept. of Land, Air and Water Resources, Davis CA (United States); Euskirchen, E.; Bi, R. [Michigan Technological Univ., School of Forestyry and Wood Products, Houghton, MI (United States); Suchanek, T. H. [California Univ., Dept of Wildlife, Fish and Conservation Biology, Davis, CA (United States); Bond, B. J. [Oregon State Univ. College of Forest Resources, Corvallis, OR (United States); Brosofske, K. D. [Rhode Island Univ., Dept. of Natural Resources Science, Kingston, RI (United States); Phillips, N. [Boston Univ., Dept. of Geography, Boston, MA (United States)

    2002-02-01

    Carbon flux (F{sub C}O{sub 2}) and net water (H{sub 2}O)Flux were measured by the eddy-covariance method at three Douglas fir -western hemlock sites located in the Wind River Valley of Washington State. The stands were approximately 20, 40 and 450 years old. Measurements were made between June 15 and October 15 of 1998 for the 40 and 450 year old stands, and of 1999 in the 20- and 450-year old stands. The objective was to determine differences, if any, among the stands in: (1) patterns of daytime carbon dioxide flux during summer and autumn; (2) empirically modelled relationships between local climatic factors and daytime carbon dioxide flux; (3) water use efficiency. The Landsberg equation, a logarithmic power function and linear regression was used to model the relationships between carbon dioxide flux and physical variables. During summer and early autumn carbon dioxide variance averaged 4.1 and 6.2 micromol m{sup 2}s{sup 1} at the 20 and 40 year-old stand respectively. In the 450 year-old stand carbon dioxide flux averaged 2.2. and 3.2 micromol m{sup 2}s{sup 1}in 1998 and 1999 respectively. Increases in vapor pressure deficit (VPD) were associated with reduced carbon dioxide flux at all three stands. The greatest apparent constraint was observed in the old-growth stand. Correlations between carbon dioxide flux and environmental variables differed among ecosystems. Soil temperature showed the greatest negative correlation and net radiation the greatest positive correlation. Water use efficiency was significantly greater in the old-growth stand in the drier summer of 1998 than in 1999. 41 refs., 1 tab. 7 figs.

  4. Estimating Landfill Methane Oxidation Using the Information of CO2/CH4 Fluxes Measured By the Eddy Covariance Method

    Science.gov (United States)

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

    2016-12-01

    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 the landfill methane oxidation fraction when the anaerobic CO2/CH4 production ratio is known. 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 with eddy covariance CO2 and CH4 emission rates at Bluff Road Landfill in Lincoln Nebraska. It predicted zero oxidation rate in the northern portion of this landfill where a membrane and vents were present. The zero oxidation rate was expected because there would be little opportunity for methane to encounter oxidizing conditions before leaving the vents. We also applied the model at the Turkey Run Landfill in Georgia to estimate the CH4 oxidation rate over a one year period. In contrast to Bluff Road Landfill, the Turkey Run Landfill did not have a membrane or vents. Instead, methane produced in the landfill had to diffuse through a 0.5 m soil cap before release to the atmosphere. We observed evidence for methane oxidation ranging from about 18% to above 60% depending upon the age of deposited waste material. The model will be briefly described, and results from the two contrasting landfills will be discussed in this presentation.

  5. Validating modelled carbon-dioxide emissions against long-term eddy-covariance measurements at the urban neighborhood-scale

    Science.gov (United States)

    Christen, A.; Coops, N. C.; Crawford, B.; Heyman, E.; Kellett, R.; Liss, K.; Oke, T. R.; Olchovski, I.; Tooke, R.; van der Laan, M.; Voogt, J. A.

    2010-12-01

    It can be expected that integrative greenhouse-gas emission modeling at block or neighborhood-scales becomes an increasingly relevant part of urban planning processes in the future. A particular challenge forms the geographical distribution of emissions and a proper validation of modeled emissions at this fine scale where consumption statistics are often lacking. Direct flux measurements of GHGs using the eddy-covariance (EC) approach could be a valuable approach to validate such fine-scale urban emission inventories. In combination with micrometeorological source-area models, EC measurements provide spatial-temporal information of emissions - at scales where utility or consumption data is not available. A residential neighborhood in Vancouver, BC, Canada is used as a case study to validate modeled carbon-dioxide (CO2) emissions against direct eddy-covariance flux measurements. The model is a combination of top-down inventory and bottom-up modelling of individual objects (buildings, vegetation, traffic counts). Carbon is conceptually tracked through quantifying inputs and outputs into the modelled urban neighborhood, as well as storage changes within the neighborhood. The spatial modelling of emissions is conceptually separated into four components - buildings, transportation, human respiration and vegetation/soils. Inputs to the emission model include automated urban object classifications (buildings, trees, land cover) based on LiDAR and optical remote sensing data in combination with census data, assessment data, traffic counts and measured radiation and climate data. Based on those inputs, spatial maps of total annual CO2 emissions (or uptake) are modeled at 50 m resolution for 4 km2. The resulting maps (building, transportation, human respiration and vegetation) are then summed to create a map of integral (net-)emissions. The mapped area overlaps with the source-area of a micrometeorological flux tower location in the center of the study area. Continuous CO2

  6. 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.

  7. 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.

  8. Field-scale and Regional Variability in Evapotranspiration over Crops in California using Eddy Covariance and Surface Renewal

    Science.gov (United States)

    Kent, E. R.; Clay, J. M.; Leinfelder-Miles, M.; Lambert, J. J.; Little, C.; Monteiro, R. O. C.; Monteiro, P. F. C.; Shapiro, K.; Rice, S.; Snyder, R. L.; Daniele, Z.; Paw U, K. T.

    2016-12-01

    Evapotranspiration (ET) estimated using a single crop coefficient and a grass reference largely ignores variability due to heterogeneity in microclimate, soils, and crop management. We employ a relatively low cost energy balance residual method using surface renewal and eddy covariance measurements to continuously estimate half-hourly and daily ET across more than 15 fields and orchards spanning four crops and two regions of California. In the Sacramento-San Joaquin River Delta, measurements were taken in corn, pasture, and alfalfa fields, with 4-5 stations in each crop type spread across the region. In the Southern San Joaquin Valley, measurements were taken in three different pistachio orchards, with one orchard having six stations instrumented to examine salinity-induced heterogeneity. We analyze field-scale and regional variability in ET and measured surface energy balance components. Cross comparisons between the eddy covariance and the surface renewal measurements confirm the robustness of the surface renewal method. A hybrid approach in which remotely sensed net radiation is combined with in situ measurements of sensible heat flux is also investigated. This work will provide ground-truth data for satellite and aerial-based ET estimates and will inform water management at the field and regional scales.

  9. 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...

  10. 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.

  11. 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

  12. 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.

  13. Evapotranspiration components determined by eddy covariance and sap flux measurements in oil palm plantations in Sumatra, Indonesia

    Science.gov (United States)

    Meijide, Ana; Röll, Alexander; Niu, Furong; June, Tania; Hölscher, Dirk; Knohl, Alexander

    2015-04-01

    The expansion of oil palm cultivation fueled by the increasing global demand for palm oil is leading to massive land transformations in tropical areas, particularly in South-East Asia. Conversions of forest land to oil palm plantations likely affect ecosystem water fluxes. However, there is a lack of information on water fluxes from oil palm plantations as well as on the partitioning of these fluxes into its different components such as transpiration and evaporation. It is expected that water fluxes from oil palm plantations vary temporally, both long-term, i.e. between different age-classes of plantations, and short-term, i.e. from day to day within a certain plantation (e.g. during or after periods of rainfall). A proper evaluation of water fluxes from oil palm plantations thus requires an experimental design encompassing these types of variability. To assess evapotranspiration (ET) rates, an eddy covariance tower was installed in a 2-year-old oil palm plantation in the lowlands of Jambi, Sumatra; it was subsequently moved to a 12-year-old oil palm plantation located in the same region. In parallel to the ET, sap flux density was measured on 16 leaf petioles on four oil palms; stand transpiration rates were derived from these measurements with stand inventory data. The parallel measurements ran for several weeks in both plantations. Preliminary results for our period of study show that the average ET rate of the 2-year-old oil palm plantation was 5.2 mm day-1; values up to 7.0 mm day-1 were observed on dry, sunny days with non-limiting soil moisture. Stand transpiration (T) by the young oil palms was very low, 0.3 mm day-1on average, and only showed a small variation between days. Under optimal environmental conditions, the ratio of T to total ET was up to 0.08 in the young plantation, while in the mature, 12-year-old plantation, it was significantly higher and reached 0.5. Transpiration rates in the mature oil palm plantation were about six- to seven-fold higher

  14. 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

  15. 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.

  16. Satellite Radar Observations of Small Eddies in the White, Barents and Kara Seas

    Directory of Open Access Journals (Sweden)

    O.A. Atadzhanova

    2017-04-01

    Full Text Available Analysis of space-time variability of small (submesoscale eddies identified in satellite radar images during the warm season in the White (2009 – 2012, Barents and Kara (2007 Seas is presented. Determination of eddy locations, their diameters and vorticity type enabled to reveal the regions of regular eddy occurrence and assess their intraseasonal variability. In total, over 3500 eddy patterns were detected with 2970 cyclonic and 621 anticyclonic eddies. The peak of eddy activity in the Barents and White seas is observed in July, in the Kara Sea – in August. Despite a significant intraseasonal variability of eddy diameters, most eddies have diameters less than 6 km. Mean values of eddy diameter range from 2.4 km for the Kara Sea to 4.7 km for the White Sea, with 3.6 km obtained for the Barents Sea. While cyclonic eddies are observed more frequently, anticyclonic eddies are typically larger in size. In the Barents Sea eddies are regularly observed near Svalbard and north to the Kola Peninsula; in the Kara Sea – between Novaya Zemlya and the Yamal Peninsula, and close to Uyedineniya and Sverdrup islands; in the White Sea – in the Dvina Bay, northward to the Solovetsky Islands and along the Tersky coast. In all the seas a significant part of the detected eddies is found near hydrological fronts of various origin.

  17. An eddy covariance study of a spruce beetle outbreak on summertime evapotranspiration and ecosystem CO2 exchange and winter sublimation dynamics

    Science.gov (United States)

    Frank, John Michael

    Water and carbon cycles are important from ecosystem to global scales because of their feedbacks with climate change and natural disturbance. In order to quantify both primary and compensating responses in an ecosystem under disturbance, an approach that observes the ecosystem in its entirety is preferred. In recent decades, the eddy covariance technique has become ubiquitous in modern ecosystem studies because its fundamental measurement scale integrates across an ecosystem. Yet, across flux networks a trend towards energy imbalance has implicated a systematic bias in these measurements that has no mechanistic explanation. This dissertation concentrates on a historical transducer shadowing correction for sonic anemometers, the fundamental instrument in eddy covariance studies, and whether the omission of it can explain these underestimated ecosystem fluxes. It then focuses on the response of water and carbon processes in a subalpine spruce-fir forest in southeastern Wyoming, USA that experienced 80% forested basal area mortality following a spruce beetle outbreak. To evaluate an uncertainty in eddy covariance measurements, a novel experiment is devised to test the consistency to which an omnidirectional sonic anemometer can measure the three dimensions, to compare of the effect of different designs and different manufacturers to link an underestimate in vertical wind velocity to the lack of transducer shadowing correction, and to construct a Bayesian model to estimate the three dimensional shadowing correction required to fix the problem. Results show that at the 60% of ecosystem flux sites in North American that use this equipment, their ecosystem flux measurements are probably underestimated by 8-12%. During the growing season, the change in ecosystem processes due to disturbance are explained through the physiological response of dying spruce trees and their observed mortality. Evapotranspiration declines immediately following the attack because of hydraulic

  18. Statistical modeling of ecosystem respiration using eddy covariance data: Maximum likelihood parameter estimation, and Monte Carlo simulation of model and parameter uncertainty, applied to three simple models

    Science.gov (United States)

    Andrew D. Richardson; David Y. Hollinger; David Y. Hollinger

    2005-01-01

    Whether the goal is to fill gaps in the flux record, or to extract physiological parameters from eddy covariance data, researchers are frequently interested in fitting simple models of ecosystem physiology to measured data. Presently, there is no consensus on the best models to use, or the ideal optimization criteria. We demonstrate that, given our estimates of the...

  19. Combining sap flow and eddy covariance approaches to derive stomatal and non-stomatal O{sub 3} fluxes in a forest stand

    Energy Technology Data Exchange (ETDEWEB)

    Nunn, A.J. [Ecophysiology of Plants, Technische Universitaet Muenchen, Am Hochanger 13, D-85354 Freising- Weihenstephan (Germany); Cieslik, S. [Institute for Environment and Sustainability, Joint Research Center, Ispra (Italy); Metzger, U. [Ecophysiology of Plants, Technische Universitaet Muenchen, Am Hochanger 13, D-85354 Freising- Weihenstephan (Germany); Wieser, G. [Federal Research and Training Centre for Forests, Natural Hazards and Landscape, Dept. of Alpine Timberline Ecophysiology, Rennweg 1, A - 6020 Innsbruck (Austria); Matyssek, R., E-mail: matyssek@wzw.tum.d [Ecophysiology of Plants, Technische Universitaet Muenchen, Am Hochanger 13, D-85354 Freising- Weihenstephan (Germany)

    2010-06-15

    Stomatal O{sub 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{sub 3} flux was 33% of the total O{sub 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{sub 3} flux and reflected stomatal regulation rather than O{sub 3} exposure, paralleling the daily courses of canopy conductance for water vapor and eddy covariance-based total stand-level O{sub 3} flux. The demonstrated combination of sap flow and eddy covariance approaches supports the development of O{sub 3} risk assessment in forests from O{sub 3} exposure towards flux-based concepts. - Combined tree sap flow and eddy covariance-based methodologies yield stomatal O{sub 3} flux as 33% in total stand flux.

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

    NARCIS (Netherlands)

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

    2010-01-01

    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

  1. The Sensible Heat Flux in the Course of the Year at Ny-Ålesund, Svalbard: Characteristics of Eddy Covariance Data and Corresponding Model Results

    Directory of Open Access Journals (Sweden)

    Georg Jocher

    2015-01-01

    Full Text Available In this paper we present one year of meteorological and flux measurements obtained near Ny-Ålesund, Spitsbergen. Fluxes are derived by the eddy covariance method and by a hydrodynamic model approach (HMA as well. Both methods are compared and analyzed with respect to season and mean wind direction. Concerning the wind field we find a clear distinction between 3 prevailing regimes (which have influence on the flux behavior mainly caused by the topography at the measurement site. Concerning the fluxes we find a good agreement between the HMA and the eddy covariance method in cases of turbulent mixing in summer but deviations at stable conditions, when the HMA almost always shows negative fluxes. Part of the deviation is based on a dependence of HMA fluxes on friction velocity and the influence of the molecular boundary layer. Moreover, the flagging system of the eddy covariance software package TK3 is briefly revised. A new quality criterion for the use of fluxes obtained by the eddy covariance method, which is based on integral turbulence characteristics, is proposed.

  2. 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

  3. 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

  4. 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.|info:eu-repo/dai/nl/304838233; 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

  5. 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.

  6. 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.

  7. Semidiurnal and seasonal variations in methane (CH4) emissions from a subtropical hydroelectric reservoir (Nam Theun 2 Reservoir) measured by eddy covariance technique

    Science.gov (United States)

    Deshmukh, Chandrashekhar; Serça, Dominique; Tardif, Raphael; Demarty, Maud; Descloux, Stéphane; Chanudet, Vincent; Guédant, Pierre; Guérin, Frédéric

    2013-04-01

    . To our knowledge, this is the first example of an inter-comparison for CH4 flux measurement where EC flux data were used to compare/validate the fluxes measured with traditional methodologies (i.e. floating chamber and funnel measurements). Semidiurnal variations of EC fluxes were observed with two peaks per day - one in early morning and one in the afternoon, linked to the semi-diurnal variation of the atmospheric pressure. Due to the larger drop in atmospheric pressure in the late morning than in the night, the noon flux peak is higher than the night flux peak. Both funnel and EC techniques show that ebullition of CH4 increased from 5 ± 3.5 to 28 ± 16 mmol.m-2.day-1 with the depth of the water column increasing from 10.5 to 2 m. This result suggests that the significant seasonal variation in CH4 emissions by ebullition was essentially driven by the water level variations. Keywords: Methane emissions, eddy covariance, floating chambers, submerged funnels, methods intercomparison, semidiurnal variation, seasonal variation, subtropical hydroelectric reservoir, Nam Theun 2 reservoir

  8. Detection of Bay of Bengal eddies from TOPEX and insitu observations

    Digital Repository Service at National Institute of Oceanography (India)

    Ali, M.M.; Sharma, R.; Gopalakrishna, V.V.

    anticyclonic eddy is located around 13 degrees N and 83 degrees E from the TOPEX observations averaged over 10-19 August 1993. The thermal sections pass through the southern periphery of the eddy with a prominent trough over the eddy region. The crest noticed...

  9. Fluxes of Submicron Organic Aerosol above London Measured by Eddy Covariance using the Aerodyne HR-ToF-AMS

    Science.gov (United States)

    Phillips, G. J.; di Marco, C. F.; Farmer, D.; Kimmel, J. R.; Jimenez, J. L.; Nemitz, E.

    2009-12-01

    Urban centres are large sources of sub-micron particles. The myriad of emission sources combined with the complex interaction between regional aerosol and the particulate and gaseous photochemistry make for a complex system. It is evident that particulate emissions from cities will affect the regional atmosphere as well as the environment within the urban area. Aerosol particles have been associated with respiratory and cardio-vascular disease and are also linked with the climate through scattering of radiation and indirect effects such as cloud formation. The Aerodyne Aerosol Mass Spectrometer (AMS) provides a powerful tool to elucidate the sources and processing of organic aerosol in the urban atmosphere. Normally this is done through concentration measurements, by statistical analysis of the organic mass spectra, e.g. using Positive Matrix Factorization (PMF). Recently the quadrupole based AMS (Q-AMS) has been used for the micrometeorological measurement of organic aerosol fluxes above several cities, based on high frequency measurements of individual masses (m/z) representative of different organic mass fractions. While providing a major step forward towards quantification of urban organic aerosol emissions and processing, the interpretation of Q-AMS flux data requires assumptions to scale up signals on individual m/z to total organic mass fluxes. In this paper we present chemically-speciated and size-segregated number aerosol fluxes measured using the next generation eddy covariance flux system based on the Aerodyne HR-ToF-AMS, now capable of recording fast-response eddy-covariance time-series of all m/z simultaneously. This allows organic mass fluxes to be calculated more quantitatively and provides 'flux mass spectra' in addition to concentration mass spectra, which produces novel information on the local emission and processing of organic aerosols in the urban environment, while concentration analysis includes the regional background. The measurements were

  10. 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

  11. 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.

  12. Association between sap flow-derived and eddy covariance-derived measurements of forest canopy CO2 uptake.

    Science.gov (United States)

    Klein, Tamir; Rotenberg, Eyal; Tatarinov, Fyodor; Yakir, Dan

    2016-01-01

    The carbon sink intensity of the biosphere depends on the balance between gross primary productivity (GPP) of forest canopies and ecosystem respiration. GPP, however, cannot be directly measured and estimates are not well constrained. A new approach relying on canopy transpiration flux measured as sap flow, and water-use efficiency inferred from carbon isotope analysis (GPPSF ) has been proposed, but not tested against eddy covariance-based estimates (GPPEC ). Here we take advantage of parallel measurements using the two approaches at a semi-arid pine forest site to compare the GPPSF and GPPEC estimates on diurnal to annual timescales. GPPSF captured the seasonal dynamics of GPPEC (GPPSF  = 0.99 × GPPEC , r(2)  = 0.78, RMSE = 0.82, n = 457 d) with good agreement at the annual timescale (653 vs 670 g C m(-2)  yr(-1) ). Both methods showed that GPP ranged between 1 and 8 g C m(-2)  d(-1) , and the GPPSF /GPPEC ratio was between 0.5 and 2.0 during 82% of the days. Carbon uptake dynamics at the individual tree scale conformed with leaf scale rates of net assimilation. GPPSF can produce robust estimations of tree- and canopy-scale rates of CO2 uptake, providing constraints and greatly extending current GPPEC estimations. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

  13. 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.

  14. 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.

  15. Measuring evapotranspiration and carbon dioxide fluxes in Mid-South US rice (Oryza Sativa) with eddy covariance

    Science.gov (United States)

    Fong, B.; Reba, M. L.

    2015-12-01

    Rice (Oryza sativa), a staple crop for a large portion of the Earth's population, is grown under flooded soil conditions. This results in greater water use than most other agricultural crops. Nearly 75% of US rice is grown the Mid-South states of the US. The objective of this study is to measure the evapotranspiration (ET) and carbon dioxide flux of conventionally flooded, commercial sized rice fields in this region. Measurements were made throughout the entire growing season during 2012, 2013, and 2014. The mean daily uptake of CO2 emissions under flooded soil conditions was at 4.0 g m-2 day-1, four times greater during flood than post flood, while ET was measured during flood at 3.12 mm day-1 was two times greater than post flood. Entire season measurements are important to characterize the micrometeorological conditions over agriculture fields. Future work will use eddy covariance to compare alternate irrigation methods on the net ecosystem exchange in commercial sized rice fields.

  16. The Chance Model: A Tool For Separating The Photosynthetic and Respiration Components of Forest Net Ecosystem Exchange and For Data Gap Filling In The Eddy Covariance Measurement Database

    Science.gov (United States)

    Longdoz, B.; Aubinet, M.; Francois, L.

    The CHANCE model simulates CO2, H2O and energy fluxes in temperate forest ecosystems. It has been calibrated and validated for a beech forest located in Viel- salm (Belgium), an experimental site included in the CARBOEUROFLUX network and equipped with an eddy covariance system measuring CO2, latent and sensible heat net fluxes exchanged between the ecosystem and the atmosphere. CHANCE has been used to fill the gaps in the eddy covariance measurement database. The results of this method are compared with those obtained by the interpolation and parameterization usually adopted in the CARBOEUROFLUX community. Each term of the net CO2 flux (CO2 exchanges by leaf, aerial wood and soil) are computed by CHANCE. The time integration of these terms provides estimates of the gross primary productivity (GPP) and ecosystem respiration (Re). The temporal evolution of GPP and Re during the year is analysed.

  17. 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

  18. Uncertainties in Eddy Covariance fluxes due to post-field data processing: a multi-site, full factorial analysis

    Science.gov (United States)

    Sabbatini, S.; Fratini, G.; Arriga, N.; Papale, D.

    2012-04-01

    Eddy Covariance (EC) is the only technologically available direct method to measure carbon and energy fluxes between ecosystems and atmosphere. However, uncertainties related to this method have not been exhaustively assessed yet, including those deriving from post-field data processing. The latter arise because there is no exact processing sequence established for any given situation, and the sequence itself is long and complex, with many processing steps and options available. However, the consistency and inter-comparability of flux estimates may be largely affected by the adoption of different processing sequences. The goal of our work is to quantify the uncertainty introduced in each processing step by the fact that different options are available, and to study how the overall uncertainty propagates throughout the processing sequence. We propose an easy-to-use methodology to assign a confidence level to the calculated fluxes of energy and mass, based on the adopted processing sequence, and on available information such as the EC system type (e.g. open vs. closed path), the climate and the ecosystem type. The proposed methodology synthesizes the results of a massive full-factorial experiment. We use one year of raw data from 15 European flux stations and process them so as to cover all possible combinations of the available options across a selection of the most relevant processing steps. The 15 sites have been selected to be representative of different ecosystems (forests, croplands and grasslands), climates (mediterranean, nordic, arid and humid) and instrumental setup (e.g. open vs. closed path). The software used for this analysis is EddyPro™ 3.0 (www.licor.com/eddypro). The critical processing steps, selected on the basis of the different options commonly used in the FLUXNET community, are: angle of attack correction; coordinate rotation; trend removal; time lag compensation; low- and high- frequency spectral correction; correction for air density

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

    Science.gov (United States)

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

    2010-06-01

    Stomatal O3 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 O3 flux was 33% of the total O3 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 O3 flux and reflected stomatal regulation rather than O3 exposure, paralleling the daily courses of canopy conductance for water vapor and eddy covariance-based total stand-level O3 flux. The demonstrated combination of sap flow and eddy covariance approaches supports the development of O3 risk assessment in forests from O3 exposure towards flux-based concepts. Copyright 2009 Elsevier Ltd. All rights reserved.

  20. 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.

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

    DEFF Research Database (Denmark)

    Lasslop, G.; Migliavacca, M.; Bohrer, G.

    2012-01-01

    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...... 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 choice between soil or air temperature must be made on site-by-site basis by analysing the correlation between temperature and nighttime NEE. We recommend using an ensemble...

  2. Uncertainty towards the use of the angle-of-attack corrections for eddy-covariance data processing in French ecosystems

    Science.gov (United States)

    Moreaux, Virginie; Delpierre, Nicolas; Dufrêne, Eric; Joffre, Richard; Klumpp, Katja; Loustau, Denis; Berveiller, Daniel; Darsonville, Olivier; Limousin, Jean-Marc; Ourcival, Jean-Marc; Piquemal, Karim; Longdoz, Bernard

    2017-04-01

    The production/absorption of the long lived greenhouse gas (GHG) and the albedo and evapotranspiration fluctuations in forests, grasslands and croplands are responsible of atmospheric radiative forcing but the quantification of these forcings remains uncertain. The CESEC program aims to quantify the impact of climatic drifts or anthropogenic and meteorological events on the ecosystem-atmosphere exchanges of French sites by analysing the long series (at least 9 years between 2003 and 2015) of eddy covariance (EC) fluxes. One part of the CESEC project is to repost-processed homogeneously the raw EC data across the sites and the years to try to reduce the influence of the methodology and experimental design on the temporal and spatial variability. These new processed data are put together with the corresponding climatic and edaphic data and with the carbon stock inventory. A number of French experimental sites have initially used a sonic anemometer from the GILL company, such as the GILL-R3 or the GILL R3-50, coupled with a GHG analyzer to perform EC measurements and deduce GHG exchanges from different ecosystems. Within the data processing procedure of eddy flux measurements, a recent type of correction has raised among the scientific community to account for the angle of attack error due to a distorsion of the flow when the wind approaches these GILL frame-type, resulting in an imperfect sine and cosine response. Nakai and co-authors proposed a correction to compensate for this error, which is expected to improve energy balance closure. No consensus has been clearly made on the application of this correction, but it has mostly been recommanded for recent data processing. The universal flux calculation EddyPro software that we are using in our project, incorporate and recommand this correction. Based on the analysis from two forests ecosystems (FR-Fon and FR-Pue) and a grassland (FR-Lq2) in France, we performed a re-analysis of EC measurements using the corrections

  3. Using Eddy Covariance Tower Clusters To Evaluate Biogeophysical Impacts Of Land Cover In The Community Land Model (CLM)

    Science.gov (United States)

    Burakowski, E. A.; Ollinger, S. V.; Bonan, G. B.; Ouimette, A.; Lepine, L. C.; Tawfik, A. B.; Zarzycki, C. M.; Fogarty, S.; Novick, K. A.

    2015-12-01

    The Community Land Model (CLM) land surface model has been used widely to evaluate biogeophysical responses to land cover and land use change. Here, we compare surface attributes collected from eddy covariance towers clusters to uncoupled point CLM (PTCLM) simulations. The tower clusters collect surface energy fluxes over adjacent forested and deforested land surface types located within 10-km of each other in temperate eastern North America. Summer surface albedo is very well simulated over cropland, C-3 grassland, and broadleaf deciduous temperate forests. In winter, modeled snow cover persists longer in spring than at the tower sites, resulting in higher average winter and spring albedo. Latent heat does not vary significantly among the three tower sites. PTCLM underestimates forest latent heat and overestimates cropland and grassland summer latent heat. We evaluate temperature differences between forested and deforested sites due to changes in surface albedo, energy redistribution due to changes in surface roughness, and energy redistribution due to changes in latent and sensible heat partitioning (e.g., Bowen ratio). Surprisingly, temperature differences resulting from radiative forcing due to changes in surface albedo are relatively minor at the tower sites and generally too high in PTCLM. We conclude that the increased surface roughness of forests contributes strongly to nocturnal cooling over deforested tower sites in winter and daytime warming in summer. The importance of biogeophysical coupling between the land surface and atmosphere on energy redistribution due to surface roughness is explored using high-resolution (28-km) Variable Resolution Community Earth System Model (VR-CESM) simulations.

  4. Spatial variability of CO2 uptake in polygonal tundra: assessing low-frequency disturbances in eddy covariance flux estimates

    Directory of Open Access Journals (Sweden)

    N. Pirk

    2017-06-01

    Full Text Available The large spatial variability in Arctic tundra complicates the representative assessment of CO2 budgets. Accurate measurements of these heterogeneous landscapes are, however, essential to understanding their vulnerability to climate change. We surveyed a polygonal tundra lowland on Svalbard with an unmanned aerial vehicle (UAV that mapped ice-wedge morphology to complement eddy covariance (EC flux measurements of CO2. The analysis of spectral distributions showed that conventional EC methods do not accurately capture the turbulent CO2 exchange with a spatially heterogeneous surface that typically features small flux magnitudes. Nonlocal (low-frequency flux contributions were especially pronounced during snowmelt and introduced a large bias of −46 gC m−2 to the annual CO2 budget in conventional methods (the minus sign indicates a higher uptake by the ecosystem. Our improved flux calculations with the ogive optimization method indicated that the site was a strong sink for CO2 in 2015 (−82 gC m−2. Due to differences in light-use efficiency, wetter areas with low-centered polygons sequestered 47 % more CO2 than drier areas with flat-centered polygons. While Svalbard has experienced a strong increase in mean annual air temperature of more than 2 K in the last few decades, historical aerial photographs from the site indicated stable ice-wedge morphology over the last 7 decades. Apparently, warming has thus far not been sufficient to initiate strong ice-wedge degradation, possibly due to the absence of extreme heat episodes in the maritime climate on Svalbard. However, in Arctic regions where ice-wedge degradation has already initiated the associated drying of landscapes, our results suggest a weakening of the CO2 sink in polygonal tundra.

  5. Spatial variability of CO2 uptake in polygonal tundra: assessing low-frequency disturbances in eddy covariance flux estimates

    Science.gov (United States)

    Pirk, Norbert; Sievers, Jakob; Mertes, Jordan; Parmentier, Frans-Jan W.; Mastepanov, Mikhail; Christensen, Torben R.

    2017-06-01

    The large spatial variability in Arctic tundra complicates the representative assessment of CO2 budgets. Accurate measurements of these heterogeneous landscapes are, however, essential to understanding their vulnerability to climate change. We surveyed a polygonal tundra lowland on Svalbard with an unmanned aerial vehicle (UAV) that mapped ice-wedge morphology to complement eddy covariance (EC) flux measurements of CO2. The analysis of spectral distributions showed that conventional EC methods do not accurately capture the turbulent CO2 exchange with a spatially heterogeneous surface that typically features small flux magnitudes. Nonlocal (low-frequency) flux contributions were especially pronounced during snowmelt and introduced a large bias of -46 gC m-2 to the annual CO2 budget in conventional methods (the minus sign indicates a higher uptake by the ecosystem). Our improved flux calculations with the ogive optimization method indicated that the site was a strong sink for CO2 in 2015 (-82 gC m-2). Due to differences in light-use efficiency, wetter areas with low-centered polygons sequestered 47 % more CO2 than drier areas with flat-centered polygons. While Svalbard has experienced a strong increase in mean annual air temperature of more than 2 K in the last few decades, historical aerial photographs from the site indicated stable ice-wedge morphology over the last 7 decades. Apparently, warming has thus far not been sufficient to initiate strong ice-wedge degradation, possibly due to the absence of extreme heat episodes in the maritime climate on Svalbard. However, in Arctic regions where ice-wedge degradation has already initiated the associated drying of landscapes, our results suggest a weakening of the CO2 sink in polygonal tundra.

  6. 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 8600m2 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 >0.11m3m-3 during summer high insolation periods (>500Wm-2) in order to maintain favourable green roof energy partitioning, i.e. mid-day β<1. The microclimate benefit of urban green roofs can be significantly optimised by using sustainable irrigation approaches. Copyright © 2016 Elsevier B.V. All rights reserved.

  7. Combining eddy-covariance and chamber measurements to determine the methane budget from a small, heterogeneous urban wetland park

    Science.gov (United States)

    Morin, T. H.; Stefanik, K. C.; Bohrer, G.; Rey Sanchez, A. C.; Mitsch, W. J.

    2015-12-01

    Methane (CH4) emissions from wetlands have large uncertainties. They are often small in magnitude and originate from landscapes with highly heterogeneous land cover patterns posing challenges to determining their green-house gas (GHG) budget. We combined two CH4 flux measurement approaches to overcome these issues and find the overall GHG budget of a small, heterogeneous, urban wetland park. Intermittent point measurements of fluxes from chambers provided information about the heterogeneity of fluxes, while eddy-covariance flux measurements provided information about the temporal dynamics of the fluxes. Both were combined to a scaled 'fixed frame' time series, correcting for temporal variability in the spatial coverage of the tower footprint. The macrophyte-vegetated (VEG) and open-water (OW) areas followed similar cycles and emitted similar levels of CH4 throughout the year. VEG exhibited a stronger late-summer emission peak than did OW, possibly due to CH4 transport through mature vegetation. Normalizing the tower data to a fixed frame allowed us to determine the overall CH4 budget of each patch type. OW was the strongest in terms of emissions per unit area, but the larger VEG area contributed the greatest total CH4 emission. Using a scaling approach for carbon (CO2) uptake we calculated the net total GHG contribution of this urban wetland park. Because chambers are not feasible over large vegetation or over extended time periods, the net CO2 budget over the same fixed-frame was approximated over a range and cannot be accurately measured directly over all the components of the park landscape. Overall the newly constructed wetland park acted as a sink for GHG over the last 3 years.

  8. 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.

  9. Integration of near-surface remote sensing and eddy covariance measurements: new insights on managed ecosystem structure and functioning

    Science.gov (United States)

    Hatala, J.; Sonnentag, O.; Detto, M.; Runkle, B.; Vargas, R.; Kelly, M.; Baldocchi, D. D.

    2009-12-01

    Ground-based, visible light imagery has been used for different purposes in agricultural and ecological research. A series of recent studies explored the utilization of networked digital cameras to continuously monitor vegetation by taking oblique canopy images at fixed view angles and time intervals. In our contribution we combine high temporal resolution digital camera imagery, eddy-covariance, and meteorological measurements with weekly field-based hyperspectral and LAI measurements to gain new insights on temporal changes in canopy structure and functioning of two managed ecosystems in California’s Sacramento-San Joaquin River Delta: a pasture infested by the invasive perennial pepperweed (Lepidium latifolium) and a rice plantation (Oryza sativa). Specific questions we address are: a) how does year-round grazing affect pepperweed canopy development, b) is it possible to identify phenological key events of managed ecosystems (pepperweed: flowering; rice: heading) from the limited spectral information of digital camera imagery, c) is a simple greenness index derived from digital camera imagery sufficient to track leaf area index and canopy development of managed ecosystems, and d) what are the scales of temporal correlation between digital camera signals and carbon and water fluxes of managed ecosystems? Preliminary results for the pasture-pepperweed ecosystem show that year-round grazing inhibits the accumulation of dead stalks causing earlier green-up and that digital camera imagery is well suited to capture the onset of flowering and the associated decrease in photosynthetic CO2 uptake. Results from our analyses are of great relevance from both a global environmental change and land management perspective.

  10. Constraining ecosystem model with adaptive Metropolis algorithm using boreal forest site eddy covariance measurements

    Science.gov (United States)

    Mäkelä, Jarmo; Susiluoto, Jouni; Markkanen, Tiina; Aurela, Mika; Järvinen, Heikki; Mammarella, Ivan; Hagemann, Stefan; Aalto, Tuula

    2016-12-01

    efficiency. When compared to the seasonal tuning, the daily tuning is worse on the seasonal scale. However, daily parametrisation reproduced the observations for average diurnal cycle best, except for the GPP for Sodankylä validation period, where half-hourly tuned parameters were better. In general, the daily tuning provided the largest reduction in model-data mismatch. The models response to drought was unaffected by our parametrisations and further studies are needed into enhancing the dry response in JSBACH.

  11. 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

  12. Observing mesoscale eddy effects on mode-water subduction and transport in the North Pacific.

    Science.gov (United States)

    Xu, Lixiao; Li, Peiliang; Xie, Shang-Ping; Liu, Qinyu; Liu, Cong; Gao, Wendian

    2016-02-01

    While modelling studies suggest that mesoscale eddies strengthen the subduction of mode waters, this eddy effect has never been observed in the field. Here we report results from a field campaign from March 2014 that captured the eddy effects on mode-water subduction south of the Kuroshio Extension east of Japan. The experiment deployed 17 Argo floats in an anticyclonic eddy (AC) with enhanced daily sampling. Analysis of over 3,000 hydrographic profiles following the AC reveals that potential vorticity and apparent oxygen utilization distributions are asymmetric outside the AC core, with enhanced subduction near the southeastern rim of the AC. There, the southward eddy flow advects newly ventilated mode water from the north into the main thermocline. Our results show that subduction by eddy lateral advection is comparable in magnitude to that by the mean flow--an effect that needs to be better represented in climate models.

  13. Comparison of Sensible Heat Fluxes Measured by a Large Aperture Scintillometer and Eddy Covariance System over a Heterogeneous Farmland in East China

    Directory of Open Access Journals (Sweden)

    Xin Li

    2017-06-01

    Full Text Available The sensible heat is an important component in surface energy partitioning over the land surface. This paper compared the sensible heat fluxes measured by a large aperture scintillometer system (LAS and an eddy covariance system (EC over a rice paddy with a patch of mulberry seedlings in the east China coastal region during the period from 13 September–11 October 2015. During the observation period, easterlies and northerlies prevailed, and 96% easterlies and northerlies had a speed of 0–6 m s−1. The sensible heat fluxes measured by the two systems reflected that the value of HLAS generally was inclined to be larger than HEC with the average difference of 20.30 W m−2, and the uncertainty for two instruments was less than 17 W m−2. Analysis of the average footprint resulted that the mulberry seedling field always had a higher contribution to LAS than that to EC, which could be the reason that HLAS was always larger than HEC. During the days when the contributions of the mulberry seedling field to the two systems were close to each other, the sensible heat flux measurements of the two instruments were similar. The case analysis on typical sunny days showed that there would be larger sensible heat fluxes over the mulberry seedling field than in the rice paddy field especially under larger net radiation conditions.

  14. Ten years of eddy covariance measurements in Basel, Switzerland: Seasonal and interannual variabilities of urban CO2 mole fraction and flux

    Science.gov (United States)

    Schmutz, M.; Vogt, R.; Feigenwinter, C.; Parlow, E.

    2016-07-01

    Eddy covariance (EC) measurements of carbon dioxide (CO2) in urban environments are carried out widely since the late nineties. However, long-term time series are still rare and little is known about long-term tendencies, even though cities are major sources of CO2 globally. Here a full decade of EC measurements from Basel, Switzerland, is presented. An approach for the calculation of horizontal averages is presented. It improves the significance and comparability of measured fluxes from heterogeneous environments and emphasizes the need of adequate weighting by horizontal averaging in such heterogeneous urban environments, especially for the derivation of cumulative quantities like the annual net ecosystem exchange. The urban CO2 mole fraction (ρC) is compared with regional background measurements, and good agreement in terms of long-term trend and seasonal variability is found. Over the last decade an increase of 2 ppm y-1 is observed, both locally and globally. CO2 flux (FC) data are analyzed for diurnal and seasonal cycles as well as interannual variabilities. FC shows a large interannual variability in times of high source activity (e.g., during the day and in winter). In contrast, a relatively constant background flux of 5 µmol m-2 s-1 is found during periods of low source activity. The long-term trend of FC is mostly superimposed by the large temporal variability and is found to be -5% over the last 10 years.

  15. Northern Hemisphere Atmospheric Transient Eddy Fluxes from the MERRA and Their Co-variability with Ocean Frontal Variability near the Western Boundary Current Regions

    Science.gov (United States)

    Kwon, Y.-O.; Joyce, T. M.

    2012-04-01

    Time series of winter (January-March) meridional transient eddy heat and moisture fluxes ( and ) for 1979-2009 in two separate frequency bands, i.e. the synoptic (2-8 days) and intra-seasonal (8-90 days), are calculated for the whole Northern Hemisphere based on daily atmospheric variables from the NASA Modern Era Retrospective-analysis for Research and Applications (MERRA) at 1/2 degrees latitude by 2/3 degrees longitude resolution. The climatological mean transient eddy fluxes in two frequency bands exhibit markedly distinct spatial patterns. The synoptic transient eddy fluxes show storm-track variability, of which maxima are co-located with the Gulf Stream and the Kuroshio-Oyashio Extensions, respectively in each basin. On the other hand, the intra-seasonal transient eddy fluxes exhibit maxima co-located with the major orography, e.g. the Rockies. In a vertically and zonally integrated poleward heat transport sense, the maximum heat transports in the two frequency bands are similar, while the sensible heat fluxes are twice greater than the latent heat fluxes. In addition, co-variability between the meridional transient eddy heat and moisture fluxes and their divergence in the Northern Hemisphere atmosphere and the variability in the position of ocean fronts associated with the Kuroshio Extension, Oyashio Extension and Gulf Stream is examined with a focus on the interannual to decadal time scale. Statistically significant correlations are found between the as well as and the ocean fronts from the surface up to 250 hPa for all three ocean fronts. The co-variability explains approximately half of the interannual and longer variance in the synoptic band, while only ~20 % for the intra-seasonal band.

  16. Comparison of Source Partitioning Methods for CO2 and H2O Fluxes Based on High Frequency Eddy Covariance Data

    Science.gov (United States)

    Klosterhalfen, Anne; Moene, Arnold; Schmidt, Marius; Ney, Patrizia; Graf, Alexander

    2017-04-01

    Source partitioning of eddy covariance (EC) measurements of CO2 into respiration and photosynthesis is routinely used for a better understanding of the exchange of greenhouse gases, especially between terrestrial ecosystems and the atmosphere. The most frequently used methods are usually based either on relations of fluxes to environmental drivers or on chamber measurements. However, they often depend strongly on assumptions or invasive measurements and do usually not offer partitioning estimates for latent heat fluxes into evaporation and transpiration. SCANLON and SAHU (2008) and SCANLON and KUSTAS (2010) proposed an promising method to estimate the contributions of transpiration and evaporation using measured high frequency time series of CO2 and H2O fluxes - no extra instrumentation necessary. This method (SK10 in the following) is based on the spatial separation and relative strength of sources and sinks of CO2 and water vapor among the sub-canopy and canopy. Assuming that air from those sources and sinks is not yet perfectly mixed before reaching EC sensors, partitioning is estimated based on the separate application of the flux-variance similarity theory to the stomatal and non-stomatal components of the regarded fluxes, as well as on additional assumptions on stomatal water use efficiency (WUE). The CO2 partitioning method after THOMAS et al. (2008) (TH08 in the following) also follows the argument that the dissimilarities of sources and sinks in and below a canopy affect the relation between H2O and CO2 fluctuations. Instead of involving assumptions on WUE, TH08 directly screens their scattergram for signals of joint respiration and evaporation events and applies a conditional sampling methodology. In spite of their different main targets (H2O vs. CO2), both methods can yield partitioning estimates on both fluxes. We therefore compare various sub-methods of SK10 and TH08 including own modifications (e.g., cluster analysis) to each other, to established

  17. Assimilation of ocean sea-surface height observations of mesoscale eddies

    Science.gov (United States)

    Weiss, Jeffrey B.; Grooms, Ian

    2017-12-01

    Mesoscale eddies are one of the dominant sources of variability in the world's oceans. With eddy-resolving global ocean models, it becomes important to assimilate observations of mesoscale eddies to correctly represent the state of the mesoscale. Here, we investigate strategies for assimilating a reduced number of sea-surface height observations by focusing on the coherent mesoscale eddies. The study is carried out in an idealized perfect-model framework using two-layer forced quasigeostrophic dynamics, which captures the dominant dynamics of ocean mesoscale eddies. We study errors in state-estimation as well as error growth in forecasts and find that as fewer observations are assimilated, assimilating at vortex locations results in reduced state estimation and forecast errors.

  18. An eddy-covariance system with an innovative vortex intake for measuring carbon dioxide and water fluxes of ecosystems

    Science.gov (United States)

    Ma, Jingyong; Zha, Tianshan; Jia, Xin; Sargent, Steve; Burgon, Rex; Bourque, Charles P.-A.; Zhou, Xinhua; Liu, Peng; Bai, Yujie; Wu, Yajuan

    2017-03-01

    Closed-path eddy-covariance (EC) systems are used to monitor exchanges of trace gases (e.g., carbon dioxide [CO2], water vapor [H2O], nitrous oxide and methane) between the atmosphere and biosphere. Traditional EC-intake systems are equipped with inline filters to prevent airborne dust particulate from contaminating the optical windows of the sample cell which causes measurement degradation. The inline filter should have a fine pore size (1 to 20 µm is common) to adequately protect the optics and a large filtration surface area to extend the time before it clogs. However, the filter must also have minimal internal volume to preserve good frequency response. This paper reports test results of the field performance of an EC system (EC155, Campbell Scientific, Inc., Logan Utah, USA) with a prototype vortex intake replacing the inline filter of a traditional EC system. The vortex-intake design is based on fluid dynamics theory. An air sample is drawn into the vortex chamber, where it spins in a vortex flow. The initially homogenous flow is separated when particle momentum forces heavier particles to the periphery of the chamber, leaving a much cleaner airstream at the center. Clean air (75 % of total flow) is drawn from the center of the vortex chamber, through a tube, to the sample cell where it is exposed to the optical windows of the gas analyzer. The remaining 25 % of the flow carries the heavier dust particles away through a separate bypass tube. An EC155 system measured CO2 and H2O fluxes in two urban-forest ecosystems in the megalopolis of Beijing, China. These sites present a challenge for EC measurements because of the generally poor air quality which has high concentrations of suspended particulate. The closed-path EC system with vortex intake significantly reduced maintenance requirements by preserving optical signal strength and sample-cell pressure within acceptable ranges for much longer periods. The system with vortex intake also maintained an excellent

  19. Contrasting ecosystem CO2 fluxes of inland and coastal wetlands: a meta-analysis of eddy covariance data.

    Science.gov (United States)

    Lu, Weizhi; Xiao, Jingfeng; Liu, Fang; Zhang, Yue; Liu, Chang'an; Lin, Guanghui

    2017-03-01

    Wetlands play an important role in regulating the atmospheric carbon dioxide (CO2 ) concentrations and thus affecting the climate. However, there is still lack of quantitative evaluation of such a role across different wetland types, especially at the global scale. Here, we conducted a meta-analysis to compare ecosystem CO2 fluxes among various types of wetlands using a global database compiled from the literature. This database consists of 143 site-years of eddy covariance data from 22 inland wetland and 21 coastal wetland sites across the globe. Coastal wetlands had higher annual gross primary productivity (GPP), ecosystem respiration (Re ), and net ecosystem productivity (NEP) than inland wetlands. On a per unit area basis, coastal wetlands provided large CO2 sinks, while inland wetlands provided small CO2 sinks or were nearly CO2 neutral. The annual CO2 sink strength was 93.15 and 208.37 g C m(-2) for inland and coastal wetlands, respectively. Annual CO2 fluxes were mainly regulated by mean annual temperature (MAT) and mean annual precipitation (MAP). For coastal and inland wetlands combined, MAT and MAP explained 71%, 54%, and 57% of the variations in GPP, Re , and NEP, respectively. The CO2 fluxes of wetlands were also related to leaf area index (LAI). The CO2 fluxes also varied with water table depth (WTD), although the effects of WTD were not statistically significant. NEP was jointly determined by GPP and Re for both inland and coastal wetlands. However, the NEP/Re and NEP/GPP ratios exhibited little variability for inland wetlands and decreased for coastal wetlands with increasing latitude. The contrasting of CO2 fluxes between inland and coastal wetlands globally can improve our understanding of the roles of wetlands in the global C cycle. Our results also have implications for informing wetland management and climate change policymaking, for example, the efforts being made by international organizations and enterprises to restore coastal wetlands for

  20. 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

  1. Relationships Among Canopy Scale Energy Fluxes and Isoprene Flux Using Eddy Covariance Measurements Over Multiple Growing Seasons

    Science.gov (United States)

    Pressley, S. N.; Lamb, B. K.; Westberg, H.

    2003-12-01

    tool for including biogenic emissions into regional atmospheric models. Long-term measurements of isoprene flux have been collected above a northern hardwood forest at the AmeriFlux site located at the University of Michigan Biological Station (UMBS) as part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET). Measurements have been made every summer since 1998 using eddy covariance techniques, and the data are now available for determining the relationship between isoprene flux and surface energy fluxes. Using this long-term dataset we hope to improve our understanding of isoprene emissions and, thus, improve our ability to include isoprene emissions in regional and global atmospheric chemistry models.

  2. Six-week time series of eddy covariance CO2 flux at Mammoth Mountain, California: performance evaluation and role of meteorological forcing

    Energy Technology Data Exchange (ETDEWEB)

    Lewicki, Jennifer; Lewicki, J.L.; Fischer, M.L.; Hilley, G.E.

    2007-10-15

    CO{sub 2} and heat fluxes were measured over a six-week period (09/08/2006 to 10/24/2006) by the eddy covariance (EC) technique at the Horseshoe Lake tree kill (HLTK), Mammoth Mountain, CA, a site with complex terrain and high, spatially heterogeneous CO{sub 2} emission rates. EC CO{sub 2} fluxes ranged from 218 to 3500 g m{sup -2} d{sup -1} (mean = 1346 g m{sup -2} d{sup -1}). Using footprint modeling, EC CO{sub 2} fluxes were compared to CO{sub 2} fluxes measured by the chamber method on a grid repeatedly over a 10-day period. Half-hour EC CO{sub 2} fluxes were moderately correlated (R{sup 2} = 0.42) with chamber fluxes, whereas average-daily EC CO{sub 2} fluxes were well correlated (R{sup 2} = 0.70) with chamber measurements. Average daily EC CO{sub 2} fluxes were correlated with both average daily wind speed and atmospheric pressure; relationships were similar to those observed between chamber CO{sub 2} fluxes and the atmospheric parameters over a comparable time period. Energy balance closure was assessed by statistical regression of EC energy fluxes (sensible and latent heat) against available energy (net radiation, less soil heat flux). While incomplete (R{sup 2} = 0.77 for 1:1 line), the degree of energy balance closure fell within the range observed in many investigations conducted in contrasting ecosystems and climates. Results indicate that despite complexities presented by the HLTK, EC can be reliably used to monitor background variations in volcanic CO{sub 2} fluxes associated with meteorological forcing, and presumably changes related to deeply derived processes such as volcanic activity.

  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. Pseudo-observations for competing risks with covariate dependent censoring

    DEFF Research Database (Denmark)

    Binder, Nadine; Gerds, Thomas A; Andersen, Per Kragh

    2014-01-01

    that the probability of not being lost to follow-up (un-censored) is independent of the covariates. Modified pseudo-values are proposed which rely on a correctly specified regression model for the censoring times. Bias and efficiency of these methods are compared in a simulation study. Further illustration...

  5. Some observations on interpolating gauges and non-covariant gauges

    Indian Academy of Sciences (India)

    tion 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. Keywords. Non-covariant gauges; interpolating ...

  6. A Strategy to Estimate the Systematic Uncertainty of Eddy Covariance Fluxes due to the Post-field Raw Data Processing

    Science.gov (United States)

    Sabbatini, Simone; Fratini, Gerardo; Fidaleo, Marcello; Papale, Dario

    2017-04-01

    Among several sources of uncertainty characterising the fluxes of atmospheric constituents to and from a given ecosystem calculated using the eddy covariance (EC) methodology, the systematic error due to the corrections applied in the post-field raw data processing is still relatively unknown. We performed an extensive analysis aiming at quantifying this portion of the uncertainty for the CO2 exchange, and at defining a strategy of processing to be generically applied as to understand this uncertainty. We selected 11 years of raw EC data from 9 stations all over the Europe, corresponding to 4 different setups. Then we chose 2 or 3 possible valid options for each of the 8 most relevant corrections to be applied to the raw data, and produced as many outputs (1-year-long calculated hourly and half-hourly fluxes) as the combinations of all the different options (full-factorial design). Statistical analysis was used to quantify and characterise the uncertainty (n-way ANOVA) both on the (half-)hourly and the yearly cumulative fluxes. Factorial design of Experiment (DOE) was used to select a relatively small sub-group of combinations of processing options (fractional factorial design) to be applied to a given dataset in order to quantify the processing uncertainty, with a limited loss of information as compared to the full factorial. Our results show that: (i) the variability as expressed by the inter-quartile range (IQR) of the cumulate CO2 flux is between 50 and 400 gC m-2 year-1. (ii) The importance of the single corrections (factors) in terms of variance explained is not constant among datasets, but a general trend is found such that the coordinate rotation (CR) and the trend removal (TR) have often a high weight on the overall uncertainty (i.e. between 10% and 50%), while the importance of the time-lag compensation (TL) is highly variable. (iii) 2x2 interactions between factors have some importance, mostly between the most relevant ones. (iv) The percentage error of

  7. 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

  8. Simultaneous assimilation of satellite and eddy covariance data for improving terrestrial water and carbon simulations at a semi-arid woodland site in Botswana

    Directory of Open Access Journals (Sweden)

    T. Kato

    2013-02-01

    Full Text Available Terrestrial productivity in semi-arid woodlands is strongly susceptible to changes in precipitation, and semi-arid woodlands constitute an important element of the global water and carbon cycles. Here, we use the Carbon Cycle Data Assimilation System (CCDAS to investigate the key parameters controlling ecological and hydrological activities for a semi-arid savanna woodland site in Maun, Botswana. Twenty-four eco-hydrological process parameters of a terrestrial ecosystem model are optimized against two data streams separately and simultaneously: daily averaged latent heat flux (LHF derived from eddy covariance measurements, and decadal fraction of absorbed photosynthetically active radiation (FAPAR derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS.

    Assimilation of both data streams LHF and FAPAR for the years 2000 and 2001 leads to improved agreement between measured and simulated quantities not only for LHF and FAPAR, but also for photosynthetic CO2 uptake. The mean uncertainty reduction (relative to the prior over all parameters is 14.9% for the simultaneous assimilation of LHF and FAPAR, 8.5% for assimilating LHF only, and 6.1% for assimilating FAPAR only. The set of parameters with the highest uncertainty reduction is similar between assimilating only FAPAR or only LHF. The highest uncertainty reduction for all three cases is found for a parameter quantifying maximum plant-available soil moisture. This indicates that not only LHF but also satellite-derived FAPAR data can be used to constrain and indirectly observe hydrological quantities.

  9. Wintertime CO2 fluxes in an Arctic polynya using eddy covariance: Evidence for enhanced air-sea gas transfer during ice formation

    Science.gov (United States)

    Else, B. G. T.; Papakyriakou, T. N.; Galley, R. J.; Drennan, W. M.; Miller, L. A.; Thomas, H.

    2011-09-01

    Between Nov. 1 2007 and Jan. 31 2008, we calculated the air-sea flux of CO2, sensible heat, and water vapor in an Arctic polynya system (Amundsen Gulf, Canada) using eddy covariance equipment deployed on the research icebreaker CCGS Amundsen. During this time period, Amundsen Gulf was a dynamic sea ice environment composed primarily of first year ice with open water coverage varying between 1-14%. In all cases where measurements were influenced by open water we measured CO2 fluxes that were 1-2 orders of magnitude higher than those expected under similar conditions in the open ocean. Fluxes were typically directed toward the water surface with a mean flux of -4.88 μmol m-2 s-1 and a maximum of -27.95 μmol m-2 s-1. One case of rapid outgassing (mean value +2.10 μmol m-2 s-1) was also observed. The consistent patten of enhanced gas exchange over open water allows us to hypothesize that high water-side turbulence is the main cause of these events. Modification of the physical and chemical properties of the surface seawater by cooling and brine rejection may also play a role. A rough calculation using an estimate of open water coverage suggests that the contribution of these events to the annual regional air-sea CO2 exchange budget may make the winter months as important as the open water months. Although high, the uptake of CO2 fits within mixed layer dissolved inorganic carbon budgets derived for the region by other investigators.

  10. 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

  11. Assessing the Impacts of Fire on Water-Use Efficiency in Grasslands in Eastern Kansas Combining Satellite and Eddy Covariance Data

    Science.gov (United States)

    De Oliveira, G.; Brunsell, N. A.

    2016-12-01

    Burning is a land management practice commonly used on grasslands and plays an important role in these ecosystems by increasing production, determining community composition, and controlling the invasion of woody species. Without fire, many trees and shrubs species invade North American prairies, shrinking the area of the grassland. It specially occurs in the eastern tallgrass prairie where environmental conditions are more favorable for trees than in more arid west. Although the use of fire has benefits in relation to the maintenance of the structure of these ecosystems, the effects of this practice on carbon and water exchanges in grasslands are not well understood. The present study aimed to compare, using MODIS remote sensing data combined with flux tower observations, the magnitude and temporal dynamics of water-use efficiency (WUE) in four watersheds in eastern Kansas, USA. Two watersheds are located in the Konza Prairie Biological Station (KPBS), in Manhattan. The other two are located, respectively, in Lawrence, in a tallgrass prairie and deciduous forest ecotone, and in Salina, over an unburned, perennial agricultural site. These watersheds represent different grassland ecosystems, which are subjected to particular burning regimes. Eddy covariance data related, among others, to ecosystem respiration and latent heat flux, were acquired from three AmeriFlux towers located within each watershed. The MODIS products used were MOD17 (gross primary productivity) (GPP) and MOD16 (evapotranspiration) (ET). The integration of ground and satellite data was a useful proposition to analyze GPP, ET and WUE at canopy and watershed scales. It was possible to examine the variability of these parameters among grassland types and fire treatments, which may contribute to a better understanding of the direct effects of burning on the coupling between the terrestrial carbon and water cycles in grasslands of the Great Plains, as well as the role of fire on enhancing productivity

  12. Tundra is a consistent source of CO2 at a site with progressive permafrost thaw during 6 years of chamber and eddy covariance measurements

    Science.gov (United States)

    Celis, Gerardo; Mauritz, Marguerite; Bracho, Rosvel; Salmon, Verity G.; Webb, Elizabeth E.; Hutchings, Jack; Natali, Susan M.; Schädel, Christina; Crummer, Kathryn G.; Schuur, Edward A. G.

    2017-06-01

    Current and future warming of high-latitude ecosystems will play an important role in climate change through feedbacks to the global carbon cycle. This study compares 6 years of CO2 flux measurements in moist acidic tundra using autochambers and eddy covariance (Tower) approaches. We found that the tundra was an annual source of CO2 to the atmosphere as indicated by net ecosystem exchange using both methods with a combined mean of 105 ± 17 g CO2 C m-2 y-1 across methods and years (Tower 87 ± 17 and Autochamber 123 ± 14). The difference between methods was largest early in the observation period, with Autochambers indicated a greater CO2 source to the atmosphere. This discrepancy diminished through time, and in the final year the Autochambers measured a greater sink strength than tower. Active layer thickness was a significant driver of net ecosystem carbon exchange, gross ecosystem primary productivity, and Reco and could account for differences between Autochamber and Tower. The stronger source initially attributed lower summer season gross primary production (GPP) during the first 3 years, coupled with lower ecosystem respiration (Reco) during the first year. The combined suppression of GPP and Reco in the first year of Autochamber measurements could be the result of the experimental setup. Root damage associated with Autochamber soil collar installation may have lowered the plant community's capacity to fix C, but recovered within 3 years. While this ecosystem was a consistent CO2 sink during the summer, CO2 emissions during the nonsummer months offset summer CO2 uptake each year.

  13. 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

  14. Intercomparison of six fast-response sensors for the eddy-covariance flux measurement of nitrous oxide over agricultural grassland

    Science.gov (United States)

    Nemitz, Eiko; Famulari, Daniela; Ibrom, Andreas; Vermeulen, Alex; Hensen, Arjan; van den Bulk, Pim; Loubet, Benjamin; Laville, Patricia; Mammarella, Ivan; Haapanala, Sami; Lohila, Annalea; Laurila, Tuomas; Eva, Rabot; Laborde, Marie; Cowan, Nicholas; Anderson, Margaret; Helfter, Carole

    2015-04-01

    Nitrous oxide (N2O) is the third most important greenhouse gas and its terrestrial budget remains poorly constraint, with bottom up and top down estimates of country emissions often disagreeing by more than a factor of two. Whilst the measurements of the biosphere / atmosphere exchange of CO2 with micrometeorological methods is commonplace, emissions of CH4 and N2O are more commonly measured with enclosure techniques due to limitations in fast-response sensors with good signal-to-noise characteristics. Recent years have seen the development of a range of instruments based on optical spectroscopy. This started in the early 1990s with instruments based on lead salt lasers, which had temperamental long-term characteristics. More recent developments in quantum cascade lasers has lead to increasingly stable instruments, initially based on pulsed, later on continuous wave lasers. Within the context of the European FP7 Infrastructure Project InGOS ('Integrated non-CO2 Greenhouse gas Observing System'), we conducted an intercomparison of six fast response sensors for N2O: three more or less identical instruments based on off-axis Integrated Cavity Optical Spectrocopy (ICOS) (Los Gatos Research Inc.) and three instruments based on quantum cascade laser absorption spectrometry (Aerodyne Research Inc.): one older generation pulsed instrument (p-QCL) and two of the latest generation of compact continuous wave instruments (cw-QCL), operating at two different wavelengths. One of the ICOS instruments was operated with an inlet drier. In addition, the campaign was joined by a relaxed eddy-accumulation system linked to a FTIR spectrometer (Ecotech), a gradient system based on a home-built slower QCL (INRA Orleans) and a fast chamber system. Here we present the results of the study and a detailed examination of the various corrections and errors of the different instruments. Overall, with the exception of the older generation QCL, the average fluxes based on the different fast

  15. Observation of Oceanic Eddy in the Northeastern Arabian Sea Using Multisensor Remote Sensing Data

    Directory of Open Access Journals (Sweden)

    R. K. Sarangi

    2012-01-01

    Full Text Available An oceanic eddy of size about 150 kilometer diameter observed in the northeastern Arabian Sea using remote sensing satellite sensors; IRS-P4 OCM, NOAA-AVHRR and NASA Quickscat Scatterometer data. The eddy was detected in the 2nd week of February in Indian Remote Sensing satellite (IRS-P4 Ocean Color Monitor (OCM sensor retrieved chlorophyll image on 10th February 2002, between latitude 16°90′–18°50′N and longitude 66°05′–67°60′E. The chlorophyll concentration was higher in the central part of eddy (~1.5 mg/m3 than the peripheral water (~0.8 mg/m3. The eddy lasted till 10th March 2002. NOAA-AVHRR sea surface temperature (SST images generated during 15th February-15th March 2002. The SST in the eddy’s center (~23°C was lesser than the surrounding water (~24.5°C. The eddy was of cold core type with the warmer water in periphery. Quickscat Scatterometer retrieved wind speed was 8–10 m/sec. The eddy movement observed southeast to southwest direction and might helped in churning. The eddy seemed evident due to convective processes in water column. The processes like detrainment and entrainment play role in bringing up the cooler water and the bottom nutrient to surface and hence the algal blooming. This type of cold core/anti-cyclonic eddy is likely to occur during late winter/spring as a result of the prevailing climatic conditions.

  16. Measurements of VOC fluxes by Eddy-covariance with a PTR-Qi-TOF-MS over a mature wheat crop near Paris: Evaluation of data quality and uncertainties.

    Science.gov (United States)

    Buysse, Pauline; Loubet, Benjamin; Ciuraru, Raluca; Lafouge, Florence; Zurfluh, Olivier; Gonzaga-Gomez, Lais; Fanucci, Olivier; Gueudet, Jean-Christophe; Decuq, Céline; Gros, Valérie; Sarda, Roland; Zannoni, Nora

    2017-04-01

    The quantification of volatile organic compounds (VOC) fluxes exchanged by terrestrial ecosystems is of large interest because of their influence on the chemistry and composition of the atmosphere including aerosols and oxidants. Latest developments in the techniques for detecting, identifying and measuring VOC fluxes have considerably improved the abilities to get reliable estimates. Among these, the eddy-covariance (EC) methodology constitutes the most direct approach, and relies on both well-established principles (Aubinet et al. 2000) and a sound continuously worldwide improving experience. The combination of the EC methodology with the latest proton-transfer-reaction mass spectrometer (PTR-MS) device, the PTR-Qi-TOF-MS, which allows the identification and quantification of more than 500 VOC at high frequency, now provides a very powerful and precise tool for an accurate quantification of VOC fluxes on various types of terrestrial ecosystems. The complexity of the whole methodology however demands that several data quality requirements are fulfilled. VOC fluxes were measured by EC with a PTR-Qi-TOF-MS (national instrument within the ANAEE-France framework) for one month and a half over a mature wheat crop near Paris (FR-GRI ICOS site). Most important emissions (by descending order) were observed from detected compounds with mass-over-charge (m/z) ratios of 33.033 (methanol), 45.033 (acetaldehyde), 93.033 (not identified yet), 59.049 (acetone), and 63.026 (dimethyl sulfide or DMS). Emissions from higher-mass compounds, which might be due to pesticide applications at the beginning of our observation period, were also detected. Some compounds were also seen to deposit (e.g. m/z 47.013, 71.085, 75.044, 83.05) while others exhibited bidirectional fluxes (e.g. m/z 57.07, 69.07). Before analyzing VOC flux responses to meteorological and crop development drivers, a data quality check was performed which included (i) uncertainty analysis of mass and concentration

  17. Eddy covariance flux measurements of net ecosystem carbon dioxide exchange from a lowland peatland flux tower network in England and Wales

    Science.gov (United States)

    Morrison, Ross; Balzter, Heiko; Burden, Annette; Callaghan, Nathan; Cumming, Alenander; Dixon, Simon; Evans, Jonathan; Kaduk, Joerg; Page, Susan; Pan, Gong; Rayment, Mark; Ridley, Luke; Rylett, Daniel; Worrall, Fred; Evans, Christopher

    2016-04-01

    Peatlands store disproportionately large amounts of soil carbon relative to other terrestrial ecosystems. Over recent decades, the large amount of carbon stored as peat has proved vulnerable to a range of land use pressures as well as the increasing impacts of climate change. In temperate Europe and elsewhere, large tracts of lowland peatland have been drained and converted to agricultural land use. Such changes have resulted in widespread losses of lowland peatland habitat, land subsidence across extensive areas and the transfer of historically accumulated soil carbon to the atmosphere as carbon dioxide (CO2). More recently, there has been growth in activities aiming to reduce these impacts through improved land management and peatland restoration. Despite a long history of productive land use and management, the magnitude and controls on greenhouse gas emissions from lowland peatland environments remain poorly quantified. Here, results of surface-atmosphere measurements of net ecosystem CO2 exchange (NEE) from a network of seven eddy covariance (EC) flux towers located at a range of lowland peatland ecosystems across the United Kingdom (UK) are presented. This spatially-dense peatland flux tower network forms part of a wider observation programme aiming to quantify carbon, water and greenhouse gas balances for lowland peatlands across the UK. EC measurements totalling over seventeen site years were obtained at sites exhibiting large differences in vegetation cover, hydrological functioning and land management. The sites in the network show remarkable spatial and temporal variability in NEE. Across sites, annual NEE ranged from a net sink of -194 ±38 g CO2-C m-2 yr-1 to a net source of 784±70 g CO2-C m-2 yr-1. The results suggest that semi-natural sites remain net sinks for atmospheric CO2. Sites that are drained for intensive agricultural production range from a small net sink to the largest observed source for atmospheric CO2 within the flux tower network

  18. 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

  19. The Importance of Covariate Selection in Controlling for Selection Bias in Observational Studies

    Science.gov (United States)

    Steiner, Peter M.; Cook, Thomas D.; Shadish, William R.; Clark, M. H.

    2010-01-01

    The assumption of strongly ignorable treatment assignment is required for eliminating selection bias in observational studies. To meet this assumption, researchers often rely on a strategy of selecting covariates that they think will control for selection bias. Theory indicates that the most important covariates are those highly correlated with…

  20. Eddy covariance fluxes of the NO-NO2-O3 triad above a spruce forest canopy in south-eastern Germany.

    Science.gov (United States)

    Tsokankunku, A.; Zhu, Z.; Meixner, F. X.; Foken, T.; Andreae, M. O.

    2009-04-01

    We investigated the diel variability of the eddy covariance fluxes of the NO-NO2-O3 triad above a spruce forest canopy at the "Weidenbrunnen" research site (Fichtelgebirge, Germany). Measurements were part of the EGER project (ExchanGE processes in mountainous Regions), which focuses on the role of process interactions among the different scales of soil, in-canopy and atmospheric exchange processes of reactive and non-reactive trace gases and energy. The eddy covariance platform was at the top of a 32 m high tower (50˚ 08'31" N, 11˚ 52'1"E, elevation 755 m.a.s.l). The eddy covariance system consisted of a CSAT3 sonic anemometer and a high speed, high resolution NO-NO2two channel chemiluminescence analyzer (Ecophysics CLD 790 SR2). A solid-state blue-light photolytic converter was connected to the NO2 channel of the analyzer just behind the sample inlet. Ambient NO and NO2 mixing ratios were sampled via 52 m long tubes with the instrument itself located in a temperature-controlled container at the ground. The NO-NO2 analyzer was operated at 5 Hz. Additionally we measured eddy covariance fluxes of CO2 and H2O. An infrared absorption-based analyzer (LI-7000) was used to sample CO2 and H2O mixing ratios, and a fast solid-phase chemiluminescence ozone analyzer (GFAS) was deployed to measure O3 mixing ratios. All trace gas inlets were situated at 32.5 m, 20 cm below the path of the sonic anemometer. The 32m inlet of an independent NO, NO2, and O3 concentration profile measuring system was used as the calibration source for the fast ozone analyzer and the two channel NO-NO2chemiluminescence analyzer. Preliminary results show that NO and NO2advection plays a big role in the magnitude and direction of the fluxes at the site. The main source of the advection is a busy country road situated about 2 km west of the site. CO2 fluxes were also influenced by advection. Extended periods of stationarity usually occurred on Sundays when the amount of traffic was significantly

  1. 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......, with the exception of the two Mediterranean sites. We find that 3D-CMCC FEM tends to better simulate the timing of inter-annual anomalies than their magnitude within measurements' uncertainty. In six of eight sites where data are available, the model well reproduces the 2003 summer drought event. Finally, for three...

  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 (< 30 ppt) instrument (CLD790SR2, Eco Physics) for NO and NO2 and with 10 Hz for O3 (Enviscope). Additionally, measurements of turbulent and micrometeorological parameters were conducted with a profile of 3-dimensional sonic anemometers and meteorological sensors for temperature, humidity and radiation. Vertical concentration profile

  3. 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.

  4. Comparison of two closed-path cavity-based spectrometers for measuring air–water CO2 and CH4 fluxes by eddy covariance

    Directory of Open Access Journals (Sweden)

    M. Yang

    2016-11-01

    Full Text Available In recent years several commercialised closed-path cavity-based spectroscopic instruments designed for eddy covariance flux measurements of carbon dioxide (CO2, methane (CH4, and water vapour (H2O have become available. Here we compare the performance of two leading models – the Picarro G2311-f and the Los Gatos Research (LGR Fast Greenhouse Gas Analyzer (FGGA at a coastal site. Both instruments can compute dry mixing ratios of CO2 and CH4 based on concurrently measured H2O, temperature, and pressure. Additionally, we used a high throughput Nafion dryer to physically remove H2O from the Picarro airstream. Observed air–sea CO2 and CH4 fluxes from these two analysers, averaging about 12 and 0.12 mmol m−2 day−1 respectively, agree within the measurement uncertainties. For the purpose of quantifying dry CO2 and CH4 fluxes downstream of a long inlet, the numerical H2O corrections appear to be reasonably effective and lead to results that are comparable to physical removal of H2O with a Nafion dryer in the mean. We estimate the high-frequency attenuation of fluxes in our closed-path set-up, which was relatively small ( ≤  10 % for CO2 and CH4 but very large for the more polar H2O. The Picarro showed significantly lower noise and flux detection limits than the LGR. The hourly flux detection limit for the Picarro was about 2 mmol m−2 day−1 for CO2 and 0.02 mmol m−2 day−1 for CH4. For the LGR these detection limits were about 8 and 0.05 mmol m−2 day−1. Using global maps of monthly mean air–sea CO2 flux as reference, we estimate that the Picarro and LGR can resolve hourly CO2 fluxes from roughly 40 and 4 % of the world's oceans respectively. Averaging over longer timescales would be required in regions with smaller fluxes. Hourly flux detection limits of CH4 from both instruments are generally higher than the expected emissions from the open ocean, though the signal to noise of this measurement may

  5. Comparison of two closed-path cavity-based spectrometers for measuring air-water CO2 and CH4 fluxes by eddy covariance

    Science.gov (United States)

    Yang, Mingxi; Prytherch, John; Kozlova, Elena; Yelland, Margaret J.; Parenkat Mony, Deepulal; Bell, Thomas G.

    2016-11-01

    In recent years several commercialised closed-path cavity-based spectroscopic instruments designed for eddy covariance flux measurements of carbon dioxide (CO2), methane (CH4), and water vapour (H2O) have become available. Here we compare the performance of two leading models - the Picarro G2311-f and the Los Gatos Research (LGR) Fast Greenhouse Gas Analyzer (FGGA) at a coastal site. Both instruments can compute dry mixing ratios of CO2 and CH4 based on concurrently measured H2O, temperature, and pressure. Additionally, we used a high throughput Nafion dryer to physically remove H2O from the Picarro airstream. Observed air-sea CO2 and CH4 fluxes from these two analysers, averaging about 12 and 0.12 mmol m-2 day-1 respectively, agree within the measurement uncertainties. For the purpose of quantifying dry CO2 and CH4 fluxes downstream of a long inlet, the numerical H2O corrections appear to be reasonably effective and lead to results that are comparable to physical removal of H2O with a Nafion dryer in the mean. We estimate the high-frequency attenuation of fluxes in our closed-path set-up, which was relatively small ( ≤ 10 %) for CO2 and CH4 but very large for the more polar H2O. The Picarro showed significantly lower noise and flux detection limits than the LGR. The hourly flux detection limit for the Picarro was about 2 mmol m-2 day-1 for CO2 and 0.02 mmol m-2 day-1 for CH4. For the LGR these detection limits were about 8 and 0.05 mmol m-2 day-1. Using global maps of monthly mean air-sea CO2 flux as reference, we estimate that the Picarro and LGR can resolve hourly CO2 fluxes from roughly 40 and 4 % of the world's oceans respectively. Averaging over longer timescales would be required in regions with smaller fluxes. Hourly flux detection limits of CH4 from both instruments are generally higher than the expected emissions from the open ocean, though the signal to noise of this measurement may improve closer to the coast.

  6. Analyzing the impact of land cover changes on water, energy and CO2 fluxes in the West African Sudanian Savannah using Eddy Covariance stations

    Science.gov (United States)

    Berger, Sina; Bliefernicht, Jan; Mauder, Matthias; Heinzeller, Dominikus; Guug, Samuel; Quansah, Emmanuel; Hingerl, Luitpold; Aduna, Aaron; Salack, Seyni; Kunstmann, Harald

    2017-04-01

    An investigation of the impacts of land surface changes in West Africa, one of the most vulnerable regions of the world with respect to climate changes, require a sound understanding of the land-atmosphere exchange processes and their feedback mechanisms. An investigation of the impacts of land surface changes in West Africa require a sound understanding of the land-atmosphere exchange processes and their feedback mechanisms. To improve our process understanding regarding land-atmosphere interactions in the West African Sudanian Savannah, three micro-meteorological stations based on the Eddy Covariance (EC) technique have been installed in northern Ghana and in southern Burkina Faso during two field campaigns in October 2012 and January 2013. The EC stations are located along a transect of changing land cover to investigate how land surface changes influence energy, water and CO2 fluxes between the land surface and the overlying atmosphere. The measurement sites are characterized by different vegetation cover due to different land use practices (near-natural versus intensively used grassland versus a mixture of fallow and cropland). Further site characteristics such as climate, soil and relief are similar. The analysis of the EC measurements was done for a period from January 2013 to August 2016 for four typical seasons in West Africa with different wind, moisture and radiation characteristics. Firstly, monsoonal winds from the southwest blowing over moist soils and lush vegetation between June and August during the monsoon peak, secondly, Harmattan winds from the northeast blowing over desiccated soils between December and February during the dry season, as well as transition periods with winds from various directions either over decaying vegetation and increasingly dry soils between September and November, or over growing vegetation and increasingly wet soils between March and May. Energy balance closures were best during the rainy season, however, we observed

  7. 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

  8. On the use of the post-closure methods uncertainty band to evaluate the performance of land surface models against eddy covariance flux data

    Science.gov (United States)

    Ingwersen, Joachim; Imukova, Kristina; Högy, Petra; Streck, Thilo

    2017-04-01

    The energy balance of eddy covariance (EC) flux data is normally not closed. Therefore, at least if used for modeling, EC flux data are usually post-closed, i.e. the measured turbulent fluxes are adjusted so as to close the energy balance. At the current state of knowledge, however, it is not clear how to partition the missing energy in the right way. Eddy flux data therefore contain some uncertainty due to the unknown nature of the energy balance gap, which should be considered in model evaluation and the interpretation of simulation results. We propose to construct the post-closure method uncertainty band (PUB), which essentially designates the differences between non-adjusted flux data and flux data adjusted with the three post-closure methods (Bowen ratio, latent heat flux (LE) and sensible heat flux (H) method). To demonstrate this approach, simulations with the NOAH-MP land surface model were evaluated based on EC measurements conducted at a winter wheat stand in Southwest Germany in 2011, and the performance of the Jarvis and Ball-Berry stomatal resistance scheme was compared. The width of the PUB of the LE was up to 110 W/m2 (21% of net radiation). Our study shows that it is crucial to account for the uncertainty of EC flux data originating from lacking energy balance closure. Working with only a single post-closing method might result in severe misinterpretations in model-data comparisons.

  9. Using the Eddy Covariance Method, Chambers, and Box Modeling to Characterize Spatial and Temporal Trends in Greenhouse Gas Emissions over a Barley Field in the Inland Pacific Northwest

    Science.gov (United States)

    Waldo, S.; Kostyanovsky, K.; O'Keeffe, P.; Chi, J.; Pressley, S. N.; Huggins, D.; Uberuaga, D.; Lamb, B. K.

    2013-12-01

    Characterizing the dynamics of greenhouse gas (GHG) fluxes in agricultural systems is becoming increasingly important in the face of population growth and climate change. Monitoring baseline fluxes of both carbon dioxide (CO2) and nitrous oxide (N2O) over agroecosystems allows for a better understanding of how climate and management practices affect the GHG budget of a given field. In this study, fluxes of CO2 and N2O were measured and compared using the eddy covariance (EC) technique and four automated static chambers (LI-8100A). The site is outfitted with an EC tower to continuously measure fluxes of CO2, H2O, and energy as well as auxiliary meteorological variables. Both the chamber system and N2O instrument were added for a month-long period following spring fertilization and seeding. The difference in scales between the tower and the chambers allowed for analysis of the spatial variability of fluxes. For N2O, the spatial variability was very high, with up to ten-fold differences in fluxes between the four chambers. However, the magnitude of the tower-based fluxes was closest to that of the highest-emitting chamber. In addition to addressing spatial variability, the chamber measurements helped to characterize nighttime fluxes, when stable conditions often lead to gaps in eddy covariance data. Box modeling techniques were also used to fill in nocturnal data gaps. The relationship between N2O fluxes and meteorological conditions was analyzed, as well as the relationship between N2O emissions and CO2 respiration. It was found that the total N2O-N emission from the site in the one-month period following fertilization exceeded the IPCC estimate of 1% of fertilizer-N applied. Instrumented tower and one of the four chambers monitoring the exchange of GHGs over a barley field

  10. Testing Munk's hypothesis for submesoscale eddy generation using observations in the North Atlantic

    Science.gov (United States)

    Buckingham, Christian E.; Khaleel, Zammath; Lazar, Ayah; Martin, Adrian P.; Allen, John T.; Naveira Garabato, Alberto C.; Thompson, Andrew F.; Vic, Clément

    2017-08-01

    A high-resolution satellite image that reveals a train of coherent, submesoscale (6 km) vortices along the edge of an ocean front is examined in concert with hydrographic measurements in an effort to understand formation mechanisms of the submesoscale eddies. The infrared satellite image consists of ocean surface temperatures at ˜390 m resolution over the midlatitude North Atlantic (48.69°N, 16.19°W). Concomitant altimetric observations coupled with regular spacing of the eddies suggest the eddies result from mesoscale stirring, filamentation, and subsequent frontal instability. While horizontal shear or barotropic instability (BTI) is one mechanism for generating such eddies (Munk's hypothesis), we conclude from linear theory coupled with the in situ data that mixed layer or submesoscale baroclinic instability (BCI) is a more plausible explanation for the observed submesoscale vortices. Here we assume that the frontal disturbance remains in its linear growth stage and is accurately described by linear dynamics. This result likely has greater applicability to the open ocean, i.e., regions where the gradient Rossby number is reduced relative to its value along coasts and within strong current systems. Given that such waters comprise an appreciable percentage of the ocean surface and that energy and buoyancy fluxes differ under BTI and BCI, this result has wider implications for open-ocean energy/buoyancy budgets and parameterizations within ocean general circulation models. In summary, this work provides rare observational evidence of submesoscale eddy generation by BCI in the open ocean.Plain Language SummaryHere, we test Munk's theory for small-scale eddy generation using a unique set of satellite- and ship-based observations. We find that for one particular set of observations in the North Atlantic, the mechanism for eddy generation is not pure horizontal shear, as proposed by Munk et al. () and Munk (), but is instead vertical shear, or baroclinic instability

  11. Characterizing frontal eddies along the East Australian Current from HF radar observations

    Science.gov (United States)

    Schaeffer, Amandine; Gramoulle, A.; Roughan, M.; Mantovanelli, A.

    2017-05-01

    The East Australian Current (EAC) dominates the ocean circulation along south-eastern Australia, however, little is known about the submesoscale frontal instabilities associated with this western boundary current. One year of surface current measurements from HF radars, in conjunction with mooring and satellite observations, highlight the occurrence and propagation of meanders and frontal eddies along the inshore edge of the EAC. Eddies were systematically identified using the geometry of the high spatial resolution (˜1.5 km) surface currents, and tracked every hour. Cyclonic eddies were observed irregularly, on average every 7 days, with inshore radius ˜10 km. Among various forms of structures, frontal eddies associated with EAC meanders were characterized by poleward advection speeds of ˜0.3-0.4 m/s, migrating as far as 500 km south, based on satellite imagery. Flow field kinematics show that cyclonic eddies have high Rossby numbers (0.6-1.9) and enhance particle dispersion. Patches of intensified surface divergence at the leading edge of the structures are expected to generate vertical uplift. This is confirmed by subsurface measurements showing temperature uplift of up to 55 m over 24 h and rough estimates of vertical velocities of 10s of meters per day. While frontal eddies propagate through the radar domain independently of local wind stress, upfront wind can influence their stalling and growth, and can also generate large cold core eddies through intense shear. Such coherent structures are a major mechanism for the transport and entrainment of nutrient rich coastal or deep waters, influencing physical and biological dynamics, and connectivity over large distances.

  12. 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

  13. 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

  14. 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)...

  15. Upper ocean observations in eastern Caribbean Sea reveal barrier layer within a warm core eddy

    Science.gov (United States)

    Rudzin, J. E.; Shay, L. K.; Jaimes, B.; Brewster, J. K.

    2017-02-01

    Three-dimensional measurements of a large warm core eddy (WCE) and the Caribbean Current are acquired using oceanic profilers deployed during a NOAA research aircraft study in September 2014 in the eastern Caribbean Sea. Measurements of the near-surface atmosphere are also collected to examine air-sea processes over the eddy. These novel measurements showcase temperature and salinity for the eddy and background flow, upper ocean stratification, a residing barrier layer (BL), velocity structure, and water mass characteristics. The eddy's thermal structure is alike that of WCEs in the Gulf of Mexico (GoM) whereas surrounding waters have relatively deeper isotherms compared to its GoM counterparts. Analyses suggest that upper ocean stratification within the study region is due to a BL. These are the first observations of a BL inside a WCE to the best of our knowledge. Reduced shear comparisons suggest that the upper ocean, especially within the WCE, would be more resistant to tropical cyclone (TC) induced mixing than the GoM because of the BL. The eddy is suspected to originate from North Brazil Current rings, given its fresh anomalies relative to climatology and surrounding waters and its trajectory prior to sampling. Atmospheric measurements suggest the WCE is influencing the lower atmosphere along its boundaries. These observations signify that not only does this WCE have deep thermal structure and modulate the near-surface atmosphere but it is unique because it has a BL. The findings and analyses suggest that a similar eddy could potentially influence air-sea processes, such as those during TC passage.

  16. Eddy properties in the Mozambique Channel: A comparison between observations and two numerical ocean circulation models

    NARCIS (Netherlands)

    Halo, I.; Backeberg, B.; Penven, P.; Ansorge, I.; Reason, C.; Ullgren, J.E

    2014-01-01

    Analysis of satellite altimetry observations, transports estimates from a mooring array, as well as output from two different numerical ocean circulation models (ROMS and HYCOM), have been used to investigate the mesoscale eddy properties and transport variability in the Mozambique Channel. The

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

    NARCIS (Netherlands)

    Kroon-van Loon, P.S.

    2010-01-01

    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

  18. A Numerical Case Study of the Implications of Secondary Circulations to the Interpretation of Eddy-Covariance Measurements Over Small Lakes

    Science.gov (United States)

    Kenny, William T.; Bohrer, Gil; Morin, Timothy H.; Vogel, Chris S.; Matheny, Ashley M.; Desai, Ankur R.

    2017-11-01

    We use a large-eddy simulation (LES) to study the airflow patterns associated with a small inland lake surrounded by a forest of height one-tenth the radius of the lake. We combine LES results with scalar dispersion simulations to model potential biases in eddy-covariance measurements due to the heterogeneity of surface fluxes and vertical advection. The lake-to-forest transition can induce a non-zero vertical velocity component, affecting the interpretation of flux measurements. Significant horizontal gradients of mean CO2 concentration are generated by the forest carbon sink and lake carbon source, which are transported by local roughness-induced circulation. We simulate six hypothetical locations for flux towers along a downwind gradient at various heights, and calculate at each location the effects of both the average vertical advection and average turbulent-flux divergence of CO2. We compare our model results with an analytical footprint model to find that the footprint predicted by the analytical model is inaccurate due to the complexities of advection for our test case. Similar small lakes surrounded by forests are likely affected by these phenomena as well. We recommend specialized levelling of sonic anemometers to reduce the effects of non-zero wind components. Flux towers over small water bodies should be constructed at a distance 0.5-0.67 times the diameter of the lake to provide ample separation from the areas affected by the rotor effect of the upwind forest/lake transition and the updraft at the downwind edge. Finally, we also suggest the filtering of wind directions based on the Higgins ratio.

  19. 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).

  20. Observed and simulated submesoscale vertical pump of an anticyclonic eddy in the South China Sea

    Science.gov (United States)

    Zhong, Yisen; Bracco, Annalisa; Tian, Jiwei; Dong, Jihai; Zhao, Wei; Zhang, Zhiwei

    2017-03-01

    Oceanic mesoscale eddies with typical sizes of 30-200 km contain more than half of the kinetic energy of the ocean. With an average lifespan of several months, they are major contributors to the transport of heat, nutrients, plankton, dissolved oxygen and carbon in the ocean. Mesoscale eddies have been observed and studied over the past 50 years, nonetheless our understanding of the details of their structure remains incomplete due to lack of systematic high-resolution measurements. To bridge this gap, a survey of a mesoscale anticyclone was conducted in early 2014 in the South China Sea capturing its structure at submesoscale resolution. By modeling an anticyclone of comparable size and position at three horizontal resolutions the authors verify the resolution requirements for capturing the observed variability in dynamical quantities, and quantify the role of ageostrophic motions on the vertical transport associated with the anticyclone. Results indicate that different submesoscale processes contribute to the vertical transport depending on depth and distance from the eddy center, with frontogenesis playing a key role. Vertical transport by anticyclones cannot be reliably estimated by coarse-resolution or even mesoscale-resolving models, with important implications for global estimates of the eddy-driven vertical pumping of biophysical and chemical tracers.

  1. Carbon and Water Budgets in Multiple Wheat-Based Cropping Systems in the Inland Pacific Northwest US: Comparison of CropSyst Simulations with Eddy Covariance Measurements

    Directory of Open Access Journals (Sweden)

    Jinshu Chi

    2017-05-01

    Full Text Available Accurate carbon and water flux simulations for croplands are greatly dependent on high quality representation of management practices and meteorological conditions, which are key drivers of the surface-atmosphere exchange processes. Fourteen site-years of carbon and water fluxes were simulated using the CropSyst model over four agricultural sites in the inland Pacific Northwest (iPNW US from October 1, 2011 to September 30, 2015. Model performance for field-scale net ecosystem exchange of CO2 (NEE and evapotranspiration (ET was evaluated by comparing simulations with long-term eddy covariance measurements. The model captured the temporal variations of NEE and ET reasonably well with an overall r of 0.78 and 0.80, and a low RMSE of 1.82 g C m−2 d−1 and 0.84 mm d−1 for NEE and ET, respectively. The model slightly underestimated NEE and ET by 0.51 g C m−2 d−1 and 0.09 mm d−1, respectively. ET simulations showed better agreement with eddy covariance measurements than NEE. The model performed much better for the sites with detailed initial conditions (e.g., SOC content and management practice information (e.g., tillage type. The CropSyst results showed that the winter wheat fields could be annual net carbon sinks or close to neutral with the net ecosystem carbon balance (NECB ranging from 92 to −17 g C m−2, while the spring crop fields were net carbon sources or neutral with an annual NECB of −327 to −3 g C m−2. Simulations for the paired tillage sites showed that the no-till site resulted in lower CO2 emissions for the crop rotations of winter wheat-spring garbanzo, but had higher carbon loss into the atmosphere for spring canola compared to the conventional tillage site. Water budgets did not differ significantly between the two tillage systems. Winter wheat in the high-rainfall area had higher crop yields and water use efficiency but emitted larger amounts of CO2 into the atmosphere than in the low-rainfall area. Based on

  2. 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

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

    Science.gov (United States)

    Schmidt, A.; Klemm, O.

    2008-12-01

    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 s-1 that appear temporary during noontime and in the evening hours.

  4. UAVSAR Ocean Observations: Small Eddies, Oil Spills, and Someday Sea Ice

    Science.gov (United States)

    Holt, B.; Jones, C. E.; Minchew, B. M.; Collins, M.; Brekke, C.

    2012-12-01

    Unique observations using NASA's UAVSAR platform were obtained over small eddies in the Southern California Bight and over the Deepwater Horizon oil spill in the Gulf of Mexico in 2010. The eddy flights demonstrated the value of the onboard processing capability for enhancing targeted in situ ocean measurements with small boats and other aircraft of these dynamic ocean features as well as rapid-repeat observations of the eddies themselves, from which eddy velocity measurements were derived. The small eddies are primarily detected through the presence of natural biogenic surfactants, which suppress the small-scale wave field and serve as tracers of the current field. Over the Gulf of Mexico spill, unexpected results were obtained showing the polarimetric signatures to be impacted by the thickness of the oil itself, providing a potentially valuable method for first responders tasked with oil cleanup. Detection of these oil spill signatures was in great part possible due to the very low noise floor of the UAVSAR system. Combined these results have led to an evaluation of potential observation of these ocean features and marine slicks using polarimetric L-band for NASA's planned DESDynI-R mission and also compact polarimetry from the nearer term RADARSAT Constellation mission to be flown by the Canadian Space Agency. Finally, these results, combining the ocean and marine slick components together with other spaceborne SAR results motivate our initial exploration of the potential of detecting oil spills in the sea ice environment of the Arctic, where the low backscatter returns from sea ice, slicks, and winds are extensive and often ambiguous.

  5. Seasonal Dynamics of N2O and CO2 Emissions from a Corn Production System measured with the Eddy covariance and Chamber techniques

    Science.gov (United States)

    Iwuozo, S. A.; Hui, D.; Dennis, S.

    2013-12-01

    Agricultural Practices play a major role in the global fluxes of the greenhouse gases carbon dioxide, nitrous oxide, and methane. The use of fertilizer in Corn production has generated concerns about its contribution to global climate change. Thus, farmers and others concerned have become interested in more efficient fertilization management practice and reduced greenhouse gas emissions. To understand best management practices, in the 2012 and 2013 corn growing seasons, field experiments was conducted at Tennessee State University Agricultural Research and Demonstration Center in Nashville, TN. The study examines the seasonal variations of (N2O) and (CO2) emissions from soil as a function of six treatment that include inorganic nitrogen fertilizer, chicken litter and biochar application. The combinations were: regular URAN 32-0-0 liquid fertilizer (2 times) no till, regular URAN 32-0-0 liquid fertilizer (2 times) conventional till, multiple URAN applications (4 times) no till, Denitrification inhibitor with regular URAN application in no till, chicken litter with regular URAN application no till and URAN application with biochar in no tilled plots. Each treatment was replicated 6 times. N2O and CO2 emissions were measured using a closed chamber method after rainfall event(s), fertilizer applications or every two weeks whichever was shorter. Corresponding soil NH4+-N and NO3--N, soil temperature and moisture were also measured during gas sampling. Plant physiological and growth parameters were measured as appropriate and meteorological records were kept. N2O flux was also continuously measured in a commercial corn field using the eddy covariance (EC) technique fitted with a fast response N2O analyzer to check the N2O emissions at the large scale and compare it to the chamber method. Results obtained with the EC technique were comparable with the chamber methods. Preliminary data indicate that N2O and CO2 fluxes were significantly influenced by the agricultural

  6. Direct observations of formation and propagation of subpolar eddies into the subtropical North Atlantic

    CERN Document Server

    Bower, A S; Amrhein, D E; Lilly, J M

    2011-01-01

    Subsurface float and moored observations are presented to show for the first time the formation and propagation of anticyclonic submesoscale coherent vortices that transport relatively cold, fresh subpolar water to the interior subtropical North Atlantic. Acoustically tracked RAFOS floats released in the southward-flowing Western Boundary Current at the exit of the Labrador Sea reveal the formation of three of these eddies at the southern tip of the Grand Banks (42 N, 50 W). Using a recently developed method to detect eddies in float trajectories and estimate their kinematic properties, it was found that the eddies had average rotation periods of 5--7 days at radii of 1025 km, with mean rotation speeds of up to 0.3 m/s. One especially long-lived (5.1 months) eddy crossed under the Gulf Stream path and translated southwestward in the subtropical recirculation to at least 35 N, where it hit one of the Corner Rise Seamounts. Velocity, temperature and salinity measurements from a nine-month deployment of two moor...

  7. Air-sea energy exchanges measured by eddy covariance during a localised coral bleaching event, Heron Reef, Great Barrier Reef, Australia

    Science.gov (United States)

    MacKellar, Mellissa C.; McGowan, Hamish A.

    2010-12-01

    Despite the widely claimed association between climate change and coral bleaching, a paucity of data exists relating to exchanges of heat, moisture and momentum between the atmosphere and the reef-water surface. We present in situ measurements of reef-water-air energy exchanges made using the eddy covariance method during a summer coral bleaching event at Heron Reef, Australia. Under settled, cloud-free conditions and light winds, daily net radiation exceeded 800 W m-2, with up to 95% of the net radiation during the morning partitioned into heating the water column, substrate and benthic cover including corals. Heating was exacerbated by a mid-afternoon low tide when shallow reef flat water reached 34°C and near-bottom temperatures 33°C, exceeding the thermal tolerance of corals, causing bleaching. Results suggest that local to synoptic scale meteorology, particularly clear skies, solar heating, light winds and the timing of low tide were the primary controls on coral bleaching.

  8. Atmospheric controls on methane emissions from a subarctic bog in northern Quebec, Canada, using an open-path eddy covariance system

    Science.gov (United States)

    Rousseau, A. N.; Nadeau, D. F.; Parlange, M. B.; Coursolle, C.; Margolis, H. A.

    2012-12-01

    Wetlands are the largest natural source of atmospheric methane, a powerful greenhouse gas. Over such environments, methane fluxes are traditionally quantified with static or dynamic chambers and gas chromatography. Although inexpensive and portable, this method does not allow for continuous measurements besides not capturing the effect of atmospheric turbulence on methane emissions. An alternative is closed-path eddy covariance systems, but these usually require high power consumption and regular maintenance, both of which are difficult to supply in highly remote areas where most Canadian wetlands are found. In this study we deployed the new open-path methane analyzer (model Li-7700) from Li-Cor inc. along with surface energy budget sensors over a 60-ha subarctic bog from June to September 2012. The field site (53.7°N, 78.2°W) is located near James Bay within the La Grande Rivière watershed. This work discusses the presence of diurnal patterns in turbulent methane fluxes, and analyzes the effect of atmospheric stability, turbulence intensity and other atmospheric controls on fluxes magnitude and timing. Methane emissions are also quantified at the daily scale and compared to previously reported values over similar sites with other methods. A more technical discussion is also included in which advantages, drawbacks and optimal setup configuration of the instrument are presented.

  9. The Effect of Algal Blooms on Carbon Emissions in Western Lake Erie: An Integration of Remote Sensing and Eddy Covariance Measurements

    Directory of Open Access Journals (Sweden)

    Zutao Ouyang

    2017-01-01

    Full Text Available Lakes are important components for regulating carbon cycling within landscapes. Most lakes are regarded as CO2 sources to the atmosphere, except for a few eutrophic ones. Algal blooms are common phenomena in many eutrophic lakes and can cause many environmental stresses, yet their effects on the net exchange of CO2 (FCO2 at large spatial scales have not been adequately addressed. We integrated remote sensing and Eddy Covariance (EC technologies to investigate the effects that algal blooms have on FCO2 in the western basin of Lake Erie—a large lake infamous for these blooms. Three years of long-term EC data (2012–2014 at two sites were analyzed. We found that at both sites: (1 daily FCO2 significantly correlated with daily temperature, light, and wind speed during the algal bloom periods; (2 monthly FCO2 was negatively correlated with chlorophyll-a concentration; and (3 the year with larger algal blooms was always associated with lower carbon emissions. We concluded that large algal blooms could reduce carbon emissions in the western basin of Lake Erie. However, considering the complexity of processes within large lakes, the weak relationship we found, and the potential uncertainties that remain in our estimations of FCO2 and chlorophyll-a, we argue that additional data and analyses are needed to validate our conclusion and examine the underlying regulatory mechanisms.

  10. 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

  11. Eddy covariance measurements of ozone fluxes at 4 levels above and within a forest canopy in the Po valley (Italy)

    Science.gov (United States)

    Gerosa, Giacomo; Finco, Angelo; Marzuoli, Riccardo; Coyle, Mhairi; Nemitz, Eiko

    2015-04-01

    In June and July 2012, during the intensive field campaign of the ECLAIRE project, ozone fluxes as well as sensible heat and momentum fluxes were measured at four different levels at the Bosco Fontana site, a 26 m tall mixed oak-hornbeam forest in the Po valley (I). Each measuring level (41 m, 32 m, 24 m and 16 m) was equipped with a sonic anemometer and a fast ozone analyser, absolute ozone concentrations were measured by means of a UV photometer. Additional meteorological parameters were measured on the top and at each level and ozone concentrantions were measured at ground level (0.15 m) by another UV photometer. In order to compare measurements collected with different instruments, data were preliminary processed and the following methodology were applied: despiking, instantaneous rotations, WPL corrections, frequency loss corrections and calculation of the random error. The main aims of this field campaign were the description of the deposition processes within and above canopy and the test of the constant flux hypothesis. About this latter interesting features emerged: the conservation of the flux was valid for the momentum only outside the canopy and no conservation was observed for the sensible heat. On the contrary ozone fluxes showed a much more irregular behaviour: for the three upper levels, ozone fluxes were nearly constant in the first hours of the day while an enhancement of the fluxes was observed at 24 m. This latter fact was strictly linked with the in-canopy dynamics: a greater heating of the canopy was observed in the afternoon, leading to the formation of an inversion at this level. This inversion divided the in-canopy air volume into two layers: the lower one with a stable stratification and the upper one with a turbulent regime; as a consequence of this inversion a remarkable reduction of the ozone concentration was observed for the two lowest levels in the afternoon, when in the lowest layers ozone is consumed by NO emissions from soil. The

  12. Surface-atmosphere exchange of ammonia over peatland using QCL-based eddy-covariance measurements and inferential modeling

    DEFF Research Database (Denmark)

    Zöll, Undine; Brümmer, Christian; Schrader, Frederik

    2016-01-01

    tipping point in early spring with decreasing ammonia deposition velocities and increasingly bidirectional fluxes that occurred after the switch from dormant vegetation to CO2 uptake but was triggered by a significant weather change. While several biophysical parameters such as temperature, radiation...... as better adapted site-specific parameters in the model. Our study not only stresses the importance of high-quality measurements for studying and assessing land surface-atmosphere interactions but also demonstrates the potential of QCL spectrometers for continuous observation of reactive nitrogen species...

  13. Fate of carbon in Alaskan Landscapes Project: database for soils from eddy covariance tower sites, Delta Junction, AK

    Science.gov (United States)

    King, Stagg; Harden, Jennifer; Manies, Kristen L.; Munster, Jennie; White, L. Douglas

    2002-01-01

    Soils in Alaska, and in high latitude terrestrial ecosystems in general, contain significant amounts of organic carbon, most of which is believed to have accumulated since the start of the Holocene about 10 ky before present. High latitude soils are estimated to contain 30-40% of terrestrial soil carbon (Melillo et al., 1995; McGuire and Hobbie, 1997), or ~ 300-400 Gt C (Gt = 1015 g), which equals about half of the current atmospheric burden of carbon. Boreal forests in particular are estimated to have more soil carbon than any other terrestrial biome (Post et al., 1982; Chapin and Matthews, 1993). The relations among net primary production, soil carbon storage, recurrent fire disturbance, nutrients, the hydrologic cycle, permafrost and geomorphology are poorly understood in boreal forest. Fire disturbance has been suggested to play a key role in the interactions among the complex biogeochemical processes influencing carbon storage in boreal forest soils (Harden et al., 2000; Zhuang et al., 2002). There has been an observed increase in fire disturbance in North American boreal black spruce (Picea mariana) forests in recent decades (Murphy et al., 1999; Kasichke et al., 2000), concurrent with increases in Alaskan boreal and arctic surface temperatures and warming of permafrost (Osterkamp and Romanofsky, 1999). Understanding the role of fire in long term carbon storage and how recent changes in fire frequency and severity may influence future high latitude soil carbon pools is necessary for those working to understand or mitigate the effects of global climate change.

  14. 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 .

  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. Boat-Based Eddy Covariance Measurements of CO2 and H2O Exchange Over Amazon and Tapajos Rivers and Lakes

    Science.gov (United States)

    Miller, S.; Freitas, H.; Read, E.; Goulden, M.; Rocha, H.; Doughty, C.

    2004-12-01

    Recent reports suggest that gas evasion of carbon dioxide from the Amazon river and its tributaries to the atmosphere may play an important role in the regional carbon budget. These gas transfer rates were estimated using air-water concentration gradients and gas transfer coefficients (piston velocities) derived from floating chamber measurements. Chamber techniques have inherent uncertainties due to their effect on the near-surface air turbulence. The micrometeorological technique of eddy covariance is attractive since it is a direct measurement of gas exchange and samples over a much larger area. In August 2004, we mounted equipment on a small riverboat to measure CO2 and H2O fluxes from the rivers and lakes near Santarem, Para. The motion of the boat was recorded using an inertial measurement package combined with a GPS receiver, and subtracted from the measured winds. We experimented with both thin-wall Teflon tubing and headspace equilibrators to measure the concentration of CO2 in the water continuously. Our sampling strategy included both "under-way" measurements and stationary (moored) 24-hour measurements on the Amazon and Tapajos rivers, and lakes connected to these rivers. CO2 concentration in the Amazon river and a connected lake was 3000-5000 ppm, much higher than the Tapajos river and a connected lake (range 400-1200 ppm). The "signal-to-noise" ratio was therefore greater for fluxes measured above the Amazon. Preliminary calculations indicate fluxes of order 1-2 micromoles/m2/s over the Amazon and 0.6-1 micromoles/m2/s over the Tapajos, and the calculated gas transfer velocity agrees with existing ocean-based parameterizations.

  17. Assessments of carbon and water cycling in multiple agricultural ecosystems in the Inland Pacific Northwest using eddy covariance flux measurements and integrated basin-crop model simulation

    Science.gov (United States)

    Chi, J.; Maureira, F.; Waldo, S.; O'Keeffe, P.; Pressley, S. N.; Stockle, C. O.; Lamb, B. K.

    2014-12-01

    Local meteorology, crop management practices and site characteristics have important impacts on carbon and water cycling in agricultural ecosystems. This study focuses on carbon and water fluxes measured using eddy covariance (EC) methods and crop simulation models in the Inland Pacific Northwest (IPNW), in association with the Regional Approaches to Climate Change (REACCH) program. The agricultural ecosystem is currently challenged by higher pressure on water resources as a consequence of population growth and increasing exposure to impacts associated with different types of crop managements. In addition, future climate projections for this region show a likely increase in temperature and significant reductions in precipitation that will affect carbon and water dynamics. This new scenario requires an understanding of crop management by assessing efficient ways to face the impacts of climate change at the micrometeorological level, especially in regards to carbon and water flow. We focus on three different crop management sites. One site (LIND) under crop-fallow is situated in a low-rainfall area. The other two sites, one no-till site (CAF-NT) and one conventional tillage site (CAF-CT), are located in an area of high-rainfall with continuous cropping. In this study, we used CropSyst micro-basin model to simulate the responses in carbon and water budgets at each site. Based on the EC processed results for net ecosystem exchange (NEE) of CO2, the CAF-NT site was a carbon sink during 2013 when spring garbanzo was planted; while the paired CAF-CT site, under similar crop rotation and meteorological conditions, was a carbon source during the same period. The LIND site was also a carbon sink where winter wheat was growing during 2013. Model results for CAF-NT showed good agreement with the EC carbon and water flux measurements during 2013. Through comparisons between measurements and modeling results, both short and long term processes that influence carbon and water

  18. Impact of Intrathermocline eddies on seamount and oceanic island off Central Chile: Observation and modeling

    Science.gov (United States)

    Hormazabal, Samuel; Morales, Carmen; Cornejo, Marcela; Bento, Joaquim; Valencia, Luis; Auger, Pierre; Rodriguez, Angel; Correa, Marco; Anabalón, Valeria; Silva, Nelson

    2016-04-01

    In the Southeast Pacific, oceanographic processes that sustain the biological production necessary to maintain the ecosystems associated to seamounts and oceanic islands are still poorly understood. Recent studies suggest that the interaction of mesoscale and submesoescale eddies with oceanic islands and seamounts could be playing an important role in the time-space variability of primary production. In this work, research cruises, satellite data and Regional Ocean Modeling System (ROMS) results have been used to describe the main characteristics of intrathermocline eddies (ITE) and their impact on the Juan Fernández archipelago (JFA), off central Chile. The JFA is located off the coast of central Chile (33°S), and is composed of three main islands: Robinson Crusoe (RC), Alejandro Selkirk (AS) and Santa Clara (SC). Between the RC and AS are located the westernmost seamounts (JF6 and JF5) of the Juan Fernández archipelago. Satellite altimetry data (sea surface height from AVISO) were used to detect and track mesoscale eddies through eddy-tracking algorithm. Physical, chemical and biological parameters as temperature, salinity, dissolved oxygen and fluorescence were measured in the water column at JF5 and JF6, and along the coast off central Chile (30-40°S). Results from the research cruise exhibit the interaction between an ITE and the seamount JF6. Eddy-tracking results showed that the ITE observed at the JF6 was formed at the coast off central-southern Chile, traveled ~900 km seaward and after ~9 months reached the JF5 and JF6 region. Observations along the Chilean coast confirmed that the coast corresponds to the formation area of the observed ITE. In this region, ITEs are represented by subsurface lenses (~100 km diameter; 400 m thickness) of homogeneous salinity, nutrient rich and oxygen-poor equatorial subsurface water mass (ESSW) which is transported poleward by the Peru-Chile undercurrent in the coastal band and seaward by ITEs. The effect of ITEs on the

  19. Model selection for marginal regression analysis of longitudinal data with missing observations and covariate measurement error.

    Science.gov (United States)

    Shen, Chung-Wei; Chen, Yi-Hau

    2015-10-01

    Missing observations and covariate measurement error commonly arise in longitudinal data. However, existing methods for model selection in marginal regression analysis of longitudinal data fail to address the potential bias resulting from these issues. To tackle this problem, we propose a new model selection criterion, the Generalized Longitudinal Information Criterion, which is based on an approximately unbiased estimator for the expected quadratic error of a considered marginal model accounting for both data missingness and covariate measurement error. The simulation results reveal that the proposed method performs quite well in the presence of missing data and covariate measurement error. On the contrary, the naive procedures without taking care of such complexity in data may perform quite poorly. The proposed method is applied to data from the Taiwan Longitudinal Study on Aging to assess the relationship of depression with health and social status in the elderly, accommodating measurement error in the covariate as well as missing observations. © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  20. 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

  1. Mobile mapping and eddy covariance flux measurements of NH3 emissions from cattle feedlots with a portable laser-based open-path sensor

    Science.gov (United States)

    Tao, L.; Sun, K.; Pan, D.; Golston, L.; Stanton, L. G.; Ham, J. M.; Shonkwiler, K. B.; Nash, C.; Zondlo, M. A.

    2014-12-01

    Ammonia (NH3) is the dominant alkaline species in the atmosphere and an important compound in the global nitrogen cycle. There is a large uncertainty in NH3 emission inventory from agriculture, which is the largest source of NH3, including livestock farming and fertilizer applications. In recent years, a quantum cascade laser (QCL)-based open-path sensor has been developed to provide high-resolution, fast-response and high-sensitivity NH3 measurements. It has a detection limit of 150 pptv with a sample rate up to 20 Hz. This sensor has been integrated into a mobile platform mounted on the roof of a car to perform measurement of multiple trace gases. We have also used the sensor for eddy covariance (EC) flux measurements. The mobile sensing method provides high spatial resolution and fast mapping of measured gases. Meanwhile, the EC flux method offers accurate flux measurements and resolves the diurnal variability of NH3emissions. During the DISCOVER-AQ and FRAPPÉ field campaigns in 2014, this mobile platform was used to study NH3 emissions from cattle feedlot near Fort Morgan, Colorado. This specific feedlot was mapped multiple times in different days to study the variability of its plume characteristics. At the same time, we set up another open-path NH3 sensor with LICOR open-path sensors to perform EC flux measurements of NH3, CH4 and CO2 simultaneously in the same cattle feedlot as shown in Fig. 1. NH3/CH4 emission flux ratio show a strong temperature dependence from EC flux measurements. The median value of measured NH3 and CH4 emission flux ratio is 0.60 ppmv/ppmv. In contrast, the median value of ΔNH3/ΔCH4 ratios measured from mobile platform is 0.53 ppmv/ppmv for the same farm. The combination of mobile mapping and EC flux measurements with the same open-path sensors greatly improves understanding of NH3 emissions both spatially and temporally.

  2. An analysis on the influence of spatial scales on sensible heat fluxes in the north Tibetan Plateau based on Eddy covariance and large aperture scintillometer data

    Science.gov (United States)

    Sun, Genhou; Hu, Zeyong; Sun, Fanglin; Wang, Jiemin; Xie, Zhipeng; Lin, Yun; Huang, Fangfang

    2017-08-01

    The influence of spatial scales on surface fluxes is an interesting but not fully investigated question. This paper presents an analysis on the influence of spatial scales on surface fluxes in the north Tibetan Plateau based on eddy covariance (EC) and large aperture scintillometer (LAS) data at site Nagqu/BJ, combined with the land surface temperature (LST) and normalized difference vegetation index (NDVI) of moderate-resolution imaging spectroradiometer (MODIS). The analysis shows that sensible heat fluxes calculated with LAS data (H_LAS) agree reasonably well with sensible heat fluxes calculated with EC data (H_EC) in the rain and dry seasons. The difference in their footprints due to the wind direction is an important reason for the differences in H_EC and H_LAS. The H_LAS are statistically more consistent with H_EC when their footprints overlap than when their footprints do not. A detailed analysis on H_EC and H_LAS changes with net radiation and wind direction in rain and dry season indicates that the spatial heterogeneity in net radiation created by clouds contributes greatly to the differences in H_EC and H_LAS in short-term variations. A significant relationship between the difference in footprint-weighted averages of LST and difference in H_EC and H_LAS suggests that the spatial heterogeneity in LST at two spatial scales is a reason for the differences in H_EC and H_LAS and that LST has a positive correlation with the differences in H_EC and H_LAS. A significant relationship between the footprint-weighted averages of NDVI and the ratio of sensible heat fluxes at two spatial scales to net radiation (H/Rn) in the rain season supports the analysis that the spatial heterogeneity in canopy at two spatial scales is another reason for differences in H_EC and H_LAS and that canopy has a negative correlation with (H/Rn). An analysis on the influence of the difference in aerodynamic roughness lengths at two spatial scales on sensible heat fluxes shows that the

  3. Lateral eddy diffusivity estimates from simulated and observed drifter trajectories: a case study for the Agulhas Current system

    Science.gov (United States)

    Rühs, Siren; Zhurbas, Victor; Durgadoo, Jonathan V.; Biastoch, Arne

    2017-04-01

    The Lagrangian description of fluid motion by sets of individual particle trajectories is extensively used to characterize connectivity between distinct oceanic locations. One important factor influencing the connectivity is the average rate of particle dispersal, generally quantified as Lagrangian diffusivity. In addition to Lagrangian observing programs, Lagrangian analyses are performed by advecting particles with the simulated flow field of ocean general circulation models (OGCMs). However, depending on the spatio-temporal model resolution, not all scale-dependent processes are explicitly resolved in the simulated velocity fields. Consequently, the dispersal of advective Lagrangian trajectories has been assumed not to be sufficiently diffusive compared to observed particle spreading. In this study we present a detailed analysis of the spatially variable lateral eddy diffusivity characteristics of advective drifter trajectories simulated with realistically forced OGCMs and compare them with estimates based on observed drifter trajectories. The extended Agulhas Current system around South Africa, known for its intricate mesoscale dynamics, serves as a test case. We show that a state-of-the-art eddy-resolving OGCM indeed features theoretically derived dispersion characteristics for diffusive regimes and realistically represents Lagrangian eddy diffusivity characteristics obtained from observed surface drifter trajectories. The estimates for the maximum and asymptotic lateral single-particle eddy diffusivities obtained from the observed and simulated drifter trajectories show a good agreement in their spatial pattern and magnitude. We further assess the sensitivity of the simulated lateral eddy diffusivity estimates to the temporal and lateral OGCM output resolution and examine the impact of the different eddy diffusivity characteristics on the Lagrangian connectivity between the Indian Ocean and the South Atlantic.

  4. The Global Mesoscale Eddy Available Potential Energy Field in Models and Observations

    Science.gov (United States)

    Luecke, C. A.; Arbic, B. K.; Bassette, S. L.; Richman, J. G.; Shriver, J. F.; Alford, M. H.; Smedstad, O. M.; Timko, P. G.; Trossman, D. S.; Wallcraft, A. J.

    2017-11-01

    Global maps of the mesoscale eddy available potential energy (EAPE) field at a depth of 500 m are created using potential density anomalies in a high-resolution 1/12.5° global ocean model. Maps made from both a free-running simulation and a data-assimilative reanalysis of the HYbrid Coordinate Ocean Model (HYCOM) are compared with maps made by other researchers from density anomalies in Argo profiles. The HYCOM and Argo maps display similar features, especially in the dominance of western boundary currents. The reanalysis maps match the Argo maps more closely, demonstrating the added value of data assimilation. Global averages of the simulation, reanalysis, and Argo EAPE all agree to within about 10%. The model and Argo EAPE fields are compared to EAPE computed from temperature anomalies in a data set of "moored historical observations" (MHO) in conjunction with buoyancy frequencies computed from a global climatology. The MHO data set allows for an estimate of the EAPE in high-frequency motions that is aliased into the Argo EAPE values. At MHO locations, 15-32% of the EAPE in the Argo estimates is due to aliased motions having periods of 10 days or less. Spatial averages of EAPE in HYCOM, Argo, and MHO data agree to within 50% at MHO locations, with both model estimates lying within error bars observations. Analysis of the EAPE field in an idealized model, in conjunction with published theory, suggests that much of the scatter seen in comparisons of different EAPE estimates is to be expected given the chaotic, unpredictable nature of mesoscale eddies.

  5. Covariance approximation for fast and accurate computation of channelized Hotelling observer statistics

    Science.gov (United States)

    Bonetto, P.; Qi, Jinyi; Leahy, R. M.

    2000-08-01

    Describes a method for computing linear observer statistics for maximum a posteriori (MAP) reconstructions of PET images. The method is based on a theoretical approximation for the mean and covariance of MAP reconstructions. In particular, the authors derive here a closed form for the channelized Hotelling observer (CHO) statistic applied to 2D MAP images. The theoretical analysis models both the Poission statistics of PET data and the inhomogeneity of tracer uptake. The authors show reasonably good correspondence between these theoretical results and Monte Carlo studies. The accuracy and low computational cost of the approximation allow the authors to analyze the observer performance over a wide range of operating conditions and parameter settings for the MAP reconstruction algorithm.

  6. Significant Atmospheric Boundary Layer Change Observed above an Agulhas Current Warm Cored Eddy

    Directory of Open Access Journals (Sweden)

    C. Messager

    2016-01-01

    Full Text Available The air-sea impact of a warm cored eddy ejected from the Agulhas Retroflection region south of Africa was assessed through both ocean and atmospheric profiling measurements during the austral summer. The presence of the eddy causes dramatic atmospheric boundary layer deepening, exceeding what was measured previously over such a feature in the region. This deepening seems mainly due to the turbulent heat flux anomaly above the warm eddy inducing extensive deep and persistent changes in the atmospheric boundary layer thermodynamics. The loss of heat by turbulent processes suggests that this kind of oceanic feature is an important and persistent source of heat for the atmosphere.

  7. 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.

  8. Constraining Daily-To-Annual Carbon Budgets in a Brackish Tidal Marsh in the San Francisco Bay Delta: Insights on Methane and Carbon Dioxide Fluxes from Eddy Covariance Measurements

    Science.gov (United States)

    Saraceno, J.; Anderson, F. E.; Knox, S.; Windham-Myers, L.; Bergamaschi, B. A.

    2016-12-01

    Carbon cycling in coastal wetlands is difficult to measure and model due to extremely dynamic atmospheric (vertical) and hydrologic (lateral) fluxes, as well as sensitivities to dynamic land- and ocean-based drivers. Whereas atmospheric carbon is sequestered in accreted carbon stocks over millennia to maintain balance with sea level rise, annual or seasonal carbon fluxes from tidal wetlands can become net negative or net positive, as key drivers of carbon cycling, such as inundation area, soil and air temperature and salinity change over short time periods. Few studies have documented the interannual variability in the net ecosystem carbon balance for tidal-driven ecosystems. Using the eddy covariance technique, we present 2.5 years (March 2014-September 2016) of net ecosystem exchanges (NEE) for CO2 and CH4 from a historic wetland (the National Estuarine Research Reserve's Rush Ranch) in the Suisun Marsh complex of San Francisco Bay, California, where salinity ranges from oligohaline to mesohaline. Preliminary estimates show that daily rates of CO2 NEE were approximately -15 gC m-2 d-1 during the peak growing season in the summer to +10 gC m-2 d-1 during the winter months. CH4 emissions, ranged from 0 to +30 mgC m-2 d-1, a small fraction of observed rates from neighboring freshwater marshes. We have also found that using standard parameters (e.g. temperature and radiation) in an artificial neural network approach to gap-fill missing fluxes and estimate random error uncertainty were insufficient, suggesting that daily and seasonal shifts in salinity, water levels, and plant community phenology may help to reduce uncertainty in estimated values of both CO2 and CH4 fluxes. An additional aspect of this study is to investigate the significance of carbon exported through tidal exchanges, especially considering that regional estimates of carbon accretion in the soils to be only 100 gC m-2. Here we will estimate the aquatic carbon flux using proxies for dissolved

  9. State-dependent errors in a land surface model across biomes inferred from eddy covariance observations on multiple timescales

    NARCIS (Netherlands)

    Wang, T.; Brender, P.; Ciais, P.; Piao, S.; Mahecha, M.D.; Chevallier, F.; Reichstein, M.; Ottle, C.; Maignan, F.; Arain, A.; Bohrer, G.; Cescatti, A.; Kiely, G.; Law, B.E.; Lutz, M.; Montagnani, L.; Moors, E.J.

    2012-01-01

    Characterization of state-dependent model biases in land surface models can highlight model deficiencies, and provide new insights into model development. In this study, artificial neural networks (ANNs) are used to estimate the state-dependent biases of a land surface model (ORCHIDEE: ORganising

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

    Science.gov (United States)

    Jingfeng Xiaoa; Qianlai Zhuang; Beverly E. Law; Dennis D. Baldocchi; Jiquan Chen; al. et.

    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...

  11. Novel Deployment of Mobile Eddy Covariance Tower Observations Across Variations in the Built Environment in a Desert Urban Area

    Science.gov (United States)

    2015-11-03

    climate of Phoenix, AZ and Mesa, AZ is classified as a hot arid subtropical desert (Kӧppen climate classification BWh). Average annual temperature is 75...PL-ECT, which are representative of a semi - arid to desert environment because sensible heat fluxes are high. Average B is 0.53 at TG-ECT, which means...to a Local Climate Zone (LCZ) to qualitatively describe its characteristics. PV-ECT associates with LCZ C, which has a zone function of natural

  12. Satellite-observed variability of phytoplankton size classes associated with a cold eddy in the South China Sea.

    Science.gov (United States)

    Lin, Junfang; Cao, Wenxi; Wang, Guifen; Hu, Shuibo

    2014-06-15

    Ocean-color remote sensing has been used as a tool to detect phytoplankton size classes (PSCs). In this study, a three-component model of PSC was reparameterized using seven years of pigment measurements acquired in the South China Sea (SCS). The model was then used to infer PSC in a cyclonic eddy which was observed west of Luzon Island from SeaWiFS chlorophyll-a (chla) and sea-surface height anomaly (SSHA) products. Enhanced productivity and a shift in the PSC were observed, which were likely due to upwelling of nutrient-rich water into the euphotic zone. The supply of nutrients promoted the growth of larger cells (micro- and nanoplankton), and the PSC shifted to greater sizes. However, the picoplankton were still important and contributed ∼48% to total chla concentration. In addition, PSC time series revealed a lag period of about three weeks between maximum eddy intensity and maximum chlorophyll, which may have been related to phytoplankton growth rate and duration of eddy intensity. Copyright © 2014 Elsevier Ltd. All rights reserved.

  13. Investigation of natural gas plume dispersion using mobile observations and large eddy simulations

    Science.gov (United States)

    Caulton, Dana R.; Li, Qi; Golston, Levi; Pan, Da; Bou-Zeid, Elie; Fitts, Jeff; Lane, Haley; Lu, Jessica; Zondlo, Mark A.

    2016-04-01

    Recent work suggests the distribution of methane emissions from fracking operations is skewed with a small percentage of emitters contributing a large proportion of the total emissions. These sites are known as 'super-emitters.' The Marcellus shale, the most productive natural gas shale field in the United States, has received less intense focus for well-level emissions and is here used as a test site for targeted analysis between current standard trace-gas advection practices and possible improvements via advanced modeling techniques. The Marcellus shale is topographically complex, making traditional techniques difficult to implement and evaluate. For many ground based mobile studies, the inverse Gaussian plume method (IGM) is used to produce emission rates. This method is best applied to well-mixed plumes from strong point sources and may not currently be well-suited for use with disperse weak sources, short-time frame measurements or data collected in complex terrain. To assess the quality of IGM results and to improve source-strength estimations, a robust study that combines observational data with a hierarchy of models of increasing complexity will be presented. The field test sites were sampled with multiple passes using a mobile lab as well as a stationary tower. This mobile lab includes a Garmin GPS unit, Vaisala weather station (WTX520), LICOR 7700 CH4 open path sensor and LICOR 7500 CO2/H2O open path sensor. The sampling tower was constructed consisting of a Metek uSonic-3 Class A sonic anemometer, and an additional LICOR 7700 and 7500. Data were recorded for at least one hour at these sites. The modeling will focus on large eddy simulations (LES) of the wind and CH4 concentration fields for these test sites. The LES model used 2 m horizontal and 1 m vertical resolution and was integrated in time for 45 min for various test sites under stable, neutral and unstable conditions. It is here considered as the reference to which various IGM approaches can be

  14. Observed air-sea interactions in tropical cyclone Isaac over Loop Current mesoscale eddy features

    Science.gov (United States)

    Jaimes, Benjamin; Shay, Lynn K.; Brewster, Jodi K.

    2016-12-01

    Air-sea interactions during the intensification of tropical storm Isaac (2012) into a hurricane, over warm oceanic mesoscale eddy features, are investigated using airborne oceanographic and atmospheric profilers. Understanding these complex interactions is critical to correctly evaluating and predicting storm effects on marine and coastal facilities in the Gulf of Mexico, wind-driven mixing and transport of suspended matter throughout the water column, and oceanic feedbacks on storm intensity. Isaac strengthened as it moved over a Loop Current warm-core eddy (WCE) where sea surface warming (positive feedback mechanism) of ∼0.5 °C was measured over a 12-h interval. Enhanced bulk enthalpy fluxes were estimated during this intensification stage due to an increase in moisture disequilibrium between the ocean and atmosphere. These results support the hypothesis that enhanced buoyant forcing from the ocean is an important intensification mechanism in tropical cyclones over warm oceanic mesoscale eddy features. Larger values in equivalent potential temperature (θE = 365   ∘K) were measured inside the hurricane boundary layer (HBL) over the WCE, where the vertical shear in horizontal currents (δV) remained stable and the ensuing cooling vertical mixing was negligible; smaller values in θE (355   ∘K) were measured over an oceanic frontal cyclone, where vertical mixing and upper-ocean cooling were more intense due to instability development in δV . Thus, correctly representing oceanic mesoscale eddy features in coupled numerical models is important to accurately reproduce oceanic responses to tropical cyclone forcing, as well as the contrasting thermodynamic forcing of the HBL that often causes storm intensity fluctuations over these warm oceanic regimes.

  15. Submesoscale Frontal Vortices and Eddies along the East Australian Current observed by HF Radars

    Science.gov (United States)

    Roughan, M.; Schaeffer, A.; Mantovanelli, A.; Gramoulle, A.

    2016-02-01

    The East Australian Current (EAC) is the major feature of the ocean circulation along south-eastern Australia, influencing the shelf circulation, water temperature, phytoplankton to fish distribution and abundance and the regional climate. While the shedding of mesoscale warm core eddies at the EAC separation of the coast is relatively well understood, little is known about its sub-mesoscale frontal instabilities. More than 1 year of surface currents from HF Radars, in conjunction with mooring measurements, satellite sea surface temperature and ocean color, highlight for the first time the occurrence and propagation of meanders along the inshore edge of the EAC. These instabilities are mostly barotropic and migrate poleward as far as 500 km south, with advection speeds of 0.3 m/s. Investigation into the flow field kinematics shows high Rossby numbers and a strong impact on horizontal divergence and particle dispersion. Wind stress appears to influence the fate of these ageostrophic meanders, their growth and potential evolution into cyclonic cold core eddies. Such coherent structures are a major mechanism for the transport and entrainment of nutrient rich coastal waters, impacting physical and biological connectivity over large distances.

  16. Volatile organic compounds sources and sinks in a wheat canopy. Analysis based on combined eddy-covariance fluxes, in-canopy profiles and chamber measurements with a PTR-TOF-Qi-MS

    Science.gov (United States)

    Loubet, Benjamin; Gonzaga, Lais; Buysse, Pauline; Ciuraru, Raluca; Lafouge, Florence; Decuq, Céline; Zurfluh, Olivier; Fortineau, Alain; Fanucci, Olivier; Sarda-Esteve, Roland; Zannoni, Nora; Truong, Francois; Boissard, Christophe; Gros, Valérie

    2017-04-01

    Volatile organic compounds (VOC) are essential drivers of atmospheric chemistry. Many VOCs are emitted from and deposited to ecosystems. While forests and grasslands have already been substantially studied, exchanges of VOCs with crops are less known, although these ecosystems represent more than 50% of the surface in France. In this study, we analyze sources and sinks of VOCs in a wheat field (at the ICOS FR-GRI site near Paris) at anthesis based on measurements of fluxes, concentration profiles and branch chambers. The VOCs were measured using a PTR-TOF-Qi-MS (where Qi stands for Quad Ion guide). Air was successively sampled through lines located at different heights within and above the canopy, of which one was used for Eddy Covariance and located near a sonic anemometer. Additional measurements included the standard ICOS meteorological data as well as leaf area index profiles and photosynthesis curves at several heights in the canopy. We report fluxes and profiles for more than 500 VOCs. The deposition velocities of depositing compounds are compared to the maximum exchange velocity and the ozone deposition velocity. The sources and sinks location and magnitude are evaluated by inverse Lagrangian modelling assuming no reaction and simple reaction schemes in the canopy. The sources and sinks of VOC in the canopy are interpreted in terms crop phenology and the potential for reaction with ozone and NOx is evaluated. This study takes place in the ADEME CORTEA COV3ER French project (http://www6.inra.fr/cov3er).

  17. Modelling Amazonian forest eddy covariance data: a comparison of big leaf versus sun/shade models for the C-14 tower at Manaus I. Canopy photosynthesis Modelagem de dados de covariância de fluxo turbulento na floresta amazônica: uma comparação entre os modelos "folha-grande" e "sol/sombra" para a torre C-14 em Manaus. I. Fotossíntese do dossel

    Directory of Open Access Journals (Sweden)

    Lina Mercado

    2006-03-01

    Full Text Available In this study, we concentrate on modelling gross primary productivity using two simple approaches to simulate canopy photosynthesis: "big leaf" and "sun/shade" models. Two approaches for calibration are used: scaling up of canopy photosynthetic parameters from the leaf to the canopy level and fitting canopy biochemistry to eddy covariance fluxes. Validation of the models is achieved by using eddy covariance data from the LBA site C14. Comparing the performance of both models we conclude that numerically (in terms of goodness of fit and qualitatively, (in terms of residual response to different environmental variables sun/shade does a better job. Compared to the sun/shade model, the big leaf model shows a lower goodness of fit and fails to respond to variations in the diffuse fraction, also having skewed responses to temperature and VPD. The separate treatment of sun and shade leaves in combination with the separation of the incoming light into direct beam and diffuse make sun/shade a strong modelling tool that catches more of the observed variability in canopy fluxes as measured by eddy covariance. In conclusion, the sun/shade approach is a relatively simple and effective tool for modelling photosynthetic carbon uptake that could be easily included in many terrestrial carbon models.Neste trabalho foi modelada a produtividade primária bruta através de duas técnicas simples para simular a fotossíntese no dossel: os modelos "folha-grande" e "sol/sombra". Para calibrar os modelos foram utilizados os parâmetros de fotossíntese da folha, estendidos à escala do dossel e um ajuste da bioquímica do dossel em relação à covariância de vórtices turbulentos. Os modelos foram validados com as medidas feitas através da técnica de covariância de vórtices turbulentos da estação C14 do projeto LBA. Ao comparar o desempenho de ambos os modelos, conclui-se que o modelo "sol/sombra" apresenta melhores resultados numericamente (do ponto de vista da

  18. Detecting the fingerprints of complex land management practices in a tallgrass prairie site using phenocam and satellite images, and the eddy covariance technique

    Science.gov (United States)

    Burning, grazing, and baling (hay harvesting) are common management practices for tallgrass prairie. However, the impacts of these management practices on grassland phenology and carbon uptake are not well understood. Utilizing multiple observations to detect fingerprints of various management pract...

  19. Detection of subsurface-intensified eddies from observations of the sea-surface: a case study for Mediterranean Water Eddies in a long-term high-resolution simulation

    Science.gov (United States)

    Ciani, Daniele; Carton, Xavier; Barbosa Aguiar, Ana Claudia; Peliz, Alvaro; Bashmachnikov, Igor; Ienna, Federico; Chapron, Bertrand

    2017-04-01

    Subsurface-intensified eddies are ubiquitous in the world ocean. They can be generated by exchanges of water masses between semi-enclosed evaporation basins and the open ocean or by deep convection. Past and recent studies have shown that these eddies are carriers of large amounts of heat and salt, that they are coherent over inter-annual timescales and that they can migrate for several thousands of miles from their origination areas towards the open ocean. Hence, subsurface-intensified eddies can influence the three-dimensional distribution of oceanic tracers at global scale. The synoptic knowledge of the eddies positions and mean pathways is then crucial for evaluating temperature and salinity budgets in the world ocean. At present day, satellite sensors constitute the ideal tool for the synoptic and global scale observations of the ocean. Since they only provide informations on the oceanic surface, we characterized the signatures that subsurface eddies generate at the sea-surface, to determine the extent to which they can be isolated from the surrounding surface turbulence and be considered as a trace of an underlying eddy. We studied the surface signature of subsurface-intensified anticyclones (Mediterranean Water Eddies - Meddies) in a realistic, long-term (20 years) and high resolution simulation (dx = 3 km) based on the ROMS model. The novelty and advantage of this approach is given by the simultaneous availability of the full 3D eddies characteristics, the ones of the background ocean and of the sea-surface (in terms of sea-surface height, temperature and salinity). This also allowed us to speculate on a synergy between different satellite observations for the automatic detection of subsurface eddies from space. The along trajectory properties and surface signatures of more than 90 long-lived Meddies were analyzed. We showed that the Meddies constantly generate positive anomalies in sea-surface height and that these anomalies are principally related to the

  20. A Multi-Year Comparison of No-Till Versus Conventional-Till Effects on the Carbon Balance in a Corn/Soybean Agro-Ecosystem Using Eddy Covariance

    Science.gov (United States)

    Joo, E.; Slattery, R.; Meyers, T. P.; Bernacchi, C.

    2015-12-01

    Dramatic increases in atmospheric CO2 concentrations since the industrial revolution are in large part due to the release of carbon previously stored in the soil. No-till strategies have been proposed as a means to mitigate agricultural contributions to atmospheric carbon by decreasing emissions and sequestering carbon in agricultural soils while increasing water use efficiency and soil quality. However, the effects of no-till versus conventional-till practices on carbon sequestration often vary due to difficulty in quantifying soil carbon as soil properties change with management. Eddy covariance (EC) offers a more accurate method of continuously measuring the total carbon budget and does so without relying on physical soil carbon measurements. The majority of agricultural land in the Midwestern United States is farmed using the corn/soybean rotation, making it an ideal agro-ecosystem to examine the potential of adopting no-till practices on carbon and water balances. In this study, we use EC to compare carbon and water fluxes between continuous no-till and conventional-till corn/soybean sites over several years in east central Illinois. This allows the determination and comparison of 1) net ecosystem exchange (NEE) and net biome production (NEE after accounting for grain usage); 2) water use efficiency; and 3) response to climatic variation, both at short and long time scales, between the two tillage systems. We hypothesize that both carbon uptake and water use efficiency will improve with no-till practices, which in turn will improve crop responses to environmental factors such as drought and heat stress.

  1. Bayesian Inference for Multivariate Meta-regression with a Partially Observed Within-Study Sample Covariance Matrix

    Science.gov (United States)

    Yao, Hui; Kim, Sungduk; Chen, Ming-Hui; Ibrahim, Joseph G.; Shah, Arvind K.; Lin, Jianxin

    2015-01-01

    Summary Multivariate meta-regression models are commonly used in settings where the response variable is naturally multi-dimensional. Such settings are common in cardiovascular and diabetes studies where the goal is to study cholesterol levels once a certain medication is given. In this setting, the natural multivariate endpoint is Low Density Lipoprotein Cholesterol (LDL-C), High Density Lipoprotein Cholesterol (HDL-C), and Triglycerides (TG) (LDL-C, HDL-C, TG). In this paper, we examine study level (aggregate) multivariate meta-data from 26 Merck sponsored double-blind, randomized, active or placebo-controlled clinical trials on adult patients with primary hypercholesterolemia. Our goal is to develop a methodology for carrying out Bayesian inference for multivariate meta-regression models with study level data when the within-study sample covariance matrix S for the multivariate response data is partially observed. Specifically, the proposed methodology is based on postulating a multivariate random effects regression model with an unknown within-study covariance matrix Σ in which we treat the within-study sample correlations as missing data, the standard deviations of the within-study sample covariance matrix S are assumed observed, and given Σ, S follows a Wishart distribution. Thus, we treat the off-diagonal elements of S as missing data, and these missing elements are sampled from the appropriate full conditional distribution in a Markov chain Monte Carlo (MCMC) sampling scheme via a novel transformation based on partial correlations. We further propose several structures (models) for Σ, which allow for borrowing strength across different treatment arms and trials. The proposed methodology is assessed using simulated as well as real data, and the results are shown to be quite promising. PMID:26257452

  2. 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

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

    NARCIS (Netherlands)

    Beer, C.; Veenendaal, E.M.

    2010-01-01

    Terrestrial gross primary production (GPP) is the largest global CO2 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

  4. The use of disjunct eddy sampling methods for the determination of ecosystem level fluxes of trace gases

    Directory of Open Access Journals (Sweden)

    A. A. Turnipseed

    2009-02-01

    Full Text Available The concept of disjunct eddy sampling (DES for use in measuring ecosystem-level micrometeorological fluxes is re-examined. The governing equations are discussed as well as other practical considerations and guidelines concerning this sampling method as it is applied to either the disjunct eddy covariance (DEC or disjunct eddy accumulation (DEA techniques. A disjunct eddy sampling system was constructed that could either be combined with relatively slow sensors (response time of 2 to 40 s to measure fluxes using DEC, or could also be used to accumulate samples in stable reservoirs for later laboratory analysis (DEA technique. Both the DEC and DEA modes of this sampler were tested against conventional eddy covariance (EC for fluxes of either CO2 (DEC or isoprene (DEA. Good agreement in both modes was observed relative to the EC systems. However, the uncertainty in a single DEA flux measurement was considerable (~40% due to both the reduced statistical sampling and the analytical precision of the concentration difference measurements. We have also re-investigated the effects of nonzero mean vertical wind velocity on accumulation techniques as it relates to our DEA measurements. Despite the higher uncertainty, disjunct eddy sampling can provide an alternative technique to eddy covariance for determining ecosystem-level fluxes for species where fast sensors do not currently exist.

  5. The use of disjunct eddy sampling methods for the determination of ecosystem level fluxes of trace gases

    Science.gov (United States)

    Turnipseed, A. A.; Pressley, S. N.; Karl, T.; Lamb, B.; Nemitz, E.; Allwine, E.; Cooper, W. A.; Shertz, S.; Guenther, A. B.

    2009-02-01

    The concept of disjunct eddy sampling (DES) for use in measuring ecosystem-level micrometeorological fluxes is re-examined. The governing equations are discussed as well as other practical considerations and guidelines concerning this sampling method as it is applied to either the disjunct eddy covariance (DEC) or disjunct eddy accumulation (DEA) techniques. A disjunct eddy sampling system was constructed that could either be combined with relatively slow sensors (response time of 2 to 40 s) to measure fluxes using DEC, or could also be used to accumulate samples in stable reservoirs for later laboratory analysis (DEA technique). Both the DEC and DEA modes of this sampler were tested against conventional eddy covariance (EC) for fluxes of either CO2 (DEC) or isoprene (DEA). Good agreement in both modes was observed relative to the EC systems. However, the uncertainty in a single DEA flux measurement was considerable (~40%) due to both the reduced statistical sampling and the analytical precision of the concentration difference measurements. We have also re-investigated the effects of nonzero mean vertical wind velocity on accumulation techniques as it relates to our DEA measurements. Despite the higher uncertainty, disjunct eddy sampling can provide an alternative technique to eddy covariance for determining ecosystem-level fluxes for species where fast sensors do not currently exist.

  6. Latent/sensible heat and water stress retrieval performances of the SPARSE dual-source energy balance model over irrigated and rainfed agricultural crops using eddy covariance, sap flow and extra-large aperture scintillometer data

    Science.gov (United States)

    Boulet, G.; Bahir, M.; Delogu, E.; Mougenot, B.; Bousbih, S.; Raimbault, B.; Fanise, P.; Saadi, S.; Chebbi, W.; Lili-Chabaane, Z.; Rivalland, V.; Lagouarde, J. P.; Olioso, A.

    2016-12-01

    Evapotranspiration is an important component of the water cycle, especially in semi-arid lands. Its quantification is crucial for a sustainable management of scarce water resources. Evapotranspiration at large scales is often estimated through integrated water balance models forced by distributed meteorological forcing. This forcing includes irrigation inputs from surface and groundwater uptakes. Those amounts are largely unknown at most scales, including the regional scale, i.e. the working scale of institutional stakeholders. An alternative way to quantify evapotranspiration is to exploit the available surface temperature data from remote sensing as a signature of the surface energy balance. This work evaluates the SPARSE model (http://www.hydrol-earth-syst-sci.net/19/4653/2015/) forced by in-situ or MODIS surface temperatures. SPARSE is built on the same rationale as the widely used TSEB model. Its new features involve state-of-the art resistance formulations as well as the possibility to run the model in two modes: a retrieval mode to simulate evaporation and transpiration from TIR data, and a prescribed mode which simulates potential evaporation and transpiration rates. This enables to simulate not only actual fluxes but also surface and plant water stress. It ensures also an increased robustness through bounding the actual fluxes by the corresponding potential rates. A wide range of flux datasets acquired over rainfed and irrigated crops in temperate, Mediterranean and semi-arid regions are used to check the robustness of both stress levels and evapotranspiration retrievals. Two flux datasets are relevant for assessing the performance of the MODIS scale retrievals. One is an extensive rainfed oliveyard with very low (7%) vegetation cover. For this site, evapotranspiration from eddy covariance (EC) as well as transpiration from sapflow measurements are available to check the accuracy of evaporation and transpiration components computed by SPARSE. A second

  7. Observed Covariations of Aerosol Optical Depth and Cloud Cover in Extratropical Cyclones

    Science.gov (United States)

    Naud, Catherine M.; Posselt, Derek J.; van den Heever, Susan C.

    2017-10-01

    Using NASA Moderate Resolution Imaging Spectroradiometer aerosol optical depth and total cloud cover retrievals, CloudSat-CALIPSO cloud profiles, and a database of extratropical cyclones and frontal boundary locations, relationships between changes in aerosol optical depth and cloud cover in extratropical cyclones occurring over Northern Hemisphere oceans are examined. A reanalysis data set is used to constrain column water vapor and ascent strength in the cyclones in an attempt to distinguish their impact on cloud cover from the effect of changes in aerosol loading. The results suggest that high aerosol optical depth cyclones exhibit larger middle- and high-level cloud cover than their low aerosol optical depth counterparts. However, the opposite behavior is found for low-level cloud cover. These relationships are found to depend on the large-scale environment, in particular the column water vapor and vertical motion. Despite the inability of the observations to provide a causal physical link between aerosol load and cloud cover, these results can help to constrain and evaluate model simulations.

  8. Observational Estimates of the Horizontal Eddy Diffusivity and Mixing Length in the Low-Level Region of Intense Hurricanes

    Science.gov (United States)

    2011-11-01

    Hurricane, typhoon , boundary layer, turbulent fluxes, spectra, horizontal eddy 58 diffusivity, horizontal mixing length 59 60 61 62 3 1...slightly weakening on August 29, David continued moving west-northwest, 132 and became a Category 5 hurricane in the northeast Caribbean Sea. The peak...is nearly twice as large as that found in the 278 outer core region. Overall, it is found that the eddy diffusivity tends to increase with increasing

  9. Large-eddy simulation of mesoscale dynamics and entrainment around a pocket of open cells observed in VOCALS-REx RF06

    OpenAIRE

    Berner, A. H.; Bretherton, C. S.; Wood, R.

    2011-01-01

    Large-eddy simulations of a pocket of open cells (POC) based on VOCALS Regional Experiment (REx) NSF C-130 Research Flight 06 are analyzed and compared with aircraft observations. A doubly-periodic domain 192 km × 24 km with 125 m horizontal and 5 m vertical grid spacing near the capping inversion is used. The POC is realized in the model as a fixed 96 km wide region of reduced cloud droplet number concentration (Nc) based on observed values; initiali...

  10. Assessment and simulation of global terrestrial latent heat flux by synthesis of CMIP5 climate models and surface eddy covariance observations

    Science.gov (United States)

    Yunjun Yao; Shunlin Liang; Xianglan Li; Shaomin Liu; Jiquan Chen; Xiaotong Zhang; Kun Jia; Bo Jiang; Xianhong Xie; Simon Munier; Meng Liu; Jian Yu; Anders Lindroth; Andrej Varlagin; Antonio Raschi; Asko Noormets; Casimiro Pio; Georg Wohlfahrt; Ge Sun; Jean-Christophe Domec; Leonardo Montagnani; Magnus Lund; Moors Eddy; Peter D. Blanken; Thomas Grunwald; Sebastian Wolf; Vincenzo Magliulo

    2016-01-01

    The latent heat flux (LE) between the terrestrial biosphere and atmosphere is a major driver of the globalhydrological cycle. In this study, we evaluated LE simulations by 45 general circulation models (GCMs)in the Coupled Model Intercomparison Project Phase 5 (CMIP5) by a comparison...

  11. Complex Covariance

    Directory of Open Access Journals (Sweden)

    Frieder Kleefeld

    2013-01-01

    Full Text Available According to some generalized correspondence principle the classical limit of a non-Hermitian quantum theory describing quantum degrees of freedom is expected to be the well known classical mechanics of classical degrees of freedom in the complex phase space, i.e., some phase space spanned by complex-valued space and momentum coordinates. As special relativity was developed by Einstein merely for real-valued space-time and four-momentum, we will try to understand how special relativity and covariance can be extended to complex-valued space-time and four-momentum. Our considerations will lead us not only to some unconventional derivation of Lorentz transformations for complex-valued velocities, but also to the non-Hermitian Klein-Gordon and Dirac equations, which are to lay the foundations of a non-Hermitian quantum theory.

  12. Deadzones, Dying Eddies, and the Loop Current: Stability, Ventilation, and Heat Content from Buoyancy Glider Observations in the Northwest Gulf of Mexico in Spring and Summer 2015

    Science.gov (United States)

    DiMarco, S. F.; Knap, A. H.; Wang, Z.; Walpert, J.; Dreger, K.

    2016-02-01

    The northwestern Gulf of Mexico is host to a myriad of physical and biochemical processes, which govern the exchange and transport of material and volume between the coastal and offshore environments. We report on five G2 Slocum glider deployments in the northwestern Gulf during the spring and summer of 2015. The gliders were deployed in shallow (20 m) and deep (greater than 1000 m) water for a total of about 200 days. During this time, the gliders encountered a variety of environmental conditions that impact the circulation, biology, chemistry of the shelf and slope. The shallow gliders encountered coastal waters influenced by extensive flooding in terrestrial Texas that vertically stratified the water-column and was coincident with sub-pycnocline low dissolved oxygen concentration, at times below the hypoxic threshold of 2 mg/L, and elevated CDOM concentrations. These gliders also reveal high spatial variability with bottom boundary oxygen and biomass scales on the order of a few kilometers. The deep gliders were tasked to investigate shelf/slope exchange at two locations 94W and 91W. The western glider encountered a mature mesoscale circulation eddy that was actively weakening. The eastern glider simultaneously encountered a freshly separated Loop Current eddy. The vertical structure of hydrographic and dissolved oxygen parameters shows significant and distinguishable variability in each feature. The vertical structure of both features show significant departures from that which is expected based on sea surface height determined from satellite altimetry. Additionally, glider observations are compared to operational high-resolution regional numerical model output. These observations emphasize the importance of direct observations over satellite-derived products for applications that include upper ocean heat content for hurricane intensification and vertical mixing and ventilation of the oceanic interior.

  13. Large-Eddy Simulation of Shallow Cumulus over Land: A Composite Case Based on ARM Long-Term Observations at Its Southern Great Plains Site

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yunyan [Lawrence Livermore National Laboratory, Livermore, California; Klein, Stephen A. [Lawrence Livermore National Laboratory, Livermore, California; Fan, Jiwen [Pacific Northwest National Laboratory, Richland, Washington; Chandra, Arunchandra S. [Division of Meteorology and Physical Oceanography, University of Miami, Miami, Florida; Kollias, Pavlos [School of Marine and Atmospheric Sciences, Stony Brook University, State University of New York, Stony Brook, New York; Xie, Shaocheng [Lawrence Livermore National Laboratory, Livermore, California; Tang, Shuaiqi [Lawrence Livermore National Laboratory, Livermore, California

    2017-10-01

    Based on long-term observations by the Atmospheric Radiation Measurement program at its Southern Great Plains site, a new composite case of continental shallow cumulus (ShCu) convection is constructed for large-eddy simulations (LES) and single-column models. The case represents a typical daytime non-precipitating ShCu whose formation and dissipation are driven by the local atmospheric conditions and land-surface forcing, and are not influenced by synoptic weather events. The case includes: early-morning initial profiles of temperature and moisture with a residual layer; diurnally-varying sensible and latent heat fluxes which represent a domain average over different land-surface types; simplified large-scale horizontal advective tendencies and subsidence; and horizontal winds with prevailing direction and average speed. Observed composite cloud statistics are provided for model evaluation. The observed diurnal cycle is well-reproduced by LES, however the cloud amount, liquid water path, and shortwave radiative effect are generally underestimated. LES are compared between simulations with an all-or-nothing bulk microphysics and a spectral bin microphysics. The latter shows improved agreement with observations in the total cloud cover and the amount of clouds with depths greater than 300 meters. When compared with radar retrievals of in-cloud air motion, LES produce comparable downdraft vertical velocities, but a larger updraft area, velocity and updraft mass flux. Both observation and LES show a significantly larger in-cloud downdraft fraction and downdraft mass flux than marine ShCu.

  14. Large-Eddy Simulation of Shallow Cumulus over Land: A Composite Case Based on ARM Long-Term Observations at Its Southern Great Plains Site

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yunyan [Lawrence Livermore National Laboratory, Livermore, California; Klein, Stephen A. [Lawrence Livermore National Laboratory, Livermore, California; Fan, Jiwen [Pacific Northwest National Laboratory, Richland, Washington; Chandra, Arunchandra S. [Division of Meteorology and Physical Oceanography, University of Miami, Miami, Florida; Kollias, Pavlos [School of Marine and Atmospheric Sciences, Stony Brook University, State University of New York, Stony Brook, New York; Xie, Shaocheng [Lawrence Livermore National Laboratory, Livermore, California; Tang, Shuaiqi [Lawrence Livermore National Laboratory, Livermore, California

    2017-10-01

    Based on long-term observations by the Atmospheric Radiation Measurement program at its Southern Great Plains site, a new composite case of continental shallow cumulus (ShCu) convection is constructed for large-eddy simulations (LES) and single-column models. The case represents a typical daytime nonprecipitating ShCu whose formation and dissipation are driven by the local atmospheric conditions and land surface forcing and are not influenced by synoptic weather events. The case includes early morning initial profiles of temperature and moisture with a residual layer; diurnally varying sensible and latent heat fluxes, which represent a domain average over different land surface types; simplified large-scale horizontal advective tendencies and subsidence; and horizontal winds with prevailing direction and average speed. Observed composite cloud statistics are provided for model evaluation. The observed diurnal cycle is well reproduced by LES; however, the cloud amount, liquid water path, and shortwave radiative effect are generally underestimated. LES are compared between simulations with an all-or-nothing bulk microphysics and a spectral bin microphysics. The latter shows improved agreement with observations in the total cloud cover and the amount of clouds with depths greater than 300 m. When compared with radar retrievals of in-cloud air motion, LES produce comparable downdraft vertical velocities, but a larger updraft area, velocity, and updraft mass flux. Both observations and LES show a significantly larger in-cloud downdraft fraction and downdraft mass flux than marine ShCu.

  15. A daily global mesoscale ocean eddy dataset from satellite altimetry.

    Science.gov (United States)

    Faghmous, James H; Frenger, Ivy; Yao, Yuanshun; Warmka, Robert; Lindell, Aron; Kumar, Vipin

    2015-01-01

    Mesoscale ocean eddies are ubiquitous coherent rotating structures of water with radial scales on the order of 100 kilometers. Eddies play a key role in the transport and mixing of momentum and tracers across the World Ocean. We present a global daily mesoscale ocean eddy dataset that contains ~45 million mesoscale features and 3.3 million eddy trajectories that persist at least two days as identified in the AVISO dataset over a period of 1993-2014. This dataset, along with the open-source eddy identification software, extract eddies with any parameters (minimum size, lifetime, etc.), to study global eddy properties and dynamics, and to empirically estimate the impact eddies have on mass or heat transport. Furthermore, our open-source software may be used to identify mesoscale features in model simulations and compare them to observed features. Finally, this dataset can be used to study the interaction between mesoscale ocean eddies and other components of the Earth System.

  16. 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.

  17. 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.

  18. Large-eddy simulation of mesoscale dynamics and entrainment around a pocket of open cells observed in VOCALS-REx RF06

    Directory of Open Access Journals (Sweden)

    A. H. Berner

    2011-10-01

    Full Text Available Large-eddy simulations of a pocket of open cells (POC based on VOCALS Regional Experiment (REx NSF C-130 Research Flight 06 are analyzed and compared with aircraft observations. A doubly-periodic domain 192 km × 24 km with 125 m horizontal and 5 m vertical grid spacing near the capping inversion is used. The POC is realized in the model as a fixed 96 km wide region of reduced cloud droplet number concentration (Nc based on observed values; initialization and forcing are otherwise uniform across the domain. The model reproduces aircraft-observed differences in boundary-layer structure and precipitation organization between a well-mixed overcast region and a decoupled POC with open-cell precipitating cumuli, although the simulated cloud cover is too large in the POC. A sensitivity study in which Nc is allowed to advect following the turbulent flow gives nearly identical results over the 16 h length of the simulation (which starts at night and goes into the next afternoon.

    The simulated entrainment rate is nearly a factor of two smaller in the less turbulent POC than in the more turbulent overcast region. However, the inversion rises at a nearly uniform rate across the domain because powerful buoyancy restoring forces counteract horizontal inversion height gradients. A secondary circulation develops in the model that diverts subsiding free-tropospheric air away from the POC into the surrounding overcast region, counterbalancing the weaker entrainment in the POC with locally weaker subsidence.

  19. Flame Propagation Through Swirling Eddys, A Recursive Pattern

    CERN Document Server

    Ashurst, W T

    1993-01-01

    Abstract: Computed flame motion through and between swirling eddys exhibits a maximum advancement rate which is related to the time duration of flame motion between eddys. This eddy spatial structure effect upon the apparent turbulent flame speed appears to be similar to the square-root dependence observed in wrinkled flamelet data. The rate-limiting behavior at one eddy length-scale can be removed by inclusion of smaller eddys which reside between the larger eddys. This large-eddy, small-eddy concept yields a recursion relation and repeated functional iteration can be done to approximate a desired flame speed relation. As an example, an iteration to produce $S_T Currently, the iteration process is a post-diction of flame speed, but if a universality can be developed, then a predictive theory of turbulent flame propagation might be achieved.

  20. Skill of ship-following large-eddy simulations in reproducing MAGIC observations across the northeast Pacific stratocumulus to cumulus transition region

    Science.gov (United States)

    McGibbon, J.; Bretherton, C. S.

    2017-06-01

    During the Marine ARM GPCI Investigation of Clouds (MAGIC) in October 2011 to September 2012, a container ship making periodic cruises between Los Angeles, CA, and Honolulu, HI, was instrumented with surface meteorological, aerosol and radiation instruments, a cloud radar and ceilometer, and radiosondes. Here large-eddy simulation (LES) is performed in a ship-following frame of reference for 13 four day transects from the MAGIC field campaign. The goal is to assess if LES can skillfully simulate the broad range of observed cloud characteristics and boundary layer structure across the subtropical stratocumulus to cumulus transition region sampled during different seasons and meteorological conditions. Results from Leg 15A, which sampled a particularly well-defined stratocumulus to cumulus transition, demonstrate the approach. The LES reproduces the observed timing of decoupling and transition from stratocumulus to cumulus and matches the observed evolution of boundary layer structure, cloud fraction, liquid water path, and precipitation statistics remarkably well. Considering the simulations of all 13 cruises, the LES skillfully simulates the mean diurnal variation of key measured quantities, including liquid water path (LWP), cloud fraction, measures of decoupling, and cloud radar-derived precipitation. The daily mean quantities are well represented, and daily mean LWP and cloud fraction show the expected correlation with estimated inversion strength. There is a -0.6 K low bias in LES near-surface air temperature that results in a high bias of 5.6 W m-2 in sensible heat flux (SHF). Overall, these results build confidence in the ability of LES to represent the northeast Pacific stratocumulus to trade cumulus transition region.type="synopsis">type="main">Plain Language SummaryDuring the Marine ARM GPCI Investigation of Clouds (MAGIC) field campaign in October 2011 to September 2012, a cargo container ship making regular cruises between Los Angeles, CA, and Honolulu

  1. Comparison of corn transpiration, eddy covariance, and soil water loss

    Science.gov (United States)

    Stem flow gages are used to estimate plant transpiration, but only a few studies compare transpiration with other measures of soil water loss. The purpose of this study was to compare transpiration from stem flow measurements with soil water changes estimated by daily neutron probe readings. Monitor...

  2. Open software tools for eddy covariance flux partitioning

    Science.gov (United States)

    Agro-ecosystem management and assessment will benefit greatly from the development of reliable techniques for partitioning evapotranspiration (ET) into evaporation (E) and transpiration (T). Among other activities, flux partitioning can aid in evaluating consumptive vs. non-consumptive agricultural...

  3. Equatorward translation of the Vitoria Eddy in a numerical simulation

    Science.gov (United States)

    Campos, Edmo J. D.

    2006-11-01

    The Vitoria Eddy is a cyclonic vortex in the Brazil Current immediately to the South of the Vitoria-Trindade Ridge. Schmid et al. (1995) observed one such eddy that initially translated to the northeast, for about 17 days, and then moved back to the south. In this letter we report results of an eddy-resolving OGCM in which cyclonic eddies are formed in the same region. Although similar in structure to the observed feature, in our simulations the eddies present two different modes of translation. In one case, the eddy moves initially to the northeast, then remains stationary for a while, and finally moves back to the south. In the other, the eddy does not stop. It continues moving northward, crossing the Vitoria-Trindade chain and the Abrolhos Bank. In spite of not being impossible, to our knowledge this second behavior has never been reported.

  4. Covariant quantum Markovian evolutions

    Science.gov (United States)

    Holevo, A. S.

    1996-04-01

    Quantum Markovian master equations with generally unbounded generators, having physically relevant symmetries, such as Weyl, Galilean or boost covariance, are characterized. It is proven in particular that a fully Galilean covariant zero spin Markovian evolution reduces to the free motion perturbed by a covariant stochastic process with independent stationary increments in the classical phase space. A general form of the boost covariant Markovian master equation is discussed and a formal dilation to the Langevin equation driven by quantum Boson noises is described.

  5. Dynamical Processes within an Anticyclonic Eddy Revealed from Argo Floats

    Science.gov (United States)

    Zhang, W. Z.; Xue, H.; Chai, F.; Ni, Q.

    2016-02-01

    Mesoscale eddies play a significant role in supplying the nutrients required for phytoplankton blooms and redistributing biomass in the ocean. However, how anticyclonic eddies influence nutrient flux and biomass distribution remains unclear and controversial. Here we reveal two important dynamical processes (radial displacement and vertical fluctuations) within an anticyclonic eddy using observations from Argo floats. Particles in the eddy were displaced toward the eddy edge due to the imbalance of radial momentum. Vertical fluctuations below the mixed layer resulted in alternating upwelling and downwelling in the inner and outer parts of the eddy. High salinity deep water was uplifted tens of meters by the upwelling and further extended to the surface with the aid of wind effects and submesoscale effects. Vertical motions associated with the fluctuations penetrated into the layer of several hundred meters deep. These processes exhibit crucial dynamical mechanisms for the motion of particles in mature anticyclonic eddies.

  6. A western boundary current eddy characterisation study

    Science.gov (United States)

    Ribbe, Joachim; Brieva, Daniel

    2016-12-01

    The analysis of an eddy census for the East Australian Current (EAC) region yielded a total of 497 individual short-lived (7-28 days) cyclonic and anticyclonic eddies for the period 1993 to 2015. This was an average of about 23 eddies per year. 41% of the tracked individual cyclonic and anticyclonic eddies were detected off southeast Queensland between about 25 °S and 29 °S. This is the region where the flow of the EAC intensifies forming a swift western boundary current that impinges near Fraser Island on the continental shelf. This zone was also identified as having a maximum in detected short-lived cyclonic eddies. A total of 94 (43%) individual cyclonic eddies or about 4-5 per year were tracked in this region. The census found that these potentially displaced entrained water by about 115 km with an average displacement speed of about 4 km per day. Cyclonic eddies were likely to contribute to establishing an on-shelf longshore northerly flow forming the western branch of the Fraser Island Gyre and possibly presented an important cross-shelf transport process in the life cycle of temperate fish species of the EAC domain. In-situ observations near western boundary currents previously documented the entrainment, off-shelf transport and export of near shore water, nutrients, sediments, fish larvae and the renewal of inner shelf water due to short-lived eddies. This study found that these cyclonic eddies potentially play an important off-shelf transport process off the central east Australian coast.

  7. 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.

  8. Covariance evaluation system

    Energy Technology Data Exchange (ETDEWEB)

    Kawano, Toshihiko [Kyushu Univ., Fukuoka (Japan); 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 {sup 238}U reaction cross sections were calculated with this system. (author)

  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. 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.

  11. 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.

  12. Erosion of a California Undercurrent eddy by bottom topography

    Science.gov (United States)

    Torres, Hector S.; Gomez-Valdes, Jose

    2017-05-01

    Subsurface eddies are ubiquitous features in eastern boundary current systems. These phenomena tend to modulate the across-shore distribution of heat and biogeochemical tracers. A California Undercurrent eddy was detected by shipboard observations in October 2009 off the northern Baja California continental slope. The spatiotemporal variation in the California Undercurrent eddy is investigated by using a mesoscale-resolving hindcast ocean simulation. A poleward coastal current that is driven by an upwelling-wind relaxation event and the coastline geometry instigated the separation of the California Undercurrent from the slope, forming a meander-like structure, which evolved as a mesoscale eddy-like structure. The latter structure evolved as a subsurface eddy with a warm anomaly core, a distinctive feature of eddies that form from the California Undercurrent. During the initial stage, the subsurface eddy presented a cone-shape form, with the maximum amplitude of the relative vorticity in the upper section. The inviscid effect of the irregular bottom topography altered both the initial direction of propagation and the initial eddy shape: the propagation direction of the eddy changed from north-south to southwest, and the shape changed from a cone shape to a subsurface lens shape. The strong eddy-topography interactions triggered a sign change in the heat flux direction from the environment toward the eddy and vice versa through the horizontally divergent component of the velocity field, which accelerated the eddy's decay. This study shows the relevance of the synoptic wind stress events and the irregularity of the bottom topography on the mesoscale eddy activity in the southern portion of the California Current.

  13. Acoustical characteristics and simulated tomographic inversion of a cold core eddy in the Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    PrasannaKumar, S.; Navelkar, G.S.; Murty, T.V.R.; Murty, C.S.

    Acoustic characteristics of a subsurface, cold core eddy observed in the Bay of Bengal during southwest monsoon period is presented based on CTD (Conductivity Temperature Depth) data from 42 stations. The effect of the eddy is to reduce the ambient...

  14. Micromagnetics with eddy currents

    Energy Technology Data Exchange (ETDEWEB)

    Iyer, R; Millhollon, J; Long, K, E-mail: ram.iyer@ttu.edu [Room 201, Department of Mathematics and Statistics, Texas Tech University, Lubbock, TX 79409 (United States)

    2011-01-01

    In this paper, we study the modified Landau-Lifshitz-Gilbert (LLG) equation for of a conducting, magnetic body. The modified LLG equations include the magnetic field due to eddy currents in the total effective magnetic field. We derive an expression for the magnetic field due to eddy current losses and show that it is well defined. We then show that the work done by the eddy currents in opposing the change of magnetization is a Rayleigh type dissipation function, and derive the modified LLG equations using the calculus of variations. Finally, we show that the modified LLG equations lead to a decrease in the Gibbs energy. This implies that the LLG equations describes a dynamic process proceeding spontaneously forward in time.

  15. Phytoplankton bloom triggered by an anticyclonic eddy: The combined effect of eddy-Ekman pumping and winter mixing

    Science.gov (United States)

    He, Qingyou; Zhan, Haigang; Shuai, Yiping; Cai, Shuqun; Li, Qian P.; Huang, Gaolong; Li, Junmin

    2017-06-01

    Recent composite based researches reveal that anticyclonic eddies facilitate the growth of phytoplankton in the subtropical gyres. Two dynamical mechanisms, eddy-Ekman pumping and winter mixing, have been examined individually, but their relative and combined effects remain unclear. Using satellite observations and model simulations, this study investigated the process of a distinct phytoplankton bloom generated in an anticyclonic eddy in the nutrient-depleted southeastern Indian Ocean. The bloom propagated westward along with the eddy for more than 600 km from late April to August in 2010. The peak of surface chlorophyll concentration in the eddy is 2.2 times larger than the mean value of the ambient. The development of the bloom is dominated by the winter deepening of mixed layer, whose velocity in vertical nutrient flux is on average 3 times larger than that of eddy-Ekman pumping. The results of a 1-D physical-biogeochemical model demonstrate that the role of eddy-Ekman pumping is also indispensable, because it not only transports extra nutrients into the mixed layer, but also results in significant chlorophyll enrichment in subsurface water. The superposition of eddy-Ekman pumping on winter mixing triples the chlorophyll both at the surface and in the upper layer, and the entrainment of subsurface phytoplankton into the mixed layer contributes significantly to the surface bloom, especially in its initial stage. Both the satellite observations and model simulation show that eddy-Ekman pumping can lead to an early occurrence of the bloom for more than 2 weeks.

  16. Don Eddy; "Jewelry."

    Science.gov (United States)

    Schaefer, Claire

    1989-01-01

    Presents a lesson that introduces students in grades K-three to sources of design inspiration in contemporary urban settings. Using Don Eddy's painting of a jewelry store window display, asks students to describe and analyze the interplay of shape, pattern, and color. Suggests studio activities, including an activity in which students build a…

  17. Modelling of the North Atlantic eddy characteristics

    Science.gov (United States)

    Ushakov, Konstantin; Ibrayev, Rashit

    2017-04-01

    We investigate eddy characteristics of the Atlantic basin circulation and their impact on the ocean heat transport. A 15-year-long numerical experiment is performed with the global 3-dimensional z-coordinate INMIO ocean general circulation model of 0.1 deg., 49 levels resolution in conditions of the CORE-II protocol. The model is tuned to maximal intensity of eddies production by using only biharmonic filters instead of lateral viscous and diffusive terms in the model equations. Comparison with viscous and coarse-resolution simulations shows the increase of explicitly resolved heat transfer fraction and absolute values. Vertical turbulent mixing is parameterized by the Munk-Anderson scheme including convective adjustment. The sea ice is described by a simple thermodynamic submodel. The eddying velocity and temperature field components are defined as anomalies relative to the 3-month sliding mean. The regional distributions of hydrological parameters, eddy kinetic energy, heat convergence, meridional heat transport (MHT) and Atlantic meridional overturning circulation (AMOC) streamfunction, and their temporal variability are analyzed. In some parts of the basin the simulated eddy heat transport is opposite to the mean flow transport and may change direction with depth. The MHT intensity is slightly below observationally based assessments with notable influence of the East Greenland current simulation bias. The work is supported by the Russian Science Foundation (project N 14-27-00126) and performed in the Institute of Numerical Mathematics, Russian Academy of Sciences.

  18. Frame covariant nonminimal multifield inflation

    Science.gov (United States)

    Karamitsos, Sotirios; Pilaftsis, Apostolos

    2018-02-01

    We introduce a frame-covariant formalism for inflation of scalar-curvature theories by adopting a differential geometric approach which treats the scalar fields as coordinates living on a field-space manifold. This ensures that our description of inflation is both conformally and reparameterization covariant. Our formulation gives rise to extensions of the usual Hubble and potential slow-roll parameters to generalized fully frame-covariant forms, which allow us to provide manifestly frame-invariant predictions for cosmological observables, such as the tensor-to-scalar ratio r, the spectral indices nR and nT, their runnings αR and αT, the non-Gaussianity parameter fNL, and the isocurvature fraction βiso. We examine the role of the field space curvature in the generation and transfer of isocurvature modes, and we investigate the effect of boundary conditions for the scalar fields at the end of inflation on the observable inflationary quantities. We explore the stability of the trajectories with respect to the boundary conditions by using a suitable sensitivity parameter. To illustrate our approach, we first analyze a simple minimal two-field scenario before studying a more realistic nonminimal model inspired by Higgs inflation. We find that isocurvature effects are greatly enhanced in the latter scenario and must be taken into account for certain values in the parameter space such that the model is properly normalized to the observed scalar power spectrum PR. Finally, we outline how our frame-covariant approach may be extended beyond the tree-level approximation through the Vilkovisky-De Witt formalism, which we generalize to take into account conformal transformations, thereby leading to a fully frame-invariant effective action at the one-loop level.

  19. Frame covariant nonminimal multifield inflation

    Directory of Open Access Journals (Sweden)

    Sotirios Karamitsos

    2018-02-01

    Full Text Available We introduce a frame-covariant formalism for inflation of scalar-curvature theories by adopting a differential geometric approach which treats the scalar fields as coordinates living on a field-space manifold. This ensures that our description of inflation is both conformally and reparameterization covariant. Our formulation gives rise to extensions of the usual Hubble and potential slow-roll parameters to generalized fully frame-covariant forms, which allow us to provide manifestly frame-invariant predictions for cosmological observables, such as the tensor-to-scalar ratio r, the spectral indices nR and nT, their runnings αR and αT, the non-Gaussianity parameter fNL, and the isocurvature fraction βiso. We examine the role of the field space curvature in the generation and transfer of isocurvature modes, and we investigate the effect of boundary conditions for the scalar fields at the end of inflation on the observable inflationary quantities. We explore the stability of the trajectories with respect to the boundary conditions by using a suitable sensitivity parameter. To illustrate our approach, we first analyze a simple minimal two-field scenario before studying a more realistic nonminimal model inspired by Higgs inflation. We find that isocurvature effects are greatly enhanced in the latter scenario and must be taken into account for certain values in the parameter space such that the model is properly normalized to the observed scalar power spectrum PR. Finally, we outline how our frame-covariant approach may be extended beyond the tree-level approximation through the Vilkovisky–De Witt formalism, which we generalize to take into account conformal transformations, thereby leading to a fully frame-invariant effective action at the one-loop level.

  20. Deep Eddies in the Gulf of Mexico

    Science.gov (United States)

    Furey, H. H.; Bower, A. S.; Perez-Brunius, P.; Hamilton, P.

    2014-12-01

    A major Lagrangian program is currently underway to map the deep (1500-2500 m) circulation of the entire Gulf of Mexico. Beginning in 2011, more than 120 acoustically tracked RAFOS floats have been released in the eastern, central and western Gulf, many in pairs and triplets. Most floats are programmed to drift for two years, obtaining position fixes and temperature/pressure measurements three times daily. More than 80 floats have completed their missions, and results from the trajectories will be described with a focus on mesoscale eddying behavior. In particular, the first-ever observations of deep energetic anticyclonic eddies (possibly lenses) forming at and separating from a northeastward-flowing boundary current west of Campeche Bank will be discussed. The existence of these eddies has major implications for exchange between the continental slope and interior Gulf. The project is being supported by the U.S. Bureau of Ocean Energy Management (BOEM).

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Covariance Applications with Kiwi

    Science.gov (United States)

    Mattoon, C. M.; Brown, D.; Elliott, J. B.

    2012-05-01

    The Computational Nuclear Physics group at Lawrence Livermore National Laboratory (LLNL) is developing a new tool, named `Kiwi', that is intended as an interface between the covariance data increasingly available in major nuclear reaction libraries (including ENDF and ENDL) and large-scale Uncertainty Quantification (UQ) studies. Kiwi is designed to integrate smoothly into large UQ studies, using the covariance matrix to generate multiple variations of nuclear data. The code has been tested using critical assemblies as a test case, and is being integrated into LLNL's quality assurance and benchmarking for nuclear data.

  6. Covariance Applications with Kiwi

    Directory of Open Access Journals (Sweden)

    Elliott J.B.

    2012-05-01

    Full Text Available The Computational Nuclear Physics group at Lawrence Livermore National Laboratory (LLNL is developing a new tool, named ‘Kiwi’, that is intended as an interface between the covariance data increasingly available in major nuclear reaction libraries (including ENDF and ENDL and large-scale Uncertainty Quantification (UQ studies. Kiwi is designed to integrate smoothly into large UQ studies, using the covariance matrix to generate multiple variations of nuclear data. The code has been tested using critical assemblies as a test case, and is being integrated into LLNL's quality assurance and benchmarking for nuclear data.

  7. Modeling Mesoscale Eddies in the North Atlantic Ocean

    Science.gov (United States)

    Chao, Yi

    1999-01-01

    Ocean modeling plays an important role in understanding the current climatic conditions and predicting the future climate change. Modeling the ocean at eddy-permitting and/or eddy resolving resolutions (1/3 degree or higher) has a two-fold objective. One part is to represent the ocean as realistically as possible, because mesoscale eddies have an impact on the large-scale circulation. The second objective is to learn how to represent effects of mesoscale eddies without explicitly resolving them. This is particularly important for climate models which cannot be run at eddy-resolving resolutions because of the computational constraints. At JPL, a 1/6 degree latitude by 1/6 degree longitude with 37 vertical levels Atlantic Ocean model has been developed. The model is based on the Parallel Ocean Program (POP) developed at Los Alamos National Laboratory (LANL). Using the 256-processor Cray T3D, we have conducted a 40-year integration of this Atlantic eddy-resolving ocean model. A regional analysis demonstrate that many observed features associated with the Caribbean Sea eddies can be realistically simulated by this model. Analysis of this Atlantic eddy-resolving ocean model further suggests that these Caribbean Sea eddies are connected with eddies formed outside the Caribbean Sea at the confluence of the North Brazil Current (NBC) and the North Equatorial Countercurrent. The diagram of the model simulated surface current shows that the Caribbean eddies ultimately originate in the NBC retroflection region, traveling more than a year from the North Brazil coast through the Lesser Antilles into the Caribbean Sea and eventually into the Gulf of Mexico. Additional information is contained in the original.

  8. 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.

  9. Aerosol and cloud microphysics covariability in the northeast Pacific boundary layer estimated with ship-based and satellite remote sensing observations: NE Pacific Aerosol-Cloud Interactions

    Energy Technology Data Exchange (ETDEWEB)

    Painemal, David [Science Systems and Applications, Inc., Hampton Virginia USA; NASA Langley Research Center, Hampton Virginia USA; Chiu, J. -Y. Christine [Department of Meteorology, University of Reading, Reading UK; Minnis, Patrick [NASA Langley Research Center, Hampton Virginia USA; Yost, Christopher [Science Systems and Applications, Inc., Hampton Virginia USA; Zhou, Xiaoli [Department of Atmospheric and Oceanic Sciences, McGill University, Montreal Quebec Canada; Cadeddu, Maria [Environmental Science Division, Argonne National Laboratory, Lemont Illinois USA; Eloranta, Edwin [Space Science and Engineering Center, University of Wisconsin-Madison, Madison Wisconsin USA; Lewis, Ernie R. [Brookhaven National Laboratory, Upton New York USA; Ferrare, Richard [NASA Langley Research Center, Hampton Virginia USA; Kollias, Pavlos [School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook New York USA

    2017-02-27

    Ship measurements collected over the northeast Pacific along transects between the port of Los Angeles (33.7°N, 118.2°W) and Honolulu (21.3°N, 157.8°W) during May to August 2013 were utilized to investigate the covariability between marine low cloud microphysical and aerosol properties. Ship-based retrievals of cloud optical depth (τ) from a Sun photometer and liquid water path (LWP) from a microwave radiometer were combined to derive cloud droplet number concentration Nd and compute a cloud-aerosol interaction (ACI) metric defined as ACICCN = ∂ ln(Nd)/∂ ln(CCN), with CCN denoting the cloud condensation nuclei concentration measured at 0.4% (CCN0.4) and 0.3% (CCN0.3) supersaturation. Analysis of CCN0.4, accumulation mode aerosol concentration (Na), and extinction coefficient (σext) indicates that Na and σext can be used as CCN0.4 proxies for estimating ACI. ACICCN derived from 10 min averaged Nd and CCN0.4 and CCN0.3, and CCN0.4 regressions using Na and σext, produce high ACICCN: near 1.0, that is, a fractional change in aerosols is associated with an equivalent fractional change in Nd. ACICCN computed in deep boundary layers was small (ACICCN = 0.60), indicating that surface aerosol measurements inadequately represent the aerosol variability below clouds. Satellite cloud retrievals from MODerate-resolution Imaging Spectroradiometer and GOES-15 data were compared against ship-based retrievals and further analyzed to compute a satellite-based ACICCN. Satellite data correlated well with their ship-based counterparts with linear correlation coefficients equal to or greater than 0.78. Combined satellite Nd and ship-based CCN0.4 and Na yielded a maximum ACICCN = 0.88–0.92, a value slightly less than the ship-based ACICCN, but still consistent with aircraft-based studies in the eastern Pacific.

  10. Szekeres models: a covariant approach

    Science.gov (United States)

    Apostolopoulos, Pantelis S.

    2017-05-01

    We exploit the 1  +  1  +  2 formalism to covariantly describe the inhomogeneous and anisotropic Szekeres models. It is shown that an average scale length can be defined covariantly which satisfies a 2d equation of motion driven from the effective gravitational mass (EGM) contained in the dust cloud. The contributions to the EGM are encoded to the energy density of the dust fluid and the free gravitational field E ab . We show that the quasi-symmetric property of the Szekeres models is justified through the existence of 3 independent intrinsic Killing vector fields (IKVFs). In addition the notions of the apparent and absolute apparent horizons are briefly discussed and we give an alternative gauge-invariant form to define them in terms of the kinematical variables of the spacelike congruences. We argue that the proposed program can be used in order to express Sachs’ optical equations in a covariant form and analyze the confrontation of a spatially inhomogeneous irrotational overdense fluid model with the observational data.

  11. Sokolua-Mvika, Eddy

    African Journals Online (AJOL)

    Sokolua-Mvika, Eddy. Vol 23, No 1 (2016) - Articles Carence en fer, anémie et anémie ferriprive chez les donneurs de sang à Kinshasa, République Démocratique du Congo Abstract PDF. ISSN: 1937-8688. AJOL African Journals Online. HOW TO USE AJOL... for Researchers · for Librarians · for Authors · FAQ's · More ...

  12. 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...

  13. Covariant approximation averaging

    CERN Document Server

    Shintani, Eigo; Blum, Thomas; Izubuchi, Taku; Jung, Chulwoo; Lehner, Christoph

    2014-01-01

    We present a new class of statistical error reduction techniques for Monte-Carlo simulations. Using covariant symmetries, we show that correlation functions can be constructed from inexpensive approximations without introducing any systematic bias in the final result. We introduce a new class of covariant approximation averaging techniques, known as all-mode averaging (AMA), in which the approximation takes account of contributions of all eigenmodes through the inverse of the Dirac operator computed from the conjugate gradient method with a relaxed stopping condition. In this paper we compare the performance and computational cost of our new method with traditional methods using correlation functions and masses of the pion, nucleon, and vector meson in $N_f=2+1$ lattice QCD using domain-wall fermions. This comparison indicates that AMA significantly reduces statistical errors in Monte-Carlo calculations over conventional methods for the same cost.

  14. Covariant approximation averaging

    Science.gov (United States)

    Shintani, Eigo; Arthur, Rudy; Blum, Thomas; Izubuchi, Taku; Jung, Chulwoo; Lehner, Christoph

    2015-06-01

    We present a new class of statistical error reduction techniques for Monte Carlo simulations. Using covariant symmetries, we show that correlation functions can be constructed from inexpensive approximations without introducing any systematic bias in the final result. We introduce a new class of covariant approximation averaging techniques, known as all-mode averaging (AMA), in which the approximation takes account of contributions of all eigenmodes through the inverse of the Dirac operator computed from the conjugate gradient method with a relaxed stopping condition. In this paper we compare the performance and computational cost of our new method with traditional methods using correlation functions and masses of the pion, nucleon, and vector meson in Nf=2 +1 lattice QCD using domain-wall fermions. This comparison indicates that AMA significantly reduces statistical errors in Monte Carlo calculations over conventional methods for the same cost.

  15. Covariate Balancing through Naturally Occurring Strata.

    Science.gov (United States)

    Alemi, Farrokh; ElRafey, Amr; Avramovic, Ivan

    2016-12-14

    To provide an alternative to propensity scoring (PS) for the common situation where there are interacting covariates. We used 1.3 million assessments of residents of the United States Veterans Affairs nursing homes, collected from January 1, 2000, through October 9, 2012. In stratified covariate balancing (SCB), data are divided into naturally occurring strata, where each stratum is an observed combination of the covariates. Within each stratum, cases with, and controls without, the target event are counted; controls are weighted to be as frequent as cases. This weighting procedure guarantees that covariates, or combination of covariates, are balanced, meaning they occur at the same rate among cases and controls. Finally, impact of the target event is calculated in the weighted data. We compare the performance of SCB, logistic regression (LR), and propensity scoring (PS) in simulated and real data. We examined the calibration of SCB and PS in predicting 6-month mortality from inability to eat, controlling for age, gender, and nine other disabilities for 296,051 residents in Veterans Affairs nursing homes. We also performed a simulation study, where outcomes were randomly generated from treatment, 10 covariates, and increasing number of covariate interactions. The accuracy of SCB, PS, and LR in recovering the simulated treatment effect was reported. In simulated environment, as the number of interactions among the covariates increased, SCB and properly specified LR remained accurate but pairwise LR and pairwise PS, the most common applications of these tools, performed poorly. In real data, application of SCB was practical. SCB was better calibrated than linear PS, the most common method of PS. In environments where covariates interact, SCB is practical and more accurate than common methods of applying LR and PS. © Health Research and Educational Trust.

  16. A tale of two eddies: The biophysical characteristics of two contrasting cyclonic eddies in the East Australian Current System

    Science.gov (United States)

    Roughan, M.; Keating, S. R.; Schaeffer, A.; Cetina Heredia, P.; Rocha, C.; Griffin, D.; Robertson, R.; Suthers, I. M.

    2017-03-01

    Mesoscale cyclonic eddies are known to be highly productive. Less well-known are the dynamics and productivity of smaller cyclonic eddies, known as frontal eddies, that form on the landward side of western boundary currents. In this study, we investigate the physical and biogeochemical properties of two contrasting cyclonic eddies in the East Australian Current (EAC). The first ("Murphy"), a mesoscale cyclonic eddy that formed at ˜28°S with a diameter of ˜160 km and high surface chlorophyll-a concentrations, which lived ˜47 days. The second ("Freddy"), a smaller frontal eddy (˜35 km diameter) that formed from a shelf water billow ˜7 days prior to sampling at ˜31.5°S and was advected off the shelf along the EAC front (from ˜200 m to 4000 m of water). Both eddies were at least 1000 m deep with a similar steric height anomaly. We introduce and employ "the method of closest approach" using shipboard ADCP velocities to estimate the eddy centers, which reveals significant tilting through the water column. We estimate rotation rates of 4-10 days and 1-9 days and Rossby numbers 0.25-0.1 and 0.6-0.1, from the surface to 600 m for Murphy and Freddy, respectively. High-resolution altimetry measurements from the SARAL/AltiKA satellite provide estimates of the ageostrophic component of rotation. Our results show that the frontal eddy is significantly more ageostrophic, energetic, and productive than the mesoscale cyclone, despite its small size and short life (˜4 weeks). We suggest that frontal eddies have potential to contribute significantly to the net productivity of the Tasman Sea region.Plain Language SummaryWe present the first depth observations of a small cold core eddy which formed along the landward front of the East Australian Current. We contrast the observations with a typical larger cold core eddy. The observations were collected from a dedicated cruise aboard a research vessel. We show that this small Frontal Eddy is very dynamic feature. It rotates

  17. EDDIE RICKENBACKER: RACETRACK ENTREPRENEUR

    Directory of Open Access Journals (Sweden)

    W. David Lewis

    2000-01-01

    Full Text Available Edward V. (Eddie Rickenbacker (1890-1973 is best remembered for hisrecord as a combat pilot in World War I, in which he shot down 26 Germa naircraft and won fame as America’s "Ace of Aces." From 1934 until 1963 he was general manager, president, and board chairman of Eastern Air Lines, which was for a time the most profitable air carrier in the United States. This paper shows how Rickenbacker’s fiercely entrepreneurial style of management was born in his early involvement in the automobile industry, and particularly in his career as an automobile racing driver from 1909 through 1916.

  18. Sea Surface Height Variability and Eddy Statistical Properties in the Red Sea

    KAUST Repository

    Zhan, Peng

    2013-05-01

    vertical shear could convert the energy from baroclinic instability into eddy activity. Finally, numerical simulation results from the MIT general circulation model (MITgcm) are validated with previous studies and observations. The vertical structure of the simulated flux through Bab el Mandeb is successfully reproduced. Further validation with the 2010 cruise suggests that the thermocline occurs at ~200m, but the model vertical salinity gradient is lower than the observations. The model surface eddy variability is also examined, suggesting good agreement with satellite observations.

  19. Relationship between frontal dust storms and transient eddy activity in the northern hemisphere of Mars as observed by Mars Global Surveyor

    OpenAIRE

    Wang, Huiqun; Zurek, Richard W.; Richardson, Mark I.

    2005-01-01

    We have compiled a catalog of frontal dust storms in the northern hemisphere using Mars Orbiter Camera daily global maps spanning ~2.3 Martian years of Mars Global Surveyor (MGS) observations (from 1999 to 2003). The most vigorous frontal storms that flush dust to the low latitudes occur in early-mid fall and mid-late winter, away from the northern winter solstice. While many streaks are observed in the polar hood during the winter solstice period, no frontal dust storms are observed in the v...

  20. Carbon dynamics within cyclonic eddies: insights from a biomarker study.

    Science.gov (United States)

    Alonso-González, Iván J; Arístegui, Javier; Lee, Cindy; Sanchez-Vidal, Anna; Calafat, Antoni; Fabrés, Joan; Sangrá, Pablo; Mason, Evan

    2013-01-01

    It is generally assumed that episodic nutrient pulses by cyclonic eddies into surface waters support a significant fraction of the primary production in subtropical low-nutrient environments in the northern hemisphere. However, contradictory results related to the influence of eddies on particulate organic carbon (POC) export have been reported. As a step toward understanding the complex mechanisms that control export of material within eddies, we present here results from a sediment trap mooring deployed within the path of cyclonic eddies generated near the Canary Islands over a 1.5-year period. We find that, during summer and autumn (when surface stratification is stronger, eddies are more intense, and a relative enrichment in CaCO3 forming organisms occurs), POC export to the deep ocean was 2-4 times higher than observed for the rest of the year. On the contrary, during winter and spring (when mixing is strongest and the seasonal phytoplankton bloom occurs), no significant enhancement of POC export associated with eddies was observed. Our biomarker results suggest that a large fraction of the material exported from surface waters during the late-winter bloom is either recycled in the mesopelagic zone or bypassed by migrant zooplankton to the deep scattering layer, where it would disaggregate to smaller particles or be excreted as dissolved organic carbon. Cyclonic eddies, however, would enhance carbon export below 1000 m depth during the summer stratification period, when eddies are more intense and frequent, highlighting the important role of eddies and their different biological communities on the regional carbon cycle.

  1. Simulations of eddy kinetic energy transport in barotropic turbulence

    Science.gov (United States)

    Grooms, Ian

    2017-11-01

    Eddy energy transport in rotating two-dimensional turbulence is investigated using numerical simulation. Stochastic forcing is used to generate an inhomogeneous field of turbulence and the time-mean energy profile is diagnosed. An advective-diffusive model for the transport is fit to the simulation data by requiring the model to accurately predict the observed time-mean energy distribution. Isotropic harmonic diffusion of energy is found to be an accurate model in the case of uniform, solid-body background rotation (the f plane), with a diffusivity that scales reasonably well with a mixing-length law κ ∝V ℓ , where V and ℓ are characteristic eddy velocity and length scales. Passive tracer dynamics are added and it is found that the energy diffusivity is 75 % of the tracer diffusivity. The addition of a differential background rotation with constant vorticity gradient β leads to significant changes to the energy transport. The eddies generate and interact with a mean flow that advects the eddy energy. Mean advection plus anisotropic diffusion (with reduced diffusivity in the direction of the background vorticity gradient) is moderately accurate for flows with scale separation between the eddies and mean flow, but anisotropic diffusion becomes a much less accurate model of the transport when scale separation breaks down. Finally, it is observed that the time-mean eddy energy does not look like the actual eddy energy distribution at any instant of time. In the future, stochastic models of the eddy energy transport may prove more useful than models of the mean transport for predicting realistic eddy energy distributions.

  2. 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...

  3. Covariant Magnetic Connection Hypersurfaces

    CERN Document Server

    Pegoraro, F

    2016-01-01

    In the single fluid, nonrelativistic, ideal-Magnetohydrodynamic (MHD) plasma description magnetic field lines play a fundamental role by defining dynamically preserved "magnetic connections" between plasma elements. Here we show how the concept of magnetic connection needs to be generalized in the case of a relativistic MHD description where we require covariance under arbitrary Lorentz transformations. This is performed by defining 2-D {\\it magnetic connection hypersurfaces} in the 4-D Minkowski space. This generalization accounts for the loss of simultaneity between spatially separated events in different frames and is expected to provide a powerful insight into the 4-D geometry of electromagnetic fields when ${\\bf E} \\cdot {\\bf B} = 0$.

  4. Covariate analysis of bivariate survival data

    Energy Technology Data Exchange (ETDEWEB)

    Bennett, L.E.

    1992-01-01

    The methods developed are used to analyze the effects of covariates on bivariate survival data when censoring and ties are present. The proposed method provides models for bivariate survival data that include differential covariate effects and censored observations. The proposed models are based on an extension of the univariate Buckley-James estimators which replace censored data points by their expected values, conditional on the censoring time and the covariates. For the bivariate situation, it is necessary to determine the expectation of the failure times for one component conditional on the failure or censoring time of the other component. Two different methods have been developed to estimate these expectations. In the semiparametric approach these expectations are determined from a modification of Burke's estimate of the bivariate empirical survival function. In the parametric approach censored data points are also replaced by their conditional expected values where the expected values are determined from a specified parametric distribution. The model estimation will be based on the revised data set, comprised of uncensored components and expected values for the censored components. The variance-covariance matrix for the estimated covariate parameters has also been derived for both the semiparametric and parametric methods. Data from the Demographic and Health Survey was analyzed by these methods. The two outcome variables are post-partum amenorrhea and breastfeeding; education and parity were used as the covariates. Both the covariate parameter estimates and the variance-covariance estimates for the semiparametric and parametric models will be compared. In addition, a multivariate test statistic was used in the semiparametric model to examine contrasts. The significance of the statistic was determined from a bootstrap distribution of the test statistic.

  5. Objective mapping of observed sub-surface mesoscale cold core eddy in the Bay of Bengal by stochastic inverse technique with tomographically simulated travel times

    Digital Repository Service at National Institute of Oceanography (India)

    Murty, T.V.R.; Rao, M.M.M.; Sadhuram, Y.; Sridevi, B.; Maneesha, K.; SujithKumar, S.; Prasanna, P.L.; Murthy, K.S.R.

    compared with the conventional method. In OAT, path averaged data along the ray is used. Another advantage of the acoustic tomography is that it is one of the remote sensing techniques to explore ocean interior, where the direct observation is difficult... assume a reference ocean stratified in the vertical direction, and trace the sound ray paths from a source to a receiver (eigenrays). For this purpose, the climatologically mean state of the ocean could be used as the reference state. Tracing...

  6. 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.

  7. Deriving covariant holographic entanglement

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Xi [School of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540 (United States); Lewkowycz, Aitor [Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States); Rangamani, Mukund [Center for Quantum Mathematics and Physics (QMAP), Department of Physics, University of California, Davis, CA 95616 (United States)

    2016-11-07

    We provide a gravitational argument in favour of the covariant holographic entanglement entropy proposal. In general time-dependent states, the proposal asserts that the entanglement entropy of a region in the boundary field theory is given by a quarter of the area of a bulk extremal surface in Planck units. The main element of our discussion is an implementation of an appropriate Schwinger-Keldysh contour to obtain the reduced density matrix (and its powers) of a given region, as is relevant for the replica construction. We map this contour into the bulk gravitational theory, and argue that the saddle point solutions of these replica geometries lead to a consistent prescription for computing the field theory Rényi entropies. In the limiting case where the replica index is taken to unity, a local analysis suffices to show that these saddles lead to the extremal surfaces of interest. We also comment on various properties of holographic entanglement that follow from this construction.

  8. Eddy sensors for small diameter stainless steel tubes.

    Energy Technology Data Exchange (ETDEWEB)

    Skinner, Jack L.; Morales, Alfredo Martin; Grant, J. Brian; Korellis, Henry James; LaFord, Marianne Elizabeth; Van Blarigan, Benjamin; Andersen, Lisa E.

    2011-08-01

    The goal of this project was to develop non-destructive, minimally disruptive eddy sensors to inspect small diameter stainless steel metal tubes. Modifications to Sandia's Emphasis/EIGER code allowed for the modeling of eddy current bobbin sensors near or around 1/8-inch outer diameter stainless steel tubing. Modeling results indicated that an eddy sensor based on a single axial coil could effectively detect changes in the inner diameter of a stainless steel tubing. Based on the modeling results, sensor coils capable of detecting small changes in the inner diameter of a stainless steel tube were designed, built and tested. The observed sensor response agreed with the results of the modeling and with eddy sensor theory. A separate limited distribution SAND report is being issued demonstrating the application of this sensor.

  9. 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)].

  10. Covariant Deformation Quantization of Free Fields

    OpenAIRE

    Harrivel, Dikanaina

    2006-01-01

    We define covariantly a deformation of a given algebra, then we will see how it can be related to a deformation quantization of a class of observables in Quantum Field Theory. Then we will investigate the operator order related to this deformation quantization.

  11. 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.

  12. Evaluation of Water Use Efficiency Derived from MODIS Products against Eddy Variance Measurements in China

    Directory of Open Access Journals (Sweden)

    Li Zhang

    2015-08-01

    Full Text Available Water use efficiency (WUE is a useful indicator to illustrate the interaction of carbon and water cycles in terrestrial ecosystems. MODIS gross primary production (GPP and evapotranspiration (ET products have been used to analyze the spatial and temporal patterns of WUE and their relationships with environmental factors at regional and global scales. Although MODIS GPP and ET products have been evaluated using eddy covariance flux measurements, the accuracy of WUE estimated from MODIS products has not been well quantified. In this paper, we evaluated WUE estimated from MODIS GPP and ET products against eddy covariance measurements of GPP and ET during 2003–2008 at eight sites of the Chinese flux observation and research network (ChinaFLUX and conducted sensitivity analysis to investigate the possible key contributors to the bias of MODIS products. Results show that MODIS products underestimate eight-day water use efficiency in four forest ecosystems and one cropland ecosystem with the bias from −0.36–−2.28 g·C·kg−1 H2O, while overestimating it in three grassland ecosystems with the bias from 0.26–1.11 g·C·kg−1 H2O. Mean annual WUE was underestimated by 14%–54% at four forest sites, 45% at one cropland site and 7% at an alpine grassland site, but overestimated by 66% and 9% at a temperate grassland site and an alpine meadow site, respectively. The underestimation of WUE by MODIS data results from underestimated GPP and overestimated ET at four forest sites, while MODIS WUE values are significantly overvalued mainly due to underestimated ET in the three grassland ecosystems. The maximum light use efficiency and fraction of photosynthetically-active radiation (FPAR were the two most sensitive factors to the estimation of WUE derived from the MODIS GPP and ET algorithms. The error in meteorological data partly caused the overestimation of ET and accordingly underestimation in WUE in subtropical and tropical forests. The bias of

  13. Compact, Low-power Nitrous Oxide Monitor for Eddy Flux Soil Emission Measurements

    Science.gov (United States)

    Shorter, Joanne; Nelson, David; McManus, Barry; Zahniser, Mark

    2015-04-01

    Nitrous oxide, N2O, is one of the most important greenhouse and ozone-depleting gases. The concentration of N2O in the atmosphere has been increasing at a rate of 0.3% per year, with this rise believed to be largely due to soil emissions and agricultural practices (Park et al. 2011; Park et al. 2012). The eddy covariance technique, which requires fast (~10 Hz) measurement of mixing ratios and wind data, is perhaps the most effective technique available to quantify the exchange of gases between the atmosphere and the biosphere. It is very useful for addressing the high spatial and temporal variability of nitrous oxide emissions from soils. Nitrous oxide monitors appropriate for eddy covariance measurements generally require large flow rates (~10 - 15 slpm) and high speed, high power vacuum pumps (500 lpm, 600 W). These requirements complicate and in some environments prevent successful field deployment. We have addressed this by developing a compact, low-power nitrous oxide monitor for eddy flux or soil chamber measurements with a dramatically reduced sample cell volume. The sample volume is reduced nearly 5 fold (from 500 to 108 cm3) with only a two-fold reduction in optical path length (from 76 m to 36 m). The new multi-pass cell has an aluminum tube insert with a tapered internal volume that follows the mode envelope of the multi-pass spot pattern. This permits the use of a much smaller, lower power pump while still achieving high precision and fast response. Precision of 26 parts per trillion (ppt) in 1 sec was achieved with a 1/e response time of 0.14 s using a relatively low speed vacuum pump (100 lpm, 350 W). Further reductions in cell volume are planned which should permit sensitive eddy covariance measurements of nitrous oxide using an even smaller, lower power pump (60 lpm, 160 W) and modest sample flow rates (~2 slpm). We have also recently studied the application of a standard ARI nitrous oxide monitor to measurement of N2O isotopologues emitted into

  14. 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.

  15. Toward relaxed eddy accumulation measurements of sediment-water exchange in aquatic ecosystems

    Science.gov (United States)

    Lemaire, Bruno J.; Noss, Christian; Lorke, Andreas

    2017-09-01

    Solute transport across the sediment-water interface has major implications for water quality and biogeochemical cycling in aquatic ecosystems. Existing measurement techniques, however, are not capable of resolving sediment-water fluxes of most constituents under in situ flow conditions. We investigated whether relaxed eddy accumulation (REA), a micrometeorological technique with conditional sampling of turbulent updrafts and downdrafts, can be adapted to the aquatic environment. We simulated REA fluxes by reanalyzing eddy covariance measurements from a riverine lake. We found that the empirical coefficient that relates mass fluxes to the concentration difference between both REA samples is invariant with scalar and flow and responds as predicted by a joint Gaussian distribution of linearly correlated variables. Simulated REA fluxes differed on average by around 30% from eddy covariance fluxes (mean absolute error). Assessment of the lower quantification limit suggests that REA can potentially be applied for measuring benthic fluxes of a new range of constituents that cannot be assessed by standard eddy covariance methods.

  16. Role of mesoscale eddies on the variability of biogenic flux in the northern and central Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Vidya, P.J.; PrasannaKumar, S.

    in the NBBT and CBBT matched well with the reported life span of cyclonic eddies in the BoB [Chen et al., 2012; Cheng et al., 2013]. Hence, we examined the role of mesoscale eddies in the above observed variability. 3.3 Eddy identification Mesoscale... periods at NBBT and CBBT. However, we focus our attention to only cyclonic eddy as they can enhance the biological production in the BoB through eddy-pumping of nutrients [Prasanna Kumar et al., 2007; Muraleedharan et al., 2007; Nuncio, 2007; Kurien et...

  17. Imposed quasi-normality in covariance structure analysis

    NARCIS (Netherlands)

    Koning, Ruud H.; Neudecker, H.; Wansbeek, T.

    1993-01-01

    In the analysis of covariance structures, the distance between an observed covariance matrix S of order k x k and C(6) E(S) is minimized by searching over the 8-space. The criterion leading to a best asymptotically normal (BAN) estimator of 0 is found by minimizing the difference between vecS and

  18. A three domain covariance framework for EEG/MEG data

    NARCIS (Netherlands)

    Ros, B.P.; Bijma, F.; de Gunst, M.C.M.; de Munck, J.C.

    2015-01-01

    In this paper we introduce a covariance framework for the analysis of single subject EEG and MEG data that takes into account observed temporal stationarity on small time scales and trial-to-trial variations. We formulate a model for the covariance matrix, which is a Kronecker product of three

  19. 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.

  20. Covariance Models for Hydrological Applications

    Science.gov (United States)

    Hristopulos, Dionissios

    2014-05-01

    This methodological contribution aims to present some new covariance models with applications in the stochastic analysis of hydrological processes. More specifically, we present explicit expressions for radially symmetric, non-differentiable, Spartan covariance functions in one, two, and three dimensions. The Spartan covariance parameters include a characteristic length, an amplitude coefficient, and a rigidity coefficient which determines the shape of the covariance function. Different expressions are obtained depending on the value of the rigidity coefficient and the dimensionality. If the value of the rigidity coefficient is much larger than one, the Spartan covariance function exhibits multiscaling. Spartan covariance models are more flexible than the classical geostatatistical models (e.g., spherical, exponential). Their non-differentiability makes them suitable for modelling the properties of geological media. We also present a family of radially symmetric, infinitely differentiable Bessel-Lommel covariance functions which are valid in any dimension. These models involve combinations of Bessel and Lommel functions. They provide a generalization of the J-Bessel covariance function, and they can be used to model smooth processes with an oscillatory decay of correlations. We discuss the dependence of the integral range of the Spartan and Bessel-Lommel covariance functions on the parameters. We point out that the dependence is not uniquely specified by the characteristic length, unlike the classical geostatistical models. Finally, we define and discuss the use of the generalized spectrum for characterizing different correlation length scales; the spectrum is defined in terms of an exponent α. We show that the spectrum values obtained for exponent values less than one can be used to discriminate between mean-square continuous but non-differentiable random fields. References [1] D. T. Hristopulos and S. Elogne, 2007. Analytic properties and covariance functions of

  1. Remote field eddy current testing

    Energy Technology Data Exchange (ETDEWEB)

    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.

  2. Growing eddies reduce tailing in rough-walled rock fractures

    Science.gov (United States)

    Yeo, I. W.; Lee, S. H.; Lee, K. K.; Detwiler, R. L.

    2015-12-01

    We present the first direct observation of fluid flow and solute transport in a microscopic rough-walled fracture using micro-PIV to assess the evolution of non-Fickian tailing as eddies developed at larger fluid velocities. These observations demonstrated a previously-unidentified, important phenomenon: normalized BTCs became highly skewed towards later times up until a limiting fluid velocity, beyond which tailing decreased and peak concentrations increased. Further microscopic observation of particle trajectories clarified the likely cause of the reduced tailing at higher velocities. Tailing increased until the onset of eddies in large-aperture regions. As eddies became fully developed, particles were initially entrained in the eddies, but then cast back into the main flow channel, which reduced tailing. Numerical studies designed to more clearly understand the 3D nature of flow and transport showed that streamlines swirled near the fracture walls in a large-aperture region and re-entered the main flow channel. These numerical results support our interpretation of the experimental observation. This study, based on combined direct observations and numerical simulations, clearly demonstrated that there was no well-defined separation stream surface delineating so-called immobile (recirculation) and mobile zones in the 3D nature of the flow and transport and the tails decreased with growing eddies due to mass transfer by advective paths from eddies into the main flow channels. These experimental and numerical results contradict results from numerous previous studies based upon simulations in 2D fracture geometries and highlight the need for caution when using 2D simulations to understand 3D transport processes.

  3. Parametric Covariance Model for Horizon-Based Optical Navigation

    Science.gov (United States)

    Hikes, Jacob; Liounis, Andrew J.; Christian, John A.

    2016-01-01

    This Note presents an entirely parametric version of the covariance for horizon-based optical navigation measurements. The covariance can be written as a function of only the spacecraft position, two sensor design parameters, the illumination direction, the size of the observed planet, the size of the lit arc to be used, and the total number of observed horizon points. As a result, one may now more clearly understand the sensitivity of horizon-based optical navigation performance as a function of these key design parameters, which is insight that was obscured in previous (and nonparametric) versions of the covariance. Finally, the new parametric covariance is shown to agree with both the nonparametric analytic covariance and results from a Monte Carlo analysis.

  4. Dummy covariates in CUB models

    Directory of Open Access Journals (Sweden)

    Maria Iannario

    2013-05-01

    Full Text Available In this paper we discuss the use of dummy variables as sensible covariates in a class of statistical models which aim at explaining the subjects’ preferences with respect to several items. After a brief introduction to CUB models, the work considers statistical interpretations of dummy covariates. Then, a simulation study is performed to evaluate the power discrimination of an asymptotic test among sub-populations. Some empirical evidences and concluding remarks end the paper.

  5. Chlorophyll transported by mesoscale eddies in the Southeastern Tropical Indian Ocean

    Science.gov (United States)

    Yang, Guang; zhao, Xia; Yu, Weidong

    2017-04-01

    The effect of eddies on the surface chlorophyll-a (CHL) offshore distribution in the Southeastern Tropical Indian Ocean (SETIO; 95°-115°E, 5°-20°S) was studied from 1997 to 2010. During this period, a high CHL extension was observed to be closely accompanied with strong eddy activities. Our results show that the high CHL is mainly associated with cyclonic eddies (CEs), which pump the subsurface nutrients to the upper ocean and trap and increase the amount of CHL inside the eddies. Moreover, to investigate the relationship between the eddy activity and CHL offshore extension in the SETIO region, we analyzed the mean CHL with the eddies detected from altimeter data, which showed that the amount of CHL inside CEs is significantly greater than the mean background value and the amount of CHL inside anticyclonic eddies (AEs) as well within 400 km offshore. This result indicates that the high CHL offshore extension in the SETIO could be sustained by the vertical nutrient pumping and horizontal advection of eddies. Furthermore, CHL showed significant seasonal variation in the SETIO. The nearshore CHL seasonal variation is controlled by the Asian-Australia monsoon, whereas the offshore CHL seasonal variation is significantly enhanced by eddy activity.

  6. Southern Ocean Eddy Heat Flux and Eddy-Mean Flow Interactions in Drake Passage

    Science.gov (United States)

    Foppert, Annie

    The Antarctic Circumpolar Current (ACC) is a complex current system composed of multiple jets that is both unique to the world's oceans and relatively under observed compared with other current systems. Observations taken by current- and pressure-recording inverted echo sounders (CPIES) over four years, from November 2007 to November 2011, quantify the mean structure of one of the main jets of the ACC - the Polar Front - in a composite-mean sense. While the array of CPIES deployed in Drake Passage included a 3 x 7 local dynamics array, analysis of the Polar Front makes use of the line of CPIES that spanned the width of Drake Passage (C-Line). The Polar Front tends to prefer one of two locations, separated along the C-Line by 1° of latitude, with the core of the jet centered on corresponding geopotential height contours (with a 17 cm dierence between the northern and southern jets). Potential vorticity fields suggest that the Polar Front is susceptible to baroclinic instability, regardless of whether it is found upstream (farther south along the C-Line) or downstream (farther north along the C-Line) of the Shackleton Fracture Zone (SFZ), yet the core of the jet remains a barrier to smaller-scale mixing, as inferred from estimated mixing lengths. Within the local dynamics array of CPIES, the observed offset between eddy heat flux (EHF) and eddy kinetic energy (EKE) and the alignment of EHF with sea surface height (SSH) standard deviation motivates a proxy for depth-integrated EHF that can be estimated from available satellite SSH data. An eddy-resolving numerical model develops the statistics of a logarithmic fit between SSH standard deviation and cross-frontal EHF that is applied to the ACC in a circumglobal sense. We find 1.06 PW enters the ACC from the north and 0.02 PW exits towards Antarctica. The magnitude of the estimated EHF, along with contemporaneous estimates of the mean heat flux, suggests that the air-sea heat flux south of the PF is an overestimate

  7. 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

  8. Quantifying How Observations Inform a Numerical Reanalysis of Hawaii

    Science.gov (United States)

    Powell, B. S.

    2017-11-01

    When assimilating observations into a model via state-estimation, it is possible to quantify how each observation changes the modeled estimate of a chosen oceanic metric. Using an existing 2 year reanalysis of Hawaii that includes more than 31 million observations from satellites, ships, SeaGliders, and autonomous floats, I assess which observations most improve the estimates of the transport and eddy kinetic energy. When the SeaGliders were in the water, they comprised less than 2.5% of the data, but accounted for 23% of the transport adjustment. Because the model physics constrains advanced state-estimation, the prescribed covariances are propagated in time to identify observation-model covariance. I find that observations that constrain the isopycnal tilt across the transport section provide the greatest impact in the analysis. In the case of eddy kinetic energy, observations that constrain the surface-driven upper ocean have more impact. This information can help to identify optimal sampling strategies to improve both state-estimates and forecasts.

  9. Unravelling Lorentz Covariance and the Spacetime Formalism

    Directory of Open Access Journals (Sweden)

    Cahill R. T.

    2008-10-01

    Full Text Available We report the discovery of an exact mapping from Galilean time and space coordinates to Minkowski spacetime coordinates, showing that Lorentz covariance and the space-time construct are consistent with the existence of a dynamical 3-space, and absolute motion. We illustrate this mapping first with the standard theory of sound, as vibrations of a medium, which itself may be undergoing fluid motion, and which is covariant under Galilean coordinate transformations. By introducing a different non-physical class of space and time coordinates it may be cast into a form that is covariant under Lorentz transformations wherein the speed of sound is now the invariant speed. If this latter formalism were taken as fundamental and complete we would be lead to the introduction of a pseudo-Riemannian spacetime description of sound, with a metric characterised by an invariant speed of sound. This analysis is an allegory for the development of 20th century physics, but where the Lorentz covariant Maxwell equations were constructed first, and the Galilean form was later constructed by Hertz, but ignored. It is shown that the Lorentz covariance of the Maxwell equations only occurs because of the use of non-physical space and time coordinates. The use of this class of coordinates has confounded 20th century physics, and resulted in the existence of a allowing dynamical 3-space being overlooked. The discovery of the dynamics of this 3-space has lead to the derivation of an extended gravity theory as a quantum effect, and confirmed by numerous experiments and observations

  10. Unravelling Lorentz Covariance and the Spacetime Formalism

    Directory of Open Access Journals (Sweden)

    Cahill R. T.

    2008-10-01

    Full Text Available We report the discovery of an exact mapping from Galilean time and space coordinates to Minkowski spacetime coordinates, showing that Lorentz covariance and the space- time construct are consistent with the existence of a dynamical 3-space, and “absolute motion”. We illustrate this mapping first with the standard theory of sound, as vibra- tions of a medium, which itself may be undergoing fluid motion, and which is covari- ant under Galilean coordinate transformations. By introducing a different non-physical class of space and time coordinates it may be cast into a form that is covariant under “Lorentz transformations” wherein the speed of sound is now the “invariant speed”. If this latter formalism were taken as fundamental and complete we would be lead to the introduction of a pseudo-Riemannian “spacetime” description of sound, with a metric characterised by an “invariant speed of sound”. This analysis is an allegory for the development of 20th century physics, but where the Lorentz covariant Maxwell equa- tions were constructed first, and the Galilean form was later constructed by Hertz, but ignored. It is shown that the Lorentz covariance of the Maxwell equations only occurs because of the use of non-physical space and time coordinates. The use of this class of coordinates has confounded 20th century physics, and resulted in the existence of a “flowing” dynamical 3-space being overlooked. The discovery of the dynamics of this 3-space has lead to the derivation of an extended gravity theory as a quantum effect, and confirmed by numerous experiments and observations

  11. Coastal Kelvin waves and dynamics of Gulf of Aden eddies

    Science.gov (United States)

    Valsala, Vinu K.; Rao, Rokkam R.

    2016-10-01

    The Gulf of Aden (GA) is a small semi-enclosed oceanic region between the Red Sea and the western Arabian Sea. The GA is characterised with westward propagating cyclonic and anti-cyclonic eddies throughout the year. The genesis and propagation of these eddies into the GA have been the focus of several studies which concluded that oceanic instabilities (both barotropic and baroclinic) as well as the Rossby waves from the Arabian Sea are the responsible mechanisms for the presence and maintenance of these eddies. Using a high-resolution ( 11 km) reduced gravity hydrodynamic layered model with controlled lateral boundary conditions at the three sides of the GA here we show yet another factor, the coastally propagating Kelvin waves along the coastal Arabia (coasts of Oman and Yemen), is also critically important in setting up a favourable condition for the oceanic instabilities and sustenance of meso-scale eddies in the GA. These Kelvin waves at both seasonal and intra-seasonal time scales are found play an important role in the timing and amplitudes of eddies observed in the GA.

  12. Evolution of physical and biological characteristics of mesoscale eddy in north-central Red Sea

    KAUST Repository

    Zarokanellos, Nikolaos

    2015-04-01

    Eddies appear to be important to both the physical and biogeochemical dynamics of the Red Sea. Numerical simulations of physical dynamics and remote sensing studies of chlorophyll concentration and sea surface height in the Red Sea indicate their importance to the upper portions of the sea (Raitsos et al., 2013; Yao et al., 2014; Zhan et al., 2014). Despite their apparent importance, process studies of these eddies have been lacking. In March 2013 we began an extended observational study of the north-central Red Sea (NCRS) where anticyclonic eddies have been observed. The study began with a ship-based characterization of the eddy and was followed by a three-month observational time series using an autonomous glider equipped with a CTD, oxygen sensor, and optical sensors for chlorophyll, CDOM and optical backscatter. The ship-based study captured an initial snapshot of an anticyclonic eddy and it\\'s associated biological and bio-optical distributions. Initially, chlorophyll distributions tended to mirror the density distribution, with deeper isopycnals and chlorophyll maximum depth in the anticyclonic eddy center. The anticyclone eddy in March had an along basin diameter of 150 km, penetrated vertically less than 150 m and elevated near surface chlorophyll concentrations appeared along its outer boundary. The shallowing of the pycnocline of the outer boundaries of the anticyclone eddy on March may elevate nutrients into the lower euphotic zone, contributing to phytoplankton productivity and biomass within the eddy. This eddy contains most of the kinetic energy of the region with the maximum velocities up to 30 - 35 cm/s. The eddy appeared to interact with the coastal reefs where exchange particulate and dissolved matter may occur. The autonomous glider provided the spring-to-summer progression of the system with increasing stratification, shallowing of the subsurface chlorophyll maximum, and fluctuations in the position and intensity of the eddy. Our glider effort

  13. The influence of Gulf Stream eddies and meanders on near-surface chlorophyll

    Science.gov (United States)

    Gaube, Peter; McGillicuddy, Dennis J.

    2017-04-01

    The Gulf Stream region contains strong mesoscale variability that significantly influences planktonic ecosystems residing therein. Meanders of the Gulf Stream can be identified as eastward propagating features in maps of sea level anomaly. These meanders can become unstable and pinch off to form nonlinear mesoscale eddies (rings) that trap large parcels of water. Following formation, ecosystems trapped within these eddies are subjected to temporally varying vertical velocities throughout their lifetime. As a result of both horizontal advection and vertical fluxes, multiple physical-biological mechanisms can simultaneously influence phytoplankton communities trapped in eddies. In this study we examine how the near-surface chlorophyll field (CHL) evolves in meanders and eddies by comparing satellite observations with an eddy-resolving ocean model. Prior in situ and satellite observations have revealed that during the formation of cyclonic Gulf Stream meanders, water with elevated CHL is transported southward. In anticyclonic meanders, water with reduced CHL is transported northward. Alternating submesoscale patches of upwelling and downwelling occur along the meandering front; however, evidence of a biological response to meander-induced vertical motion was not observed in meander-centric composite averages. During the formation of nonlinear Gulf Stream eddies, elevated and suppressed CHL is trapped and subsequently transported westward in cyclones and anticyclones, respectively. Following formation, CHL is observed to increase in the cores of anticyclones. The observed positive trend in CHL in anticyclones is consistent with the influence of eddy-induced Ekman pumping (eddy/wind interaction) that generates upwelling in anticyclones and downwelling in cyclones. To substantiate the influence of eddy-induced Ekman pumping on CHL in Gulf Stream eddies, two separate eddy-resolving physical-biological simulations are compared. The first simulation is forced with a

  14. Time tracking and interaction of energy-eddies at different scales

    Science.gov (United States)

    Cardesa, Jose I.; Vela-Martin, Alberto; Jimenez, Javier

    2016-11-01

    We study the energy cascade through coherent structures obtained in time-resolved simulations of incompressible, statistically steady isotropic turbulence. The structures are defined as geometrically connected regions of the flow with high kinetic energy. We compute the latter by band-pass filtering the velocity field around a scale r. We analyse the dynamics of structures extracted with different r, which are a proxy for eddies containing energy at those r. We find that the size of these "energy-eddies" scales with r, while their lifetime scales with the local eddy-turnover r 2 / 3ɛ - 1 / 3 , where ɛ is the energy dissipation averaged over all space and time. Furthermore, a statistical analysis over the lives of the eddies shows a slight predominance of the splitting over the merging process. When we isolate the eddies which do not interact with other eddies of the same scale, we observe a parent-child dependence by which, on average, structures are born at scale r during the decaying part of the life of a structure at scale r' > r . The energy-eddy at r' lives in the same region of space as that at r. Finally, we investigate how interactions between eddies at the same scale are echoed across other scales. Funded by the ERC project Coturb.

  15. Covariant Description of Isothermic Surfaces

    Science.gov (United States)

    Tafel, J.

    2016-12-01

    We present a covariant formulation of the Gauss-Weingarten equations and the Gauss-Mainardi-Codazzi equations for surfaces in 3-dimensional curved spaces. We derive a coordinate invariant condition on the first and second fundamental form which is locally necessary and sufficient for the surface to be isothermic. We show how to construct isothermic coordinates.

  16. 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.

  17. The influence of Loop Current perturbations on the formation and evolution of Tortugas eddies in the southern Straits of Florida

    Science.gov (United States)

    Fratantoni, Paula S.; Lee, Thomas N.; Podesta, Guillermo P.; Muller-Karger, Frank

    1998-10-01

    Large cyclonic eddies on the northern edge of the Florida Current are the dominant mesoscale features within the southern Straits of Florida. The most prominent of these features is a quasi-stationary eddy that forms near the Dry Tortugas. Our observations, compiled from 3 years of advanced very high resolution radiometer measurements in the Straits of Florida and Gulf of Mexico, demonstrate a strong relationship between the generation of anticyclonic rings from the Gulf of Mexico Loop Current and the evolution of Tortugas eddies within the southern Straits of Florida. In six cases, Tortugas eddies evolve from cyclonic frontal eddies which form along the boundary of the Loop Current. The eddies remain stationary near the Dry Tortugas until they are impacted by an approaching Loop Current frontal eddy. The length of time an eddy spends near the Dry Tortugas is increased when the Loop Current sheds an anticyclonic ring. The involvement of a Loop Current frontal eddy in the ring-shedding process results in a delay in its, and hence the Tortugas eddy's, downstream propagation. Results suggest that the lifetime of a Tortugas eddy can be as long as 140 days when a ring-shedding event occurs, or as short as 50 days in the absence of any ring-shedding events. Upon entering the Straits of Florida, the Tortugas eddies are deformed by the narrowing topography and shrink to approximately 55% of their original size as they propagated downstream. The shrinking of these eddies is accompanied by an accelerated translation from 5 km/d in the western Straits of Florida to 16 km/d in the east.

  18. Multivariate covariance generalized linear models

    DEFF Research Database (Denmark)

    Bonat, W. H.; Jørgensen, Bent

    2016-01-01

    We propose a general framework for non-normal multivariate data analysis called multivariate covariance generalized linear models, designed to handle multivariate response variables, along with a wide range of temporal and spatial correlation structures defined in terms of a covariance link...... function combined with a matrix linear predictor involving known matrices. The method is motivated by three data examples that are not easily handled by existing methods. The first example concerns multivariate count data, the second involves response variables of mixed types, combined with repeated...... measures and longitudinal structures, and the third involves a spatiotemporal analysis of rainfall data. The models take non-normality into account in the conventional way by means of a variance function, and the mean structure is modelled by means of a link function and a linear predictor. The models...

  19. Assessment of Spatial Representativeness of Eddy Covariance Flux Data from Flux Tower to Regional Grid

    Directory of Open Access Journals (Sweden)

    Hesong Wang

    2016-09-01

    Full Text Available Combining flux tower measurements with remote sensing or land surface models is generally regarded as an efficient method to scale up flux data from site to region. However, due to the heterogeneous nature of the vegetated land surface, the changing flux source areas and the mismatching between ground source areas and remote sensing grids, direct use of in-situ flux measurements can lead to major scaling bias if their spatial representativeness is unknown. Here, we calculate and assess the spatial representativeness of 15 flux sites across northern China in two aspects: first, examine how well a tower represents fluxes from the specific targeted vegetation type, which is called vegetation-type level; and, second, examine how representative is the flux tower footprint of the broader landscape or regional extents, which is called spatial-scale level. We select fraction of target vegetation type (FTVT and Normalized Difference Vegetation Index (NDVI as key indicators to calculate the spatial representativeness of 15 EC sites. Then, these sites were ranked into four grades based on FTVT or cluster analysis from high to low in order: (1 homogeneous; (2 representative; (3 acceptable; and (4 disturbed measurements. The results indicate that: (1 Footprint climatology for each site was mainly distributed in an irregular shape, had similar spatial pattern as spatial distribution of prevailing wind direction; (2 At vegetation-type level, the number of homogeneous, representative, acceptable and disturbed measurements is 8, 4, 1 and 2, respectively. The average FTVT was 0.83, grass and crop sites had greater representativeness than forest sites; (3 At spatial-scale level, flux sites with zonal vegetation had greater representativeness than non-zonal vegetation sites, and the scales were further divided into three sub-scales: (a in flux site scale, the average of absolute NDVI bias was 4.34%, the number of the above four grades is 9, 4, 1 and 1, respectively; (b in remote sensing pixel scale, the average of absolute NDVI bias was 8.27%, the number is 7, 2, 2 and 4, respectively; (c in land model grid scale, the average of absolute NDVI bias was 12.13%, the number is 5, 4, 3 and 3. These results demonstrate the variation of spatial representativeness of flux measurements among different application levels and scales and highlighted the importance of proper interpretation of EC flux measurements. These results also suggest that source area of EC flux should be involved in model validation and/or calibration with EC flux measurements.

  20. On the use of integrating FLUXNET eddy covariance and remote sensing data for model evaluation

    Science.gov (United States)

    Reichstein, Markus; Jung, Martin; Beer, Christian; Carvalhais, Nuno; Tomelleri, Enrico; Lasslop, Gitta; Baldocchi, Dennis; Papale, Dario

    2010-05-01

    The current FLUXNET database (www.fluxdata.org) of CO2, water and energy exchange between the terrestrial biosphere and the atmosphere contains almost 1000 site-years with data from more than 250 sites, encompassing all major biomes of the world and being processed in a standardized way (1-3). In this presentation we show that the information in the data is sufficient to derive generalized empirical relationships between vegetation/respective remote sensing information, climate and the biosphere-atmosphere exchanges across global biomes. These empirical patterns are used to generate global grids of the respective fluxes and derived properties (e.g. radiation and water-use efficiencies or climate sensitivities in general, bowen-ratio, AET/PET ratio). For example we revisit global 'text-book' numbers such as global Gross Primary Productivity (GPP) estimated since the 70's as ca. 120PgC (4), or global evapotranspiration (ET) estimated at 65km3/yr-1 (5) - for the first time with a more solid and direct empirical basis. Evaluation against independent data at regional to global scale (e.g. atmospheric CO2 inversions, runoff data) lends support to the validity of our almost purely empirical up-scaling approaches. Moreover climate factors such as radiation, temperature and water balance are identified as driving factors for variations and trends of carbon and water fluxes, with distinctly different sensitivities between different vegetation types. Hence, these global fields of biosphere-atmosphere exchange and the inferred relations between climate, vegetation type and fluxes should be used for evaluation or benchmarking of climate models or their land-surface components, while overcoming scale-issues with classical point-to-grid-cell comparisons. 1. M. Reichstein et al., Global Change Biology 11, 1424 (2005). 2. D. Baldocchi, Australian Journal of Botany 56, 1 (2008). 3. D. Papale et al., Biogeosciences 3, 571 (2006). 4. D. E. Alexander, R. W. Fairbridge, Encyclopedia of Environmental Science (Springer, Heidelberg, 1999), pp. 741. 5. T. Oki, S. Kanae, Science 313, 1068 (Aug 25, 2006)

  1. Eddy covariance and scintillation measurements of atmospheric exchange processes over different types of vegetation

    NARCIS (Netherlands)

    Nieveen, J.P.

    1999-01-01

    Introduction and objectives

    Good comprehension of the energy and mass cycles and their effect on climate dynamics is crucial to understanding, predicting and anticipating ecological changes due to possible future climate perturbations. Here direct and long-term flux

  2. Assessing Crop Coefficients for Natural Vegetated Areas Using Satellite Data and Eddy Covariance Stations

    Directory of Open Access Journals (Sweden)

    Chiara Corbari

    2017-11-01

    Full Text Available The Food and Agricultural Organization (FAO method for potential evapotranspiration assessment is based on the crop coefficient, which allows one to relate the reference evapotranspiration of well irrigated grass to the potential evapotranspiration of specific crops. The method was originally developed for cultivated species based on lysimeter measurements of potential evapotranspiration. Not many applications to natural vegetated areas exist due to the lack of available data for these species. In this paper we investigate the potential of using evapotranspiration measurements acquired by micrometeorological stations for the definition of crop coefficient functions of natural vegetated areas and extrapolation to ungauged sites through remotely sensed data. Pastures, deciduous and evergreen forests have been considered and lower crop coefficient values are found with respect to FAO data.

  3. Cosmology of a covariant Galilean field.

    Science.gov (United States)

    De Felice, Antonio; Tsujikawa, Shinji

    2010-09-10

    We study the cosmology of a covariant scalar field respecting a Galilean symmetry in flat space-time. We show the existence of a tracker solution that finally approaches a de Sitter fixed point responsible for cosmic acceleration today. The viable region of model parameters is clarified by deriving conditions under which ghosts and Laplacian instabilities of scalar and tensor perturbations are absent. The field equation of state exhibits a peculiar phantomlike behavior along the tracker, which allows a possibility to observationally distinguish the Galileon gravity from the cold dark matter model with a cosmological constant.

  4. Subduction in an Eddy-Resolving State Estimate of the Northeast Atlantic Ocean

    Science.gov (United States)

    Gebbie, Geoffrey

    2004-01-01

    Are eddies an important contributor to subduction in the eastern subtropical gyre? Here, an adjoint model is used to combine a regional, eddy-resolving numerical model with observations to produce a state estimate of the ocean circulation. The estimate is a synthesis of a variety of in- situ observations from the Subduction Experiment, TOPEX/POSEIDON altimetry, and the MTI General Circulation Model. The adjoint method is successful because the Northeast Atlantic Ocean is only weakly nonlinear. The state estimate provides a physically-interpretable, eddy-resolving information source to diagnose subduction. Estimates of eddy subduction for the eastern subtropical gyre of the North Atlantic are larger than previously calculated from parameterizations in coarse-resolution models. Furthermore, eddy subduction rates have typical magnitudes of 15% of the total subduction rate. Eddies contribute as much as 1 Sverdrup to water-mass transformation, and hence subduction, in the North Equatorial Current and the Azores Current. The findings of this thesis imply that the inability to resolve or accurately parameterize eddy subduction in climate models would lead to an accumulation of error in the structure of the main thermocline, even in the relatively-quiescent eastern subtropical gyre.

  5. Large-eddy simulation of contrails

    Energy Technology Data Exchange (ETDEWEB)

    Chlond, A. [Max-Planck-Inst. fuer Meteorologie, Hamburg (Germany)

    1997-12-31

    A large eddy simulation (LES) model has been used to investigate the role of various external parameters and physical processes in the life-cycle of contrails. The model is applied to conditions that are typical for those under which contrails could be observed, i.e. in an atmosphere which is supersaturated with respect to ice and at a temperature of approximately 230 K or colder. The sensitivity runs indicate that the contrail evolution is controlled primarily by humidity, temperature and static stability of the ambient air and secondarily by the baroclinicity of the atmosphere. Moreover, it turns out that the initial ice particle concentration and radiative processes are of minor importance in the evolution of contrails at least during the 30 minutes simulation period. (author) 9 refs.

  6. Eddy current compensated double diffusion encoded (DDE) MRI.

    Science.gov (United States)

    Mueller, Lars; Wetscherek, Andreas; Kuder, Tristan Anselm; Laun, Frederik Bernd

    2017-01-01

    Eddy currents might lead to image distortions in diffusion-weighted echo planar imaging. A method is proposed to reduce their effects on double diffusion encoding (DDE) MRI experiments and the thereby derived microscopic fractional anisotropy (μFA). The twice-refocused spin echo scheme was adapted for DDE measurements. To assess the effect of individual diffusion encodings on the image distortions, measurements of a grid of plastic rods in water were performed. The effect of eddy current compensation on μFA measurements was evaluated in the brains of six healthy volunteers. The use of an eddy current compensation reduced the signal variation. As expected, the distortions caused by the second encoding were larger than those of the first encoding, entailing a stronger need to compensate for them. For an optimal result, however, both encodings had to be compensated. The artifact reduction strongly improved the measurement of the μFA in ventricles and gray matter by reducing the overestimation. An effect of the compensation on absolute μFA values in white matter was not observed. It is advisable to compensate both encodings in DDE measurements for eddy currents. Magn Reson Med 77:328-335, 2017. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

  7. Empirical State Error Covariance Matrix for Batch Estimation

    Science.gov (United States)

    Frisbee, Joe

    2015-01-01

    State estimation techniques effectively provide mean state estimates. However, the theoretical state error covariance matrices provided as part of these techniques often suffer from a lack of confidence in their ability to describe the uncertainty in the estimated states. By a reinterpretation of the equations involved in the weighted batch least squares algorithm, it is possible to directly arrive at an empirical state error covariance matrix. The proposed empirical state error covariance matrix will contain the effect of all error sources, known or not. This empirical error covariance matrix may be calculated as a side computation for each unique batch solution. Results based on the proposed technique will be presented for a simple, two observer and measurement error only problem.

  8. Disjunct eddy accumulation flux measurements of individual VOCs from an urban environment

    Science.gov (United States)

    Velasco, Erik; Pressley, Shelley; Grivicke, Rasa; Allwine, Eugene; Jobson, B. Tom; Westberg, Hal; Molina, Luisa T.; Lamb, Brian

    2010-05-01

    As part of the MILAGRO-2006 study a flux tower was deployed at urban Mexico City to measure turbulent fluxes of trace gases. Fluxes of individual volatile organic compounds (VOCs) were measured using a disjunct eddy accumulation (DEA) sampler with ionization detector/gas chromatography (GC-FID) analysis. The DEA method partitions the air into two reservoirs based on the magnitude and direction of the vertical wind speed. The VOCs concentrations in both reservoirs are analyzed and used to determine the fluxes with the vertical wind velocities. Although this method is not as precise as other micrometeorological techniques, such as the eddy covariance method, it provides the ability to directly measure the fluxes of an extended number of individual species using off-line sensors without relying on similarity scaling or empirical parameters. According to our knowledge these measurements constitute the first time that the DEA method was applied in an urban environment. A comparison of the DEA fluxes of selected aromatic and olefinic species measured in parallel by the more accurate eddy covariance and disjunct eddy covariance techniques coupled with fast-response analytical sensors evidenced a flux under-prediction by the DEA method. However, this under-prediction was consistent and constant for the species compared, allowing an analysis of the DEA fluxes in terms of relative magnitudes and ratios. It was found that fluxes of alkane species were the dominant VOCs fluxes, which is consistent with ambient concentration measurements and the local emissions inventory. Among the top 20 mean VOCs fluxes measured during daytime, 11 corresponded to alkanes, followed by 5 aromatics, 2 olefins, 1 alkyne and 1 oxygenated.

  9. Visualization and assessment of spatio-temporal covariance properties

    KAUST Repository

    Huang, Huang

    2017-11-23

    Spatio-temporal covariances are important for describing the spatio-temporal variability of underlying random fields in geostatistical data. For second-order stationary random fields, there exist subclasses of covariance functions that assume a simpler spatio-temporal dependence structure with separability and full symmetry. However, it is challenging to visualize and assess separability and full symmetry from spatio-temporal observations. In this work, we propose a functional data analysis approach that constructs test functions using the cross-covariances from time series observed at each pair of spatial locations. These test functions of temporal lags summarize the properties of separability or symmetry for the given spatial pairs. We use functional boxplots to visualize the functional median and the variability of the test functions, where the extent of departure from zero at all temporal lags indicates the degree of non-separability or asymmetry. We also develop a rank-based nonparametric testing procedure for assessing the significance of the non-separability or asymmetry. Essentially, the proposed methods only require the analysis of temporal covariance functions. Thus, a major advantage over existing approaches is that there is no need to estimate any covariance matrix for selected spatio-temporal lags. The performances of the proposed methods are examined by simulations with various commonly used spatio-temporal covariance models. To illustrate our methods in practical applications, we apply it to real datasets, including weather station data and climate model outputs.

  10. An intrathermocline eddy and a tropical cyclone in the Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Gordon, A.L.; Shroyer, E.; Murty, V.S.N.

    (ITE). An eddy tracking algorithm3 first detects the anticyclone near 13°N, 89°E on 24 August 2013, roughly 550 km from the location of the ship transect of the ITE. After the RV Revelle ITE observation the weak positive sea surface anomaly... from the surface intensified anticyclonic eddy on 27 November 2013. Intrathermocline Eddies An ITE, a class of subsurface vorticities4, have been detected in numerous regions including marginal seas, east- ern boundary currents, and within subtropical...

  11. Oceanic eddies in synthetic aperture radar images

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Melting ice is a tracer in this case. Shear cyclonic elements at the south- ern and eastern parts of the eddy periphery are well seen in both images. In a time of 3 days between the images the eddy shape and spatial ori- entation were not changed, however displacement of shear elements at its periphery in the direc-.

  12. Oceanic eddies in synthetic aperture radar images

    Indian Academy of Sciences (India)

    ... and in bays, spin-off eddies and mushroom-like structures (vortex dipoles) are given and discussed. It is shown that a common feature for most of the eddies detected in the SAR images is a broad spectrum of spatial scales, spiral shape and shear nature. It is concluded that the spaceborne SARs give valuable information ...

  13. 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...

  14. Acoustic propagations in the presence of a subsurface cold core eddy in the Bay of Bengal - A case study

    Digital Repository Service at National Institute of Oceanography (India)

    PrasannaKumar, S.; Navelkar, G.S.; Murty, T.V.R.; Murty, C.S.

    Acoustic characteristics of a cold core eddy, observed in the Bay of Bengal during southwest monsoon period is studied using CTD data along the western boundary. The presence of eddy brings about a reduction in the ambient sound speEd. by 10 m.s sup...

  15. Local atmospheric response to warm mesoscale ocean eddies in the Kuroshio-Oyashio Confluence region.

    Science.gov (United States)

    Sugimoto, Shusaku; Aono, Kenji; Fukui, Shin

    2017-09-19

    In the extratropical regions, surface winds enhance upward heat release from the ocean to atmosphere, resulting in cold surface ocean: surface ocean temperature is negatively correlated with upward heat flux. However, in the western boundary currents and eddy-rich regions, the warmer surface waters compared to surrounding waters enhance upward heat release-a positive correlation between upward heat release and surface ocean temperature, implying that the ocean drives the atmosphere. The atmospheric response to warm mesoscale ocean eddies with a horizontal extent of a few hundred kilometers remains unclear because of a lack of observations. By conducting regional atmospheric model experiments, we show that, in the Kuroshio-Oyashio Confluence region, wintertime warm eddies heat the marine atmospheric boundary layer (MABL), and accelerate westerly winds in the near-surface atmosphere via the vertical mixing effect, leading to wind convergence around the eastern edge of eddies. The warm-eddy-induced convergence forms local ascending motion where convective precipitation is enhanced, providing diabatic heating to the atmosphere above MABL. Our results indicate that warm eddies affect not only near-surface atmosphere but also free atmosphere, and possibly synoptic atmospheric variability. A detailed understanding of warm eddy-atmosphere interaction is necessary to improve in weather and climate projections.

  16. Feasibility of conductivity imaging using subject eddy currents induced by switching of MRI gradients.

    Science.gov (United States)

    Oran, Omer Faruk; Ider, Yusuf Ziya

    2017-05-01

    To investigate the feasibility of low-frequency conductivity imaging based on measuring the magnetic field due to subject eddy currents induced by switching of MRI z-gradients. We developed a simulation model for calculating subject eddy currents and the magnetic fields they generate (subject eddy fields). The inverse problem of obtaining conductivity distribution from subject eddy fields was formulated as a convection-reaction partial differential equation. For measuring subject eddy fields, a modified spin-echo pulse sequence was used to determine the contribution of subject eddy fields to MR phase images. In the simulations, successful conductivity reconstructions were obtained by solving the derived convection-reaction equation, suggesting that the proposed reconstruction algorithm performs well under ideal conditions. However, the level of the calculated phase due to the subject eddy field in a representative object indicates that this phase is below the noise level and cannot be measured with an uncertainty sufficiently low for accurate conductivity reconstruction. Furthermore, some artifacts other than random noise were observed in the measured phases, which are discussed in relation to the effects of system imperfections during readout. Low-frequency conductivity imaging does not seem feasible using basic pulse sequences such as spin-echo on a clinical MRI scanner. Magn Reson Med 77:1926-1937, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  17. A note on covariant dynamical semigroups

    Science.gov (United States)

    Holevo, A. S.

    1993-04-01

    It is shown that in the standard representation of the generator of a norm continuous dynamical semigroup, which is covariant with respect to a unitary representation of an amenable group, the completely positive part can always be chosen covariant and the Hamiltonian commuting with the representation. The structure of the generator of a translation covariant dynamical semigroup is described.

  18. Covariant gauges at finite temperature

    OpenAIRE

    Landshoff, P V; Rebhan, A

    1992-01-01

    A prescription is presented for real-time finite-temperature perturbation theory in covariant gauges, in which only the two physical degrees of freedom of the gauge-field propagator acquire thermal parts. The propagators for the unphysical degrees of freedom of the gauge field, and for the Faddeev-Popov ghost field, are independent of temperature. This prescription is applied to the calculation of the one-loop gluon self-energy and the two-loop interaction pressure, and is found to be simpler...

  19. Eddy-Resolving Simulation of the Atlantic Water Circulation in the Fram Strait With Focus on the Seasonal Cycle

    Science.gov (United States)

    Wekerle, Claudia; Wang, Qiang; von Appen, Wilken-Jon; Danilov, Sergey; Schourup-Kristensen, Vibe; Jung, Thomas

    2017-11-01

    Eddy driven recirculation of Atlantic Water (AW) in the Fram Strait modifies the amount of heat that reaches the Arctic Ocean, but is difficult to constrain in ocean models due to very small Rossby radius there. In this study, we explore the effect of resolved eddies on the AW circulation in a locally eddy-resolving simulation of the global Finite-Element-Sea ice-Ocean Model (FESOM) integrated for the years 2000-2009, by focusing on the seasonal cycle. An eddy-permitting simulation serves as a control run. Our results suggest that resolving local eddy dynamics is critical to realistically simulate ocean dynamics in the Fram Strait. Strong eddy activity simulated by the eddy-resolving model, with peak in winter and lower values in summer, is comparable in magnitude and seasonal cycle to observations from a long-term mooring array, whereas the eddy-permitting simulation underestimates the observed magnitude. Furthermore, a strong cold bias in the central Fram Strait present in the eddy-permitting simulation is reduced due to resolved eddy dynamics, and AW transport into the Arctic Ocean is increased with possible implications for the Arctic Ocean heat budget. Given the good agreement between the eddy-resolving model and measurements, it can help filling gaps that point-wise observations inevitably leave. For example, the path of the West Spitsbergen Current offshore branch, measured in the winter months by the mooring array, is shown to continue cyclonically around the Molloy Deep in the model, representing the major AW recirculation branch in this season.

  20. A three domain covariance framework for EEG/MEG data.

    Science.gov (United States)

    Roś, Beata P; Bijma, Fetsje; de Gunst, Mathisca C M; de Munck, Jan C

    2015-10-01

    In this paper we introduce a covariance framework for the analysis of single subject EEG and MEG data that takes into account observed temporal stationarity on small time scales and trial-to-trial variations. We formulate a model for the covariance matrix, which is a Kronecker product of three components that correspond to space, time and epochs/trials, and consider maximum likelihood estimation of the unknown parameter values. An iterative algorithm that finds approximations of the maximum likelihood estimates is proposed. Our covariance model is applicable in a variety of cases where spontaneous EEG or MEG acts as source of noise and realistic noise covariance estimates are needed, such as in evoked activity studies, or where the properties of spontaneous EEG or MEG are themselves the topic of interest, like in combined EEG-fMRI experiments in which the correlation between EEG and fMRI signals is investigated. We use a simulation study to assess the performance of the estimator and investigate the influence of different assumptions about the covariance factors on the estimated covariance matrix and on its components. We apply our method to real EEG and MEG data sets. Copyright © 2015 Elsevier Inc. All rights reserved.

  1. Random sampling and validation of covariance matrices of resonance parameters

    Science.gov (United States)

    Plevnik, Lucijan; Zerovnik, Gašper

    2017-09-01

    Analytically exact methods for random sampling of arbitrary correlated parameters are presented. Emphasis is given on one hand on the possible inconsistencies in the covariance data, concentrating on the positive semi-definiteness and consistent sampling of correlated inherently positive parameters, and on the other hand on optimization of the implementation of the methods itself. The methods have been applied in the program ENDSAM, written in the Fortran language, which from a file from a nuclear data library of a chosen isotope in ENDF-6 format produces an arbitrary number of new files in ENDF-6 format which contain values of random samples of resonance parameters (in accordance with corresponding covariance matrices) in places of original values. The source code for the program ENDSAM is available from the OECD/NEA Data Bank. The program works in the following steps: reads resonance parameters and their covariance data from nuclear data library, checks whether the covariance data is consistent, and produces random samples of resonance parameters. The code has been validated with both realistic and artificial data to show that the produced samples are statistically consistent. Additionally, the code was used to validate covariance data in existing nuclear data libraries. A list of inconsistencies, observed in covariance data of resonance parameters in ENDF-VII.1, JEFF-3.2 and JENDL-4.0 is presented. For now, the work has been limited to resonance parameters, however the methods presented are general and can in principle be extended to sampling and validation of any nuclear data.

  2. Cyclonic eddies in the eastern Gulf of Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Vukovich, F.M.; Maul, G.A.

    1985-01-01

    Cold-domed cyclonic eddies juxtaposed to the cyclonic shear side of the Gulf Loop Current are observed in simultaneously obtained hydrodgraphic, current meter mooring, and satellite infrared data. The cyclones are initially observed in the satellite data as cold perturbations on the northern extreme of the current and grow either into a cold tongue or a quasi-stable meander off the Dry Tortugas, Florida. Area shipboard surveys show closed isopleths of temperature and salinity, and surface geostropic current speeds relative to 1000 db are in excess of 100 cm s/sup -1/. The diameter of the cold domes varied from 80 to 120 km. Separation of large anticyclonic rings is always observed to be preceded by cylonic eddies in the transition zone between Campeche Bank and the West Florida Shelf, but only on the eastern side. Not every cyclonic eddy off Dry Tortugas is associated with the separation of an anticyclonic ring; some are eroded away by the Florida Current, but they have never been observed in 10 years of satellite data to advect eastward through the Straits of Florida.

  3. Empirical Likelihood in Nonignorable Covariate-Missing Data Problems.

    Science.gov (United States)

    Xie, Yanmei; Zhang, Biao

    2017-04-20

    Missing covariate data occurs often in regression analysis, which frequently arises in the health and social sciences as well as in survey sampling. We study methods for the analysis of a nonignorable covariate-missing data problem in an assumed conditional mean function when some covariates are completely observed but other covariates are missing for some subjects. We adopt the semiparametric perspective of Bartlett et al. (Improving upon the efficiency of complete case analysis when covariates are MNAR. Biostatistics 2014;15:719-30) on regression analyses with nonignorable missing covariates, in which they have introduced the use of two working models, the working probability model of missingness and the working conditional score model. In this paper, we study an empirical likelihood approach to nonignorable covariate-missing data problems with the objective of effectively utilizing the two working models in the analysis of covariate-missing data. We propose a unified approach to constructing a system of unbiased estimating equations, where there are more equations than unknown parameters of interest. One useful feature of these unbiased estimating equations is that they naturally incorporate the incomplete data into the data analysis, making it possible to seek efficient estimation of the parameter of interest even when the working regression function is not specified to be the optimal regression function. We apply the general methodology of empirical likelihood to optimally combine these unbiased estimating equations. We propose three maximum empirical likelihood estimators of the underlying regression parameters and compare their efficiencies with other existing competitors. We present a simulation study to compare the finite-sample performance of various methods with respect to bias, efficiency, and robustness to model misspecification. The proposed empirical likelihood method is also illustrated by an analysis of a data set from the US National Health and

  4. Large eddy simulations of compressible magnetohydrodynamic turbulence

    Science.gov (United States)

    Grete, Philipp

    2017-02-01

    Supersonic, magnetohydrodynamic (MHD) turbulence is thought to play an important role in many processes - especially in astrophysics, where detailed three-dimensional observations are scarce. Simulations can partially fill this gap and help to understand these processes. However, direct simulations with realistic parameters are often not feasible. Consequently, large eddy simulations (LES) have emerged as a viable alternative. In LES the overall complexity is reduced by simulating only large and intermediate scales directly. The smallest scales, usually referred to as subgrid-scales (SGS), are introduced to the simulation by means of an SGS model. Thus, the overall quality of an LES with respect to properly accounting for small-scale physics crucially depends on the quality of the SGS model. While there has been a lot of successful research on SGS models in the hydrodynamic regime for decades, SGS modeling in MHD is a rather recent topic, in particular, in the compressible regime. In this thesis, we derive and validate a new nonlinear MHD SGS model that explicitly takes compressibility effects into account. A filter is used to separate the large and intermediate scales, and it is thought to mimic finite resolution effects. In the derivation, we use a deconvolution approach on the filter kernel. With this approach, we are able to derive nonlinear closures for all SGS terms in MHD: the turbulent Reynolds and Maxwell stresses, and the turbulent electromotive force (EMF). We validate the new closures both a priori and a posteriori. In the a priori tests, we use high-resolution reference data of stationary, homogeneous, isotropic MHD turbulence to compare exact SGS quantities against predictions by the closures. The comparison includes, for example, correlations of turbulent fluxes, the average dissipative behavior, and alignment of SGS vectors such as the EMF. In order to quantify the performance of the new nonlinear closure, this comparison is conducted from the

  5. Eddy Generation and Shedding in a Tidally Energetic Channel

    Science.gov (United States)

    McIlvenny, J.; Gillibrand, P. A.; Walters, R. A.

    2016-02-01

    The Pentland Firth in northern Scotland, and its subsidiary channel the Inner Sound, are currently under scrutiny as the first tidal energy array in the world is installed during 2016. The tidal flows in the channel and sound have been intensively observed and modelled in recent years, and the turbulent nature of the flow, with features of eddy generation and shedding, is becoming increasingly well known. Turbulence and eddies pose potential risks to the turbine infrastructure through enhanced stress on the blades, while understanding environmental effects of energy extraction also requires accurate simulation of the hydrodynamics of the flow. Here, we apply a mixed finite element/finite volume hydrodynamic model to the northern Scottish shelf, with a particular focus on flows through the Pentland Firth and the Inner Sound. We use an unstructured grid model, which allows the open boundaries to be far removed from the region of interest, while still allowing a grid spacing of 40m in the Inner Sound. The model employs semi-implicit techniques to solve the momentum and free surface equations, and semi-Lagrangian methods to solve the material derivative in the momentum equation, making it fast, robust and accurate and suitable for simulating flows in irregular coastal ocean environments. The model is well suited to address questions relating to tidal energy potential. We present numerical simulations of tidal currents in The Pentland Firth and Inner Sound. Observed velocities in the Inner Sound, measured by moored ADCP deployments, reach speeds of up to 5 m s-1 and the model successfully reproduces these strong currents. In the simulations, eddies are formed by interactions between the strong flow and the northern and southern headlands on the island of Stroma; some of these eddies are trapped and remain locked in position, whereas others are shed and transported away from the generation zone. We track the development and advection of eddies in relation to the site of

  6. Covariance Evaluation Methodology for Neutron Cross Sections

    Energy Technology Data Exchange (ETDEWEB)

    Herman,M.; Arcilla, R.; Mattoon, C.M.; Mughabghab, S.F.; Oblozinsky, P.; Pigni, M.; Pritychenko, b.; Songzoni, A.A.

    2008-09-01

    We present the NNDC-BNL methodology for estimating neutron cross section covariances in thermal, resolved resonance, unresolved resonance and fast neutron regions. The three key elements of the methodology are Atlas of Neutron Resonances, nuclear reaction code EMPIRE, and the Bayesian code implementing Kalman filter concept. The covariance data processing, visualization and distribution capabilities are integral components of the NNDC methodology. We illustrate its application on examples including relatively detailed evaluation of covariances for two individual nuclei and massive production of simple covariance estimates for 307 materials. Certain peculiarities regarding evaluation of covariances for resolved resonances and the consistency between resonance parameter uncertainties and thermal cross section uncertainties are also discussed.

  7. An Empirical State Error Covariance Matrix for Batch State Estimation

    Science.gov (United States)

    Frisbee, Joseph H., Jr.

    2011-01-01

    State estimation techniques serve effectively to provide mean state estimates. However, the state error covariance matrices provided as part of these techniques suffer from some degree of lack of confidence in their ability to adequately describe the uncertainty in the estimated states. A specific problem with the traditional form of state error covariance matrices is that they represent only a mapping of the assumed observation error characteristics into the state space. Any errors that arise from other sources (environment modeling, precision, etc.) are not directly represented in a traditional, theoretical state error covariance matrix. Consider that an actual observation contains only measurement error and that an estimated observation contains all other errors, known and unknown. It then follows that a measurement residual (the difference between expected and observed measurements) contains all errors for that measurement. Therefore, a direct and appropriate inclusion of the actual measurement residuals in the state error covariance matrix will result in an empirical state error covariance matrix. This empirical state error covariance matrix will fully account for the error in the state estimate. By way of a literal reinterpretation of the equations involved in the weighted least squares estimation algorithm, it is possible to arrive at an appropriate, and formally correct, empirical state error covariance matrix. The first specific step of the method is to use the average form of the weighted measurement residual variance performance index rather than its usual total weighted residual form. Next it is helpful to interpret the solution to the normal equations as the average of a collection of sample vectors drawn from a hypothetical parent population. From here, using a standard statistical analysis approach, it directly follows as to how to determine the standard empirical state error covariance matrix. This matrix will contain the total uncertainty in the

  8. 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.

  9. Rotating concave eddy current probe

    Science.gov (United States)

    Roach, Dennis P [Albuquerque, NM; Walkington, Phil [Albuquerque, NM; Rackow, Kirk A [Albuquerque, NM; Hohman, Ed [Albuquerque, NM

    2008-04-01

    A rotating concave eddy current probe for detecting fatigue cracks hidden from view underneath the head of a raised head fastener, such as a buttonhead-type rivet, used to join together structural skins, such as aluminum aircraft skins. The probe has a recessed concave dimple in its bottom surface that closely conforms to the shape of the raised head. The concave dimple holds the probe in good alignment on top of the rivet while the probe is rotated around the rivet's centerline. One or more magnetic coils are rigidly embedded within the probe's cylindrical body, which is made of a non-conducting material. This design overcomes the inspection impediment associated with widely varying conductivity in fastened joints.

  10. Stochastic precipitation generator with hidden state covariates

    Science.gov (United States)

    Kim, Yongku; Lee, GyuWon

    2017-08-01

    Time series of daily weather such as precipitation, minimum temperature and maximum temperature are commonly required for various fields. Stochastic weather generators constitute one of the techniques to produce synthetic daily weather. The recently introduced approach for stochastic weather generators is based on generalized linear modeling (GLM) with covariates to account for seasonality and teleconnections (e.g., with the El Niño). In general, stochastic weather generators tend to underestimate the observed interannual variance of seasonally aggregated variables. To reduce this overdispersion, we incorporated time series of seasonal dry/wet indicators in the GLM weather generator as covariates. These seasonal time series were local (or global) decodings obtained by a hidden Markov model of seasonal total precipitation and implemented in the weather generator. The proposed method is applied to time series of daily weather from Seoul, Korea and Pergamino, Argentina. This method provides a straightforward translation of the uncertainty of the seasonal forecast to the corresponding conditional daily weather statistics.

  11. Covariates of alcohol consumption among career firefighters.

    Science.gov (United States)

    Piazza-Gardner, A K; Barry, A E; Chaney, E; Dodd, V; Weiler, R; Delisle, A

    2014-12-01

    Little is known about rates of alcohol consumption in career firefighters. To assess the quantity and frequency of alcohol consumption among career firefighters and the covariates that influence consumption levels. A convenience sample of career firefighters completed an online, self-administered, health assessment survey. Hierarchical binary logistic regression assessed the ability of several covariates to predict binge drinking status. The majority of the sample (n = 160) consumed alcohol (89%), with approximately one-third (34%) having a drinking binge in the past 30 days. The regression model explained 13-18% of the variance in binge drinking status and correctly classified 71% of cases. Race (P firefighters were 1.08 times less likely to binge drink (95% CI: 0.87-0.97). Drinking levels observed in this study exceed those of the general adult population, including college students. Thus, it appears that firefighters represent an at-risk drinking group. Further investigations addressing reasons for alcohol use and abuse among firefighters are warranted. This study and subsequent research will provide information necessary for the development and testing of tailored interventions aimed at reducing firefighter alcohol consumption. © The Author 2014. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  12. Contribution of mesoscale eddies to Black Sea ventilation

    Science.gov (United States)

    Capet, Arthur; Mason, Evan; Pascual, Ananda; Grégoire, Marilaure

    2017-04-01

    The shoaling of the Black Sea oxycline is one of the most urgent environmental issues in the Black Sea. The permanent oxycline derives directly from the Black Sea permanent stratification and has shoaled alarmingly in the last decades, due to a shifting balance between oxygen consumption and ventilation processes (Capet et al. 2016). The understanding of this balance is thus of the utmost importance and requires to quantify 1) the export of nutrients and organic materials from the shelf regions to the open sea and 2) the ventilation processes. These two processes being influenced by mesoscale features, it is critical to understand the role of the semi-permanent mesoscale structures in horizontal (center/periphery) and vertical (diapycnal and isopycnal) exchanges. A useful insight can be obtained by merging observations from satellite altimeter and in situ profilers (ARGO). In such composite analyses, eddies are first automatically identified and tracked from altimeter data (Mason et al. 2014, py-eddy-tracker). Vertical ARGO profiles are then expressed in terms of their position relative to eddy centers and radii. Derived statistics indicate how consistently mesoscale eddies alter the vertical structure, and provide a deeper understanding of the associated horizontal and vertical fluxes. However, this data-based approach is limited in the Black Sea due to the lower quality of gridded altimetric products in the vicinity of the coast, where semi-permanent mesoscale structures prevail. To complement the difficult analysis of this sparse dataset, a compositing methodology. is also applied to model outputs from the 5km GHER-BHAMBI Black Sea implementation (CMEMS BS-MFC). Characteristic biogeochemical anomalies associated with eddies in the model are analyzed per se, and compared to the observation-based analysis. Capet, A., Stanev, E. V., Beckers, J.-M., Murray, J. W., and Grégoire, M.: Decline of the Black Sea oxygen inventory, Biogeosciences, 13, 1287-1297, doi:10

  13. 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

    are larger than the Ked maximum value corresponding to the criterion. Analysis of the experimental data on meteor train observations shows that energy dissipation with a small rate of about 0.2 W kg−1 sometimes can induce turbulence with eddy scales very close to the scale height of the atmosphere. Our results also explain the discrepancy between the large cooling rates calculated by Vlasov and Kelley (2014 and the temperatures given by the MSIS-E-90 model because, in these cases, the measured eddy diffusion coefficients used in calculating the cooling rates are larger than the maximum value presented above.

  14. Covariance-enhanced discriminant analysis.

    Science.gov (United States)

    Xu, Peirong; Zhu, J I; Zhu, Lixing; Li, Y I

    Linear discriminant analysis has been widely used to characterize or separate multiple classes via linear combinations of features. However, the high dimensionality of features from modern biological experiments defies traditional discriminant analysis techniques. Possible interfeature correlations present additional challenges and are often underused in modelling. In this paper, by incorporating possible interfeature correlations, we propose a covariance-enhanced discriminant analysis method that simultaneously and consistently selects informative features and identifies the corresponding discriminable classes. Under mild regularity conditions, we show that the method can achieve consistent parameter estimation and model selection, and can attain an asymptotically optimal misclassification rate. Extensive simulations have verified the utility of the method, which we apply to a renal transplantation trial.

  15. Variability of the Somali Current and eddies during the southwest monsoon regimes

    Science.gov (United States)

    Trott, Corinne B.; Subrahmanyam, Bulusu; Murty, V. S. N.

    2017-09-01

    The meso-scale eddies and currents in the Arabian Sea are analyzed using different satellite observations, Simple Oceanic Data Assimilation (SODA) reanalysis, and Ocean Reanalysis System 4 (ORAS4) from 1993 to 2016 to investigate the impacts of Southwest (SW) Monsoon strength on Somali Current (SC) mesoscale circulations such as the Great Whirl (GW), the Socotra Eddy (SE), the Southern Gyre (SG), and smaller eddies. Increased Ekman pumping during stronger SW monsoons strengthens coastal upwelling along the Somali coast. The Arabian Sea basin-wide anticyclonic circulation and presence of the GW form mesoscale circulation patterns favourable to advection of upwelled waters eastward into the central Arabian Sea. In September, after the SW monsoon winds reach peak strength in July and August, a higher number of discrete anticyclonic eddies with higher (> 20 cm) sea surface height anomalies develop in strong and normal intensity SW monsoon seasons than weaker SW monsoon seasons.

  16. Eddy Current Testing, RQA/M1-5330.17.

    Science.gov (United States)

    National Aeronautics and Space Administration, Huntsville, AL. George C. Marshall Space Flight Center.

    As one in the series of classroom training handbooks, prepared by the U.S. space program, instructional material is presented in this volume concerning familiarization and orientation on eddy current testing. The subject is presented under the following headings: Introduction, Eddy Current Principles, Eddy Current Equipment, Eddy Current Methods,…

  17. Statistical uncertainty of eddy flux-based estimates of gross ecosystem carbon exchange at Howland Forest, Maine

    Science.gov (United States)

    Hagen, S. C.; Braswell, B. H.; Linder, E.; Frolking, S.; Richardson, A. D.; Hollinger, D. Y.

    2006-04-01

    We present an uncertainty analysis of gross ecosystem carbon exchange (GEE) estimates derived from 7 years of continuous eddy covariance measurements of forest-atmosphere CO2 fluxes at Howland Forest, Maine, USA. These data, which have high temporal resolution, can be used to validate process modeling analyses, remote sensing assessments, and field surveys. However, separation of tower-based net ecosystem exchange (NEE) into its components (respiration losses and photosynthetic uptake) requires at least one application of a model, which is usually a regression model fitted to nighttime data and extrapolated for all daytime intervals. In addition, the existence of a significant amount of missing data in eddy flux time series requires a model for daytime NEE as well. Statistical approaches for analytically specifying prediction intervals associated with a regression require, among other things, constant variance of the data, normally distributed residuals, and linearizable regression models. Because the NEE data do not conform to these criteria, we used a Monte Carlo approach (bootstrapping) to quantify the statistical uncertainty of GEE estimates and present this uncertainty in the form of 90% prediction limits. We explore two examples of regression models for modeling respiration and daytime NEE: (1) a simple, physiologically based model from the literature and (2) a nonlinear regression model based on an artificial neural network. We find that uncertainty at the half-hourly timescale is generally on the order of the observations themselves (i.e., ˜100%) but is much less at annual timescales (˜10%). On the other hand, this small absolute uncertainty is commensurate with the interannual variability in estimated GEE. The largest uncertainty is associated with choice of model type, which raises basic questions about the relative roles of models and data.

  18. Events of equatorward translation of the Vitoria Eddy

    Science.gov (United States)

    Arruda, Wilton Z.; Campos, Edmo J. D.; Zharkov, Volodymyr; Soutelino, Rafael G.; da Silveira, Ilson C. A.

    2013-11-01

    The Vitoria Eddy (VE) is a cyclone in the Brazil Current (BC) formed immediately to the south of the Vitoria-Trindade Ridge. Using altimetric derived SSH and outputs of a regional ocean model, we show evidences that once the VE is shed from a BC meander, if it is not reabsorbed, it follows a northward path crossing the Vitoria-Trindade Ridge. In all observed events of equatorward translation, the VE interacts with the anticyclonic Abrolhos Eddy (AE) centered about 19°S-37°W. Depending on the strength of the AE, the VE can take one of two different paths: one orbiting the AE and the other tight to the bathymetric lines. During the entire translation, the AE is under the influence of the equatorward intermediate flow of the Intermediate Western Boundary Current/North Brazil Undercurrent system, a key factor for its equatorward translation.

  19. The use of mesoscale eddies by juvenile loggerhead sea turtles (Caretta caretta) in the southwestern Atlantic.

    Science.gov (United States)

    Gaube, Peter; Barceló, Caren; McGillicuddy, Dennis J; Domingo, Andrés; Miller, Philip; Giffoni, Bruno; Marcovaldi, Neca; Swimmer, Yonat

    2017-01-01

    Marine animals, such as turtles, seabirds and pelagic fishes, are observed to travel and congregate around eddies in the open ocean. Mesoscale eddies, large swirling ocean vortices with radius scales of approximately 50-100 km, provide environmental variability that can structure these populations. In this study, we investigate the use of mesoscale eddies by 24 individual juvenile loggerhead sea turtles (Caretta caretta) in the Brazil-Malvinas Confluence region. The influence of eddies on turtles is assessed by collocating the turtle trajectories to the tracks of mesoscale eddies identified in maps of sea level anomaly. Juvenile loggerhead sea turtles are significantly more likely to be located in the interiors of anticyclones in this region. The distribution of surface drifters in eddy interiors reveals no significant association with the interiors of cyclones or anticyclones, suggesting higher prevalence of turtles in anticyclones is a result of their behavior. In the southern portion of the Brazil-Malvinas Confluence region, turtle swimming speed is significantly slower in the interiors of anticyclones, when compared to the periphery, suggesting that these turtles are possibly feeding on prey items associated with anomalously low near-surface chlorophyll concentrations observed in those features.

  20. Adjoint sensitivity studies of loop current and eddy shedding in the Gulf of Mexico

    KAUST Repository

    Gopalakrishnan, Ganesh

    2013-07-01

    Adjoint model sensitivity analyses were applied for the loop current (LC) and its eddy shedding in the Gulf of Mexico (GoM) using the MIT general circulation model (MITgcm). The circulation in the GoM is mainly driven by the energetic LC and subsequent LC eddy separation. In order to understand which ocean regions and features control the evolution of the LC, including anticyclonic warm-core eddy shedding in the GoM, forward and adjoint sensitivities with respect to previous model state and atmospheric forcing were computed using the MITgcm and its adjoint. Since the validity of the adjoint model sensitivities depends on the capability of the forward model to simulate the real LC system and the eddy shedding processes, a 5 year (2004–2008) forward model simulation was performed for the GoM using realistic atmospheric forcing, initial, and boundary conditions. This forward model simulation was compared to satellite measurements of sea-surface height (SSH) and sea-surface temperature (SST), and observed transport variability. Despite realistic mean state, standard deviations, and LC eddy shedding period, the simulated LC extension shows less variability and more regularity than the observations. However, the model is suitable for studying the LC system and can be utilized for examining the ocean influences leading to a simple, and hopefully generic LC eddy separation in the GoM. The adjoint sensitivities of the LC show influences from the Yucatan Channel (YC) flow and Loop Current Frontal Eddy (LCFE) on both LC extension and eddy separation, as suggested by earlier work. Some of the processes that control LC extension after eddy separation differ from those controlling eddy shedding, but include YC through-flow. The sensitivity remains stable for more than 30 days and moves generally upstream, entering the Caribbean Sea. The sensitivities of the LC for SST generally remain closer to the surface and move at speeds consistent with advection by the high-speed core of

  1. Process Specification for Eddy Current Inspection

    Science.gov (United States)

    Koshti, Ajay

    2011-01-01

    This process specification establishes the minimum requirements for eddy current inspection of flat surfaces, fastener holes, threaded fasteners and seamless and welded tubular products made from nonmagnetic alloys such as aluminum and stainless steel.

  2. Parameter inference with estimated covariance matrices

    Science.gov (United States)

    Sellentin, Elena; Heavens, Alan F.

    2016-02-01

    When inferring parameters from a Gaussian-distributed data set by computing a likelihood, a covariance matrix is needed that describes the data errors and their correlations. If the covariance matrix is not known a priori, it may be estimated and thereby becomes a random object with some intrinsic uncertainty itself. We show how to infer parameters in the presence of such an estimated covariance matrix, by marginalizing over the true covariance matrix, conditioned on its estimated value. This leads to a likelihood function that is no longer Gaussian, but rather an adapted version of a multivariate t-distribution, which has the same numerical complexity as the multivariate Gaussian. As expected, marginalization over the true covariance matrix improves inference when compared with Hartlap et al.'s method, which uses an unbiased estimate of the inverse covariance matrix but still assumes that the likelihood is Gaussian.

  3. Quantification of ocean model error covariances in an ensemble of high-resolution Bay of Biscay simulations using stochastic modeling of the wind forcing

    Science.gov (United States)

    Vervatis, Vassilios; Testut, Charles-Emmanuel; De Mey, Pierre; Ayoub, Nadia; Chanut, Jerome; Bricaud, Clement

    2014-05-01

    An important factor of any Data Assimilation (DA) scheme is the estimation of the background error covariances. This study is linked to the design of a DA system, based on the ensemble Kalman Filter and the ocean model NEMO. The work is part of the Research and Development activities of LEGOS/CNRS and Mercator-Ocean French teams within the European MyOcean2 project. As a key step towards DA, we perform sensitivity experiments devoted to the evaluation of the model errors and their dynamic, primarily due to wind forcing uncertainties in a free-surface coastal configuration of the Bay of Biscay. More in details, a stochastic approach of a twin experiment is carried out, by applying spatiotemporal Gaussian perturbations in the wind forcing, as an inertial incertitude of the system. A rank histogram is performed to select a member inside the ensemble spread serving as an SSH/SST observational array. The forecast trajectories of 100 members are used to assess the background error statistics of the ocean model. An ensemble normal probability analysis depicts the linear dependence of ocean surface variables and wind perturbations in the abyssal plain. In the coastal areas and in the shelf non Gaussian behavior is revealed. Initially, the ensemble variance is characterized by a moderate increase in the periphery of eddies and in the river mouths. A rapid increase follows observed mainly in the SSH, due to a chaotic evolution across members of the eddies trajectories. The convergence of covariances presents that a few members are sufficient to depict the spatial pattern of variance, whereas a large ensemble is needed to represent errors and correlations in the domain. Artificial experiments are used to increase the ensemble spread, mainly in the coastal areas and in the shelf, by applying temporal filters. Towards that direction, stochastic processes are investigated to increase the ensemble spread, by perturbing other variables than the wind. Ensemble forecasts, driven by

  4. Eddy Current Model of Ball Lightning

    OpenAIRE

    Shelton, J. D.

    2011-01-01

    Eddy Current Model of Ball Lightning Calculations show that high-energy ball lightning may consist of a ball of plasma containing a large circular electric current arising as an eddy current generated by lightning. Synthetic ball lightning might serve as a method of plasma confinement for purposes of nuclear fusion. In this paper, three articles concerning ball lightning and the related phenomenon of large ball lightning are combined to provide insight into this rarely glimpsed occurrence.

  5. What are the best covariates for developing non-stationary rainfall Intensity-Duration-Frequency relationship?

    Science.gov (United States)

    Agilan, V.; Umamahesh, N. V.

    2017-03-01

    Present infrastructure design is primarily based on rainfall Intensity-Duration-Frequency (IDF) curves with so-called stationary assumption. However, in recent years, the extreme precipitation events are increasing due to global climate change and creating non-stationarity in the series. Based on recent theoretical developments in the Extreme Value Theory (EVT), recent studies proposed a methodology for developing non-stationary rainfall IDF curve by incorporating trend in the parameters of the Generalized Extreme Value (GEV) distribution using Time covariate. But, the covariate Time may not be the best covariate and it is important to analyze all possible covariates and find the best covariate to model non-stationarity. In this study, five physical processes, namely, urbanization, local temperature changes, global warming, El Niño-Southern Oscillation (ENSO) cycle and Indian Ocean Dipole (IOD) are used as covariates. Based on these five covariates and their possible combinations, sixty-two non-stationary GEV models are constructed. In addition, two non-stationary GEV models based on Time covariate and one stationary GEV model are also constructed. The best model for each duration rainfall series is chosen based on the corrected Akaike Information Criterion (AICc). From the findings of this study, it is observed that the local processes (i.e., Urbanization, local temperature changes) are the best covariate for short duration rainfall and global processes (i.e., Global warming, ENSO cycle and IOD) are the best covariate for the long duration rainfall of the Hyderabad city, India. Furthermore, the covariate Time is never qualified as the best covariate. In addition, the identified best covariates are further used to develop non-stationary rainfall IDF curves of the Hyderabad city. The proposed methodology can be applied to other situations to develop the non-stationary IDF curves based on the best covariate.

  6. Delving three-dimensional structure of mesoscale eddies in the Northern South China Sea from seismic reflection transects

    Science.gov (United States)

    Xing, Tao

    2017-04-01

    The seismic oceanography technique, a new option to oceanographers, is capable of capturing oceanic fine scale structures of oceanic mesoscale eddies. Mesoscale eddy has significant influence on the ocean thermodynamics and dynamics, biology, and military and civil activities, and is always the hot focus in oceanography. Most of the former eddy studies are focused on the sea surface and little is known about the vertical structures of eddies. Unraveling the three-dimensional structure of mesoscale eddies has been limited by the lack of observations and the complex dynamics of the system. Using an abundance of seismic data, satellite altimeter data and an automated eddy detection scheme, three-dimensional structure of mesoscale eddies during its propagation and evolution are examined in the Northern South China Sea (NSCS). During seismic data processing, after seismic prestack time migration, high-density bispectral analysis method in geovation seismic data process system is applicated. The results show that high-density bispectral analysis method could achieve a speed-by-point analysis and solve the effect of anisotropy at far offset in the vertical inhomogeneous media, and the image quality of final PSTM profile is effectively improved. The possible outcome of this study would advance our understanding of the interaction between the flow and mesoscale eddy.

  7. Treatment Effects with Many Covariates and Heteroskedasticity

    DEFF Research Database (Denmark)

    Cattaneo, Matias D.; Jansson, Michael; Newey, Whitney K.

    The linear regression model is widely used in empirical work in Economics. Researchers often include many covariates in their linear model specification in an attempt to control for confounders. We give inference methods that allow for many covariates and heteroskedasticity. Our results...... then propose a new heteroskedasticity consistent standard error formula that is fully automatic and robust to both (conditional) heteroskedasticity of unknown form and the inclusion of possibly many covariates. We apply our findings to three settings: (i) parametric linear models with many covariates, (ii......) semiparametric semi-linear models with many technical regressors, and (iii) linear panel models with many fixed effects...

  8. On spectral distribution of high dimensional covariation matrices

    DEFF Research Database (Denmark)

    Heinrich, Claudio; Podolskij, Mark

    In this paper we present the asymptotic theory for spectral distributions of high dimensional covariation matrices of Brownian diffusions. More specifically, we consider N-dimensional Itô integrals with time varying matrix-valued integrands. We observe n equidistant high frequency data points...... of the underlying Brownian diffusion and we assume that N/n -> c in (0,oo). We show that under a certain mixed spectral moment condition the spectral distribution of the empirical covariation matrix converges in distribution almost surely. Our proof relies on method of moments and applications of graph theory....

  9. Positive semidefinite integrated covariance estimation, factorizations and asynchronicity

    DEFF Research Database (Denmark)

    Sauri, Orimar; Lunde, Asger; Laurent, Sébastien

    2017-01-01

    An estimator of the ex-post covariation of log-prices under asynchronicity and microstructure noise is proposed. It uses the Cholesky factorization of the covariance matrix in order to exploit the heterogeneity in trading intensities to estimate the different parameters sequentially with as many...... observations as possible. The estimator is positive semidefinite by construction. We derive asymptotic results and confirm their good finite sample properties by means of a Monte Carlo simulation. In the application we forecast portfolio Value-at-Risk and sector risk exposures for a portfolio of 52 stocks. We...

  10. 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 with the proport......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...... 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...

  11. Noisy covariance matrices and portfolio optimization II

    Science.gov (United States)

    Pafka, Szilárd; Kondor, Imre

    2003-03-01

    Recent studies inspired by results from random matrix theory (Galluccio et al.: Physica A 259 (1998) 449; Laloux et al.: Phys. Rev. Lett. 83 (1999) 1467; Risk 12 (3) (1999) 69; Plerou et al.: Phys. Rev. Lett. 83 (1999) 1471) found that covariance matrices determined from empirical financial time series appear to contain such a high amount of noise that their structure can essentially be regarded as random. This seems, however, to be in contradiction with the fundamental role played by covariance matrices in finance, which constitute the pillars of modern investment theory and have also gained industry-wide applications in risk management. Our paper is an attempt to resolve this embarrassing paradox. The key observation is that the effect of noise strongly depends on the ratio r= n/ T, where n is the size of the portfolio and T the length of the available time series. On the basis of numerical experiments and analytic results for some toy portfolio models we show that for relatively large values of r (e.g. 0.6) noise does, indeed, have the pronounced effect suggested by Galluccio et al. (1998), Laloux et al. (1999) and Plerou et al. (1999) and illustrated later by Laloux et al. (Int. J. Theor. Appl. Finance 3 (2000) 391), Plerou et al. (Phys. Rev. E, e-print cond-mat/0108023) and Rosenow et al. (Europhys. Lett., e-print cond-mat/0111537) in a portfolio optimization context, while for smaller r (around 0.2 or below), the error due to noise drops to acceptable levels. Since the length of available time series is for obvious reasons limited in any practical application, any bound imposed on the noise-induced error translates into a bound on the size of the portfolio. In a related set of experiments we find that the effect of noise depends also on whether the problem arises in asset allocation or in a risk measurement context: if covariance matrices are used simply for measuring the risk of portfolios with a fixed composition rather than as inputs to optimization, the

  12. Removing Wave Artifacts from Eddy Correlation Data

    Science.gov (United States)

    Neumann, Andreas; Brand, Andreas

    2017-04-01

    The German Wadden Sea is an extensive system of back-barrier tidal basins along the margin of the southern North Sea. Due to their high productivity and the strong retention potential of labile organic carbon high mineralization rates are expected in this system. Since the sediment bed is sandy, the oxygen fluxes across the sediment-water interface (SWI) may be enhanced by strong tidal currents as well as by wind-induced surface waves. In order to measure oxygen fluxes in-situ without disturbance of the sediment, the Eddy Correlation method (ECM) was introduced to aquatic geoscience by Berg et al. (2003). The method is based on correlating turbulent fluctuations of oxygen concentration and vertical velocity measured at high frequency above the SWI. The method integrates over spatial heterogeneities and allows the observation of total benthic oxygen fluxes in complex systems where other methods like flux chamber deployments and oxygen profile measurements in the sediment fail. Therefore, the method should also reflect effects like the enhancement of oxygen fluxes by porewater advection driven by waves and currents over sandy sediments. Unfortunately the ECM suffers from wave contamination due to stirring sensitivity of the electrodes, spatial separation between the oxygen electrode and the location of velocity measurement as well as by a tilt of the measurement setup at the deployment side. In order to correct for this wave contamination we tested the method of spectral reconstruction initially introduced by Bricker and Monismith (2007) for the determination of Reynolds-stresses in wave-affected environments. In short, this method attempts to remove the wave signal from the Power spectral densities of oxygen concentration and vertical velocity fluctuations by cutting off the wave peak in these spectra. The wave contribution to the co-spectrum between both quantities is then reconstructed by assuming that the phasing in the wave band is dominated by the waves. Based

  13. C-GLORSv5: an improved multipurpose global ocean eddy-permitting physical reanalysis

    Science.gov (United States)

    Storto, Andrea; Masina, Simona

    2016-11-01

    Global ocean reanalyses combine in situ and satellite ocean observations with a general circulation ocean model to estimate the time-evolving state of the ocean, and they represent a valuable tool for a variety of applications, ranging from climate monitoring and process studies to downstream applications, initialization of long-range forecasts and regional studies. The purpose of this paper is to document the recent upgrade of C-GLORS (version 5), the latest ocean reanalysis produced at the Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC) that covers the meteorological satellite era (1980-present) and it is being updated in delayed time mode. The reanalysis is run at eddy-permitting resolution (1/4° horizontal resolution and 50 vertical levels) and consists of a three-dimensional variational data assimilation system, a surface nudging and a bias correction scheme. With respect to the previous version (v4), C-GLORSv5 contains a number of improvements. In particular, background- and observation-error covariances have been retuned, allowing a flow-dependent inflation in the globally averaged background-error variance. An additional constraint on the Arctic sea-ice thickness was introduced, leading to a realistic ice volume evolution. Finally, the bias correction scheme and the initialization strategy were retuned. Results document that the new reanalysis outperforms the previous version in many aspects, especially in representing the variability of global heat content and associated steric sea level in the last decade, the top 80 m ocean temperature biases and root mean square errors, and the Atlantic Ocean meridional overturning circulation; slight worsening in the high-latitude salinity and deep ocean temperature emerge though, providing the motivation for further tuning of the reanalysis system. The dataset is available in NetCDF format at doi:10.1594/PANGAEA.857995.

  14. Covariant Spectator Theory of heavy–light and heavy mesons and the predictive power of covariant interaction kernels

    Energy Technology Data Exchange (ETDEWEB)

    Leitão, Sofia, E-mail: sofia.leitao@tecnico.ulisboa.pt [CFTP, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Stadler, Alfred, E-mail: stadler@uevora.pt [Departamento de Física, Universidade de Évora, 7000-671 Évora (Portugal); CFTP, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Peña, M.T., E-mail: teresa.pena@tecnico.ulisboa.pt [Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); CFTP, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Biernat, Elmar P., E-mail: elmar.biernat@tecnico.ulisboa.pt [CFTP, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)

    2017-01-10

    The Covariant Spectator Theory (CST) is used to calculate the mass spectrum and vertex functions of heavy–light and heavy mesons in Minkowski space. The covariant kernel contains Lorentz scalar, pseudoscalar, and vector contributions. The numerical calculations are performed in momentum space, where special care is taken to treat the strong singularities present in the confining kernel. The observed meson spectrum is very well reproduced after fitting a small number of model parameters. Remarkably, a fit to a few pseudoscalar meson states only, which are insensitive to spin–orbit and tensor forces and do not allow to separate the spin–spin from the central interaction, leads to essentially the same model parameters as a more general fit. This demonstrates that the covariance of the chosen interaction kernel is responsible for the very accurate prediction of the spin-dependent quark–antiquark interactions.

  15. Effect of eddy transport on the nutrient supply into the euphotic zone simulated in an eddy-permitting ocean ecosystem model

    Science.gov (United States)

    Sumata, Hiroshi; Hashioka, Taketo; Suzuki, Tatsuo; Yoshie, Naoki; Okunishi, Takeshi; Aita, Maki N.; Sakamoto, Takashi T.; Ishida, Akio; Okada, Naosuke; Yamanaka, Yasuhiro

    2010-10-01

    Hindcast experiment with an eddy-permitting ocean ecosystem model was performed in order to investigate the process of nutrient supply into the euphotic zone by vertical and horizontal fluxes with multiple time scales. The model reasonably reproduced the basin-scale spatial pattern of biological production and its seasonal cycles with eddy fields, statistically consistent with those observed in the satellite images. The model results illustrated the nutrient cycle in the euphotic zone with mesoscale eddies, in which the vertical advection with mesoscale spatial variation and convection with relatively large spatial variation supply nutrients into the euphotic zone, and the horizontal advection redistributes them within the euphotic zone, thereby fueling biological production. The vertical advection associated with mean flow supplies a substantial part of nutrients from the aphotic zone, and contributions from time-varied vertical fluxes are limited within the tropical region and regions where strong meandering currents exist. Horizontal advection due to seasonal and eddy fluctuations plays an important role in the redistribution process, in addition to that effected by temporal-mean advection. The relative importance of these fluctuations strongly depends on the horizontal scales of vertical nutrient supply, in contrast to the relatively small effects eddy fields have on heat or fresh-water transport in the global ocean.

  16. 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.

  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 classi......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....... In a multi-state framework, a first approach uses internal covariates to define additional (intermediate) transient states in the competing risks model. Another approach is to apply the landmark analysis as described by van Houwelingen [Scandinavian Journal of Statistics 2007, 34, 70-85] in order to study...

  18. The statistical behaviour of attached eddies

    Science.gov (United States)

    Woodcock, J. D.; Marusic, I.

    2015-01-01

    Townsend's attached eddy hypothesis forms the basis of an established model of the logarithmic layer in wall-bounded turbulent flows in which this inertially dominated region is characterised by a hierarchy of geometrically self-similar eddying motions that scale with their distance to the wall. The hypothesis has gained considerable support from high Reynolds number measurements of the second-order moments of the fluctuating velocities. Recently, Meneveau and Marusic ["Generalized logarithmic law for high-order moments in turbulent boundary layers," J. Fluid Mech. 719, R1 (2013)] presented experimental evidence that all even-ordered moments of the streamwise velocity will exhibit a logarithmic dependence on the distance from the wall. They demonstrated that this was consistent with the attached eddy hypothesis, so long as the velocity distribution is assumed to be Gaussian (which allows the use of the central limit theorem). In this paper, we derive this result from the attached eddy model without assuming a Gaussian velocity distribution, and find that such logarithmic behaviours are valid in the large Reynolds number limit. We also revisit the physical and mathematical basis of the attached eddy hypothesis, in order to increase rigour and minimise the assumptions required to apply the hypothesis. To this end, we have extended the proof of Campbell's theorem to apply to the velocity field corresponding to a forest of variously sized eddies that are randomly placed on the wall. This enables us to derive all moments of the velocity in the logarithmic region, including cross-correlations between different components of the velocity. By contrast, previous studies of the attached eddy hypothesis have considered only the mean velocity and its second order moments. From this, we obtain qualitatively correct skewnesses and flatnesses for the spanwise and wall-normal fluctuations. The issue of the Reynolds number dependence of von Kármán's constant is also addressed.

  19. Covariant diagrams for one-loop matching

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zhengkang [Michigan Univ., Ann Arbor, MI (United States). Michigan Center for Theoretical Physics; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2016-10-15

    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 gaugecovariant 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. A cautionary note on generalized linear models for covariance of unbalanced longitudinal data

    KAUST Repository

    Huang, Jianhua Z.

    2012-03-01

    Missing data in longitudinal studies can create enormous challenges in data analysis when coupled with the positive-definiteness constraint on a covariance matrix. For complete balanced data, the Cholesky decomposition of a covariance matrix makes it possible to remove the positive-definiteness constraint and use a generalized linear model setup to jointly model the mean and covariance using covariates (Pourahmadi, 2000). However, this approach may not be directly applicable when the longitudinal data are unbalanced, as coherent regression models for the dependence across all times and subjects may not exist. Within the existing generalized linear model framework, we show how to overcome this and other challenges by embedding the covariance matrix of the observed data for each subject in a larger covariance matrix and employing the familiar EM algorithm to compute the maximum likelihood estimates of the parameters and their standard errors. We illustrate and assess the methodology using real data sets and simulations. © 2011 Elsevier B.V.

  1. An Empirical State Error Covariance Matrix Orbit Determination Example

    Science.gov (United States)

    Frisbee, Joseph H., Jr.

    2015-01-01

    State estimation techniques serve effectively to provide mean state estimates. However, the state error covariance matrices provided as part of these techniques suffer from some degree of lack of confidence in their ability to adequately describe the uncertainty in the estimated states. A specific problem with the traditional form of state error covariance matrices is that they represent only a mapping of the assumed observation error characteristics into the state space. Any errors that arise from other sources (environment modeling, precision, etc.) are not directly represented in a traditional, theoretical state error covariance matrix. First, consider that an actual observation contains only measurement error and that an estimated observation contains all other errors, known and unknown. Then it follows that a measurement residual (the difference between expected and observed measurements) contains all errors for that measurement. Therefore, a direct and appropriate inclusion of the actual measurement residuals in the state error covariance matrix of the estimate will result in an empirical state error covariance matrix. This empirical state error covariance matrix will fully include all of the errors in the state estimate. The empirical error covariance matrix is determined from a literal reinterpretation of the equations involved in the weighted least squares estimation algorithm. It is a formally correct, empirical state error covariance matrix obtained through use of the average form of the weighted measurement residual variance performance index rather than the usual total weighted residual form. Based on its formulation, this matrix will contain the total uncertainty in the state estimate, regardless as to the source of the uncertainty and whether the source is anticipated or not. It is expected that the empirical error covariance matrix will give a better, statistical representation of the state error in poorly modeled systems or when sensor performance

  2. Thin phytoplankton layer formation at eddies, filaments, and fronts in a coastal upwelling zone

    Science.gov (United States)

    Johnston, T. M. Shaun; Cheriton, Olivia M.; Pennington, J. Timothy; Chavez, Francisco P.

    2009-02-01

    On two cruises in August and September 2003 (hereafter cruises 2 and 3) during wind relaxations and transitions to upwelling conditions, thin layers of phytoplankton were observed in or a few meters below the stratified transition layer at the mixed layer base and in regions of sheared flow on the flanks of eddies, filaments, and fronts near Monterey Bay, California. On an earlier cruise in August (cruise 1), no thin layers were found after a prolonged wind relaxation. Chlorophyll concentrations and shear were both an order of magnitude less than on cruises 2 and 3. Our vertical profiles were made using a fluorometer mounted on a conductivity-temperature-depth package, which was lowered from the ship as slowly as 0.25ms-1 every 10 km on five ˜80-km cross-shore transects. Remotely sensed sea-surface temperature, chlorophyll, and currents are required to understand the temporal and spatial evolution of the circulation and to interpret the quasi-synoptic in situ data. Decorrelation scales are ˜20km from lagged temperature and salinity covariances. Objectively mapped sections of the in situ data indicate the waters containing thin layers were recently upwelled at either the Point Sur or Point Año Nuevo upwelling centers. Spatially limited distributions of phytoplankton at the coastal upwelling centers ( ˜40km alongshore, 20 km cross-shore, and 30 m thick) were transformed into thin layers by current shear and isolated from wind-driven vertical mixing by the stratification maximum of the transition layer. Vertically sheared horizontal currents on the flanks of the eddies, filaments, and fronts horizontally stretched and vertically thinned phytoplankton distributions. These thin, elongated structures were then observed as thin layers of phytoplankton in vertical fluorescence profiles at four stations on cruise 2 and eight stations on cruise 3. Light winds during relaxations did not mix away these thin layers. On cruise 2, thin layers were found at eddies at the

  3. Random sampling and validation of covariance matrices of resonance parameters

    Directory of Open Access Journals (Sweden)

    Plevnik Lucijan

    2017-01-01

    Full Text Available Analytically exact methods for random sampling of arbitrary correlated parameters are presented. Emphasis is given on one hand on the possible inconsistencies in the covariance data, concentrating on the positive semi-definiteness and consistent sampling of correlated inherently positive parameters, and on the other hand on optimization of the implementation of the methods itself. The methods have been applied in the program ENDSAM, written in the Fortran language, which from a file from a nuclear data library of a chosen isotope in ENDF-6 format produces an arbitrary number of new files in ENDF-6 format which contain values of random samples of resonance parameters (in accordance with corresponding covariance matrices in places of original values. The source code for the program ENDSAM is available from the OECD/NEA Data Bank. The program works in the following steps: reads resonance parameters and their covariance data from nuclear data library, checks whether the covariance data is consistent, and produces random samples of resonance parameters. The code has been validated with both realistic and artificial data to show that the produced samples are statistically consistent. Additionally, the code was used to validate covariance data in existing nuclear data libraries. A list of inconsistencies, observed in covariance data of resonance parameters in ENDF-VII.1, JEFF-3.2 and JENDL-4.0 is presented. For now, the work has been limited to resonance parameters, however the methods presented are general and can in principle be extended to sampling and validation of any nuclear data.

  4. Scale-dependent background-error covariance localisation

    Directory of Open Access Journals (Sweden)

    Mark Buehner

    2015-12-01

    Full Text Available A new approach is presented and evaluated for efficiently applying scale-dependent spatial localisation to ensemble background-error covariances within an ensemble-variational data assimilation system. The approach is primarily motivated by the requirements of future data assimilation systems for global numerical weather prediction that will be capable of resolving the convective scale. Such systems must estimate the global and synoptic scales at least as well as current global systems while also effectively making use of information from frequent and spatially dense observation networks to constrain convective-scale features. Scale-dependent covariance localisation allows a wider range of scales to be efficiently estimated while simultaneously assimilating all available observations. In the context of an idealised numerical experiment, it is shown that using scale-dependent localisation produces an improved ensemble-based estimate of spatially varying covariances as compared with standard spatial localisation. When applied to an ensemble of Arctic sea-ice concentration, it is demonstrated that strong spatial gradients in the relative contribution of different spatial scales in the ensemble covariances result in strong spatial variations in the overall amount of spatial localisation. This feature is qualitatively similar to what might be expected when applying an adaptive localisation approach that estimates a spatially varying localisation function from the ensemble itself. When compared with standard spatial localisation, scale-dependent localisation also results in a lower analysis error for sea-ice concentration over all spatial scales.

  5. Observation

    Science.gov (United States)

    Kripalani, Lakshmi A.

    2016-01-01

    The adult who is inexperienced in the art of observation may, even with the best intentions, react to a child's behavior in a way that hinders instead of helping the child's development. Kripalani outlines the need for training and practice in observation in order to "understand the needs of the children and...to understand how to remove…

  6. Algal-bacterial co-variation in streams: a cross-stream comparison

    Science.gov (United States)

    Xueqing Gao; Ola A. Olapade; Mark W. Kershner; Laura G. Leff

    2004-01-01

    Algal-bacterial co-variation has been frequently observed in lentic and marine environments, but the existence of such relationships in lotic ecosystems is not well established. To examine possible co-variation, bacterial number and chlorophyll-a concentration in water and sediments of nine streams from different regions in the USA were examined. In the water, a strong...

  7. Covariant quantizations in plane and curved spaces

    Energy Technology Data Exchange (ETDEWEB)

    Assirati, J.L.M. [University of Sao Paulo, Institute of Physics, Sao Paulo (Brazil); Gitman, D.M. [Tomsk State University, Department of Physics, Tomsk (Russian Federation); P.N. Lebedev Physical Institute, Moscow (Russian Federation); University of Sao Paulo, Institute of Physics, Sao Paulo (Brazil)

    2017-07-15

    We present covariant quantization rules for nonsingular finite-dimensional classical theories with flat and curved configuration spaces. In the beginning, we construct a family of covariant quantizations in flat spaces and Cartesian coordinates. This family is parametrized by a function ω(θ), θ element of (1,0), which describes an ambiguity of the quantization. We generalize this construction presenting covariant quantizations of theories with flat configuration spaces but already with arbitrary curvilinear coordinates. Then we construct a so-called minimal family of covariant quantizations for theories with curved configuration spaces. This family of quantizations is parametrized by the same function ω(θ). Finally, we describe a more wide family of covariant quantizations in curved spaces. This family is already parametrized by two functions, the previous one ω(θ) and by an additional function Θ(x,ξ). The above mentioned minimal family is a part at Θ = 1 of the wide family of quantizations. We study constructed quantizations in detail, proving their consistency and covariance. As a physical application, we consider a quantization of a non-relativistic particle moving in a curved space, discussing the problem of a quantum potential. Applying the covariant quantizations in flat spaces to an old problem of constructing quantum Hamiltonian in polar coordinates, we directly obtain a correct result. (orig.)

  8. Covariance specification and estimation to improve top-down Green House Gas emission estimates

    Science.gov (United States)

    Ghosh, S.; Lopez-Coto, I.; Prasad, K.; Whetstone, J. R.

    2015-12-01

    The National Institute of Standards and Technology (NIST) operates the North-East Corridor (NEC) project and the Indianapolis Flux Experiment (INFLUX) in order to develop measurement methods to quantify sources of Greenhouse Gas (GHG) emissions as well as their uncertainties in urban domains using a top down inversion method. Top down inversion updates prior knowledge using observations in a Bayesian way. One primary consideration in a Bayesian inversion framework is the covariance structure of (1) the emission prior residuals and (2) the observation residuals (i.e. the difference between observations and model predicted observations). These covariance matrices are respectively referred to as the prior covariance matrix and the model-data mismatch covariance matrix. It is known that the choice of these covariances can have large effect on estimates. The main objective of this work is to determine the impact of different covariance models on inversion estimates and their associated uncertainties in urban domains. We use a pseudo-data Bayesian inversion framework using footprints (i.e. sensitivities of tower measurements of GHGs to surface emissions) and emission priors (based on Hestia project to quantify fossil-fuel emissions) to estimate posterior emissions using different covariance schemes. The posterior emission estimates and uncertainties are compared to the hypothetical truth. We find that, if we correctly specify spatial variability and spatio-temporal variability in prior and model-data mismatch covariances respectively, then we can compute more accurate posterior estimates. We discuss few covariance models to introduce space-time interacting mismatches along with estimation of the involved parameters. We then compare several candidate prior spatial covariance models from the Matern covariance class and estimate their parameters with specified mismatches. We find that best-fitted prior covariances are not always best in recovering the truth. To achieve

  9. About Eddy Currents in Induction Melting Processes

    Directory of Open Access Journals (Sweden)

    Gafiţa Nicolae-Bogdan

    2008-05-01

    Full Text Available In this paper we present a method forcomputing the eddy currents in induction meltingprocesses for non-ferrous alloys. We take intoconsideration the situation when only the crucible ismoving, inside the coils. This fact makes differentialcomputation methods to be hard to apply, because isnecessary to generate a new mesh and a new systemmatrix for every for every new position of the cruciblerelated to the coils. Integral methods cancel thisdrawback because the mesh is generated only for thedomains with eddy currents. For integral methods, themesh and the inductance matrix remain unchangedduring the movement of the crucible; only the free termsof the equation system will change.

  10. The structure of temperature field in mesoscale eddies at the surface of the ocean in the Drake Passage.

    Science.gov (United States)

    Gritsenko, Alexander; Tarakanov, Roman

    2017-04-01

    The study of mesoscale eddies of the Antarctic Circumpolar Current (ACC) were performed on the basis of satellite data on the Absolute Dynamic Topography (ADT) produced by Ssalto/Duacs and distributed by Aviso, with support from Cnes (http://www.aviso.altimetry.fr/duacs/), and data on the ocean surface temperature (SST) of the Australian Centre of Weather and Climate research CAWCR (The Centre for Australian Weather and Climate research), calculated in the framework of the GAMSSA project (Global Australian Multi-Sensor SST Analysis, http://data.nodc.noaa.gov/las/getUI .do?dsid = id-c80878d11f & varid = analysed_sst-id-c80878d11f & auto = true/). We developed an algorithm and implemented a program for detection and mapping of cyclonic and anticyclonic mesoscale (synoptic) eddies in the ADT field for arbitrary day of the 19-year series of satellite observations. Preliminary results of the parameters and spatial distribution of mesoscale eddies in the region of the Drake Passage were obtained. The main part of eddies with different signs is associated with meandering jets and fronts of the ACC. To study the structure of the eddy surface temperature the eddy contours in the ADT field were mapped in the field of satellite SST for the same dates as the ADT data. Isotherms in cyclones and anticyclones reveal asymmetrical distribution of temperature. In the eastern (usually front) part of the cyclonic eddy, where the water transfer is directed from the low latitudes (clockwise in the Southern Hemisphere) to the high latitudes, the temperature is higher, and in the west (usually rear) part, where the water transfer is directed from high to low latitudes, it is lower. At the same time, the isotherms in cyclonic eddies deflected up in the form of domes and oriented to the northern or north-eastern direction. In the anticyclones, on the contrary, the isotherms deflected down in the form of cups and oriented mainly to the south. It should be noted that many of natural processes

  11. A Lagrangian biogeochemical study of an eddy in the Northeast Atlantic

    Science.gov (United States)

    Jickells, T. D.; Liss, P. S.; Broadgate, W.; Turner, S.; Kettle, A. J.; Read, J.; Baker, J.; Cardenas, L. M.; Carse, F.; Hamren-Larssen, M.; Spokes, L.; Steinke, M.; Thompson, A.; Watson, A.; Archer, S. D.; Bellerby, R. G. J.; Law, C. S.; Nightingale, P. D.; Liddicoat, M. I.; Widdicombe, C. E.; Bowie, A.; Gilpin, L. C.; Moncoiffé, G.; Savidge, G.; Preston, T.; Hadziabdic, P.; Frost, T.; Upstill-Goddard, R.; Pedrós-Alió, C.; Simó, R.; Jackson, A.; Allen, A.; DeGrandpre, M. D.

    2008-03-01

    We report the results of an experiment in the Northeast Atlantic in which sulphur hexafluoride (SF 6) was released within an eddy and the behaviour of trace gases, nutrients and productivity followed within a Lagrangian framework over a period of 24 days. Measurements were also made in the air above the eddy in order to estimate air-sea exchange rates for some components. The physical, biological and biogeochemical properties of the eddy resemble those of other eddies studied in this area, suggesting that the results we report may be applicable beyond the specific eddy studied. During a period of low wind speed at the start of the experiment, we are able to quantitatively describe and balance the nutrient and carbon budgets for the eddy. We also report concentrations of various trace gases in the region which are similar to those observed in other studies and we estimate exchange rates for several trace gases. We show that the importance of gas exchange over other loss terms varies with time and also varies for the different gases. We show that the various trace gases considered (CO 2, dimethyl sulphide (DMS), N 2O, CH 4, non-methane-hydrocarbons, methyl bromide, methyl iodide and volatile selenium species) are all influenced by physical and biological processes, but the overall distribution and temporal variability of individual gases are different to one another. A storm disrupted the stratification in the eddy during the experiment, resulting in enhanced nutrient supply to surface waters, enhanced gas exchange rates and a change in plankton community, which we quantify, although overall productivity was little changed. Emphasis is placed on the regularity of storms in the temperate ocean and the importance of these stochastic processes in such systems.

  12. Process modeling studies of physical mechanisms of the formation of an anticyclonic eddy in the central Red Sea

    KAUST Repository

    Chen, Changsheng

    2014-02-01

    Surface drifters released in the central Red Sea during April 2010 detected a well-defined anticyclonic eddy around 23°N. This eddy was ∼45–60 km in radius, with a swirl speed up to ∼0.5 m/s. The eddy feature was also evident in monthly averaged sea surface height fields and in current profiles measured on a cross-isobath, shipboard CTD/ADCP survey around that region. The unstructured-grid, Finite-Volume Community Ocean Model (FVCOM) was configured for the Red Sea and process studies were conducted to establish the conditions necessary for the eddy to form and to establish its robustness. The model was capable of reproducing the observed anticyclonic eddy with the same location and size. Diagnosis of model results suggests that the eddy can be formed in a Red Sea that is subject to seasonally varying buoyancy forcing, with no wind, but that its location and structure are significantly altered by wind forcing, initial distribution of water stratification and southward coastal flow from the upstream area. Momentum analysis indicates that the flow field of the eddy was in geostrophic balance, with the baroclinic pressure gradient forcing about the same order of magnitude as the surface pressure gradient forcing.

  13. Modulating Effects of Mesoscale Oceanic Eddies on Sea Surface Temperature Response to Tropical Cyclones Over the Western North Pacific

    Science.gov (United States)

    Ma, Zhanhong; Fei, Jianfang; Huang, Xiaogang; Cheng, Xiaoping

    2018-01-01

    The impact of mesoscale oceanic eddies on the temporal and spatial characteristics of sea surface temperature (SST) response to tropical cyclones is investigated in this study based on composite analysis of cyclone-eddy interactions over the western North Pacific. The occurrence times of maximum cooling, recovery time, and spatial patterns of SST response are specially evaluated. The influence of cold-core eddies (CCEs) renders the mean occurrence time of maximum SST cooling to become about half a day longer than that in eddy-free condition, while warm-core eddies (WCEs) have little effect on this facet. The recovery time of SST cooling also takes longer in presence of CCEs, being overall more pronounced for stronger or slower tropical cyclones. The effect of WCEs on the recovery time is again not significant. The modulation of maximum SST decrease by WCEs for category 2-5 storms is found to be remarkable in the subtropical region but not evident in the tropical region, while the role of CCEs is remarkable in both regions. The CCEs are observed to change the spatial characteristics of SST response, with enhanced SST decrease initially at the right side of storm track. During the recovery period the strengthened SST cooling by CCEs propagates leftward gradually, with a feature similar as both the westward-propagating eddies and the recovery of cold wake. These results underscore the importance of resolving mesoscale oceanic eddies in coupled numerical models to improve the prediction of storm-induced SST response.

  14. Covariant Structure of Models of Geophysical Fluid Motion

    Science.gov (United States)

    Dubos, Thomas

    2018-01-01

    Geophysical models approximate classical fluid motion in rotating frames. Even accurate approximations can have profound consequences, such as the loss of inertial frames. If geophysical fluid dynamics are not strictly equivalent to Newtonian hydrodynamics observed in a rotating frame, what kind of dynamics are they? We aim to clarify fundamental similarities and differences between relativistic, Newtonian, and geophysical hydrodynamics, using variational and covariant formulations as tools to shed the necessary light. A space-time variational principle for the motion of a perfect fluid is introduced. The geophysical action is interpreted as a synchronous limit of the relativistic action. The relativistic Levi-Civita connection also has a finite synchronous limit, which provides a connection with which to endow geophysical space-time, generalizing Cartan (1923). A covariant mass-momentum budget is obtained using covariance of the action and metric-preserving properties of the connection. Ultimately, geophysical models are found to differ from the standard compressible Euler model only by a specific choice of a metric-Coriolis-geopotential tensor akin to the relativistic space-time metric. Once this choice is made, the same covariant mass-momentum budget applies to Newtonian and all geophysical hydrodynamics, including those models lacking an inertial frame. Hence, it is argued that this mass-momentum budget provides an appropriate, common fundamental principle of dynamics. The postulate that Euclidean, inertial frames exist can then be regarded as part of the Newtonian theory of gravitation, which some models of geophysical hydrodynamics slightly violate.

  15. Proportional Hazards Model with Covariate Measurement Error and Instrumental Variables.

    Science.gov (United States)

    Song, Xiao; Wang, Ching-Yun

    2014-12-01

    In biomedical studies, covariates with measurement error may occur in survival data. Existing approaches mostly require certain replications on the error-contaminated covariates, which may not be available in the data. In this paper, we develop a simple nonparametric correction approach for estimation of the regression parameters in the proportional hazards model using a subset of the sample where instrumental variables are observed. The instrumental variables are related to the covariates through a general nonparametric model, and no distributional assumptions are placed on the error and the underlying true covariates. We further propose a novel generalized methods of moments nonparametric correction estimator to improve the efficiency over the simple correction approach. The efficiency gain can be substantial when the calibration subsample is small compared to the whole sample. The estimators are shown to be consistent and asymptotically normal. Performance of the estimators is evaluated via simulation studies and by an application to data from an HIV clinical trial. Estimation of the baseline hazard function is not addressed.

  16. Hierarchical matrix approximation of large covariance matrices

    KAUST Repository

    Litvinenko, Alexander

    2015-01-05

    We approximate large non-structured covariance matrices in the H-matrix format with a log-linear computational cost and storage O(nlogn). We compute inverse, Cholesky decomposition and determinant in H-format. As an example we consider the class of Matern covariance functions, which are very popular in spatial statistics, geostatistics, machine learning and image analysis. Applications are: kriging and op- timal design.

  17. Hierarchical matrix approximation of large covariance matrices

    KAUST Repository

    Litvinenko, Alexander

    2015-01-07

    We approximate large non-structured covariance matrices in the H-matrix format with a log-linear computational cost and storage O(n log n). We compute inverse, Cholesky decomposition and determinant in H-format. As an example we consider the class of Matern covariance functions, which are very popular in spatial statistics, geostatistics, machine learning and image analysis. Applications are: kriging and optimal design

  18. Selection and evolution of causally covarying traits.

    Science.gov (United States)

    Morrissey, Michael B

    2014-06-01

    When traits cause variation in fitness, the distribution of phenotype, weighted by fitness, necessarily changes. The degree to which traits cause fitness variation is therefore of central importance to evolutionary biology. Multivariate selection gradients are the main quantity used to describe components of trait-fitness covariation, but they quantify the direct effects of traits on (relative) fitness, which are not necessarily the total effects of traits on fitness. Despite considerable use in evolutionary ecology, path analytic characterizations of the total effects of traits on fitness have not been formally incorporated into quantitative genetic theory. By formally defining "extended" selection gradients, which are the total effects of traits on fitness, as opposed to the existing definition of selection gradients, a more intuitive scheme for characterizing selection is obtained. Extended selection gradients are distinct quantities, differing from the standard definition of selection gradients not only in the statistical means by which they may be assessed and the assumptions required for their estimation from observational data, but also in their fundamental biological meaning. Like direct selection gradients, extended selection gradients can be combined with genetic inference of multivariate phenotypic variation to provide quantitative prediction of microevolutionary trajectories. © 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.

  19. Local Lorentz covariance in finite-dimensional local quantum physics

    Science.gov (United States)

    Raasakka, Matti

    2017-10-01

    We show that local Lorentz covariance arises canonically as the group of transformations between local thermal states in the framework of local quantum physics, given the following three postulates: (i) Local observable algebras are finite-dimensional. (ii) Minimal local observable algebras are isomorphic to M2(C ) , the observable algebra of a single qubit. (iii) The vacuum restricted to any minimal local observable algebra is a nonmaximally mixed thermal state. The derivation reveals a new and surprising relation between spacetime structure and local quantum states. In particular, we show how local restrictions of the vacuum can determine the connection between different local inertial reference frames.

  20. Large-Eddy-Simulation-based analysis of complex flow structures ...

    Indian Academy of Sciences (India)

    CFD offers different turbulence modelling techniques with an aim to predict realistic flow approximations. Large Eddy Simulation (LES) offers a more accurate solution to this, in which the larger eddies are resolved while smaller eddies are modelled; hence predictions using LES are more realistic. Further, in turbulence ...

  1. Large Eddy Simulations using oodlesDST

    Science.gov (United States)

    2016-01-01

    from Monash University and joined Materials Research Laboratories in 1983 after positions at the University of Strathclyde, Glasgow; Queen Mary...Sidebottom, W.T., Ooi, A and Jones, D., “Large-Eddy Simulation of Flow past a Circular Cylinder at ReD = 3900”, presented at the 18th Australasian

  2. Large-Eddy Simulation and Multigrid Methods

    Energy Technology Data Exchange (ETDEWEB)

    Falgout,R D; Naegle,S; Wittum,G

    2001-06-18

    A method to simulate turbulent flows with Large-Eddy Simulation on unstructured grids is presented. Two kinds of dynamic models are used to model the unresolved scales of motion and are compared with each other on different grids. Thereby the behavior of the models is shown and additionally the feature of adaptive grid refinement is investigated. Furthermore the parallelization aspect is addressed.

  3. Wind changes above warm Agulhas Current eddies

    CSIR Research Space (South Africa)

    Roualt, M

    2016-10-01

    Full Text Available Sea-surface temperature (SST), altimetry derived sea-level anomalies (SLA) and surface current are used south of the Agulhas Current to identify warm core mesoscale ocean eddies presenting a distinct SST perturbation superior to 1(supo...

  4. Eddy-Resolving Global Ocean Prediction

    Science.gov (United States)

    2009-07-01

    discovered in the JES [Gordon et al., 2002; Talley et ai, 2004]. Such eddies are far from ubiquitous in the world ocean and were not found in the four...Springer. Netherlands. Shriver, J. F., and H. E. Hurlburt (1997), The contribution of the global thermohaline circulation to the Pacific to

  5. Eddy current sensing of intermetallic composite consolidation

    Science.gov (United States)

    Dharmasena, Kumar P.; Wadley, Haydn N. G.

    1991-01-01

    A finite element method is used to explore the feasibility and optimization of a probe-typ