WorldWideScience

Sample records for amplify high-latitude warming

  1. Low clouds suppress Arctic air formation and amplify high-latitude continental winter warming.

    Science.gov (United States)

    Cronin, Timothy W; Tziperman, Eli

    2015-09-15

    High-latitude continents have warmed much more rapidly in recent decades than the rest of the globe, especially in winter, and the maintenance of warm, frost-free conditions in continental interiors in winter has been a long-standing problem of past equable climates. We use an idealized single-column atmospheric model across a range of conditions to study the polar night process of air mass transformation from high-latitude maritime air, with a prescribed initial temperature profile, to much colder high-latitude continental air. We find that a low-cloud feedback--consisting of a robust increase in the duration of optically thick liquid clouds with warming of the initial state--slows radiative cooling of the surface and amplifies continental warming. This low-cloud feedback increases the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature, effectively suppressing Arctic air formation. The time it takes for the surface air temperature to drop below freezing increases nonlinearly to ∼ 10 d for initial maritime surface air temperatures of 20 °C. These results, supplemented by an analysis of Coupled Model Intercomparison Project phase 5 climate model runs that shows large increases in cloud water path and surface cloud longwave forcing in warmer climates, suggest that the "lapse rate feedback" in simulations of anthropogenic climate change may be related to the influence of low clouds on the stratification of the lower troposphere. The results also indicate that optically thick stratus cloud decks could help to maintain frost-free winter continental interiors in equable climates.

  2. Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect.

    Science.gov (United States)

    Swann, Abigail L; Fung, Inez Y; Levis, Samuel; Bonan, Gordon B; Doney, Scott C

    2010-01-26

    Arctic climate is projected to change dramatically in the next 100 years and increases in temperature will likely lead to changes in the distribution and makeup of the Arctic biosphere. A largely deciduous ecosystem has been suggested as a possible landscape for future Arctic vegetation and is seen in paleo-records of warm times in the past. Here we use a global climate model with an interactive terrestrial biosphere to investigate the effects of adding deciduous trees on bare ground at high northern latitudes. We find that the top-of-atmosphere radiative imbalance from enhanced transpiration (associated with the expanded forest cover) is up to 1.5 times larger than the forcing due to albedo change from the forest. Furthermore, the greenhouse warming by additional water vapor melts sea-ice and triggers a positive feedback through changes in ocean albedo and evaporation. Land surface albedo change is considered to be the dominant mechanism by which trees directly modify climate at high-latitudes, but our findings suggest an additional mechanism through transpiration of water vapor and feedbacks from the ocean and sea-ice.

  3. Increased Ocean Heat Convergence Into the High Latitudes With CO 2 Doubling Enhances Polar-Amplified Warming: OCEAN HEAT AND POLAR WARMING

    Energy Technology Data Exchange (ETDEWEB)

    Singh, H. A. [Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, U.S. DOE Office of Science, Richland WA USA; Rasch, P. J. [Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, U.S. DOE Office of Science, Richland WA USA; Rose, B. E. J. [Department of Atmospheric and Environmental Sciences, State University of New York at Albany, Albany NY USA

    2017-10-18

    We isolate the role of the ocean in polar climate change by directly evaluating how changes in ocean dynamics with quasi-equilibrium CO2-doubling impact high-latitude climate. With CO2-doubling, the ocean heat flux convergence (OHFC) shifts poleward in winter in both hemispheres. Imposing this pattern of perturbed OHFC in a global climate model results in a poleward shift in ocean-to-atmosphere turbulent heat fluxes (both sensible and latent) and sea ice retreat; the high-latitudes warm while the midlatitudes cool, thereby amplifying polar warming. Furthermore, midlatitude cooling is propagated to the polar mid-troposphere on isentropic surfaces, augmenting the (positive) lapse rate feedback at high latitudes. These results highlight the key role played by the partitioning of meridional energy transport changes between the atmosphere and ocean in high-latitude climate change.

  4. Temperature-induced water stress in high-latitude forests in response to natural and anthropogenic warming.

    Science.gov (United States)

    Trahan, Matthew W; Schubert, Brian A

    2016-02-01

    The Arctic is particularly sensitive to climate change, but the independent effects of increasing atmospheric CO2 concentration (pCO2 ) and temperature on high-latitude forests are poorly understood. Here, we present a new, annually resolved record of stable carbon isotope (δ(13) C) data determined from Larix cajanderi tree cores collected from far northeastern Siberia in order to investigate the physiological response of these trees to regional warming. The tree-ring record, which extends from 1912 through 1961 (50 years), targets early twentieth-century warming (ETCW), a natural warming event in the 1920s to 1940s that was limited to Northern hemisphere high latitudes. Our data show that net carbon isotope fractionation (Δ(13) C), decreased by 1.7‰ across the ETCW, which is consistent with increased water stress in response to climate warming and dryer soils. To investigate whether this signal is present across the northern boreal forest, we compiled published carbon isotope data from 14 high-latitude sites within Europe, Asia, and North America. The resulting dataset covered the entire twentieth century and spanned both natural ETCW and anthropogenic Late Twentieth-Century Warming (~0.7 °C per decade). After correcting for a ~1‰ increase in Δ(13) C in response to twentieth century pCO2 rise, a significant negative relationship (r = -0.53, P forests across the twentieth century, of which approximately half is attributed to a decrease in stomatal conductance in order to conserve water in response to drying conditions, with the other half being attributed to increasing pCO2 . We conclude that annual tree-ring records from northern high-latitude forests record the effects of climate warming and pCO2 rise across the twentieth century. © 2015 John Wiley & Sons Ltd.

  5. Variable responses of benthic communities to anomalously warm sea temperatures on a high-latitude coral reef.

    Science.gov (United States)

    Bridge, Tom C L; Ferrari, Renata; Bryson, Mitch; Hovey, Renae; Figueira, Will F; Williams, Stefan B; Pizarro, Oscar; Harborne, Alastair R; Byrne, Maria

    2014-01-01

    High-latitude reefs support unique ecological communities occurring at the biogeographic boundaries between tropical and temperate marine ecosystems. Due to their lower ambient temperatures, they are regarded as potential refugia for tropical species shifting poleward due to rising sea temperatures. However, acute warming events can cause rapid shifts in the composition of high-latitude reef communities, including range contractions of temperate macroalgae and bleaching-induced mortality in corals. While bleaching has been reported on numerous high-latitude reefs, post-bleaching trajectories of benthic communities are poorly described. Consequently, the longer-term effects of thermal anomalies on high-latitude reefs are difficult to predict. Here, we use an autonomous underwater vehicle to conduct repeated surveys of three 625 m(2) plots on a coral-dominated high-latitude reef in the Houtman Abrolhos Islands, Western Australia, over a four-year period spanning a large-magnitude thermal anomaly. Quantification of benthic communities revealed high coral cover (>70%, comprising three main morphospecies) prior to the bleaching event. Plating Montipora was most susceptible to bleaching, but in the plot where it was most abundant, coral cover did not change significantly because of post-bleaching increases in branching Acropora. In the other two plots, coral cover decreased while macroalgal cover increased markedly. Overall, coral cover declined from 73% to 59% over the course of the study, while macroalgal cover increased from 11% to 24%. The significant differences in impacts and post-bleaching trajectories among plots underline the importance of understanding the underlying causes of such variation to improve predictions of how climate change will affect reefs, especially at high-latitudes.

  6. Variable responses of benthic communities to anomalously warm sea temperatures on a high-latitude coral reef.

    Directory of Open Access Journals (Sweden)

    Tom C L Bridge

    Full Text Available High-latitude reefs support unique ecological communities occurring at the biogeographic boundaries between tropical and temperate marine ecosystems. Due to their lower ambient temperatures, they are regarded as potential refugia for tropical species shifting poleward due to rising sea temperatures. However, acute warming events can cause rapid shifts in the composition of high-latitude reef communities, including range contractions of temperate macroalgae and bleaching-induced mortality in corals. While bleaching has been reported on numerous high-latitude reefs, post-bleaching trajectories of benthic communities are poorly described. Consequently, the longer-term effects of thermal anomalies on high-latitude reefs are difficult to predict. Here, we use an autonomous underwater vehicle to conduct repeated surveys of three 625 m(2 plots on a coral-dominated high-latitude reef in the Houtman Abrolhos Islands, Western Australia, over a four-year period spanning a large-magnitude thermal anomaly. Quantification of benthic communities revealed high coral cover (>70%, comprising three main morphospecies prior to the bleaching event. Plating Montipora was most susceptible to bleaching, but in the plot where it was most abundant, coral cover did not change significantly because of post-bleaching increases in branching Acropora. In the other two plots, coral cover decreased while macroalgal cover increased markedly. Overall, coral cover declined from 73% to 59% over the course of the study, while macroalgal cover increased from 11% to 24%. The significant differences in impacts and post-bleaching trajectories among plots underline the importance of understanding the underlying causes of such variation to improve predictions of how climate change will affect reefs, especially at high-latitudes.

  7. Dependence of Arctic climate on the latitudinal position of stationary waves and to high-latitudes surface warming

    Science.gov (United States)

    Shin, Yechul; Kang, Sarah M.; Watanabe, Masahiro

    2017-12-01

    Previous studies suggest large uncertainties in the stationary wave response under global warming. Here, we investigate how the Arctic climate responds to changes in the latitudinal position of stationary waves, and to high-latitudes surface warming that mimics the effect of Arctic sea ice loss under global warming. To generate stationary waves in an atmospheric model coupled to slab ocean, a series of experiments is performed where the thermal forcing with a zonal wavenumber-2 (with zero zonal-mean) is prescribed at the surface at different latitude bands in the Northern Hemisphere. When the stationary waves are generated in the subtropics, the cooling response dominates over the warming response in the lower troposphere due to cloud radiative effects. Then, the low-level baroclinicity is reduced in the subtropics, which gives rise to a poleward shift of the eddy driven jet, thereby inducing substantial cooling in the northern high latitudes. As the stationary waves are progressively generated at higher latitudes, the zonal-mean climate state gradually becomes more similar to the integration with no stationary waves. These differences in the mean climate affect the Arctic climate response to high-latitudes surface warming. Additional surface heating over the Arctic is imposed to the reference climates in which the stationary waves are located at different latitude bands. When the stationary waves are positioned at lower latitudes, the eddy driven jet is located at higher latitude, closer to the prescribed Arctic heating. As baroclinicity is more effectively perturbed, the jet shifts more equatorward that accompanies a larger reduction in the poleward eddy transport of heat and momentum. A stronger eddy-induced descending motion creates greater warming over the Arctic. Our study calls for a more accurate simulation of the present-day stationary wave pattern to enhance the predictability of the Arctic warming response in a changing climate.

  8. Meta-analysis of high-latitude nitrogen-addition and warming studies implies ecological mechanisms overlooked by land models

    Science.gov (United States)

    Bouskill, N. J.; Riley, W. J.; Tang, J. Y.

    2014-12-01

    Accurate representation of ecosystem processes in land models is crucial for reducing predictive uncertainty in energy and greenhouse gas feedbacks with the climate. Here we describe an observational and modeling meta-analysis approach to benchmark land models, and apply the method to the land model CLM4.5 with two versions of belowground biogeochemistry. We focused our analysis on the aboveground and belowground responses to warming and nitrogen addition in high-latitude ecosystems, and identified absent or poorly parameterized mechanisms in CLM4.5. While the two model versions predicted similar soil carbon stock trajectories following both warming and nitrogen addition, other predicted variables (e.g., belowground respiration) differed from observations in both magnitude and direction, indicating that CLM4.5 has inadequate underlying mechanisms for representing high-latitude ecosystems. On the basis of observational synthesis, we attribute the model-observation differences to missing representations of microbial dynamics, aboveground and belowground coupling, and nutrient cycling, and we use the observational meta-analysis to discuss potential approaches to improving the current models. However, we also urge caution concerning the selection of data sets and experiments for meta-analysis. For example, the concentrations of nitrogen applied in the synthesized field experiments (average = 72 kg ha-1 yr-1) are many times higher than projected soil nitrogen concentrations (from nitrogen deposition and release during mineralization), which precludes a rigorous evaluation of the model responses to likely nitrogen perturbations. Overall, we demonstrate that elucidating ecological mechanisms via meta-analysis can identify deficiencies in ecosystem models and empirical experiments.

  9. Testing species distribution models across space and time: high latitude butterflies and recent warming

    DEFF Research Database (Denmark)

    Eskildsen, Anne; LeRoux, Peter C.; Heikkinen, Risto K.

    2013-01-01

    changes at expanding range margins can be predicted accurately. Location. Finland. Methods. Using 10-km resolution butterfly atlas data from two periods, 1992–1999 (t1) and 2002–2009 (t2), with a significant between-period temperature increase, we modelled the effects of climatic warming on butterfly...... butterfly distributions under climate change. Model performance was lower with independent compared to non-independent validation and improved when land cover and soil type variables were included, compared to climate-only models. SDMs performed less well for highly mobile species and for species with long......Aim. To quantify whether species distribution models (SDMs) can reliably forecast species distributions under observed climate change. In particular, to test whether the predictive ability of SDMs depends on species traits or the inclusion of land cover and soil type, and whether distributional...

  10. Meta-analysis of high-latitude nitrogen-addition and warming studies imply ecological mechanisms overlooked by land models

    Science.gov (United States)

    Bouskill, N. J.; Riley, W. J.; Tang, J.

    2014-08-01

    Accurate representation of ecosystem processes in land models is crucial for reducing predictive uncertainty in energy and greenhouse gas feedbacks with the atmosphere. Here we describe an observational and modeling meta-analysis approach to benchmark land models, and apply the method to the land model CLM4.5 with two versions of belowground biogeochemistry. We focused our analysis on the above and belowground high-latitude ecosystem responses to warming and nitrogen addition, and identified mechanisms absent, or poorly parameterized in CLM4.5. While the two model versions predicted similar trajectories for soil carbon stocks following both types of perturbation, other variables (e.g., belowground respiration) differed from the observations in both magnitude and direction, indicating the underlying mechanisms are inadequate for representing high-latitude ecosystems. The observational synthesis attribute these differences to missing representations of microbial dynamics, characterization of above and belowground functional processes, and nutrient competition. We use the observational meta-analyses to discuss potential approaches to improving the current models (e.g., the inclusion of dynamic vegetation or different microbial functional guilds), however, we also raise a cautionary note on the selection of data sets and experiments to be included in a meta-analysis. For example, the concentrations of nitrogen applied in the synthesized field experiments (average =72 kg ha-1 yr-1) are many times higher than projected soil nitrogen concentrations (from nitrogen deposition and release during mineralization), which preclude a rigorous evaluation of the model responses to nitrogen perturbation. Overall, we demonstrate here that elucidating ecological mechanisms via meta-analysis can identify deficiencies in both ecosystem models and empirical experiments.

  11. Warm mid-Cretaceous high-latitude sea-surface temperatures from the southern Tethys Ocean and cool high-latitude sea-surface temperatures from the Arctic Ocean: asymmetric worldwide distribution of dinoflagellates

    Science.gov (United States)

    Masure, Edwige; Desmares, Delphine; Vrielynck, Bruno

    2014-05-01

    Dealing with 87 articles and using a Geographical Information System, Masure and Vrielynck (2009) have mapped worldwide biogeography of 38 Late Albian dinoflagellate cysts and have demonstrated Cretaceous oceanic bioclimatic belts. For comparison 30 Aptian species derived from 49 studies (Masure et al., 2013) and 49 Cenomanian species recorded from 33 articles have been encountered. Tropical, Subtropical, Boreal, Austral, bipolar and cosmopolitan species have been identified and Cretaceous dinoflagellate biomes are introduced. Asymmetric distribution of Aptian and Late Albian/Cenomanian subtropical Tethyan species, from 40°N to 70°S, demonstrates asymmetric Aptian and Late Albian/Cenomanian Sea Surface Temperature (SST) gradients with warm water masses in high latitudes of Southern Ocean. The SST gradients were stronger in the Northern Hemisphere than in the Southern Hemisphere. We note that Aptian and Late Albian/Cenomanian dinoflagellates restricted to subtropical and subpolar latitudes met and mixed at 35-40°N, while they mixed from 30°S to 70°S and from 50°S to 70°S respectively in the Southern Hemisphere. Mixing belts extend on 5° in the Northern Hemisphere and along 40° (Aptian) and 20° (Late Albian/Cenomanian) in the Southern one. The board southern mixing belt of Tethyan and Austral dinoflagellates suggest co-occurrence of warm and cold currents. We record climatic changes such as the Early Aptian cooler period and Late Aptian and Albian warming through the poleward migration of species constrained to cool water masses. These species sensitive to temperature migrated from 35°N to 55°N through the shallow Greenland-Norwergian Seaway connecting the Central Atlantic and the Arctic Ocean. While Tethyan species did not migrate staying at 40°N. We suggest that the Greenland-Norwergian Seaway might has been a barrier until Late Albian/Cenomanian for oceanic Tethyan dinoflagellates stopped either by the shallow water column or temperature and salinity

  12. Amplified Arctic warming by phytoplankton under greenhouse warming.

    Science.gov (United States)

    Park, Jong-Yeon; Kug, Jong-Seong; Bader, Jürgen; Rolph, Rebecca; Kwon, Minho

    2015-05-12

    Phytoplankton have attracted increasing attention in climate science due to their impacts on climate systems. A new generation of climate models can now provide estimates of future climate change, considering the biological feedbacks through the development of the coupled physical-ecosystem model. Here we present the geophysical impact of phytoplankton, which is often overlooked in future climate projections. A suite of future warming experiments using a fully coupled ocean-atmosphere model that interacts with a marine ecosystem model reveals that the future phytoplankton change influenced by greenhouse warming can amplify Arctic surface warming considerably. The warming-induced sea ice melting and the corresponding increase in shortwave radiation penetrating into the ocean both result in a longer phytoplankton growing season in the Arctic. In turn, the increase in Arctic phytoplankton warms the ocean surface layer through direct biological heating, triggering additional positive feedbacks in the Arctic, and consequently intensifying the Arctic warming further. Our results establish the presence of marine phytoplankton as an important potential driver of the future Arctic climate changes.

  13. Influence of high-latitude warming and land-use changes in the early 20th century northern Eurasian CO2 sink

    Science.gov (United States)

    Bastos, Ana; Peregon, Anna; Gani, Érico A.; Khudyaev, Sergey; Yue, Chao; Li, Wei; Gouveia, Célia M.; Ciais, Philippe

    2018-06-01

    While the global carbon budget (GCB) is relatively well constrained over the last decades of the 20th century [1], observations and reconstructions of atmospheric CO2 growth rate present large discrepancies during the earlier periods [2]. The large uncertainty in GCB has been attributed to the land biosphere, although it is not clear whether the gaps between observations and reconstructions are mainly because land-surface models (LSMs) underestimate inter-annual to decadal variability in natural ecosystems, or due to inaccuracies in land-use change reconstructions. As Eurasia encompasses about 15% of the terrestrial surface, 20% of the global soil organic carbon pool and constitutes a large CO2 sink, we evaluate the potential contribution of natural and human-driven processes to induce large anomalies in the biospheric CO2 fluxes in the early 20th century. We use an LSM specifically developed for high-latitudes, that correctly simulates Eurasian C-stocks and fluxes from observational records [3], in order to evaluate the sensitivity of the Eurasian sink to the strong high-latitude warming occurring between 1930 and 1950. We show that the LSM with improved high-latitude phenology, hydrology and soil processes, contrary to the group of LSMs in [2], is able to represent enhanced vegetation growth linked to boreal spring warming, consistent with tree-ring time-series [4]. By compiling a dataset of annual agricultural area in the Former Soviet Union that better reflects changes in cropland area linked with socio-economic fluctuations during the early 20th century, we show that land-abadonment during periods of crisis and war may result in reduced CO2 emissions from land-use change (44%–78% lower) detectable at decadal time-scales. Our study points to key processes that may need to be improved in LSMs and LUC datasets in order to better represent decadal variability in the land CO2 sink, and to better constrain the GCB during the pre-observational record.

  14. Qualitative models of global warming amplifiers

    NARCIS (Netherlands)

    Milošević, U.; Bredeweg, B.; de Kleer, J.; Forbus, K.D.

    2010-01-01

    There is growing interest from ecological experts to create qualitative models of phenomena for which numerical information is sparse or missing. We present a number of successful models in the field of environmental science, namely, the domain of global warming. The motivation behind the effort is

  15. High Latitude Polygons

    Science.gov (United States)

    2005-01-01

    26 September 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows polygonal patterned ground on a south high-latitude plain. The outlines of the polygons, like the craters and hills in this region, are somewhat enhanced by the presence of bright frost left over from the previous winter. On Earth, polygons at high latitudes would usually be attributed to the seasonal freezing and thawing cycles of ground ice. The origin of similar polygons on Mars is less certain, but might also be an indicator of ground ice. Location near: 75.3oS, 113.2oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  16. High latitude ionospheric structure

    International Nuclear Information System (INIS)

    1984-06-01

    The Earth's ionosphere is an important element in solar-terrestrial energy transfer processes. As a major terrestrial sink for many solar and magnetospheric events, the ionosphere has characteristic features that are traced to such seemingly remote phenomena as solar flares, radiation belt wave-particle interactions and magnetospheric substorms. In considering the multiple of solar-terrestrial plasma interactions, it is important to recognize that the high-latitude ionosphere is not altogether a simple receptor of various energy deposition processes. The high-altitude ionosphere plays an active feedback role by controlling the conductivity at the base of far-reaching magnetic field lines and by providing a plasma source for the magnetosphere. Indeed, the role of the ionosphere during magnetospheric substorms is emerging as a topic for meaningful study in the overall picture of magnetospheric-ionospheric coupling

  17. Recently amplified arctic warming has contributed to a continual global warming trend

    Science.gov (United States)

    Huang, Jianbin; Zhang, Xiangdong; Zhang, Qiyi; Lin, Yanluan; Hao, Mingju; Luo, Yong; Zhao, Zongci; Yao, Yao; Chen, Xin; Wang, Lei; Nie, Suping; Yin, Yizhou; Xu, Ying; Zhang, Jiansong

    2017-12-01

    The existence and magnitude of the recently suggested global warming hiatus, or slowdown, have been strongly debated1-3. Although various physical processes4-8 have been examined to elucidate this phenomenon, the accuracy and completeness of observational data that comprise global average surface air temperature (SAT) datasets is a concern9,10. In particular, these datasets lack either complete geographic coverage or in situ observations over the Arctic, owing to the sparse observational network in this area9. As a consequence, the contribution of Arctic warming to global SAT changes may have been underestimated, leading to an uncertainty in the hiatus debate. Here, we constructed a new Arctic SAT dataset using the most recently updated global SATs2 and a drifting buoys based Arctic SAT dataset11 through employing the `data interpolating empirical orthogonal functions' method12. Our estimate of global SAT rate of increase is around 0.112 °C per decade, instead of 0.05 °C per decade from IPCC AR51, for 1998-2012. Analysis of this dataset shows that the amplified Arctic warming over the past decade has significantly contributed to a continual global warming trend, rather than a hiatus or slowdown.

  18. Process contributions to the intermodel spread in amplified Arctic warming

    Science.gov (United States)

    Boeke, R.; Taylor, P. C.

    2016-12-01

    The Arctic is warming at a rate more than twice the global average. This robust climate system response to an external forcing is referred to as Arctic Amplification (AA). While Coupled Model Intercomparison Project 5 (CMIP5) climate models simulate AA, the largest intermodel spread in projected warming is also found in the Arctic. Quantifying the amount of polar warming relative to global warming influences how society adapts to climate change; a 2°C increase in global mean temperature would result in a polar warming between 4-8°C according to the intermodel spread in CMIP5 simulations. A trove of previous work has considered AA diagnostically using variations in the surface energy budget to attribute the intermodel spread in AA to an assortment of feedbacks—surface albedo, cloud, surface turbulent flux, and atmospheric and oceanic energy transport. We consider a systems-thinking approach treating AA as a process that evolves over time. We hypothesize that two specific components of the AA process are most important and influence the intermodel spread. (1) The inability of the Arctic system to effectively remove excess heat sourced from natural variability. The change in the efficiency of the `Arctic air conditioner' is thought to be due to thinner and less extensive sea ice and the resulting ice albedo feedback. (2) The process through which energy is stored in the ocean and exchanged with the atmosphere within the context of the sea ice annual cycle is also important. This study uses CMIP5 simulations from the historical and RCP8.5 (Representative Concentration Pathway; an emission scenario with forcing increasing to 8.5 W m-2 by 2100) to analyze how the AA process operates in present and future climate. The intermodel spread in these processes and the influence on the spread in AA are discussed. This approach identifies models that more realistically simulate the AA process and will aid in narrowing intermodel spread in Arctic surface temperature

  19. Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures.

    Science.gov (United States)

    Douglas, Peter M J; Affek, Hagit P; Ivany, Linda C; Houben, Alexander J P; Sijp, Willem P; Sluijs, Appy; Schouten, Stefan; Pagani, Mark

    2014-05-06

    Paleoclimate studies suggest that increased global warmth during the Eocene epoch was greatly amplified at high latitudes, a state that climate models cannot fully reproduce. However, proxy estimates of Eocene near-Antarctic sea surface temperatures (SSTs) have produced widely divergent results at similar latitudes, with SSTs above 20 °C in the southwest Pacific contrasting with SSTs between 5 and 15 °C in the South Atlantic. Validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites. Here, we present multiproxy data from Seymour Island, near the Antarctic Peninsula, that provides well-constrained evidence for annual SSTs of 10-17 °C (1σ SD) during the middle and late Eocene. Comparison of the same paleotemperature proxy at Seymour Island and at the East Tasman Plateau indicate the presence of a large and consistent middle-to-late Eocene SST gradient of ∼7 °C between these two sites located at similar paleolatitudes. Intermediate-complexity climate model simulations suggest that enhanced oceanic heat transport in the South Pacific, driven by deep-water formation in the Ross Sea, was largely responsible for the observed SST gradient. These results indicate that very warm SSTs, in excess of 18 °C, did not extend uniformly across the Eocene southern high latitudes, and suggest that thermohaline circulation may partially control the distribution of high-latitude ocean temperatures in greenhouse climates. The pronounced zonal SST heterogeneity evident in the Eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands.

  20. Continuously amplified warming in the Alaskan Arctic: Implications for estimating global warming hiatus

    Science.gov (United States)

    Wang, Kang; Zhang, Tingjun; Zhang, Xiangdong; Clow, Gary D.; Jafarov, Elchin E.; Overeem, Irina; Romanovsky, Vladimir; Peng, Xiaoqing; Cao, Bin

    2017-01-01

    Historically, in situ measurements have been notoriously sparse over the Arctic. As a consequence, the existing gridded data of surface air temperature (SAT) may have large biases in estimating the warming trend in this region. Using data from an expanded monitoring network with 31 stations in the Alaskan Arctic, we demonstrate that the SAT has increased by 2.19°C in this region, or at a rate of 0.23°C/decade during 1921–2015. Meanwhile, we found that the SAT warmed at 0.71°C/decade over 1998–2015, which is 2 to 3 times faster than the rate established from the gridded data sets. Focusing on the “hiatus” period 1998–2012 as identified by the Intergovernmental Panel on Climate Change (IPCC) report, the SAT has increased at 0.45°C/decade, which captures more than 90% of the regional trend for 1951–2012. We suggest that sparse in situ measurements are responsible for underestimation of the SAT change in the gridded data sets. It is likely that enhanced climate warming may also have happened in the other regions of the Arctic since the late 1990s but left undetected because of incomplete observational coverage.

  1. High Latitude Dust in the Earth System

    Science.gov (United States)

    Bullard, Joanna E.; Baddock, Matthew; Bradwell, Tom; Crusius, John; Darlington, Eleanor; Gaiero, Diego; Gasso, Santiago; Gisladottir, Gudrun; Hodgkins, Richard; McCulloch, Robert; hide

    2016-01-01

    Natural dust is often associated with hot, subtropical deserts, but significant dust events have been reported from cold, high latitudes. This review synthesizes current understanding of high-latitude (> or = 50degN and > or = 40degS) dust source geography and dynamics and provides a prospectus for future research on the topic. Although the fundamental processes controlling aeolian dust emissions in high latitudes are essentially the same as in temperate regions, there are additional processes specific to or enhanced in cold regions. These include low temperatures, humidity, strong winds, permafrost and niveo-aeolian processes all of which can affect the efficiency of dust emission and distribution of sediments. Dust deposition at high latitudes can provide nutrients to the marine system, specifically by contributing iron to high-nutrient, low-chlorophyll oceans; it also affects ice albedo and melt rates. There have been no attempts to quantify systematically the expanse, characteristics, or dynamics of high-latitude dust sources. To address this, we identify and compare the main sources and drivers of dust emissions in the Northern (Alaska, Canada, Greenland, and Iceland) and Southern (Antarctica, New Zealand, and Patagonia) Hemispheres. The scarcity of year-round observations and limitations of satellite remote sensing data at high latitudes are discussed. It is estimated that under contemporary conditions high-latitude sources cover >500,000 sq km and contribute at least 80-100 Tg/yr1 of dust to the Earth system (approx. 5% of the global dust budget); both are projected to increase under future climate change scenarios.

  2. High-Latitude Space Plasma Physics

    International Nuclear Information System (INIS)

    Hultqvist, B.; Hagfors, T.

    1983-01-01

    This book constitutes the proceedings of the Nobel Symposium No. 54 on High Latitude Magnetospheric/Ionospheric Plasma Physics. The main purpose of the symposium was to prepare for the European research effort in space plasma physics in the mid-1980's, in which two major constituents are the European Incoherent Scatter Association (EISCAT) facilities and the Swedish satellite Viking. The physics of the high-latitude ionosphere and how this part of near space is affected by the properties of the solar wind and the interplanetary magnetic field are explored. A detailed discussion is provided on high-latitude magnetospheric physics at altitudes of 1-2 earth radii, the main focus of the Viking project. Specific topics considered include the role of the auroral ionosphere in magnetospheric substorms, the low altitude cleft, ionospheric modification and stimulated emissions, plasma physics on auroral field lines, solar wind-magnetosphere energy coupling, cold plasma distribution above a few thousand kilometers at high latitudes, hot electrons in and above the auroral ionosphere, the correlation of auroral kilometric radiation with visual auroras and with Birkeland currents, electrostatic waves in the topside ionosphere, solitary waves and double layers, and an Alfven wave model of auroral arcs

  3. Land–atmosphere feedbacks amplify aridity increase over land under global warming

    Science.gov (United States)

    Berg, Alexis; Findell, Kirsten; Lintner, Benjamin; Giannini, Alessandra; Seneviratne, Sonia I.; van den Hurk, Bart; Lorenz, Ruth; Pitman, Andy; Hagemann, Stefan; Meier, Arndt; Cheruy, Frédérique; Ducharne, Agnès; Malyshev, Sergey; Milly, Paul C. D.

    2016-01-01

    The response of the terrestrial water cycle to global warming is central to issues including water resources, agriculture and ecosystem health. Recent studies indicate that aridity, defined in terms of atmospheric supply (precipitation, P) and demand (potential evapotranspiration, Ep) of water at the land surface, will increase globally in a warmer world. Recently proposed mechanisms for this response emphasize the driving role of oceanic warming and associated atmospheric processes. Here we show that the aridity response is substantially amplified by land–atmosphere feedbacks associated with the land surface’s response to climate and CO2 change. Using simulations from the Global Land Atmosphere Coupling Experiment (GLACE)-CMIP5 experiment, we show that global aridity is enhanced by the feedbacks of projected soil moisture decrease on land surface temperature, relative humidity and precipitation. The physiological impact of increasing atmospheric CO2 on vegetation exerts a qualitatively similar control on aridity. We reconcile these findings with previously proposed mechanisms by showing that the moist enthalpy change over land is unaffected by the land hydrological response. Thus, although oceanic warming constrains the combined moisture and temperature changes over land, land hydrology modulates the partitioning of this enthalpy increase towards increased aridity.

  4. Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures

    NARCIS (Netherlands)

    Douglas, P.M.J.; Affek, H.P.; Ivany, L.C.; Houben, A.J.P.; Sijp, W.P.; Sluijs, A.; Schouten, S.; Pagani, M.

    2014-01-01

    Paleoclimate studies suggest that increased global warmth during the Eocene epoch was greatly amplified at high latitudes, a state that climate models cannot fully reproduce. However, proxy estimates of Eocene near-Antarctic sea surface temperatures (SSTs) have produced widely divergent results at

  5. Statistical evidences of absorption at high latitudes

    International Nuclear Information System (INIS)

    Fesenko, B.I.

    1980-01-01

    Evidences are considered which indicate to the significant effect of the irregular interstellar absorption at high latitudes b. The number density of faint galaxies grows with the increasing |b| even at the values of |b| exceeding 50 deg. The effects of interstellar medium are traced even in the directions of the stars and globular clusters with very low values of the colour excess. The coefficient of absorption, Asub(B)=0.29+-0.05, was estimated from the colours of the bright E-galaxies [ru

  6. Intensified Arctic warming under greenhouse warming by vegetation–atmosphere–sea ice interaction

    International Nuclear Information System (INIS)

    Jeong, Jee-Hoon; Kug, Jong-Seong; Linderholm, Hans W; Chen, Deliang; Kim, Baek-Min; Jun, Sang-Yoon

    2014-01-01

    Observations and modeling studies indicate that enhanced vegetation activities over high latitudes under an elevated CO 2 concentration accelerate surface warming by reducing the surface albedo. In this study, we suggest that vegetation-atmosphere-sea ice interactions over high latitudes can induce an additional amplification of Arctic warming. Our hypothesis is tested by a series of coupled vegetation-climate model simulations under 2xCO 2 environments. The increased vegetation activities over high latitudes under a 2xCO 2 condition induce additional surface warming and turbulent heat fluxes to the atmosphere, which are transported to the Arctic through the atmosphere. This causes additional sea-ice melting and upper-ocean warming during the warm season. As a consequence, the Arctic and high-latitude warming is greatly amplified in the following winter and spring, which further promotes vegetation activities the following year. We conclude that the vegetation-atmosphere-sea ice interaction gives rise to additional positive feedback of the Arctic amplification. (letter)

  7. High Latitude Corals Tolerate Severe Cold Spell

    Directory of Open Access Journals (Sweden)

    Chenae A. Tuckett

    2018-01-01

    Full Text Available Climatically extreme weather events often drive long-term ecological responses of ecosystems. By disrupting the important symbiosis with zooxanthellae, Marine Cold Spells (MCS can cause bleaching and mortality in tropical and subtropical scleractinian corals. Here we report on the effects of a severe MCS on high latitude corals, where we expected to find bleaching and mortality. The MCS took place off the coast of Perth (32°S, Western Australia in 2016. Bleaching was assessed before (2014 and after (2017 the MCS from surveys of permanent plots, and with timed bleaching searches. Temperature data was recorded with in situ loggers. During the MCS temperatures dipped to the coldest recorded in ten years (15.3°C and periods of <17°C lasted for up to 19 days. Only 4.3% of the surveyed coral colonies showed signs of bleaching. Bleaching was observed in 8 species where those most affected were Plesiastrea versipora and Montipora mollis. These findings suggest that high latitude corals in this area are tolerant of cold stress and are not persisting near a lethal temperature minimum. It has not been established whether other environmental conditions are limiting these species, and if so, what the implications are for coral performance on these reefs in a warmer future.

  8. Empirical high-latitude electric field models

    International Nuclear Information System (INIS)

    Heppner, J.P.; Maynard, N.C.

    1987-01-01

    Electric field measurements from the Dynamics Explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn-dusk OGO 6 measurements (J.P. Heppner, 1977). The analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones. Paralleling the previous analysis, the modeling is based on the distinctly different polar cap and dayside convective patterns that occur as a function of the sign of the Y component of the interplanetary magnetic field. The objective, which is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns, is met by deriving one pattern (model BC) for the northern hemisphere with a +Y interplanetary magnetic field (IMF) and southern hemisphere with a -Y IMF and two patterns (models A and DE) for the northern hemisphere with a -Y IMF and southern hemisphere with a +Y IMF. The most significant large-scale revisions of the OGO 6 models are (1) on the dayside where the latitudinal overlap of morning and evening convection cells reverses with the sign of the IMF Y component, (2) on the nightside where a westward flow region poleward from the Harang discontinuity appears under model BC conditions, and (3) magnetic local time shifts in the positions of the convection cell foci. The modeling above was followed by a detailed examination of cases where the IMF Z component was clearly positive (northward). Neglecting the seasonally dependent cases where irregularities obscure pattern recognition, the observations range from reasonable agreement with the new BC and DE models, to cases where different characteristics appeared primarily at dayside high latitudes

  9. Paleoclimate records at high latitude in Arctic during the Paleogene

    Science.gov (United States)

    Salpin, Marie; Schnyder, Johann; Baudin, François; Suan, Guillaume; Labrousse, Loïc; Popescu, Speranta; Suc, Jean-Pierre

    2015-04-01

    Paleoclimate records at high latitude in Arctic during the Paleogene SALPIN Marie1,2, SCHNYDER Johann1,2, BAUDIN François1,2, SUAN Guillaume3, LABROUSSE Loïc1,2, POPESCU Speranta4, SUC Jean-Pierre1,4 1: Sorbonne Universités, UPMC Univ Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F 75005, Paris, France 2: CNRS, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F 75005 Paris, France 3: UCB Lyon 1, UMR 5276, LGLTPE, 69622 Villeurbanne Cedex, France 4: GEOBIOSTRATDATA.CONSULTING, 385 Route du Mas Rillier 69140 Rillieux la Pape, France The Paleogene is a period of important variations of the Earth climate system either in warming or cooling. The climatic optima of the Paleogene have been recognized both in continental and marine environment. This study focus on high latitudes of the northern hemisphere, in the Arctic Basin. The basin has had an influence on the Cenozoic global climate change according to its polar position. Is there a specific behaviour of the Arctic Basin with respect to global climatic stimuli? Are there possible mechanisms of coupling/decoupling of its dynamics with respect to the global ocean? To answer these questions a unique collection of sedimentary series of Paleogene age interval has been assembled from the Laurentian margin in Northern Yukon (Canada) and from the Siberian margin (New Siberian Islands). Selected continental successions of Paleocene-Eocene age were used to study the response of the Arctic system to known global events, e.g. the climatic optima of the Paleogene (the so-called PETM, ETM2 or the Azolla events). Two sections of Paleocene-Eocene age were sampled near the Mackenzie delta, the so-called Coal Mine (CoMi) and Caribou Hills (CaH) sections. The aim of the study is to precise the climatic fluctuations and to characterise the source rock potential of the basin, eventually linked to the warming events. This study is based on data of multi-proxy analyses: mineralogy on bulk and clay

  10. High-latitude ocean ventilation and its role in Earth's climate transitions.

    Science.gov (United States)

    Naveira Garabato, Alberto C; MacGilchrist, Graeme A; Brown, Peter J; Evans, D Gwyn; Meijers, Andrew J S; Zika, Jan D

    2017-09-13

    The processes regulating ocean ventilation at high latitudes are re-examined based on a range of observations spanning all scales of ocean circulation, from the centimetre scales of turbulence to the basin scales of gyres. It is argued that high-latitude ocean ventilation is controlled by mechanisms that differ in fundamental ways from those that set the overturning circulation. This is contrary to the assumption of broad equivalence between the two that is commonly adopted in interpreting the role of the high-latitude oceans in Earth's climate transitions. Illustrations of how recognizing this distinction may change our view of the ocean's role in the climate system are offered.This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'. © 2017 The Authors.

  11. Nightside High Latitude Magnetic Impulse Events

    Science.gov (United States)

    Engebretson, M. J.; Connors, M. G.; Braun, D.; Posch, J. L.; Kaur, M.; Guillon, S.; Hartinger, M.; Kim, H.; Behlke, R.; Reiter, K.; Jackel, B. J.; Russell, C. T.

    2017-12-01

    High latitude Magnetic Impulse Events (MIEs), isolated pulses with periods 5-10 min, were first noted in ground-based magnetometer data near local noon, and are now understood to be signatures of transient pressure increases in the solar wind (sudden impulses - SIs) and/or in the ion foreshock (traveling convection vortex events - TCVs). However, solitary pulses with considerably larger amplitude (ΔB up to 1500 nT) have often been observed in the night sector at these same latitudes. These events are not directly associated with transient external pressure increases, and are often large enough to produce significant ground induced currents. Although many night sector MIEs occur in association with substorm signatures, others appear to be very isolated. We present here a survey of intense MIE events identified in magnetometer data from the AUTUMNX and MACCS arrays in eastern Arctic Canada at all local times between July 1, 2014 and June 30, 2017. We also show maps of horizontal and vertical perturbations and maximum dB/dt values, as well as sample magnetograms, for several example events using data from these and other arrays in Arctic Canada, as well as in West Greenland and Antarctica, the latter to show the conjugate nature of these events. A basic relation to GIC data in the Hydro-Québec electrical transmission network in eastern Canada has been determined and will be discussed.

  12. Ionospheric hot spot at high latitudes

    International Nuclear Information System (INIS)

    Schunk, R.W.; Sojka, J.J.

    1982-01-01

    A hot spot (or spots) can occur in the high-latitude ionosphere depending on the plasma convection pattern. The hot spot corresponds to a small magnetic local time-magnetic latitude region of elevated ion temperatures located near the dusk and/or dawn meridians. For asymmetric convection electric field patterns, with enhanced flow in either the dusk or dawn sector of the polar cap, a single hot spot should occur in association with the strong convection cell. However, on geomagnetically disturbed days, two strong convection cells can occur, and hence, two hot spots should exist. The hot spot should be detectable when the electric field in the strong convection cell exceeds about 40 mV m -1 . For electric fields of the order of 100 mV m -1 in the convection cell, the ion temperature in the hot spot is greatest at low altitudes, reaching 4000 0 K at 160 km, and decreases with altitude in the F-region. An ionospheric hot spot (or spots) can be expected at all seasons and for a wide range of solar cycle conditions

  13. Vulnerability of high-latitude soil organic carbon in North America to disturbance

    Science.gov (United States)

    Grosse, Guido; Harden, Jennifer W.; Turetsky, Merritt; McGuire, A. David; Camill, Philip; Tarnocai, Charles; Frolking, Steve; Schuur, Edward A.G.; Jorgenson, Torre; Marchenko, Sergei; Romanovsky, Vladimir; Wickland, Kimberly P.; French, Nancy; Waldrop, Mark P.; Bourgeau-Chavez, Laura L.; Striegl, Robert G.

    2011-01-01

    This synthesis addresses the vulnerability of the North American high-latitude soil organic carbon (SOC) pool to climate change. Disturbances caused by climate warming in arctic, subarctic, and boreal environments can result in significant redistribution of C among major reservoirs with potential global impacts. We divide the current northern high-latitude SOC pools into (1) near-surface soils where SOC is affected by seasonal freeze-thaw processes and changes in moisture status, and (2) deeper permafrost and peatland strata down to several tens of meters depth where SOC is usually not affected by short-term changes. We address key factors (permafrost, vegetation, hydrology, paleoenvironmental history) and processes (C input, storage, decomposition, and output) responsible for the formation of the large high-latitude SOC pool in North America and highlight how climate-related disturbances could alter this pool's character and size. Press disturbances of relatively slow but persistent nature such as top-down thawing of permafrost, and changes in hydrology, microbiological communities, pedological processes, and vegetation types, as well as pulse disturbances of relatively rapid and local nature such as wildfires and thermokarst, could substantially impact SOC stocks. Ongoing climate warming in the North American high-latitude region could result in crossing environmental thresholds, thereby accelerating press disturbances and increasingly triggering pulse disturbances and eventually affecting the C source/sink net character of northern high-latitude soils. Finally, we assess postdisturbance feedbacks, models, and predictions for the northern high-latitude SOC pool, and discuss data and research gaps to be addressed by future research.

  14. The sponge genus Ephydatia from the high-latitude middle Eocene: environmental and evolutionary significance.

    Science.gov (United States)

    Pisera, Andrzej; Manconi, Renata; Siver, Peter A; Wolfe, Alexander P

    2016-01-01

    The freshwater sponge species Ephydatia cf. facunda Weltner, 1895 (Spongillida, Spongillidae) is reported for the first time as a fossil from middle Eocene lake sediments of the Giraffe kimberlite maar in northern Canada. The sponge is represented by birotule gemmuloscleres as well as oxea megascleres. Today, E. facunda inhabits warm-water bodies, so its presence in the Giraffe locality provides evidence of a warm climate at high latitudes during the middle Eocene. The morphological similarity of the birotules to modern conspecific forms suggests protracted morphological stasis, comparable to that reported for other siliceous microfossils from the same locality.

  15. Glacier-influenced sedimentation on high-latitude continental margins

    National Research Council Canada - National Science Library

    Dowdeswell, J. A; Cofaigh, C. Ó

    2002-01-01

    This book examines the process and patterns of glacier-influenced sedimentation on high-latitude continental margins and the geophysical and geological signatures of the resulting sediments and landform...

  16. Non-native and native organisms moving into high elevation and high latitude ecosystems in an era of climate change

    DEFF Research Database (Denmark)

    Pauchard, Aníbal; Milbau, Ann; Albihn, Ann

    2016-01-01

    Cold environments at high elevation and high latitude are often viewed as resistant to biological invasions. However, climate warming, land use change and associated increased connectivity all increase the risk of biological invasions in these environments. Here we present a summary of the key di...

  17. High-latitude dust in the Earth system

    Science.gov (United States)

    Bullard, Joanna E; Baddock, Matthew; Bradwell, Tom; Crusius, John; Darlington, Eleanor; Gaiero, Diego; Gasso, Santiago; Gisladottir, Gudrun; Hodgkins, Richard; McCulloch, Robert; NcKenna Neuman, Cheryl; Mockford, Tom; Stewart, Helena; Thorsteinsson, Throstur

    2016-01-01

    Natural dust is often associated with hot, subtropical deserts, but significant dust events have been reported from cold, high latitudes. This review synthesizes current understanding of high-latitude (≥50°N and ≥40°S) dust source geography and dynamics and provides a prospectus for future research on the topic. Although the fundamental processes controlling aeolian dust emissions in high latitudes are essentially the same as in temperate regions, there are additional processes specific to or enhanced in cold regions. These include low temperatures, humidity, strong winds, permafrost and niveo-aeolian processes all of which can affect the efficiency of dust emission and distribution of sediments. Dust deposition at high latitudes can provide nutrients to the marine system, specifically by contributing iron to high-nutrient, low-chlorophyll oceans; it also affects ice albedo and melt rates. There have been no attempts to quantify systematically the expanse, characteristics, or dynamics of high-latitude dust sources. To address this, we identify and compare the main sources and drivers of dust emissions in the Northern (Alaska, Canada, Greenland, and Iceland) and Southern (Antarctica, New Zealand, and Patagonia) Hemispheres. The scarcity of year-round observations and limitations of satellite remote sensing data at high latitudes are discussed. It is estimated that under contemporary conditions high-latitude sources cover >500,000 km2 and contribute at least 80–100 Tg yr−1 of dust to the Earth system (~5% of the global dust budget); both are projected to increase under future climate change scenarios.

  18. Relationships between vegetation dynamics and hydroclimatic drivers in the northern high-latitude uplands

    Science.gov (United States)

    Wang, H.; Tetzlaff, D.; Buttle, J. M.; Carey, S. K.; Laudon, H.; McNamara, J. P.; Soulsby, C.; Spence, C.

    2015-12-01

    IPCC projections show that climate warming will be particularly high in northern high-latitude regions, which has profound ecohydrological implications: a small rise of temperature may result in lower water availability in summer due to less rainfall and more evapotranspiration, increase flooding risks by accelerating melting rates in spring, and more rain rather than snow in winter, etc. These impacts will affect vegetation communities by altering timing of the spring "green-up" and fall "senescence". Change in vegetation water use will feedback to atmospheric and hydrological cycles. Here, we report results from the PLATO "Plant-water interlinkages in northern uplands - mediation of climate change?" project where we investigate water uptake by plants and consequent water availability in northern regions along a cross-regional climate gradient to understand future responses to change in high-latitude uplands. Six sites in Sweden (Krycklan), Canada (Wolf Creek; Baker Creek; Dorset), Scotland (Girnock) and the USA (Dry Creek) span moisture and energy gradients found at high-latitudes. We are presenting preliminary results of vegetation phenology changes from 2000 to 2014 by analysing remote sensing vegetation indices. The relationship between vegetation phenology and climatic drivers (temperature and precipitation) is also investigated.

  19. EDITORIAL: Northern Hemisphere high latitude climate and environmental change

    Science.gov (United States)

    Groisman, Pavel; Soja, Amber

    2007-10-01

    High Northern Hemisphere latitudes are undergoing rapid and significant change associated with climate warming. Climatic change in this region interacts with and affects the rate of the global change through atmospheric circulation, biogeophysical, and biogeochemical feedbacks. Changes in the surface energy balance, hydrologic cycle, and carbon budget feedback to regional and global weather and climate systems. Two-thirds of the Northern Hemisphere high latitude land mass resides in Northern Eurasia (~20% of the global land mass), and this region has undergone sweeping socio-economic change throughout the 20th century. How this carbon-rich, cold region component of the Earth system functions as a regional entity and interacts with and feeds back to the greater global system is to a large extent unknown. To mitigate the deficiencies in understanding these feedbacks, which may in turn hamper our understanding of the global change rates and patterns, an initiative was formed. Three years ago the Northern Eurasia Earth Science Partnership Initiative (NEESPI) was established to address large-scale and long-term manifestations of climate and environmental change in this region. The NEESPI Science Plan and its Executive Summary have been published at the NEESPI web site (neespi.org). Since 2004, NEESPI participants have been able to seed several waves of research proposals to international and national funding agencies and institutions and also contribute to the International Polar Year. Currently, NEESPI is widely recognized and endorsed by several Earth System Science Partnership (ESSP) programmes and projects: the International Geosphere and Biosphere Programme, the World Climate Research Programme through the Global Energy and Water Cycle Experiment and Climate and Cryosphere Projects, the Global Water System Project, Global Carbon Project, Global Land Project, and the Integrated Land Ecosystem—Atmosphere Processes Study. Through NEESPI, more than 100 individually

  20. Amplified North Atlantic Warming in the Late Pliocene by Changes in Arctic Gateways

    Science.gov (United States)

    Otto-Bliesner, B. L.; Jahn, A.; Feng, R.; Brady, E. C.; Hu, A.; Lofverstrom, M.

    2017-12-01

    Reconstructions of the late Pliocene (mid-Piacenzian, 3.3 - 3.0 million years ago) sea surface temperature (SST) find much warmer conditions in the North Atlantic than modern. The much warmer SSTs, up to 8.8°C from sites with good dating and replicates from several different types of proxies, have been difficult for climate models to reproduce. Even with the slow feedbacks of a reduced Greenland ice sheet and expansion of boreal forests to the Arctic Ocean over Canada and Eurasia, models cannot warm the North Atlantic sufficiently to match the reconstructed SSTs. An enhancement of the Atlantic Meridional Overturning Circulation (AMOC) during the late Pliocene, proposed as a possible mechanism based on ocean core records of δ13C, also is not present in the model simulations. Here, we present CESM simulations using a new reconstruction of late Pliocene paleogeography that has the Bering Strait (BS) and Canadian Arctic Archipelago (CAA) Straits closed. We find that the closure of these small Arctic gateways strengthens the AMOC, by inhibiting freshwater (FW) transport from the Pacific to the Arctic Ocean and from the Arctic Ocean to the Labrador Sea, leading to warmer sea surface temperatures in the North Atlantic. The cutoff of the short export route through the CAA results in a more saline Labrador and south Greenland Sea with increased deep convection. At the same time, as all FW now leaves the Arctic east of Greenland, there is a freshening of and decreased deepwater formation in the Norwegian Sea. Overall, the AMOC strengthens. This past time period has implications for a future Earth under more responsible scenarios of emissions. Late Pliocene atmospheric carbon dioxide concentrations are estimated to have ranged between 350 and 450 ppmv and the paleogeography is relatively similar to modern. Our study indicates that the state of the Arctic gateways may influence the sensitivity of the North Atlantic climate in complex ways, and better understanding of the

  1. High-Latitude Ionospheric Dynamics During Conditions of Northward IMF

    Science.gov (United States)

    Sharber, J. R.

    1996-01-01

    In order to better understand the physical processes operating during conditions of northward interplanetary magnetic field (IMF), in situ measurements from the Dynamics Explorer-2 (low altitude) polar satellite and simultaneous observations from the auroral imager on the Dynamics Explorer-1 (high altitude) satellite were used to investigate the relationships between optical emissions, particle precipitation, and convective flows in the high-latitude ionosphere. Field aligned current and convective flow patterns during IMF north include polar cap arcs, the theta aurora or transpolar arc, and the 'horse-collar' aurora. The initial part of the study concentrated on the electrodynamics of auroral features in the horse-collar aurora, a contracted but thickened emission region in which the dawn and dusk portions can spread to very high latitudes, while the latter part focused on the evolution of one type of IMF north auroral pattern to another, specifically the quiet-time horse-collar pattern to a theta aurora.

  2. An accelerating high-latitude jet in Earth's core

    OpenAIRE

    Livermore, PW; Hollerbach, R; Finlay, CC

    2017-01-01

    Observations of the change in Earth's magnetic field—the secular variation—provide information about the motion of liquid metal within the core that is responsible for the magnetic field's generation. High-resolution observations from the European Space Agency's Swarm satellite mission show intense field change at high latitude, localized in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we show that this feature can be explained by a localized, no...

  3. High-latitude tree-ring data: Records of climatic change and ecological response

    International Nuclear Information System (INIS)

    Graumlich, L.J.

    1991-01-01

    Tree-ring data provide critical information regarding two fundamental questions as to the role of the polar regions in global change: (1) what is the nature of climatic variability? and (2) what is the response of vegetation to climatic variability? Tree-ring-based climatic reconstructions document the variability of the climate system on time scales of years to centuries. Dendroclimatic reconstructions indicate that the climatic episodes defined on the basis of documentary evidence in western Europe (i.e., Medieval Warm Episode, ca. A.D. 1000-1300; Little Ice Age, ca. A.D. 1550-1850) can be observed at some high-latitude sites (ex., Polar Urals). Spatial variation in long-term temperature trends (ex., northern Fennoscandia vs. Polar Urals) demonstrates the importance of regional-scale climatic controls. When collated into global networks, proxy-based climatic reconstructions can be used to test hypotheses as to the relative importance of external forcing vs. internal variation in governing climatic variation. Specifically, such a global network would allow the quantification of the climatic response to various permutations of factors thought to be important in governing decadal- to centennial-scale climatic variation. Tree populations respond to annual- to centennial-scale climatic variation through changes in rates of growth, establishment, and mortality. Tree-ring studies that document multiple aspects of high-latitude treeline dynamics (i.e., the timing of tree establishment, mortality, and changes from krummholz to upright growth) indicate a complex interaction between growth form, population processes, and environmental variability. Such interactions result in varying sensitivities of high-latitude trees to climatic change

  4. THEORY OF SOLAR MERIDIONAL CIRCULATION AT HIGH LATITUDES

    International Nuclear Information System (INIS)

    Dikpati, Mausumi; Gilman, Peter A.

    2012-01-01

    We build a hydrodynamic model for computing and understanding the Sun's large-scale high-latitude flows, including Coriolis forces, turbulent diffusion of momentum, and gyroscopic pumping. Side boundaries of the spherical 'polar cap', our computational domain, are located at latitudes ≥ 60°. Implementing observed low-latitude flows as side boundary conditions, we solve the flow equations for a Cartesian analog of the polar cap. The key parameter that determines whether there are nodes in the high-latitude meridional flow is ε = 2ΩnπH 2 /ν, where Ω is the interior rotation rate, n is the radial wavenumber of the meridional flow, H is the depth of the convection zone, and ν is the turbulent viscosity. The smaller the ε (larger turbulent viscosity), the fewer the number of nodes in high latitudes. For all latitudes within the polar cap, we find three nodes for ν = 10 12 cm 2 s –1 , two for 10 13 , and one or none for 10 15 or higher. For ν near 10 14 our model exhibits 'node merging': as the meridional flow speed is increased, two nodes cancel each other, leaving no nodes. On the other hand, for fixed flow speed at the boundary, as ν is increased the poleward-most node migrates to the pole and disappears, ultimately for high enough ν leaving no nodes. These results suggest that primary poleward surface meridional flow can extend from 60° to the pole either by node merging or by node migration and disappearance.

  5. Containment test in area of high latitude and low temperature

    International Nuclear Information System (INIS)

    Cai Jiantao; Ni Yongsheng; Jia Wutong

    2014-01-01

    The effects of high latitude and low temperature on containment test are detailed analyzed from the view of design, equipment, construct and start-up, and the solution is put forward. The major problems resolved is as below: the effects of low temperature and high wind on defect inspection of the containment surface, the effects of test load on the affiliated equipment of containment in the condition of low temperature, and the effects of low temperature on the containment leak rate measurement. Application in Hongyanhe Unit 1 showed that the proposed scheme can effectively overcome the influence of adverse weather on the containment test. (authors)

  6. Climate Change Impacts on Sediment Yield in Headwaters of a High-latitude Region in China

    Science.gov (United States)

    Zhou, Y.; Xu, Y. J.; Wang, J., , Dr; Weihua, X.; Huang, Y.

    2017-12-01

    Climate change is expected to have strongest effects in higher latitude regions. Despite intensive research on possible hydrological responses to global warming in these regions, our knowledge of climate change on surface erosion and sediment yield in high-latitude headwaters is limited. In this study, we used the Soil and Water Assessment Tool (SWAT) to predict future runoff and sediment yield from the headwaters of a high-latitude river basin in China's far northeast. The SWAT model was first calibrated with historical discharge records and the model parameterization achieved satisfactory validation. The calibrated model was then applied to two greenhouse gas concentration trajectories, RCP4.5 and RCP8.5, for the period from 2020 to 2050 to estimate future runoff. Sediment yields for this period were predicted using a discharge-sediment load rating curve developed from field measurements in the past nine years. Our preliminary results show an increasing trend of sediment yield under both climate change scenarios, and that the increase is more pronounced in the summer and autumn months. Changes in precipitation and temperature seem to exert variable impacts on runoff and sediment yield at interannual and seasonal scales in these headwaters. These findings imply that the current river basin management in the region needs to be reviewed and improved in order to be effective under a changing climate.

  7. Ionosphere Scintillation at Low and High Latitudes (Modelling vs Measurement)

    Science.gov (United States)

    Béniguel, Yannick

    2016-04-01

    This paper will address the problem of scintillations characteristics, focusing on the parameters of interest for a navigation system. Those parameters are the probabilities of occurrence of simultaneous fading, the bubbles surface at IPP level, the cycle slips and the fades duration statistics. The scintillation characteristics obtained at low and high latitudes will be compared. These results correspond to the data analysis performed after the ESA Monitor ionosphere measurement campaign [1], [2]. A second aspect of the presentation will be the modelling aspect. It has been observed that the phase scintillation dominates at high latitudes while the intensity scintillation dominates at low latitudes. The way it can be reproduced and implemented in a propagation model (e.g. GISM model [3]) will be presented. Comparisons of measurements with results obtained by modelling will be presented on some typical scenarios. References [1] R. Prieto Cerdeira, Y. Beniguel, "The MONITOR project: architecture, data and products", Ionospheric Effects Symposium, Alexandria (Va), May 2011 [2] Y. Béniguel, R Orus-Perez , R. Prieto-Cerdeira , S. Schlueter , S. Scortan, A. Grosu "MONITOR 2: ionospheric monitoring network in support to SBAS and other GNSS and scientific purposes", IES Conference, Alexandria (Va), May 2015-05-22 [3] Y. Béniguel, P. Hamel, "A Global Ionosphere Scintillation Propagation Model for Equatorial Regions", Journal of Space Weather Space Climate, 1, (2011), doi: 10.1051/swsc/2011004

  8. High-latitude molecular clouds and infrared cirrus

    International Nuclear Information System (INIS)

    Vries, H.W. de.

    1988-01-01

    The high-latitude infrared cirrus detected by IRAS is identified with atomic and molecular clouds. These clouds are small (usually less than 1 sq. deg.) and show weak CO emission. On the basis of a distance of 100 pc they are characterized by a mass of a few solar masses and a radius of about 1 pc. Thermal radiation by dust as a results of heating by the diffuse interstellar radiation field is the most-plausible origin of the cirrus emission at far-infrared wavelengths. On the basis of plausible assumptions regarding the uniformity of both the gas-to-dust ratio and the heating and cooling of the dust, the flux density at 100 μm from regions with low visual extinction should be a good tracer of the gas column density. Indeed, the data show an approximately linear proportionality between N(HI), obtained from 21-cm observations, and I 100 (HI), the flux density from dust associated with HI. If the ratio of column density to flux density in high-latitude molecular clouds is equal to the corresponding relation in atomic ones, a value for the ratio of H 2 column density to CO velocity-integrated radiation temperature may be obtained. Although low-mass clouds may be large in number, the fraction of the Galactic molecular mass in the form of these clouds is probably no more than 1%

  9. Climatically induced floristic changes across the Eocene-Oligocene transition in the northern high latitudes, Yukon Territory, Canada

    Energy Technology Data Exchange (ETDEWEB)

    Ridgway, K.D.; Sweet, A.R.; Cameron, A.R. [Purdue University, West Lafayette, IN (United States). Dept. of Earth and Atmospheric Sciences

    1995-06-01

    Global temperature decline associated with the Eocene-Oligocene transition resulted in extinctions of plants and animals in both marine and nonmarine environments. The extensive stratigraphic exposures, well-preserved palynological assemblages, and interbedded coal seams of the nonmarine Amphitheatre Formation, Burwash Basin, Yukon Territory, provide a comprehensive record of this transition. The formation spans a paleoclimatically significant interval otherwise poorly represented in high-latitude deposits of the northwestern Cordiller. Palynological data constrained by the chronologic and stratigraphic framework established for the Amphitheatre Formation indicate that the global temperature decline resulted in a shift from warm temperate, angiosperm-dominated to cooler temperate, gymnosperm-dominated (mainly coniferous) forest types. Petrographic compositional changes in the coals document the same plant community changes. The floristic data also indicate that, at high latitudes, there may have been a change to a wetter and less seasonal climate during the overall global cooling trend.

  10. Vorticity and divergence in the high-latitude upper thermosphere

    International Nuclear Information System (INIS)

    Thayer, J.P.; Killeen, T.L.

    1991-01-01

    Measurements made from the Dynamics Explorer-2 satellite in November 1981 through January 1982 and November 1982 through January 1983 have been analyzed to determine the divergence and vertical component of vorticity of the high-latitude neutral wind field in the upper thermosphere for quiet (kp≤6) geomagnetic conditions and for both northern (winter) and southern (summer) hemispheres in the polar thermosphere and provides insight into the relative strengths of the different sources of momentum and energy responsible for driving the winds. The principal findings from this work include the following: The mean neutral wind pattern is dominated by rotational flow rather than by divergent flow, with a typical vorticity: divergence ratio of ∼ 2:1 for active conditions and ∼ 4:1 for quiet conditions. Comparison of the divergence and vorticity patterns for quiet and active conditions indicates that the divergent component of the neutral flow intensifies more significantly with increasing geomagnetic activity than does the rotational component

  11. CONDITIONED ANALYSIS OF HIGH-LATITUDE SOLAR WIND INTERMITTENCY

    International Nuclear Information System (INIS)

    D'Amicis, R.; Consolini, G.; Bavassano, B.; Bruno, R.

    2012-01-01

    The solar wind is a turbulent medium displaying intermittency. Its intermittent features have been widely documented and studied, showing how the intermittent character is different in fast and slow wind. In this paper, a statistical conditioned analysis of the solar wind intermittency for a period of high-latitude fast solar wind is presented. In particular, the intermittent features are investigated as a function of the Alfvénic degree of fluctuations at a given scale. The results show that the main contribution to solar wind intermittency is due to non-Alfvénic structures, while Alfvénic increments are found to be characterized by a smaller level of intermittency than the previous ones. Furthermore, the lifetime statistics of Alfvénic periods are discussed in terms of a multiscale texture of randomly oriented flux tubes.

  12. Microinstabilities in the high latitude F region: a brief review

    International Nuclear Information System (INIS)

    Gary, S.P.

    1983-01-01

    This is a review of the theory of plasma microinstabilities that may arise in the high latitude F region ionosphere below 1000 km. Three free energy sources are considered: a density gradient perpendicular to the ambient magnetic field B, a current parallel to B and a steady electric field perpendicular to B. The BGK model for charged-neutral collisions is used, and the short wavelength properties of the universal density drift, current convective and E x B gradient drift instabilities are compared. At sufficiently high altitudes and sufficiently steep gradients, the universal instability is the short wavelength mode most likely to grow and, through wave-particle diffusion, to cause relatively steep wavenumber dependences in power spectra

  13. CO observations of southern high-latitude clouds

    International Nuclear Information System (INIS)

    Keto, E.R.; Myers, P.C.

    1986-01-01

    Results from a survey of 2.6 mm emission in the J = 1 to 0 transition of CO of clouds are reported for 15 high Galactic latitude clouds and three clouds located on the fringe of a large molecular cloud in the Chameleon dark cloud complex. The line widths, excitation temperatures, sizes, and n(CO)/N(H2) ratio of these clouds are similar to those seen in dark clouds. The densities, extinctions, and masses of the high-latitude clouds are one order of magnitude less than those found in dark clouds. For its size and velocity dispersion, the typical cloud has a mass of at least 10 times less than that needed to bind the cloud by self-gravity alone. External pressures are needed to maintain the typical cloud in equilibrium, and these values are consistent with several estimates of the intercloud pressure. 32 references

  14. Energetic Particles at High Latitudes of the Heliosphere

    International Nuclear Information System (INIS)

    Zhang Ming

    2004-01-01

    Ulysses has by now made two complete out-of-ecliptic orbits around the sun. The first encounter of the solar poles occurred in 1994-1995, when the sun was near the minimum of its activity cycle, while the second one was in 2000-2001, when the sun was at solar maximum. To our surprise, energetic particles of all origins at high latitude are not much different from those we observe near the ecliptic for at least these two phases of solar cycle. The latitude gradients of galactic and anomalous cosmic rays are positive but small at the 1994-1995 solar minimum and almost zero at the 2000-2001 solar maximum, while temporal solar cycle variation dominates their flux variation at all latitudes. Solar energetic particles from all large gradual events can be seen at both Ulysses and Earth no matter how large their spatial separations from the solar event are, and the particle flux often reaches a uniform level in the entire inner heliosphere within a few days after event onset and remains so throughout the decay phase that can sometimes last over a month. Energetic particles accelerated by low-latitude CIRs can appear at high latitudes, far beyond the latitudinal range of CIRs. All these observations suggest that latitudinal transport of energetic particles is quite easy. In addition, because the average magnetic field is radial at the pole, The Ulysses observations indicate that parallel diffusion and drift in the radial direction need to be reduced at the poles relative to their equatorial values. To achieve such behaviors of particle transport, the heliospheric magnetic field needs a significant latitudinal component at the poles. A non-zero latitudinal magnetic field component can be produced by latitudinal motion of the magnetic field line in solar corona, which can be in form of either random walk suggested by Jokipii or large scale systematic motion suggested by Fisk

  15. Seasonal variations of the high-latitude F region for

    International Nuclear Information System (INIS)

    Sojka, J.J.; Schunk, R.W.; Raitt, W.J.

    1982-01-01

    We combined a plasma convection model with an inosphere-atmospheric composition model in order to study the seasonal variations of the high-latitude F region for strong convection. Our numerical study produced time-dependent, three-dimensional, ion density distributions for the ions NO + , O 2 + , N 2 + , O + , N + , and He + . We covered the high-latitude ionosphere above 42 0 N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. From our study we found the following: (1) For strong convection, the high-altitude ionosphere exhibits a significant UT variation both during winter and summer. (2) In general, the electron density is lower in winter than in summer. However, at certain universal times the electron density in the dayside polar cap is larger in winter than in summer owing to the effect of the mid-latitude 'winter anomaly' in combination with strong antisunward convection. (3) In both summer and winter, the major region of low electron density is associated with the main or mid-latitudde trough. The trough is deeper and its local time extend is much greater in winter than in summer. (4) Typically, the electron density exhibits a much larger variation with altitude in winter than in summer. (5) The ion composition and molecular/atomic ion transition altitude are highly UT dependent in both summer and winter. (6) The ion composition also displays a significant seasonal variation. However, at a given location the seasonal variation can be opposite at different universal times. (7) High-speed convection cells should display a marked seasonal variation, with a much larger concentration of molecular ions near the F region peak in summer than in winter

  16. Daylighting in linear atrium buildings at high latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Matusiak, Barbara

    1998-12-31

    This thesis proposes new criteria for visual comfort based on knowledge of visual perception and a method for estimating the modelling ability of light by using inter-reflection calculations. Simplified calculations are presented for the daylight factor in linear building structures, using the projected solid angle principle, for uniform sky and for CIE overcast sky conditions. The calculations are compared with experimental results. Simple diagrams are created based on calculations of the mean daylight factor in rooms adjacent to a narrow street. These diagrams and presented formulas and tables can be used as a simple design tool. Daylighting strategies for linear atrium buildings at high latitudes are developed and examined. These strategies are divided into three groups: (1) the atrium space and facades as light conductor/reflector, (2) the glass roof as a light conductor, and (3) light reflectors on the neighbouring roof. The atrium space and facade strategies are subdivided into passive and active. The strategies connected to the glazed roof includes different configurations of glazing: horizontal, single pitched, double pitched, and the use of laser cut panels and prismatic panels in the glazed roof. The shapes of reflectors on the neighbouring roof are a flat reflector, a parabolic reflector and a parabolic concentrator. Strategies from all three groups are examined on a physical model of scale 1:20 in the artificial sky of mirror box type. Simulations with artificial sun have also been done. The results from model studies are compared with computer simulations. All the active daylighting systems designed for use in the atrium space or on the atrium facades have a huge potential for use in atrium buildings. From the strategies connected with the glazed roof the negatively sloped glass is found to be the best alternative for glazed roofs at high latitudes. Among the roof reflectors, the flat one performs best. 82 refs., 122 figs., 27 tabs.

  17. Energy-Efficient Office Buildings at High Latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Lerum, V.

    1996-12-31

    This doctoral thesis describes a method for energy efficient office building design at high latitudes and cold climates. The method combines daylighting, passive solar heating, solar protection, and ventilative cooling. The thesis focuses on optimal design of an equatorial-facing fenestration system. A spreadsheet framework linking existing simplified methods is used. The daylight analysis uses location specific data on frequency distribution of diffuse daylight on vertical surfaces to estimate energy savings from optimal window and room configurations in combination with a daylight-responsive electric lighting system. The passive solar heating analysis is a generalization of a solar load ratio method adapted to cold climates by combining it with the Norwegian standard NS3031 for winter months when the solar savings fraction is negative. The emphasis is on very high computational efficiency to permit rapid and comprehensive examination of a large number of options early in design. The procedure is illustrated for a location in Trondheim, Norway, testing the relative significance of various design improvement options relative to a base case. The method is also tested for two other locations in Norway, at latitudes 58 and 70 degrees North. The band of latitudes between these limits covers cities in Alaska, Canada, Greenland, Iceland, Scandinavia, Finland, Russia, and Northern Japan. A comprehensive study of the ``whole building approach`` shows the impact of integrated daylighting and low-energy design strategies. In general, consumption of lighting electricity may be reduced by 50-80%, even at extremely high latitudes. The reduced internal heat from electric lights is replaced by passive solar heating. 113 refs., 85 figs., 25 tabs.

  18. Aspects on interactions between mid- to high latitude atmospheric circulation and some surface processes

    International Nuclear Information System (INIS)

    Byrkjedal, Oeyvind

    2006-01-01

    The Arctic is a hot topic in Climate Research. A large number of signs of a warming Arctic Climate have been identified the latest years. This is of major concern in light of the increasing atmospheric content of greenhouse gases. The climate research community projects future warming of the climate in the high latitudes as a response to increased amounts of anthropogenic release of greenhouse gases since the pre-industrial era. The overall objectives of this work has been to study the mid- and high latitude climate and climate variability, and to evaluate how well some climate processes that contribute to determine the Arctic climate and variability are represented and simulated in climate models. A new data set of storm tracks trajectories and statistics over the Northern Hemisphere for the period 1948-2002 has been developed. The variability of the cyclones extending to the Nordic Seas is studied in particular, and it is found that both the number of storms and their intensity exhibits a strong decadal and interannual variability. The ocean volume transports into and out of the Nordic Seas shows a relatively close relation to the wintertime cyclone intensity and cyclone count. To have confidence in future projections of climate, it is necessary to evaluate how the model behaves in a climate regime different from modern day. To do this two model simulations of the last glacial maximum (LGM) was performed. The reconstructions of sea surface temperatures in the Nordic Seas in LGM differ from perennial sea ice cover to having open ocean during the summer. The large scale atmospheric circulation patterns of the two different climate reconstructions are studied. It is found that the perennial sea ice cover produces a circulation pattern which may be too zonal to support the existence of the large north Eurasian ice sheets. In the case with seasonally open ocean the air masses carries larger amounts of heat and moisture towards the ice sheets and represents a larger

  19. A numerical modeling study of the interaction between the tides and the circulation forced by high-latitude plasma convection

    International Nuclear Information System (INIS)

    Mikkelsen, I.S.; Larsen, M.F.

    1991-01-01

    A spectral, time-varying thermospheric general circulation model has been used to study the nonlinear interaction at high latitudes between the tides propagating into the thermosphere from below and the circulation induced by magnetospheric forcing and in situ solar heating. The model is discrete in the vertical with 27 layers spaced by half a scale height. In the horizontal, the fields are expanded in a series of spherical harmonics using a triangular truncation at wave number 31, equivalent to a homogeneous global resolution with a minimum wavelength of 1,270 km. A hypothetical uniform grid point model would require a horizontal spacing of 417 km to describe the same minimum wavelength. In the high-latitude F region the tides affect the dusk vortex of the neutral flow very little, but the dawn vortex is either suppressed or amplified dependent upon the universal time and tidal phase. In the E region neutral flow, both the dusk and dawn vortices are shifted in local time by the tides, again as a function of universal time and tidal phase. At dusk a nonlinear amplification of the sunward winds occurs for certain combination of parameters, and at dawn the winds may be completely suppressed. Below 120 km altitude the magnetospheric forcing creates a single cyclonic vortex which is also sensitive to the high-latitude tidal structure

  20. Recent changes in phenology over the northern high latitudes detected from multi-satellite data

    International Nuclear Information System (INIS)

    Zeng Heqing; Jia Gensuo; Epstein, Howard

    2011-01-01

    Phenology of vegetation is a sensitive and valuable indicator of the dynamic responses of terrestrial ecosystems to climate change. Therefore, to better understand and predict ecosystems dynamics, it is important to reduce uncertainties in detecting phenological changes. Here, changes in phenology over the past several decades across the northern high-latitude region (≥60°N) were examined by calibrating and analyzing time series of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Very High Resolution Radiometer (AVHRR). Over the past decade (2000–10), an expanded length of the growing season (LOS) was detected by MODIS, largely due to an earlier start of the growing season (SOS) by 4.7 days per decade and a delayed end of the growing season (EOS) by 1.6 days per decade over the northern high latitudes. There were significant differences between North America and Eurasia in phenology from 2000 to 2010 based on MODIS data (SOS: df = 21, F = 49.02, p < 0.0001; EOS: df = 21, F = 49.25, p < 0.0001; LOS: df = 21, F = 79.40, p < 0.0001). In northern America, SOS advanced by 11.5 days per decade, and EOS was delayed by 2.2 days per decade. In Eurasia, SOS advanced by 2.7 days per decade, and EOS was delayed by 3.5 days per decade. SOS has likely advanced due to the warming Arctic during April and May. Our results suggest that in recent decades the longer vegetation growing seasons can be attributed to more advanced SOS rather than delayed EOS. AVHRR detected longer LOS over the past three decades, largely related to delayed EOS rather than advanced SOS. These two datasets are significantly different in key phenological parameters (SOS: df = 17, F = 14.63, p = 0.0015; EOS: df = 17, F = 38.69, p < 0.0001; LOS: df = 17, F = 16.47, p = 0.0009) from 2000 to 2008 over the northern high latitudes. Thus, further inter-calibration between the sensors is needed to resolve the inconsistency and to better understand long-term trends of vegetation growth

  1. A prediction and damage assessment model for snowmelt flood events in middle and high latitudes Region

    Science.gov (United States)

    Qiao, C.; Huang, Q.; Chen, T.; Zhang, X.

    2017-12-01

    In the context of global warming, the snowmelt flood events in the mountainous area of the middle and high latitudes are increasingly frequent and create severe casualties and property damages. Carrying out the prediction and risk assessment of the snowmelt flood is of great importance in the water resources management, the flood warning and prevention. Based on the remote sensing and GIS techniques, the relationships of the variables influencing the snowmelt flood such as the snow area, the snow depth, the air temperature, the precipitation, the land topography and land covers are analyzed and a prediction and damage assessment model for snowmelt floods is developed. This model analyzes and predicts the flood submerging area, flood depth, flood grade, and the damages of different underlying surfaces in the study area in a given time period based on the estimation of snowmelt amount, the snowmelt runoff, the direction and velocity of the flood. Then it was used to predict a snowmelt flood event in the Ertis River Basin in northern Xinjiang, China, during March and June, 2005 and to assess its damages including the damages of roads, transmission lines, settlements caused by the floods and the possible landslides using the hydrological and meteorological data, snow parameter data, DEM data and land use data. A comparison was made between the prediction results from this model and observation data including the flood measurement and its disaster loss data, which suggests that this model performs well in predicting the strength and impact area of snowmelt flood and its damage assessment. This model will be helpful for the prediction and damage assessment of snowmelt flood events in the mountainous area in the middle and high latitudes in spring, which has great social and economic significance because it provides a relatively reliable method for snowmelt flood prediction and reduces the possible damages caused by snowmelt floods.

  2. Supersonic plasma flow between high latitude conjugate ionospheres

    International Nuclear Information System (INIS)

    Roesler, G.

    1975-01-01

    The polar wind problem has been investigated for closed field lines in situations where one of the two conjugate ionospheric regions is fully illuminated by the sun and the other darkness (solstices at high latitudes). A supersonic flow between hemispheres is possible; the magnetospheric part of this flow must be symmetric with respect to the equator. The daytime fluxes are proportional to the neutral hydrogen density. Fluxes of the order of 10 8 cm -2 sec -1 are only possible with density considerably higher than given by CIRA models. For stationary solutions higher flow speeds are needed on the dark side than provided from the illuminated side. It is concluded that shock waves with upward velocities of about 5 km/sec would form above the dark ionosphere. This implies a reduction by a factor of 3 to 5 of the plasma influx into the dark hemisphere, whereby F-layer densities of only up to 2 x 10 4 cm -3 can be maintained. (orig.) [de

  3. Tracking strategy for photovoltaic solar systems in high latitudes

    International Nuclear Information System (INIS)

    Quesada, Guillermo; Guillon, Laura; Rousse, Daniel R.; Mehrtash, Mostafa; Dutil, Yvan; Paradis, Pierre-Luc

    2015-01-01

    Highlights: • In cloudy conditions tracking the sun is ineffective. • A methodology to estimate a theoretical threshold for solar tracking was developed. • A tracking strategy to maximize electricity production was proposed. - Abstract: Several studies show that from about 20% to 50% more solar energy can be recovered by using photovoltaic systems that track the sun rather than systems set at a fixed angle. For overcast or cloudy days, recent studies propose the use of a set position in which each photovoltaic panel faces toward the zenith (horizontal position). Compared to a panel that follows the sun’s path, this approach claims that a horizontal panel increases the amount of solar radiation captured and subsequently the quantity of electricity produced. The present work assesses a solar tracking photovoltaic panel hourly and seasonally in high latitudes. A theoretical method based on an isotropic sky model was formulated, implemented, and used in a case study analysis of a grid-connected photovoltaic system in Montreal, Canada. The results obtained, based on the definition of a critical hourly global solar radiation, were validated numerically and experimentally. The study confirmed that a zenith-set sun tracking strategy for overcast or mostly cloudy days in summer is not advantageous

  4. High latitude plasma convection: Predictions for EISCAT and Sondre Stromfjord

    International Nuclear Information System (INIS)

    Sojka, J.J.; Raitt, W.J.; Schunk, R.W.

    1979-01-01

    We have used a plasma convection model to predict diurnal patterns of horizontal drift velocities in the vicinity of the EISCAT incoherent scatter facility at Tromso, Norway and for Sondre Stromfjord, Greenland, a proposed new incoherent scatter facility site. The convection model includes the offset of 11.4 0 between the geographic and geomagnetic poles (northern hemisphere), the tendency of plasma to corotate about the geographic pole, and a magnetospheric electric field mapped to a circle about a center offset by 5 0 in the antisunward direction from the magnetic pole. Four different magnetospheric electric field configurations were considered, including a constant cross-tail electric field, asymmetric electric fields with enhancements on the dawn and dusk sides of the polar cap, and an electric field pattern that is not aligned parallel to the noon-midnight magnetic meridian. The different electric field configurations produce different signatures in the plasma convection pattern which are clearly identified. Both of the high-latitude sites are better suited to study magnetospheric convection effects than either Chatanika, Alaska or Millstone Hill, Massachusetts. Also, each site appears to have unique capabilities with regard to studying certain aspects of the magnetospheric electric field

  5. Geosynchronous inclined orbits for high-latitude communications

    Science.gov (United States)

    Fantino, E.; Flores, R. M.; Di Carlo, M.; Di Salvo, A.; Cabot, E.

    2017-11-01

    We present and discuss a solution to the growing demand for satellite telecommunication coverage in the high-latitude geographical regions (beyond 55°N), where the signal from geostationary satellites is limited or unavailable. We focus on the dynamical issues associated to the design, the coverage, the maintenance and the disposal of a set of orbits selected for the purpose. Specifically, we identify a group of highly inclined, moderately eccentric geosynchronous orbits derived from the Tundra orbit (geosynchronous, eccentric and critically inclined). Continuous coverage can be guaranteed by a constellation of three satellites in equally spaced planes and suitably phased. By means of a high-precision model of the terrestrial gravity field and the relevant environmental perturbations, we study the evolution of these orbits. The effects of the different perturbations on the ground track (which is more important for coverage than the orbital elements themselves) are isolated and analyzed. The physical model and the numerical setup are optimized with respect to computing time and accuracy. We show that, in order to maintain the ground track unchanged, the key parameters are the orbital period and the argument of perigee. Furthermore, corrections to the right ascension of the ascending node are needed in order to preserve the relative orientation of the orbital planes. A station-keeping strategy that minimizes propellant consumption is then devised, and comparisons are made between the cost of a solution based on impulsive maneuvers and one with continuous thrust. Finally, the issue of end-of-life disposal is discussed.

  6. An accelerating high-latitude jet in Earth's core

    Science.gov (United States)

    Livermore, P. W.; Finlay, C. C.; Hollerbach, R.

    2017-12-01

    Observations of the change in Earth's magnetic field, the secular variation, provide information on the motion of liquid metal within the core that is responsible for its generation. The very latest high-resolution observations from ESA's Swarm satellite mission show intense field change at high-latitude localised in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we explain this feature with a localised, nonaxisymmetric, westwards jet of 420 km width on the tangent cylinder, the cylinder of fluid within the core that is aligned with the rotation axis and tangent to the solid inner core. We find that the jet has increased in magnitude by a factor of three over the period 2000-2016 to about 40 km/yr, and is now much stronger than typical large-scale flows inferred for the core. The current accelerating phase may be a part of a longer term fluctuation of the jet causing both eastwards and westwards movement of magnetic features over historical periods, and may contribute to recent changes in torsional wave activity and the rotation direction of the inner core.

  7. Effects of space weather on high-latitude ground systems

    Science.gov (United States)

    Pirjola, Risto

    Geomagnetically induced currents (GIC) in technological systems, such as power grids, pipelines, cables and railways, are a ground manifestation of space weather. The first GIC observations were already made in early telegraph equipment more than 150 years ago. In power networks, GIC may saturate transformers with possible harmful consequences extending even to a collapse of the whole system or to permanent damage of transformers. In pipelines, GIC and the associated pipe-to-soil voltages may enhance corrosion or disturb surveys associated with corrosion control. GIC are driven by the geoelectric field induced by a geomagnetic variation at the Earth’s surface. The electric and magnetic fields are primarily produced by ionospheric currents and secondarily affected by the ground conductivity. Of great importance is the auroral electrojet with other rapidly varying currents indicating that GIC are a particular high-latitude problem. In this paper, we summarize the GIC research done in Finland during about 25 years, and discuss the calculation of GIC in a given network. Special attention is paid to modelling a power system. It is shown that, when considering GIC at a site, it is usually sufficient to take account for a smaller grid in the vicinity of the particular site. Modelling GIC also provides a basis for developing forecasting and warning methods of GIC.

  8. The single event upset environment for avionics at high latitude

    International Nuclear Information System (INIS)

    Sims, A.J.; Dyer, C.S.; Peerless, C.L.; Farren, J.

    1994-01-01

    Modern avionic systems for civil and military applications are becoming increasingly reliant upon embedded microprocessors and associated memory devices. The phenomenon of single event upset (SEU) is well known in space systems and designers have generally been careful to use SEU tolerant devices or to implement error detection and correction (EDAC) techniques where appropriate. In the past, avionics designers have had no reason to consider SEU effects but is clear that the more prevalent use of memory devices combined with increasing levels of IC integration will make SEU mitigation an important design consideration for future avionic systems. To this end, it is necessary to work towards producing models of the avionics SEU environment which will permit system designers to choose components and EDAC techniques which are based on predictions of SEU rates correct to much better than an order of magnitude. Measurements of the high latitude SEU environment at avionics altitude have been made on board a commercial airliner. Results are compared with models of primary and secondary cosmic rays and atmospheric neutrons. Ground based SEU tests of static RAMs are used to predict rates in flight

  9. Tundra shrubification and tree-line advance amplify arctic climate warming: results from an individual-based dynamic vegetation model

    Science.gov (United States)

    Zhang, Wenxin; Miller, Paul A.; Smith, Benjamin; Wania, Rita; Koenigk, Torben; Döscher, Ralf

    2013-09-01

    One major challenge to the improvement of regional climate scenarios for the northern high latitudes is to understand land surface feedbacks associated with vegetation shifts and ecosystem biogeochemical cycling. We employed a customized, Arctic version of the individual-based dynamic vegetation model LPJ-GUESS to simulate the dynamics of upland and wetland ecosystems under a regional climate model-downscaled future climate projection for the Arctic and Subarctic. The simulated vegetation distribution (1961-1990) agreed well with a composite map of actual arctic vegetation. In the future (2051-2080), a poleward advance of the forest-tundra boundary, an expansion of tall shrub tundra, and a dominance shift from deciduous to evergreen boreal conifer forest over northern Eurasia were simulated. Ecosystems continued to sink carbon for the next few decades, although the size of these sinks diminished by the late 21st century. Hot spots of increased CH4 emission were identified in the peatlands near Hudson Bay and western Siberia. In terms of their net impact on regional climate forcing, positive feedbacks associated with the negative effects of tree-line, shrub cover and forest phenology changes on snow-season albedo, as well as the larger sources of CH4, may potentially dominate over negative feedbacks due to increased carbon sequestration and increased latent heat flux.

  10. Tundra shrubification and tree-line advance amplify arctic climate warming: results from an individual-based dynamic vegetation model

    International Nuclear Information System (INIS)

    Zhang Wenxin; Miller, Paul A; Smith, Benjamin; Wania, Rita; Koenigk, Torben; Döscher, Ralf

    2013-01-01

    One major challenge to the improvement of regional climate scenarios for the northern high latitudes is to understand land surface feedbacks associated with vegetation shifts and ecosystem biogeochemical cycling. We employed a customized, Arctic version of the individual-based dynamic vegetation model LPJ-GUESS to simulate the dynamics of upland and wetland ecosystems under a regional climate model–downscaled future climate projection for the Arctic and Subarctic. The simulated vegetation distribution (1961–1990) agreed well with a composite map of actual arctic vegetation. In the future (2051–2080), a poleward advance of the forest–tundra boundary, an expansion of tall shrub tundra, and a dominance shift from deciduous to evergreen boreal conifer forest over northern Eurasia were simulated. Ecosystems continued to sink carbon for the next few decades, although the size of these sinks diminished by the late 21st century. Hot spots of increased CH 4 emission were identified in the peatlands near Hudson Bay and western Siberia. In terms of their net impact on regional climate forcing, positive feedbacks associated with the negative effects of tree-line, shrub cover and forest phenology changes on snow-season albedo, as well as the larger sources of CH 4 , may potentially dominate over negative feedbacks due to increased carbon sequestration and increased latent heat flux. (letter)

  11. High Latitude Reefs: A Potential Refuge for Reef Builders

    Science.gov (United States)

    Amat, A.; Bates, N.

    2003-04-01

    Coral reefs globally show variable signs of deterioration or community structure changes due to a host of anthropogenic and natural factors. In these global scenarios, rates of calcification by reef builders such as Scleractinian corals are predicted to significantly decline in the future due to the increase in atmospheric CO_2. When considering the response of reefs to the present climate change, temperature effects should also be taken into account. Here, we investigate the simultaneous impact of temperature and CO_2 on the high-latitude Bermuda coral reef system (32^oN, 64^oE)through a series of in vitro experiments at different CO_2 levels and seasonally different summer (27^oC) and winter (20^oC) temperature conditions. Four species of Scleractinian corals (Porites astreoides, Diploria labyrinthiformis, Madracis mirabilis and decactis) were acclimated for three months at: 20^oC and 27^oC (both with CO_2 levels at 400 ppm (control) and 700 ppm). Growth was assessed by buoyant weight techniques during the acclimation period. Photosynthesis, respiration and calcification were measured at the end of this period using respirometric chambers. A reproduction experiment was also undertaken under 27^oC. Photosynthesis mainly remains constant or increases under high CO_2 conditions. The results of the integrated calcification measurements confirm the hypothesis that an increase in CO_2 induces a decrease in calcification. However an increase in photosynthesis can be observed when CO_2 is unfavorable for calcification suggesting that a biological control of calcification through photosynthesis could prevent a drop in the calcification potential. Buoyant weight results indicate that the CO_2 impact could be less detrimental under lower temperature. This result will be compared with the instantaneous calcification measurements in the chambers and some in situ coral growth assessments in winter and summer conditions. The consequences for the response of marginal reefs

  12. Seasonal dependence of high-latitude electric fields

    International Nuclear Information System (INIS)

    de la Beaujardiere, O.; Leger, C.; Alcayde, D.; Fontanari, J.

    1991-01-01

    The seasonal dependence of the high-latitude electric field was investigated using Sondrestrom incoherent scatter radar data. Average ExB drifts were derived from 5 years of measurements centered around solar minimum. The electrostatic potentials that best fit the observed average electric field were calculated. It was found that the large-scale convection pattern significantly changes with season. This change involves the overall shape of the convection pattern, as well as the electric field intensity, and thus the total dawn-dusk potential across the polar cap. The cross polar cap potential drop is largest in fall, followed by winter, spring and summer. The small difference found between the summer and winter cross polar cap potential can be attributed to differing field-aligned potential drops. In view of the well-known relationship between field-aligned currents and parallel potential drop, this is consistent with the observations that Birkeland currents are larger in the summer than in winter. Changes in the overall shape of the convection pattern are consistent with the simple notion that the whole pattern is shifted toward the nightside as well as, to a lesser extent, toward the dawnside in summer as compared to winter. This assumption is based on the following observed effects: (1) The rotation of the overall convection pattern toward earlier local times with respect to the noon-midnight direction is maximum for summer on the dayside. (2) On the nightside, the Harang discontinuity is typically located within the radar field of view (Λ=67 to 82) in the winter averaged patterns, but it is equatorward of the field of view in summer. (3) The line that joins the dawn and dusk potential maxima is shifted toward the midnight sector in summer as compared to winter by about 5 degree. (4) In the dawn cell, the latitude of the convection reversal is the lowest during summer; in the dusk cell the latitude of the reversal is the lowest during winter

  13. Ion escape fluxes from the terrestrial high-latitude ionosphere

    International Nuclear Information System (INIS)

    Barakat, A.R.; Schunk, R.W.; Moore, T.E.; Waite, J.H. Jr.

    1987-01-01

    The coupled continuity and momentum equations for H + , O + , and electrons were solved for the terrestrial ionosphere in order to determine the limiting ion escape fluxes at high latitudes. The effects of solar cycle, season, geomagnetic activity, and the altitude of the acceleration region on the ion escape fluxes were studied for average conditions. In addition, a systematic parameter study was conducted to determine the extent to which variations in ionospheric conditions (for example, electron temperature, ion temperature, induced vertical ion drifts, etc.) can affect the results. The main conclusions of the study are as follows: (1) as solar activity increases, the general trend is for an increase in the limiting O + escape flux and a decrease in the limiting H + escape flux; (2) in winter the limiting escape fluxes of both O + and H + are larger than those in summer, particularly for low geomagnetic activity; (3) the O + content of the ion outflow increases with increasing ''demand'' imposed on the ionosphere by a high-altitude acceleration process, with increasing solar activity, with increasing geomagnetic activity, with increasing solar elevation from winter to summer, and with a lowering of the altitude of the acceleration region; (4) when H + is in a near-diffusive equilibrium state and a selective mechanism accelerates O + , the limiting O + escape flux is significantly reduced compared to that obtained when an H + outflow also occurs; and (5) at a given time or location the general trends described above can be significantly modified or even reversed owing to natural variations of the ionospheric ion and electron temperatures, induced vertical ion drifts, etc. The general trends obtained for average conditions appear to mimic the qualitative behavior determined from statistically averaged data for comparable absolute escape flux magnitudes

  14. Mapping high-latitude plasma convection with coherent HF radars

    International Nuclear Information System (INIS)

    Ruohoniemi, J.M.; Greenwald, R.A.; Baker, K.B.; Villain, J.-P.; Hanuise, C.; Kelly, J.

    1989-01-01

    In this decade, a new technique for the study of ionosphere electrodynamics has been implemented in an evolving generation of high-latitude HF radars. Coherent backscatter from electron density irregularities at F region altitudes is utilized to observe convective plasma motion. The electronic beam forming and scanning capabilities of the radars afford an excellent combination of spatial (∼50 km) and temporal (∼1 min) resolution of the large-scale (∼10 6 km 2 ) convection pattern. In this paper, we outline the methods developed to synthesize the HF radar data into two-dimensional maps of convection velocity. Although any single radar can directly measure only the line-of-sight, or radial, component of the plasma motion, the convection pattern is sometimes so uniform and stable that scanning in azimuth serves to determine the transverse component as well. Under more variable conditions, data from a second radar are necessary to unambiguously resolve velocity vectors. In either case, a limited region of vector solution can be expanded into contiguous areas of single-radar radial velocity data by noting that the convection must everywhere be divergence-free, i.e., ∇·v=0. It is thus often possible to map velocity vectors without extensive second-radar coverage. We present several examples of two-dimensional velocity maps. These show instances of L shell-aligned flow in the dusk sector, the reversal of convection near magnetic midnight, and counterstreaming in the dayside cleft. We include a study of merged coherent and incoherent radar data that illustrates the applicability of these methods to other ionospheric radar systems. copyright American Geophysical Union 1989

  15. Amplified warming projections for high altitude regions of the northern hemisphere mid-latitudes from CMIP5 models

    International Nuclear Information System (INIS)

    Rangwala, Imtiaz; Sinsky, Eric; Miller, James R

    2013-01-01

    We use output from global climate models available from the Coupled Model Intercomparison Project Phase 5 (CMIP5) for three different greenhouse gas emission scenarios to investigate whether the projected warming in mountains by the end of the 21st century is significantly different from that in low elevation regions. To remove the effects of latitudinal variation in warming rates, we focus on seasonal changes in the mid-latitude band of the northern hemisphere between 27.5° N and 40° N, where the two major mountain systems are the Tibetan Plateau/Himalayas in Asia and the Rocky Mountains in the United States. Results from the multi-model ensemble indicate that warming rates in mountains will be enhanced relative to non-mountain regions at the same latitude, particularly during the cold season. The strongest correlations of enhanced warming with elevation are obtained for the daily minimum temperature during winter, with the largest increases found for the Tibetan Plateau/Himalayas. The model projections indicate that this occurs, in part, because of proportionally greater increases in downward longwave radiation at higher elevations in response to increases in water vapor. The mechanisms for enhanced increases in winter and spring maximum temperatures in the Rockies appear to be influenced more by increases in surface absorption of solar radiation owing to a reduced snow cover. Furthermore, the amplification of warming with elevation is greater for a higher greenhouse gas emission scenario. (letter)

  16. Ecosystem responses to recent oceanographic variability in high-latitude Northern Hemisphere ecosystems

    Science.gov (United States)

    Mueter, Franz J.; Broms, Cecilie; Drinkwater, Kenneth F.; Friedland, Kevin D.; Hare, Jonathan A.; Hunt, George L., Jr.; Melle, Webjørn; Taylor, Maureen

    2009-04-01

    As part of the international MENU collaboration, we compared and contrasted ecosystem responses to climate-forced oceanographic variability across several high latitude regions of the North Pacific (Eastern Bering Sea (EBS) and Gulf of Alaska (GOA)) and North Atlantic Oceans (Gulf of Maine/Georges Bank (GOM/GB) and the Norwegian/Barents Seas (NOR/BAR)). Differences in the nitrate content of deep source waters and incoming solar radiation largely explain differences in average primary productivity among these ecosystems. We compared trends in productivity and abundance at various trophic levels and their relationships with sea-surface temperature. Annual net primary production generally increases with annual mean sea-surface temperature between systems and within the EBS, BAR, and GOM/GB. Zooplankton biomass appears to be controlled by both top-down (predation by fish) and bottom-up forcing (advection, SST) in the BAR and NOR regions. In contrast, zooplankton in the GOM/GB region showed no evidence of top-down forcing but appeared to control production of major fish populations through bottom-up processes that are independent of temperature variability. Recruitment of several fish stocks is significantly and positively correlated with temperature in the EBS and BAR, but cod and pollock recruitment in the EBS has been negatively correlated with temperature since the 1977 shift to generally warmer conditions. In each of the ecosystems, fish species showed a general poleward movement in response to warming. In addition, the distribution of groundfish in the EBS has shown a more complex, non-linear response to warming resulting from internal community dynamics. Responses to recent warming differ across systems and appear to be more direct and more pronounced in the higher latitude systems where food webs and trophic interactions are simpler and where both zooplankton and fish species are often limited by cold temperatures.

  17. Automated Detection of Thermo-Erosion in High Latitude Ecosystems

    Science.gov (United States)

    Lara, M. J.; Chipman, M. L.; Hu, F.

    2017-12-01

    conditions or wildfire. This work demonstrates the utility of meso-scale high frequency remote sensing products for advancing high latitude permafrost research.

  18. Mountain birch – potentially large source of sesquiterpenes into high latitude atmosphere

    Directory of Open Access Journals (Sweden)

    A. Arneth

    2009-11-01

    Full Text Available Emissions of volatile organic compounds (VOCs from mountain birches were measured in Abisko, northern Sweden. Mountain birches make up the majority of the tree biomass in Scandinavian high latitudes, a region subject to significant climate warming. The measurements were carried out in two growing seasons. The emissions of four branches, each from a different individual tree, were measured in June–August 2006 and one of them again in July 2007. The measurements were conducted using a dynamic flow through chamber covered with Teflon film. The studied mountain birches were found to emit substantial amounts of linalool, monoterpenes and sesquiterpenes. The monoterpene emission was dominated by sabinene. The magnitude and composition of the sesquiterpene emission changed dramatically between the years. For example, the average α-farnesene emission potential in 2006 was almost 2600 ng gdw−1 h−1 (3.5 pmol gdw−1 s−1 while in 2007 α-farnesene was not detected at all. Also the emissions of other sesquiterpenes decreased in 2007 to a fraction of that in 2006. One possible explanation for the change in emissions is the herbivory damage that occurred in the area in 2004. Herbivory is known to enhance the emissions of sesquiterpenes, especially those of α-farnesene, and the effect may last for several years.

  19. High-latitude cooling associated with landscape changes from North American boreal forest fires

    Directory of Open Access Journals (Sweden)

    B. M. Rogers

    2013-02-01

    Full Text Available Fires in the boreal forests of North America are generally stand-replacing, killing the majority of trees and initiating succession that may last over a century. Functional variation during succession can affect local surface energy budgets and, potentially, regional climate. Burn area across Alaska and Canada has increased in the last few decades and is projected to be substantially higher by the end of the 21st century because of a warmer climate with longer growing seasons. Here we simulated changes in forest composition due to altered burn area using a stochastic model of fire occurrence, historical fire data from national inventories, and succession trajectories derived from remote sensing. When coupled to an Earth system model, younger vegetation from increased burning cooled the high-latitude atmosphere, primarily in the winter and spring, with noticeable feedbacks from the ocean and sea ice. Results from multiple scenarios suggest that a doubling of burn area would cool the surface by 0.23 ± 0.09 °C across boreal North America during winter and spring months (December through May. This could provide a negative feedback to winter warming on the order of 3–5% for a doubling, and 14–23% for a quadrupling, of burn area. Maximum cooling occurs in the areas of greatest burning, and between February and April when albedo changes are largest and solar insolation is moderate. Further work is needed to integrate all the climate drivers from boreal forest fires, including aerosols and greenhouse gasses.

  20. The palaeobiology of high latitude birds from the early Eocene greenhouse of Ellesmere Island, Arctic Canada.

    Science.gov (United States)

    Stidham, Thomas A; Eberle, Jaelyn J

    2016-02-12

    Fossils attributable to the extinct waterfowl clade Presbyornithidae and the large flightless Gastornithidae from the early Eocene (~52-53 Ma) of Ellesmere Island, in northernmost Canada are the oldest Cenozoic avian fossils from the Arctic. Except for its slightly larger size, the Arctic presbyornithid humerus is not distinguishable from fossils of Presbyornis pervetus from the western United States, and the Gastornis phalanx is within the known size range of mid-latitude individuals. The occurrence of Presbyornis above the Arctic Circle in the Eocene could be the result of annual migration like that of its living duck and geese relatives, or it may have been a year-round resident similar to some Eocene mammals on Ellesmere and some extant species of sea ducks. Gastornis, along with some of the mammalian and reptilian members of the Eocene Arctic fauna, likely over-wintered in the Arctic. Despite the milder (above freezing) Eocene climate on Ellesmere Island, prolonged periods of darkness occurred during the winter. Presence of these extinct birds at both mid and high latitudes on the northern continents provides evidence that future increases in climatic warming (closer to Eocene levels) could lead to the establishment of new migratory or resident populations within the Arctic Circle.

  1. Novel Solar Sail Mission Concepts for High-Latitude Earth and Lunar Observation

    NARCIS (Netherlands)

    Heiligers, M.J.; Parker, Jeffrey S.; Macdonald, Malcolm

    2016-01-01

    This paper proposes the use of solar sail periodic orbits in the Earth-Moon system for ob-servation of the high-latitudes of the Earth and Moon. At the Earth, the high-latitudes will be crucial in answering questions concerning global climate change, monitoring space weather events and ensuring

  2. ORCHIDEE-MICT (v8.4.1), a land surface model for the high latitudes: model description and validation

    Science.gov (United States)

    Guimberteau, Matthieu; Zhu, Dan; Maignan, Fabienne; Huang, Ye; Yue, Chao; Dantec-Nédélec, Sarah; Ottlé, Catherine; Jornet-Puig, Albert; Bastos, Ana; Laurent, Pierre; Goll, Daniel; Bowring, Simon; Chang, Jinfeng; Guenet, Bertrand; Tifafi, Marwa; Peng, Shushi; Krinner, Gerhard; Ducharne, Agnès; Wang, Fuxing; Wang, Tao; Wang, Xuhui; Wang, Yilong; Yin, Zun; Lauerwald, Ronny; Joetzjer, Emilie; Qiu, Chunjing; Kim, Hyungjun; Ciais, Philippe

    2018-01-01

    The high-latitude regions of the Northern Hemisphere are a nexus for the interaction between land surface physical properties and their exchange of carbon and energy with the atmosphere. At these latitudes, two carbon pools of planetary significance - those of the permanently frozen soils (permafrost), and of the great expanse of boreal forest - are vulnerable to destabilization in the face of currently observed climatic warming, the speed and intensity of which are expected to increase with time. Improved projections of future Arctic and boreal ecosystem transformation require improved land surface models that integrate processes specific to these cold biomes. To this end, this study lays out relevant new parameterizations in the ORCHIDEE-MICT land surface model. These describe the interactions between soil carbon, soil temperature and hydrology, and their resulting feedbacks on water and CO2 fluxes, in addition to a recently developed fire module. Outputs from ORCHIDEE-MICT, when forced by two climate input datasets, are extensively evaluated against (i) temperature gradients between the atmosphere and deep soils, (ii) the hydrological components comprising the water balance of the largest high-latitude basins, and (iii) CO2 flux and carbon stock observations. The model performance is good with respect to empirical data, despite a simulated excessive plant water stress and a positive land surface temperature bias. In addition, acute model sensitivity to the choice of input forcing data suggests that the calibration of model parameters is strongly forcing-dependent. Overall, we suggest that this new model design is at the forefront of current efforts to reliably estimate future perturbations to the high-latitude terrestrial environment.

  3. Climate change between the mid and late Holocene in northern high latitudes – Part 2: Model-data comparisons

    Directory of Open Access Journals (Sweden)

    K. Holmgren

    2010-09-01

    Full Text Available The climate response over northern high latitudes to the mid-Holocene orbital forcing has been investigated in three types of PMIP (Paleoclimate Modelling Intercomparison Project simulations with different complexity of the modelled climate system. By first undertaking model-data comparison, an objective selection method has been applied to evaluate the capability of the climate models to reproduce the spatial response pattern seen in proxy data. The possible feedback mechanisms behind the climate response have been explored based on the selected model simulations. Subsequent model-model comparisons indicate the importance of including the different physical feedbacks in the climate models. The comparisons between the proxy-based reconstructions and the best fit selected simulations show that over the northern high latitudes, summer temperature change follows closely the insolation change and shows a common feature with strong warming over land and relatively weak warming over ocean at 6 ka compared to 0 ka. Furthermore, the sea-ice-albedo positive feedback enhances this response. The reconstructions of temperature show a stronger response to enhanced insolation in the annual mean temperature than winter and summer temperature. This is verified in the model simulations and the behaviour is attributed to the larger contribution from the large response in autumn. Despite a smaller insolation during winter at 6 ka, a pronounced warming centre is found over Barents Sea in winter in the simulations, which is also supported by the nearby northern Eurasian continental and Fennoscandian reconstructions. This indicates that in the Arctic region, the response of the ocean and the sea ice to the enhanced summer insolation is more important for the winter temperature than the synchronous decrease of the insolation.

  4. Environmental variation, vegetation distribution, carbon dynamics and water/energy exchange at high latitudes

    Science.gov (United States)

    McGuire, A.D.; Wirth, C.; Apps, M.; Beringer, J.; Clein, J.; Epstein, H.; Kicklighter, D.W.; Bhatti, J.; Chapin, F. S.; De Groot, B.; Efremov, D.; Eugster, W.; Fukuda, M.; Gower, T.; Hinzman, L.; Huntley, B.; Jia, G.J.; Kasischke, E.; Melillo, J.; Romanovsky, V.; Shvidenko, A.; Vaganov, E.; Walker, D.

    2002-01-01

    The responses of high latitude ecosystems to global change involve complex interactions among environmental variables, vegetation distribution, carbon dynamics, and water and energy exchange. These responses may have important consequences for the earth system. In this study, we evaluated how vegetation distribution, carbon stocks and turnover, and water and energy exchange are related to environmental variation spanned by the network of the IGBP high latitude transects. While the most notable feature of the high latitude transects is that they generally span temperature gradients from southern to northern latitudes, there are substantial differences in temperature among the transects. Also, along each transect temperature co-varies with precipitation and photosynthetically active radiation, which are also variable among the transects. Both climate and disturbance interact to influence latitudinal patterns of vegetation and soil carbon storage among the transects, and vegetation distribution appears to interact with climate to determine exchanges of heat and moisture in high latitudes. Despite limitations imposed by the data we assembled, the analyses in this study have taken an important step toward clarifying the complexity of interactions among environmental variables, vegetation distribution, carbon stocks and turnover, and water and energy exchange in high latitude regions. This study reveals the need to conduct coordinated global change studies in high latitudes to further elucidate how interactions among climate, disturbance, and vegetation distribution influence carbon dynamics and water and energy exchange in high latitudes.

  5. Macrobioerosion in Porites corals in subtropical northern South China Sea: a limiting factor for high-latitude reef framework development

    Science.gov (United States)

    Chen, Tianran; Li, Shu; Yu, Kefu

    2013-03-01

    Bioerosion is an important limiting factor in carbonate accretion and reef framework development; however, few studies have quantified the direct impact of macroborers on high-latitude coral communities, which are viewed as potential refuge during a period of global warming. In this study, internal macrobioerosion of Porites corals was examined at Daya Bay, subtropical northern South China Sea. The principal borers were the bivalve Lithophaga spp. and the sponges Cliona spp. and Cliothosa spp. (≥80 %), while sipunculid and polychaete worms and barnacles accounted for small amounts of bioerosion (≤20 %). Porites corals were heavily bioeroded in areas impacted by aquacultural and urban activities (10.34-27.55 %) compared with corals in relatively unpolluted areas (2.18-6.76 %). High levels of bioerosion, especially boring bivalve infestation, significantly weaken the corals and increase their susceptibility to dislodgement and fragmentation in typhoons, limiting accumulation of limestone framework. This study implies that carbonate accretion and reef development for high-latitude coral communities may be limited in future high-CO2 and eutrophication-stressed environments.

  6. The high latitude heliosphere. Proceedings. 28. ESLAB Symposium, Friedrichshafen (Germany), 19 - 21 Apr 1994.

    Science.gov (United States)

    Marsden, R. G.

    1995-04-01

    The following topics were dealt with: high latitude heliosphere, Ulysses mission, corona, spectra, coronal holes, composition, solar wind, He, plasma, streams, interplanetary magnetic field, plasma waves, radio bursts, energetic particles, cosmic rays, and interstellar gas.

  7. Effects of High-Latitude Forcing Uncertainty on the Low-Latitude and Midlatitude Ionosphere

    Science.gov (United States)

    Pedatella, N. M.; Lu, G.; Richmond, A. D.

    2018-01-01

    Ensemble simulations are performed using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) in order to understand the role of high-latitude forcing uncertainty on the low-latitude and midlatitude ionosphere response to the April 2010 geomagnetic storm. The ensemble is generated by perturbing either the high-latitude electric potential or auroral energy flux in the assimilative mapping for ionosphere electrodynamics (AMIE). Simulations with perturbed high-latitude electric potential result in substantial intraensemble variability in the low-latitude and midlatitude ionosphere response to the geomagnetic storm, and the ensemble standard deviation for the change in NmF2 reaches 50-100% of the mean change. Such large intraensemble variability is not seen when perturbing the auroral energy flux. In this case, the effects of the forcing uncertainty are primarily confined to high latitudes. We therefore conclude that the specification of high-latitude electric fields is an important source of uncertainty when modeling the low-latitude and midlatitude ionosphere response to a geomagnetic storm. A multiple linear regression analysis of the results indicates that uncertainty in the storm time changes in the equatorial electric fields, neutral winds, and neutral composition can all contribute to the uncertainty in the ionosphere electron density. The results of the present study provide insight into the possible uncertainty in simulations of the low-latitude and midlatitude ionosphere response to geomagnetic storms due to imperfect knowledge of the high-latitude forcing.

  8. Sporadic-E and spread-F in high latitude region

    International Nuclear Information System (INIS)

    Tao, Kazuhiko

    1974-01-01

    The heretofore made morphological studies of sporadic-E and spread-F as the typical irregularities of electron density are reviewed. These phenomena have close correlation with other geophysical phenomena which occur in the atmosphere of superhigh altitude in high latitude region. Many of these phenomena occur from same causes. Although the quantitative data are insufficient, the sporadic-E and spread-F in high latitude region are supposed to be caused by the precipitating charged particles falling from magnetosphere. A system, which can observe such phenomena simultaneously using the measuring instruments carried by satellites in the atmosphere of high altitude over high latitude region, is desirable to solve such problems. In detail, the morphological study on sporadic-E obtained from the observation of vertically projected ionosphere and the morphological study on sporadic-E from the observation of forward scattering and slanting entrance are reviewed. The correlation of the occurrence frequency of sporadic-E with solar activity, geomagnetic activity and other phenomena was studied. The morphological study on spread-F occurrence is reviewed. The observation of the spread-F in high latitude region by the application of top side sounding is reviewed. The correlation of the sporadic-E and spread-F in high latitude region with other geophysical phenomena is discussed. Finally, the discrete phenomenon and the diffuse phenomenon are discussed too. (Iwakiri, K.)

  9. Spectral classification of medium-scale high-latitude F region plasma density irregularities

    International Nuclear Information System (INIS)

    Singh, M.; Rodriguez, P.; Szuszczewicz, E.P.; Sachs Freeman Associates, Bowie, MD)

    1985-01-01

    The high-latitude ionosphere represents a highly structured plasma. Rodriguez and Szuszczewicz (1984) reported a wide range of plasma density irregularities (150 km to 75 m) at high latitudes near 200 km. They have shown that the small-scale irregularities (7.5 km to 75 m) populated the dayside oval more often than the other phenomenological regions. It was suggested that in the lower F region the chemical recombination is fast enough to remove small-scale irregularities before convection can transport them large distances, leaving structured particle precipitation as the dominant source term for irregularities. The present paper provides the results of spectral analyses of pulsed plasma probe data collected in situ aboard the STP/S3-4 satellite during the period March-September 1978. A quantitative description of irregularity spectra in the high-latitude lower F region plasma density is given. 22 references

  10. Proposed UK high-latitude rocket campaign in late 1976/early 1977

    International Nuclear Information System (INIS)

    Thomas, G.R.; Bryant, D.A.

    1975-01-01

    The second major UK high-latitude rocket campaign is scheduled for late 1976/early 19777 at Andoya. The proposed experiments provide a comprehensive set of measurements of high-latitude phenomena and include studies of the sources and acceleration of auroral particles, the stability of plasma flow, wave-particle interactions, and the response of the atmosphere and ionosphere to enhanced geomagnetic activity. These experiments require co-ordinated launching of high-latitude (740-950 km) and small, medium-altitude (320-370km) rockets. The provisional campaign plan includes four Skylark 12's (with Skylark 11 as a possible substitute), one Skylark 7 (with Skylark 6 as a possible substitute), and five Fulmars (with Skylark 10A as a possible substitute). Some of the experiments require simultaneous measurements by GEOS in the European sector (early 1977), but the remainder could be carried out in late 1976

  11. Local endemicity and high diversity characterise high-latitude coral- Symbiodinium partnerships

    Science.gov (United States)

    Wicks, L. C.; Sampayo, E.; Gardner, J. P. A.; Davy, S. K.

    2010-12-01

    Obligate symbiotic dinoflagellates ( Symbiodinium) residing within the tissues of most reef invertebrates are important in determining the tolerance range of their host. Coral communities living at high latitudes experience wide fluctuations in environmental conditions and thus provide an ideal system to gain insights into the range within which the symbiotic relationship can be sustained. Further, understanding whether and how symbiont communities associated with high-latitude coral reefs are different from their tropical counterparts will provide clues to the potential of corals to cope with marginal or changing conditions. However, little is known of the host and symbiont partnerships at high latitudes. Symbiodinium diversity and specificity of high-latitude coral communities were explored using denaturing gradient gel electrophoresis (PCR-DGGE) analysis of the internal transcribed spacer regions (ITS1 and ITS2) of the ribosomal DNA at Lord Howe Island (31°S; Australia), and the Kermadec Islands (29°S; New Zealand). All but one host associated with clade C Symbiodinium, the exception being a soft coral ( Capnella sp.) that contained Symbiodinium B1. Besides ‘host-generalist’ Symbiodinium types C1 and C3, approximately 72% of the Symbiodinium identified were novel C types, and zonation of symbionts in relation to environmental parameters such as depth and turbidity was evident in certain host species. The high-latitude Symbiodinium communities showed little overlap and relatively high diversity compared with communities sampled on the tropical Great Barrier Reef. Although host specificity was maintained in certain species, others shared symbionts and this potential reduction of fidelity at high-latitude locations may be the result of locally challenging and highly variable environmental conditions.

  12. Remote sensing of high-latitude ionization profiles by ground-based and spaceborne instrumentation

    International Nuclear Information System (INIS)

    Vondrak, R.R.

    1981-01-01

    Ionospheric specification and modeling are now largely based on data provided by active remote sensing with radiowave techniques (ionosondes, incoherent-scatter radars, and satellite beacons). More recently, passive remote sensing techniques have been developed that can be used to monitor quantitatively the spatial distribution of high-latitude E-region ionization. These passive methods depend on the measurement, or inference, of the energy distribution of precipitating kilovolt electrons, the principal source of the nighttime E-region at high latitudes. To validate these techniques, coordinated measurements of the auroral ionosphere have been made with the Chatanika incoherent-scatter radar and a variety of ground-based and spaceborne sensors

  13. Unveiling climate and ice-sheet history from drilling in high-latitude margins and future perspectives

    Science.gov (United States)

    Escutia Dotti, Carlota

    2010-05-01

    Polar ice is an important component of the climate system, affecting global sea level, ocean circulation and heat transport, marine productivity, and albedo. During the last decades drilling in the Arctic (IODP ACEX and Bering Expeditions) and in Antarctica (ODP Legs 178, 188, IODP Expedition 318 and ANDRILL) has revealed regional information about sea ice and ice sheets development and evolution. Integration of this data with numerical modeling provide an understanding of the early development of the ice sheets and their variability through the Cenozoic. Much of this work points to atmospheric CO2 and other greenhouse gases concentrations as important triggering mechanism driving the onset of glaciation and subsequent ice volume variability. With current increasing atmospheric greenhouse gases concentrations resulting in rapidly rising global temperatures, studies of polar climates become increasingly prominent on the research agenda. Despite of the relevance of the high-latitudes in the global climate systems, the short- and long-term history of the ice sheets and sea-ice and its relationships with paleoclimatic, paleoceanographic, and sea level changes is still poorly understood. A multinational, multiplatform scientific drilling strategy is being developed to recover key physical evidence from selected high-latitude areas. This strategy is aimed at addressing key knowledge gaps about the role of polar ice in climate change, targeting questions such as timing of events, rates of change, tipping points, regional variations, and northern vs. southern hemispheres (in phase or out-of-phase) variability. This data is critical to provide constrains to sea-ice and ice sheet models, which are the basis for forecasting the future of the cryosphere in a warming world.

  14. Mechanism for the formation of sporadic-E layers in the high-latitude ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Vlasov, M.N.; Mishin, E.V.; Telegin, V.A.

    1980-09-01

    A model of the collective interaction of precipitating electrons and the ionospheric plasma is used to explain the formation of short-duration sporadic-E layers in the high-latitude ionosphere. The changes produced in electron density by this collective interaction mechanism are considered.

  15. Boundary layer plasmas as a source for high-latitude, early afternoon, auroral arcs

    International Nuclear Information System (INIS)

    Lundin, R.; Evans, D.S.

    1985-02-01

    Simultaneous measurements of hot boundary layer plasma from PROGNOZ-7 and particle precipitation from the TIROS/NOAA satellite in nearly magnetically conjugate regions have been used to study the dynamo process responsible for the formation of high latitude, early afternoon, auroral arcs. Characteristic for the PROGNOZ-7 observations in the dayside boundary layer at high latitudes is the frequent occurrence of regions with injected magnetosheath plasma embedded in a 'halo' of antisunward flowing magnetosphere plasma. The injected magnetosheath plasma have several features which indicate that it also acts as a local source of EMF in the boundary layer. The process resembles that of a local MHD dynamo driven by the excess drift velocity of the injected magnetosheath plasma relative to the background magnetospheric plasma. The dynamo region is capable of driving fielc-aligned currents that couple to the ionosphere, where the upward current is associated with the high latitude auroral arcs. We demonstrate that the large-scale morphology as well as the detailed data intercomparison between PROGNOZ-7 and TIROS-N both agree well with a local injection of magnetosheath plasma into the dayside boundary layer as the main dynamo process powering the high-latitude, early afternoon auroral arcs. (Author)

  16. Current state and prospects of carbon management in high latitudes of Northern Eurasia

    Science.gov (United States)

    Schepaschenko, Dmitry; Shvidenko, Anatoly

    2010-05-01

    The current state and trajectories of future development of natural landscapes in high latitudes of Northern Eurasia are defined inter alia by (1) current unsatisfactory social and economic situation in boreal Northern Eurasia; (2) the dramatic magnitude of on-going and expected climatic change (warming up to 10-12oC under global warming at 4oC); (3) increasing anthropogenic pressure, particularly in regions of intensive oil and gas exploration and extraction; (4) large areas of sparsely populated and practically unmanaged land; (5) vulnerability of northern ecosystems which historically developed under cold climates and buffering capacity of which is not well known; (6) risk of catastrophic natural disturbances (fire, insect outbreaks) whose frequency and severity have accelerated during recent decades; and (7) high probability of irreversible changes of vegetation cover. These specifics are overlapped with insufficient governance of natural renewable resources (e.g., forests) and destructed practice of industrial development of new territories (oil and gas extraction and exploration, metallurgy etc.). Based on a full carbon account for terrestrial vegetation ecosystems of Northern Eurasia, we analyze the relative impacts of major drivers on magnitude and uncertainty of the Net Ecosystem Carbon Balance (NECB) under current and expected climate and environment. Dynamic trends and interannual variability of NECB are mostly dependent on weather conditions during growth seasons of individual years, regimes of natural disturbances, and anthropogenic impacts on ecosystems. In a short term, disturbances and human impacts cause a theoretically 'manageable' part of the full carbon account, which on average is estimated to be of about 20% of annual net primary production. In a long term, thawing of permafrost and change of hydrological regimes of vast territories may result in a catastrophic decline of the forested area and wide distribution of 'green desertification'. The

  17. Fiber Amplifiers

    DEFF Research Database (Denmark)

    Rottwitt, Karsten

    2017-01-01

    The chapter provides a discussion of optical fiber amplifiers and through three sections provides a detailed treatment of three types of optical fiber amplifiers, erbium doped fiber amplifiers (EDFA), Raman amplifiers, and parametric amplifiers. Each section comprises the fundamentals including...... the basic physics and relevant in-depth theoretical modeling, amplifiers characteristics and performance data as a function of specific operation parameters. Typical applications in fiber optic communication systems and the improvement achievable through the use of fiber amplifiers are illustrated....

  18. Geologic isolation of nuclear waste at high latitudes: the role of ice sheets

    Science.gov (United States)

    Person, M.; McIntosh, J.; Iverson, N.; Neuzil, C.E.; Bense, V.

    2012-01-01

    Geologic isolation of high-level nuclear waste from the biosphere requires special consideration in countries at high latitudes (>40°N) owing to the possibility of future episodes of continental glaciation (Talbot 1999). It is now widely recognized that Pleistocene continental glaciations have had a profound effect on rates of sediment erosion (Cuffey & Paterson 2010) and deformation including tectonic thrusting (Pedersen 2005) as well as groundwater flow (Person et al. 2007; Lemieux et al. 2008a,b,c). In addition, glacial mechanical loads may have generated anomalous, or fossil, pore pressures within certain clay-rich confining units (e.g. Vinard et al. 2001). Because high-level nuclear wastes must be isolated from the biosphere as long as 1 million years (McMurry et al. 2003), the likelihood of one or more continental ice sheets overrunning high-latitude sites must be considered.

  19. Response of the convecting high-latitude F layer to a powerful HF wave

    Directory of Open Access Journals (Sweden)

    G. I. Mingaleva

    1997-10-01

    Full Text Available A numerical model of the high-latitude ionosphere, which takes into account the convection of the ionospheric plasma, has been developed and utilized to simulate the F-layer response at auroral latitudes to high-power radio waves. The model produces the time variations of the electron density, positive ion velocity, and ion and electron temperature profiles within a magnetic field tube carried over an ionospheric heater by the convection electric field. The simulations have been performed for the point with the geographic coordinates of the ionospheric HF heating facility near Tromso, Norway, when it is located near the midnight magnetic meridian. The calculations have been made for equinox, at high-solar-activity, and low-geomagnetic-activity conditions. The results indicate that significant variations of the electron temperature, positive ion velocity, and electron density profiles can be produced by HF heating in the convecting high-latitude F layer.

  20. Response of the convecting high-latitude F layer to a powerful HF wave

    Directory of Open Access Journals (Sweden)

    G. I. Mingaleva

    Full Text Available A numerical model of the high-latitude ionosphere, which takes into account the convection of the ionospheric plasma, has been developed and utilized to simulate the F-layer response at auroral latitudes to high-power radio waves. The model produces the time variations of the electron density, positive ion velocity, and ion and electron temperature profiles within a magnetic field tube carried over an ionospheric heater by the convection electric field. The simulations have been performed for the point with the geographic coordinates of the ionospheric HF heating facility near Tromso, Norway, when it is located near the midnight magnetic meridian. The calculations have been made for equinox, at high-solar-activity, and low-geomagnetic-activity conditions. The results indicate that significant variations of the electron temperature, positive ion velocity, and electron density profiles can be produced by HF heating in the convecting high-latitude F layer.

  1. Significance of scatter radar studies of E and F region irregularities at high latitudes

    International Nuclear Information System (INIS)

    Greenwald, R.A.

    1983-01-01

    This chapter considers the mechanisms by which electron density irregularities may be generated in the high latitude ionosphere and the techniques through which they are observed with ground base radars. The capabilities of radars used for studying these irregularities are compared with the capabilities of radars used for incoherent scatter measurements. The use of irregularity scatter techniques for dynamic studies of larger scale structured phenomena is discussed. Topics considered include E-region irregularities, observations with auroral radars, plasma drifts associated with a westward travelling surge, and ionospheric plasma motions associated with resonant waves. It is shown why high latitude F-region irregularity studies must be made in the HF frequency band (3-30 MHz). The joint use of the European Incoherent Scatter Association (EISCAT), STARE and SAFARI facilities is examined, and it is concluded that the various techniques will enhance each other and provide a better understanding of the various processes being studied

  2. Keeping It Local: Dispersal Limitations of Coral Larvae to the High Latitude Coral Reefs of the Houtman Abrolhos Islands.

    Science.gov (United States)

    Markey, Kathryn L; Abdo, Dave A; Evans, Scott N; Bosserelle, Cyprien

    2016-01-01

    In 2011 the first recorded bleaching event for the high latitude Houtman Abrolhos Islands (HAI) coral communities was documented. This bleaching event highlighted the question of whether a supply of 'heat tolerant' coral recruits from the tropical north would be sufficient to provide a level of resistance for these reefs to future warming events. Using Lagrangian modelling we showed that due to its regional isolation, large-scale larval input from potential tropical northern source populations to the HAI is unlikely, despite the southward flowing Leeuwin current. Successful recruitment to artificial substrates was recorded following the bleaching event. However, this was negligible (0.4 ± 0.1 recruits per tile) compared to 2013 post impact recruitment (128.8 ± 15.8 recruits per tile). Our data therefore provides preliminary evidence suggesting that the connectivity of the HAI with coral communities in the north is limited, and population maintenance and recovery is likely driven primarily by self-recruitment. Given the low thermal tolerance of the HAI coral communities, the dominance of Acropora, and the apparent reliance on self-recruitment, an increased frequency of thermally anomalous conditions at the HAI (such as experienced in 2011) has the potential to reduce the long-term stability of the HAI coral populations and species that depend upon them.

  3. Keeping It Local: Dispersal Limitations of Coral Larvae to the High Latitude Coral Reefs of the Houtman Abrolhos Islands.

    Directory of Open Access Journals (Sweden)

    Kathryn L Markey

    Full Text Available In 2011 the first recorded bleaching event for the high latitude Houtman Abrolhos Islands (HAI coral communities was documented. This bleaching event highlighted the question of whether a supply of 'heat tolerant' coral recruits from the tropical north would be sufficient to provide a level of resistance for these reefs to future warming events. Using Lagrangian modelling we showed that due to its regional isolation, large-scale larval input from potential tropical northern source populations to the HAI is unlikely, despite the southward flowing Leeuwin current. Successful recruitment to artificial substrates was recorded following the bleaching event. However, this was negligible (0.4 ± 0.1 recruits per tile compared to 2013 post impact recruitment (128.8 ± 15.8 recruits per tile. Our data therefore provides preliminary evidence suggesting that the connectivity of the HAI with coral communities in the north is limited, and population maintenance and recovery is likely driven primarily by self-recruitment. Given the low thermal tolerance of the HAI coral communities, the dominance of Acropora, and the apparent reliance on self-recruitment, an increased frequency of thermally anomalous conditions at the HAI (such as experienced in 2011 has the potential to reduce the long-term stability of the HAI coral populations and species that depend upon them.

  4. Simultaneous measurement of aurora-related, irregular magnetic pulsations at northern and southern high latitudes

    International Nuclear Information System (INIS)

    Arnoldy, R.L.; Rajashekar, R.; Cahill, L.J. Jr.; Engebretson, M.J.; Rosenberg, T.J.; Mende, S.B.

    1987-01-01

    A dominant feature of high-latitude magnetic pulsations is large-amplitude irregular pulsations (Pi) which are closely correlated with the movement of the observing station under particle precipitation, producing the dayside auroral and the high-latitude expansion of nightside aurora. The dayside Pi-1 pulsation maximum centered about local magnetic noon has no strong seasonal dependence, indicating that the dayside aurora illuminates both hemispheres independent of the latitude of the subsolar point. The summer noon pulsation maximum has, however, a greater longitudinal extent than the winter noon maximum, as measured at 74 degree-75 degree invariant latitude. The nightside magnetic pulsations are bursts of Pi (PiB) having an average duration of 15 min. From Defense Meteorological Satellite Program photos the auroral forms related to the high-latitude PiB can be identified as the poleward discrete arc generally having a large longitudinal extent. If the auroral forms are very similar in both hemispheres, then the large longitudinal extent coupled with movement of the auroral could explain why 85% of the PiB events have onsets within 10 min at opposite hemisphere sites (South Pole, Antarctica, and Sondre Stromfjord, Greenland) separated in local magnetic time by about 1.5 hours. There is no seasonal dependence in the statistical occurrence of PiB, nor in its simultaneity in opposite hemispheres. Apparently, the seasonal distortion of the tail plasma sheet has little effect on the acceleration of high-latitude auroral beams. The actual several minute time difference in opposite hemisphere onsets of PiB is probably due to the westward/poleward motion of the longitudinally extended aurora

  5. Impacts of high-latitude volcanic eruptions on ENSO and AMOC.

    Science.gov (United States)

    Pausata, Francesco S R; Chafik, Leon; Caballero, Rodrigo; Battisti, David S

    2015-11-10

    Large volcanic eruptions can have major impacts on global climate, affecting both atmospheric and ocean circulation through changes in atmospheric chemical composition and optical properties. The residence time of volcanic aerosol from strong eruptions is roughly 2-3 y. Attention has consequently focused on their short-term impacts, whereas the long-term, ocean-mediated response has not been well studied. Most studies have focused on tropical eruptions; high-latitude eruptions have drawn less attention because their impacts are thought to be merely hemispheric rather than global. No study to date has investigated the long-term effects of high-latitude eruptions. Here, we use a climate model to show that large summer high-latitude eruptions in the Northern Hemisphere cause strong hemispheric cooling, which could induce an El Niño-like anomaly, in the equatorial Pacific during the first 8-9 mo after the start of the eruption. The hemispherically asymmetric cooling shifts the Intertropical Convergence Zone southward, triggering a weakening of the trade winds over the western and central equatorial Pacific that favors the development of an El Niño-like anomaly. In the model used here, the specified high-latitude eruption also leads to a strengthening of the Atlantic Meridional Overturning Circulation (AMOC) in the first 25 y after the eruption, followed by a weakening lasting at least 35 y. The long-lived changes in the AMOC strength also alter the variability of the El Niño-Southern Oscillation (ENSO).

  6. Analysis of High-Latitude lonospheric Processes During HSS and CME-Induced Geomagnetic Storms

    DEFF Research Database (Denmark)

    Durgonics, Tibor; Komjathy, Attila; Verkhoglyadova, Olga

    processes responsible for the negative phase have less pronounced impact on the diurnal TEC variations than on patch formation. We also investigated and assessed storm influences on airborne navigation at high-latitudes in order to determine the possible cause of the radio communication disturbances....... This effort may lead us to a better understanding of the phenomenon and might help develop communication hardware that is more resistant to such effects....

  7. Carbon dioxide in northern high latitude oceans: Anthropogenic increase and air-sea flux variability

    International Nuclear Information System (INIS)

    Omar, Abdirahman M.

    2003-01-01

    The aim of this thesis is to further our knowledge of carbon dioxide in the northern high latitude oceans (northern North Atlantic, Barents Sea, and Arctic Ocean) by studying the anthropogenic change in the oceanic CO2, the inter-annual variability of the air-sea CO2 flux, and the relationship between this variability and changes in other oceanic processes. An introductory chapter and four papers are presented. Descriptions of the seawater carbonate system parameters, air-sea exchange of CO2, and related processes are given in the introduction chapter. The anthropogenic increase in partial pressure of CO2 (pCO2) in the surface water of the Barents Sea is evaluated in paper I. The effect of alternations of the Barents Sea climate between cold and warm modes on the annual cycles of seawater fugacity and air-sea flux of CO2 is investigated in paper II. Oceanic uptake of atmospheric CO2 associated with the seasonal formation of sea ice in Storfjorden and the implication for the entire Arctic Ocean is studied in paper III. An assessment of the variations of the air-sea flux of CO2 in the northern North Atlantic for 20 winters (1981-2001) is carried out in paper IV. PCO2 in the surface water of the Barents Sea is shown to have increased parallel with the atmospheric pCO2 between 1967 and 2000-2001 (paper I). This was determined by comparing seawater pCO2 from 1967 with that from 2000-2001. The former was estimated from surface seawater temperature (SST) while the latter was computed from data of total dissolved inorganic carbon and alkalinity. A procedure which accounts for the natural variability was applied and the difference between seawater pC02 of 1967 and that of 2000-2001 is attributed to the uptake of excess CO2. In the Atlantic sector of the Barents Sea, the surface seawater fugacity of CO2 (fCO s''w) is shown to be lower than the atmospheric fCO2 throughout the year, implying that the area is an annual sink of atmospheric CO2 (paper II). Additionally, changes

  8. Carbon dioxide in northern high latitude oceans: Anthropogenic increase and air-sea flux variability

    Energy Technology Data Exchange (ETDEWEB)

    Omar, Abdirahman M.

    2003-07-01

    The aim of this thesis is to further our knowledge of carbon dioxide in the northern high latitude oceans (northern North Atlantic, Barents Sea, and Arctic Ocean) by studying the anthropogenic change in the oceanic CO2, the inter-annual variability of the air-sea CO2 flux, and the relationship between this variability and changes in other oceanic processes. An introductory chapter and four papers are presented. Descriptions of the seawater carbonate system parameters, air-sea exchange of CO2, and related processes are given in the introduction chapter. The anthropogenic increase in partial pressure of CO2 (pCO2) in the surface water of the Barents Sea is evaluated in paper I. The effect of alternations of the Barents Sea climate between cold and warm modes on the annual cycles of seawater fugacity and air-sea flux of CO2 is investigated in paper II. Oceanic uptake of atmospheric CO2 associated with the seasonal formation of sea ice in Storfjorden and the implication for the entire Arctic Ocean is studied in paper III. An assessment of the variations of the air-sea flux of CO2 in the northern North Atlantic for 20 winters (1981-2001) is carried out in paper IV. PCO2 in the surface water of the Barents Sea is shown to have increased parallel with the atmospheric pCO2 between 1967 and 2000-2001 (paper I). This was determined by comparing seawater pCO2 from 1967 with that from 2000-2001. The former was estimated from surface seawater temperature (SST) while the latter was computed from data of total dissolved inorganic carbon and alkalinity. A procedure which accounts for the natural variability was applied and the difference between seawater pC02 of 1967 and that of 2000-2001 is attributed to the uptake of excess CO2. In the Atlantic sector of the Barents Sea, the surface seawater fugacity of CO2 (fCO s''w) is shown to be lower than the atmospheric fCO2 throughout the year, implying that the area is an annual sink of atmospheric CO2 (paper II). Additionally

  9. Predicting Wetland Distribution Changes under Climate Change and Human Activities in a Mid- and High-Latitude Region

    Directory of Open Access Journals (Sweden)

    Dandan Zhao

    2018-03-01

    Full Text Available Wetlands in the mid- and high-latitudes are particularly vulnerable to environmental changes and have declined dramatically in recent decades. Climate change and human activities are arguably the most important factors driving wetland distribution changes which will have important implications for wetland ecological functions and services. We analyzed the importance of driving variables for wetland distribution and investigated the relative importance of climatic factors and human activity factors in driving historical wetland distribution changes. We predicted wetland distribution changes under climate change and human activities over the 21st century using the Random Forest model in a mid- and high-latitude region of Northeast China. Climate change scenarios included three Representative Concentration Pathways (RCPs based on five general circulation models (GCMs downloaded from the Coupled Model Intercomparison Project, Phase 5 (CMIP5. The three scenarios (RCP 2.6, RCP 4.5, and RCP 8.5 predicted radiative forcing to peak at 2.6, 4.5, and 8.5 W/m2 by the 2100s, respectively. Our results showed that the variables with high importance scores were agricultural population proportion, warmness index, distance to water body, coldness index, and annual mean precipitation; climatic variables were given higher importance scores than human activity variables on average. Average predicted wetland area among three emission scenarios were 340,000 ha, 123,000 ha, and 113,000 ha for the 2040s, 2070s, and 2100s, respectively. Average change percent in predicted wetland area among three periods was greatest under the RCP 8.5 emission scenario followed by RCP 4.5 and RCP 2.6 emission scenarios, which were 78%, 64%, and 55%, respectively. Losses in predicted wetland distribution were generally around agricultural lands and expanded continually from the north to the whole region over time, while the gains were mostly associated with grasslands and water in the

  10. Hemispheric Asymmetry of Global Warming Explained by a Conceptual Model

    Science.gov (United States)

    Funke, C. S.; Alexeev, V. A.

    2017-12-01

    Polar Amplification, the process of amplified warming at high latitudes, manifests itself differently in the Arctic and Antarctic. Not only is the temperature increase in the Arctic more pronounced than in the Antarctic but the dramatic sea ice decline in the Arctic over the last few decades also contrasts sharply with trendless to weak positive trend of Antarctic sea ice throughout the same period. This asymmetric behavior is often partly attributed to the differences in configuration of continents in the Arctic and Antarctic: the Arctic Ocean is surrounded by land while the Southern Ocean has a continent in the middle. A simple conceptual energy balance model of Budyko-Sellers type, accounting for differences between the Northern and Southern hemispheres, is applied to study the mechanisms of climate sensitivity to a variety of forcings. Asymmetry in major modes of variability is explained using an eigenmode analysis of the linearized model. Negative forcings over Antarctica such as from ozone depletion were found to have an amplified effect on southern hemisphere climate and may be an important cause of the muted warming and slightly positive Antarctic sea ice trend.

  11. ORCHIDEE-MICT (v8.4.1, a land surface model for the high latitudes: model description and validation

    Directory of Open Access Journals (Sweden)

    M. Guimberteau

    2018-01-01

    Full Text Available The high-latitude regions of the Northern Hemisphere are a nexus for the interaction between land surface physical properties and their exchange of carbon and energy with the atmosphere. At these latitudes, two carbon pools of planetary significance – those of the permanently frozen soils (permafrost, and of the great expanse of boreal forest – are vulnerable to destabilization in the face of currently observed climatic warming, the speed and intensity of which are expected to increase with time. Improved projections of future Arctic and boreal ecosystem transformation require improved land surface models that integrate processes specific to these cold biomes. To this end, this study lays out relevant new parameterizations in the ORCHIDEE-MICT land surface model. These describe the interactions between soil carbon, soil temperature and hydrology, and their resulting feedbacks on water and CO2 fluxes, in addition to a recently developed fire module. Outputs from ORCHIDEE-MICT, when forced by two climate input datasets, are extensively evaluated against (i temperature gradients between the atmosphere and deep soils, (ii the hydrological components comprising the water balance of the largest high-latitude basins, and (iii CO2 flux and carbon stock observations. The model performance is good with respect to empirical data, despite a simulated excessive plant water stress and a positive land surface temperature bias. In addition, acute model sensitivity to the choice of input forcing data suggests that the calibration of model parameters is strongly forcing-dependent. Overall, we suggest that this new model design is at the forefront of current efforts to reliably estimate future perturbations to the high-latitude terrestrial environment.

  12. Developments in Acoustic Navigation and Communication for High-Latitude Ocean Research

    Science.gov (United States)

    Gobat, J.; Lee, C.

    2006-12-01

    Developments in autonomous platforms (profiling floats, drifters, long-range gliders and propeller-driven vehicles) offer the possibility of unprecedented access to logistically difficult polar regions that challenge conventional techniques. Currently, however, navigation and telemetry for these platforms rely on satellite positioning and communications poorly suited for high-latitude applications where ice cover restricts access to the sea surface. A similar infrastructure offering basin-wide acoustic geolocation and telemetry would allow the community to employ autonomous platforms to address previously intractable problems in Arctic oceanography. Two recent efforts toward the development of such an infrastructure are reported here. As part of an observational array monitoring fluxes through Davis Strait, development of real-time RAFOS acoustic navigation for gliders has been ongoing since autumn 2004. To date, test deployments have been conducted in a 260 Hz field in the Pacific and 780 Hz fields off Norway and in Davis Strait. Real-time navigation accuracy of ~1~km is achievable. Autonomously navigating gliders will operate under ice cover beginning in autumn 2006. In addition to glider navigation development, the Davis Strait array moorings carry fixed RAFOS recorders to study propagation over a range of distances under seasonally varying ice cover. Results from the under-ice propagation and glider navigation experiments are presented. Motivated by the need to coordinate these types of development efforts, an international group of acousticians, autonomous platform developers, high-latitude oceanographers and marine mammal researchers gathered in Seattle, U.S.A. from 27 February -- 1 March 2006 for an NSF Office of Polar Programs sponsored Acoustic Navigation and Communication for High-latitude Ocean Research (ANCHOR) workshop. Workshop participants focused on summarizing the current state of knowledge concerning Arctic acoustics, navigation and communications

  13. Seasonal Dependence of Geomagnetic Active-Time Northern High-Latitude Upper Thermospheric Winds

    Science.gov (United States)

    Dhadly, Manbharat S.; Emmert, John T.; Drob, Douglas P.; Conde, Mark G.; Doornbos, Eelco; Shepherd, Gordon G.; Makela, Jonathan J.; Wu, Qian; Nieciejewski, Richard J.; Ridley, Aaron J.

    2018-01-01

    This study is focused on improving the poorly understood seasonal dependence of northern high-latitude F region thermospheric winds under active geomagnetic conditions. The gaps in our understanding of the dynamic high-latitude thermosphere are largely due to the sparseness of thermospheric wind measurements. With current observational facilities, it is infeasible to construct a synoptic picture of thermospheric winds, but enough data with wide spatial and temporal coverage have accumulated to construct a meaningful statistical analysis. We use long-term data from eight ground-based and two space-based instruments to derive climatological wind patterns as a function of magnetic local time, magnetic latitude, and season. These diverse data sets possess different geometries and different spatial and solar activity coverage. The major challenge is to combine these disparate data sets into a coherent picture while overcoming the sampling limitations and biases among them. In our previous study (focused on quiet time winds), we found bias in the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) cross-track winds. Here we empirically quantify the GOCE bias and use it as a correction profile for removing apparent bias before empirical wind formulation. The assimilated wind patterns exhibit all major characteristics of high-latitude neutral circulation. The latitudinal extent of duskside circulation expands almost 10∘ from winter to summer. The dawnside circulation subsides from winter to summer. Disturbance winds derived from geomagnetic active and quiet winds show strong seasonal and latitudinal variability. Comparisons between wind patterns derived here and Disturbance Wind Model (DWM07) (which have no seasonal dependence) suggest that DWM07 is skewed toward summertime conditions.

  14. High-Latitude Topside Ionospheric Vertical Electron Density Profile Changes in Response to Large Magnetic Storms

    Science.gov (United States)

    Benson, Robert F.; Fainberg, Joseph; Osherovich, Vladimir A.; Truhlik, Vladimir; Wang, Yongli; Bilitza, Dieter; Fung, Shing F.

    2016-01-01

    Large magnetic-storm-induced changes were detected in high-latitude topside vertical electron density profiles Ne(h) in a database of profiles and digital topside ionograms, from the International Satellites for Ionospheric Studies (ISIS) program, that enabled Ne(h) profiles to be obtained in nearly the same region of space before, during, and after a major magnetic storm (Dst -100nT). Storms where Ne(h) profiles were available in the high-latitude Northern Hemisphere had better coverage of solar wind parameters than storms with available Ne(h) profiles in the high-latitude Southern Hemisphere. Large Ne(h) changes were observed during all storms, with enhancements and depletions sometimes near a factor of 10 and 0.1, respectively, but with substantial differences in the responses in the two hemispheres. Large spatial andor temporal Ne(h) changes were often observed during Dst minimum and during the storm recovery phase. The storm-induced Ne(h) changes were the most pronounced and consistent in the Northern Hemisphere in that large enhancements were observed during winter nighttime and large depletions during winter and spring daytime. The limited available cases suggested that these Northern Hemisphere enhancements increased with increases of the time-shifted solar wind velocity v, magnetic field B, and with more negative values of the B components except for the highest common altitude (1100km) of the profiles. There was also some evidence suggesting that the Northern Hemisphere depletions were related to changes in the solar wind parameters. Southern Hemisphere storm-induced enhancements and depletions were typically considerably less with depletions observed during summer nighttime conditions and enhancements during summer daytime and fall nighttime conditions.

  15. H I and dust in the high latitude dark cloud L1642

    International Nuclear Information System (INIS)

    Liljestroem, T.; Mattila, K.

    1989-01-01

    The high latitude dark cloud L1642 in the 21 cm H I region was mapped using a 100 m radio telescope. A remarkable H I line broadening from 2.5 to 2.9 km/s is observed over a small area on the bright side of L1642, i.e., the side facing the galactic plane. Results are presented concerning the effects of the asymmetrical UV radiation field of OB stars on the H I gas and the very small dust grains associated with L1642

  16. Paleosecular variation analysis of high-latitude paleomagnetic data from the volcanic island of Jan Mayen

    Science.gov (United States)

    Cromwell, G.; Tauxe, L.; Staudigel, H.; Pedersen, L. R.; Constable, C.; Pedersen, R.; Duncan, R. A.; Staudigel, P.

    2009-12-01

    Recent investigation of high-latitude paleomagnetic data from the Erebus Volcanic Province (EVP), Antarctica shows a departure from magnetic dipole predictions for paleointensity data for the period 0-5 Ma. The average EVP paleointensity (31.5 +/- 2.4 μT) is equivalent to low-latitude measurements (1) or approximately half the strength predicted for a dipole at high-latitude. Also, paleosecular variation models (e.g., 2,3) predict dispersions of directions that are much lower than the high latitude observations. Observed low intensity values may be the result of reduced convective flow inside the tangent cylinder of the Earth’s core or insufficient temporal sampling (1). More high-latitude paleomagnetic data are necessary in order to investigate the cause of the depressed intensity values and to provide better geographic and temporal resolution for future statistical paleosecular variation models. To address this, we carried out two field seasons, one in Spitzbergen (79°N, 14°E) and one on the young volcanic island of Jan Mayen (71°N, 8°W). The latter sampling effort was guided by age analyses of samples obtained by P. Imsland (unpublished and 4). We will present new paleodirectional and paleointensity data from a total of 25 paleomagnetic sites. These data enhance the temporal resolution of global paleomagnetic data and allow for a more complete evaluation of the time-averaged magnetic field from 0-5 Ma. We will present a new analysis of paleosecular variation based on our new data, in combination with other recently published data sets. (1) Lawrence, K.P., L.Tauxe, H. Staudigel, C.G. Constable, A. Koppers, W. MacIntosh, C.L. Johnson, Paleomagnetic field properties at high southern latitude. Geochemistry Geophysics Geosystems 10 (2009). (2) McElhinny, M.W., P.L. McFadden, Paleosecular variation over the past 5 Myr based on a new generalized database. Geophysics Journal International 131 (1997), 240-252. (3) Tauxe, L., Kent, D.V., A simplified statistical

  17. Interstellar extinction from photometric surveys: application to four high-latitude areas

    Science.gov (United States)

    Malkov, Oleg; Karpov, Sergey; Kilpio, Elena; Sichevsky, Sergey; Chulkov, Dmitry; Dluzhnevskaya, Olga; Kovaleva, Dana; Kniazev, Alexei; Mickaelian, Areg; Mironov, Alexey; Murthy, Jayant; Sytov, Alexey; Zhao, Gang; Zhukov, Aleksandr

    2018-04-01

    Information on interstellar extinction and dust properties may be obtained from modern large photometric surveys data. Virtual Observatory facilities allow users to make a fast and correct cross-identification of objects from various surveys. It yields a multicolor photometry data on detected objects and makes it possible to estimate stellar parameters and calculate interstellar extinction. A 3D extinction map then can be constructed. The method was applied to 2MASS, SDSS, GALEX and UKIDSS surveys. Results for several high-latitude areas are obtained, compared with independent sources and discussed here.

  18. Interstellar extinction from photometric surveys: application to four high-latitude areas

    Directory of Open Access Journals (Sweden)

    Malkov Oleg

    2018-04-01

    Full Text Available Information on interstellar extinction and dust properties may be obtained from modern large photometric surveys data. Virtual Observatory facilities allow users to make a fast and correct cross-identification of objects from various surveys. It yields a multicolor photometry data on detected objects and makes it possible to estimate stellar parameters and calculate interstellar extinction. A 3D extinction map then can be constructed. The method was applied to 2MASS, SDSS, GALEX and UKIDSS surveys. Results for several high-latitude areas are obtained, compared with independent sources and discussed here.

  19. Effects of Abrupt Variations of Solar Wind Dynamic Pressure on the High-Latitude Ionosphere

    Directory of Open Access Journals (Sweden)

    Igino Coco

    2011-01-01

    Full Text Available We show the results of a statistical study on the effects in the high-latitude ionosphere of abrupt variations of solar wind dynamic pressure, using Super Dual Auroral Radar Network (SuperDARN data in both hemispheres. We find that, during periods of quiet ionospheric conditions, the amount of radar backscatter increases when a variation in the dynamic pressure occurs, both positive (increase of the pressure and negative (decrease of the pressure. We also investigate the behaviour of the Cross-Polar Cap Potential (CPCP during pressure variations and show preliminary results.

  20. Non-native and native organisms moving into high elevation and high latitude ecosystems in an era of climate change: new challenges for ecology and conservation

    Science.gov (United States)

    Pauchard, Aníbal; Albihn, Ann; Alexander, Jake; Burgess, Treena; Daehler, Curt; Essl, Franz; Evengard, Birgitta; Greenwood, Greg; Haider, Sylvia; Lenoir, Jonathan; McDougall, K.; Milbau, Ann; Muths, Erin L.; Nunez, Martin; Pellissier, Lois; Rabitsch, Wolfgang; Rew, Lisa; Robertson, Mark; Sanders, Nathan; Kueffer, Christoph

    2016-01-01

    Cold environments at high elevation and high latitude are often viewed as resistant to biological invasions. However, climate warming, land use change and associated increased connectivity all increase the risk of biological invasions in these environments. Here we present a summary of the key discussions of the workshop ‘Biosecurity in Mountains and Northern Ecosystems: Current Status and Future Challenges’ (Flen, Sweden, 1–3 June 2015). The aims of the workshop were to (1) increase awareness about the growing importance of species expansion—both non-native and native—at high elevation and high latitude with climate change, (2) review existing knowledge about invasion risks in these areas, and (3) encourage more research on how species will move and interact in cold environments, the consequences for biodiversity, and animal and human health and wellbeing. The diversity of potential and actual invaders reported at the workshop and the likely interactions between them create major challenges for managers of cold environments. However, since these cold environments have experienced fewer invasions when compared with many warmer, more populated environments, prevention has a real chance of success, especially if it is coupled with prioritisation schemes for targeting invaders likely to have greatest impact. Communication and co-operation between cold environment regions will facilitate rapid response, and maximise the use of limited research and management resources.

  1. Modeling interactions of soil hydrological dynamics and soil thermal and permafrost dynamics and their effects on carbon cycling in northern high latitudes

    Science.gov (United States)

    Zhuang, Q.; Tang, J.

    2008-12-01

    Large areas of northern high latitude ecosystems are underlain with permafrost. The warming temperature and fires deteriorate the stability of those permafrost, altering hydrological cycle, and consequently soil temperature and active layer depth. These changes will determine the fate of large carbon pools in soils and permafrost over the region. We developed a modeling framework of hydrology, permafrost, and biogeochemical dynamics based on our existing modules of these components. The framework was incorporated with a new snow dynamics module and the effects of soil moisture on soil thermal properties. The framework was tested for tundra and boreal forest ecosystems at field sites with respect to soil thermal and hydrological regimes in Alaska and was then applied to the whole Alaskan ecosystems for the period of 1923-2000 at a daily time step. Our two sets of simulations with and without considering soil moisture effects indicated that the soil temperature profile and active layer depth between two simulations are significant different. The differences of soil thermal regime would expect to result in different carbon dynamics. Next, we will verify the framework with the observed data of soil moisture and soil temperature at poor-drain, moderate-drain, and well-drain boreal forest sites in Alaska. With the verified framework, we will evaluate the effects of interactions of soil thermal and hydrological dynamics on carbon dynamics for the whole northern high latitudes.

  2. Electric fields, Joule and particle heating in the high latitude thermosphere. [Review

    Energy Technology Data Exchange (ETDEWEB)

    Brekke, A [Auroral Observatory, Tromsoe (Norway)

    1976-08-01

    A short review of the recent high latitude measurements of ionospheric electric fields is given. The importance of investigating large-scale and slowly-varying electric fields in order to study magnetospheric convection is stressed. The motion of such high energetic phenomena as auroral forms and spread E-region echoes must be treated by extreme caution when interpreted as a manifestation of convection motion. The relationship between the ionospheric source and polarization field is still an unanswered problem. It is indicated that progress can be made in this respect when electric fields and conductivities are measured simultaneously in the ionosphere. Evidence is shown at one occasion that the meridional component during an auroral sunstorm might be mainly a polarization field. The height-integrated Joule heating rate is occasionally found to be far larger than the solar radiation input at auroral altitudes. The presence of this additional heat source at any time of day is expected to have a strong impact on the global-scale atmospheric dynamics. From comparisons made between Joule and particle heating it appears that the two components are comparable. It is expected that high latitude incoherent radars will contribute substantially to the understanding of these phenomena in the near future.

  3. The role played by thermal feedback in heated Farley-Buneman waves at high latitudes

    Directory of Open Access Journals (Sweden)

    J.-P. St.-Maurice

    2000-05-01

    Full Text Available It is becoming increasingly clear that electron thermal effects have to be taken into account when dealing with the theory of ionospheric instabilities in the high-latitude ionosphere. Unfortunately, the mathematical complexity often hides the physical processes at work. We follow the limiting cases of a complex but systematic generalized fluid approach to get to the heart of the thermal processes that affect the stability of E region waves during electron heating events. We try to show as simply as possible under what conditions thermal effects contribute to the destabilization of strongly field-aligned (zero aspect angle Farley-Buneman modes. We show that destabilization can arise from a combination of (1 a reduction in pressure gradients associated with temperature fluctuations that are out of phase with density fluctuations, and (2 thermal diffusion, which takes the electrons from regions of enhanced temperatures to regions of negative temperature fluctuations, and therefore enhanced densities. However, we also show that, contrary to what has been suggested in the past, for modes excited along the E0×B direction thermal feedback decreases the growth rate and raises the threshold speed of the Farley-Buneman instability. The increase in threshold speed appears to be important enough to explain the generation of `Type IV' waves in the high-latitude ionosphere.Key words: Ionosphere (auroral ionosphere; iono- spheric irregularities; plasma waves and instabilities

  4. Contrasting vulnerability of drained tropical and high-latitude peatlands to fluvial loss of stored carbon

    Science.gov (United States)

    Evans, Chris D.; Page, Susan E.; Jones, Tim; Moore, Sam; Gauci, Vincent; Laiho, Raija; Hruška, Jakub; Allott, Tim E. H.; Billett, Michael F.; Tipping, Ed; Freeman, Chris; Garnett, Mark H.

    2014-11-01

    Carbon sequestration and storage in peatlands rely on consistently high water tables. Anthropogenic pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of peat-forming vegetation and exposure of previously anaerobic peat to aerobic decomposition. This can shift peatlands from net CO2 sinks to large CO2 sources, releasing carbon held for millennia. Peatlands also export significant quantities of carbon via fluvial pathways, mainly as dissolved organic carbon (DOC). We analyzed radiocarbon (14C) levels of DOC in drainage water from multiple peatlands in Europe and Southeast Asia, to infer differences in the age of carbon lost from intact and drained systems. In most cases, drainage led to increased release of older carbon from the peat profile but with marked differences related to peat type. Very low DOC-14C levels in runoff from drained tropical peatlands indicate loss of very old (centuries to millennia) stored peat carbon. High-latitude peatlands appear more resilient to drainage; 14C measurements from UK blanket bogs suggest that exported DOC remains young (use changes in the tropics. Data from the UK Peak District, an area where air pollution and intensive land management have triggered Sphagnum loss and peat erosion, suggest that additional anthropogenic pressures may trigger fluvial loss of much older (>500 year) carbon in high-latitude systems. Rewetting at least partially offsets drainage effects on DOC age.

  5. Characteristics of high-latitude precursor flows ahead of dipolarization fronts

    Science.gov (United States)

    Li, Jia-Zheng; Zhou, Xu-Zhi; Runov, Andrei; Angelopoulos, Vassilis; Liu, Jiang; Pan, Dong-Xiao; Zong, Qiu-Gang

    2017-05-01

    Dipolarization fronts (DFs), earthward propagating structures in the magnetotail current sheet characterized by sharp enhancements of northward magnetic field, are capable of converting electromagnetic energy into particle kinetic energy. The ions previously accelerated and reflected at the DFs can contribute to plasma flows ahead of the fronts, which have been identified as DF precursor flows in both the near-equatorial plasma sheet and far from it, near the plasma sheet boundary. Using observations from the THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft, we show that the earthward particle and energy flux enhancements ahead of DFs are statistically larger farther away from the neutral sheet (at high latitudes) than in the near-equatorial region. High-latitude particle and energy fluxes on the DF dawnside are found to be significantly greater than those on the duskside, which is opposite to the dawn-dusk asymmetries previously found near the equatorial region. Using forward and backward tracing test-particle simulations, we then explain and reproduce the observed latitude-dependent characteristics of DF precursor flows, providing a better understanding of ion dynamics associated with dipolarization fronts.

  6. Space Weather effects on airline communications in the high latitude regions

    Science.gov (United States)

    Honary, Farideh

    2014-05-01

    Efficient air traffic management depends on reliable communications between aircraft and the air traffic control centres at all times. At high latitudes, and especially on polar routing, VHF ground infrastructure does not exist and the aircraft have to rely on HF radio for communications. HF relies on reflections from the ionosphere to achieve long distance communications. Unfortunately the high latitude ionosphere is affected by space weather events. During such events HF radio communication can be severely disrupted and aircraft are forced to use longer low latitude routes with consequent increased flight time, fuel consumption and cost. This presentation describes a new research programme at the University of Lancaster in collaboration with the University of Leicester, Solar Metrics Ltd and Natural Resources Canada for the development of a nowcasting and forecasting HF communications tool designed for the particular needs of civilian airlines. This project funded by EPSRC will access a wide variety of solar and interplanetary measurements to derive a complete picture of space weather disturbances affecting radio absorption and reflection

  7. Parallel Gene Expression Differences between Low and High Latitude Populations of Drosophila melanogaster and D. simulans.

    Science.gov (United States)

    Zhao, Li; Wit, Janneke; Svetec, Nicolas; Begun, David J

    2015-05-01

    Gene expression variation within species is relatively common, however, the role of natural selection in the maintenance of this variation is poorly understood. Here we investigate low and high latitude populations of Drosophila melanogaster and its sister species, D. simulans, to determine whether the two species show similar patterns of population differentiation, consistent with a role for spatially varying selection in maintaining gene expression variation. We compared at two temperatures the whole male transcriptome of D. melanogaster and D. simulans sampled from Panama City (Panama) and Maine (USA). We observed a significant excess of genes exhibiting differential expression in both species, consistent with parallel adaptation to heterogeneous environments. Moreover, the majority of genes showing parallel expression differentiation showed the same direction of differential expression in the two species and the magnitudes of expression differences between high and low latitude populations were correlated across species, further bolstering the conclusion that parallelism for expression phenotypes results from spatially varying selection. However, the species also exhibited important differences in expression phenotypes. For example, the genomic extent of genotype × environment interaction was much more common in D. melanogaster. Highly differentiated SNPs between low and high latitudes were enriched in the 3' UTRs and CDS of the geographically differently expressed genes in both species, consistent with an important role for cis-acting variants in driving local adaptation for expression-related phenotypes.

  8. Maturity group classification and maturity locus genotyping of early-maturing soybean varieties from high-latitude cold regions.

    Science.gov (United States)

    Jia, Hongchang; Jiang, Bingjun; Wu, Cunxiang; Lu, Wencheng; Hou, Wensheng; Sun, Shi; Yan, Hongrui; Han, Tianfu

    2014-01-01

    With the migration of human beings, advances of agricultural sciences, evolution of planting patterns and global warming, soybeans have expanded to both tropical and high-latitude cold regions (HCRs). Unlike other regions, HCRs have much more significant and diverse photoperiods and temperature conditions over seasons or across latitudes, and HCR soybeans released there show rich diversity in maturity traits. However, HCR soybeans have not been as well classified into maturity groups (MGs) as other places. Therefore, it is necessary to identify MGs in HCRs and to genotype the maturity loci. Local varieties were collected from the northern part of Northeast China and the far-eastern region of Russia. Maturity group reference (MGR) soybeans of MGs MG000, MG00, and MG0 were used as references during field experiments. Both local varieties and MGR soybeans were planted for two years (2010-2011) in Heihe (N 50°15', E 127°27', H 168.5 m), China. The days to VE (emergence), R1 (beginning bloom) and R7 (beginning maturity) were recorded and statistically analyzed. Furthermore, some varieties were further genotyped at four molecularly-identified maturity loci E1, E2, E3 and E4. The HCR varieties were classified into MG0 or even more early-maturing. In Heihe, some varieties matured much earlier than MG000, which is the most early-maturing known MG, and clustered into a separate group. We designated the group as MG0000, following the convention of MGs. HCR soybeans had relatively stable days to beginning bloom from emergence. The HCR varieties diversified into genotypes of E1, E2, E3 and E4. These loci had different effects on maturity. HCRs diversify early-maturing MGs of soybean. MG0000, a new MG that matures much earlier than known MGs, was developed. HCR soybean breeding should focus more on shortening post-flowering reproductive growth. E1, E2, E3, and E4 function differentially.

  9. Behavioral Strategies of Lanternfishes (Family Myctophidae) in a High-Latitude Fjord and the Tropical Red Sea

    KAUST Repository

    Dypvik, Eivind

    2012-12-01

    The diel vertical migration (DVM) and feeding periodicity of myctophids (lanternfishes) were studied in the high-latitude Masfjorden, Norway, and the tropical Red Sea. In Masfjorden, a bottom-mounted echo sounder permitted continuous studies throughout the year, and revealed a diverse seasonal DVM behavior. During spring and summer, when zooplankton peaks in the epipelagic zone, migrating glacier lanternfish performed normal DVM (NDVM), ascending to the epipelagic zone during night and residing below ~200m during daytime. During autumn and winter, when Calanus overwinters between ~150–300 m, migrating glacier lanternfish mainly performed inverse DVM (IDVM), ascending to feed on Calanus in mid-waters during daytime. Non migrating (NoDVM) individuals were present all year below ~300 m in Masfjorden. In the Red Sea, where zooplankton has an epipelagic distribution, the whole population of skinnycheek lanternfish performed NDVM, feeding in the epipelagic zone at night, while residing at ~500–750 m during daytime. The warm waters of the Red Sea were hypothesized to limit the time individuals can stay in the mesopelagic zone without migrating to feed in the epipelagic layers. The DVM behavior of myctophids largely seemed to relate to the distribution of zooplankton, and it was hypothesized that NDVM will prevail with epipelagic distribution of prey, while IDVM and NoDVM are common in areas where zooplankton migrate seasonally to mesopelagic depths. Potential predators were continuously present, found to apparently attack glacier lanternfish, at mesopelagic depth in Masfjorden. Thus, myctophids are under threat of predation even at mesopelagic depth.

  10. Distribution of Polycystine Radiolarians in Bottom Surface Sediments and Its Relation to Summer Sea Temperature in the High-Latitude North Atlantic

    Directory of Open Access Journals (Sweden)

    Alexander Matul

    2017-10-01

    Full Text Available An objective of the study is to get new biogeographic information on the modern polycystine radiolarians from the high-latitude North Atlantic. The quantitative radiolarian dataset was compiled from publications and own micropaleontological counts from samples of the bottom surface sediments of the North Atlantic north of 40°N and Nordic Seas. Standard statistical treatment of micropaleontological data by factor analysis reveals five radiolarian assemblages which have their highest load at the specific temperature range in agreement with the oceanographic setting. An occurrence of radiolarian assemblages reflects extension and interaction of the warm North Atlantic and cold Polar/Arctic waters. Radiolarian distribution exhibits good correlation with the climatically averaged summer sea temperature on depth level of 200 m.

  11. Advantageous GOES IR results for ash mapping at high latitudes: Cleveland eruptions 2001

    Science.gov (United States)

    Gu, Yingxin; Rose, William I.; Schneider, D.J.; Bluth, G.J.S.; Watson, I.M.

    2005-01-01

    The February 2001 eruption of Cleveland Volcano, Alaska allowed for comparisons of volcanic ash detection using two-band thermal infrared (10-12 ??m) remote sensing from MODIS, AVHRR, and GOES 10. Results show that high latitude GOES volcanic cloud sensing the range of about 50 to 65??N is significantly enhanced. For the Cleveland volcanic clouds the MODIS and AVHRR data have zenith angles 6-65 degrees and the GOES has zenith angles that are around 70 degrees. The enhancements are explained by distortion in the satellite view of the cloud's lateral extent because the satellite zenith angles result in a "side-looking" aspect and longer path lengths through the volcanic cloud. The shape of the cloud with respect to the GOES look angle also influences the results. The MODIS and AVHRR data give consistent retrievals of the ash cloud evolution over time and are good corrections for the GOES data. Copyright 2005 by the American Geophysical Union.

  12. Population dynamic of high latitude copepods - with emphasis on Metridia longa

    DEFF Research Database (Denmark)

    Kjellerup, Sanne

    2014-01-01

    , sampling only the upper water column during the day-as is a usual procedure-would underestimate this potential key species. Reproduction patterns of the large calanoids suggested lifecycles adapted to the seasonal and episodic food availability, and consequently had a pulsed reproduction. In contrast...... in the fjord, was more restricted and indicated a life-history strategy that combines the advantages of eggcarrying with inter-clutch duration independent of hatching time. Our findings stress the need for sampling with small meshed nets, sampling deeper in the water column, and sampling both diurnally......High latitude ecosystems are shaped by seasonality in light, ranging from complete darkness in winter to midnight sun in summer, influencing both temperature and primary production. Copepods are important grazers on phytoplankton in marine systems and occupy a central role in the marine food...

  13. Newton's second law versus modified-inertia MOND: A test using the high-latitude effect

    International Nuclear Information System (INIS)

    Ignatiev, A. Yu.

    2008-01-01

    The modified-inertia MOND is an approach that proposes a change in Newton's second law at small accelerations as an alternative to dark matter. Recently it was suggested that this approach can be tested in terrestrial laboratory experiments. One way of doing the test is based on the static high-latitude equinox modified-inertia effect: around each equinox date, 2 spots emerge on the Earth where static bodies experience spontaneous displacement due to the violation of Newton's second law required by the modified-inertia MOND. Here, a detailed theory of this effect is developed and estimates of the magnitude of the signal due to the effect are obtained. The expected displacement of a mirror in a gravitational-wave interferometer is found to be about 10 -14 m. Some experimental aspects of the proposal are discussed

  14. Are some of the luminous high-latitude stars accretion-powered runaways?

    International Nuclear Information System (INIS)

    Leonard, P.J.T.; Hills, J.G.; Dewey, R.J.

    1992-01-01

    It is well known that (1) runaway stars can be produced via supernova explosions in close binary systems, (2) most of such runaways should possess neutron star companions, and (3) neutron stars receive randomly oriented kicks of ≅ 100 to 200 km s -1 at birth. We find that this kick sometimes has the right amplitude and direction to make the neutron star fall into the runaway. Accretion onto a neutron star is a source of energy that is roughly an order of magnitude more mass efficient than nuclear burning. Thus, runaways containing neutron stars may live much longer than would normally be expected, which would allow them to travel great distances from their birthplaces during their lifetimes. Some of the early B-type stars far from the Galactic plane and the high-latitude F and G-type supergiants may be accretion-powered runaway stars

  15. GPS phase scintillation at high latitudes during the geomagnetic storm of 17-18 March 2015

    DEFF Research Database (Denmark)

    Prikryl, P.; Ghoddousi-Fard, R.; Weygand, J. M.

    2016-01-01

    The geomagnetic storm of 17–18 March 2015 was caused by the impacts of a coronal mass ejection and a high-speed plasma stream from a coronal hole. The high-latitude ionosphere dynamics is studied using arrays of ground-based instruments including GPS receivers, HF radars, ionosondes, riometers......, and magnetometers. The phase scintillation index is computed for signals sampled at a rate of up to 100 Hz by specialized GPS scintillation receivers supplemented by the phase scintillation proxy index obtained from geodetic-quality GPS data sampled at 1 Hz. In the context of solar wind coupling...... to the magnetosphere-ionosphere system, it is shown that GPS phase scintillation is primarily enhanced in the cusp, the tongue of ionization that is broken into patches drawn into the polar cap from the dayside storm-enhanced plasma density, and in the auroral oval. In this paper we examine the relation between...

  16. Dinosaurs on the North Slope, Alaska: High latitude, latest cretaceous environments

    Science.gov (United States)

    Brouwers, E.M.; Clemens, W.A.; Spicer, R.A.; Ager, T.A.; Carter, L.D.; Sliter, W.V.

    1987-01-01

    Abundant skeletal remains demonstrate that lambeosaurine hadrosaurid, tyrannosaurid, and troodontid dinosaurs lived on the Alaskan North Slope during late Campanian-early Maestrichtian time (about 66 to 76 million years ago) in a deltaic environment dominated by herbaceous vegetation. The high ground terrestrial plant community was a mild- to cold-temperate forest composed of coniferous and broad leaf trees. The high paleolatitude (about 70?? to 85?? North) implies extreme seasonal variation in solar insolation, temperature, and herbivore food supply. Great distances of migration to contemporaneous evergreen floras and the presence of both juvenile and adult hadrosaurs suggest that they remained at high latitudes year-round. This challenges the hypothesis that short-term periods of darkness and temperature decrease resulting from a bolide impact caused dinosaurian extinction.

  17. Existence of a component corotating with the earth in high-latitude disturbance magnetic fields

    Science.gov (United States)

    Suzuki, A.; Kim, J. S.; Sugiura, M.

    1982-01-01

    A study of the data from the high-latitude North American IMS network of magnetic stations suggests that there is a component in substorm perturbations that corotates with the earth. It is as yet not certain whether the existence of this component stems from the corotation of a part of the magnetospheric plasma involved in the substorm mechanism or if it is a 'phase change' resulting from the control of the substorm manifestations by the earth's main magnetic field which is not axially symmetric. There are other geophysical phenomena showing a persistence of longitudinal variations corotating with the earth. These phenomena are of significance for a better understanding of ionosphere-magnetosphere coupling.

  18. Progress in understanding of land surface/atmosphere exchanges at high latitudes

    DEFF Research Database (Denmark)

    Harding, R.J.; Gryning, Sven-Erik; Halldin, S.

    2001-01-01

    This paper summarises some of the key results from two European field programmes, WINTEX and LAPP, undertaken in the Boreal/Arctic regions in 1996-98. Both programmes have illustrated the very important role that snow plays within these areas, not only in the determination of energy, water...... and carbon fluxes in the winter, but also in controlling the length of the summer active season, and hence the overall carbon budget. These studies make a considerable advance in our knowledge of the fluxes from snow-covered landscape and the interactions between snow and vegetation. Also some of the first...... desert in the high arctic. The overall annual budgets are everywhere limited by the very short active season in these regions. The heat flux over a high latitude boreal forest during late winter was found to be high. At low solar angles the forest shades most of the snow surface, therefore an important...

  19. Impact of future Arctic shipping on high-latitude black carbon deposition (Invited)

    Science.gov (United States)

    Corbett, J. J.; Browse, J.; Carslaw, K. S.; Schmidt, A.

    2013-12-01

    The retreat of Arctic sea-ice has led to renewed calls to exploit Arctic shipping routes. The diversion of ship traffic through the Arctic will shorten shipping routes and possibly reduce global shipping emissions. However, deposition of black carbon (BC) aerosol emitted by additional Arctic ships could cause a reduction in the albedo of snow and ice, accelerating snow-melt and sea-ice loss. We use recently compiled Arctic shipping emission inventories for 2004 and 2050 together with a global aerosol microphysics model GLOMAP coupled to the chemical transport model TOMCAT to quantify the contribution of future Arctic shipping to high-latitude BC deposition. Emission rates of SOx (SO2 and SO4) and particulate matter (PM) were estimated for 2050 under both business-as-usual and high-growth scenarios. BC particles are assumed to be water-insoluble at emission but can become active in cloud drop formation through soluble material accumulation. After BC particles become cloud-active they are more efficiently wet scavenged, which accounts for 80% of modeled BC deposition. Current-day Arctic shipping contributes 0.3% to the BC mass deposited north of 60N (250 Gg). About 50% of modelled BC deposition is on open ocean, suggesting that current Arctic ship traffic may not significantly contribute to BC deposition on central Arctic sea ice. However, 6 - 8% of deposited BC on the west coast of Greenland originates from local ship traffic. Moreover, in-Arctic shipping contributes some 32% to high-latitude ship-sourced deposition despite accounting for less than 1.0% of global shipping emissions. This suggests that control of in-Arctic shipping BC emissions could yield greater decrease in high-latitude BC deposition than a similar control strategy applied only to the extra-Arctic shipping industry. Arctic shipping in 2050 will contribute less than 1% to the total BC deposition north of 60N due to the much greater relative contribution of BC transported from non-shipping sources

  20. Regional-Scale High-Latitude Extreme Geoelectric Fields Pertaining to Geomagnetically Induced Currents

    Science.gov (United States)

    Pulkkinen, Antti; Bernabeu, Emanuel; Eichner, Jan; Viljanen, Ari; Ngwira, Chigomezyo

    2015-01-01

    Motivated by the needs of the high-voltage power transmission industry, we use data from the high-latitude IMAGE magnetometer array to study characteristics of extreme geoelectric fields at regional scales. We use 10-s resolution data for years 1993-2013, and the fields are characterized using average horizontal geoelectric field amplitudes taken over station groups that span about 500-km distance. We show that geoelectric field structures associated with localized extremes at single stations can be greatly different from structures associated with regionally uniform geoelectric fields, which are well represented by spatial averages over single stations. Visual extrapolation and rigorous extreme value analysis of spatially averaged fields indicate that the expected range for 1-in-100-year extreme events are 3-8 V/km and 3.4-7.1 V/km, respectively. The Quebec reference ground model is used in the calculations.

  1. Comparison of high-latitude thermospheric meridionalwinds I: optical and radar experimental comparisons

    Directory of Open Access Journals (Sweden)

    E. M. Griffin

    2004-03-01

    Full Text Available Thermospheric neutral winds at Kiruna, Sweden (67.4°N, 20.4°E are compared using both direct optical Fabry-Perot Interferometer (FPI measurements and those derived from European incoherent scatter radar (EISCAT measurements. This combination of experimental data sets, both covering well over a solar cycle of data, allows for a unique comparison of the thermospheric meridional component of the neutral wind as observed by different experimental techniques. Uniquely in this study the EISCAT measurements are used to provide winds for comparison using two separate techniques: the most popular method based on the work of Salah and Holt (1974 and the Meridional Wind Model (MWM (Miller et al., 1997 application of servo theory. The balance of forces at this location that produces the observed diurnal pattern are investigated using output from the Coupled Thermosphere and Ionosphere (CTIM numerical model. Along with detailed comparisons from short periods the climatological behaviour of the winds have been investigated for seasonal and solar cycle dependence using the experimental techniques. While there are features which are consistent between the 3 techniques, such as the evidence of the equinoctial asymmetry, there are also significant differences between the techniques both in terms of trends and absolute values. It is clear from this and previous studies that the high-latitude representation of the thermospheric neutral winds from the empirical Horizontal Wind Model (HWM, though improved from earlier versions, lacks accuracy in many conditions. The relative merits of each technique are discussed and while none of the techniques provides the perfect data set to address model performance at high-latitude, one or more needs to be included in future HWM reformulations.

    Key words. Meteorology and atmospheric dynamics (thermospheric dynamics, Ionosphere (ionosphere-atmosphere interactions, auroral ionosphere

  2. Comparison of high-latitude thermospheric meridionalwinds I: optical and radar experimental comparisons

    Directory of Open Access Journals (Sweden)

    E. M. Griffin

    2004-03-01

    Full Text Available Thermospheric neutral winds at Kiruna, Sweden (67.4°N, 20.4°E are compared using both direct optical Fabry-Perot Interferometer (FPI measurements and those derived from European incoherent scatter radar (EISCAT measurements. This combination of experimental data sets, both covering well over a solar cycle of data, allows for a unique comparison of the thermospheric meridional component of the neutral wind as observed by different experimental techniques. Uniquely in this study the EISCAT measurements are used to provide winds for comparison using two separate techniques: the most popular method based on the work of Salah and Holt (1974 and the Meridional Wind Model (MWM (Miller et al., 1997 application of servo theory. The balance of forces at this location that produces the observed diurnal pattern are investigated using output from the Coupled Thermosphere and Ionosphere (CTIM numerical model. Along with detailed comparisons from short periods the climatological behaviour of the winds have been investigated for seasonal and solar cycle dependence using the experimental techniques. While there are features which are consistent between the 3 techniques, such as the evidence of the equinoctial asymmetry, there are also significant differences between the techniques both in terms of trends and absolute values. It is clear from this and previous studies that the high-latitude representation of the thermospheric neutral winds from the empirical Horizontal Wind Model (HWM, though improved from earlier versions, lacks accuracy in many conditions. The relative merits of each technique are discussed and while none of the techniques provides the perfect data set to address model performance at high-latitude, one or more needs to be included in future HWM reformulations. Key words. Meteorology and atmospheric dynamics (thermospheric dynamics, Ionosphere (ionosphere-atmosphere interactions, auroral ionosphere

  3. Comparison of high-latitude thermospheric meridional winds I: optical and radar experimental comparisons

    Energy Technology Data Exchange (ETDEWEB)

    Griffin, E.M.; Mueller-Wodarg, I.C.F.; Aruliah, A.; Aylward, A. [Atmospheric Physics Lab., Univ. Coll. London, London (United Kingdom)

    2004-07-01

    Thermospheric neutral winds at Kiruna, Sweden (67.4 N, 20.4 E) are compared using both direct optical fabry-perot interferometer (FPI) measurements and those derived from European incoherent scatter radar (EISCAT) measurements. This combination of experimental data sets, both covering well over a solar cycle of data, allows for a unique comparison of the thermospheric meridional component of the neutral wind as observed by different experimental techniques. Uniquely in this study the EISCAT measurements are used to provide winds for comparison using two separate techniques: the most popular method based on the work of Salah and Holt (1974) and the meridional wind model (MWM) (Miller et al., 1997) application of servo theory. The balance of forces at this location that produces the observed diurnal pattern are investigated using output from the coupled thermosphere and ionosphere (CTIM) numerical model. Along with detailed comparisons from short periods the climatological behaviour of the winds have been investigated for seasonal and solar cycle dependence using the experimental techniques. While there are features which are consistent between the 3 techniques, such as the evidence of the equinoctial asymmetry, there are also significant differences between the techniques both in terms of trends and absolute values. It is clear from this and previous studies that the high-latitude representation of the thermospheric neutral winds from the empirical horizontal wind model (HWM), though improved from earlier versions, lacks accuracy in many conditions. The relative merits of each technique are discussed and while none of the techniques provides the perfect data set to address model performance at high-latitude, one or more needs to be included in future HWM reformulations. (orig.)

  4. Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.

    Directory of Open Access Journals (Sweden)

    A. Eisenhauer

    2009-01-01

    Full Text Available The accurate reconstruction of sea surface temperature (SST history in climate-sensitive regions (e.g. tropical and polar oceans became a challenging task in palaeoceanographic research. Biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin. highlight an urgent need to explore complementary SST proxies for these cool-water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin. is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5°C associated with salinities below 33.0 (±0.5‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin., becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability.

  5. Statistical study of high-latitude plasma flow during magnetospheric substorms

    Directory of Open Access Journals (Sweden)

    G. Provan

    2004-11-01

    Full Text Available We have utilised the near-global imaging capabilities of the Northern Hemisphere SuperDARN radars, to perform a statistical superposed epoch analysis of high-latitude plasma flows during magnetospheric substorms. The study involved 67 substorms, identified using the IMAGE FUV space-borne auroral imager. A substorm co-ordinate system was developed, centred on the magnetic local time and magnetic latitude of substorm onset determined from the auroral images. The plasma flow vectors from all 67 intervals were combined, creating global statistical plasma flow patterns and backscatter occurrence statistics during the substorm growth and expansion phases. The commencement of the substorm growth phase was clearly observed in the radar data 18-20min before substorm onset, with an increase in the anti-sunward component of the plasma velocity flowing across dawn sector of the polar cap and a peak in the dawn-to-dusk transpolar voltage. Nightside backscatter moved to lower latitudes as the growth phase progressed. At substorm onset a flow suppression region was observed on the nightside, with fast flows surrounding the suppressed flow region. The dawn-to-dusk transpolar voltage increased from ~40kV just before substorm onset to ~75kV 12min after onset. The low-latitude return flow started to increase at substorm onset and continued to increase until 8min after onset. The velocity flowing across the polar-cap peaked 12-14min after onset. This increase in the flux of the polar cap and the excitation of large-scale plasma flow occurred even though the IMF Bz component was increasing (becoming less negative during most of this time. This study is the first to statistically prove that nightside reconnection creates magnetic flux and excites high-latitude plasma flow in a similar way to dayside reconnection and that dayside and nightside reconnection, are two separate time-dependent processes.

  6. Nitrogen Dioxide long term trends at mid and high latitudes by means of ground based observations

    Science.gov (United States)

    Bortoli, D.; Petritoli, A.; Giovanelli, G.; Kostadinov, I.; Ravegnani, F.

    2003-04-01

    The interactions between mid- and high latitudes atmospheric changes are going to be one of the main issue for the future of stratospheric and tropospheric chemistry research. A more detailed study of the ozone trends as well as a wider comprehension of the interactions with lower and higher latitudes are maybe the main arguments to which scientist should address their works in order to build-up a more detailed picture of what scenarios we have to face in the near future. GASCODs type spectrometers (Gas Analyzer Spectrometer Correlating Optical Differences) are installed at the "Ottavio Vittori" research station (44.11N, 10.42E, 2165 m asl) since June 1993, at the Italian Antarctic Station (74.69S, 164.12E) since December 1995 and at the STIL-BAS station (42.42N, 25.63E) since 1999. The instruments measure zenith scattered solar radiation between 407 and 464 nm. Nitrogen dioxide total column is retrieved with DOAS methodology. The seasonal trend of NO2 vc values is reported and it shows the expected behaviour: maximum values during the summer period while the minimum occur in the winter season in both the hemispheres. A typical behaviour of the AMPM ratio at high latitudes is highlight. A Fourier analysis is proposed as a tool to investigate the long-term components of nitrogen dioxide stratospheric amount. Results are presented and the NO2 trend is evidenced and commented. ACKNOWLEDGMENTS: The author Daniele Bortoli was financially supported by the Subprograma Ciência e Tecnologia do 3° Quadro Comunitário de Apoio. The National Antarctic Research Program (PNRA) and the Quantification and Interpretation of Long-Term UV-Vis Observations of the Stratosphere (QUILT) project supported this research.

  7. Investigating Changes in the High-Latitude Topside Ionosphere During Large Magnetic Storms

    Science.gov (United States)

    Fainberg, Joseph; Benson, Robert F.; Osherovich, Vladimir; Truhlik, Vladimir; Wang, Yongli; Fung, Shing; Bilitza, Dieter

    2009-01-01

    A search was conducted to locate periods of nearly simultaneous solar-wind and high latitude topside-ionospheric data during magnetic storms. The focus was on the 20-yr interval from 1965 to 1985 when both solar-wind and Alouette/ISIS topside-sounder data are potentially available. The search yielded 125 large magnetic storms (minimum Dst less than 100) and 280 moderate magnetic storms (minimum Dst between -60 and -100). Solar wind data were available for most, but not all, of these storms. A search of the available high-latitude topside electron-density Ne(h) profiles available from the National Space Science Data Center (NSSDC), both from manual inspection of 35-mm film ionograms in the 1960s and more recent auto-processing of ISIS-2 topside digital ionograms using the TOPIST software, during 9-day intervals associated with the 125 large magnetic storm minimum Dst times yielded the following results: 31 intervals had 10 or more manual-scaled profiles (21 intervals had more than 100 profiles and 5 of these had more than 1,000 profiles), and 34 intervals had 10 or more TOPIST profiles (2 intervals had more than 100 profiles). In addition, a search of the available Alouette-2, ISIS-1 and ISIS-2 digital ionograms during the above periods has yielded encouraging initial results in that many ISIS-1 ionograms were found for the early time intervals. Future work will include the search for 35-mm film ionograms during selected intervals. This presentation will illustrate the results of this investigation to date.

  8. Operation amplifier

    NARCIS (Netherlands)

    Tetsuya, Saito; Nauta, Bram

    2008-01-01

    To provide an operation amplifier which improves power source voltage removal ratios while assuring phase compensation characteristics, and therefore can be realized with a small-scale circuit and low power consumption. SOLUTION: The operation amplifier comprises: a differential amplifier circuit 1;

  9. The north-south asymmetry of solar filaments separately at low and high latitudes in solar cycle 23

    International Nuclear Information System (INIS)

    Kong De-Fang; Qu Zhi-Ning; Guo Qiao-Ling

    2015-01-01

    We present the results of a study on the north-south asymmetry of solar filaments at low (<50°) and high (>60°) latitudes using daily filament numbers from January 1998 to November 2008 (solar cycle 23). It is found that the northern hemisphere is dominant at low latitudes for cycle 23. However, a similar asymmetry does not occur for solar filaments at high latitudes. The present study indicates that the hemispheric asymmetry of solar filaments at high latitudes in a cycle appears to have little connection with that at low latitudes. Our results support that the observed magnetic fields at high latitudes include two components: one comes from the emergence of the magnetic fields from the solar interior and the other comes from the drift of the magnetic activity at low latitudes. (research papers)

  10. High-latitude steppe vegetation and the mineral nutrition of Pleistocene herbivores

    Science.gov (United States)

    Davydov, S. P.; Davydova, A.; Makarevich, R.; Loranty, M. M.; Boeskorov, G.

    2014-12-01

    High-latitude steppes were widespread and zonal in the Late Pleistocene and formed a landscape basis for the Mammoth Biome. Now the patches of these steppes survived on steep slopes under southern aspects. These steppes serve as unique information sources about the Late Pleistocene "Mammoth" steppe. Numerous data obtained by palynological, carpological, and DNA analysis of plant remains from feces and stomach contents of Pleistocene herbivore mummies, as well as from buried soils and enclosing deposits show that they are similar to modern steppe plant assemblage in taxa composition. Plant's nutrient concentrations are of fundamental importance across Pleistocene grass-rich ecosystems because of their role in the support of large herbivores. The average weight of an adult mammoth skeleton (about 0.5 tons) and of a woolly rhinoceros (about 0.2 tons) clearly suggests this. Detailed studies on fossil bone remains showed mineral deficiency in large Pleistocene herbivores. A three-year study of ash and mineral contents of two types of relict steppe vegetation at the Kolyma Lowland, Arctic Siberia has been carried out. Nowadays refugia of similar vegetation are located not far (1 - 15km) from the Yedoma permafrost outcrops were abundant fossil remains are found. Dominant species of the steppe vegetation were sampled. Preliminary studies indicate that the ash-content varied 1.5-2 times in speceies of steppe herbs. The Ca, P, Mg, K element contents was higher for most steppe species than in the local herbaceous vegetation, especially in Ca and P. One of the most important elements of the mineral nutrition, the phosphorus, was always found in higher concentrations in the steppe vegetation than in plants of recently dominant landscapes of the study area. It should be noted that the mineral nutrient content of the modern steppe vegetation of Siberian Arctic is comparable to that of the recent zonal steppe of Transbaikal Region. This study supports the hypothesis that

  11. Southern high latitude dune fields on Mars: Morphology, aeolian inactivity, and climate change

    Science.gov (United States)

    Fenton, L.K.; Hayward, R.K.

    2010-01-01

    In a study area spanning the martian surface poleward of 50?? S., 1190 dune fields have been identified, mapped, and categorized based on dune field morphology. Dune fields in the study area span ??? 116400km2, leading to a global dune field coverage estimate of ???904000km2, far less than that found on Earth. Based on distinct morphological features, the dune fields were grouped into six different classes that vary in interpreted aeolian activity level from potentially active to relatively inactive and eroding. The six dune field classes occur in specific latitude zones, with a sequence of reduced activity and degradation progressing poleward. In particular, the first signs of stabilization appear at ???60?? S., which broadly corresponds to the edge of high concentrations of water-equivalent hydrogen content (observed by the Neutron Spectrometer) that have been interpreted as ground ice. This near-surface ground ice likely acts to reduce sand availability in the present climate state on Mars, stabilizing high latitude dunes and allowing erosional processes to change their morphology. As a result, climatic changes in the content of near-surface ground ice are likely to influence the level of dune activity. Spatial variation of dune field classes with longitude is significant, suggesting that local conditions play a major role in determining dune field activity level. Dune fields on the south polar layered terrain, for example, appear either potentially active or inactive, indicating that at least two generations of dune building have occurred on this surface. Many dune fields show signs of degradation mixed with crisp-brinked dunes, also suggesting that more than one generation of dune building has occurred since they originally formed. Dune fields superposed on early and late Amazonian surfaces provide potential upper age limits of ???100My on the south polar layered deposits and ???3Ga elsewhere at high latitudes. No craters are present on any identifiable dune

  12. Seasonal and diurnal variability of the meteor flux at high latitudes observed using PFISR

    Science.gov (United States)

    Sparks, J. J.; Janches, D.; Nicolls, M. J.; Heinselman, C. J.

    2009-05-01

    We report in this and a companion paper [Fentzke, J.T., Janches, D., Sparks, J.J., 2008. Latitudinal and seasonal variability of the micrometeor input function: A study using model predictions and observations from Arecibo and PFISR. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.07.015] a complete seasonal study of the micrometeor input function (MIF) at high latitudes using meteor head-echo radar observations performed with the Poker Flat Incoherent Scatter Radar (PFISR). This flux is responsible for a number of atmospheric phenomena; for example, it could be the source of meteoric smoke that is thought to act as condensation nuclei in the formation of ice particles in the polar mesosphere. The observations presented here were performed for full 24-h periods near the summer and winter solstices and spring and autumn equinoxes, times at which the seasonal variability of the MIF is predicted to be large at high latitudes [Janches, D., Heinselman, C.J., Chau, J.L., Chandran, A., Woodman, R., 2006. Modeling of the micrometeor input function in the upper atmosphere observed by High Power and Large Aperture Radars, JGR, 11, A07317, doi:10.1029/2006JA011628]. Precise altitude and radar instantaneous line-of-sight (radial) Doppler velocity information are obtained for each of the hundreds of events detected every day. We show that meteor rates, altitude, and radial velocity distributions have a large seasonal dependence. This seasonal variability can be explained by a change in the relative location of the meteoroid sources with respect to the observer. Our results show that the meteor flux into the upper atmosphere is strongly anisotropic and its characteristics must be accounted for when including this flux into models attempting to explain related aeronomical phenomena. In addition, the measured acceleration and received signal strength distribution do not seem to depend on season; which may suggest that these observed

  13. Solar eclipses at high latitudes: ionospheric effects in the lower ionosphere

    Science.gov (United States)

    Cherniakov, S.

    2017-12-01

    The partial reflection facility of the Polar Geophysical Institute (the Tumanny observatory, 69.0N, 35.7E) has observed behavior of the high-latitude lower ionosphere during the 20 March 2015 total solar eclipse. There were several effects during the eclipse. At the heights of 60-80 km the ionosphere has shown the effect of a "short night", but at the higher altitudes local enhanced electron concentration had a wave-like form. Data received by the riometer of the Tumanny observatory have also shown wave-like behavior. The behavior can be explained by influence of acoustic-gravity waves which originated after cooling of the atmosphere during the lunar shadow supersonic movement, and transport processes during the eclipse. During the 21 August 2017 solar eclipse there was a substorm at the high latitudes. But after the end of the substorm in the region of the Tumanny observatory the observed amplitudes of the reflected waves had wave effects which could be connected with the coming waves from the region of the eclipse. The wave features were also shown in the behavior of the total electron content (TEC) of the lower ionosphere. During several solar eclipses it was implemented observations of lower ionosphere behavior by the partial reflection facility of the Tumanny observatory. The consideration of the lower ionosphere TEC had revealed common features in the TEC behavior during the eclipses. The photochemical theory of processes in the lower ionosphere is very complicated and up to now it is not completely developed. Therefore introduction of the effective coefficients determining the total speed of several important reactions has been widely adopted when modeling the D-region of the ionosphere. However, experimental opportunities for obtaining effective recombination coefficients are rather limited. One of the methods to estimate effective recombination coefficients uses the phenomenon of a solar eclipse. During solar eclipses at the partial reflection facility of

  14. High-latitude poynting flux from combined Iridium and SuperDARN data

    Directory of Open Access Journals (Sweden)

    C. L. Waters

    2004-09-01

    Full Text Available Field-aligned currents convey stress between the magnetosphere and ionosphere, and the associated low altitude magnetic and electric fields reflect the flow of electromagnetic energy to the polar ionosphere. We introduce a new technique to measure the global distribution of high latitude Poynting flux, S||, by combining electric field estimates from the Super Dual Auroral Radar Network (SuperDARN with magnetic perturbations derived using magnetometer data from the Iridium satellite constellation. Spherical harmonic methods are used to merge the data sets and calculate S|| for any magnetic local time (MLT from the pole to 60° magnetic latitude (MLAT. The effective spatial resolutions are 2° MLAT, 2h MLT, and the time resolution is about one hour due to the telemetry rate of the Iridium magnetometer data. The technique allows for the assessment of high-latitude net S|| and its spatial distribution on one hour time scales with two key advantages: (1 it yields the net S|| including the contribution of neutral winds; and (2 the results are obtained without recourse to estimates of ionosphere conductivity. We present two examples, 23 November 1999, 14:00-15:00 UT, and 11 March 2000, 16:00-17:00 UT, to test the accuracy of the technique and to illustrate the distributions of S|| that it gives. Comparisons with in-situ S|| estimates from DMSP satellites show agreement to a few mW/m2 and in the locations of S|| enhancements to within the technique's resolution. The total electromagnetic energy flux was 50GW for these events. At auroral latitudes, S|| tends to maximize in the morning and afternoon in regions less than 5° in MLAT by two hours in MLT having S||=10 to 20mW/m2 and total power up to 10GW. The power poleward of the Region 1 currents is about one

  15. High-latitude poynting flux from combined Iridium and SuperDARN data

    Directory of Open Access Journals (Sweden)

    C. L. Waters

    2004-09-01

    Full Text Available Field-aligned currents convey stress between the magnetosphere and ionosphere, and the associated low altitude magnetic and electric fields reflect the flow of electromagnetic energy to the polar ionosphere. We introduce a new technique to measure the global distribution of high latitude Poynting flux, S||, by combining electric field estimates from the Super Dual Auroral Radar Network (SuperDARN with magnetic perturbations derived using magnetometer data from the Iridium satellite constellation. Spherical harmonic methods are used to merge the data sets and calculate S|| for any magnetic local time (MLT from the pole to 60° magnetic latitude (MLAT. The effective spatial resolutions are 2° MLAT, 2h MLT, and the time resolution is about one hour due to the telemetry rate of the Iridium magnetometer data. The technique allows for the assessment of high-latitude net S|| and its spatial distribution on one hour time scales with two key advantages: (1 it yields the net S|| including the contribution of neutral winds; and (2 the results are obtained without recourse to estimates of ionosphere conductivity. We present two examples, 23 November 1999, 14:00-15:00 UT, and 11 March 2000, 16:00-17:00 UT, to test the accuracy of the technique and to illustrate the distributions of S|| that it gives. Comparisons with in-situ S|| estimates from DMSP satellites show agreement to a few mW/m2 and in the locations of S|| enhancements to within the technique's resolution. The total electromagnetic energy flux was 50GW for these events. At auroral latitudes, S|| tends to maximize in the morning and afternoon in regions less than 5° in MLAT by two hours in MLT having S||=10 to 20mW/m2 and total power up to 10GW. The power poleward of the Region 1 currents is about one-third of the total power, indicating significant energy flux over the polar cap.

  16. An integrated approach for estimation of methane emissions from wetlands and lakes in high latitude regions

    Science.gov (United States)

    Chiu, C.; Bowling, L. C.; Podest, E.; Bohn, T. J.; Lettenmaier, D. P.; Schroeder, R.; McDonald, K. C.

    2009-04-01

    In recent years, there has been increasing evidence of significant alteration in the extent of lakes and wetlands in high latitude regions due in part to thawing permafrost, as well as other changes governing surface and subsurface hydrology. Methane is a 23 times more efficient greenhouse gas than carbon dioxide; changes in surface water extent, and the associated subsurface anaerobic conditions, are important controls on methane emissions in high latitude regions. Methane emissions from wetlands vary substantially in both time and space, and are influenced by plant growth, soil organic matter decomposition, methanogenesis, and methane oxidation controlled by soil temperature, water table level and net primary productivity (NPP). The understanding of spatial and temporal heterogeneity of surface saturation, thermal regime and carbon substrate in northern Eurasian wetlands from point measurements are limited. In order to better estimate the magnitude and variability of methane emissions from northern lakes and wetlands, we present an integrated assessment approach based on remote sensing image classification, land surface modeling and process-based ecosystem modeling. Wetlands classifications based on L-band JERS-1 SAR (100m) and ALOS PALSAR (~30m) are used together with topographic information to parameterize a lake and wetland algorithm in the Variable Infiltration Capacity (VIC) land surface model at 25 km resolution. The enhanced VIC algorithm allows subsurface moisture exchange between surface water and wetlands and includes a sub-grid parameterization of water table position within the wetland area using a generalized topographic index. Average methane emissions are simulated by using the Walter and Heimann methane emission model based on temporally and spatially varying soil temperature, net primary productivity and water table generated from the modified VIC model. Our five preliminary study areas include the Z. Dvina, Upper Volga, Yeloguy, Syum, and Chaya

  17. Climate Change Impacts on Flow and Suspended Sediment Yield in Headwaters of High-Latitude Regions—A Case Study in China’s Far Northeast

    Directory of Open Access Journals (Sweden)

    Yuyan Zhou

    2017-12-01

    Full Text Available Climate change is expected to have stronger effects on water resources in higher latitude regions. Despite intensive research on possible hydrological responses in those regions to a warmer environment, our knowledge on erosion and sediment yield induced by the climate change in high-latitude headwaters is still limited. In this study, we estimated suspended sediment yields from 2021 to 2050 in a typical headwater area of far Northeast China to elucidate potential impacts of future climate change on surface runoff and erosion in higher latitude regions. We first parameterized the Soil and Water Assessment Tool (SWAT using historical measurements to estimate runoff from the river basin. The model performed well in both the calibration (2006–2011 and the validation (2012–2014 periods, with an R2 of 0.85 and 0.88 and a Nash-Sutcliffe Efficiency (NSE of 0.7 and 0.73, respectively. We also utilized historical measurements on sediment yields from the period 2006–2014 to develop a runoff-sediment yield rating curve, and the rating curve obtained an excellent goodness of fit (R2 = 0.91, p < 0.001. We then applied the calibrated SWAT model to two climate change projections, also known as Representative Concentration Pathways (RCP4.5 and RCP8.5, for the period from 2021 to 2050 to obtain future runoff estimates. These runoff estimates were then used to predict future sediment yield by using the developed runoff-sediment yield rating curve. Our study found a significant increase of annual sediment yield (p < 0.05 for both climate change projections (RCP4.5 = 237%; RCP8.5 = 133% in this, China’s high-latitude region. The increases of sediment yield were prevalent in summer and autumn, varying from 102–299% between the two RCPs scenarios. Precipitation was the dominated factor that determined the variation of runoff and sediment yield. A warming climate could bring more snowmelt-induced spring runoff and longer rainy days in autumn, hence leading

  18. Responses of CO2 Fluxes to Arctic Browning Events in a Range of High Latitude, Shrub-Dominated Ecosystems

    Science.gov (United States)

    Phoenix, G. K.; Treharne, R.; Emberson, L.; Tømmervik, H. A.; Bjerke, J. W.

    2017-12-01

    impacts of different event drivers of arctic browning on the main ecosystem CO2 fluxes at a range of sites. These insights provide an important step towards incorporating extreme events into our understanding of how ecosystem CO2 balance at high latitudes will respond to continuing climate change.

  19. Effects of Birkeland current limitation on high-latitude convection patterns

    International Nuclear Information System (INIS)

    Marklund, G.T.; Raadu, M.A.; Lindqvist, P.-A.

    1984-12-01

    It is shown how the high-latitude convection pattern may be mo- dified by substorm-enhanced polarization electric fields. These are generated whenever the flow of those Birkeland currents which are associated with ionospheric conductivity gradients is limited. Such Birkeland currents are fed mainly by the enhanced Pedersen current in the evening and morning sectors of the auro- ral oval and by the enhanced Hall current around local midnight. As the current limitation increases, the ionospheric potential, represented here by a symmetric two-cell pattern, will rotate clockwise and deform, just as the associated Birkeland current distribution. The resulting patterns are shown to agree well with observations. A pronounced westward intrusion of the equi- potential contours occurs in the auroral oval, and may be asso- ciated with the Westward Travelling Surge. This feature does not however require any assumed longitudinal conductivity gradi- ents. Rather it falls out naturally when the limitation of the enhanced Pedersen current is taken into account. (Author)

  20. Lake trout otolith chronologies as multidecadal indicators of high-latitude freshwater ecosystems

    Science.gov (United States)

    Black, B.A.; Von Biela, V.R.; Zimmerman, C.E.; Brown, Randy J.

    2013-01-01

    High-latitude ecosystems are among the most vulnerable to long-term climate change, yet continuous, multidecadal indicators by which to gauge effects on biology are scarce, especially in freshwater environments. To address this issue, dendrochronology (tree-ring analysis) techniques were applied to growth-increment widths in otoliths from lake trout (Salvelinus namaycush) from the Chandler Lake system, Alaska (68.23°N, 152.70°W). All otoliths were collected in 1987 and exhibited highly synchronous patterns in growth-increment width. Increments were dated, the widths were measured, and age-related growth declines were removed using standard dendrochronology techniques. The detrended time series were averaged to generate an annually resolved chronology, which continuously spanned 1964–1984. The chronology positively and linearly correlated with August air temperature over the 22-year interval (p fish metabolic rate or lake productivity. Given the broad distribution of lake trout within North America, this study suggests that otolith chronologies could be used to examine responses between freshwater ecosystems and environmental variability across a range of temporal and spatial scales.

  1. Ecological legacies of Indigenous fire management in high-latitude coastal temperate rainforests, Canada

    Science.gov (United States)

    Hoffman, K.; Lertzman, K. P.; Starzomski, B. M.

    2016-12-01

    Anthropogenic burning is considered to have little impact on coastal temperate rainforest fire regimes in the Pacific Northwest (PNW) of North America, yet few long-term fire histories have been reconstructed in these forests. We use a multidisciplinary approach to reconstruct the ecological impact, scale, and legacies of historic fire regime variability in high-latitude coastal temperate rainforests located in British Columbia, Canada. We map seven centuries of fire activity with fire scars and records of stand establishment, and examine patterns in the distribution and composition of vegetation to assess whether fire was historically used as a tool for resource management. We conduct a paired study of 20 former Indigenous habitation and control sites across a 100 km2 island group to relate historic fire activity with long-term patterns of human land use and contemporary lightning strike densities. Fires were significantly associated with the locations of former Indigenous habitation sites, low and mixed in severity, and likely intentionally used to influence the composition and structure of vegetation, thus increasing the productivity of culturally important plants such as western redcedar, berry-producing shrubs, and bracken fern. Centuries of repeated anthropogenic burning have resulted in a mosaic of vegetation types in different stages of succession. These data are directly relevant to the management of contemporary forests as they do not support the widespread contention that old growth coastal temperate rainforests in this region are pristine landscapes where fire is rare, but more likely the result of long-term human land use practices.

  2. Diffuse galactic gamma rays at intermediate and high latitudes. Pt. 1. Constraints on the ISM properties

    Energy Technology Data Exchange (ETDEWEB)

    Cholis, Ilias; Tavakoli, Maryam; Ullio, Piero [SISSA, Trieste (Italy); INFN, Trieste (Italy); Evoli, Carmelo [SISSA, Trieste (Italy); Chinese Academy of Sciences, Beijing (China). National Astronomical Observatories; Maccione, Luca [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2011-06-15

    We study the high latitude (vertical stroke b vertical stroke >10 ) diffuse {gamma}-ray emission in the Galaxy in light of the recently published data from the Fermi collaboration at energies between 100 MeV and 100 GeV. The unprecedented accuracy in these measurements allows to probe and constrain the properties of sources and propagation of cosmic rays (CRs) in the Galaxy, as well as confirming conventional assumptions made on the interstellar medium (ISM). Using the publicly available DRAGON code, that has been shown to reproduce local measurements of CRs, we study assumptions made in the literature on HI and H2 gas distributions in the ISM, and non spatially uniform models of diffusion in the Galaxy. By performing a combined analysis of CR and {gamma}-ray spectra, we derive constraints on the properties of the ISM gas distribution and the vertical scale height of galactic CR diffusion, which may have implications also on indirect Dark Matter detection. We also discuss some of the possible interpretations of the break at {proportional_to}230 GeV in CR protons and helium spectra, recently observed by PAMELA and their impact on {gamma}-rays. (orig.)

  3. Imaging of structures in the high-latitude ionosphere: model comparisons

    Directory of Open Access Journals (Sweden)

    D. W. Idenden

    Full Text Available The tomographic reconstruction technique generates a two-dimensional latitude versus height electron density distribution from sets of slant total electron content measurements (TEC along ray paths between beacon satellites and ground-based radio receivers. In this note, the technique is applied to TEC values obtained from data simulated by the Sheffield/UCL/SEL Coupled Thermosphere/Ionosphere/Model (CTIM. A comparison of the resulting reconstructed image with the 'input' modelled data allows for verification of the reconstruction technique. All the features of the high-latitude ionosphere in the model data are reproduced well in the tomographic image. Reconstructed vertical TEC values follow closely the modelled values, with the F-layer maximum density (NmF2 agreeing generally within about 10%. The method has also been able successfully to reproduce underlying auroral-E ionisation over a restricted latitudinal range in part of the image. The height of the F2 peak is generally in agreement to within about the vertical image resolution (25 km.

    Key words. Ionosphere (modelling and forecasting; polar ionosphere · Radio Science (instruments and techniques

  4. Lake trout otolith chronologies as multidecadal indicators of high-latitude freshwater ecosystems

    Science.gov (United States)

    Black, B.A.; Von Biela, V.R.; Zimmerman, C.E.; Brown, Randy J.

    2013-01-01

    High-latitude ecosystems are among the most vulnerable to long-term climate change, yet continuous, multidecadal indicators by which to gauge effects on biology are scarce, especially in freshwater environments. To address this issue, dendrochronology (tree-ring analysis) techniques were applied to growth-increment widths in otoliths from lake trout (Salvelinus namaycush) from the Chandler Lake system, Alaska (68.23°N, 152.70°W). All otoliths were collected in 1987 and exhibited highly synchronous patterns in growth-increment width. Increments were dated, the widths were measured, and age-related growth declines were removed using standard dendrochronology techniques. The detrended time series were averaged to generate an annually resolved chronology, which continuously spanned 1964–1984. The chronology positively and linearly correlated with August air temperature over the 22-year interval (p otolith chronologies could be used to examine responses between freshwater ecosystems and environmental variability across a range of temporal and spatial scales.

  5. Coral bleaching on high-latitude marginal reefs at Sodwana Bay, South Africa

    International Nuclear Information System (INIS)

    Celliers, Louis; Schleyer, Michael H.

    2002-01-01

    Coral bleaching, involving the expulsion of symbiotic zooxanthellae from the host cells, poses a major threat to coral reefs throughout their distributional range. The role of temperature in coral bleaching has been extensively investigated and is widely accepted. A bleaching event was observed on the marginal high-latitude reefs of South Africa located at Sodwana Bay during the summer months of 2000. This was associated with increased sea temperatures with high seasonal peaks in summer and increased radiation in exceptionally clear water. The bleaching was limited to Two-mile Reef and Nine-mile Reef at Sodwana Bay and affected -1 from May 1994 to April 2000. High maximum temperatures were measured (>29 deg. C). The lowest mean monthly and the mean maximum monthly temperatures at which coral bleaching occurred were 27.5 and 28.8 deg. C, respectively, while the duration for which high temperatures occurred in 2000 was 67 days at ≥27.5 deg. C (4 days at ≥28.8 deg. C). Increased water clarity and radiation appeared to be a synergistic cause in the coral bleaching encountered at Sodwana Bay

  6. Diffuse galactic gamma rays at intermediate and high latitudes. I. Constraints on the ISM properties

    International Nuclear Information System (INIS)

    Cholis, Ilias; Tavakoli, Maryam; Evoli, Carmelo; Ullio, Piero; Maccione, Luca

    2012-01-01

    We study the high latitude (|b| > 10°) diffuse γ-ray emission in the Galaxy in light of the recently published data from the Fermi collaboration at energies between 100 MeV and 100 GeV. The unprecedented accuracy in these measurements allows to probe and constrain the properties of sources and propagation of cosmic rays (CRs) in the Galaxy, as well as confirming conventional assumptions made on the interstellar medium (ISM). Using the publicly available DRAGON code, that has been shown to reproduce local measurements of CRs, we study assumptions made in the literature on atomic (HI) and molecular hydrogen (H2) gas distributions in the ISM, and non spatially uniform models of diffusion in the Galaxy. By performing a combined analysis of CR and γ-ray spectra, we derive constraints on the properties of the ISM gas distribution and the vertical scale height of galactic CR diffusion, which may have implications also on indirect Dark Matter detection. We also discuss some of the possible interpretations of the break at high rigidity in CR protons and helium spectra, recently observed by PAMELA and their impact on γ-rays

  7. High-latitude Pc 1 bursts arising in the dayside boundary layer region

    International Nuclear Information System (INIS)

    Hansen, H.J.; Fraser, B.J.; Menk, F.W.; Hu, Y.D.; Newell, P.T.; Meng, C.I.; Morris, R.J.

    1992-01-01

    Dayside Pc 1 geomagnetic pulsation bursts have been studied using a three-station array of induction magnetometers located at high latitudes. Associated magnetic variations in the form of solitary pulses often lead the Pc 1 bursts by 1 to 2 min. These pulses are typically associated with riometer absorption events and consequently the precipitation of fluxes of keV electrons. The Pc 1 bursts are interpreted as resulting from ion cyclotron waves which have propagated to the ionosphere from the equatorial boundary layer region. The associated boundary layer ions, identified by the low-altitude DMSP F7 satellite, range between 1 and 5 keV in energy. These particles are considered to be the most likely free energy source for the ion cyclotron waves. It is considered that such resonant ions enter the magnetosphere via the cleft and cusp because this enables a prenoon time of occurrence of most of the observations to be explained. Measured time delays of 40 to 120 s between the associated riometer absorption and Pc 2 bursts are consistent with an ion cyclotron wave generations region located in the equatorial magnetosphere

  8. High latitude stratospheric electrical measurements in fair and foul weather under various solar conditions

    International Nuclear Information System (INIS)

    Holzworth, R.H.

    1981-01-01

    Stratospheric electric field and conductivity measurements during a wide variety of weather and solar conditions are presented. These data are all from high latitude sites in the months of either April or August. The vector electric field is determined by orthogonal double probes connected through high impedance inputs to differential electrometers. The direct conductivity measurement involves determining the relaxation time constant of the medium after refloating a shorted pair of separated probes. Vertical electric field data from several balloon flights with average duration of 18 h at ceiling in fair weather are shown to be well modeled by a simple exponential altitude dependent equation. Examples of solar flare and magnetospheric effects on stratospheric electric fields are shown. Data collected over electrified clouds and thunderstorms are presented along with a discussion of the thunderstorm related electric currents. Lightning stroke signatures in the stratosphere during a large thunderstorm are identified in the electric field data. Current surges through the stratosphere due to DC currents as well as the sferic are calculated. In nearly 1000 h of balloon data no direct solar influence is identified in these data except during major flares. (author)

  9. An accelerating high-latitude jet in Earth’s core

    Science.gov (United States)

    Livermore, Philip W.; Hollerbach, Rainer; Finlay, Christopher C.

    2017-01-01

    Observations of the change in Earth’s magnetic field--the secular variation--provide information about the motion of liquid metal within the core that is responsible for the magnetic field’s generation. High-resolution observations from the European Space Agency’s Swarm satellite mission show intense field change at high latitude, localized in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we show that this feature can be explained by a localized, non-axisymmetric, westward jet of 420 km width on the tangent cylinder, the cylinder of fluid within the core that is aligned with the rotation axis and tangent to the solid inner core. We find that the jet has increased in magnitude by a factor of three over the period 2000-2016 to about 40 km yr-1, and is now much stronger than typical large-scale flows inferred for the core. We suggest that the current accelerating phase may be part of a longer-term fluctuation of the jet causing both eastward and westward movement of magnetic features over historical periods, and may contribute to recent changes in torsional-wave activity and the rotation direction of the inner core.

  10. A note on chaotic vs. stochastic behavior of the high-latitude ionospheric plasma density fluctuations

    Directory of Open Access Journals (Sweden)

    A. W. Wernik

    1996-01-01

    Full Text Available Four data sets of density fluctuations measured in-situ by the Dynamics Explorer (DE 2 were analyzed in an attempt to study chaotic nature of the high-latitude turbulence and, in this way to complement the conventional spectral analysis. It has been found that the probability distribution function of density differences is far from Gaussian and similar to that observed in the intermittent fluid or MBD turbulence. This indicates that ionospheric density fluctuations are not stochastic but coherent to some extent. Wayland's and surrogate data tests for determinism in a time series of density data allowed us to differentiate between regions of intense shear and moderate shear. We observe that in the region of strong field aligned currents (FAC and intense shear, or along the convection in the collisional regime, ionospheric turbulence behaves like a random noise with non-Gaussian statistics implying that the underlying physical process is nondeterministic. On the other hand, when FACs are weak, and shear is moderate or observations made in the inertial regime the turbulence is chaotic. The attractor dimension is lowest (1.9 for 'old' convected irregularities. The dimension 3.2 is found for turbulence in the inertial regime and considerably smaller (2.4 in the collisional regime. It is suggested that a high dimension in the inertial regime may be caused by a complicated velocity structure in the shear instability region.

  11. Advances in Understanding the Role of Frozen Precipitation in High Latitude Hydrology

    Science.gov (United States)

    L'Ecuyer, T. S.; Wood, N.; Smalley, M.; McIlhattan, E.; Kulie, M.

    2017-12-01

    Satellite-based millimeter wavelength radar observations provide a unique perspective on the global character of frozen precipitation that has been difficult to detect using conventional spaceborne precipitation sensors. This presentation will describe the methodology underpinning the ten-year CloudSat global snowfall product and discuss the results of a number of complementary approaches that have been adopted to quantify its uncertainties. These datasets are shedding new light on the distribution, character, and impacts of frozen precipitation on high latitude hydrology. Inferred regional snowfall accumulations, for example, provide valuable constraints on projected changes in precipitation and mass balance on the Antarctic ice sheet in climate models. When placed in the broader context of complementary observations from other A-Train sensors, instantaneous snowfall estimates also hint at the large-scale processes that influence snow formation including air-sea interactions associated with cold-air outbreaks, lake-effect snows, and orographic enhancement. Simultaneous CloudSat and CALIPSO observations further emphasize the important role snowfall plays in the lifetime of super-cooled liquid containing clouds in the Arctic and highlight a model deficiency with important implications for surface energy and mass balance on the Greenland ice sheet.

  12. Characterization of the Ionospheric Scintillations at High Latitude using GPS Signal

    Science.gov (United States)

    Mezaoui, H.; Hamza, A. M.; Jayachandran, P. T.

    2013-12-01

    Transionospheric radio signals experience both amplitude and phase variations as a result of propagation through a turbulent ionosphere; this phenomenon is known as ionospheric scintillations. As a result of these fluctuations, Global Positioning System (GPS) receivers lose track of signals and consequently induce position and navigational errors. Therefore, there is a need to study these scintillations and their causes in order to not only resolve the navigational problem but in addition develop analytical and numerical radio propagation models. In order to quantify and qualify these scintillations, we analyze the probability distribution functions (PDFs) of L1 GPS signals at 50 Hz sampling rate using the Canadian High arctic Ionospheric Network (CHAIN) measurements. The raw GPS signal is detrended using a wavelet-based technique and the detrended amplitude and phase of the signal are used to construct probability distribution functions (PDFs) of the scintillating signal. The resulting PDFs are non-Gaussian. From the PDF functional fits, the moments are estimated. The results reveal a general non-trivial parabolic relationship between the normalized fourth and third moments for both the phase and amplitude of the signal. The calculated higher-order moments of the amplitude and phase distribution functions will help quantify some of the scintillation characteristics and in the process provide a base for forecasting, i.e. develop a scintillation climatology model. This statistical analysis, including power spectra, along with a numerical simulation will constitute the backbone of a high latitude scintillation model.

  13. Diffuse galactic gamma rays at intermediate and high latitudes. Pt. 1. Constraints on the ISM properties

    International Nuclear Information System (INIS)

    Cholis, Ilias; Tavakoli, Maryam; Ullio, Piero; Evoli, Carmelo

    2011-06-01

    We study the high latitude (vertical stroke b vertical stroke >10 ) diffuse γ-ray emission in the Galaxy in light of the recently published data from the Fermi collaboration at energies between 100 MeV and 100 GeV. The unprecedented accuracy in these measurements allows to probe and constrain the properties of sources and propagation of cosmic rays (CRs) in the Galaxy, as well as confirming conventional assumptions made on the interstellar medium (ISM). Using the publicly available DRAGON code, that has been shown to reproduce local measurements of CRs, we study assumptions made in the literature on HI and H2 gas distributions in the ISM, and non spatially uniform models of diffusion in the Galaxy. By performing a combined analysis of CR and γ-ray spectra, we derive constraints on the properties of the ISM gas distribution and the vertical scale height of galactic CR diffusion, which may have implications also on indirect Dark Matter detection. We also discuss some of the possible interpretations of the break at ∝230 GeV in CR protons and helium spectra, recently observed by PAMELA and their impact on γ-rays. (orig.)

  14. GPS scintillations and total electron content climatology in the southern low, middle and high latitude regions

    Directory of Open Access Journals (Sweden)

    Luca Spogli

    2013-06-01

    Full Text Available In recent years, several groups have installed high-frequency sampling receivers in the southern middle and high latitude regions, to monitor ionospheric scintillations and the total electron content (TEC changes. Taking advantage of the archive of continuous and systematic observations of the ionosphere on L-band by means of signals from the Global Positioning System (GPS, we present the first attempt at ionospheric scintillation and TEC mapping from Latin America to Antarctica. The climatology of the area considered is derived through Ground-Based Scintillation Climatology, a method that can identify ionospheric sectors in which scintillations are more likely to occur. This study also introduces the novel ionospheric scintillation 'hot-spot' analysis. This analysis first identifies the crucial areas of the ionosphere in terms of enhanced probability of scintillation occurrence, and then it studies the seasonal variation of the main scintillation and TEC-related parameters. The results produced by this sophisticated analysis give significant indications of the spatial/ temporal recurrences of plasma irregularities, which contributes to the extending of current knowledge of the mechanisms that cause scintillations, and consequently to the development of efficient tools to forecast space-weather-related ionospheric events.

  15. The geomagnetic cutoff rigidities at high latitudes for different solar wind and geomagnetic conditions

    International Nuclear Information System (INIS)

    Chu, W.; Univ. of Chinese Academy of Sciences, Beijing; Qin, G.

    2016-01-01

    Studying the access of the cosmic rays (CRs) into the magnetosphere is important to understand the coupling between the magnetosphere and the solar wind. In this paper we numerically studied CRs' magnetospheric access with vertical geomagnetic cutoff rigidities using the method proposed by Smart and Shea (1999). By the study of CRs' vertical geomagnetic cutoff rigidities at high latitudes we obtain the CRs' window (CRW) whose boundary is determined when the vertical geomagnetic cutoff rigidities drop to a value lower than a threshold value. Furthermore, we studied the area of CRWs and found out they are sensitive to different parameters, such as the z component of interplanetary magnetic field (IMF), the solar wind dynamic pressure, AE index, and Dst index. It was found that both the AE index and Dst index have a strong correlation with the area of CRWs during strong geomagnetic storms. However, during the medium storms, only AE index has a strong correlation with the area of CRWs, while Dst index has a much weaker correlation with the area of CRWs. This result on the CRW can be used for forecasting the variation of the cosmic rays during the geomagnetic storms.

  16. Metal stress consequences on frost hardiness of plants at northern high latitudes: a review and hypothesis

    International Nuclear Information System (INIS)

    Taulavuori, Kari; Prasad, M.N.V.; Taulavuori, Erja; Laine, Kari

    2005-01-01

    This paper reviews the potential of trace/heavy metal-induced stress to reduce plant frost hardiness at northern high latitudes. The scientific questions are first outlined prior to a brief summary of heavy metal tolerance. The concepts of plant capacity and survival adaptation were used to formulate a hypothesis, according to which heavy metal stress may reduce plant frost hardiness for the following reasons: (1) Heavy metals change membrane properties through impaired resource acquisition and subsequent diminution of the cryoprotectant pool. (2) Heavy metals change membrane properties directly through oxidative stress, i.e. an increase of active oxygen species. (3) The involved co-stress may further increase oxidative stress. (4) The risk of frost injury increases due to membrane alterations. An opposite perspective was also discussed: could metal stress result in enhanced plant frost hardiness? This phenomenon could be based on the metabolism (i.e. glutathione, polyamines, proline, heat shock proteins) underlying a possible general adaptation syndrome of stress (GAS). As a result of the review it was suggested that metal-induced stress seems to reduce rather than increase plant frost hardiness. - Metal stress may reduce plant frost hardiness

  17. Metal stress consequences on frost hardiness of plants at northern high latitudes: a review and hypothesis.

    Science.gov (United States)

    Taulavuori, Kari; Prasad, M N V; Taulavuori, Erja; Laine, Kari

    2005-05-01

    This paper reviews the potential of trace/heavy metal-induced stress to reduce plant frost hardiness at northern high latitudes. The scientific questions are first outlined prior to a brief summary of heavy metal tolerance. The concepts of plant capacity and survival adaptation were used to formulate a hypothesis, according to which heavy metal stress may reduce plant frost hardiness for the following reasons: (1) Heavy metals change membrane properties through impaired resource acquisition and subsequent diminution of the cryoprotectant pool. (2) Heavy metals change membrane properties directly through oxidative stress, i.e. an increase of active oxygen species. (3) The involved co-stress may further increase oxidative stress. (4) The risk of frost injury increases due to membrane alterations. An opposite perspective was also discussed: could metal stress result in enhanced plant frost hardiness? This phenomenon could be based on the metabolism (i.e. glutathione, polyamines, proline, heat shock proteins) underlying a possible general adaptation syndrome of stress (GAS). As a result of the review it was suggested that metal-induced stress seems to reduce rather than increase plant frost hardiness.

  18. Metal stress consequences on frost hardiness of plants at northern high latitudes: a review and hypothesis

    Energy Technology Data Exchange (ETDEWEB)

    Taulavuori, Kari [Department of Biology, University of Oulu, PO Box 3000, FIN-90014, Oulu (Finland)]. E-mail: kari.taulavuori@oulu.fi; Prasad, M.N.V. [Department of Plant Sciences, University of Hyderabad, Hyderabad 500 046, Andhra Pradesh (India); Taulavuori, Erja [Department of Biology, University of Oulu, PO Box 3000, FIN-90014, Oulu (Finland); Laine, Kari [Department of Biology, University of Oulu, PO Box 3000, FIN-90014, Oulu (Finland)

    2005-05-01

    This paper reviews the potential of trace/heavy metal-induced stress to reduce plant frost hardiness at northern high latitudes. The scientific questions are first outlined prior to a brief summary of heavy metal tolerance. The concepts of plant capacity and survival adaptation were used to formulate a hypothesis, according to which heavy metal stress may reduce plant frost hardiness for the following reasons: (1) Heavy metals change membrane properties through impaired resource acquisition and subsequent diminution of the cryoprotectant pool. (2) Heavy metals change membrane properties directly through oxidative stress, i.e. an increase of active oxygen species. (3) The involved co-stress may further increase oxidative stress. (4) The risk of frost injury increases due to membrane alterations. An opposite perspective was also discussed: could metal stress result in enhanced plant frost hardiness? This phenomenon could be based on the metabolism (i.e. glutathione, polyamines, proline, heat shock proteins) underlying a possible general adaptation syndrome of stress (GAS). As a result of the review it was suggested that metal-induced stress seems to reduce rather than increase plant frost hardiness. - Metal stress may reduce plant frost hardiness.

  19. Effects of electric fields and other processes upon the nighttime high-latitude F layer

    International Nuclear Information System (INIS)

    Schunk, R.W.; Banks, P.M.; Raitt, W.J.

    1976-01-01

    We have studied the dynamics of the nighttime high-latitude F region with special emphasis on the formation of the electron density trough region which lies equatorward of the auroral oval. It is found that the absence of photoionization together with ordinary ionic recombination and slow plasma convection velocity can give a deep trough over a period of many hours. However, the normal global pattern of electric fields has regions of plasma convection sufficiently rapid to affect that rate of O + +N 2 reactions and to speed the rate of ionospheric decay. In addition, the escape of thermal plasma via the polar wind as well as N 2 vibrational excitation and enhanced N 2 densities act to deplete the ionosphere. In combination these destructive processes can readily account for the great variety of troughs found by experimentation. Thus it appears that there is no single cause for the observed troughs but that at various times, different processes act together to create density depressions of substantial magnitude

  20. Elevated temperatures and bleaching on a high latitude coral reef: the 1988 Bermuda event

    Science.gov (United States)

    Cook, Clayton B.; Logan, Alan; Ward, Jack; Luckhurst, Brian; Berg, Carl J.

    1990-03-01

    Sea temperatures were normal in Bermuda during 1987, when Bermuda escaped the episodes of coral bleaching which were prevalent throughout the Caribbean region. Survey transecs in 1988 on 4 6 m reefs located on the rim margin and on a lagoonal patch reef revealed bleaching only of zoanthids between May and July. Transect and tow surveys in August and September revealed bleaching of several coral species; Millepora alcicornis on rim reefs was the most extensively affected. The frequency of bleaching in this species, Montastrea annularis and perhaps Diploria labyrinthiformis was significantly higher on outer reefs than on inshore reefs. This bleaching period coincided with the longest period of elevated sea temperatures in Bermuda in 38 years (28.9 30.9°C inshore, >28° offshore). By December, when temperatures had returned to normal, bleaching of seleractinians continued, but bleaching of M. alcicornis on the outer reefs was greatly reduced. Our observations suggest that corals which normally experience wide temperature ranges are less sensitive to thermal stress, and that high-latitude reef corals are sensitive to elevated temperatures which are within the normal thermal range of corals at lower latitudes.

  1. The influence of conductivities consistent with field-aligned currents on high-latitude convection patterns

    International Nuclear Information System (INIS)

    Blomberg, L.G.; Marklund, G.T.

    1988-02-01

    The influence on the high-latitude ionospheric convection of conductivities associated with upward field-aligned currents is investigated. Potential patterns are calculated from a given distribution of field-aligned currents and a conductivity model. The resulting patterns are shown to be modified considerably by including a coupling term between the conductivity and the field-aligned current in the conductivity model. The clockwise rotation of the entire potential pattern is reduced when the conductivity enhancement coincides with the regions of upward field-aligned current. Also, the electric field within these regions turns out to be rather insensitive to change in the magnitude of the current. In regions of downward current or when the current-dependent conductivity is excluded there is on the other hand an almost linear relationship between current and electric field. Although the particles producing the conductivity enhancement may not be the same as those carrying the major part of the field-aligned current it is clear from observations that there is a positive correlation between upward current conductivity. Therefore, the simple relationship used in this study is believed to reflect rather well the principal features of the current-conductivity coupling, which is of im- portance to the modelling of ionospheric electrodynamics. (With 26 refs.) (authors)

  2. Global Warming: A Reduced Threat?.

    Science.gov (United States)

    Michaels, Patrick J.; Stooksbury, David E.

    1992-10-01

    One popular and apocalyptic vision of the world influenced by increasing concentrations of infrared-absorbing trace gases is that of ecological disaster brought about by rapidly rising temperatures, sea level, and evaporation rates. This vision developed from a suite of climate models that have since considerably changed in both their dynamics and their estimates of prospective warming. Observed temperatures indicate that much more warming should already have taken place than predicted by earlier models in the Northern Hemisphere, and that night, rather than day, readings in that hemisphere show a relative warming. A high-latitude polar-night warming or a general night warming could be either benign or beneficial. A large number of plant species show both increased growth and greater water-use efficiency under enhanced carbon dioxide.An extensive body of evidence now indicates that anthropo-generated sulfate emissions are mitigating some of the warming, and that increased cloudiness as a result of these emissions will further enhance night, rather than day, warming. The sulfate emissions, though, are not sufficient to explain all of the night warming. However, the sensitivity of climate to anthropogenerated aerosols, and the general lack of previously predicted warming, could drastically alter the debate on global warming in favor of less expensive policies.

  3. Operation Amplifier

    NARCIS (Netherlands)

    Tetsuya, Saito; Nauta, Bram

    2011-01-01

    PROBLEM TO BE SOLVED: To provide an operation amplifier which improves power source voltage removal ratios while assuring phase compensation characteristics, and therefore can be realized with a small-scale circuit and low power consumption. SOLUTION: The operation amplifier comprises: a

  4. Operation Amplifier

    NARCIS (Netherlands)

    Tetsuya, S.; Nauta, Bram

    2007-01-01

    PROBLEM TO BE SOLVED: To provide an operation amplifier which improves power source voltage removal ratios while assuring phase compensation characteristics, and therefore can be realized with a small-scale circuit and low power consumption. ; SOLUTION: The operation amplifier comprises: a

  5. Operational amplifiers

    CERN Document Server

    Dostal, Jiri

    1993-01-01

    This book provides the reader with the practical knowledge necessary to select and use operational amplifier devices. It presents an extensive treatment of applications and a practically oriented, unified theory of operational circuits.Provides the reader with practical knowledge necessary to select and use operational amplifier devices. Presents an extensive treatment of applications and a practically oriented, unified theory of operational circuits

  6. Amplifier Distortion

    Science.gov (United States)

    Keeports, David

    2006-12-01

    By definition, a high fidelity amplifier's instantaneous output voltage is directly proportional to its instantaneous input voltage. While high fidelity is generally valued in the amplification of recorded music, nonlinearity, also known as distortion, is desirable in the amplification of some musical instruments. In particular, guitar amplifiers exploit nonlinearity to increase both the harmonic content and sustain of a guitar's sound. I will discuss how both modifications in sound result from saturation of triode tubes and transistors. Additionally, I will describe the difference in the symmetry of saturation curves for transistors and tubes and the reason why tube guitar amplifiers are generally considered to be superior to solid-state amplifiers. Finally, I will discuss attempts to use solid-state electronics to replicate the sound of tube amplifiers.

  7. Dayside magnetic ULF power at high latitudes: A possible long-term proxy for the solar wind velocity?

    DEFF Research Database (Denmark)

    Vennerstrøm, Susanne

    1999-01-01

    We examine the occurrence of dayside high-latitude magnetic variations with periods between 2 and 10 min statistically using data from around 20 magnetic stations in Greenland, Scandinavia, and Canada, many of which have been in operation for a full solar cycle. We derive time series of the power...

  8. Impact of high-latitude energy input on the mid- and low-latitude ionosphere and thermosphere

    Science.gov (United States)

    Lu, G.; Sheng, C.

    2017-12-01

    High-latitude energy input has a profound impact on the ionosphere and thermosphere especially during geomagnetic storms. Intense auroral particle precipitation ionizes neutral gases and modifies ionospheric conductivity; collisions between neutrals and fast-moving ions accelerate the neutral winds and produce Joule frictional heating; and the excess Joule and particle heating causes atmospheric upwelling and changes neutral composition due to the rising of the heavier, molecular-rich air. In addition, impulsive Joule heating launches large-scale gravity waves that propagate equatorward toward middle and low latitudes and even into the opposite hemisphere, altering the mean global circulation of the thermosphere. Furthermore, high-latitude electric field can also directly penetrate to lower latitudes under rapidly changing external conditions, causing prompt ionospheric variations in the mid- and low-latitude regions. To study the effects of high-latitude energy input, we apply the different convection and auroral precipitation patterns based on both empirical models and the AMIE outputs. We investigate how the mid- and low-latitude regions respond to the different specifications of high-latitude energy input. The main purpose of the study is to delineate the various dynamical, electrodynamical, and chemical processes and to determine their relative importance in the resulting ionospheric and thermospheric properties at mid and low latitudes.

  9. Space weather effects on airline communications in the high latitude regions

    Science.gov (United States)

    Stocker, Alan; Siddle, Dave; Warrington, Mike; Honary, Farideh; Zaalov, Nikolay; Homam, Mariyam; Boteler, David; Danskin, Donald; de Franceschi, Georgiana; Ascaneus, Svend

    2013-04-01

    In the polar regions, ground-based VHF facilities for air-traffic control are lacking (and non-existent on the Russian side of the pole) and satellite communication systems either not available or expensive to retrofit to current aircraft and hence there remains a need for HF communication systems. Unfortunately, at these latitudes space weather can significantly affect the propagation of HF radio signals and the forecasting techniques currently employed by the airline industry are somewhat crude. In this paper, a new project that aims to provide forecasting of HF propagation characteristics for use by civilian airlines operating over polar routes will be described and preliminary results presented. Previous work in this area [e.g. Stocker et al., 2007] has focussed on taking HF signal measurements (e.g. SNR, delay and Doppler spread, and direction of arrival) on a limited number of propagation paths and developing an ionospheric model that incorporates high latitude features (e.g. polar patches and arcs) which, when combined with raytracing, allows the broad characteristics of the observations to be reproduced [Warrington et al., 2012]. The new project will greatly extend this work and consists of a number of stages. Firstly, HF measurements from an extensive network of purpose built transmitters and receivers spanning the Arctic regions will be collected and analysed. In order to test a wide variety of scenarios, the propagation paths will have different characteristics, e.g. different lengths and covering different parts of the northern ionosphere (i.e. polar cap paths where both terminals are in the polar cap, trans-auroral paths, and sub-auroral paths) and observations will be taken at a range of HF frequencies for a period covering the current (so far weak) solar maximum and part of the declining phase. Simultaneously, high latitude absorption measurements utilising the Global Riometer Array (GLORIA) will be collected and analysed. Next, the observations of

  10. Snowmelt in a High Latitude Mountain Catchment: Effect of Vegetation Cover and Elevation

    Science.gov (United States)

    Pomeroy, J. W.; Essery, R. L.; Ellis, C. R.; Hedstrom, N. R.; Janowicz, R.; Granger, R. J.

    2004-12-01

    The energetics and mass balance of snowpacks in the premelt and melt period were compared from three elevation bands in a high latitude mountain catchment, Wolf Creek Research Basin, Yukon. Elevation is strongly correlated with vegetation cover and in this case the three elevation bands (low, middle, high) correspond to mature spruce forest, dense shrub tundra and sparse tundra (alpine). Measurements of radiation, ground heat flux, snow depth, snowfall, air temperature, wind speed were made on a half-hourly basis at the three elevations for a 10 year period. Sondes provided vertical gradients of air temperature, humidity, wind speed and air pressure. Snow depth and density surveys were conducted monthly. Comparisons of wind speed, air temperature and humidity at three elevations show that the expected elevational gradients in the free atmosphere were slightly enhanced just above the surface canopies, but that the climate at the snow surface was further influenced by complex canopy effects. Premelt snow accumulation was strongly affected by intercepted snow in the forest and blowing snow sublimation in the sparse tundra but not by the small elevational gradients in snowfall. As a result the maximum premelt SWE was found in the mid-elevation shrub tundra and was roughly double that of the sparse tundra or forest. Minimum variability of SWE was observed in the forest and shrub tundra (CV=0.25) while in the sparse tundra variability doubled (CV=0.5). Snowmelt was influenced by differences in premelt accumulation as well as differences in the net energy fluxes to snow. Elevation had a strong effect on the initiation of melt with the forest melt starting on average 16 days before the shrub tundra and 19 days before the sparse tundra. Mean melt rates showed a maximum in middle elevations and increased from 860 kJ/day in the forest to 1460 kJ/day in the sparse tundra and 2730 kJ/day in the shrub tundra. The forest canopy reduced melt while the shrub canopy enhanced it

  11. Ozone trends at northern mid- and high latitudes – a European perspective

    Directory of Open Access Journals (Sweden)

    N. R. P. Harris

    2008-05-01

    Full Text Available The EU CANDIDOZ project investigated the chemical and dynamical influences on decadal ozone trends focusing on the Northern Hemisphere. High quality long-term ozone data sets, satellite-based as well as ground-based, and the long-term meteorological reanalyses from ECMWF and NCEP are used together with advanced multiple regression models and atmospheric models to assess the relative roles of chemistry and transport in stratospheric ozone changes. This overall synthesis of the individual analyses in CANDIDOZ shows clearly one common feature in the NH mid latitudes and in the Arctic: an almost monotonic negative trend from the late 1970s to the mid 1990s followed by an increase. In most trend studies, the Equivalent Effective Stratospheric Chlorine (EESC which peaked in 1997 as a consequence of the Montreal Protocol was observed to describe ozone loss better than a simple linear trend. Furthermore, all individual analyses point to changes in dynamical drivers, such as the residual circulation (responsible for the meridional transport of ozone into middle and high latitudes playing a key role in the observed turnaround. The changes in ozone transport are associated with variations in polar chemical ozone loss via heterogeneous ozone chemistry on PSCs (polar stratospheric clouds. Synoptic scale processes as represented by the new equivalent latitude proxy, by conventional tropopause altitude or by 250 hPa geopotential height have also been successfully linked to the recent ozone increases in the lowermost stratosphere. These show significant regional variation with a large impact over Europe and seem to be linked to changes in tropospheric climate patterns such as the North Atlantic Oscillation. Some influence in recent ozone increases was also attributed to the rise in solar cycle number 23. Changes from the late 1970s to the mid 1990s were found in a number of characteristics of the Arctic vortex. However, only one trend was found when more recent

  12. A high-latitude, low-latitude boundary layer model of the convection current system

    International Nuclear Information System (INIS)

    Siscoe, G.L.; Lotko, W.; Sonnerup, B.U.O.

    1991-01-01

    Observations suggest that both the high- and low-latitude boundary layers contribute to magnetospheric convection, and that their contributions are linked. In the interpretation pursued here, the high-latitude boundary layer (HBL) generates the voltage while the low-latitude boundary layer (LBL) generates the current for the part of the convection electric circuit that closes through the ionosphere. This paper gives a model that joins the high- and low-latitude boundary layers consistently with the ionospheric Ohm's law. It describes an electric circuit linking both boundary layers, the region 1 Birkeland currents, and the ionospheric Pedersen closure currents. The model works by using the convection electric field that the ionosphere receives from the HBL to determine two boundary conditions to the equations that govern viscous LBL-ionosphere coupling. The result provides the needed self-consistent coupling between the two boundary layers and fully specifies the solution for the viscous LBL-ionosphere coupling equations. The solution shows that in providing the current required by the ionospheric Ohm's law, the LBL needs only a tenth of the voltage that spans the HBL. The solution also gives the latitude profiles of the ionospheric electric field, parallel currents, and parallel potential. It predicts that the plasma in the inner part of the LBL moves sunward instead of antisunward and that, as the transpolar potential decreases below about 40 kV, reverse polarity (region 0) currents appear at the poleward border of the region 1 currents. A possible problem with the model is its prediction of a thin boundary layer (∼1000 km), whereas thicknesses inferred from satellite data tend to be greater

  13. Global Hybrid Simulations of The Magnetopause Boundary Layers In Low- and High-latitude Magnetic Reconnections

    Science.gov (United States)

    Lin, Y.; Perez, J. D.

    A 2-D global hybrid simulation is carried out to study the structure of the dayside mag- netopause in the noon-midnight meridian plane associated with magnetic reconnec- tion. In the simulation the bow shock, magnetosheath, and magnetopause are formed self-consistently by supersonic solar wind passing the geomagnetic field. The recon- nection events at high- and low-latitudes are simulated for various IMF conditions. The following results will be presented. (1) Large-amplitude rotational discontinuities and Alfvén waves are present in the quasi-steady reconnection layer. (2) The rotational discontinuity possesses an electron sense, or right-hand polarization in the magnetic field as the discontinuity forms from the X line. Later, however, the rotational dis- continuity tends to evolve to a structure with a smallest field rotational angle and thus may reverse its sense of the field rotation. The Walén relation is tested for elec- tron and ion flows in the magnetopause rotational discontinuities with left-hand and right-hand polarizations. (3) The structure of the magnetopause discontinuities and that of the accelerated/decelerated flows are modified significantly by the presence of the local magnetosheath flow. (4) Field-aligned currents are generated in the magne- topause rotational discontinuities. Part of the magnetopause currents propagate with Alfvén waves along the field lines into the polar ionosphere, contributing to the field- aligned current system in the high latitudes. The generation of the parallel currents under northward and southward IMF conditions is investigated. (5) Finally, typical ion velocity distributions will be shown at various locations across the magnetopause northward and southward of the X lines. The ion distributions associated with single or multiple X lines will be discussed.

  14. Comparison of high-latitude thermospheric meridional winds II: combined FPI, radar and model climatologies

    Energy Technology Data Exchange (ETDEWEB)

    Griffin, E.M.; Aruliah, A.; Mueller-Wodarg, I.C.F.; Aylward, A. [Atmospheric Physics Lab., Univ. Coll. London, London (United Kingdom)

    2004-07-01

    The climatological behaviour of the thermospheric meridional wind above Kiruna, Sweden (67.4 N, 20.4 E) has been investigated for seasonal and solar cycle dependence using six different techniques, comprising both model and experimental sources. Model output from both the empirical Horizontal Wind Model (HWM) (Hedin et al., 1988) and the numerical coupled thermosphere and ionosphere model (CTIM) are compared to the measured behaviour at kiruna, as a single site example. The empirical International Reference Ionosphere (IRI) model is used as input to an implementation of servo theory, to provide another climatology combining empirical input with a theoretical framework. The experimental techniques have been introduced in a companion paper in this issue and provide climatologies from direct measurements, using fabry-perot interferometers (FPI), together with 2 separate techniques applied to the European incoherent scatter radar (EISCAT) database to derive neutral winds. One of these techniques uses the same implementation of servo theory as has been used with the IRI model. Detailed comparisons for each season and solar activity category allow for conclusions to be drawn as to the major influences on the climatological behaviour of the wind at this latitude. Comparison of the incoherent scatter radar (ISR) derived neutral winds with FPI, empirical model and numerical model winds is important to our understanding and judgement of the validity of the techniques used to derive thermospheric wind databases. The comparisons also test model performance and indicate possible reasons for differences found between the models. In turn, the conclusions point to possible improvements in their formulation. In particular it is found that the empirical models are over-reliant on mid-latitude data in their formulation, and fail to provide accurate estimates of the winds at high-latitudes. (orig.)

  15. Comparison of high-latitude thermospheric meridionalwinds II: combined FPI, radar and model Climatologies

    Directory of Open Access Journals (Sweden)

    E. M. Griffin

    2004-03-01

    Full Text Available The climatological behaviour of the thermospheric meridional wind above Kiruna, Sweden (67.4°N, 20.4°E has been investigated for seasonal and solar cycle dependence using six different techniques, comprising both model and experimental sources. Model output from both the empirical Horizontal Wind Model (HWM (Hedin et al., 1988 and the numerical Coupled Thermosphere and Ionosphere Model (CTIM are compared to the measured behaviour at Kiruna, as a single site example. The empirical International Reference Ionosphere (IRI model is used as input to an implementation of servo theory, to provide another climatology combining empirical input with a theoretical framework. The experimental techniques have been introduced in a companion paper in this issue and provide climatologies from direct measurements, using Fabry-Perot Interferometers (FPI, together with 2 separate techniques applied to the European Incoherent Scatter radar (EISCAT database to derive neutral winds. One of these techniques uses the same implementation of servo theory as has been used with the IRI model. Detailed comparisons for each season and solar activity category allow for conclusions to be drawn as to the major influences on the climatological behaviour of the wind at this latitude. Comparison of the incoherent scatter radar (ISR derived neutral winds with FPI, empirical model and numerical model winds is important to our understanding and judgement of the validity of the techniques used to derive thermospheric wind databases. The comparisons also test model performance and indicate possible reasons for differences found between the models. In turn, the conclusions point to possible improvements in their formulation. In particular it is found that the empirical models are over-reliant on mid-latitude data in their formulation, and fail to provide accurate estimates of the winds at high-latitudes.

    Key words. Meteorology and atmospheric dynamics (thermospheric dynamics

  16. Comparison of high-latitude thermospheric meridionalwinds II: combined FPI, radar and model Climatologies

    Directory of Open Access Journals (Sweden)

    E. M. Griffin

    2004-03-01

    Full Text Available The climatological behaviour of the thermospheric meridional wind above Kiruna, Sweden (67.4°N, 20.4°E has been investigated for seasonal and solar cycle dependence using six different techniques, comprising both model and experimental sources. Model output from both the empirical Horizontal Wind Model (HWM (Hedin et al., 1988 and the numerical Coupled Thermosphere and Ionosphere Model (CTIM are compared to the measured behaviour at Kiruna, as a single site example. The empirical International Reference Ionosphere (IRI model is used as input to an implementation of servo theory, to provide another climatology combining empirical input with a theoretical framework. The experimental techniques have been introduced in a companion paper in this issue and provide climatologies from direct measurements, using Fabry-Perot Interferometers (FPI, together with 2 separate techniques applied to the European Incoherent Scatter radar (EISCAT database to derive neutral winds. One of these techniques uses the same implementation of servo theory as has been used with the IRI model. Detailed comparisons for each season and solar activity category allow for conclusions to be drawn as to the major influences on the climatological behaviour of the wind at this latitude. Comparison of the incoherent scatter radar (ISR derived neutral winds with FPI, empirical model and numerical model winds is important to our understanding and judgement of the validity of the techniques used to derive thermospheric wind databases. The comparisons also test model performance and indicate possible reasons for differences found between the models. In turn, the conclusions point to possible improvements in their formulation. In particular it is found that the empirical models are over-reliant on mid-latitude data in their formulation, and fail to provide accurate estimates of the winds at high-latitudes. Key words. Meteorology and atmospheric dynamics (thermospheric dynamics

  17. Theoretical study of the high-latitude ionosphere's response to multicell convection patterns

    International Nuclear Information System (INIS)

    Sojka, J.J.; Schunk, R.W.

    1987-01-01

    It is well known that the convection electric fields have an important effect on the ionosphere at high latitudes and that a quantitative understanding of their effect requires a knowledge of the plasma convection pattern. When the interplanetary magnetic field (IMF) is southward, plasma convection at F region altitudes displays a two-cell pattern with antisunward flow over the polar cap and return flow at lower latitudes. However, when the IMF is northward, multiple convection cells can exist, with both sunward flow and auroral precipitation (theta aurora) in the polar cap. The characteristic ionospheric signatures associated with multicell convection patterns were studied with the aid of a three-dimensional time-dependent ionospheric model. Two-, three-, and four-cell patterns were considered and the ionosphere's response was calculated for the same cross-tail potential and for solar maximum and winter conditions in the northern hemisphere. As expected, there are major distinguishing ionospheric features associated with the different convection patterns, particularly in the polar cap. For two-cell convection the antisunward flow the plasma from the dayside into the polar cap. For two-cell convection the antisunward flow of plasma from the dayside into the polar cap acts to maintain the densities in this region in winter. For four-cell convection, on the other hand, the two aditional convection cells in the polar cap are in darkness most of the time, and the resulting O + decay acts to produce twin polar holes that are separated by a sun-aligned ridge of enhanced ionization due to theta aurora precipitation

  18. The excitation of plasma convection in the high-latitude ionosphere

    International Nuclear Information System (INIS)

    Lockwood, M.; Cowley, S.W.H.; Freeman, M.P.

    1990-01-01

    Recent observations of ionospheric flows by ground-based radars, in particular by the European Incoherent Scatter (EISCAT) facility using the Polar experiment, together with previous analyses of the response of geomagnetic disturbance to variations of the interplanetary magnetic field (IMF), suggest that convection in the high-latitude ionosphere should be considered to be the sum of two intrinsically time-dependent patterns, one driven by solar wind-magnetosphere coupling at the dayside magnetopause, the other by the release of energy in the geomagnetic tail (mainly by dayside and nightside reconnection, respectively). The flows driven by dayside coupling are largest on the dayside, where they usually dominate, are associated with an expanding polar cap area, and are excited and decay on ∼ 10-min time scales following southward and northward turnings of the IMF, respectively. The latter finding indicates that the production of new open flux at the dayside magnetopause excites magnetospheric and ionospheric flow only for a short interval, ∼ 10 min, such that the flow driven by this source subsequently decays on this time scale unless maintained by the production of more open flux tubes. Correspondingly, the flows excited by the release of energy in the tail, mainly during substorms, are largest on the nightside, are associated with a contracting polar cap boundary, and are excited on ∼ 1-hour time scales following a southward turn of the IMF. In general, the total ionospheric flow will be the sum of the flows produced by these two sources, such that due to their different response times to changes in the IMF, considerable variations in the flow pattern can occur for a given direction and strength ofthe IMF. Consequently, the ionospheric electric field cannot generally be regarded as arising from a simple mapping of the solar wind electric field along open flux tubes

  19. Seasonal patterns in the nocturnal distributionand behavior of the mesopelagic fish Maurolicus muelleri at high latitudes

    KAUST Repository

    Prihartato, Perdana

    2015-02-17

    Acoustic scattering layers (SL) ascribed to pearlside Maurolicus muelleri were studied in Masfjorden, Norway, using upward-looking echo sounders cabled to shore for continuous long-term measurements. The acoustic studies were accompanied by continuous measurements of surface light and supplemented with intermittent field campaigns. From autumn to spring, young M. muelleri formed an SL in the upper ∼75 to 150 m in the daytime, characterized by migration to near-surface water near dusk, subsequent \\'midnight sinking\\', followed by a dawn ascent before a return to the daytime habitat. Light levels were ∼1 order of magnitude lower during the dawn ascent than for ascent in the afternoon, with the latter terminating before fish reached upper layers on ∼1/3 of the nights from late November to mid-April. Adults showed less tendency of migration during autumn and winter, until the SLs of young and adults merged in late spring, and thereafter displayed coherent migration behavior. The midnight sinking became progressively deeper from autumn to winter but was strongly reduced from mid-May when the darkest nocturnal light intensity (PAR) at the surface was above 10-3 μmol m-2 s-1. The pearlside took on schooling in upper waters during the even lighter nights in early June, with minimum light of ∼5 × 10-3 to 10-1 μmol m-2 s-1 at the surface. Nocturnal schooling ceased in early July, and midnight sinking reappeared in mid-August. We suggest that the strong variation in nocturnal light intensity at high latitudes provides changing trade-offs between visual foraging and avoiding predators and hence varying time budgets for feeding in the upper, productive layers.

  20. Signature of rapid subauroral ion drifts in the high-latitude ionosphere structure

    International Nuclear Information System (INIS)

    Galperin, Y.I.; Khalipov, V.L.; Filippov, V.M.

    1986-01-01

    Characteristics of fast subauroral ion drifts were studied for several cases where synchronous satellite measurements and ground-based ionospheric data from vertical and oblique-incidence sounding were available. Also some relevant data were analyzed concerning apparent irregularities drift velocity measurements by the multipoint spaced receiver at HF range (DI method). Changes of high-latitude ionosphere structure were investigated to identify the signature on the ionograms, and to provide a semiquantitative description of this phenomenon. It is shown that, above a particular station, the time development of the rapid subauroral ion drift band, or the ''polarization jet'' according to Galperin et al., 1973, 1974 in about 5-30 minutes leads to the formation of a trough which is narrow in latitude (approximately 100-200 km) but extended in longitude (several hours of MLT) and rather deep (N sub(emin)approximately 2.10 4 cm -3 in the electron density distribution in the F-region. Such narrow troughs can be observed in the evening sector superimposed on the undisturbed ionization density level, while in the near-midnight sector they contribute to the deepening of the preexisting, and much wider, main ionospheric through A qualitative scenario for the formation of the ''trough in the trough'' on the nightside, as a result of the increase of the loss processes related to rapid drift speed, is supported by ''synthetic'' ionograms deduced from numerical ray-tracing calculations for a model electron density distribution that is in reasonable accord with the observed vertical and oblique sounding ionograms and from satellite data

  1. Coral bleaching on high-latitude marginal reefs at Sodwana Bay, South Africa

    Energy Technology Data Exchange (ETDEWEB)

    Celliers, Louis; Schleyer, Michael H

    2002-12-01

    Coral bleaching, involving the expulsion of symbiotic zooxanthellae from the host cells, poses a major threat to coral reefs throughout their distributional range. The role of temperature in coral bleaching has been extensively investigated and is widely accepted. A bleaching event was observed on the marginal high-latitude reefs of South Africa located at Sodwana Bay during the summer months of 2000. This was associated with increased sea temperatures with high seasonal peaks in summer and increased radiation in exceptionally clear water. The bleaching was limited to Two-mile Reef and Nine-mile Reef at Sodwana Bay and affected <12% of the total living cover on Two-mile Reef. Montipora spp., Alveopora spongiosa and Acropora spp. were bleached, as well as some Alcyoniidae (Sinularia dura, Lobophytum depressum, L. patulum). A cyclical increase in sea temperature (with a period of 5-6 years) was recorded during 1998-2000 in addition to the regional temperature increase caused by the El Nino Southern Oscillation phenomenon. The mean sea temperature increased at a rate of 0.27 deg. C year{sup -1} from May 1994 to April 2000. High maximum temperatures were measured (>29 deg. C). The lowest mean monthly and the mean maximum monthly temperatures at which coral bleaching occurred were 27.5 and 28.8 deg. C, respectively, while the duration for which high temperatures occurred in 2000 was 67 days at {>=}27.5 deg. C (4 days at {>=}28.8 deg. C). Increased water clarity and radiation appeared to be a synergistic cause in the coral bleaching encountered at Sodwana Bay.

  2. High-Latitude Wintertime Urban Pollution: Particulate Matter Composition and Temporal Trends in Fairbanks, Alaska

    Science.gov (United States)

    Simpson, W. R.; Nattinger, K.; Hooper, M.

    2017-12-01

    High latitude cities often experience severe pollution episodes during wintertime exacerbated by thermal inversion trapping of pollutant emissions. Fairbanks, Alaska is an extreme example of this problem, currently being classified by the US Environmental Protection Agency (EPA) as a "serious" non-attainment area for fine particulate matter (PM2.5). For this reason, we have studied the chemical composition of PM2.5 at multiple EPA monitoring sites in the non-attainment area from 2006 to the present. The chemical composition is dominated by organic carbon with lesser amounts of black carbon and inorganic ionic species such as ammonium, sulfate, and nitrate. We find large spatial differences in composition and amount of PM2.5 that indicate a different mix of sources in residential areas as compared to the city center. Specifically, the difference in composition is consistent with increased wood smoke source in the residential areas. The extent to which organic matter could be secondary (formed through conversion of emitted gases) is also an area needing study. Ammonium sulfate is responsible for about a fifth to a quarter of the particles mass during the darkest months, possibly indicating a non-photochemical source of sulfate, but the chemical mechanism for this possible transformation is unclear. Therefore, we quantified the relationship between particulate sulfate concentrations and gas-phase sulfur dioxide concentrations along with particulate metals and inferred particulate acidity with the hopes that these data can assist in elucidation of the mechanism of particulate sulfate formation. We also analyze temporal trends in PM2.5 composition in an attempt to understand how the problem is changing over time and find most trends are small despite regulatory changes. Improving mechanistic understanding of particulate formation under cold and dark conditions could assist in reducing air-quality-related health effects.

  3. Dawn song in natural and artificial continuous day: Light pollution affects songbirds at high latitudes.

    Science.gov (United States)

    Derryberry, Elizabeth P

    2017-10-01

    In Focus: Da Silva, A., & Kempenaers, B. (2017). Singing from North to South: Latitudinal variation in timing of dawn singing under natural and artificial light conditions. Journal of Animal Ecology, 86, 1286-1297. doi: 10.1111/1365-2656.12739 Satellite images of the world at night show bright dots connected by glowing lines crisscrossing the globe. As these connect-the-dots become brighter and expand into more and more remote regions, much of the flora and fauna of the world are experiencing evolutionarily unprecedented levels of light at night. Light cues are essential to most physiological and behavioural processes, and so the need to measure the effects of light pollution on these processes is critical. In this issue, Da Silva and Kempenaers take on this task using an important reproductive behaviour in songbirds-dawn song. The geographic, temporal and taxonomic breadth of sampling in this study allows for a close examination of a potentially complex interaction between light pollution and natural variation in the behaviour of dawn singing across latitude, season and species. Their extensive dataset highlights complexity in how songbirds respond to light pollution. Although light pollution has a strong effect on the timing of dawn song, not all songbirds respond the same way to light pollution, and the effects of light pollution vary with changes in natural light levels. Early dawn singers show more flexibility in the timing of dawn song across the season and across latitudes than late dawn singers, and also appear less affected by light pollution at high latitudes than are late dawn singers. These findings suggest that not all songbirds are responding to artificial continuous daylight as they do to natural continuous daylight, highlighting the general need to measure the fitness effects of light pollution. © 2017 The Author. Journal of Animal Ecology © 2017 British Ecological Society.

  4. Analysis of Wind Vorticity and Divergence in the High-latitude Lower Thermosphere: Dependence on the Interplanetary Magnetic Field (IMF

    Directory of Open Access Journals (Sweden)

    Young-Sil Kwak

    2008-12-01

    Full Text Available To better understand the physical processes that control the high-latitude lower thermospheric dynamics, we analyze the divergence and vorticity of the high-latitude neutral wind field in the lower thermosphere during the southern summertime for different IMF conditions. For this study the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEG CM is used. The analysis of the large-scale vorticity and divergence provides basic understanding flow configurations to help elucidate the momentum sources that ultimately determine the total wind field in the lower polar thermosphere and provides insight into the relative strengths of the different sources of momentum responsible for driving winds. The mean neutral wind pattern in the high-latitude lower thermosphere is dominated by rotational flow, imparted primarily through the ion drag force, rather than by divergent flow, imparted primarily through Joule and solar heating. The difference vorticity, obtained by subtracting values with zero IMF from those with non-zero IMF, in the high-latitude lower thermosphere is much larger than the difference divergence for all IMF conditions, indicating that a larger response of the thermospheric wind system to enhancement in the momentum input generating the rotational motion with elevated IMF than the corresponding energy input generating the divergent motion. the difference vorticity in the high-latitude lower thermosphere depends on the direction of the IMF. The difference vorticity for negative and positive B_y shows positive and negative, respectively, at higher magnetic latitudes than -70°. For negative B_z, the difference vorticities have positive in the dusk sector and negative in the dawn sector. The difference vorticities for positive B_z have opposite sign. Negative IMF B_z has a stronger effect on the vorticity than does positive B_z.

  5. The Effect of Elevated CO2 and Increased Temperature on in Vitro Fertilization Success and Initial Embryonic Development of Single Male:Female Crosses of Broad-Cast Spawning Corals at Mid- and High-Latitude Locations

    Directory of Open Access Journals (Sweden)

    Miriam Schutter

    2015-05-01

    Full Text Available The impact of global climate change on coral reefs is expected to be most profound at the sea surface, where fertilization and embryonic development of broadcast-spawning corals takes place. We examined the effect of increased temperature and elevated CO2 levels on the in vitro fertilization success and initial embryonic development of broadcast-spawning corals using a single male:female cross of three different species from mid- and high-latitude locations: Lyudao, Taiwan (22° N and Kochi, Japan (32° N. Eggs were fertilized under ambient conditions (27 °C and 500 μatm CO2 and under conditions predicted for 2100 (IPCC worst case scenario, 31 °C and 1000 μatm CO2. Fertilization success, abnormal development and early developmental success were determined for each sample. Increased temperature had a more profound influence than elevated CO2. In most cases, near-future warming caused a significant drop in early developmental success as a result of decreased fertilization success and/or increased abnormal development. The embryonic development of the male:female cross of A. hyacinthus from the high-latitude location was more sensitive to the increased temperature (+4 °C than the male:female cross of A. hyacinthus from the mid-latitude location. The response to the elevated CO2 level was small and highly variable, ranging from positive to negative responses. These results suggest that global warming is a more significant and universal stressor than ocean acidification on the early embryonic development of corals from mid- and high-latitude locations.

  6. Land Cover Mapping in Northern High Latitude Permafrost Regions with Satellite Data: Achievements and Remaining Challenges

    Directory of Open Access Journals (Sweden)

    Annett Bartsch

    2016-11-01

    resolution around 30 m has been shown to be suitable for a range of applications. This implies that the current Landsat-8, as well as Sentinel-2 missions would be adequate as input data. Recent studies have exemplified the value of Synthetic Aperture Radar (SAR in tundra regions. SAR missions may be therefore of added value for large-scale high latitude land cover mapping.

  7. Statistical properties of Joule heating rate, electric field and conductances at high latitudes

    Directory of Open Access Journals (Sweden)

    A. T. Aikio

    2009-07-01

    Full Text Available Statistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat from 6 March to 6 April 2006. The data are from the same season (close to vernal equinox and from similar sunspot conditions (about 1.5 years before the sunspot minimum providing an excellent set of data to study the MLT and Kp dependence of parameters with high temporal and spatial resolution.

    All the parameters show a clear MLT variation, which is different for low and high Kp conditions. Our results indicate that the response of morning sector conductances and conductance ratios to increased magnetic activity is stronger than that of the evening sector. The co-location of Pedersen conductance maximum and electric field maximum in the morning sector produces the largest Joule heating rates 03–05 MLT for Kp≥3. In the evening sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in the nightside are statistically observed at 23 MLT, which is the location of the electric Harang discontinuity.

    An important outcome of the paper are the fitted functions for the Joule heating rate as a function of electric field magnitude, separately for four MLT sectors and two activity levels (Kp<3 and Kp≥3. In addition to the squared electric field, the fit includes a linear term to study the possible anticorrelation or correlation between electric field and conductance. In the midday sector, positive correlation is found as well as in the morning sector for the high activity case. In the midnight and evening sectors, anticorrelation between electric field and conductance is obtained, i.e. high electric fields are associated with low conductances. This is expected to occur in the return current regions adjacent to

  8. An automated approach for mapping persistent ice and snow cover over high latitude regions

    Science.gov (United States)

    Selkowitz, David J.; Forster, Richard R.

    2016-01-01

    We developed an automated approach for mapping persistent ice and snow cover (glaciers and perennial snowfields) from Landsat TM and ETM+ data across a variety of topography, glacier types, and climatic conditions at high latitudes (above ~65°N). Our approach exploits all available Landsat scenes acquired during the late summer (1 August–15 September) over a multi-year period and employs an automated cloud masking algorithm optimized for snow and ice covered mountainous environments. Pixels from individual Landsat scenes were classified as snow/ice covered or snow/ice free based on the Normalized Difference Snow Index (NDSI), and pixels consistently identified as snow/ice covered over a five-year period were classified as persistent ice and snow cover. The same NDSI and ratio of snow/ice-covered days to total days thresholds applied consistently across eight study regions resulted in persistent ice and snow cover maps that agreed closely in most areas with glacier area mapped for the Randolph Glacier Inventory (RGI), with a mean accuracy (agreement with the RGI) of 0.96, a mean precision (user’s accuracy of the snow/ice cover class) of 0.92, a mean recall (producer’s accuracy of the snow/ice cover class) of 0.86, and a mean F-score (a measure that considers both precision and recall) of 0.88. We also compared results from our approach to glacier area mapped from high spatial resolution imagery at four study regions and found similar results. Accuracy was lowest in regions with substantial areas of debris-covered glacier ice, suggesting that manual editing would still be required in these regions to achieve reasonable results. The similarity of our results to those from the RGI as well as glacier area mapped from high spatial resolution imagery suggests it should be possible to apply this approach across large regions to produce updated 30-m resolution maps of persistent ice and snow cover. In the short term, automated PISC maps can be used to rapidly

  9. Statistical properties of Joule heating rate, electric field and conductances at high latitudes

    Directory of Open Access Journals (Sweden)

    A. T. Aikio

    2009-07-01

    Full Text Available Statistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat from 6 March to 6 April 2006. The data are from the same season (close to vernal equinox and from similar sunspot conditions (about 1.5 years before the sunspot minimum providing an excellent set of data to study the MLT and Kp dependence of parameters with high temporal and spatial resolution. All the parameters show a clear MLT variation, which is different for low and high Kp conditions. Our results indicate that the response of morning sector conductances and conductance ratios to increased magnetic activity is stronger than that of the evening sector. The co-location of Pedersen conductance maximum and electric field maximum in the morning sector produces the largest Joule heating rates 03–05 MLT for Kp≥3. In the evening sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in the nightside are statistically observed at 23 MLT, which is the location of the electric Harang discontinuity. An important outcome of the paper are the fitted functions for the Joule heating rate as a function of electric field magnitude, separately for four MLT sectors and two activity levels (Kp<3 and Kp≥3. In addition to the squared electric field, the fit includes a linear term to study the possible anticorrelation or correlation between electric field and conductance. In the midday sector, positive correlation is found as well as in the morning sector for the high activity case. In the midnight and evening sectors, anticorrelation between electric field and conductance is obtained, i.e. high electric fields are associated with low conductances. This is expected to occur in the return current regions adjacent to auroral arcs as a result of ionosphere-magnetosphere coupling, as discussed by Aikio et al. (2004 In

  10. High-latitude electromagnetic and particle energy flux during an event with sustained strongly northward IMF

    Directory of Open Access Journals (Sweden)

    H. Korth

    2005-06-01

    Full Text Available We present a case study of a prolonged interval of strongly northward orientation of the interplanetary magnetic field on 16 July 2000, 16:00-19:00 UT to characterize the energy exchange between the magnetosphere and ionosphere for conditions associated with minimum solar wind-magnetosphere coupling. With reconnection occurring tailward of the cusp under northward IMF conditions, the reconnection dynamo should be separated from the viscous dynamo, presumably driven by the Kelvin-Helmholtz (KH instability. Thus, these conditions are also ideal for evaluating the contribution of a viscous interaction to the coupling process. We derive the two-dimensional distribution of the Poynting vector radial component in the northern sunlit polar ionosphere from magnetic field observations by the constellation of Iridium satellites together with drift meter and magnetometer observations from the Defense Meteorological Satellite Program (DMSP F13 and F15 satellites. The electromagnetic energy flux is then compared with the particle energy flux obtained from auroral images taken by the far-ultraviolet (FUV instrument on the Imager for Magnetopause to Aurora Global Exploration (IMAGE spacecraft. The electromagnetic energy input to the ionosphere of 51 GW calculated from the Iridium/DMSP observations is eight times larger than the 6 GW due to particle precipitation all poleward of 78° MLAT. This result indicates that the energy transport is significant, particularly as it is concentrated in a small region near the magnetic pole, even under conditions traditionally considered to be quiet and is dominated by the electromagnetic flux. We estimate the contributions of the high and mid-latitude dynamos to both the Birkeland currents and electric potentials finding that high-latitude reconnection accounts for 0.8 MA and 45kV while we attribute <0.2MA and ~5kV to an interaction at lower latitudes having the sense of a viscous interaction. Given that these

  11. Strong signatures of high-latitude blocks and subtropical ridges in winter PM10 over Europe

    Science.gov (United States)

    Ordonez, C.; Garrido-Perez, J. M.; Garcia-Herrera, R.

    2017-12-01

    Atmospheric blocking is associated with persistent, slow-moving high pressure systems that interrupt the eastward progress of extratropical storm systems at middle and high latitudes. Subtropical ridges are low latitude structures manifested as bands of positive geopotential height anomalies extending from sub-tropical latitudes towards extra-tropical regions. We have quantified the impact of blocks and ridges on daily PM10 (particulate matter ≤ 10 µm) observations obtained from the European Environment Agency's air quality database (AirBase) for the winter period of 2000-2010. For this purpose, the response of the PM10 concentrations to the location of blocks and ridges with centres in two main longitudinal sectors (Atlantic, ATL, 30˚-0˚ W; European, EUR, 0˚-30˚ E) is examined. EUR blocking is associated with a collapse of the boundary layer as well as reduced wind speeds and precipitation occurrence, yielding large positive anomalies which average 12 µg m-3 over the whole continent. Conversely, the enhanced zonal flow around 50˚-60˚ N and the increased occurrence of precipitation over northern-central Europe on days with ATL ridges favour the ventilation of the boundary layer and the impact of washout processes, reducing PM10 concentrations on average by around 8 µg m-3. The presence of EUR blocks is also concurrent with an increased probability of exceeding the European air quality target (50 µg m-3 for 24-h averaged PM10) and the local 90th percentiles for this pollutant at many sites, while the opposite effect is found for ridges. In addition, the effect of synoptic persistence on the PM10 concentrations is particularly strong for EUR blocks. Finally, we have found that the effect of both synoptic patterns can partly control the interannual variability of winter mean PM10 at many sites of north-western and central Europe, with coefficients of determination (R2) exceeding 0.80 for southern Germany. These results indicate that the response of the

  12. Emergent Behavior of Arctic Precipitation in Response to Enhanced Arctic Warming

    Science.gov (United States)

    Anderson, Bruce T.; Feldl, Nicole; Lintner, Benjamin R.

    2018-03-01

    Amplified warming of the high latitudes in response to human-induced emissions of greenhouse gases has already been observed in the historical record and is a robust feature evident across a hierarchy of model systems, including the models of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The main aims of this analysis are to quantify intermodel differences in the Arctic amplification (AA) of the global warming signal in CMIP5 RCP8.5 (Representative Concentration Pathway 8.5) simulations and to diagnose these differences in the context of the energy and water cycles of the region. This diagnosis reveals an emergent behavior between the energetic and hydrometeorological responses of the Arctic to warming: in particular, enhanced AA and its associated reduction in dry static energy convergence is balanced to first order by latent heating via enhanced precipitation. This balance necessitates increasing Arctic precipitation with increasing AA while at the same time constraining the magnitude of that precipitation increase. The sensitivity of the increase, 1.25 (W/m2)/K ( 240 (km3/yr)/K), is evident across a broad range of historical and projected AA values. Accounting for the energetic constraint on Arctic precipitation, as a function of AA, in turn informs understanding of both the sign and magnitude of hydrologic cycle changes that the Arctic may experience.

  13. 26-Day Variations of 7 MeV Electrons at high Latitudes and their Implications on the Heliospheric Magnetic Field

    Science.gov (United States)

    Sternal, Oliver; Engelbrecht, Eugene; Burger, Renier; Dunzlaff, Phillip; Ferreira, Stefan; Fichtner, Horst; Heber, Bernd; Kopp, Andreas; Potgieter, Marius; Scherer, Klaus

    The transport of energetic particles in the heliosphere is usually described by the Parker trans-port equation including the physical processes of diffusion, drift, convection and adiabatic energy changes. The Ulysses spacecraft provides unique insight into the flux of MeV electrons at high latitudes. In this contribution, we compare our model results for the Parker HMF model and the Fisk-type Schwadron-Parker HMF model to Ulysses measurements. The elec-tron flux at high latitudes has been used as a remote sensing method to investigate the imprint of a Fisk-type HMF. We show here for the first time that such an imprint exists and deduce a limitation on the Fisk HMF angle β.

  14. Shallow food for deep divers: Dynamic foraging behavior of male sperm whales in a high latitude habitat

    DEFF Research Database (Denmark)

    Teloni, Valeria; Johnson, M.P.; Miller, P.J.O.

    2008-01-01

    Groups of female and immature sperm whales live at low latitudes and show a stereotypical diving and foraging behavior with dives lasting about 45 min to depths of between 400 and 1200 m. In comparison, physically mature male sperm whales migrate to high latitudes where little is known about...... their foraging behavior and ecology. Here we use acoustic recording tags to study the diving and acoustic behavior of male sperm whales foraging off northern Norway. Sixty-five hours of tag data provide detailed information about the movements and sound repertoire of four male sperm whales performing 83 dives...... epipelagic prey, is consistent with the hypothesis that male sperm whales may migrate to high latitudes to access a productive, multi-layered foraging habitat....

  15. Recent Intensified Winter Coldness in the Mid-High Latitudes of Eurasia and Its Relationship with Daily Extreme Low Temperature Variability

    Directory of Open Access Journals (Sweden)

    Chuhan Lu

    2016-01-01

    Full Text Available Observational records in recent decades show a large-scale decrease in the cold-season temperature variance in the Northern Hemisphere midlatitudes under continuous global warming. However, severe low temperature events in winter frequently occurred in midlatitude Eurasia (MEA in the last decade. Here, we define a new coldness intensity (CI index for the near-surface based on the amplitude of daily anomalously cold temperatures in winter to demonstrate the CI of the variability of low temperature extremes. The results show that a sign-consistent mode dominates the CI variation in MEA, with a marked intensification during the last decade via empirical orthogonal function (EOF analysis. This leading mode is significantly related to the frequency of winter extreme events. The associated circulations are characterized by a remarkable anomalous anticyclone in Northwest Eurasia, which induced substantial cold advection in MEA. The widespread intensified CI in MEA is closely linked with strong surface anticyclones and synoptic blocking in the mid-high latitudes (25°E–85°E. Coincidently, positive phase shifts of the first two leading modes of the extratropical circulation, which feature similar blocking-like anomalies in the northwestern Eurasian subarctic, jointly play an important role in the recent frequency of severe winters.

  16. Large-scale traveling ionospheric disturbances observed using GPS receivers over high-latitude and equatorial regions

    Science.gov (United States)

    Idrus, Intan Izafina; Abdullah, Mardina; Hasbi, Alina Marie; Husin, Asnawi; Yatim, Baharuddin

    2013-09-01

    This paper presents the first results of large-scale traveling ionospheric disturbances (LSTIDs) observation during two moderate magnetic storm events on 28 May 2011 (SYM-H∼ -94 nT and Dst∼-80 nT) and 6 August 2011 (SYM-H∼-126 nT and Dst∼-113 nT) over the high-latitude region in Russia, Sweden, Norway, Iceland and Greenland and equatorial region in the Peninsular Malaysia using vertical total electron content (VTEC) from the Global Positioning System (GPS) observations measurement. The propagation of the LSTID signatures in the GPS TEC measurements over Peninsular Malaysia was also investigated using VTEC map. The LSTIDs were found to propagate both equatorward and poleward directions during these two events. The results showed that the LSTIDs propagated faster at high-latitude region with an average phase velocity of 1074.91 m/s than Peninsular Malaysia with an average phase velocity of 604.84 m/s. The LSTIDs at the high-latitude region have average periods of 150 min whereas the ones observed over Peninsular Malaysia have average periods of 115 min. The occurrences of these LSTIDs were also found to be the subsequent effects of substorm activities in the auroral region. To our knowledge, this is the first result of observation of LSTIDs over Peninsular Malaysia during the 24th solar cycle.

  17. In Situ Balloon-Borne Ice Particle Imaging in High-Latitude Cirrus

    Science.gov (United States)

    Kuhn, Thomas; Heymsfield, Andrew J.

    2016-09-01

    Cirrus clouds reflect incoming solar radiation, creating a cooling effect. At the same time, these clouds absorb the infrared radiation from the Earth, creating a greenhouse effect. The net effect, crucial for radiative transfer, depends on the cirrus microphysical properties, such as particle size distributions and particle shapes. Knowledge of these cloud properties is also needed for calibrating and validating passive and active remote sensors. Ice particles of sizes below 100 µm are inherently difficult to measure with aircraft-mounted probes due to issues with resolution, sizing, and size-dependent sampling volume. Furthermore, artefacts are produced by shattering of particles on the leading surfaces of the aircraft probes when particles several hundred microns or larger are present. Here, we report on a series of balloon-borne in situ measurements that were carried out at a high-latitude location, Kiruna in northern Sweden (68N 21E). The method used here avoids these issues experienced with the aircraft probes. Furthermore, with a balloon-borne instrument, data are collected as vertical profiles, more useful for calibrating or evaluating remote sensing measurements than data collected along horizontal traverses. Particles are collected on an oil-coated film at a sampling speed given directly by the ascending rate of the balloon, 4 m s-1. The collecting film is advanced uniformly inside the instrument so that an always unused section of the film is exposed to ice particles, which are measured by imaging shortly after sampling. The high optical resolution of about 4 µm together with a pixel resolution of 1.65 µm allows particle detection at sizes of 10 µm and larger. For particles that are 20 µm (12 pixel) in size or larger, the shape can be recognized. The sampling volume, 130 cm3 s-1, is well defined and independent of particle size. With the encountered number concentrations of between 4 and 400 L-1, this required about 90- to 4-s sampling times to

  18. On the influence of shrub height and expansion on northern high latitude climate

    International Nuclear Information System (INIS)

    Bonfils, C J W; Phillips, T J; Cameron-Smith, P; Lawrence, D M; Riley, W J; Subin, Z M

    2012-01-01

    There is a growing body of empirical evidence documenting the expansion of shrub vegetation in the circumpolar Arctic in response to climate change. Here, we conduct a series of idealized experiments with the Community Climate System Model to analyze the potential impact on boreal climate of a large-scale tundra-to-shrub conversion. The model responds to an increase in shrub abundance with substantial atmospheric heating arising from two seasonal land–atmosphere feedbacks: a decrease in surface albedo and an evapotranspiration-induced increase in atmospheric moisture content. We demonstrate that the strength and timing of these feedbacks are sensitive to shrub height and the time at which branches and leaves protrude above the snow. Taller and aerodynamically rougher shrubs lower the albedo earlier in the spring and transpire more efficiently than shorter shrubs. These mechanisms increase, in turn, the strength of the indirect sea-ice albedo and ocean evaporation feedbacks contributing to additional regional warming. Finally, we find that an invasion of tall shrubs tends to systematically warm the soil, deepen the active layer, and destabilize the permafrost (with increased formation of taliks under a future scenario) more substantially than an invasion of short shrubs. (letter)

  19. High-latitude plasma convection during Northward IMF as derived from in-situ magnetospheric Cluster EDI measurements

    Directory of Open Access Journals (Sweden)

    M. Förster

    2008-09-01

    Full Text Available In this study, we investigate statistical, systematic variations of the high-latitude convection cell structure during northward IMF. Using 1-min-averages of Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for six and a half years (February 2001 till July 2007, and mapping the spatially distributed measurements to a common reference plane at ionospheric level in a magnetic latitude/MLT grid, we obtained regular drift patterns according to the various IMF conditions. We focus on the particular conditions during northward IMF, where lobe cells at magnetic latitudes >80° with opposite (sunward convection over the central polar cap are a permanent feature in addition to the main convection cells at lower latitudes. They are due to reconnection processes at the magnetopause boundary poleward of the cusp regions. Mapped EDI data have a particular good coverage within the central part of the polar cap, so that these patterns and their dependence on various solar wind conditions are well verified in a statistical sense. On average, 4-cell convection pattern are shown as regular structures during periods of nearly northward IMF with the tendency of a small shift toward negative clock angles. The positions of these high-latitude convection foci are within 79° to 85° magnetic latitude and 09:00–15:00 MLT. The MLT positions are approximately symmetric ±2 h about 11:30 MLT, i.e. slightly offset from midday toward prenoon hours, while the maximum (minimum potential of the high-latitude cells is at higher magnetic latitudes near their maximum potential difference at ≈−10° to −15° clock angle for the North (South Hemisphere. With increasing clock angle distances from ≈IMFBz+, a gradual transition occurs from the 4-cell pattern via a 3-cell to the common 2-cell convection pattern, in the course of which one of the medium-scale high-latitude dayside cells diminishes and disappears while the

  20. Amplified Policymaking

    Science.gov (United States)

    Prince, Katherine; Woempner, Carolyn

    2010-01-01

    This brief examines the policy implications of two drivers of change presented in the "2020 Forecast: Creating the Future of Learning"-- Pattern Recognition and Amplified Organization. These drivers point toward a series of cultural shifts and illuminate how we are developing new ways of organizing, constructing, and managing knowledge.…

  1. High-Latitude Topside Ionospheric Vertical Electron-Density-Profile Changes in Response to Large Magnetic Storms

    Science.gov (United States)

    Benson, Robert F.; Fainberg, Joseph; Osherovich, Vladimir A.; Truhlik, Vladimir; Wang, Yongli; Bilitza, Dieter; Fung, Shing F.

    2015-01-01

    Large magnetic-storm induced changes have been detected in high-latitude topside vertical electron-density profiles Ne(h). The investigation was based on the large database of topside Ne(h) profiles and digital topside ionograms from the International Satellites for Ionospheric Studies (ISIS) program available from the NASA Space Physics Data Facility (SPDF) at http://spdf.gsfc.nasa.gov/isis/isis-status.html. This large database enabled Ne(h) profiles to be obtained when an ISIS satellite passed through nearly the same region of space before, during, and after a major magnetic storm. A major goal was to relate the magnetic-storm induced high-latitude Ne(h) profile changes to solar-wind parameters. Thus an additional data constraint was to consider only storms where solar-wind data were available from the NASA/SPDF OMNIWeb database. Ten large magnetic storms (with Dst less than -100 nT) were identified that satisfied both the Ne(h) profile and the solar-wind data constraints. During five of these storms topside ionospheric Ne(h) profiles were available in the high-latitude northern hemisphere and during the other five storms similar ionospheric data were available in the southern hemisphere. Large Ne(h) changes were observed during each one of these storms. Our concentration in this paper is on the northern hemisphere. The data coverage was best for the northern-hemisphere winter. Here Ne(h) profile enhancements were always observed when the magnetic local time (MLT) was between 00 and 03 and Ne(h) profile depletions were always observed between 08 and 10 MLT. The observed Ne(h) deviations were compared with solar-wind parameters, with appropriate time shifts, for four storms.

  2. Effects of high latitude protected areas on bird communities under rapid climate change.

    Science.gov (United States)

    Santangeli, Andrea; Rajasärkkä, Ari; Lehikoinen, Aleksi

    2017-06-01

    Anthropogenic climate change is rapidly becoming one of the main threats to biodiversity, along with other threats triggered by human-driven land-use change. Species are already responding to climate change by shifting their distributions polewards. This shift may create a spatial mismatch between dynamic species distributions and static protected areas (PAs). As protected areas represent one of the main pillars for preserving biodiversity today and in the future, it is important to assess their contribution in sheltering the biodiversity communities, they were designated to protect. A recent development to investigate climate-driven impacts on biological communities is represented by the community temperature index (CTI). CTI provides a measure of the relative temperature average of a community in a specific assemblage. CTI value will be higher for assemblages dominated by warm species compared with those dominated by cold-dwelling species. We here model changes in the CTI of Finnish bird assemblages, as well as changes in species densities, within and outside of PAs during the past four decades in a large boreal landscape under rapid change. We show that CTI has markedly increased over time across Finland, with this change being similar within and outside PAs and five to seven times slower than the temperature increase. Moreover, CTI has been constantly lower within than outside of PAs, and PAs still support communities, which show colder thermal index than those outside of PAs in the 1970s and 1980s. This result can be explained by the higher relative density of northern species within PAs than outside. Overall, our results provide some, albeit inconclusive, evidence that PAs may play a role in supporting the community of northern species. Results also suggest that communities are, however, shifting rapidly, both inside and outside of PAs, highlighting the need for adjusting conservation measures before it is too late. © 2016 John Wiley & Sons Ltd.

  3. Winter warming from large volcanic eruptions

    Science.gov (United States)

    Robock, Alan; Mao, Jianping

    1992-01-01

    An examination of the Northern Hemisphere winter surface temperature patterns after the 12 largest volcanic eruptions from 1883-1992 shows warming over Eurasia and North America and cooling over the Middle East which are significant at the 95-percent level. This pattern is found in the first winter after tropical eruptions, in the first or second winter after midlatitude eruptions, and in the second winter after high latitude eruptions. The effects are independent of the hemisphere of the volcanoes. An enhanced zonal wind driven by heating of the tropical stratosphere by the volcanic aerosols is responsible for the regions of warming, while the cooling is caused by blocking of incoming sunlight.

  4. Statistics of high-altitude and high-latitude O+ ion outflows observed by Cluster/CIS

    Directory of Open Access Journals (Sweden)

    A. Korth

    2005-07-01

    Full Text Available The persistent outflows of O+ ions observed by the Cluster CIS/CODIF instrument were studied statistically in the high-altitude (from 3 up to 11 RE and high-latitude (from 70 to ~90 deg invariant latitude, ILAT polar region. The principal results are: (1 Outflowing O+ ions with more than 1keV are observed above 10 RE geocentric distance and above 85deg ILAT location; (2 at 6-8 RE geocentric distance, the latitudinal distribution of O+ ion outflow is consistent with velocity filter dispersion from a source equatorward and below the spacecraft (e.g. the cusp/cleft; (3 however, at 8-12 RE geocentric distance the distribution of O+ outflows cannot be explained by velocity filter only. The results suggest that additional energization or acceleration processes for outflowing O+ ions occur at high altitudes and high latitudes in the dayside polar region. Keywords. Magnetospheric physics (Magnetospheric configuration and dynamics, Solar wind-magnetosphere interactions

  5. High-latitude dayside electric fields and currents during strong northward interplanetary magnetic field: Observations and model simulation

    International Nuclear Information System (INIS)

    Clauer, C.R.; Friis-Christensen, E.

    1988-01-01

    On July 23, 1983, the Interplanetary Magnetic Field turned strongly northward, becoming about 22 nT for several hours. Using a combined data set of ionospheric convection measurements made by the Sondre Stromfjord incoherent scatter radar and convection inferred from Greenland magnetometer measurements, we observe the onset of the reconfiguration of the high-latitude ionospheric currents to occur about 3 min following the northward IMF encountering the magnetopause. The large-scale reconfiguration of currents, however, appears to evolve over a period of about 22 min. Using a computer model in which the distribution of field-aligned current in the polar cleft is directly determined by the strength and orientation of the interplanetary electric field, we are able to simulate the time-varying pattern of ionospheric convection, including the onset of high-latitude ''reversed convection'' cells observed to form during the interval of strong northward IMF. These observations and the simulation results indicate that the dayside polar cap electric field observed during strong northward IMF is produced by a direct electrical current coupling with the solar wind. copyright American Geophysical Union 1988

  6. The Deep Space Gateway Lightning Mapper (DLM) — Monitoring Global Change and Thunderstorm Processes through Observations of Earth's High-Latitude Lightning from Cis-Lunar Orbit

    Science.gov (United States)

    Lang, T. J.; Blakeslee, R. J.; Cecil, D. J.; Christian, H. J.; Gatlin, P. N.; Goodman, S. J.; Koshak, W. J.; Petersen, W. A.; Quick, M.; Schultz, C. J.; Tatum, P. F.

    2018-02-01

    We propose the Deep Space Gateway Lightning Mapper (DLM) instrument. The primary goal of the DLM is to optically monitor Earth's high-latitude (50° and poleward) total lightning not observed by current and planned spaceborne lightning mappers.

  7. The Deep Space Gateway Lightning Mapper (DLM) - Monitoring Global Change and Thunderstorm Processes Through Observations of Earth's High-Latitude Lightning from Cis-Lunar Orbit

    Science.gov (United States)

    Lang, Timothy; Blakeslee, R. J.; Cecil, D. J.; Christian, H. J.; Gatlin, P. N.; Goodman, S. J.; Koshak, W. J.; Petersen, W. A.; Quick, M.; Schultz, C. J.; hide

    2018-01-01

    Function: Monitor global change and thunderstorm processes through observations of Earth's high-latitude lightning. This instrument will combine long-lived sampling of individual thunderstorms with long-term observations of lightning at high latitudes: How is global change affecting thunderstorm patterns; How do high-latitude thunderstorms differ from low-latitude? Why is the Gateway the optimal facility for this instrument / research: Expected DSG (Deep Space Gateway) orbits will provide nearly continuous viewing of the Earth's high latitudes (50 degrees latitude and poleward); These regions are not well covered by existing lightning mappers (e.g., Lightning Imaging Sensor / LIS, or Geostationary Lightning Mapper / GLM); Polar, Molniya, Tundra, etc. Earth orbits have significant drawbacks related to continuous coverage and/or stable FOVs (Fields of View).

  8. Simulated high-latitude soil thermal dynamics during the past four decades

    Science.gov (United States)

    Peng, S.; Ciais, P.; Wang, T.; Gouttevin, I.; McGuire, A.D.; Lawrence, D.; Burke, E.; Chen, X.; Delire, C.; Koven, C.; MacDougall, A.; Rinke, A.; Saito, K.; Zhang, W.; Alkama, R.; Bohn, T. J.; Decharme, B.; Hajima, T.; Ji, D.; Lettenmaier, D.P.; Miller, P.A.; Moore, J.C.; Smith, B.; Sueyoshi, T.

    2015-01-01

    Soil temperature (Ts ) change is a key indicator of the dynamics of permafrost. On seasonal and inter-annual time scales, the variability of Ts determines the active layer depth, which regulates hydrological soil properties and biogeochemical processes. On the multi-decadal scale, increasing T 5 s not only drives permafrost thaw/retreat, but can also trigger and accelerate the decomposition of soil organic carbon. The magnitude of permafrost carbon feedbacks is thus closely linked to the rate of change of soil thermal regimes. In this study, we used nine process-based ecosystem models with permafrost processes, all forced by different observation-based climate forcing during the period 1960–2000, to characterize the warming rate of Ts 10 in permafrost regions. There is a large spread of Ts trends at 20 cm depth across the models, with trend values ranging from 0.010 ± 0.003 to 0.031 ± 0.005 ◦C yr−1 . Most models show smaller increase in Ts with increasing depth. Air temperature (Ta ) and longwave downward radiation (LWDR) are the main drivers of Ts trends, but their relative contributions differ 15 amongst the models. Different trends of LWDR used in the forcing of models can explain 61 % of their differences in Ts trends, while trends of Ta only explain 5 % of the differences in Ts trends. Uncertain climate forcing contributes a larger uncertainty in Ts trends (0.021 ± 0.008 ◦C yr−1 , mean ± SD) than the uncertainty of model structure (0.012 ± 0.001 ◦C yr−1 ), diagnosed from the range of response between different mod- 20 els, normalized to the same forcing. In addition, the loss rate of near-surface permafrost area, defined as total area where the maximum seasonal active layer thickness (ALT) is less than 3 m loss rate is found to be significantly correlated with the magnitude of the trends of Ts at 1 m depth across the models (R = −0.85, P = 0.003), but not with the initial total near-surface permafrost area (R = −0.30, P = 0.438). The

  9. A Study on the Ionosphere and Thermosphere Interaction Based on NCAR-TIEGCM: Dependence of the Interplanetary Magnetic Field (IMF on the Momentum Forcing in the High-Latitude Lower Thermosphere

    Directory of Open Access Journals (Sweden)

    Young-Sil Kwak

    2005-06-01

    Full Text Available To understand the physical processes that control the high-latitude lower thermospheric dynamics, we quantify the forces that are mainly responsible for maintaining the high-latitude lower thermospheric wind system with the aid of the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM. Momentum forcing is statistically analyzed in magnetic coordinates, and its behavior with respect to the magnitude and orientation of the interplanetary magnetic field (IMF is further examined. By subtracting the values with zero IMF from those with non-zero IMF, we obtained the difference winds and forces in the high-latitude lower thermosphere( 0.8 |bar{B}_z| or negative(B_y 0.3125 |bar{B}_y| or negative(B_z 125 km the primary forces that determine the variations of the neutral winds are the pressure gradient, Coriolis and rotational Pedersen ion drag forces; however, at various locations and times significant contributions can be made by the horizontal advection force. On the other hand, at lower altitudes(108-125 km the pressure gradient, Coriolis and non-rotational Hall ion drag forces determine the variations of the neutral winds. At lower altitudes(<108 km it tends to generate a geostrophic motion with the balance between the pressure gradient and Coriolis forces. The northward component of IMF bar{B}_y-dependent average momentum forces act more significantly on the neutral motion except for the ion drag. At lower altitudes(108-125 km for negative IMF-bar{B}_y condition the ion drag force tends to generate a warm clockwise circulation with downward vertical motion associated with the adiabatic compress heating in the polar cap region. For positive IMF-bar{B}_y condition it tends to generate a cold anticlockwise circulation with upward vertical motion associated with the adiabatic expansion cooling in the polar cap region. For negative IMF-bar{B}_z the ion drag force tends to generate a

  10. Ground-based and satellite observations of high-latitude auroral activity in the dusk sector of the auroral oval

    Directory of Open Access Journals (Sweden)

    K. Kauristie

    Full Text Available On 7 December 2000, during 13:30–15:30 UT the MIRACLE all-sky camera at Ny Ålesund observed auroras at high-latitudes (MLAT ~ 76 simultaneously when the Cluster spacecraft were skimming the magnetopause in the same MLT sector (at ~ 16:00–18:00 MLT. The location of the auroras (near the ionospheric convection reversal boundary and the clear correlation between their dynamics and IMF variations suggests their close relationship with R1 currents. Consequently, we can assume that the Cluster spacecraft were making observations in the magnetospheric region associated with the auroras, although exact magnetic conjugacy between the ground-based and satellite observations did not exist. The solar wind variations appeared to control both the behaviour of the auroras and the magnetopause dynamics. Auroral structures were observed at Ny Ålesund especially during periods of negative IMF BZ. In addition, the Cluster spacecraft experienced periodic (T ~ 4 - 6 min encounters between magnetospheric and magnetosheath plasmas. These undulations of the boundary can be interpreted as a consequence of tailward propagating magnetopause surface waves. Simultaneous dusk sector ground-based observations show weak, but discernible magnetic pulsations (Pc 5 and occasionally periodic variations (T ~ 2 - 3 min in the high-latitude auroras. In the dusk sector, Pc 5 activity was stronger and had characteristics that were consistent with a field line resonance type of activity. When IMF BZ stayed positive for a longer period, the auroras were dimmer and the spacecraft stayed at the outer edge of the magnetopause where they observed electromagnetic pulsations with T ~ 1 min. We find these observations interesting especially from the viewpoint of previously presented studies relating poleward-moving high-latitude auroras with pulsation activity and MHD waves propagating at the magnetospheric boundary layers

  11. Cluster observations of the high-latitude magnetopause and cusp: initial results from the CIS ion instruments

    Directory of Open Access Journals (Sweden)

    J. M. Bosqued

    2001-09-01

    Full Text Available Launched on an elliptical high inclination orbit (apogee: 19.6 RE since January 2001 the Cluster satellites have been conducting the first detailed three-dimensional studies of the high-latitude dayside magnetosphere, including the exterior cusp, neighbouring boundary layers and magnetopause regions. Cluster satellites carry the CIS ion spectrometers that provide high-precision, 3D distributions of low-energy (<35 keV/e ions every 4 s. This paper presents the first two observations of the cusp and/or magnetopause behaviour made under different interplanetary magnetic field (IMF conditions. Flow directions, 3D distribution functions, density profiles and ion composition profiles are analyzed to demonstrate the high variability of high-latitude regions. In the first crossing analyzed (26 January 2001, dusk side, IMF-BZ < 0, multiple, isolated boundary layer, magnetopause and magnetosheath encounters clearly occurred on a quasi-steady basis for ~ 2 hours. CIS ion instruments show systematic accelerated flows in the current layer and adjacent boundary layers on the Earthward side of the magnetopause. Multi-point analysis of the magnetopause, combining magnetic and plasma data from the four Cluster spacecraft, demonstrates that oscillatory outward-inward motions occur with a normal speed of the order of ± 40 km/s; the thickness of the high-latitude current layer is evaluated to be of the order of 900–1000 km. Alfvénic accelerated flows and D-shaped distributions are convincing signatures of a magnetic reconnection occurring equatorward of the Cluster satellites. Moreover, the internal magnetic and plasma structure of a flux transfer event (FTE is analyzed in detail; its size along the magnetopause surface is ~ 12 000 km and it convects with a velocity of ~ 200 km/s. The second event analyzed (2 February 2001 corresponds to the first Cluster pass within the cusp when the IMF-BZ component was northward directed. The analysis of relevant CIS plasma

  12. Cluster observations of the high-latitude magnetopause and cusp: initial results from the CIS ion instruments

    Directory of Open Access Journals (Sweden)

    J. M. Bosqued

    Full Text Available Launched on an elliptical high inclination orbit (apogee: 19.6 RE since January 2001 the Cluster satellites have been conducting the first detailed three-dimensional studies of the high-latitude dayside magnetosphere, including the exterior cusp, neighbouring boundary layers and magnetopause regions. Cluster satellites carry the CIS ion spectrometers that provide high-precision, 3D distributions of low-energy (<35 keV/e ions every 4 s. This paper presents the first two observations of the cusp and/or magnetopause behaviour made under different interplanetary magnetic field (IMF conditions. Flow directions, 3D distribution functions, density profiles and ion composition profiles are analyzed to demonstrate the high variability of high-latitude regions. In the first crossing analyzed (26 January 2001, dusk side, IMF-BZ < 0, multiple, isolated boundary layer, magnetopause and magnetosheath encounters clearly occurred on a quasi-steady basis for ~ 2 hours. CIS ion instruments show systematic accelerated flows in the current layer and adjacent boundary layers on the Earthward side of the magnetopause. Multi-point analysis of the magnetopause, combining magnetic and plasma data from the four Cluster spacecraft, demonstrates that oscillatory outward-inward motions occur with a normal speed of the order of ± 40 km/s; the thickness of the high-latitude current layer is evaluated to be of the order of 900–1000 km. Alfvénic accelerated flows and D-shaped distributions are convincing signatures of a magnetic reconnection occurring equatorward of the Cluster satellites. Moreover, the internal magnetic and plasma structure of a flux transfer event (FTE is analyzed in detail; its size along the magnetopause surface is ~ 12 000 km and it convects with a velocity of ~ 200 km/s. The second event analyzed (2 February 2001 corresponds to the first Cluster pass within the cusp when the IMF-BZ component was northward directed. The analysis of

  13. Polar conic current sheets as sources and channels of energetic particles in the high-latitude heliosphere

    Science.gov (United States)

    Khabarova, Olga; Malova, Helmi; Kislov, Roman; Zelenyi, Lev; Obridko, Vladimir; Kharshiladze, Alexander; Tokumaru, Munetoshi; Sokół, Justyna; Grzedzielski, Stan; Fujiki, Ken'ichi; Malandraki, Olga

    2017-04-01

    The existence of a large-scale magnetically separated conic region inside the polar coronal hole has been predicted by the Fisk-Parker hybrid heliospheric magnetic field model in the modification of Burger and co-workers (Burger et al., ApJ, 2008). Recently, long-lived conic (or cylindrical) current sheets (CCSs) have been found from Ulysses observations at high heliolatitudes (Khabarova et al., ApJ, 2017). The characteristic scale of these structures is several times lesser than the typical width of coronal holes, and the CCSs can be observed at 2-3 AU for several months. CCS crossings in 1994 and 2007 are characterized by sharp decreases in the solar wind speed and plasma beta typical for predicted profiles of CCSs. In 2007, a CCS was detected directly over the South Pole and strongly highlighted by the interaction with comet McNaught. The finding is confirmed by restorations of solar coronal magnetic field lines that reveal the occurrence of conic-like magnetic separators over the solar poles both in 1994 and 2007. Interplanetary scintillation data analysis also confirms the existence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. The occurrence of long-lived CCSs in the high-latitude solar wind could shed light on how energetic particles reach high latitudes. Energetic particle enhancements up to tens MeV were observed by Ulysses at edges of CCSs both in 1994 and 2007. In 1994 this effect was clearer, probably due to technical reasons. Accelerated particles could be produced either by magnetic reconnection at the edges of a CCS in the solar corona or in the solar wind. We discuss the role of high-latitude CCSs in propagation of energetic particles in the heliosphere and revisit previous studies of energetic particle enhancements at high heliolatitudes. We also suggest that the existence of a CCS can modify the distribution of the solar wind as a function of heliolatitude and consequently impact ionization

  14. CUTLASS HF radar observations of high-latitude azimuthally propagating vortical currents in the nightside ionosphere during magnetospheric substorms

    Directory of Open Access Journals (Sweden)

    J. A. Wild

    Full Text Available High-time resolution CUTLASS observations and ground-based magnetometers have been employed to study the occurrence of vortical flow structures propagating through the high-latitude ionosphere during magnetospheric substorms. Fast-moving flow vortices (~800 m s-1 associated with Hall currents flowing around upward directed field-aligned currents are frequently observed propagating at high speed (~1 km s-1 azimuthally away from the region of the ionosphere associated with the location of the substorm expansion phase onset. Furthermore, a statistical analysis drawn from over 1000 h of high-time resolution, nightside radar data has enabled the characterisation of the bulk properties of these vortical flow systems. Their occurrence with respect to substorm phase has been investigated and a possible generation mechanism has been suggested.

    Key words: Ionosphere (auroral ionosphere; electric fields and currents · Magnetospheric physics (storms and substorms

  15. The effects of neutral inertia on ionospheric currents in the high-latitude thermosphere following a geomagnetic storm

    International Nuclear Information System (INIS)

    Deng, W.; Killeen, T.L.; Burns, A.G.; Roble, R.G.; Slavin, J.A.; Wharton, L.E.

    1993-01-01

    The authors extend previous work with a National Center for Atmospheric Research (NCAR) thermosphere/ionosphere general circulation model (TIGCM), to study dynamo effects in the high latitude thermosphere. Ionospheric convection can drive neutral currents in much the same pattern by means of ion drag reactions. It has been observed that ion currents established during magnetic storms can induce neutral currents which persist for hours after the end of the storm. Model results have shown that such currents can account for up to 80 percent of the Hall currents in the period immediately following storms. Here this previous work is extended and compared with experimental observations. The authors simulate time dependent Hall currents, field-aligned currents, and electrical power fluxes coupling the magnetosphere and ionosphere. They discuss their results in terms of a loaded magnetosphere, which accounts for the fact that the neutral currents can also induce currents and electric fields in the ionosphere

  16. Correlation of wind and solar power in high-latitude arctic areas in Northern Norway and Svalbard

    Directory of Open Access Journals (Sweden)

    Solbakken Kine

    2016-01-01

    Full Text Available This paper assesses the possibilities for combining wind and solar power in a household-scale hybrid renewable energy system in arctic high-latitude areas in the North of Norway. By combining two complementary renewable energy sources, the efficiency and reliability of the power output can be improved compared to a system utilizing wind or solar power independently. This paper assesses the correlation between wind and solar power on different timescales in four different locations in Northern Norway and Svalbard. For all locations complementary characteristics of wind and solar power are found, however, the strength of the correlation is highly variable for each location and for the different timescales. The best correlation for all places is found on a monthly timescale. HOMER is used to run simulations on hybrid renewable energy systems (HRES for each location. For three of the four locations the HRES produces more power than what is consumed in the household.

  17. Turbulence scales in the high-latitude ionosphere and their signatures upon echoes detected by SuperDARN HF radars

    International Nuclear Information System (INIS)

    Vallieres, Xavier

    2002-01-01

    SuperDARN is a coherent HF radar network dedicated to the study of high-latitude ionospheric plasma convection and finds its major applications in the field of Sun/Earth connection. This work deals with the interactions between a transmitted radar wave and ionisation gradients at different scales and their impact on measurements. Studies are performed in order to detect the ion cyclotron signature, superimposed to turbulent motions, in observed spectra. On the other hand, the role of intermediate scales (from hundreds of meters to kilometers) on spectral width estimation is evidenced. Statistical studies show that the value of this parameter depends upon transmitted frequency and echo range. We propose an interpretation in terms of a wave front de-correlation during propagation and validate it with numerical simulations based upon realistic ionospheric parameters. (author) [fr

  18. Plant hydraulic strategies and their variability at high latitudes: insights from a southern Canadian boreal forest site

    Science.gov (United States)

    Pappas, C.; Matheny, A. M.; Maillet, J.; Baltzer, J. L.; Stephens, J.; Barr, A.; Black, T. A.; Sonnentag, O.

    2016-12-01

    Boreal forests cover about one third of the world's forested area with a large part of the boreal zone located in Canada. These high-latitude ecosystems respond rapidly to environmental changes. Plant water stress and the resulting drought-induced mortality has been recently hypothesised as a major driver of forest changes in western Canada. Although boreal forests often exhibit low floristic complexity, local scale abiotic heterogeneities may lead to highly variable plant functional traits and thus to diverging plant responses to environmental changes. However, detailed measurements of plant hydraulic strategies and their inter- and intra-specific variability are still lacking for these ecosystems. Here, we quantify plant water use and hydraulic strategies of black spruce (Picea mariana) and larch (Larix laricina), that are widespread in the boreal zone, at a long-term monitoring site located in central Saskatchewan (53.99° N, 105.12° W; elevation 628.94 m a.s.l.). The site is characterized by a mature black spruce overstorey that dominates the landscape with few larch individuals. The ground cover consists mainly of mosses with some peat moss and lichens over a rich soil organic layer. Tree-level sap flux density, measured with Granier-style thermal dissipation probes (N=39), and concurrently recorded radial stem dynamics, measured with high frequency dendrometers (N=13), are used to quantify plant hydraulic functioning during the 2016 growing season. Hydrometeorological measurements, including soil moisture and micrometeorological data, are used to describe environmental constraints in plant water use. Tree-level dynamics are then integrated to the landscape and compared with ecosystem-level evapotranspiration measurements from an adjacent eddy-covariance flux tower. This experimental design allows us to quantify the main environmental drivers that shape plant hydraulic strategies in this southern boreal zone and to provide new insights into the inter- and

  19. Early onset of significant local warming in low latitude countries

    International Nuclear Information System (INIS)

    Mahlstein, I; Knutti, R; Solomon, S; Portmann, R W

    2011-01-01

    The Earth is warming on average, and most of the global warming of the past half-century can very likely be attributed to human influence. But the climate in particular locations is much more variable, raising the question of where and when local changes could become perceptible enough to be obvious to people in the form of local warming that exceeds interannual variability; indeed only a few studies have addressed the significance of local signals relative to variability. It is well known that the largest total warming is expected to occur in high latitudes, but high latitudes are also subject to the largest variability, delaying the emergence of significant changes there. Here we show that due to the small temperature variability from one year to another, the earliest emergence of significant warming occurs in the summer season in low latitude countries (∼25 deg. S-25 deg. N). We also show that a local warming signal that exceeds past variability is emerging at present, or will likely emerge in the next two decades, in many tropical countries. Further, for most countries worldwide, a mean global warming of 1 deg. C is sufficient for a significant temperature change, which is less than the total warming projected for any economically plausible emission scenario. The most strongly affected countries emit small amounts of CO 2 per capita and have therefore contributed little to the changes in climate that they are beginning to experience.

  20. Non-Hawaiian lithostratigraphy of Louisville seamounts and the formation of high-latitude oceanic islands and guyots

    Science.gov (United States)

    Buchs, David M.; Williams, Rebecca; Sano, Shin-ichi; Wright, V. Paul

    2018-05-01

    Guyots are large seamounts with a flat summit that is generally believed to form due to constructional biogenic and/or erosional processes during the formation of volcanic islands. However, despite their large abundance in the oceans, there are still very few direct constraints on the nature and formation of guyots, in particular those formed at high latitude that lack a thick cap of shallow-marine carbonate rocks. It is largely accepted based on geophysical constraints and surficial observations/sampling that the summit platform of these guyots is shaped by wave abrasion during post-volcanic subsidence of volcanic islands. Here we provide novel constraints on this hypothesis and the summit geology of guyots with a lithostratigraphic analysis of cores from three Louisville seamounts (South Pacific) collected during Expedition 330 of the Integrated Ocean Drilling Program (IODP). Thirteen lithofacies of sedimentary and volcanic deposits are described, which include facies not previously recognized on the top of guyots, and offer a new insight into the formation of high-latitude oceanic islands on a fast-moving plate. Our results reveal that the lithostratigraphy of Louisville seamounts preserves a very consistent record of the formation and drowning of volcanic islands, with from bottom to top: (i) volcaniclastic sequences with abundant lava-fed delta deposits, (ii) submarine to subaerial shield lava flows, (iii) post-volcanic shallow to deeper marine sedimentary rocks lacking thick reef deposits, (iv) post-erosional rejuvenated volcanic rocks, and (v) pelagic sediments. Recognition of erosional boundaries between subaerial lava flows and shallow-marine sedimentary rocks provides novel support for post-volcanic wave planation of guyots. However, the summit geology of Louisville seamounts is dissimilar to that of high-latitude Hawaiian-Emperor guyots that have emplaced in a similar tectonic and environmental setting and that include thicker lava stacks with apparently

  1. Comparison of atmospheric CO2 columns at high latitudes from ground-based and satellite-based methods

    Science.gov (United States)

    Jacobs, N.; Simpson, W. R.; Parker, H. A.; Tu, Q.; Blumenstock, T.; Dubey, M. K.; Hase, F.; Osterman, G. B.

    2017-12-01

    Total column measurements of carbon-dioxide (CO2) from the Orbiting Carbon Observatory-2 (OCO-2) satellite have been validated at mid-latitudes by comparison to the Total Carbon Column Observing Network (TCCON), but there are still a limited number of sites providing high-latitude validation data for satellite observations of CO2, and no TCCON sites in Alaska. To understand the global distribution of CO2 sources and sinks, it is essential that we increase the abundance of validation sites, particularly in the climate-sensitive high-latitude Boreal forest. Therefore, we began the Arctic Mobile Infrared Greenhouse Gas Observations (AMIGGO) campaign in the Boreal Forest region around Fairbanks, Alaska with the goal of satellite validation and measurement of natural ecosystem fluxes. In this campaign, we used the EM27/SUN mobile solar-viewing Fourier-transform infrared spectrometer (EM27/SUN FTS) to retrieve the total CO2 column and column-averaged dry-air mole fraction of CO2 (XCO2) with the GGG2014 algorithm. The EM27/SUN FTS was developed by the Karlsruhe Institute of Technology (KIT) in collaboration with Bruker optics (Gisi et al., 2012, doi:10.5194/amt-5-2969-2012) and has been deployed in urban areas to measure anthropogenic fluxes of CO2 and CH4. To evaluate the EM27/SUN performance, co-located observations were made with two EM27/SUN spectrometers, and we found that XCO2 differences between spectrometers were small (0.24ppm on average) and very stable over time. In this presentation, we report on 14 OCO-2 targeted overpasses that occurred from August 2016 through July 2017, along with additional targets obtained during ongoing observations in 2017. We investigate underlying reasons for observed differences between OCO-2 and ground-based XCO2 using methods developed by Wunch et al. (2017, doi:10.5194/amt-10-2209-2017). As an additional point of comparison, coincident aircraft observations by NOAA Earth System Research Laboratory (ESRL) Global Monitoring

  2. Multiple Flux Rope Events at the High-Latitude Magnetopause: Cluster/Rapid Observation on January 26, 2001

    Science.gov (United States)

    Huang, Zong-Ying; Pu, Zu-Yin; Xiao, Chi-Jie; Xong, Qui-Gang; Fu, Sui-Yan; Xie, Lun; Shi, Quan-Qi; Cao, Jin-Bin; Liu, Zhen-Xing; Shen, Cao; Shi, Jian-Kui; Lu, Li; Wang, Nai-Quan; Chen, Tao; Fritz, T.; Glasmeier, K.-H.; Daly, P.; Reme, H.

    2004-04-01

    From 11:10 to 11:40UT on January 26, 2001 the four Cluster II spacecraft were located in the duskside high latitude regions of the magnetosheath and magnetosheath boundary layer (MSBL). During this time Interval the interplanetary magnetic field (IMF) had a negative Bz component. A detailed study on the multiple flux ropes (MFRs) observed in this period is conducted in this paper. It is found that: (1) The multiple flux ropes in the high latitude MSBL appeared quasi-periodically with a repeated time period of about 78s, which is much shorter than the averaged occurring period (about 8-11min) of the flux transfer events (FTEs) at the dayside magnetopause (MP). (2) All the flux ropes observed in this event had a strong core magnetic field. The axial orientation of the most flux ropes is found to lie in the direction of the minimum magnetic field variance; a few flux ropes had their axes lying in the direction of the middle magnetic field variance; while for the remainders their principle axes could not be determined by the method of Principal Axis Analysis (PAA). The reason that causes this complexity relys on the different trajectories of the spacecraft passing through the flux ropes. (3) Each flux rope had a good corresponding HT frame of reference in which it was in a quasi-steady state. All flux ropes moved along the surface of the MP in a similar direction indicating that these flux ropes all came from the dawnside low latitude. Their radial scale is 1-2RE, comparable to the normal diameter of FTEs observed atthe dayside MP. (4) The energetic ions originated from the magnetosphere flowed out to the magnetosheath on the whole, while the solar wind plasma flowed into the magnetosphere along the axis of the flux ropes. The flux ropes offered channels for the transport of the solar wind plasma into the magnetosphere and the escaping of the magnetospheric plasma into the interplanetary space. (5) Each event was accompanied by an enhanced reversal of the dusk

  3. The Vertical-Tube Solar Collector: A Low-Cost Design Suitable for Temperate High-Latitude Locations

    Directory of Open Access Journals (Sweden)

    Luis Juanicó

    2014-01-01

    Full Text Available A new low-cost solar collector based on thick (4.5′′ vertical tubes related to the previous design based on long 1.5′′ plastic hoses connected directly between water-grid supply and consumption is presented. This novel design could noticeably improve its performance for temperate locations mid and high latitudes, as was demonstrated by dynamic thermal modeling. This tool has been useful for understanding the particular characteristics of this kind of water-pond collector and besides, for noticeably improving its performance by optimizing its parameters, like tube diameter and number of glazing layers. By this way, the optimized design could fully satisfy the household demand up to midnight along the whole year for Buenos Aires (35°S and during summers (remaining as a useful preheater for the whole year for Ushuaia (55°S. Besides, its high simplicity makes it available for user’s own construction, costing down 50 dollars for a single-family unit.

  4. A synthesis of thermokarst lake water balance in high-latitude regions of North America from isotope tracers

    Science.gov (United States)

    MacDonald, Lauren A.; Wolfe, Brent B.; Turner, Kevin W.; Anderson, Lesleigh; Arp, Christopher D.; Birks, Jean; Bouchard, Frédéric; Edwards, Thomas W.D.; Farquharson, Nicole; Hall, Roland I.; McDonald, Ian; Narancic, Biljana; Ouimet, Chantal; Pienitz, Reinhard; Tondu, Jana; White, Hilary

    2017-01-01

    Numerous studies utilizing remote sensing imagery and other methods have documented that thermokarst lakes are undergoing varied hydrological transitions in response to recent climate changes, from surface area expansion to drainage and evaporative desiccation. Here, we provide a synthesis of hydrological conditions for 376 lakes of mainly thermokarst origin across high-latitude North America. We assemble surface water isotope compositions measured during the past decade at five lake-rich landscapes including Arctic Coastal Plain (Alaska), Yukon Flats (Alaska), Old Crow Flats (Yukon), northwestern Hudson Bay Lowlands (Manitoba), and Nunavik (Quebec). These landscapes represent the broad range of thermokarst environments by spanning gradients in meteorological, permafrost, and vegetation conditions. An isotope framework was established based on flux-weighted long-term averages of meteorological conditions for each lake to quantify water balance metrics. The isotope composition of source water and evaporation-to-inflow ratio for each lake were determined, and the results demonstrated a substantial array of regional and subregional diversity of lake hydrological conditions. Controls on lake water balance and how these vary among the five landscapes and with differing environmental drivers are assessed. Findings reveal that lakes in the Hudson Bay Lowlands are most vulnerable to evaporative desiccation, whereas those in Nunavik are most resilient. However, we also identify the complexity in predicting hydrological responses of these thermokarst landscapes to future climate change.

  5. Causes of spring vegetation growth trends in the northern mid–high latitudes from 1982 to 2004

    International Nuclear Information System (INIS)

    Mao Jiafu; Shi Xiaoying; Thornton, Peter E; Piao Shilong; Wang Xuhui

    2012-01-01

    The Community Land Model version 4 (CLM4) is applied to explore the spatial–temporal patterns of spring (April–May) vegetation growth trends over the northern mid–high latitudes (NMH) (>25°N) between 1982 and 2004. During the spring season through the 23 yr period, both the satellite-derived and simulated normalized difference vegetation index (NDVI) anomalies show a statistically significant correlation and an overall greening trend within the study area. Consistently with the observed NDVI–temperature relation, the CLM4 NDVI shows a significant positive association with the spring temperature anomaly for the NMH, North America and Eurasia. Large study areas experience temperature discontinuity associated with contrasting NDVI trends. Before and after the turning point (TP) of the temperature trends, climatic variability plays a dominant role, while the other environmental factors exert minor effects on the NDVI tendencies. Simulated vegetation growth is broadly stimulated by the increasing atmospheric CO 2 . Trends show that nitrogen deposition increases NDVI mostly in southeastern China, and decreases NDVI mainly in western Russia after the temperature TP. Furthermore, land use-induced NDVI trends vary roughly with the respective changes in land management practices (crop areas and forest coverage). Our results highlight how non-climatic factors mitigate or exacerbate the impact of temperature on spring vegetation growth, particularly across regions with intensive human activity. (letter)

  6. Observation of temperatures and emission rates from the OH and O 2 nightglow over a southern high latitude station

    Science.gov (United States)

    Chung, J.-K.; Kim, Y. H.; Won, Y.-I.; Moon, B. K.; Oh, T. H.

    2006-01-01

    A Spectral Airglow Temperature Imager (SATI) was operated at King Sejong Station (62°13'S, 58°47'W), Korea Antarctic Research Station during the period of March, 2002-September, 2003. We analyze rotational temperatures and emission rates of the O 2 (0-1) and OH (6-2) nightglows obtained at 67 nights with clear sky lasting more than 4 h. A spectral analysis of the dataset shows two dominant oscillations with periods of 4 and 6 h. The 6-h oscillations have a nearly constant phase, whereas the 4-h oscillations have nearly random phases. Although the harmonic periods of both oscillations are suggestive of tidal origin, the 4-h oscillation may have interference by other sources such as gravity waves. The 6-h oscillations could be interpreted as zonally symmetric non-migrating tides because migrating tides except high order modes have very weak amplitudes at high latitudes according to the classical tidal theory. For most cases of the observed oscillations the temperature peak leads the intensity peak, which is consistent with theoretical models for zonally symmetric tides, but contrary to other theoretical models for waves. It is needed to resolve among theoretical models whether or not zonally symmetric tide cause temperature variation prior to intensity variation in mesospheric airglows.

  7. High-latitude tree growth and satellite vegetation indices: Correlations and trends in Russia and Canada (1982-2008)

    Science.gov (United States)

    Berner, Logan T.; Beck, Pieter S. A.; Bunn, Andrew G.; Lloyd, Andrea H.; Goetz, Scott J.

    2011-03-01

    Vegetation in northern high latitudes affects regional and global climate through energy partitioning and carbon storage. Spaceborne observations of vegetation, largely based on the normalized difference vegetation index (NDVI), suggest decreased productivity during recent decades in many regions of the Eurasian and North American boreal forests. To improve interpretation of NDVI trends over forest regions, we examined the relationship between NDVI from the advanced very high resolution radiometers and tree ring width measurements, a proxy of tree productivity. We collected tree core samples from spruce, pine, and larch at 22 sites in northeast Russia and northwest Canada. Annual growth rings were measured and used to generate site-level ring width index (RWI) chronologies. Correlation analysis was used to assess the association between RWI and summer NDVI from 1982 to 2008, while linear regression was used to examine trends in both measurements. The correlation between NDVI and RWI was highly variable across sites, though consistently positive (r = 0.43, SD = 0.19, n = 27). We observed significant temporal autocorrelation in both NDVI and RWI measurements at sites with evergreen conifers (spruce and pine), though weak autocorrelation at sites with deciduous conifers (larch). No sites exhibited a positive trend in both NDVI and RWI, although five sites showed negative trends in both measurements. While there are technological and physiological limitations to this approach, these findings demonstrate a positive association between NDVI and tree ring measurements, as well as the importance of considering lagged effects when modeling vegetation productivity using satellite data.

  8. A Study of Solar Flare Effects on Mid and High Latitude Radio Wave Propagation using SuperDARN.

    Science.gov (United States)

    Ruohoniemi, J. M.; Chakraborty, S.; Baker, J. B.

    2017-12-01

    Over the Horizon (OTH) communication is strongly dependent on the state of the ionosphere, which is sensitive to solar X-ray flares. The Super Dual Auroral Radar Network (SuperDARN), whose working principle is dependent on trans-ionospheric radio communication, uses HF radio waves to remotely sense the ionosphere. The backscatter returns from the terrestrial surface (also known as ground-scatter) transit the ionosphere four times and simulate the operation of an HF communications link. SuperDARN backscatter signal properties are altered (strongly attenuated and changes apparent phase) during a sudden ionospheric disturbance following a solar flare, commonly known as Short-Wave Fadeout or SWF. During an SWF the number of SuperDARN backscatter echoes drops suddenly (≈1 min) and sharply, often to near zero, and recovers within 30 minutes to an hour. In this study HF propagation data (SuperDARN backscatter) obtained during SWF events are analyzed for the purpose of validating and improving the performance of HF absorption models, such as, Space Weather Prediction Center (SWPC) D-region Absorption model (DRAP) and CCMC physics based AbbyNormal model. We will also present preliminary results from a physics based model for the mid and high latitude ionospheric response to flare-driven space weather anomalies, which can be used to estimate different physical parameters of the ionosphere such as electron density, collision frequency, absorption coefficients, response time of D-region etc.

  9. High-Latitude Neutral Density Structures Investigated by Utilizing Multi-Instrument Satellite Data and NRLMSISE-00 Simulations

    Science.gov (United States)

    Horvath, Ildiko; Lovell, Brian C.

    2018-02-01

    This study investigates various types of neutral density features developed in the cusp region during magnetically active and quiet times. Multi-instrument Challenging Minisatellite Payload data provide neutral density, electron temperature, neutral wind speed, and small-scale field-aligned current (SS-FAC) values. Gravity Recovery and Climate Experiment neutral density data are also employed. During active times, cusp densities or density spikes appeared with their underlying flow channels (FCs) and enhanced SS-FACs implying upwelling, fueled by Joule heating, within/above FCs. Both the moderate nightside cusp enhancements under disturbed conditions and the minor dayside cusp enhancements under quiet conditions developed without any underlying FC and enhanced SS-FACs implying the role of particle precipitation in their development. Observations demonstrate the relations of FCs, density spikes, and upwelling-related divergent flows and their connections to the underlying (1) dayside magnetopause reconnection depositing magnetospheric energy into the high-latitude region and (2) Joule heating-driven disturbance dynamo effects. Results provide observational evidence that the moderate nightside cusp enhancements and the minor dayside cusp enhancements detected developed due to direct heating by weak particle precipitation. Chemical compositions related to the dayside density spike and low cusp densities are modeled by Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar Extended 2000. Modeled composition outputs for the dayside density spike's plasma environment depict some characteristic upwelling signatures. Oppositely, in the case of low dayside cusp densities, composition outputs show opposite characteristics due to the absence of upwelling.

  10. Causes of spring vegetation greenness trends in the northern mid-high latitudes from 1982 to 2004

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Jiafu [ORNL; Shi, Xiaoying [ORNL; Thornton, Peter E [ORNL; Shilong, Dr. Piao [Peking University; Xuhui, Dr. Wang [Peking University

    2012-01-01

    The Community Land Model version 4 (CLM4) is applied to explore the spatial temporal patterns of spring (April May) vegetation growth trends over the northern mid high latitudes (NMH) (>25 N) between 1982 and 2004. During the spring season through the 23 yr period, both the satellite-derived and simulated normalized difference vegetation index (NDVI) anomalies show a statistically significant correlation and an overall greening trend within the study area. Consistently with the observed NDVI temperature relation, the CLM4 NDVI shows a significant positive association with the spring temperature anomaly for the NMH, North America and Eurasia. Large study areas experience temperature discontinuity associated with contrasting NDVI trends. Before and after the turning point (TP) of the temperature trends, climatic variability plays a dominant role, while the other environmental factors exert minor effects on the NDVI tendencies. Simulated vegetation growth is broadly stimulated by the increasing atmospheric CO2. Trends show that nitrogen deposition increases NDVI mostly in southeastern China, and decreases NDVI mainly in western Russia after the temperature TP. Furthermore, land use-induced NDVI trends vary roughly with the respective changes in land management practices (crop areas and forest coverage). Our results highlight how non-climatic factors mitigate or exacerbate the impact of temperature on spring vegetation growth, particularly across regions with intensive human activity.

  11. Radar observations of high-latitude lower-thermospheric and upper-mesospheric winds and their response to geomagnetic activity

    International Nuclear Information System (INIS)

    Johnson, R.M.

    1987-01-01

    Observations made by the Chatanika, Alaska, incoherent scatter radar during the summer months of 1976 to 1081 are analyzed to obtain high resolution lower-thermospheric neutral winds. Average winds and their tidal components are presented and compared to previous observational and model results. Upper-mesospheric neutral-wind observations obtained by the Poke Flat, Alaska Mesosphere-Stratosphere-Troposphere (MST) radar during the summer months of 1980 to 1982 are investigated statistically for evidence of variations due to geomagnetic activity. Observation of upper-mesospheric neutral winds made during two energetic Solar Proton Events (SPEs) by the Poker Flat, MST radar are presented. These results allow the low-altitude limits of magnetospheric coupling to the neutral atmosphere to be determined. Lower-thermospheric neutral winds are coupled to the ion convection driven by typical magnetospheric forcing above about 100 km. Coupling to lower atmospheric levels does not occur except during intervals of extreme disturbance of the magnetosphere-ionosphere-thermosphere system which are also accompanied by dramatically increased ionization in the high-latitude mesosphere, such as SPEs

  12. Performances of Kevlar and Polyethylene as radiation shielding on-board the International Space Station in high latitude radiation environment.

    Science.gov (United States)

    Narici, Livio; Casolino, Marco; Di Fino, Luca; Larosa, Marianna; Picozza, Piergiorgio; Rizzo, Alessandro; Zaconte, Veronica

    2017-05-10

    Passive radiation shielding is a mandatory element in the design of an integrated solution to mitigate the effects of radiation during long deep space voyages for human exploration. Understanding and exploiting the characteristics of materials suitable for radiation shielding in space flights is, therefore, of primary importance. We present here the results of the first space-test on Kevlar and Polyethylene radiation shielding capabilities including direct measurements of the background baseline (no shield). Measurements are performed on-board of the International Space Station (Columbus modulus) during the ALTEA-shield ESA sponsored program. For the first time the shielding capability of such materials has been tested in a radiation environment similar to the deep-space one, thanks to the feature of the ALTEA system, which allows to select only high latitude orbital tracts of the International Space Station. Polyethylene is widely used for radiation shielding in space and therefore it is an excellent benchmark material to be used in comparative investigations. In this work we show that Kevlar has radiation shielding performances comparable to the Polyethylene ones, reaching a dose rate reduction of 32 ± 2% and a dose equivalent rate reduction of 55 ± 4% (for a shield of 10 g/cm 2 ).

  13. Interhemispheric differences and solar cycle effects of the high-latitude ionospheric convection patterns deduced from Cluster EDI observations

    Science.gov (United States)

    Förster, Matthias; Haaland, Stein

    2015-04-01

    Here, we present a study of ionospheric convection at high latitudes that is based on satellite measurements of the Electron Drift Instrument (EDI) on-board the Cluster satellites, which were obtained over a full solar cycle (2001-2013). The mapped drift measurements are covering both hemispheres and a variety of different solar wind and interplanetary magnetic field (IMF) conditions. The large amount of data allows us to perform more detailed statistical studies. We show that flow patterns and polar cap potentials can differ between the two hemispheres on statistical average for a given IMF orientation. In particular, during southward directed IMF conditions, and thus enhanced energy input from the solar wind, we find that the southern polar cap has a higher cross polar cap potential. We also find persistent north-south asymmetries which cannot be explained by external drivers alone. Much of these asymmetries can probably be explained by significant differences in the strength and configuration of the geomagnetic field between the Northern and Southern Hemisphere. Since the ionosphere is magnetically connected to the magnetosphere, this difference will also be reflected in the magnetosphere in the form of different feedback from the two hemispheres. Consequently, local ionospheric conditions and the geomagnetic field configuration are important for north-south asymmetries in large regions of geospace. The average convection is higher during periods with high solar activity. Although local ionospheric conditions may play a role, we mainly attribute this to higher geomagnetic activity due to enhanced solar wind - magnetosphere interactions.

  14. Evaluating the Dominant Components of Warming in Pliocene Climate Simulations

    Science.gov (United States)

    Hill, D. J.; Haywood, A. M.; Lunt, D. J.; Hunter, S. J.; Bragg, F. J.; Contoux, C.; Stepanek, C.; Sohl, L.; Rosenbloom, N. A.; Chan, W.-L.; hide

    2014-01-01

    The Pliocene Model Intercomparison Project (PlioMIP) is the first coordinated climate model comparison for a warmer palaeoclimate with atmospheric CO2 significantly higher than pre-industrial concentrations. The simulations of the mid-Pliocene warm period show global warming of between 1.8 and 3.6 C above pre-industrial surface air temperatures, with significant polar amplification. Here we perform energy balance calculations on all eight of the coupled ocean-atmosphere simulations within PlioMIP Experiment 2 to evaluate the causes of the increased temperatures and differences between the models. In the tropics simulated warming is dominated by greenhouse gas increases, with the cloud component of planetary albedo enhancing the warming in most of the models, but by widely varying amounts. The responses to mid-Pliocene climate forcing in the Northern Hemisphere midlatitudes are substantially different between the climate models, with the only consistent response being a warming due to increased greenhouse gases. In the high latitudes all the energy balance components become important, but the dominant warming influence comes from the clear sky albedo, only partially offset by the increases in the cooling impact of cloud albedo. This demonstrates the importance of specified ice sheet and high latitude vegetation boundary conditions and simulated sea ice and snow albedo feedbacks. The largest components in the overall uncertainty are associated with clouds in the tropics and polar clear sky albedo, particularly in sea ice regions. These simulations show that albedo feedbacks, particularly those of sea ice and ice sheets, provide the most significant enhancements to high latitude warming in the Pliocene.

  15. Coupled thermo-geophysical inversion for high-latitude permafrost monitoring - assessment of the method and practical considerations

    Science.gov (United States)

    Tomaskovicova, Sonia; Paamand, Eskild; Ingeman-Nielsen, Thomas; Bauer-Gottwein, Peter

    2013-04-01

    difference between the synthetic and the measured apparent resistivities is minimized in a least-squares inversion procedure by adjusting the thermal parameters of the heat model. A site-specific calibration is required since the relation between unfrozen water content and temperature is strongly dependent on the grain size of the soil. We present details of an automated permanent field measurement setup that has been established to collect the calibration data in Ilulissat, West Greenland. Considering the station location in high latitude environment, this setup is unique of its kind since the installation of automated geophysical stations in the Arctic conditions is a challenging task. The main issues are related to availability of adapted equipment, high demand on robustness of the equipment and method due to the harsh environment, remoteness of the field sites and related powering issues of such systems. By showing the results from the new-established geoelectrical station over the freezing period in autumn 2012, we prove the 2D time lapse resistivity tomography to be an effective method for permafrost monitoring in high latitudes. We demonstrate the effectivity of time lapse geoelectrical signal for petrophysical relationship calibration, which is enhanced comparing to sparse measurements.

  16. Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm

    Directory of Open Access Journals (Sweden)

    A. Grocott

    Full Text Available We present SuperDARN radar observations of the ionospheric flow during a well-observed high-latitude substorm which occurred during steady northward IMF conditions on 2 December 1999. These data clearly demonstrate the excitation of large-scale flow associated with the substorm expansion phase, with enhanced equatorward flows being observed in the pre-midnight local time sector of the expansion phase auroral bulge and westward electrojet, and enhanced return sunward flows being present at local times on either side, extending into the dayside sector. The flow pattern excited was thus of twin-vortex form, with foci located at either end of the substorm auroral bulge, as imaged by the Polar VIS UV imager. Estimated total transpolar voltages were ~40 kV prior to expansion phase onset, grew to ~80 kV over a ~15 min interval during the expansion phase, and then decayed to ~35 kV over ~10 min during recovery. The excitation of the large-scale flow pattern resulted in the development of magnetic disturbances which extended well outside of the region directly disturbed by the substorm, depending upon the change in the flow and the local ionospheric conductivity. It is estimated that the nightside reconnection rate averaged over the 24-min interval of the substorm was ~65– 75 kV, compared with continuing dayside reconnection rates of ~30–45 kV. The net closure of open flux during the sub-storm was thus ~0.4–0.6 × 108 Wb, representing ~15–20% of the open flux present at onset, and corresponding to an overall contraction of the open-closed field line boundary by ~1° latitude.

    Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; plasma convection

  17. The Largs high-latitude oxygen isotope anomaly (New Zealand) and climatic controls of oxygen isotopes in magma

    International Nuclear Information System (INIS)

    Blattner, P.; Williams, J.G.

    1991-01-01

    In northern Fiordland the Brook Street terrane of New Zealand consists of two units - the predominantly basaltic Plato and the predominantly andesitic Largs terrane. The Permian Plato terrane has normal to slightly enriched δ 18 O values, whereas the Largs terrane, which is of similar pre-early Triassic age, has not yielded a single normal δ 18 O SMOW result, with all of 17 total rocks showing less than 3.2per mille, seven less than -4per mille, and two less than -9per mille. These strongly anomalous data confirm an earlier suggested terrestrial character of Largs deposition, and demand the presence of Permo-Triassic geothermal systems running on subAntarctic to Antarctic meteoric water. The skewed data spectrum suggests a relatively immature flow system and likely values for the recharge water are -20per mille δ 18 O or less. For a climate distribution similar to the present one, inlcuding polar ice caps, this would indicate over 70deg of southern latitude. Rafts and xenoliths of Largs rocks have been entrained within Mackay Intrusives in the early Triassic. On field evidence the Mackay magmas have also intruded an early Darran Complex, but this complex has been substantially reactivated in the Cretaceous. It has δ 18 O values near 5.0per mille, which is distinctly low for island arc magmas. Since the complex is isotopically homogenous, its δ 18 O is unlikely to be a direct effect of the relatively shallow Largs terrane. More probable is a climate related slight depression of the δ 18 O of magma sources, in which other high-latitude, low-δ 18 O sediments and geothermal systems have been involved. (orig.)

  18. Model study of the influence of solar wind parameters on electric currents and fields in middle atmosphere at high latitudes

    International Nuclear Information System (INIS)

    Tonev, P.; Velinov, P.

    2012-01-01

    The electric currents and fields in the strato/mesosphere and lower ionosphere are a result mainly of tropospheric electrical generators (thunderstorms and electrified clouds) which principally determine their global distributions and magnitudes. There are, however, additional sources, e.g. the solar wind (SW), whose contribution to these currents and fields is realized by SW-magnetosphere-ionosphere coupling. This last causes creation of large trans-polar electric potential difference VPC in each polar cap of ∼ 30–140 kV and of horizontal scale ∼ 3000 km which is realized through field-aligned currents (FAC) and is controlled by SW parameters. The potential difference VPC forces formation of closure currents in the dynamo-region. Our study by simulation shows that much smaller currents penetrate into the lower atmospheric regions and influence characteristics of the global atmospheric electrical circuit (GEC). Also, the downward mapping of the horizontal electric fields due to the potential difference VPC leads to creation of very small, but non-negligible vertical electric fields at sea level. They have been demonstrated experimentally as significant (up to few tens of per cent) SW-controlled modifications of the GEC electric characteristics at the ground, at polar latitudes. Our model, based on simulation of Maxwell’s equations in the region 0–160 km under steady-state conditions show that similar but relatively much larger SW-dominated modifications of GEC characteristics take place in the strato/mesosphere and lower ionosphere at polar and high latitudes

  19. Snowmelt water drives higher soil erosion than rainfall water in a mid-high latitude upland watershed

    Science.gov (United States)

    Wu, Yuyang; Ouyang, Wei; Hao, Zengchao; Yang, Bowen; Wang, Li

    2018-01-01

    The impacts of precipitation and temperature on soil erosion are pronounced in mid-high latitude areas, which lead to seasonal variations in soil erosion. Determining the critical erosion periods and the reasons behind the increased erosion loads are essential for soil management decisions. Hence, integrated approaches combining experiments and modelling based on field investigations were applied to investigate watershed soil erosion characteristics and the dynamics of water movement through soils. Long-term and continuous data for surface runoff and soil erosion variation characteristics of uplands in a watershed were observed via five simulations by the Soil and Water Assessment Tool (SWAT). In addition, laboratory experiments were performed to quantify the actual soil infiltrabilities in snowmelt seasons (thawed treatment) and rainy seasons (non-frozen treatment). The results showed that over the course of a year, average surface runoff and soil erosion reached peak values of 31.38 mm and 1.46 t ha-1 a-1, respectively, in the month of April. They also ranked high in July and August, falling in the ranges of 23.73 mm to 24.91 mm and 0.55 t ha-1 a-1 to 0.59 t ha-1 a-1, respectively. With the infiltration time extended, thawed soils showed lower infiltrabilities than non-frozen soils, and the differences in soil infiltration amounts between these two were considerable. These results highlighted that soil erosion was very closely and positively correlated with surface runoff. Soil loss was higher in snowmelt periods than in rainy periods due to the higher surface runoff in early spring, and the decreased soil infiltrability in snowmelt periods contributed much to this higher surface runoff. These findings are helpful for identification of critical soil erosion periods when making soil management before critical months, especially those before snowmelt periods.

  20. Distribution and Characteristics of Boulder Halos at High Latitudes on Mars: Ground Ice and Surface Processes Drive Surface Reworking

    Science.gov (United States)

    Levy, J. S.; Fassett, C. I.; Rader, L. X.; King, I. R.; Chaffey, P. M.; Wagoner, C. M.; Hanlon, A. E.; Watters, J. L.; Kreslavsky, M. A.; Holt, J. W.; Russell, A. T.; Dyar, M. D.

    2018-02-01

    Boulder halos are circular arrangements of clasts present at Martian middle to high latitudes. Boulder halos are thought to result from impacts into a boulder-poor surficial unit that is rich in ground ice and/or sediments and that is underlain by a competent substrate. In this model, boulders are excavated by impacts and remain at the surface as the crater degrades. To determine the distribution of boulder halos and to evaluate mechanisms for their formation, we searched for boulder halos over 4,188 High Resolution Imaging Science Experiment images located between 50-80° north and 50-80° south latitude. We evaluate geological and climatological parameters at halo sites. Boulder halos are about three times more common in the northern hemisphere than in the southern hemisphere (19% versus 6% of images) and have size-frequency distributions suggesting recent Amazonian formation (tens to hundreds of millions of years). In the north, boulder halo sites are characterized by abundant shallow subsurface ice and high thermal inertia. Spatial patterns of halo distribution indicate that excavation of boulders from beneath nonboulder-bearing substrates is necessary for the formation of boulder halos, but that alone is not sufficient. Rather, surface processes either promote boulder halo preservation in the north or destroy boulder halos in the south. Notably, boulder halos predate the most recent period of near-surface ice emplacement on Mars and persist at the surface atop mobile regolith. The lifetime of observed boulders at the Martian surface is greater than the lifetime of the craters that excavated them. Finally, larger minimum boulder halo sizes in the north indicate thicker icy soil layers on average throughout climate variations driven by spin/orbit changes during the last tens to hundreds of millions of years.

  1. The structure of mid- and high-latitude ionosphere during September 1999 storm event obtained from GPS observations

    Directory of Open Access Journals (Sweden)

    I. I. Shagimuratov

    Full Text Available TEC data, obtained from over 60 GPS stations, were used to study the ionospheric effects of the 12–16 September 1999 magnetic storm over Europe. The spatial and temporal changes of the ionosphere were analysed as a time series of TEC maps, which present 15 min averages of TEC. The data set consisting of GPS observations, collected by a dense network of European stations, with sampling rate of 30 s, enable the creation of TEC maps with high spatial and temporal resolution. The storm included the positive as well as the negative phase. The positive phase took place during the first storm day of 12 September 1999. The short-lived daytime TEC enhancement was observed at all latitudes. The maximal enhancement reached a factor of 1.3–1.5. On the second and third days, the negative phase of the storm developed. The TEC decrease was registered regardless of time of the day. The TEC depression exceeded 70% relative to quiet days. On the following days (15 and 16 September, a significant daytime enhancement of TEC was observed once again. The complex occurrence of the ionospheric storm was probably related to the features of development of the magnetic storm. We found out that during the storm the large and medium-scale irregularities developed in the high-latitude ionosphere. The multi-stations technique, employed to create TEC maps, was particularly successful while studying the mid-latitude ionospheric trough. We found out that the essential changes of TEC during the storm, which were registered at the auroral and sub-auroral ionosphere, were connected with the effect of the trough and its dynamics, which depends on geomagnetic activity.

    Key words. Ionosphere (ionospheric disturbances; auroral ionosphere; mid-latitude ionosphere

  2. Long-term dynamics of a high-latitude coral reef community at Sodwana Bay, South Africa

    Science.gov (United States)

    Porter, S. N.; Schleyer, M. H.

    2017-06-01

    Dynamics in reef cover, mortality and recruitment success of a high-latitude coral community in South Africa were studied over 20 yr with the aim to detect the effects of climate change. Coral communities at this locality are the southernmost on the African continent, non-accretive, attain high biodiversity and are dominated by soft corals. Long-term monitoring within fixed transects on representative reef was initiated in 1993 and has entailed annual photo-quadrat surveys and hourly temperature logging. Although sea temperatures rose by 0.15 °C p.a. at the site up to 2000, they have subsequently been decreasing, and the overall trend based on monthly means has been a significant decrease of 0.03 °C p.a. Despite this, minor bleaching was encountered in the region during the 1998 El Niño-Southern Oscillation event, again in the summer of 2000/2001 and in 2005. A significant decreasing trend of 0.95% p.a. in soft coral cover has been evident throughout the monitoring period, attributable to significant decreases in Sinularia and Lobophytum spp. cover. In contrast, hard coral cover gradually and significantly increased up to 2005, this being largely attributable to increases in cover by Acropora spp. Recruitment success and mortality of both soft and hard corals has displayed high inter-annual variability with increasing but non-significant trends in the last 5 yr. The reduction in soft coral cover has been more consistent and greater than that of hard corals, but it is difficult at this stage to attribute this to changes in water quality, acidification-linked accretion or temperature.

  3. The Relationship of High-Latitude Thermospheric Wind With Ionospheric Horizontal Current, as Observed by CHAMP Satellite

    Science.gov (United States)

    Huang, Tao; Lühr, Hermann; Wang, Hui; Xiong, Chao

    2017-12-01

    The relationship between high-latitude ionospheric currents (Hall current and field-aligned current) and thermospheric wind is investigated. The 2-D patterns of horizontal wind and equivalent current in the Northern Hemisphere derived from the CHAMP satellite are considered for the first time simultaneously. The equivalent currents show strong dependences on both interplanetary magnetic field (IMF) By and Bz components. However, IMF By orientation is more important in controlling the wind velocity patterns. The duskside wind vortex as well as the antisunward wind in the morning polar cap is more evident for positive By. To better understand their spatial relation in different sectors, a systematic superposed epoch analysis is applied. Our results show that in the dusk sector, the vectors of the zonal wind and equivalent current are anticorrelated, and both of them form a vortical flow pattern for different activity levels. The currents and zonal wind are intensified with the increase of merging electric field. However, on the dawnside, where the relation is less clear, antisunward zonal winds dominate. Plasma drift seems to play a less important role for the wind than neutral forces in this sector. In the noon sector, the best anticorrelation between equivalent current and wind is observed for a positive IMF By component and it is less obvious for negative By. A clear seasonal effect with current intensities increasing from winter to summer is observed in the noon sector. Different from the currents, the zonal wind intensity shows little dependence on seasons. Our results indicate that the plasma drift and the neutral forces are of comparable influence on the zonal wind at CHAMP altitude in the noon sector.

  4. Early Spring Post-Fire Snow Albedo Dynamics in High Latitude Boreal Forests Using Landsat-8 OLI Data

    Science.gov (United States)

    Wang, Zhuosen; Erb, Angela M.; Schaaf, Crystal B.; Sun, Qingsong; Liu, Yan; Yang, Yun; Shuai, Yanmin; Casey, Kimberly A.; Roman, Miguel O.

    2016-01-01

    thus play an important role in characterizing the carbon cycle and ecosystem processes of high latitude systems.

  5. Carbon stocks and fluxes in the high latitudes: using site-levelbreak data to evaluate Earth system models

    DEFF Research Database (Denmark)

    Chadburn, S. E.; Krinner, G.; Porada, P.

    2017-01-01

    from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France). We use a site-level approach in which...

  6. Evolution determines how global warming and pesticide exposure will shape predator‐prey interactions with vector mosquitoes

    DEFF Research Database (Denmark)

    Tran, Tam H.; Janssens, Lizanne; Dinh, Khuong Van

    2016-01-01

    How evolution may mitigate the effects of global warming and pesticide exposure on predator–prey interactions is directly relevant for vector control. Using a space-for-time substitution approach, we addressed how 4°C warming and exposure to the pesticide endosulfan shape the predation on Culex...... pipiens mosquitoes by damselfly predators from replicated low- and high-latitude populations. Although warming was only lethal for the mosquitoes, it reduced predation rates on these prey. Possibly, under warming escape speeds of the mosquitoes increased more than the attack efficiency of the predators...... at the high latitude will be reduced under warming unless predators evolve toward the current low-latitude phenotype or low-latitude predators move poleward...

  7. Temporal-spatial patterns of three types of pesticide loadings in a middle-high latitude agricultural watershed.

    Science.gov (United States)

    Ouyang, Wei; Cai, Guanqing; Tysklind, Mats; Yang, Wanyin; Hao, Fanghua; Liu, Hongbin

    2017-10-01

    Pesticide loadings to watersheds increase during agricultural development and may vary in accordance with different crop types and seasons. High pesticide loadings can potentially result in polluted stream water. The objective of this study was to determine the pesticide loadings and concentrations of three typical pesticides (atrazine, oxadiazon, and isoprothiolane) in river water from a middle-high latitude agricultural watershed in northern China. During this study, we evaluated the watershed pesticide loss patterns for two crop types over three decades. For this purpose, we integrated data from field investigations, laboratory experiments, and modeling simulations involving a distributed hydrological solute transport model (Soil and Water Assessment Tool, SWAT). SWAT was employed to compare the temporal-spatial fate and behaviors of atrazine, oxadiazon, and isoprothiolane from 1990 to 2014 in a watershed area amounting to 141.5 km 2 . The results showed that the three pesticides could be detected at different locations throughout the watershed, and isoprothiolane was detected at the maximum value of 1.082 μg/L in surface runoff of paddy land. The temporal trend for the yearly loading of atrazine decreased slightly over time, but the trends for oxadiazon and isoprothiolane increased markedly over an 18-year analysis period. In regard to the pesticide concentrations in water, atrazine was associated with the largest value of nearly 1.4 μg/L. July and August were the found to be prime periods for pesticide loss from paddy land, and the biggest monthly loss of atrazine from dryland appeared in June. Under similar usage conditions, isoprothiolane loading from paddy fields ranked as the largest one among the three types of pesticides and reached up to 17 g/ha. Limited monitoring data were useful for validating the model, which yielded valuable temporal-spatial data on the fate of pesticides in this watershed. With the expansion of paddy rice cultivation, risks

  8. Turning up the heat: increasing temperature and coral bleaching at the high latitude coral reefs of the Houtman Abrolhos Islands.

    Science.gov (United States)

    Abdo, David A; Bellchambers, Lynda M; Evans, Scott N

    2012-01-01

    Coral reefs face increasing pressures particularly when on the edge of their distributions. The Houtman Abrolhos Islands (Abrolhos) are the southernmost coral reef system in the Indian Ocean, and one of the highest latitude reefs in the world. These reefs have a unique mix of tropical and temperate marine fauna and flora and support 184 species of coral, dominated by Acropora species. A significant La Niña event during 2011 produced anomalous conditions of increased temperature along the whole Western Australian coastline, producing the first-recorded widespread bleaching of corals at the Abrolhos. We examined long term trends in the marine climate at the Abrolhos using historical sea surface temperature data (HadISST data set) from 1900-2011. In addition in situ water temperature data for the Abrolhos (from data loggers installed in 2008, across four island groups) were used to determine temperature exposure profiles. Coupled with the results of coral cover surveys conducted annually since 2007; we calculated bleaching thresholds for monitoring sites across the four Abrolhos groups. In situ temperature data revealed maximum daily water temperatures reached 29.54°C in March 2011 which is 4.2°C above mean maximum daily temperatures (2008-2010). The level of bleaching varied across sites with an average of ∼12% of corals bleached. Mortality was high, with a mean ∼50% following the 2011 bleaching event. Prior to 2011, summer temperatures reached a mean (across all monitoring sites) of 25.1°C for 2.5 days. However, in 2011 temperatures reached a mean of 28.1°C for 3.3 days. Longer term trends (1900-2011) showed mean annual sea surface temperatures increase by 0.01°C per annum. Long-term temperature data along with short-term peaks in 2011, outline the potential for corals to be exposed to more frequent bleaching risk with consequences for this high latitude coral reef system at the edge of its distribution.

  9. On the importance of appropriate precipitation gauge catch correction for hydrological modelling at mid to high latitudes

    Science.gov (United States)

    Stisen, S.; Højberg, A. L.; Troldborg, L.; Refsgaard, J. C.; Christensen, B. S. B.; Olsen, M.; Henriksen, H. J.

    2012-11-01

    precipitation correction should be carried out for studies requiring a sound dynamic description of hydrological processes, and it is of particular importance when using hydrological models to make predictions for future climates when the snow/rain composition will differ from the past climate. This conclusion is expected to be applicable for mid to high latitudes, especially in coastal climates where winter precipitation types (solid/liquid) fluctuate significantly, causing climatological mean correction factors to be inadequate.

  10. On the importance of appropriate precipitation gauge catch correction for hydrological modelling at mid to high latitudes

    Directory of Open Access Journals (Sweden)

    S. Stisen

    2012-11-01

    . We conclude that TSV precipitation correction should be carried out for studies requiring a sound dynamic description of hydrological processes, and it is of particular importance when using hydrological models to make predictions for future climates when the snow/rain composition will differ from the past climate. This conclusion is expected to be applicable for mid to high latitudes, especially in coastal climates where winter precipitation types (solid/liquid fluctuate significantly, causing climatological mean correction factors to be inadequate.

  11. Modelling horizontal and vertical concentration profiles of ozone and oxides of nitrogen within high-latitude urban areas

    International Nuclear Information System (INIS)

    Nicholson, J.P.; Weston, K.J.

    2001-01-01

    Urban ozone concentrations are determined by the balance between ozone destruction, chemical production and supply through advection and turbulent down-mixing from higher levels. At high latitudes, low levels of solar insolation and high horizontal advection speeds reduce the photochemical production and the spatial ozone concentration patterns are largely determined by the reaction of ozone with nitric oxide and dry deposition to the surface. A Lagrangian column model has been developed to simulate the mean (monthly and annual) three-dimensional structure in ozone and nitrogen oxides (NO x ) concentrations in the boundary-layer within and immediately around an urban area. The short-time-scale photochemical processes of ozone and NO x , as well as emissions and deposition to the ground, are simulated. The model has a horizontal resolution of 1x1km and high resolution in the vertical. It has been applied over a 100x100km domain containing the city of Edinburgh (at latitude 56 o N) to simulate the city-scale processes of pollutants. Results are presented, using averaged wind-flow frequencies and appropriate stability conditions, to show the extent of the depletion of ozone by city emissions. The long-term average spatial patterns in the surface ozone and NO x concentrations over the model domain are reproduced quantitatively. The model shows the average surface ozone concentrations in the urban area to be lower than the surrounding rural areas by typically 50% and that the areas experiencing a 20% ozone depletion are generally restricted to within the urban area. The depletion of the ozone concentration to less than 50% of the rural surface values extends only 20m vertically above the urban area. A series of monitoring sites for ozone, nitric oxide and nitrogen dioxide on a north-south transect through the city - from an urban, through a semi-rural, to a remote rural location - allows the comparison of modelled with observed data for the mean diurnal cycle of ozone

  12. Snow driven Radiative Forcing in High Latitude Areas of Disturbance Using Higher Resolution Albedo Products from Landsat and Sentinel-2

    Science.gov (United States)

    Erb, A.; Li, Z.; Schaaf, C.; Wang, Z.; Rogers, B. M.

    2017-12-01

    Land surface albedo plays an important role in the surface energy budget and radiative forcing by determining the proportion of absorbed incoming solar radiation available to drive photosynthesis and surface heating. In Arctic regions, albedo is particularly sensitive to land cover and land use change (LCLUC) and modeling efforts have shown it to be the primary driver of effective radiative forcing from the biogeophysical effects of LCLUC. In boreal forests, the effects of these changes are complicated during snow covered periods when newly exposed, highly reflective snow can serve as the primary driver of radiative forcing. In Arctic biomes disturbance scars from fire, pest and harvest can remain in the landscape for long periods of time. As such, understanding the magnitude and persistence of these disturbances, especially in the shoulder seasons, is critical. The Landsat and Sentinel-2 Albedo Products couple 30m and 20m surface reflectances with concurrent 500m BRDF Products from the MODerate resolution Imaging Spectroradiometer (MODIS). The 12 bit radiometric fidelity of Sentinel-2 and Landsat-8 allow for the inclusion of high-quality, unsaturated albedo calculations over snow covered surfaces at scales more compatible with fragmented landscapes. Recent work on the early spring albedo of fire scars has illustrated significant post-fire spatial heterogeneity of burn severity at the landscape scale and highlights the need for a finer spatial resolution albedo record. The increased temporal resolution provided by multiple satellite instruments also allows for a better understanding of albedo dynamics during the dynamic shoulder seasons and in historically difficult high latitude locations where persistent cloud cover limits high quality retrievals. Here we present how changes in the early spring albedo of recent boreal forest disturbance in Alaska and central Canada affects landscape-scale radiative forcing. We take advantage of the long historical Landsat record

  13. Amplifier for nuclear spectrometry

    International Nuclear Information System (INIS)

    Suarez Canner, E.

    1996-01-01

    The spectroscopy amplifier model AE-020 is designed to adjust suitable the pulses coming from nuclear radiation detectors. Due to is capacity and specifications, the amplifier can be used together with high and medium resolution spectroscopy system

  14. Portable musical instrument amplifier

    Science.gov (United States)

    Christian, David E.

    1990-07-24

    The present invention relates to a musical instrument amplifier which is particularly useful for electric guitars. The amplifier has a rigid body for housing both the electronic system for amplifying and processing signals from the guitar and the system's power supply. An input plug connected to and projecting from the body is electrically coupled to the signal amplifying and processing system. When the plug is inserted into an output jack for an electric guitar, the body is rigidly carried by the guitar, and the guitar is operatively connected to the electrical amplifying and signal processing system without use of a loose interconnection cable. The amplifier is provided with an output jack, into which headphones are plugged to receive amplified signals from the guitar. By eliminating the conventional interconnection cable, the amplifier of the present invention can be used by musicians with increased flexibility and greater freedom of movement.

  15. Global warming

    International Nuclear Information System (INIS)

    Anon.

    1992-01-01

    Canada's Green Plan strategy for dealing with global warming is being implemented as a multidepartmental partnership involving all Canadians and the international community. Many of the elements of this strategy are built on an existing base of activities predating the Green Plan. Elements of the strategy include programs to limit emissions of greenhouse gases, such as initiatives to encourage more energy-efficient practices and development of alternate fuel sources; studies and policy developments to help Canadians prepare and adapt to climate change; research on the global warming phenomenon; and stimulation of international action on global warming, including obligations arising out of the Framework Convention on Climate Change. All the program elements have been approved, funded, and announced. Major achievements to date are summarized, including improvements in the Energy Efficiency Act, studies on the socioeconomic impacts of global warming, and participation in monitoring networks. Milestones associated with the remaining global warming initiatives are listed

  16. Using stable isotopes to assess surface water source dynamics and hydrological connectivity in a high-latitude wetland and permafrost influenced landscape

    Science.gov (United States)

    Ala-aho, P.; Soulsby, C.; Pokrovsky, O. S.; Kirpotin, S. N.; Karlsson, J.; Serikova, S.; Vorobyev, S. N.; Manasypov, R. M.; Loiko, S.; Tetzlaff, D.

    2018-01-01

    Climate change is expected to alter hydrological and biogeochemical processes in high-latitude inland waters. A critical question for understanding contemporary and future responses to environmental change is how the spatio-temporal dynamics of runoff generation processes will be affected. We sampled stable water isotopes in soils, lakes and rivers on an unprecedented spatio-temporal scale along a 1700 km transect over three years in the Western Siberia Lowlands. Our findings suggest that snowmelt mixes with, and displaces, large volumes of water stored in the organic soils and lakes to generate runoff during the thaw season. Furthermore, we saw a persistent hydrological connection between water bodies and the landscape across permafrost regions. Our findings help to bridge the understanding between small and large scale hydrological studies in high-latitude systems. These isotope data provide a means to conceptualise hydrological connectivity in permafrost and wetland influenced regions, which is needed for an improved understanding of future biogeochemical changes.

  17. Monitoring Coral Health to Determine Coral Bleaching Response at High Latitude Eastern Australian Reefs: An Applied Model for A Changing Climate

    OpenAIRE

    Dalton, Steven J.; Carroll, Andrew G.

    2011-01-01

    Limited information is available on the bleaching susceptibility of coral species that dominate high latitude reefs along the eastern seaboard of Australia. The main aims of this study were to: (i) monitor coral health and spatial patterns of coral bleaching response at the Solitary Islands Marine Park (SIMP) and Lord Howe Island Marine Park (LHIMP), to determine variability of bleaching susceptibility among coral taxa; (ii) predict coral bleaching thresholds at 30 °S and 31.5 °S, extrapolate...

  18. A search for pre-main sequence stars in the high-latitude molecular clouds. II - A survey of the Einstein database

    Science.gov (United States)

    Caillault, Jean-Pierre; Magnani, Loris

    1990-01-01

    The preliminary results are reported of a survey of every EINSTEIN image which overlaps any high-latitude molecular cloud in a search for X-ray emitting pre-main sequence stars. This survey, together with complementary KPNO and IRAS data, will allow the determination of how prevalent low mass star formation is in these clouds in general and, particularly, in the translucent molecular clouds.

  19. Investigating the Role of Biogeochemical Processes in the Northern High Latitudes on Global Climate Feedbacks Using an Efficient Scalable Earth System Model

    Energy Technology Data Exchange (ETDEWEB)

    Jain, Atul K. [Univ. of Illinois, Urbana-Champaign, IL (United States)

    2016-09-14

    The overall objectives of this DOE funded project is to combine scientific and computational challenges in climate modeling by expanding our understanding of the biogeophysical-biogeochemical processes and their interactions in the northern high latitudes (NHLs) using an earth system modeling (ESM) approach, and by adopting an adaptive parallel runtime system in an ESM to achieve efficient and scalable climate simulations through improved load balancing algorithms.

  20. Amplification factor variable amplifier

    NARCIS (Netherlands)

    Akitsugu, Oshita; Nauta, Bram

    2007-01-01

    PROBLEM TO BE SOLVED: To provide an amplification factor variable amplifier capable of achieving temperature compensation of an amplification factor over a wide variable amplification factor range. ; SOLUTION: A Gilbert type amplification factor variable amplifier 11 amplifies an input signal and

  1. Amplification factor variable amplifier

    NARCIS (Netherlands)

    Akitsugu, Oshita; Nauta, Bram

    2010-01-01

    PROBLEM TO BE SOLVED: To provide an amplification factor variable amplifier capable of achieving temperature compensation of an amplification factor over a wide variable amplification factor range. ;SOLUTION: A Gilbert type amplification factor variable amplifier 11 amplifies an input signal and can

  2. Influence of high latitude light conditions on sensory quality and contents of health and sensory-related compounds in swede roots (Brassica napus L. ssp. rapifera Metzg.).

    Science.gov (United States)

    Mølmann, Jørgen Ab; Hagen, Sidsel Fiskaa; Bengtsson, Gunnar B; Johansen, Tor J

    2018-02-01

    Vegetable growers in Arctic areas must increasingly rely on market strategies based on regional origin and product quality. Swede roots (rutabaga) were grown in a phytotron to investigate the effect of high latitude light conditions on sensory quality and some health and sensory-related compounds. Experimental treatments included modifications of 24 h natural day length (69° 39' N) by moving plants at daily intervals to dark chambers with either no light, fluorescent growth light and/or low intensity photoperiod extension. Shortening the photosynthetic light period to 12 h produced smaller roots than 15.7 h and 18 h, with highest scores for bitter and sulfur taste, and lowest scores for sweetness, acidic taste and fibrousness. The photoperiod in combination with the photosynthetic light period also had an influence on glucosinolate (GLS) contents, with lowest concentrations in 24 h natural light and highest in 12 h natural light. Concentrations of vitamin C, glucose, fructose and sucrose were not significantly influenced by any of the treatments. High latitude light conditions, with long photosynthetic light periods and 24 h photoperiod, can enhance sweet/less bitter taste and reduce GLS contents in swede roots, compared to growth under short day conditions. This influence of light conditions on eating quality may benefit marketing of regional products from high latitudes. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

  3. Empirical model of the high-latitude boundary of the Earth's outer radiation belt at altitudes of up to 1000 km

    Science.gov (United States)

    Kalegaev, V. V.; Barinova, W. O.; Myagkova, I. N.; Eremeev, V. E.; Parunakyan, D. A.; Nguyen, M. D.; Barinov, O. G.

    2018-01-01

    An empirical model of the high-latitude boundary of the outer Earth's radiation belt (ERB) has been presented, which is based on the measurement data of electron fluxes on the polar low-orbit CORONAS-Photon, Meteor-M1, and Meteor-M2 satellites. The boundary was determined by a sharp decrease to the background level of the flux of trapped electrons with energies of 100 or 200 keV in the polar part of the profile of the outer radiation belt. A numerical algorithm has been implemented to determine the time moment, when the fastest flux changes are recorded. The primary search was carried out, first, on 30 s averaged data, then repeated on data with a higher resolution. A functional dependence was obtained in order to approximate the obtained set of intersections of the boundary by elliptical curve. The empirical model constructed using the CORONAS-Photon measurement data in the epoch of anomalously low geomagnetic activity reflects the longitude structure of the high-latitude boundary of the outer radiation belt associated with the internal Earth's magnetic field (MF), as well as its dependence on the universal time. Based on the data of intersections of the high-latitude boundary of the outer ERB (OERB) in the epoch of 2014-2016, the latitudinal shift of the boundary to the equator dependent on geomagnetic activity has been determined, as well as the nightside shift of the boundary due to the diurnal rotation of the Earth.

  4. A theoretical and empirical study of the response of the high latitude thermosphere to the sense of the 'Y' component of the interplanetary magnetic field

    International Nuclear Information System (INIS)

    Rees, D.; Fuller-Rowell, T.J.; Gordon, R.

    1986-01-01

    The strength and direction of the Interplanetary Magnetic Field (IMF) controls the transfer of solar wind momentum and energy to the high latitude thermosphere in a direct fashion. The sense of ''Y'' component of the IMF (BY) creates a significant asymmetry of the magnetospheric convection pattern as mapped onto the high latitude thermosphere and ionosphere. The resulting response of the polar thermospheric winds during periods when BY is either positive or negative is quite distinct, with pronounced changes in the relative strength of thermospheric winds in the dusk-dawn parts of the polar cap and in the dawn part of the auroral oval. In a study of four periods when there was a clear signature of BY, observed by the ISEE-3 satellite, with observations of polar winds and electric fields from the Dynamics Explorer-2 satellite and with wind observations by a ground-based Fabry-Perot interferometer located in Kiruna, Northern Sweden, it is possible to explain features of the high latitude thermospheric circulation using three dimensional global models including BY dependent, asymmetric, polar convection fields. Anomalously zonal wind velocities are often observed, for BY positive and when BY is negative. These are matched by the observation of strong anti-sunward polar-cap wind jets from the DE-2 satellite, on the dusk side with BY negative, and on the dawn side with BY positive. (author)

  5. Results of PMIP2 coupled simulations of the Mid-Holocene and Last Glacial Maximum – Part 2: feedbacks with emphasis on the location of the ITCZ and mid- and high latitudes heat budget

    Directory of Open Access Journals (Sweden)

    Y. Zhao

    2007-06-01

    Full Text Available A set of coupled ocean-atmosphere(-vegetation simulations using state of the art climate models is now available for the Last Glacial Maximum (LGM and the Mid-Holocene (MH through the second phase of the Paleoclimate Modeling Intercomparison Project (PMIP2. Here we quantify the latitudinal shift of the location of the Intertropical Convergence Zone (ITCZ in the tropical regions during boreal summer and the change in precipitation in the northern part of the ITCZ. For both periods the shift is more pronounced over the continents and East Asia. The maritime continent is the region where the largest spread is found between models. We also clearly establish that the larger the increase in the meridional temperature gradient in the tropical Atlantic during summer at the MH, the larger the change in precipitation over West Africa. The vegetation feedback is however not as large as found in previous studies, probably due to model differences in the control simulation. Finally, we show that the feedback from snow and sea-ice at mid and high latitudes contributes for half of the cooling in the Northern Hemisphere for the LGM, with the remaining being achieved by the reduced CO2 and water vapour in the atmosphere. For the MH the snow and albedo feedbacks strengthen the spring cooling and enhance the boreal summer warming, whereas water vapour reinforces the late summer warming. These feedbacks are modest in the Southern Hemisphere. For the LGM most of the surface cooling is due to CO2 and water vapour.

  6. Ground thermal and geomechanical conditions in a permafrost-affected high-latitude rock avalanche site (Polvartinden, northern Norway)

    Science.gov (United States)

    Frauenfelder, Regula; Isaksen, Ketil; Lato, Matthew J.; Noetzli, Jeannette

    2018-04-01

    On 26 June 2008, a rock avalanche detached in the northeast facing slope of Polvartinden, a high-alpine mountain in Signaldalen, northern Norway. Here, we report on the observed and modelled past and present near-surface temperature regime close to the failure zone, as well as on a subsequent simulation of the subsurface temperature regime, and on initial geomechanical mapping based on laser scanning. The volume of the rock avalanche was estimated to be approximately 500 000 m3. The depth to the actual failure surface was found to range from 40 m at the back of the failure zone to 0 m at its toe. Visible in situ ice was observed in the failure zone just after the rock avalanche. Between September 2009 and August 2013, ground surface temperatures were measured with miniature temperature data loggers at 14 different localities, close to the original failure zone along the northern ridge of Polvartinden and on the valley floor. The results from these measurements and from a basic three-dimensional heat conduction model suggest that the lower altitudinal limit of permafrost at present is at 600-650 m a.s.l., which corresponds to the upper limit of the failure zone. A coupling of our in situ data with regional climate data since 1958 suggests a general gradual warming and that the period with highest mean near surface temperatures on record ended four months before the Signaldalen rock avalanche detached. A comparison with a transient permafrost model run at 10 m depth, representative for areas where snow accumulates, strengthen these findings, which are also in congruence with measurements in nearby permafrost boreholes. It is likely that permafrost in and near the failure zone is presently subject to degradation. This degradation, in combination with the extreme warm year antecedent to the rock failure, is seen to have played an important role in the detaching of the Signaldalen rock avalanche.

  7. Late Holocene climate and chemical change at high latitudes: case studies from contaminated sites in subarctic and arctic Canada

    Science.gov (United States)

    Galloway, Jennifer M.; Cooney, Darryl; Crann, Carley; Falck, Hendrik; Howell, Dana; Jamieson, Heather; Macumber, Andrew; Nasser, Nawaf; Palmer, Michael; Patterson, R. Timothy; Parsons, Michael; Roe, Helen M.; Sanei, Hamed; Spence, Christopher; Stavinga, Drew; Swindles, Graeme T.

    2015-04-01

    preserved in the lake sediment cores are informed by our characterization of sediments from over 50 lakes in the region. In the longer record obtained from the Giant Mine area we show that the concentration of aqua regia leached As increases prior to resource development and that concentrations are variable over millennia. Lowest concentrations of As in the ~3500 cal yr BP record are coincident with regional Neoglacial cooling. As concentrations begin to increase from concentrations near 100 ppm to over 1000 ppm in the lastest Holocene, coincident with a period of regional warming associated with the Medieval Warm period, although at this point we cannot rule out post-depositional remobilization of As from higher in the sediment column. Concentrations in excess of 10,000 ppm at the top of the sediment core are likely associated with anthropogenic release of this contaminant. At the more northern Courageous Lake site, the sediment record extends back about a hundred years, and reveals that concentrations of As in lake sediments prior to development of the area were about 40 ppm. Increases in As are associated with drilling and mine production but continued increases after 1999 may be due to remobilization of As due to on-going climate warming, recent remediation efforts, or vertical movement of this element in the sediment column.

  8. Oscillators and operational amplifiers

    OpenAIRE

    Lindberg, Erik

    2005-01-01

    A generalized approach to the design of oscillators using operational amplifiers as active elements is presented. A piecewise-linear model of the amplifier is used so that it make sense to investigate the eigenvalues of the Jacobian of the differential equations. The characteristic equation of the general circuit is derived. The dynamic nonlinear transfer characteristic of the amplifier is investigated. Examples of negative resistance oscillators are discussed.

  9. Ground thermal and geomechanical conditions in a permafrost-affected high-latitude rock avalanche site (Polvartinden, northern Norway

    Directory of Open Access Journals (Sweden)

    R. Frauenfelder

    2018-04-01

    Full Text Available On 26 June 2008, a rock avalanche detached in the northeast facing slope of Polvartinden, a high-alpine mountain in Signaldalen, northern Norway. Here, we report on the observed and modelled past and present near-surface temperature regime close to the failure zone, as well as on a subsequent simulation of the subsurface temperature regime, and on initial geomechanical mapping based on laser scanning. The volume of the rock avalanche was estimated to be approximately 500 000 m3. The depth to the actual failure surface was found to range from 40 m at the back of the failure zone to 0 m at its toe. Visible in situ ice was observed in the failure zone just after the rock avalanche. Between September 2009 and August 2013, ground surface temperatures were measured with miniature temperature data loggers at 14 different localities, close to the original failure zone along the northern ridge of Polvartinden and on the valley floor. The results from these measurements and from a basic three-dimensional heat conduction model suggest that the lower altitudinal limit of permafrost at present is at 600–650 m a.s.l., which corresponds to the upper limit of the failure zone. A coupling of our in situ data with regional climate data since 1958 suggests a general gradual warming and that the period with highest mean near surface temperatures on record ended four months before the Signaldalen rock avalanche detached. A comparison with a transient permafrost model run at 10 m depth, representative for areas where snow accumulates, strengthen these findings, which are also in congruence with measurements in nearby permafrost boreholes. It is likely that permafrost in and near the failure zone is presently subject to degradation. This degradation, in combination with the extreme warm year antecedent to the rock failure, is seen to have played an important role in the detaching of the Signaldalen rock avalanche.

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

    Science.gov (United States)

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

    2017-12-01

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

  11. Late Cretaceous paleosols as paleoclimate proxies of high-latitude Southern Hemisphere: Mata Amarilla Formation, Patagonia, Argentina

    Science.gov (United States)

    Varela, Augusto N.; Raigemborn, M. Sol; Richiano, Sebastián; White, Tim; Poiré, Daniel G.; Lizzoli, Sabrina

    2018-01-01

    Although there is general consensus that a global greenhouse climate characterized the mid-Cretaceous, details of the climate state of the mid-Cretaceous Southern Hemisphere are less clearly understood. In particular, continental paleoclimate reconstructions are scarce and exclusively derived from paleontological records. Using paleosol-derived climofunction studies of the mid- to Upper Cretaceous Mata Amarilla Formation, southern Patagonia, Argentina, we present a reconstruction of the mid-Cretaceous climate of southern South America. Our results indicate that at 60° south paleolatitude during the Cenomanian-Santonian stages, the climate was subtropical temperate-warm (12 °C ± 2.1 °C) and humid (1404 ± 108 mm/yr) with marked rainfall seasonality. These results are consistent with both previous estimations from the fossil floras of the Mata Amarilla Formation and other units of the Southern Hemisphere, and with the previous observations of the displacement of tropical and subtropical floras towards the poles in both hemispheres. The data presented here show a more marked seasonality and slightly lower mean annual precipitation and mean annual temperature values than those recorded at the same paleolatitudes in the Northern Hemisphere.

  12. Using thermal limits to assess establishment of fish dispersing to high-latitude and high-elevation watersheds

    Science.gov (United States)

    Dunmall, Karen M.; Mochnacz, Neil J.; Zimmerman, Christian E.; Lean, Charles; Reist, James D.

    2016-01-01

    Distributional shifts of biota to higher latitudes and elevations are presumably influenced by species-specific physiological tolerances related to warming temperatures. However, it is establishment rather than dispersal that may be limiting colonizations in these cold frontier areas. In freshwater ecosystems, perennial groundwater springs provide critical winter thermal refugia in these extreme environments. By reconciling the thermal characteristics of these refugia with the minimum thermal tolerances of life stages critical for establishment, we develop a strategy to focus broad projections of northward and upward range shifts to the specific habitats that are likely for establishments. We evaluate this strategy using chum salmon (Oncorhynchus keta) and pink salmon (Oncorhynchus gorbuscha) that seem poised to colonize Arctic watersheds. Stream habitats with a minimum temperature of 4 °C during spawning and temperatures above 2 °C during egg incubation were most vulnerable to establishments by chum and pink salmon. This strategy will improve modelling forecasts of range shifts for cold freshwater habitats and focus proactive efforts to conserve both newly emerging fisheries and native species at northern and upper distributional extremes.

  13. Equatorward dispersion of a high-latitude volcanic plume and its relation to the Asian summer monsoon: a case study of the Sarychev eruption in 2009

    Science.gov (United States)

    Wu, Xue; Griessbach, Sabine; Hoffmann, Lars

    2017-11-01

    Tropical volcanic eruptions have been widely studied for their significant contribution to stratospheric aerosol loading and global climate impacts, but the impact of high-latitude volcanic eruptions on the stratospheric aerosol layer is not clear and the pathway of transporting aerosol from high latitudes to the tropical stratosphere is not well understood. In this work, we focus on the high-latitude volcano Sarychev (48.1° N, 153.2° E), which erupted in June 2009, and the influence of the Asian summer monsoon (ASM) on the equatorward dispersion of the volcanic plume. First, the sulfur dioxide (SO2) emission time series and plume height of the Sarychev eruption are estimated with SO2 observations of the Atmospheric Infrared Sounder (AIRS) and a backward trajectory approach using the Lagrangian particle dispersion model Massive-Parallel Trajectory Calculations (MPTRAC). Then, the transport and dispersion of the plume are simulated using the derived SO2 emission time series. The transport simulations are compared with SO2 observations from AIRS and validated with aerosol observations from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). The MPTRAC simulations show that about 4 % of the sulfur emissions were transported to the tropical stratosphere within 50 days after the beginning of the eruption, and the plume dispersed towards the tropical tropopause layer (TTL) through isentropic transport above the subtropical jet. The MPTRAC simulations and MIPAS aerosol data both show that between the potential temperature levels of 360 and 400 K, the equatorward transport was primarily driven by anticyclonic Rossby wave breaking enhanced by the ASM in boreal summer. The volcanic plume was entrained along the anticyclone flows and reached the TTL as it was transported southwestwards into the deep tropics downstream of the anticyclone. Further, the ASM anticyclone influenced the pathway of aerosols by isolating an aerosol hole inside of the ASM, which

  14. Multi-event study of high-latitude thermospheric wind variations at substorm onset with a Fabry-Perot interferometer at Tromsoe, Norway

    Science.gov (United States)

    Xu, H.; Shiokawa, K.; Oyama, S. I.; Otsuka, Y.

    2017-12-01

    We studied the high-latitude thermospheric wind variations near the onset time of isolated substorms. Substorm-related energy input from the magnetosphere to the polar ionosphere modifies the high-latitude ionosphere and thermosphere. For the first time, this study showed the characteristics of high-latitude thermospheric wind variations at the substorm onset. We also investigated the possibility of these wind variations as a potential trigger of substorm onset by modifying the ionospheric current system (Kan, 1993). A Fabry-Perot interferometer (FPI) at Tromsoe, Norway provided wind measurements estimated from Doppler shift of both red-line (630.0 nm for the F region) and green-line (557.7 nm for the E region) emissions of aurora and airglow. We used seven-year data sets obtained from 2009 to 2015 with a time resolution of 13 min. We first identified the onset times of local isolated substorms using ground-based magnetometer data obtained at the Tromsoe and Bear Island stations, which belongs to the IMAGE magnetometer chain. We obtained 4 red-line events and 5 green-line events taken place at different local times. For all these events, the peak locations of westward ionospheric currents identified by the ground-based magnetometer chain were located at the poleward side of Tromsoe. Then, we calculated two weighted averages of wind velocities for 30 min around the onset time and 30 min after the onset time of substorms. We evaluated differences between these two weighted averages to estimate the strength of wind changes. The observed wind changes at these substorm onsets were less than 49 m/s (26 m/s) for red-line (green-line) events, which are much smaller than the typical plasma convection speed. This indicates that the plasma motion caused by substorm-induced thermospheric winds through ion-neutral collisions is a minor effect as the driver of high-latitude plasma convection, as well as the triggering of substorm onset. We discuss possible causes of these

  15. Changes in the High-Latitude Topside Ionospheric Vertical Electron-Density Profiles in Response to Solar-Wind Perturbations During Large Magnetic Storms

    Science.gov (United States)

    Benson, Robert F.; Fainberg, Joseph; Osherovich, Vladimir; Truhlik, Vladimir; Wang, Yongli; Arbacher, Becca

    2011-01-01

    The latest results from an investigation to establish links between solar-wind and topside-ionospheric parameters will be presented including a case where high-latitude topside electron-density Ne(h) profiles indicated dramatic rapid changes in the scale height during the main phase of a large magnetic storm (Dst wind data obtained from the NASA OMNIWeb database indicated that the magnetic storm was due to a magnetic cloud. This event is one of several large magnetic storms being investigated during the interval from 1965 to 1984 when both solar-wind and digital topside ionograms, from either Alouette-2, ISIS-1, or ISIS-2, are potentially available.

  16. FLUIDIC AC AMPLIFIERS.

    Science.gov (United States)

    Several fluidic tuned AC Amplifiers were designed and tested. Interstage tuning and feedback designs are considered. Good results were obtained...corresponding Q’s as high as 12. Element designs and test results of one, two, and three stage amplifiers are presented. AC Modulated Carrier Systems

  17. Antares laser power amplifier

    International Nuclear Information System (INIS)

    Stine, R.D.; Ross, G.F.; Silvernail, C.

    1979-01-01

    The overall design of the Antares laser power amplifier is discussed. The power amplifier is the last stage of amplification in the 100-kJ Antares laser. In the power amplifier a single, cylindrical, grid-controlle, cold-cathode electron gun is surrounded by 12 large-aperture CO 2 electron-beam sustained laser discharge sectors. Each power amplifier will deliver 18 kJ and the six modules used in Antares will produce the required 100 kJ for delivery to the target. A large-scale interaction between optical, mechanical, and electrical disciplines is required to meet the design objectives. Significant component advances required by the power amplifier design are discussed

  18. Why high-latitude clouds in our galaxy and the highly redshifted clouds observed in front of QSOs do not belong to the same parent population

    International Nuclear Information System (INIS)

    Wolfe, A.M.

    1983-01-01

    International Ultraviolet Explorer observations of high-latitude gas in our Galaxy reveal the presence of both C II and C IV absorption in the spectra of stars with z>2 kpc. On the other hand, C II is generally absent from unbiased samples of QSO redshift systems with C IV absorption. Comparison between the equivalent-width distributions of the QSO sample and of the galactic sample (which is suitably corrected for contamination by disk absorption) shows that a probability that the two samples are drawn from the same parent population is less than 1% for C II and less than 10% for C IV. Thus, contrary to prevailing opinion, it is highly unlikely that gaseous halos comprised of material with properties of the high-latitude gas are responsible for the bulk of known QSO redshift systems. However, gaseous halos with bimodal states of ionization, or in which the ionization state is a unique function of redshift, are compatible with QSO absorption statistics

  19. The microbial fate of carbon in high-latitude seas: Impact of the microbial loop on oceanic uptake of CO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Yager, P.L.

    1996-12-31

    This dissertation examines pelagic microbial processes in high-latitude seas, how they affect regional and global carbon cycling, and how they might respond to hypothesized changes in climate. Critical to these interests is the effect of cold temperature on bacterial activity. Also important is the extent to which marine biological processes in general impact the inorganic carbon cycle. The study area is the Northeast Water (NEW) Polynya, a seasonally-recurrent opening in the permanent ice situated over the northeastern Greenland continental shelf. This work was part of an international, multi-disciplinary research project studying carbon cycling in the coastal Arctic. The first chapter describes a simple model which links a complex marine food web to a simplified ocean and atmosphere. The second chapter investigates the inorganic carbon inventory of the summertime NEW Polynya surface waters to establish the effect of biological processes on the air-sea pCO{sub 2} gradient. The third and fourth chapters use a kinetic approach to examine microbial activities in the NEW Polynya as a function of temperature and dissolved organic substrate concentration, testing the so-called Pomeroy hypothesis that microbial activity is disproportionately reduced at low environmental temperatures owing to increased organic substrate requirements. Together, the suite of data collected on microbial activities, cell size, and grazing pressure suggest how unique survival strategies adopted by an active population of high-latitude bacteria may contribute to, rather than detract from, an efficient biological carbon pump.

  20. Drift motions of small-scale irregularities in the high-latitude F region: An experimental comparison with plasma drift motions

    International Nuclear Information System (INIS)

    Ruohoniemi, J.M.; Greenwald, R.A.; Baker, K.B.; Villain, J.P.; McCready, M.A.

    1987-01-01

    On the evening of January 6, 1986, coordinated observations were carried out with the Johns Hopkins University Applied Physics Laboratory HF coherent scatter radar at Goose Bay, Labrador, and the SRI International incoherent scatter radar at Sondre Stromfjord, Greenland. The common field of view comprised a section of high-latitude F region ionosphere centered on the great circle plane between the radar sites. Over a 40-min period, the HF radar observed strong backscatter from small-scale (13.9 m) field-aligned irregularities. The bulk line-of-sight drift velocity of the irregularities is deduced from the backscatter data. The returns collected simultaneously with the incoherent scatter radar are processed for estimates of the mean line-of-sight ion velocity. Approximately 100 distinct comparisons are possible between the two sets of velocity estimates. Reversals exceeding 1,000 m/s are present in both. In this paper, the authors demonstrate a correspondence between the measured irregularity and ion drifts that is consistent with the supposition that the motion of the irregularities is dominated by convective drift of the ambient plasma. This indicates that the small-scale irregularities detected by HF radars in the high-latitude F region can serve as tracers of ionospheric convective drift

  1. Carbon stocks and fluxes in the high latitudes: using site-level data to evaluate Earth system models

    Science.gov (United States)

    Chadburn, Sarah E.; Krinner, Gerhard; Porada, Philipp; Bartsch, Annett; Beer, Christian; Belelli Marchesini, Luca; Boike, Julia; Ekici, Altug; Elberling, Bo; Friborg, Thomas; Hugelius, Gustaf; Johansson, Margareta; Kuhry, Peter; Kutzbach, Lars; Langer, Moritz; Lund, Magnus; Parmentier, Frans-Jan W.; Peng, Shushi; Van Huissteden, Ko; Wang, Tao; Westermann, Sebastian; Zhu, Dan; Burke, Eleanor J.

    2017-11-01

    It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France). We use a site-level approach in which comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow. We show that if the models simulate the correct leaf area index (LAI), the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with a similar LAI. The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our analysis suggests that

  2. Auto-Zero Differential Amplifier

    Science.gov (United States)

    Quilligan, Gerard T. (Inventor); Aslam, Shahid (Inventor)

    2017-01-01

    An autozero amplifier may include a window comparator network to monitor an output offset of a differential amplifier. The autozero amplifier may also include an integrator to receive a signal from a latched window comparator network, and send an adjustment signal back to the differential amplifier to reduce an offset of the differential amplifier.

  3. Controlled soil warming powered by alternative energy for remote field sites.

    Science.gov (United States)

    Johnstone, Jill F; Henkelman, Jonathan; Allen, Kirsten; Helgason, Warren; Bedard-Haughn, Angela

    2013-01-01

    Experiments using controlled manipulation of climate variables in the field are critical for developing and testing mechanistic models of ecosystem responses to climate change. Despite rapid changes in climate observed in many high latitude and high altitude environments, controlled manipulations in these remote regions have largely been limited to passive experimental methods with variable effects on environmental factors. In this study, we tested a method of controlled soil warming suitable for remote field locations that can be powered using alternative energy sources. The design was tested in high latitude, alpine tundra of southern Yukon Territory, Canada, in 2010 and 2011. Electrical warming probes were inserted vertically in the near-surface soil and powered with photovoltaics attached to a monitoring and control system. The warming manipulation achieved a stable target warming of 1.3 to 2 °C in 1 m(2) plots while minimizing disturbance to soil and vegetation. Active control of power output in the warming plots allowed the treatment to closely match spatial and temporal variations in soil temperature while optimizing system performance during periods of low power supply. Active soil heating with vertical electric probes powered by alternative energy is a viable option for remote sites and presents a low-disturbance option for soil warming experiments. This active heating design provides a valuable tool for examining the impacts of soil warming on ecosystem processes.

  4. Controlled soil warming powered by alternative energy for remote field sites.

    Directory of Open Access Journals (Sweden)

    Jill F Johnstone

    Full Text Available Experiments using controlled manipulation of climate variables in the field are critical for developing and testing mechanistic models of ecosystem responses to climate change. Despite rapid changes in climate observed in many high latitude and high altitude environments, controlled manipulations in these remote regions have largely been limited to passive experimental methods with variable effects on environmental factors. In this study, we tested a method of controlled soil warming suitable for remote field locations that can be powered using alternative energy sources. The design was tested in high latitude, alpine tundra of southern Yukon Territory, Canada, in 2010 and 2011. Electrical warming probes were inserted vertically in the near-surface soil and powered with photovoltaics attached to a monitoring and control system. The warming manipulation achieved a stable target warming of 1.3 to 2 °C in 1 m(2 plots while minimizing disturbance to soil and vegetation. Active control of power output in the warming plots allowed the treatment to closely match spatial and temporal variations in soil temperature while optimizing system performance during periods of low power supply. Active soil heating with vertical electric probes powered by alternative energy is a viable option for remote sites and presents a low-disturbance option for soil warming experiments. This active heating design provides a valuable tool for examining the impacts of soil warming on ecosystem processes.

  5. Carbon stocks and fluxes in the high latitudes: using site-level data to evaluate Earth system models

    Directory of Open Access Journals (Sweden)

    S. E. Chadburn

    2017-11-01

    Full Text Available It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France. We use a site-level approach in which comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow. We show that if the models simulate the correct leaf area index (LAI, the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with a similar LAI. The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our

  6. Global warming

    International Nuclear Information System (INIS)

    Houghton, John

    2005-01-01

    'Global warming' is a phrase that refers to the effect on the climate of human activities, in particular the burning of fossil fuels (coal, oil and gas) and large-scale deforestation, which cause emissions to the atmosphere of large amounts of 'greenhouse gases', of which the most important is carbon dioxide. Such gases absorb infrared radiation emitted by the Earth's surface and act as blankets over the surface keeping it warmer than it would otherwise be. Associated with this warming are changes of climate. The basic science of the 'greenhouse effect' that leads to the warming is well understood. More detailed understanding relies on numerical models of the climate that integrate the basic dynamical and physical equations describing the complete climate system. Many of the likely characteristics of the resulting changes in climate (such as more frequent heat waves, increases in rainfall, increase in frequency and intensity of many extreme climate events) can be identified. Substantial uncertainties remain in knowledge of some of the feedbacks within the climate system (that affect the overall magnitude of change) and in much of the detail of likely regional change. Because of its negative impacts on human communities (including for instance substantial sea-level rise) and on ecosystems, global warming is the most important environmental problem the world faces. Adaptation to the inevitable impacts and mitigation to reduce their magnitude are both necessary. International action is being taken by the world's scientific and political communities. Because of the need for urgent action, the greatest challenge is to move rapidly to much increased energy efficiency and to non-fossil-fuel energy sources

  7. Noise in Optical Amplifiers

    DEFF Research Database (Denmark)

    Jeppesen, Palle

    1997-01-01

    Noise in optical amplifiers is discussed on the basis of photons and electromagntic fields. Formulas for quantum noise from spontaneous emission, signal-spontaneous beat noise and spontaneous-spontaneous beat noise are derived.......Noise in optical amplifiers is discussed on the basis of photons and electromagntic fields. Formulas for quantum noise from spontaneous emission, signal-spontaneous beat noise and spontaneous-spontaneous beat noise are derived....

  8. Toward Improved Estimation of the Dynamic Topography and Ocean Circulation in the High Latitude and Arctic Ocean: The Importance of GOCE

    DEFF Research Database (Denmark)

    Johannessen, J. A.; Raj, R. P.; Nilsen, J. E. Ø.

    2014-01-01

    The Arctic plays a fundamental role in the climate system and shows significant sensitivity to anthropogenic climate forcing and the ongoing climate change. Accelerated changes in the Arctic are already observed, including elevated air and ocean temperatures, declines of the summer sea ice extent...... quantify this. Moreover, changes in the temperature and salinity of surface waters in the Arctic Ocean and Nordic Seas may also influence the flow of dense water through the Denmark Strait, which are found to be a precursor for changes in the Atlantic meridional overturning circulation with a lead time...... circulation and transport variability in the high latitude and Arctic Ocean. In this respect, this study combines in situ hydrographical data, surface drifter data and direct current meter measurements, with coupled sea ice–ocean models, radar altimeter data and the latest GOCE-based geoid in order...

  9. A search for pre-main-sequence stars in high-latitude molecular clouds. 3: A survey of the Einstein database

    Science.gov (United States)

    Caillault, Jean-Pierre; Magnani, Loris; Fryer, Chris

    1995-01-01

    In order to discern whether the high-latitude molecular clouds are regions of ongoing star formation, we have used X-ray emission as a tracer of youthful stars. The entire Einstein database yields 18 images which overlap 10 of the clouds mapped partially or completely in the CO (1-0) transition, providing a total of approximately 6 deg squared of overlap. Five previously unidentified X-ray sources were detected: one has an optical counterpart which is a pre-main-sequence (PMS) star, and two have normal main-sequence stellar counterparts, while the other two are probably extragalactic sources. The PMS star is located in a high Galactic latitude Lynds dark cloud, so this result is not too suprising. The translucent clouds, though, have yet to reveal any evidence of star formation.

  10. A primer on potential impacts, management priorities, and future directions for Elodea spp. in high latitude systems: learning from the Alaskan experience

    Science.gov (United States)

    Carey, Michael P.; Sethi, Suresh A; Larsen, Sabrina J; Rich, Cecil F

    2016-01-01

    Invasive species introductions in Arctic and Subarctic ecosystems are growing as climate change manifests and human activity increases in high latitudes. The aquatic plants of the genus Elodea are potential invaders to Arctic and Subarctic ecosystems circumpolar and at least one species is already established in Alaska, USA. To illustrate the problems of preventing, eradicating, containing, and mitigating aquatic, invasive plants in Arctic and Subarctic ecosystems, we review the invasion dynamics of Elodea and provide recommendations for research and management efforts in Alaska. Foremost, we conclude the remoteness of Arctic and Subarctic systems such as Alaska is no longer a protective attribute against invasions, as transportation pathways now reach throughout these regions. Rather, high costs of operating in remote Arctic and Subarctic systems hinders detection of infestations and limits eradication or mitigation, emphasizing management priorities of prevention and containment of aquatic plant invaders in Alaska and other Arctic and Subarctic systems.

  11. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae and the discussion of a life history pattern for gymnotiforms from high latitudes.

    Directory of Open Access Journals (Sweden)

    Julia Giora

    Full Text Available The reproductive biology and feeding habits of the electric fish Brachyhypopomus gauderio were studied. The species has seasonal reproductive behavior, with breeding occurring during the Southern Hemisphere spring and summer, and having a positive relation with the photoperiod variation. Brachyhypopomus gauderio was defined as a fractional spawner, with low relative fecundity and high first maturation size. Sexual dimorphism was registered, males undergoing hypertrophy of the distal portion of caudal filament. The results on reproductive biology herein obtained are in agreement with data concerning gymnotiforms from Southern Brazil and Uruguay, pointing to an ecological pattern for the species from high latitudes, differing from species with tropical distribution. According to the analysis of the food items, B. gauderio feed mainly on autochthonous insects, likewise the other gymnotiforms previously investigated, leading to conclude that there is no variation on the diet of the species of the order related to climatic conditions or even to habitat of occurrence.

  12. New advantages of the combined GPS and GLONASS observations for high-latitude ionospheric irregularities monitoring: case study of June 2015 geomagnetic storm

    Science.gov (United States)

    Cherniak, Iurii; Zakharenkova, Irina

    2017-05-01

    Monitoring, tracking and nowcasting of the ionospheric plasma density disturbances using dual-frequency measurements of the Global Positioning System (GPS) signals are effectively carried out during several decades. Recent rapid growth and modernization of the ground-based segment gives an opportunity to establish a great database consisting of more than 6000 stations worldwide which provide GPS signals measurements with an open access. Apart of the GPS signals, at least two-third of these stations receive simultaneously signals transmitted by another Global Navigation Satellite System (GNSS)—the Russian system GLONASS. Today, GLONASS signal measurements are mainly used in navigation and geodesy only and very rarely for ionosphere research. We present the first results demonstrating advantages of using several independent but compatible GNSS systems like GPS and GLONASS for improvement of the permanent monitoring of the high-latitude ionospheric irregularities. For the first time, the high-resolution two-dimensional maps of ROTI perturbation were made using not only GPS but also GLONASS measurements. We extend the use of the ROTI maps for analyzing ionospheric irregularities distribution. We demonstrate that the meridional slices of the ROTI maps can be effectively used to study the occurrence and temporal evolution of the ionospheric irregularities. The meridional slices of the geographical sectors with a high density of the GPS and GLONASS measurements can represent spatio-temporal dynamics of the intense ionospheric plasma density irregularities with very high resolution, and they can be effectively used for detailed study of the space weather drivers on the processes of the ionospheric irregularities generation, development and their lifetimes. Using a representative database of 5800 ground-based GNSS stations located worldwide, we have investigated the occurrence of the high-latitude ionospheric plasma density irregularities during the geomagnetic storm of

  13. Spatio-Temporal Analysis of the Accuracy of Tropical Multisatellite Precipitation Analysis 3B42 Precipitation Data in Mid-High Latitudes of China

    Science.gov (United States)

    Cai, Yancong; Jin, Changjie; Wang, Anzhi; Guan, Dexin; Wu, Jiabing; Yuan, Fenghui; Xu, Leilei

    2015-01-01

    Satellite-based precipitation data have contributed greatly to quantitatively forecasting precipitation, and provides a potential alternative source for precipitation data allowing researchers to better understand patterns of precipitation over ungauged basins. However, the absence of calibration satellite data creates considerable uncertainties for The Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) 3B42 product over high latitude areas beyond the TRMM satellites latitude band (38°NS). This study attempts to statistically assess TMPA V7 data over the region beyond 40°NS using data obtained from numerous weather stations in 1998–2012. Comparative analysis at three timescales (daily, monthly and annual scale) indicates that adoption of a monthly adjustment significantly improved correlation at a larger timescale increasing from 0.63 to 0.95; TMPA data always exhibits a slight overestimation that is most serious at a daily scale (the absolute bias is 103.54%). Moreover, the performance of TMPA data varies across all seasons. Generally, TMPA data performs best in summer, but worst in winter, which is likely to be associated with the effects of snow/ice-covered surfaces and shortcomings of precipitation retrieval algorithms. Temporal and spatial analysis of accuracy indices suggest that the performance of TMPA data has gradually improved and has benefited from upgrades; the data are more reliable in humid areas than in arid regions. Special attention should be paid to its application in arid areas and in winter with poor scores of accuracy indices. Also, it is clear that the calibration can significantly improve precipitation estimates, the overestimation by TMPA in TRMM-covered area is about a third as much as that in no-TRMM area for monthly and annual precipitation. The systematic evaluation of TMPA over mid-high latitudes provides a broader understanding of satellite-based precipitation estimates, and these data are

  14. Spatio-temporal analysis of the accuracy of tropical multisatellite precipitation analysis 3B42 precipitation data in mid-high latitudes of China.

    Directory of Open Access Journals (Sweden)

    Yancong Cai

    Full Text Available Satellite-based precipitation data have contributed greatly to quantitatively forecasting precipitation, and provides a potential alternative source for precipitation data allowing researchers to better understand patterns of precipitation over ungauged basins. However, the absence of calibration satellite data creates considerable uncertainties for The Tropical Rainfall Measuring Mission (TRMM Multisatellite Precipitation Analysis (TMPA 3B42 product over high latitude areas beyond the TRMM satellites latitude band (38°NS. This study attempts to statistically assess TMPA V7 data over the region beyond 40°NS using data obtained from numerous weather stations in 1998-2012. Comparative analysis at three timescales (daily, monthly and annual scale indicates that adoption of a monthly adjustment significantly improved correlation at a larger timescale increasing from 0.63 to 0.95; TMPA data always exhibits a slight overestimation that is most serious at a daily scale (the absolute bias is 103.54%. Moreover, the performance of TMPA data varies across all seasons. Generally, TMPA data performs best in summer, but worst in winter, which is likely to be associated with the effects of snow/ice-covered surfaces and shortcomings of precipitation retrieval algorithms. Temporal and spatial analysis of accuracy indices suggest that the performance of TMPA data has gradually improved and has benefited from upgrades; the data are more reliable in humid areas than in arid regions. Special attention should be paid to its application in arid areas and in winter with poor scores of accuracy indices. Also, it is clear that the calibration can significantly improve precipitation estimates, the overestimation by TMPA in TRMM-covered area is about a third as much as that in no-TRMM area for monthly and annual precipitation. The systematic evaluation of TMPA over mid-high latitudes provides a broader understanding of satellite-based precipitation estimates, and these

  15. Global warming: Sea ice and snow cover

    International Nuclear Information System (INIS)

    Walsh, J.E.

    1993-01-01

    In spite of differences among global climate simulations under scenarios where atmospheric CO 2 is doubled, all models indicate at least some amplification of greenouse warming at the polar regions. Several decades of recent data on air temperature, sea ice, and snow cover of the high latitudes of the Northern Hemisphere are summarized to illustrate the general compatibility of recent variations in those parameters. Despite a data void over the Arctic Ocean, some noteworthy patterns emerge. Warming dominates in winter and spring, as projected by global climate models, with the warming strongest over subpolar land areas of Alaska, northwestern Canada, and northern Eurasia. A time-longitude summary of Arctic sea ice variations indicates that timescales of most anomalies range from several months to several years. Wintertime maxima of total sea ice extent contain no apparent secular trends. The statistical significance of trends in recent sea ice variations was evaluated by a Monte Carlo procedure, showing a statistically significant negative trend in the summer. Snow cover data over the 20-y period of record show a noticeable decrease of Arctic snow cover in the late 1980s. This is of potential climatic significance since the accompanying decrease of surface albedo leads to a rapid increase of solar heating. 21 refs., 3 figs., 1 tab

  16. Global warming

    CERN Document Server

    Hulme, M

    1998-01-01

    Global warming-like deforestation, the ozone hole and the loss of species- has become one of the late 20the century icons of global environmental damage. The threat, is not the reality, of such a global climate change has motivated governments. businesses and environmental organisations, to take serious action ot try and achieve serious control of the future climate. This culminated last December in Kyoto in the agreement for legally-binding climate protocol. In this series of three lectures I will provide a perspective on the phenomenon of global warming that accepts the scientific basis for our concern, but one that also recognises the dynamic interaction between climate and society that has always exited The future will be no different. The challenge of global warning is not to pretend it is not happening (as with some pressure groups), nor to pretend it threatens global civilisation (as with other pressure groups), and it is not even a challenge to try and stop it from happening-we are too far down the ro...

  17. Electrospun amplified fiber optics.

    Science.gov (United States)

    Morello, Giovanni; Camposeo, Andrea; Moffa, Maria; Pisignano, Dario

    2015-03-11

    All-optical signal processing is the focus of much research aiming to obtain effective alternatives to existing data transmission platforms. Amplification of light in fiber optics, such as in Erbium-doped fiber amplifiers, is especially important for efficient signal transmission. However, the complex fabrication methods involving high-temperature processes performed in a highly pure environment slow the fabrication process and make amplified components expensive with respect to an ideal, high-throughput, room temperature production. Here, we report on near-infrared polymer fiber amplifiers working over a band of ∼20 nm. The fibers are cheap, spun with a process entirely carried out at room temperature, and shown to have amplified spontaneous emission with good gain coefficients and low levels of optical losses (a few cm(-1)). The amplification process is favored by high fiber quality and low self-absorption. The found performance metrics appear to be suitable for short-distance operations, and the large variety of commercially available doping dyes might allow for effective multiwavelength operations by electrospun amplified fiber optics.

  18. Fast pulse amplifier

    International Nuclear Information System (INIS)

    Lepetit, J.; Poussier, E.

    1984-01-01

    This amplifier comprises an inverter transformer, the primary circuit of which receives a pulse and the secondary circuit of which is connected to several amplifying elements in parallel. The inverter transformer is made of coaxial cable segments winded around a magnetic torus; the cable cores connected in series constitute the primary circuit and the braiding of cables, connected in parallel, are the secondary circuit. The transformer comprises, besides, delay lines in series with each braiding of the secondary circuit, these ones are such that pulses issued from each braiding arrive together to the secondary circuit connectors. This invention applies, noticeably in the case of a high voltage amplifier, to the control of deflection blocks of particles used in medicine or in particle accelerators [fr

  19. Fast logarithmic amplifier

    International Nuclear Information System (INIS)

    Tai, I.; Hasegawa, K.

    1975-01-01

    This paper reports on the improvement of frequency characteristics of a logarithmic amplifier with a Paterson transdiode connection. The improvement of the response speed has been achieved by using a phase compensation technique. Small signal response analyses of the logging circuit revealed the effects of a series resistor Rsub(p) and a parallel capacitance Csub(p) on the response of the circuit. The improvement of the frequency characteristics are remarkable at higher current levels. These facts were proved by the practical logarithmic amplifier. (auth.)

  20. New evidence on the sequence of deglacial warming in the tropical Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.; Govil, P.

    . Quat. Sci., vol.25(7); 2010; 1138-1143 A New Evidence on Sequence of Deglacial Warming in the Tropical Indian Ocean P. Divakar Naidu 1 , Pawan Govil 1,2 1 National Institute of Oceanography, Dona Paula 403 004, Goa, India 2 National Centre... relative timing of abrupt climate warming in the tropics versus the high latitudes should be known. Therefore, the present communication is aimed to address the start of deglaciation in the Indian Ocean based on sea surface temperature (SST) derived from...

  1. Terrestrial carbon cycle affected by non-uniform climate warming

    International Nuclear Information System (INIS)

    Jianyang Xia; Yiqi Luo; Jiquan Chen; Shilong Piao; Ciais, Philippe; Shiqiang Wan

    2014-01-01

    Feedbacks between the terrestrial carbon cycle and climate change could affect many ecosystem functions and services, such as food production, carbon sequestration and climate regulation. The rate of climate warming varies on diurnal and seasonal timescales. A synthesis of global air temperature data reveals a greater rate of warming in winter than in summer in northern mid and high latitudes, and the inverse pattern in some tropical regions. The data also reveal a decline in the diurnal temperature range over 51% of the global land area and an increase over only 13%, because night-time temperatures in most locations have risen faster than daytime temperatures. Analyses of satellite data, model simulations and in situ observations suggest that the impact of seasonal warming varies between regions. For example, spring warming has largely stimulated ecosystem productivity at latitudes between 30 degrees and 90 degrees N, but suppressed productivity in other regions. Contrasting impacts of day- and night-time warming on plant carbon gain and loss are apparent in many regions. We argue that ascertaining the effects of non-uniform climate warming on terrestrial ecosystems is a key challenge in carbon cycle research. (authors)

  2. Transport and transformation of riverine neodymium isotope and rare earth element signatures in high latitude estuaries: A case study from the Laptev Sea

    Science.gov (United States)

    Laukert, Georgi; Frank, Martin; Bauch, Dorothea; Hathorne, Ed C.; Gutjahr, Marcus; Janout, Markus; Hölemann, Jens

    2017-11-01

    Marine neodymium (Nd) isotope and rare earth element (REE) compositions are valuable tracers for present and past ocean circulation and continental inputs. Yet their supply via high latitude estuaries is largely unknown. Here we present a comprehensive dissolved Nd isotope (expressed as εNd values) and REE data set together with seawater stable oxygen isotope (δ18O) compositions of samples from the Laptev Sea recovered in two Arctic summers and one winter. The Laptev Sea is a shallow Siberian Shelf sea characterized by extensive river-runoff, sea-ice production and ice transport into the Arctic Ocean. The large variability in εNd (-6 to -17), REE concentrations (16 to 600 pmol/kg for Nd) and REE patterns is controlled by freshwater supply from distinct riverine sources and open ocean Arctic Atlantic Water. Strikingly and contrary to expectations, except for cerium no evidence for significant release of REEs from particulate phases is found, which is attributed to low amounts of suspended particulate matter and high dissolved organic carbon concentrations present in the contributing rivers. Essentially all shelf waters are depleted in light (L)REEs, while the distribution of the heavy REEs shows a deficiency at the surface and a pronounced excess in the bottom layer. This distribution is consistent with REE removal through coagulation of riverine nanoparticles and colloids starting at salinities near 10 and resulting in a drop of all REE concentrations by ∼30%. With increasing salinity preferential LREE removal is observable reaching ∼75% for Nd at a salinity of 34. Although the delayed onset of dissolved REE removal contrasts with most previous observations from other estuarine environments, it agrees remarkably well with results from recent experiments simulating estuarine mixing of seawater with organic-rich river waters. In addition, melting and formation of sea ice leads to further REE depletion at the surface and strong REE enrichment near the shelf

  3. Assessment of Non-Point Source Total Phosphorus Pollution from Different Land Use and Soil Types in a Mid-High Latitude Region of China

    Directory of Open Access Journals (Sweden)

    Zhiwei Wang

    2016-11-01

    Full Text Available The transport characteristics of phosphorus in soil and the assessment of its environmental risk have become hot topics in the environmental and agricultural fields. The Sanjiang Plain is an important grain production base in China, and it is characterised by serious land use change caused by large-scale agricultural exploitation. Agricultural inputs and tillage management have destroyed the soil nutrient balance formed over long-term conditions. There are few studies on non-point source phosphorus pollution in the Sanjiang Plain, which is the largest swampy low plain in a mid-high-latitude region in China. Most studies have focused on the water quality of rivers in marsh areas, or the export mechanism of phosphorus from specific land uses. They were conducted using experimental methods or empirical models, and need further development towards mechanism models and the macro-scale. The question is how to find a way to couple processes in phosphorus cycling and a distributed hydrological model considering local hydrological features. In this study, we report an attempt to use a distributed phosphorus transport model to analyse non-point source total phosphorus pollution from different land uses and soil types on the Sanjiang Plain. The total phosphorus concentration generally shows an annually increasing trend in the study area. The total phosphorus load intensity is heterogeneous in different land use types and different soil types. The average total phosphorus load intensity of different land use types can be ranked in descending order from paddy field, dry land, wetlands, grassland, and forestland. The average total phosphorus load intensity of different soil types can be ranked in descending order: paddy soil, bog soil, planosol, meadow soil, black soil, and dark brown earth. The dry land and paddy fields account for the majority of total phosphorus load in the study area. This is mainly caused by extensive use of phosphate fertilizer on the

  4. Strong delayed interactive effects of metal exposure and warming

    DEFF Research Database (Denmark)

    Debecker, Sara; Dinh, Khuong Van; Stoks, Robby

    2017-01-01

    ’ ranges could lead to an important underestimation of the risks. We addressed all three mechanisms by studying effects of larval exposure to zinc and warming before, during, and after metamorphosis in Ischnura elegans damselflies from high- and lowlatitude populations. By integrating these mechanisms...... into a single study, we could identify two novel patterns. First, during exposure zinc did not affect survival, whereas it induced mild to moderate postexposure mortality in the larval stage and at metamorphosis, and very strongly reduced adult lifespan. This severe delayed effect across metamorphosis...... was especially remarkable in high-latitude animals, as they appeared almost insensitive to zinc during the larval stage. Second, the well-known synergism between metals and warming was manifested not only during the larval stage but also after metamorphosis, yet notably only in low-latitude damselflies...

  5. Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

    Directory of Open Access Journals (Sweden)

    S. Oyama

    2008-06-01

    Full Text Available Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT Kiruna-Sodankylä-Tromsø (KST ultrahigh frequency (UHF radar system on 9–10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutral-wind speed in the lower thermosphere. This method was also available to estimate the meridional and zonal components. The vertical neutral-wind speed at 109 km, 114 km, and 120 km heights showed large upward motions in excess of 30 m s−1 in association with an ionospheric heating event. Large downward speeds in excess of −30 m s−1 were also observed before and after the heating event. The meridional neutral-wind speed suddenly changed its direction from equatorward to poleward when the heating event began, and then returned equatorward coinciding with a decrease in the heating event. The magnetometer data from northern Scandinavia suggested that the center of the heated region was located about 80 km equatorward of Tromsø. The pressure gradient caused the lower-thermospheric wind to accelerate obliquely upward over Tromsø in the poleward direction. Acceleration of the neutral wind flowing on a vertically tilted isobar produced vertical wind speeds larger by more than two orders of magnitude than previously predicted, but still an order of magnitude smaller than observed speeds.

  6. Multiple cold resistance loci confer the high cold tolerance adaptation of Dongxiang wild rice (Oryza rufipogon) to its high-latitude habitat.

    Science.gov (United States)

    Mao, Donghai; Yu, Li; Chen, Dazhou; Li, Lanying; Zhu, Yuxing; Xiao, Yeqing; Zhang, Dechun; Chen, Caiyan

    2015-07-01

    Dongxiang wild rice is phylogenetically close to temperate japonica and contains multiple cold resistance loci conferring its adaptation to high-latitude habitat. Understanding the nature of adaptation in wild populations will benefit crop breeding in the development of climate-resilient crop varieties. Dongxiang wild rice (DXWR), the northernmost common wild rice known, possesses a high degree of cold tolerance and can survive overwintering in its native habitat. However, to date, it is still unclear how DXWR evolved to cope with low-temperature environment, resulting in limited application of DXWR in rice breeding programs. In this study, we carried out both QTL mapping and phylogenetic analysis to discern the genetic mechanism underlying the strong cold resistance. Through a combination of interval mapping and single locus analysis in two genetic populations, at least 13 QTLs for seedling cold tolerance were identified in DXWR. A phylogenetic study using both genome-wide InDel markers and markers associated with cold tolerance loci reveals that DXWR belongs to the Or-III group, which is most closely related to cold-tolerant Japonica rice rather than to the Indica cultivars that are predominant in the habitat where DXWR grows. Our study paves the way toward an understanding of the nature of adaptation to a northern habitat in O. rufipogon. The QTLs identified in DXWR in this study will be useful for molecular breeding of cold-tolerant rice.

  7. Mapping plasma structures in the high-latitude ionosphere using beacon satellite, incoherent scatter radar and ground-based magnetometer observations

    Directory of Open Access Journals (Sweden)

    T. Neubert

    2002-06-01

    Full Text Available In the autumn of the year 2000, four radio receivers capable of tracking various beacon satellites were set up along the southwestern coast of Greenland. They are used to reconstruct images of the ionospheric plasma density distribution via the tomographic method. In order to test and validate tomographic imaging under the highly variable conditions often prevailing in the high-latitude ionosphere, a time interval was selected when the Sondrestrom incoherent scatter radar conducted measurements of the ionospheric plasma density while the radio receivers tracked a number of beacon satellites. A comparison between two-dimensional images of the plasma density distribution obtained from the radar and the satellite receivers revealed generally good agreement between radar measurements and tomographic images. Observed discrepancies can be attributed to F region plasma patches moving through the field of view with a speed of several hundred meters per second, thereby smearing out the tomographic image. A notable mismatch occurred around local magnetic midnight when a magnetospheric substorm breakup occurred in the vicinity of southwest Greenland (identified from ground-based magnetometer observations. The breakup was associated with a sudden intensification of the westward auroral electrojet which was centered at about 69 and extended up to some 73 corrected geomagnetic latitude. Ground-based magnetometer data may thus have the potential of indicating when the tomographic method is at risk and may fail. We finally outline the application of tomographic imaging, when combined with magnetic field data, to estimate ionospheric Joule heating rates.

  8. Excitation thresholds of field-aligned irregularities and associated ionospheric hysteresis at very high latitudes observed using SPEAR-induced HF radar backscatter

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    2009-07-01

    Full Text Available On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs. The effective radiated power of SPEAR was varied from 1–10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt and collapse (Pc of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.

  9. Comparison of high-latitude line-of-sight ozone column density with derived ozone fields and the effects of horizontal inhomogeneity

    Directory of Open Access Journals (Sweden)

    W. H. Swartz

    2006-01-01

    Full Text Available Extensive ozone measurements were made during the second SAGE III Ozone Loss and Validation Experiment (SOLVE II. We compare high-latitude line-of-sight (LOS slant column ozone measurements from the NASA DC-8 to ozone simulated by forward integration of measurement-derived ozone fields constructed both with and without the assumption of horizontal homogeneity. The average bias and rms error of the simulations assuming homogeneity are relatively small (−6 and 10%, respectively in comparison to the LOS measurements. The comparison improves significantly (−2% bias; 8% rms error using forward integrations of three-dimensional proxy ozone fields reconstructed from potential vorticity-O3 correlations. The comparisons provide additional verification of the proxy fields and quantify the influence of large-scale ozone inhomogeneity. The spatial inhomogeneity of the atmosphere is a source of error in the retrieval of trace gas vertical profiles and column abundance from LOS measurements, as well as a complicating factor in intercomparisons that include LOS measurements at large solar zenith angles.

  10. Excitation thresholds of field-aligned irregularities and associated ionospheric hysteresis at very high latitudes observed using SPEAR-induced HF radar backscatter

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    2009-07-01

    Full Text Available On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs. The effective radiated power of SPEAR was varied from 1–10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt and collapse (Pc of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.

  11. An NDVI-Based Vegetation Phenology Is Improved to be More Consistent with Photosynthesis Dynamics through Applying a Light Use Efficiency Model over Boreal High-Latitude Forests

    Directory of Open Access Journals (Sweden)

    Siheng Wang

    2017-07-01

    Full Text Available Remote sensing of high-latitude forests phenology is essential for understanding the global carbon cycle and the response of vegetation to climate change. The normalized difference vegetation index (NDVI has long been used to study boreal evergreen needleleaf forests (ENF and deciduous broadleaf forests. However, the NDVI-based growing season is generally reported to be longer than that based on gross primary production (GPP, which can be attributed to the difference between greenness and photosynthesis. Instead of introducing environmental factors such as land surface or air temperature like previous studies, this study attempts to make VI-based phenology more consistent with photosynthesis dynamics through applying a light use efficiency model. NDVI (MOD13C2 was used as a proxy for both fractional of absorbed photosynthetically active radiation (APAR and light use efficiency at seasonal time scale. Results show that VI-based phenology is improved towards tracking seasonal GPP changes more precisely after applying the light use efficiency model compared to raw NDVI or APAR, especially over ENF.

  12. The cumulative impacts of repeated heavy rainfall, flooding and altered water quality on the high-latitude coral reefs of Hervey Bay, Queensland, Australia.

    Science.gov (United States)

    Butler, I R; Sommer, B; Zann, M; Zhao, J-X; Pandolfi, J M

    2015-07-15

    Terrestrial runoff and flooding have resulted in major impacts on coral communities worldwide, but we lack detailed understanding of flood plume conditions and their ecological effects. Over the course of repeated flooding between 2010 and 2013, we measured coral cover and water quality on the high-latitude coral reefs of Hervey Bay, Queensland, Australia. In 2013, salinity, total suspended solids, total nitrogen and total phosphorus were altered for up to six months post-flooding. Submarine groundwater caused hypo-saline conditions for a further four months. Despite the greater magnitude of flooding in 2013, declines in coral abundance (∼28%) from these floods were lower than the 2011 flood (∼40%), which occurred immediately after a decade of severe drought. There was an overall cumulative decrease of coral by ∼56% from 2010 to 2013. Our study highlights the need for local scale monitoring and research to facilitate informed management and conservation of catchments and marine environments. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. CryoSat Processing Prototype, how to generate LRM like echoes with SAR data and a Comparison to DUACS SLA over high latitudes

    Science.gov (United States)

    Picot, N.; Boy, F.; Desjonqueres, J.

    2012-12-01

    Like CryoSat, Sentinel3 embarks a doppler altimeter. While there is a long experience of LRM processing, SAR nadir looking data are new and will need in depth validation. Thanks to CryoSat data, the processing of SAR data can be experienced in orbit. The continuity to current altimeter data set (based on LRM acquisitions) has also to be analysed with details. A Cryosat Processing Prototype (C2P) has been developed on CNES side to prepare the CNES SAR ocean retracking study. this prototype allows to process SAR data in order to generate LRM like echoes on ground. Those CryoSat ocean products are routinely processed on CNES side and ingested in the SALP/DUACS system. CryoSat data have proved to be very accurate and very valuable for the ocean user community in the past monthes. For example, it has allowed to largely reduce the impact of the lost of the ESA ENVISAT mission as well as the long non availability of Jason-1 data. This paper will describe the system set up in place early 2012 to feed CryoSat data in the SALP/DUACS products and will present the routine data analysis . C2P CryoSat products will be compared with DUACS SLA estimates and a specific focus will be given over high latitudes knowing that CryoSat is the oinly mission providing sea surface estimates over latitudes above 66 degrees since the lost of the ESA ENVISAT mission.

  14. A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

    Directory of Open Access Journals (Sweden)

    J.-P. Villain

    2002-11-01

    Full Text Available The HF radars of the Super Dual Auroral Radar Network (SuperDARN provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. We have conducted a statistical study of the associated Doppler spectral width of ionospheric F-region echoes. The study has been conducted with all available radars from the Northern Hemisphere for 2 specific periods of time. Period 1 corresponds to the winter months of 1994, while period 2 covers October 1996 to March 1997. The distributions of data points and average spectral width are presented as a function of Magnetic Latitude and Magnetic Local Time. The databases are very consistent and exhibit the same features. The most stringent features are: a region of very high spectral width, collocated with the ionospheric LLBL/cusp/mantle region; an oval shaped region of high spectral width, whose equator-ward boundary matches the poleward limit of the Holzworth and Meng auroral oval. A simulation has been conducted to evaluate the geometrical and instrumental effects on the spectral width. It shows that these effects cannot account for the observed spectral features. It is then concluded that these specific spectral width characteristics are the signature of ionospheric/magnetospheric coupling phenomena.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; ionospheric irregularities

  15. Studying the Relationship between High-Latitude Geomagnetic Activity and Parameters of Interplanetary Magnetic Clouds with the Use of Artificial Neural Networks

    Science.gov (United States)

    Barkhatov, N. A.; Revunov, S. E.; Vorobjev, V. G.; Yagodkina, O. I.

    2018-03-01

    The cause-and-effect relations of the dynamics of high-latitude geomagnetic activity (in terms of the AL index) and the type of the magnetic cloud of the solar wind are studied with the use of artificial neural networks. A recurrent neural network model has been created based on the search for the optimal physically coupled input and output parameters characterizing the action of a plasma flux belonging to a certain magnetic cloud type on the magnetosphere. It has been shown that, with IMF components as input parameters of neural networks with allowance for a 90-min prehistory, it is possible to retrieve the AL sequence with an accuracy to 80%. The successful retrieval of the AL dynamics by the used data indicates the presence of a close nonlinear connection of the AL index with cloud parameters. The created neural network models can be applied with high efficiency to retrieve the AL index, both in periods of isolated magnetospheric substorms and in periods of the interaction between the Earth's magnetosphere and magnetic clouds of different types. The developed model of AL index retrieval can be used to detect magnetic clouds.

  16. A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

    Directory of Open Access Journals (Sweden)

    J.-P. Villain

    Full Text Available The HF radars of the Super Dual Auroral Radar Network (SuperDARN provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. We have conducted a statistical study of the associated Doppler spectral width of ionospheric F-region echoes. The study has been conducted with all available radars from the Northern Hemisphere for 2 specific periods of time. Period 1 corresponds to the winter months of 1994, while period 2 covers October 1996 to March 1997. The distributions of data points and average spectral width are presented as a function of Magnetic Latitude and Magnetic Local Time. The databases are very consistent and exhibit the same features. The most stringent features are: a region of very high spectral width, collocated with the ionospheric LLBL/cusp/mantle region; an oval shaped region of high spectral width, whose equator-ward boundary matches the poleward limit of the Holzworth and Meng auroral oval. A simulation has been conducted to evaluate the geometrical and instrumental effects on the spectral width. It shows that these effects cannot account for the observed spectral features. It is then concluded that these specific spectral width characteristics are the signature of ionospheric/magnetospheric coupling phenomena.

    Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; ionospheric irregularities

  17. Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

    Directory of Open Access Journals (Sweden)

    S. Oyama

    2008-06-01

    Full Text Available Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT Kiruna-Sodankylä-Tromsø (KST ultrahigh frequency (UHF radar system on 9–10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutral-wind speed in the lower thermosphere. This method was also available to estimate the meridional and zonal components. The vertical neutral-wind speed at 109 km, 114 km, and 120 km heights showed large upward motions in excess of 30 m s−1 in association with an ionospheric heating event. Large downward speeds in excess of −30 m s−1 were also observed before and after the heating event. The meridional neutral-wind speed suddenly changed its direction from equatorward to poleward when the heating event began, and then returned equatorward coinciding with a decrease in the heating event. The magnetometer data from northern Scandinavia suggested that the center of the heated region was located about 80 km equatorward of Tromsø. The pressure gradient caused the lower-thermospheric wind to accelerate obliquely upward over Tromsø in the poleward direction. Acceleration of the neutral wind flowing on a vertically tilted isobar produced vertical wind speeds larger by more than two orders of magnitude than previously predicted, but still an order of magnitude smaller than observed speeds.

  18. Inconclusive Predictions and Contradictions: A Lack of Consensus on Seed Germination Response to Climate Change at High Altitude and High Latitude

    Directory of Open Access Journals (Sweden)

    Ganesh K. Jaganathan

    2016-01-01

    Full Text Available Climate change directly affects arctic-alpine plants and acute responses to increased temperatures may be seen in their reproductive fitness and germination ability. However, uncertainties prevail in predicting whether a future warmer climate favors or hampers seed germination in high latitude and high altitude soils and seed germination research in such systems has not been able to provide generalizable patterns of response. The available literature on this subject has been conducted at various locations contributing to difficulties in predicting the response of arctic-alpine seeds to climate change. Here, we show that discrepancies in seed collection, dormancy breaking treatments, and germination conditions found in the published literature are possible reasons for our inability to draw large scale conclusions. We explore how these factors influence the results and highlight the fact that many of the previous investigations have reported the effects of warmer temperature, rather than a warmer climate and all the associated complex environmental interactions, on seed germination. We recommend that long-term monitoring of seed response to treatments that mimic the present and future alpine climate is likely to produce more ecologically meaningful insights and suggest several practical steps that researchers can take that would facilitate greater coherence between studies.

  19. Quantifying global soil carbon losses in response to warming.

    Science.gov (United States)

    Crowther, T W; Todd-Brown, K E O; Rowe, C W; Wieder, W R; Carey, J C; Machmuller, M B; Snoek, B L; Fang, S; Zhou, G; Allison, S D; Blair, J M; Bridgham, S D; Burton, A J; Carrillo, Y; Reich, P B; Clark, J S; Classen, A T; Dijkstra, F A; Elberling, B; Emmett, B A; Estiarte, M; Frey, S D; Guo, J; Harte, J; Jiang, L; Johnson, B R; Kröel-Dulay, G; Larsen, K S; Laudon, H; Lavallee, J M; Luo, Y; Lupascu, M; Ma, L N; Marhan, S; Michelsen, A; Mohan, J; Niu, S; Pendall, E; Peñuelas, J; Pfeifer-Meister, L; Poll, C; Reinsch, S; Reynolds, L L; Schmidt, I K; Sistla, S; Sokol, N W; Templer, P H; Treseder, K K; Welker, J M; Bradford, M A

    2016-11-30

    The majority of the Earth's terrestrial carbon is stored in the soil. If anthropogenic warming stimulates the loss of this carbon to the atmosphere, it could drive further planetary warming. Despite evidence that warming enhances carbon fluxes to and from the soil, the net global balance between these responses remains uncertain. Here we present a comprehensive analysis of warming-induced changes in soil carbon stocks by assembling data from 49 field experiments located across North America, Europe and Asia. We find that the effects of warming are contingent on the size of the initial soil carbon stock, with considerable losses occurring in high-latitude areas. By extrapolating this empirical relationship to the global scale, we provide estimates of soil carbon sensitivity to warming that may help to constrain Earth system model projections. Our empirical relationship suggests that global soil carbon stocks in the upper soil horizons will fall by 30 ± 30 petagrams of carbon to 203 ± 161 petagrams of carbon under one degree of warming, depending on the rate at which the effects of warming are realized. Under the conservative assumption that the response of soil carbon to warming occurs within a year, a business-as-usual climate scenario would drive the loss of 55 ± 50 petagrams of carbon from the upper soil horizons by 2050. This value is around 12-17 per cent of the expected anthropogenic emissions over this period. Despite the considerable uncertainty in our estimates, the direction of the global soil carbon response is consistent across all scenarios. This provides strong empirical support for the idea that rising temperatures will stimulate the net loss of soil carbon to the atmosphere, driving a positive land carbon-climate feedback that could accelerate climate change.

  20. Amplifying genetic logic gates.

    Science.gov (United States)

    Bonnet, Jerome; Yin, Peter; Ortiz, Monica E; Subsoontorn, Pakpoom; Endy, Drew

    2013-05-03

    Organisms must process information encoded via developmental and environmental signals to survive and reproduce. Researchers have also engineered synthetic genetic logic to realize simpler, independent control of biological processes. We developed a three-terminal device architecture, termed the transcriptor, that uses bacteriophage serine integrases to control the flow of RNA polymerase along DNA. Integrase-mediated inversion or deletion of DNA encoding transcription terminators or a promoter modulates transcription rates. We realized permanent amplifying AND, NAND, OR, XOR, NOR, and XNOR gates actuated across common control signal ranges and sequential logic supporting autonomous cell-cell communication of DNA encoding distinct logic-gate states. The single-layer digital logic architecture developed here enables engineering of amplifying logic gates to control transcription rates within and across diverse organisms.

  1. Flashlamp excited fluid laser amplified

    International Nuclear Information System (INIS)

    1976-01-01

    The patent describes a laser amplifier with chambers for containing and amplifying an intensifier medium. It serves the need for a large impulse repetition rate and high intensities as required e.g. for laser isotope separation

  2. The role of meltwater-induced subsurface ocean warming in regulating the Atlantic meridional overturning in glacial climate simulations

    Energy Technology Data Exchange (ETDEWEB)

    Brady, Esther C.; Otto-Bliesner, Bette L. [National Center for Atmospheric Research, Boulder, CO (United States)

    2011-10-15

    The Community Climate System Model version 3, (CCSM3) is used to investigate the effect of the high latitude North Atlantic subsurface ocean temperature response in idealized freshwater hosing experiments on the strength of the Atlantic meridional overturning circulation (AMOC). The hosing experiments covered a range of input magnitudes at two locations in a glacial background state. Subsurface subpolar ocean warms when freshwater is added to the high latitude North Atlantic (NATL cases) and weakly cools when freshwater is added to the Gulf of Mexico (GOM cases). All cases show subsurface ocean warming in the Southern Hemisphere (SH). The sensitivity of the AMOC response to the location and magnitude of hosing is related to the induced subsurface temperature response, which affects the magnitude of the large-scale meridional pressure gradient at depth through the effect on upper ocean density. The high latitude subsurface warming induced in the NATL cases lowers the upper ocean density in the deepwater formation region enhancing a density reduction by local freshening. In the GOM cases the effect of SH warming partially offsets the effect of the high latitude freshening on the meridional density gradient. Following the end of hosing, a brief convective event occurs in the largest NATL cases which flushes some of the heat stored in the subsurface layers. This fuels a rapid rise in AMOC that lasts less than a couple of decades before subsequent freshening from increases in precipitation and sea ice melt reverses the initial increase in the meridional density gradient. Thereafter AMOC recovery slows to the rate found in comparable GOM cases. The result for these glacial transient hosing experiments is that the pace of the longer recovery is not sensitive to location of the imposed freshwater forcing. (orig.)

  3. Testing the Millennial-Scale Holocene Solar-Climate Connection in the Indo-Pacific Warm Pool

    Science.gov (United States)

    Khider, D.; Emile-Geay, J.; McKay, N.; Jackson, C. S.; Routson, C.

    2016-12-01

    The existence of 1000 and 2500-year periodicities found in reconstructions of total solar irradiance (TSI) and a number of Holocene climate records has led to the hypothesis of a causal relationship. However, attributing Holocene millennial-scale variability to solar forcing requires a mechanism by which small changes in total irradiance can influence a global climate response. One possible amplifier within the climate system is the ocean. If this is the case, then we need to know more about where and how this may be occurring. On the other hand, the similarity in spectral peaks could be merely coincidental, and this should be made apparent by a lack of coherence in how that power and phasing are distributed in time and space. The plausibility of the solar forcing hypothesis is assessed through a Bayesian model of the age uncertainties affecting marine sedimentary records that is propagated through spectral analysis of the climate and forcing signals at key frequencies. Preliminary work on Mg/Ca and alkenone records from the Indo-Pacific Warm Pool suggests that despite large uncertainties in the location of the spectral peaks within each individual record arising from age model uncertainty, sea surface variability on timescales of 1025±36 years and 2427±133 years (±standard error of the mean of the median periodicity in each record) are present in at least 95% and 70% of the ensemble spectra, respectively. However, we find a long phase delay between the peak in forcing and the maximum response in at least one of the records, challenging the solar forcing hypothesis and requiring further investigation between low- and high-latitude signals. Remarkably, all records suggest a periodicity near 1470±85 years, reminiscent of the cycles characteristic of Marine Isotope Stage 3; these cycles are absent from existing records of TSI, further questioning the millennial solar-climate connection.

  4. Improved-Bandwidth Transimpedance Amplifier

    Science.gov (United States)

    Chapsky, Jacob

    2009-01-01

    The widest available operational amplifier, with the best voltage and current noise characteristics, is considered for transimpedance amplifier (TIA) applications where wide bandwidth is required to handle fast rising input signals (as for time-of-flight measurement cases). The added amplifier inside the TIA feedback loop can be configured to have slightly lower voltage gain than the bandwidth reduction factor.

  5. Density and temperature of energetic electrons in the Earth's magnetotail derived from high-latitude GPS observations during the declining phase of the solar cycle

    Directory of Open Access Journals (Sweden)

    M. H. Denton

    2011-10-01

    Full Text Available Single relativistic-Maxwellian fits are made to high-latitude GPS-satellite observations of energetic electrons for the period January 2006–November 2010; a constellation of 12 GPS space vehicles provides the observations. The derived fit parameters (for energies ~0.1–1.0 MeV, in combination with field-line mapping on the nightside of the magnetosphere, provide a survey of the energetic electron density and temperature distribution in the magnetotail between McIlwain L-values of L=6 and L=22. Analysis reveals the characteristics of the density-temperature distribution of energetic electrons and its variation as a function of solar wind speed and the Kp index. The density-temperature characteristics of the magnetotail energetic electrons are very similar to those found in the outer electron radiation belt as measured at geosynchronous orbit. The energetic electron density in the magnetotail is much greater during increased geomagnetic activity and during fast solar wind. The total electron density in the magnetotail is found to be strongly correlated with solar wind speed and is at least a factor of two greater for high-speed solar wind (VSW=500–1000 km s−1 compared to low-speed solar wind (VSW=100–400 km s−1. These results have important implications for understanding (a how the solar wind may modulate entry into the magnetosphere during fast and slow solar wind, and (b if the magnetotail is a source or a sink for the outer electron radiation belt.

  6. Estimation of the soil heat flux/net radiation ratio based on spectral vegetation indexes in high-latitude Arctic areas

    International Nuclear Information System (INIS)

    Jacobsen, A.; Hansen, B.U.

    1999-01-01

    The vegetation communities in the Arctic environment are very sensitive to even minor climatic variations and therefore the estimation of surface energy fluxes from high-latitude vegetated areas is an important subject to be pursued. This study was carried out in July-August and used micro meteorological data, spectral reflectance signatures, and vegetation biomass to establish the relation between the soil heat flux/net radiation (G / Rn) ratio and spectral vegetation indices (SVIs). Continuous measurements of soil temperature and soil heat flux were used to calculate the surface ground heat flux by use of conventional methods, and the relation to surface temperature was investigated. Twenty-seven locations were established, and six samples per location, including the measurement of the surface temperature and net radiation to establish the G/Rn ratio and simultaneous spectral reflectance signatures and wet biomass estimates, were registered. To obtain regional reliability, the locations were chosen in order to represent the different Arctic vegetation communities in the study area; ranging from dry tundra vegetation communities (fell fields and dry dwarf scrubs) to moist/wet tundra vegetation communities (snowbeds, grasslands and fens). Spectral vegetation indices, including the simple ratio vegetation index (RVI) and the normalized difference vegetation index (NDVI), were calculated. A comparison of SVIs to biomass proved that RVI gave the best linear expression, and NDVI the best exponential expression. A comparison of SVIs and the surface energy flux ratio G / Rn proved that NDVI gave the best linear expression. SPOT HRV images from July 1989 and 1992 were used to map NDVI and G / Rn at a regional scale. (author)

  7. Application of Satellite Solar-Induced Chlorophyll Fluorescence to Understanding Large-Scale Variations in Vegetation Phenology and Function Over Northern High Latitude Forests

    Science.gov (United States)

    Jeong, Su-Jong; Schimel, David; Frankenberg, Christian; Drewry, Darren T.; Fisher, Joshua B.; Verma, Manish; Berry, Joseph A.; Lee, Jung-Eun; Joiner, Joanna

    2016-01-01

    This study evaluates the large-scale seasonal phenology and physiology of vegetation over northern high latitude forests (40 deg - 55 deg N) during spring and fall by using remote sensing of solar-induced chlorophyll fluorescence (SIF), normalized difference vegetation index (NDVI) and observation-based estimate of gross primary productivity (GPP) from 2009 to 2011. Based on GPP phenology estimation in GPP, the growing season determined by SIF time-series is shorter in length than the growing season length determined solely using NDVI. This is mainly due to the extended period of high NDVI values, as compared to SIF, by about 46 days (+/-11 days), indicating a large-scale seasonal decoupling of physiological activity and changes in greenness in the fall. In addition to phenological timing, mean seasonal NDVI and SIF have different responses to temperature changes throughout the growing season. We observed that both NDVI and SIF linearly increased with temperature increases throughout the spring. However, in the fall, although NDVI linearly responded to temperature increases, SIF and GPP did not linearly increase with temperature increases, implying a seasonal hysteresis of SIF and GPP in response to temperature changes across boreal ecosystems throughout their growing season. Seasonal hysteresis of vegetation at large-scales is consistent with the known phenomena that light limits boreal forest ecosystem productivity in the fall. Our results suggest that continuing measurements from satellite remote sensing of both SIF and NDVI can help to understand the differences between, and information carried by, seasonal variations vegetation structure and greenness and physiology at large-scales across the critical boreal regions.

  8. Towards a more detailed representation of high-latitude vegetation in the global land surface model ORCHIDEE (ORC-HL-VEGv1.0)

    Science.gov (United States)

    Druel, Arsène; Peylin, Philippe; Krinner, Gerhard; Ciais, Philippe; Viovy, Nicolas; Peregon, Anna; Bastrikov, Vladislav; Kosykh, Natalya; Mironycheva-Tokareva, Nina

    2017-12-01

    Simulation of vegetation-climate feedbacks in high latitudes in the ORCHIDEE land surface model was improved by the addition of three new circumpolar plant functional types (PFTs), namely non-vascular plants representing bryophytes and lichens, Arctic shrubs and Arctic C3 grasses. Non-vascular plants are assigned no stomatal conductance, very shallow roots, and can desiccate during dry episodes and become active again during wet periods, which gives them a larger phenological plasticity (i.e. adaptability and resilience to severe climatic constraints) compared to grasses and shrubs. Shrubs have a specific carbon allocation scheme, and differ from trees by their larger survival rates in winter, due to protection by snow. Arctic C3 grasses have the same equations as in the original ORCHIDEE version, but different parameter values, optimised from in situ observations of biomass and net primary productivity (NPP) in Siberia. In situ observations of living biomass and productivity from Siberia were used to calibrate the parameters of the new PFTs using a Bayesian optimisation procedure. With the new PFTs, we obtain a lower NPP by 31 % (from 55° N), as well as a lower roughness length (-41 %), transpiration (-33 %) and a higher winter albedo (by +3.6 %) due to increased snow cover. A simulation of the water balance and runoff and drainage in the high northern latitudes using the new PFTs results in an increase of fresh water discharge in the Arctic ocean by 11 % (+140 km3 yr-1), owing to less evapotranspiration. Future developments should focus on the competition between these three PFTs and boreal tree PFTs, in order to simulate their area changes in response to climate change, and the effect of carbon-nitrogen interactions.

  9. Topside Electron Density Representations for Middle and High Latitudes: A Topside Parameterization for E-CHAIM Based On the NeQuick

    Science.gov (United States)

    Themens, David R.; Jayachandran, P. T.; Bilitza, Dieter; Erickson, Philip J.; Häggström, Ingemar; Lyashenko, Mykhaylo V.; Reid, Benjamin; Varney, Roger H.; Pustovalova, Ljubov

    2018-02-01

    In this study, we present a topside model representation to be used by the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM). In the process of this, we also present a comprehensive evaluation of the NeQuick's, and by extension the International Reference Ionosphere's, topside electron density model for middle and high latitudes in the Northern Hemisphere. Using data gathered from all available incoherent scatter radars, topside sounders, and Global Navigation Satellite System Radio Occultation satellites, we show that the current NeQuick parameterization suboptimally represents the shape of the topside electron density profile at these latitudes and performs poorly in the representation of seasonal and solar cycle variations of the topside scale thickness. Despite this, the simple, one variable, NeQuick model is a powerful tool for modeling the topside ionosphere. By refitting the parameters that define the maximum topside scale thickness and the rate of increase of the scale height within the NeQuick topside model function, r and g, respectively, and refitting the model's parameterization of the scale height at the F region peak, H0, we find considerable improvement in the NeQuick's ability to represent the topside shape and behavior. Building on these results, we present a new topside model extension of the E-CHAIM based on the revised NeQuick function. Overall, root-mean-square errors in topside electron density are improved over the traditional International Reference Ionosphere/NeQuick topside by 31% for a new NeQuick parameterization and by 36% for a newly proposed topside for E-CHAIM.

  10. Biogeography of seabirds within a high-latitude ecosystem: Use of a data-assimilative ocean model to assess impacts of mesoscale oceanography

    Science.gov (United States)

    Santora, Jarrod A.; Eisner, Lisa B.; Kuletz, Kathy J.; Ladd, Carol; Renner, Martin; Hunt, George L., Jr.

    2018-02-01

    . Biogeographic assessments of LMEs that integrate top predator distributions resolve critical habitat requirements and will benefit assessment of climate change impacts (e.g., sea-ice loss) predicted to affect high-latitude marine ecosystems.

  11. Assessment of Evolving TRMM-Based Real-Time Precipitation Estimation Methods and Their Impacts on Hydrologic Prediction in a High-Latitude Basin

    Science.gov (United States)

    Yong, Bin; Hong, Yang; Ren, Li-Liang; Gourley, Jonathan; Huffman, George J.; Chen, Xi; Wang, Wen; Khan, Sadiq I.

    2013-01-01

    The real-time availability of satellite-derived precipitation estimates provides hydrologists an opportunity to improve current hydrologic prediction capability for medium to large river basins. Due to the availability of new satellite data and upgrades to the precipitation algorithms, the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis real-time estimates (TMPA-RT) have been undergoing several important revisions over the past ten years. In this study, the changes of the relative accuracy and hydrologic potential of TMPA-RT estimates over its three major evolving periods were evaluated and inter-compared at daily, monthly and seasonal scales in the high-latitude Laohahe basin in China. Assessment results show that the performance of TMPA-RT in terms of precipitation estimation and streamflow simulation was significantly improved after 3 February 2005. Overestimation during winter months was noteworthy and consistent, which is suggested to be a consequence from interference of snow cover to the passive microwave retrievals. Rainfall estimated by the new version 6 of TMPA-RT starting from 1 October 2008 to present has higher correlations with independent gauge observations and tends to perform better in detecting rain compared to the prior periods, although it suffers larger mean error and relative bias. After a simple bias correction, this latest dataset of TMPA-RT exhibited the best capability in capturing hydrologic response among the three tested periods. In summary, this study demonstrated that there is an increasing potential in the use of TMPA-RT in hydrologic streamflow simulations over its three algorithm upgrade periods, but still with significant challenges during the winter snowing events.

  12. The relationship between small-scale and large-scale ionospheric electron density irregularities generated by powerful HF electromagnetic waves at high latitudes

    Directory of Open Access Journals (Sweden)

    E. D. Tereshchenko

    2006-11-01

    Full Text Available Satellite radio beacons were used in June 2001 to probe the ionosphere modified by a radio beam produced by the EISCAT high-power, high-frequency (HF transmitter located near Tromsø (Norway. Amplitude scintillations and variations of the phase of 150- and 400-MHz signals from Russian navigational satellites passing over the modified region were observed at three receiver sites. In several papers it has been stressed that in the polar ionosphere the thermal self-focusing on striations during ionospheric modification is the main mechanism resulting in the formation of large-scale (hundreds of meters to kilometers nonlinear structures aligned along the geomagnetic field (magnetic zenith effect. It has also been claimed that the maximum effects caused by small-scale (tens of meters irregularities detected in satellite signals are also observed in the direction parallel to the magnetic field. Contrary to those studies, the present paper shows that the maximum in amplitude scintillations does not correspond strictly to the magnetic zenith direction because high latitude drifts typically cause a considerable anisotropy of small-scale irregularities in a plane perpendicular to the geomagnetic field resulting in a deviation of the amplitude-scintillation peak relative to the minimum angle between the line-of-sight to the satellite and direction of the geomagnetic field lines. The variance of the logarithmic relative amplitude fluctuations is considered here, which is a useful quantity in such studies. The experimental values of the variance are compared with model calculations and good agreement has been found. It is also shown from the experimental data that in most of the satellite passes a variance maximum occurs at a minimum in the phase fluctuations indicating that the artificial excitation of large-scale irregularities is minimum when the excitation of small-scale irregularities is maximum.

  13. Simplified design of IC amplifiers

    CERN Document Server

    Lenk, John

    1996-01-01

    Simplified Design of IC Amplifiers has something for everyone involved in electronics. No matter what skill level, this book shows how to design and experiment with IC amplifiers. For experimenters, students, and serious hobbyists, this book provides sufficient information to design and build IC amplifier circuits from 'scratch'. For working engineers who design amplifier circuits or select IC amplifiers, the book provides a variety of circuit configurations to make designing easier.Provides basics for all phases of practical design.Covers the most popular forms for amplif

  14. Publisher Correction: Recently amplified arctic warming has contributed to a continual global warming trend

    Science.gov (United States)

    Huang, Jianbin; Zhang, Xiangdong; Zhang, Qiyi; Lin, Yanluan; Hao, Mingju; Luo, Yong; Zhao, Zongci; Yao, Yao; Chen, Xin; Wang, Lei; Nie, Suping; Yin, Yizhou; Xu, Ying; Zhang, Jiansong

    2018-04-01

    In the version of this Letter originally published, the increments on the y axis of Fig. 3 were incorrectly labelled as `0.0; 0.2; 0.2; 0.3'; they should have read `0.0; 0.1; 0.2; 0.3'. This has now been corrected in all versions of the Letter.

  15. Wideband amplifier design

    CERN Document Server

    Hollister, Allen L

    2007-01-01

    In this book, the theory needed to understand wideband amplifier design using the simplest models possible will be developed. This theory will be used to develop algebraic equations that describe particular circuits used in high frequency design so that the reader develops a ""gut level"" understanding of the process and circuit. SPICE and Genesys simulations will be performed to show the accuracy of the algebraic models. By looking at differences between the algebraic equations and the simulations, new algebraic models will be developed that include parameters originally left out of the model

  16. Building valve amplifiers

    CERN Document Server

    Jones, Morgan

    2013-01-01

    Building Valve Amplifiers is a unique hands-on guide for anyone working with tube audio equipment--as an electronics hobbyist, audiophile or audio engineer. This 2nd Edition builds on the success of the first with technology and technique revisions throughout and, significantly, a major new self-build project, worked through step-by-step, which puts into practice the principles and techniques introduced throughout the book. Particular attention has been paid to answering questions commonly asked by newcomers to the world of the valve, whether audio enthusiasts tackling their first build or

  17. Superconducting digital logic amplifier

    International Nuclear Information System (INIS)

    Przybysz, J.X.

    1989-01-01

    This paper describes a superconducting digital logic amplifier for interfacing between a Josephson junction logic circuit having output current and a higher voltage semiconductor circuit input. The amplifier comprising: an input terminal for connection to a; an output terminal for connection to a semiconductor circuit input; an input, lower critical current, Josephson junction having first and second terminals; a first series string of at least three lower critical current Josephson junctions. The first series string being connected to the first terminal of the input Josephson junction such that the first series string is in series with the input Josephson junction to provide a series combination. The input terminal being connected to the first terminal of the input Josephson junction, and with the critical current of the lower critical current Josephson junctions of the input Josephson junction and the first series Josephson junctions being less than the output current of the low voltage Josephson junction circuit; a second series string of at least four higher critical current Josephson junctions. The second string being connected in parallel with the series combination to provide parallel strings having an upper common connection and a lower common connection. The lower common connection being connected to the second terminal of the input Josephson junction and the upper common connection being connected to the output terminal; and a pulsed DC current source connected the parallel strings at the upper common connection. The DC current source having a current at least equal to the critical current of the higher critical current Josephson junctions

  18. Cascade energy amplifier

    International Nuclear Information System (INIS)

    Barzilov, A.P.; Gulevich, A.V.; Kukharchuk, O.F.

    2000-01-01

    The technical problem of long-life fission product and minor actinide incineration and production of plutonium fuel in the prospective nuclear systems will arise at significant scales of nuclear power industry development. Subcritical nuclear reactors driven by extemal neutron sources (energy amplifiers) are considered as incinerators of toxicity of complete nuclear industry. In the frames of this concept, the subcritical reactor part consisting of two coupled blanket regions (inner fast neutron spectrum core and outer thermal core) driven by extemal neutron source is discussed. Two types of source are studied: spallation target and 14-MeV fusion bum of micropellets. Liquid metal Pb-Bi is considered as target material and coolant of inner fast core. Thermal core is a heavy-water subcritical reactor of the Candu-type. The fast core is protected from thermal neutrons influence with the boron shield. All reactor technologies used in this concept are tested during years of operation and commercially available. Thus, the cascade energy amplifiers have a set of advantages in comparison with traditional concepts: in energy production, in transmutation efficiency, and in economics. (authors)

  19. Evolutionary and ecological differentiation in the pantropical to warm-temperate seaweed Digenea simplex (Rhodophyta)

    NARCIS (Netherlands)

    Pakker, H; Klerk, H; vanCampen, JH; Olsen, JL; Breeman, AM

    Genetic differentiation among geographic isolates of the pantropical to warm-temperate red alga Digenea simplex (Wulfen) C. Agardh was investigated using random amplified polymorphic DNA (RAPD) markers, crossing studies, and temperature tolerances experiments. Eleven isolates representing

  20. Humid Heat Waves at different warming levels

    Science.gov (United States)

    Russo, S.; Sillmann, J.; Sterl, A.

    2017-12-01

    The co-occurrence of consecutive hot and humid days during a heat wave can strongly affect human health. Here, we quantify humid heat wave hazard in the recent past and at different levels of global warming.We find that the magnitude and apparent temperature peak of heat waves, such as the ones observed in Chicago in 1995 and China in 2003, have been strongly amplified by humidity. Climate model projections suggest that the percentage of area where heat wave magnitude and peak are amplified by humidity increases with increasing warming levels. Considering the effect of humidity at 1.5o and 2o global warming, highly populated regions, such as the Eastern US and China, could experience heat waves with magnitude greater than the one in Russia in 2010 (the most severe of the present era).The apparent temperature peak during such humid-heat waves can be greater than 55o. According to the US Weather Service, at this temperature humans are very likely to suffer from heat strokes. Humid-heat waves with these conditions were never exceeded in the present climate, but are expected to occur every other year at 4o global warming. This calls for respective adaptation measures in some key regions of the world along with international climate change mitigation efforts.

  1. Monitoring Coral Health to Determine Coral Bleaching Response at High Latitude Eastern Australian Reefs: An Applied Model for A Changing Climate

    Directory of Open Access Journals (Sweden)

    Andrew G. Carroll

    2011-09-01

    Full Text Available Limited information is available on the bleaching susceptibility of coral species that dominate high latitude reefs along the eastern seaboard of Australia. The main aims of this study were to: (i monitor coral health and spatial patterns of coral bleaching response at the Solitary Islands Marine Park (SIMP and Lord Howe Island Marine Park (LHIMP, to determine variability of bleaching susceptibility among coral taxa; (ii predict coral bleaching thresholds at 30 °S and 31.5 °S, extrapolated from published bleaching threshold data; and (iii propose a subtropical northern New South Wales coral bleaching model from biological and physical data. Between 2005 and 2007 minor bleaching was observed in dominant coral families including Pocilloporidae, Poritidae and Dendrophylliidae in the SIMP and Pocilloporidae, Poritidae and Acroporidae (Isopora and Montipora spp. in the LHIMP, with a clear difference in bleaching susceptibility found between sites, both within and between locations. Bleaching susceptibility was highest in Porites spp. at the most offshore island site within the SIMP during summer 2005. Patterns of subtropical family bleaching susceptibility within the SIMP and LHIMP differed to those previously reported for the central Great Barrier Reef (GBR. These differences may be due to a number of factors, including temperature history and/or the coral hosts association with different zooxanthellae clades, which may have lower thermal tolerances. An analysis of published estimates of coral bleaching thresholds from the Caribbean, South Africa, GBR and central and northern Pacific regions suggests that the bleaching threshold at 30–31.5 °S ranges between 26.5–26.8 °C. This predicted threshold was confirmed by an extensive coral bleaching event on the world’s southernmost coral reef at Lord Howe Island, during the 2010 austral summer season. These results imply that dominant coral taxa at subtropical reefs along the eastern Australian

  2. High resolution carbon isotope stratigraphy and glendonite occurrences of the Christopher Formation, Sverdrup Basin (Axel Heiberg Island, Canada): implications for mid Cretaceous high latitude climate change

    Science.gov (United States)

    Herrle, Jens O.; Schröder-Adams, Claudia J.; Galloway, Jennifer M.; Pugh, Adam T.

    2013-04-01

    Understanding the evolution of Canada's Arctic region, as a crucial component of Earth's climate system, is fundamental to assess short and long-term climate, environmental, and paleogeographic change. However, the stratigraphy and paleoenvironmental evolution of the Cretaceous Arctic is poorly constrained and a detailed bio- and chemostratigraphic correlation of major mid-Cretaceous paleoceanographic turning points such as Oceanic Anoxic Events, cold snaps, and biotic turnovers with key locations of the high- and low latitudes is missing. Here we present for the first time a high resolution bio- and carbon isotope stratigraphy of the Arctic Albian Christopher Formation of the Sverdrup Basin at Glacier Fiord in the southern part of Axel Heiberg Island, Canadian High Arctic. By using these techniques we developed a high temporal framework to record major environmental changes as it is indicated by the occurrence of glendonites and sandstone intervals of our studied Albian succession. The Albian Christopher Formation is a shale dominated marine unit with a thickness of approximately 1200 m. Several transgressive/ regressive cycles can be recognized by prograding shoreface units that break up mudrock deposition. In addition, glendonites are mainly found in the lower part of the Christopher Formation. Glendonites are pseudomorphs of calcite, after the metastable mineral ikaite, and have been often described from high latitude Permian, Jurassic and Cretaceous marine environments from the Canadian Arctic, Spitsbergen and Australia. The formation of glendonites takes place in the uppermost layer of the sediment and requires near-freezing temperatures, high salinity, and orthophosphate-rich bottom water. Although the presence of glendonites implies a range of paleoenvironmental conditions there is a consensus in the scientific literature that they reflect cooler paleoenvironmental conditions. Preliminary bio- and carbon isotope stratigraphic results suggest that the

  3. Plant functional types in Earth system models: past experiences and future directions for application of dynamic vegetation models in high-latitude ecosystems.

    Science.gov (United States)

    Wullschleger, Stan D; Epstein, Howard E; Box, Elgene O; Euskirchen, Eugénie S; Goswami, Santonu; Iversen, Colleen M; Kattge, Jens; Norby, Richard J; van Bodegom, Peter M; Xu, Xiaofeng

    2014-07-01

    Earth system models describe the physical, chemical and biological processes that govern our global climate. While it is difficult to single out one component as being more important than another in these sophisticated models, terrestrial vegetation is a critical player in the biogeochemical and biophysical dynamics of the Earth system. There is much debate, however, as to how plant diversity and function should be represented in these models. Plant functional types (PFTs) have been adopted by modellers to represent broad groupings of plant species that share similar characteristics (e.g. growth form) and roles (e.g. photosynthetic pathway) in ecosystem function. In this review, the PFT concept is traced from its origin in the early 1800s to its current use in regional and global dynamic vegetation models (DVMs). Special attention is given to the representation and parameterization of PFTs and to validation and benchmarking of predicted patterns of vegetation distribution in high-latitude ecosystems. These ecosystems are sensitive to changing climate and thus provide a useful test case for model-based simulations of past, current and future distribution of vegetation. Models that incorporate the PFT concept predict many of the emerging patterns of vegetation change in tundra and boreal forests, given known processes of tree mortality, treeline migration and shrub expansion. However, representation of above- and especially below-ground traits for specific PFTs continues to be problematic. Potential solutions include developing trait databases and replacing fixed parameters for PFTs with formulations based on trait co-variance and empirical trait-environment relationships. Surprisingly, despite being important to land-atmosphere interactions of carbon, water and energy, PFTs such as moss and lichen are largely absent from DVMs. Close collaboration among those involved in modelling with the disciplines of taxonomy, biogeography, ecology and remote sensing will be

  4. Rayleigh lidar observations of enhanced stratopause temperature over Gadanki (13.5° N, 79.2° E) during major stratospheric warming in 2006

    Science.gov (United States)

    Sridharan, S.; Sathishkumar, S.; Raghunath, K.

    2009-01-01

    Rayleigh lidar observations of temperature structure and gravity wave activity were carried out at Gadanki (13.5° N, 79.2° E) during January-February 2006. A major stratospheric warming event occurred at high latitude during the end of January and early February. There was a sudden enhancement in the stratopause temperature over Gadanki coinciding with the date of onset of the major stratospheric warming event which occurred at high latitudes. The temperature enhancement persisted even after the end of the high latitude major warming event. During the same time, the UKMO (United Kingdom Meteorological Office) zonal mean temperature showed a similar warming episode at 10° N and cooling episode at 60° N around the region of stratopause. This could be due to ascending (descending) motions at high (low) latitudes above the critical level of planetary waves, where there was no planetary wave flux. The time variation of the gravity wave potential energy computed from the temperature perturbations over Gadanki shows variabilities at planetary wave periods, suggesting a non-linear interaction between gravity waves and planetary waves. The space-time analysis of UKMO temperature data at high and low latitudes shows the presence of similar periodicities of planetary wave of zonal wavenumber 1.

  5. Rayleigh lidar observations of enhanced stratopause temperature over Gadanki (13.5° N, 79.2° E during major stratospheric warming in 2006

    Directory of Open Access Journals (Sweden)

    S. Sridharan

    2009-01-01

    Full Text Available Rayleigh lidar observations of temperature structure and gravity wave activity were carried out at Gadanki (13.5° N, 79.2° E during January–February 2006. A major stratospheric warming event occurred at high latitude during the end of January and early February. There was a sudden enhancement in the stratopause temperature over Gadanki coinciding with the date of onset of the major stratospheric warming event which occurred at high latitudes. The temperature enhancement persisted even after the end of the high latitude major warming event. During the same time, the UKMO (United Kingdom Meteorological Office zonal mean temperature showed a similar warming episode at 10° N and cooling episode at 60° N around the region of stratopause. This could be due to ascending (descending motions at high (low latitudes above the critical level of planetary waves, where there was no planetary wave flux. The time variation of the gravity wave potential energy computed from the temperature perturbations over Gadanki shows variabilities at planetary wave periods, suggesting a non-linear interaction between gravity waves and planetary waves. The space-time analysis of UKMO temperature data at high and low latitudes shows the presence of similar periodicities of planetary wave of zonal wavenumber 1.

  6. Prediction on global warming-up. Chikyu ondanka wo yosokusuru

    Energy Technology Data Exchange (ETDEWEB)

    Noda, A [Meteorological Research Institute, Tsukuba (Japan)

    1993-05-01

    This paper introduces models to predict global warming-up caused by greenhouse effect of the earth and increase in greenhouse effect gases, and the prediction results. As a result of CO2 doubling experiments using three-dimensional climate models in predicting the global warming-up, a model that predicted a sharp rise in annual average ground temperatures on the entire earth showed a larger increase in precipitation. According to the result of the CO2 doubling experiments using atmosphere-ocean coupling models, it was learned that the temperature rises higher in high latitude regions rather than rising uniformly over the earth on the whole. The fact that the temperature rise when CO2 has been doubled in a CO2 gradually increasing experiment is smaller than in the doubling experiment can be understood as a delaying effect of oceans generated from their thermal inertia. The former experiment showed a remarkable non-symmetry between the Southern and Northern hemispheres, reflecting the effect of the great oceanic circulation. Increase in cloud amount has an effect of either cooling or warming the earth, but the cooling effect surpasses the warming effect reportedly. Sulfuric acid aerosol in the troposphere is thought to influence the process of solar radiation transmitting through the atmosphere and have an effect to cool down the ground surface. 12 refs., 6 figs.

  7. Nanoscale electromechanical parametric amplifier

    Science.gov (United States)

    Aleman, Benjamin Jose; Zettl, Alexander

    2016-09-20

    This disclosure provides systems, methods, and apparatus related to a parametric amplifier. In one aspect, a device includes an electron source electrode, a counter electrode, and a pumping electrode. The electron source electrode may include a conductive base and a flexible conductor. The flexible conductor may have a first end and a second end, with the second end of the flexible conductor being coupled to the conductive base. A cross-sectional dimension of the flexible conductor may be less than about 100 nanometers. The counter electrode may be disposed proximate the first end of the flexible conductor and spaced a first distance from the first end of the flexible conductor. The pumping electrode may be disposed proximate a length of the flexible conductor and spaced a second distance from the flexible conductor.

  8. Linear pulse amplifier

    International Nuclear Information System (INIS)

    Tjutju, R.L.

    1977-01-01

    Pulse amplifier is standard significant part of spectrometer. Apart from other type of amplification, it's a combination of amplification and pulse shaping. Because of its special purpose the device should fulfill the following : High resolution is desired to gain a high yield comparable to its actual state of condition. High signal to noise is desired to nhν resolution. High linearity to facilitate calibration. A good overload recovery, in order to the device will capable of analizing a low energy radiation which appear joinly on the high energy fields. Other expections of the device are its economical and practical use its extentive application. For that reason it's built on a standard NIM principle. Taking also into account the above mentioned considerations. High quality component parts are used throughout, while its availability in the domestic market is secured. (author)

  9. Ocean Heat Uptake Slows 21st Century Surface Warming Driven by Extratropical Cloud Feedbacks

    Science.gov (United States)

    Frey, W.; Maroon, E.; Pendergrass, A. G.; Kay, J. E.

    2017-12-01

    Equilibrium climate sensitivity (ECS), the warming in response to instantaneously doubled CO2, has long been used to compare climate models. In many models, ECS is well correlated with warming produced by transient forcing experiments. Modifications to cloud phase at high latitudes in a state-of-the-art climate model, the Community Earth System Model (CESM), produce a large increase in ECS (1.5 K) via extratropical cloud feedbacks. However, only a small surface warming increase occurs in a realistic 21st century simulation including a full-depth dynamic ocean and the "business as usual" RCP8.5 emissions scenario. In fact, the increase in surface warming is only barely above the internal variability-generated range in the CESM Large Ensemble. The small change in 21st century warming is attributed to subpolar ocean heat uptake in both hemispheres. In the Southern Ocean, the mean-state circulation takes up heat while in the North Atlantic a slowdown in circulation acts as a feedback to slow surface warming. These results show the importance of subpolar ocean heat uptake in controlling the pace of warming and demonstrate that ECS cannot be used to reliably infer transient warming when it is driven by extratropical feedbacks.

  10. Modeling of semiconductor optical amplifiers

    DEFF Research Database (Denmark)

    Mørk, Jesper; Bischoff, Svend; Berg, Tommy Winther

    We discuss the modelling of semiconductor optical amplifiers with emphasis on their high-speed properties. Applications in linear amplification as well as ultrafast optical signal processing are reviewed. Finally, the possible role of quantum-dot based optical amplifiers is discussed.......We discuss the modelling of semiconductor optical amplifiers with emphasis on their high-speed properties. Applications in linear amplification as well as ultrafast optical signal processing are reviewed. Finally, the possible role of quantum-dot based optical amplifiers is discussed....

  11. Warm liquid calorimetry for LHC

    CERN Document Server

    Geulig,E; Wallraff,W; Bézaguet, Alain-Arthur; Cavanna, F; Cinnini, P; Cittolin, Sergio; Dreesen, P; Demoulin, M; Dunps, L; Fucci, A; Gallay, G; Givernaud, Alain; Gonidec, A; Jank, Werner; Maurin, Guy; Placci, Alfredo; Porte, J P; Radermacher, E; Samyn, D; Schinzel, D; Schmidt, W F; CERN. Geneva. Detector Research and Development Committee

    1990-01-01

    Results from the beam tests of the U/TMP "warm liquid" calorimeter show that such a technique is very promising for the LHC. Our aim is to extend this programme and design a calorimeter that can satisfy the requirements of high rates, high radiation levels, compensation, uniformity and granularity, as well as fully contain hadronic showers. We propose to construct liquid ionization chambers operated at very high fields, capable of collecting the total charge produced by ionizing particles within times comparable to the bunch crossing time of the future Collider. For this reason we plan to extend the current programme on tetramethylpentane (TMP) to tetramethylsilane (TMSi). An electromagnetic calorimeter consisting of very high field ionization chambers filled with TMSi as sensitive medium with Uranium and/or other high density material as absorber will first be built (to be followed by a full-scale calorimeter module), on which newly designed fast amplifiers and readout electronics will be tested. In addition...

  12. Evolution determines how global warming and pesticide exposure will shape predator-prey interactions with vector mosquitoes.

    Science.gov (United States)

    Tran, Tam T; Janssens, Lizanne; Dinh, Khuong V; Op de Beeck, Lin; Stoks, Robby

    2016-07-01

    How evolution may mitigate the effects of global warming and pesticide exposure on predator-prey interactions is directly relevant for vector control. Using a space-for-time substitution approach, we addressed how 4°C warming and exposure to the pesticide endosulfan shape the predation on Culex pipiens mosquitoes by damselfly predators from replicated low- and high-latitude populations. Although warming was only lethal for the mosquitoes, it reduced predation rates on these prey. Possibly, under warming escape speeds of the mosquitoes increased more than the attack efficiency of the predators. Endosulfan imposed mortality and induced behavioral changes (including increased filtering and thrashing and a positional shift away from the bottom) in mosquito larvae. Although the pesticide was only lethal for the mosquitoes, it reduced predation rates by the low-latitude predators. This can be explained by the combination of the evolution of a faster life history and associated higher vulnerabilities to the pesticide (in terms of growth rate and lowered foraging activity) in the low-latitude predators and pesticide-induced survival selection in the mosquitoes. Our results suggest that predation rates on mosquitoes at the high latitude will be reduced under warming unless predators evolve toward the current low-latitude phenotype or low-latitude predators move poleward.

  13. Sudden Stratospheric Warming Compendium

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Sudden Stratospheric Warming Compendium (SSWC) data set documents the stratospheric, tropospheric, and surface climate impacts of sudden stratospheric warmings. This...

  14. [Phylogenetic diversity and cold-adaptive hydrolytic enzymes of culturable psychrophilic bacteria associated with sea ice from high latitude ocean, Artic].

    Science.gov (United States)

    Yu, Yong; Li, Hui-Rong; Chen, Bo; Zeng, Yin-Xin; He, Jian-Feng

    2006-04-01

    The phylogenetic diversity of culturable psychrophilic bacteria associated with sea ice from high latitude sea (77 degrees 30'N - 81 degrees 12'N), Canadian Basin and Greenland sea Arctic, was investigated. A total of 37 psychrophilic strains were isolated using three different methods of ( i ) spread plate method: 100 microL of each dilution ice-melt sample was spreaded onto the surface of Marine 2216 agar (DIFCO laboratories, Detroit, MI) and incubated for 2 to 6 weeks at 4 degrees C; ( ii ) bath culture and spread plate method: 1 mL of sample was added to 9mL of NSW (unamended natural seawater, 0.2 microm prefiltered and autoclaved) and incubated for 1 months at - 1 degrees C, then spread plate method was used to isolate bacterial strains from the pre-cultured samples; ( iii ) cold shock, bath culture and spread plate method: samples were exposed to - 20 degrees C for 24h, then bacterial strains isolated by bath culture and spread plate method under aerobic conditions. Nearly half of psychrophilic strains are isolated by using method iii . 16S rDNA nearly full-length sequence analysis reveal that psychrophilic strains fall in two phylogenetic divisions, gamma-proteobacteria (in the genera Colwellia, Marinobacter, Shewanella, Thalassomonas, Glaciecola, Marinomonas and Pseudoalteromonas) and Cytophaga-Flexibacter-Bacteroides (in the genera Flavobacterium and Psychroflexus). Nine of bacterial isolates (BSi20007, BSi20497, BSi20517, BSi20537, BSi20170, BSi20001, BSi20002, BSi20675 and BSi20101) quite likely represent novel species (16S rDNA sequence similarity below 97%). One of strains (BSi20002) from Canadian Basin shows 100% sequence similarity to the Antarctic Weddell sea ice isolate Marinobacter sp. ANT8277, suggesting bacteria may have a bipolar distribution at the species level. AF283859 sequences were submitted to the BLAST search program of the National Center for Biotechnology Information website (NCBI, http://www. ncbi. nlm.nih. gov). Twenty sequences

  15. CERN: Energy amplifier

    International Nuclear Information System (INIS)

    Anon.

    1995-01-01

    Even under the heavy burden of responsibility as CERN's Director General from 1989-3 the fertile mind of Carlo Rubbia the scientist was never still. A long-time Rubbia 'hobby' has been the search for new sources of nuclear energy, exploiting knowledge and skills from high energy physics. An initial objective was to adopt heavy ion techniques to induce controlled thermonuclear fusion, but in 1994 this quest changed direction. Putting the problems of thermonuclear fusion aside, Rubbia began to explore an alternative route to energy production through controlled nuclear fission. The idea is to use a particle accelerator producing neutrons by spallation (interaction of particles with a target) to feed a fuel/moderator assembly where the neutrons multiply by fission chain reactions. If the energy liberated becomes substantially greater than that needed to drive the accelerator, the process has a net gain and becomes selfsupporting. Hence the name ''Energy Amplifier'' (EA). Similar systems for energy production or for nuclear waste incineration have been proposed at Los Alamos and in Japan and Russia, but appear to require the prior development of innovative linear accelerators. For Rubbia's Amplifier, the requisite accelerator is a reasonable extrapolation of an existing cyclotron such that at the Swiss Paul Scherrer Institute. Moreover, the EA would require fuel rods very similar to those of conventional reactors, rather than demand-ing new technology using liquid fuel loops (molten salts) with on-line separation of radioactive products. Unlike a reactor, the EA's fission reaction is not self-sustaining: it is sub-critical and needs a continuous supply of neutrons from the accelerator. This makes Chernobyl-type meltdowns unlikely: if the accelerator stops, the reaction stops too. Another major advantage is that the old dream of using thorium as a fuel is now made possible. Thorium is not itself fissile, but under neutron

  16. Millimeter-wave power amplifiers

    CERN Document Server

    du Preez, Jaco

    2017-01-01

    This book provides a detailed review of millimeter-wave power amplifiers, discussing design issues and performance limitations commonly encountered in light of the latest research. Power amplifiers, which are able to provide high levels of output power and linearity while being easily integrated with surrounding circuitry, are a crucial component in wireless microwave systems. The book is divided into three parts, the first of which introduces readers to mm-wave wireless systems and power amplifiers. In turn, the second focuses on design principles and EDA concepts, while the third discusses future trends in power amplifier research. The book provides essential information on mm-wave power amplifier theory, as well as the implementation options and technologies involved in their effective design, equipping researchers, circuit designers and practicing engineers to design, model, analyze, test and implement high-performance, spectrally clean and energy-efficient mm-wave systems.

  17. Polar warming in the middle atmosphere of Mars

    Science.gov (United States)

    Deming, D.; Mumma, M. J.; Espenak, F.; Kostiuk, T.; Zipoy, D.

    1986-01-01

    During the 1984 Mars opposition, ground-based laser heterodyne spectroscopy was obtained for the nonthermal core emission of the 10.33-micron R(8) and 10.72-micron P(32) lines of C-12(O-16)2 at 23 locations on the Martian disk. It is deduced on the basis of these data that the temperature of the middle Martian atmosphere varies with latitude, and a meridional gradient of 0.4-0.9 K/deg latitude is indicated. The highest temperatures are noted to lie at high latitudes in the winter hemisphere; as in the terrestrial case of seasonal effects at the menopause, this winter polar warming in the Martian middle atmosphere requires departures from radiative equilibrium. Two-dimensional circulation model comparisons with these results indicate that atmospheric dust may enhance this dynamical heating at high winter latitudes.

  18. Divergent surface and total soil moisture projections under global warming

    Science.gov (United States)

    Berg, Alexis; Sheffield, Justin; Milly, Paul C.D.

    2017-01-01

    Land aridity has been projected to increase with global warming. Such projections are mostly based on off-line aridity and drought metrics applied to climate model outputs but also are supported by climate-model projections of decreased surface soil moisture. Here we comprehensively analyze soil moisture projections from the Coupled Model Intercomparison Project phase 5, including surface, total, and layer-by-layer soil moisture. We identify a robust vertical gradient of projected mean soil moisture changes, with more negative changes near the surface. Some regions of the northern middle to high latitudes exhibit negative annual surface changes but positive total changes. We interpret this behavior in the context of seasonal changes in the surface water budget. This vertical pattern implies that the extensive drying predicted by off-line drought metrics, while consistent with the projected decline in surface soil moisture, will tend to overestimate (negatively) changes in total soil water availability.

  19. Recent Global Warming as Observed by AIRS and Depicted in GISSTEMP and MERRA-2

    Science.gov (United States)

    Susskind, Joel; Lee, Jae; Iredell, Lena

    2017-01-01

    AIRS Version-6 monthly mean level-3 surface temperature products confirm the result, depicted in the GISSTEMP dataset, that the earth's surface temperature has been warming since early 2015, though not before that. AIRS is at a higher spatial resolution than GISSTEMP, and produces sharper spatial features which are otherwise in excellent agreement with those of GISSTEMP. Version-6 AO Ts anomalies are consistent with those of Version-6 AIRS/AMSU. Version-7 AO anomalies should be even more accurate, especially at high latitudes. ARCs of MERRA-2 Ts anomalies are spurious as a result of a discontinuity which occurred somewhere between 2007 and 2008. This decreases global mean trends.

  20. Preliminary Evidence for the Amplification of Global Warming in Shallow, Intertidal Estuarine Waters

    Science.gov (United States)

    Over the past 50 years, mean annual water temperature in northeastern U.S. estuaries has increased by approximately 1.2°C, with most of the warming recorded in the winter and early spring. We hypothesize that this warming may be amplified in the shallow (<2m), nearshore portions ...

  1. A Contribution by Ice Nuclei to Global Warming

    Science.gov (United States)

    Zeng, Xiping; Tao, Wei-Kuo; Zhang, Minghua; Hou, Arthur Y.; Xie, Shaocheng; Lang, Stephen; Li, Xiaowen; Starr, David O.; Li, Xiaofan

    2009-01-01

    Ice nuclei (IN) significantly affect clouds via supercooled droplets, that in turn modulate atmospheric radiation and thus climate change. Since the IN effect is relatively strong in stratiform clouds but weak in convective ones, the overall effect depends on the ratio of stratiform to convective cloud amount. In this paper, 10 years of TRMM (Tropical Rainfall Measuring Mission) satellite data are analyzed to confirm that stratiform precipitation fraction increases with increasing latitude, which implies that the IN effect is stronger at higher latitudes. To quantitatively evaluate the IN effect versus latitude, large-scale forcing data from ten field campaigns are used to drive a CRM (cloud-resolving model) to generate longterm cloud simulations. As revealed in the simulations, the increase in the net downward radiative flux at the TOA (top of the atmosphere) from doubling the current IN concentrations is larger at higher latitude, which is attributed to the meridional tendency in the stratiform precipitation fraction. Surface warming from doubling the IN concentrations, based on the radiative balance of the globe, is compared with that from anthropogenic COZ . It is found that the former effect is stronger than the latter in middle and high latitudes but not in the Tropics. With regard to the impact of IN on global warming, there are two factors to consider: the radiative effect from increasing the IN concentration and the increase in IN concentration itself. The former relies on cloud ensembles and thus varies mainly with latitude. In contrast, the latter relies on IN sources (e.g., the land surface distribution) and thus varies not only with latitude but also longitude. Global desertification and industrialization provide clues on the geographic variation of the increase in IN concentration since pre-industrial times. Thus, their effect on global warming can be inferred and then be compared with observations. A general match in geographic and seasonal

  2. Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM

    Directory of Open Access Journals (Sweden)

    M. Heinemann

    2009-12-01

    Full Text Available We investigate the late Paleocene/early Eocene (PE climate using the coupled atmosphere-ocean-sea ice model ECHAM5/MPI-OM. The surface in our PE control simulation is on average 297 K warm and ice-free, despite a moderate atmospheric CO2 concentration of 560 ppm. Compared to a pre-industrial reference simulation (PR, low latitudes are 5 to 8 K warmer, while high latitudes are up to 40 K warmer. This high-latitude amplification is in line with proxy data, yet a comparison to sea surface temperature proxy data suggests that the Arctic surface temperatures are still too low in our PE simulation.

    To identify the mechanisms that cause the PE-PR surface temperature differences, we fit two simple energy balance models to the ECHAM5/MPI-OM results. We find that about 2/3 of the PE-PR global mean surface temperature difference are caused by a smaller clear sky emissivity due to higher atmospheric CO2 and water vapour concentrations in PE compared to PR; 1/3 is due to a smaller planetary albedo. The reduction of the pole-to-equator temperature gradient in PE compared to PR is due to (1 the large high-latitude effect of the higher CO2 and water vapour concentrations in PE compared to PR, (2 the lower Antarctic orography, (3 the smaller surface albedo at high latitudes, and (4 longwave cloud radiative effects. Our results support the hypothesis that local radiative effects rather than increased meridional heat transports were responsible for the "equable" PE climate.

  3. Competition magnifies the impact of a pesticide in a warming world by reducing heat tolerance and increasing autotomy.

    Science.gov (United States)

    Op de Beeck, Lin; Verheyen, Julie; Stoks, Robby

    2018-02-01

    There is increasing concern that standard laboratory toxicity tests may be misleading when assessing the impact of toxicants, because they lack ecological realism. Both warming and biotic interactions have been identified to magnify the effects of toxicants. Moreover, while biotic interactions may change the impact of toxicants, toxicants may also change the impact of biotic interactions. However, studies looking at the impact of biotic interactions on the toxicity of pesticides and vice versa under warming are very scarce. Therefore, we tested how warming (+4 °C), intraspecific competition (density treatment) and exposure to the pesticide chlorpyrifos, both in isolation and in combination, affected mortality, cannibalism, growth and heat tolerance of low- and high-latitude populations of the damselfly Ischnura elegans. Moreover, we addressed whether toxicant exposure, potentially in interaction with competition and warming, increased the frequency of autotomy, a widespread antipredator mechanism. Competition increased the toxicity of chlorpyrifos and made it become lethal. Cannibalism was not affected by chlorpyrifos but increased at high density and under warming. Chlorpyrifos reduced heat tolerance but only when competition was high. This is the first demonstration that a biotic interaction can be a major determinant of 'toxicant-induced climate change sensitivity'. Competition enhanced the impact of chlorpyrifos under warming for high-latitude larvae, leading to an increase in autotomy which reduces fitness in the long term. This points to a novel pathway how transient pesticide pulses may cause delayed effects on populations in a warming world. Our results highlight that the interplay between biotic interactions and toxicants have a strong relevance for ecological risk assessment in a warming polluted world. Copyright © 2017 Elsevier Ltd. All rights reserved.

  4. Small signal microwave amplifier design

    CERN Document Server

    Grosch, Theodore

    2000-01-01

    This book explains techniques and examples for designing stable amplifiers for high-frequency applications in which the signal is small and the amplifier circuit is linear. An in-depth discussion of linear network theory provides the foundation needed to develop actual designs. Examples throughout the book will show you how to apply the knowledge gained in each chapter leading to the complex design of low noise amplifiers. Many exercises at the end of each chapter will help students to practice their skills. The solutions to these design problems are available in an accompanying solutions book

  5. Final amplifier design and mercury

    International Nuclear Information System (INIS)

    Rose, E.A.; Hanson, D.E.

    1991-01-01

    The final amplifier for the Mercury KrF excimer facility is being designed. The design exercise involves extensive modeling to predict amplifier performance. Models of the pulsed-power system, including a Child-Langmuir diode with closure, electron-beam energy deposition, KrF laser kinetics, amplified spontaneous emission (ASE), a time-dependent laser extraction in the presence of ASE are presented as a design package. The design exercise indicates that the energy objective of Phase I -- 100 joules -- will be met

  6. Irrigation enhances local warming with greater nocturnal warming effects than daytime cooling effects

    Science.gov (United States)

    Chen, Xing; Jeong, Su-Jong

    2018-02-01

    To meet the growing demand for food, land is being managed to be more productive using agricultural intensification practices, such as the use of irrigation. Understanding the specific environmental impacts of irrigation is a critical part of using it as a sustainable way to provide food security. However, our knowledge of irrigation effects on climate is still limited to daytime effects. This is a critical issue to define the effects of irrigation on warming related to greenhouse gases (GHGs). This study shows that irrigation led to an increasing temperature (0.002 °C year-1) by enhancing nighttime warming (0.009 °C year-1) more than daytime cooling (-0.007 °C year-1) during the dry season from 1961-2004 over the North China Plain (NCP), which is one of largest irrigated areas in the world. By implementing irrigation processes in regional climate model simulations, the consistent warming effect of irrigation on nighttime temperatures over the NCP was shown to match observations. The intensive nocturnal warming is attributed to energy storage in the wetter soil during the daytime, which contributed to the nighttime surface warming. Our results suggest that irrigation could locally amplify the warming related to GHGs, and this effect should be taken into account in future climate change projections.

  7. New Packaging for Amplifier Slabs

    Energy Technology Data Exchange (ETDEWEB)

    Riley, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Thorsness, C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Suratwala, T. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Steele, R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Rogowski, G. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-03-18

    The following memo provides a discussion and detailed procedure for a new finished amplifier slab shipping and storage container. The new package is designed to maintain an environment of <5% RH to minimize weathering.

  8. Operational amplifiers theory and design

    CERN Document Server

    Huijsing, Johan

    2017-01-01

    This proven textbook guides readers to a thorough understanding of the theory and design of operational amplifiers (OpAmps). The core of the book presents systematically the design of operational amplifiers, classifying them into a periodic system of nine main overall configurations, ranging from one gain stage up to four or more stages. This division enables circuit designers to recognize quickly, understand, and choose optimal configurations. Characterization of operational amplifiers is given by macro models and error matrices, together with measurement techniques for their parameters. Definitions are given for four types of operational amplifiers depending on the grounding of their input and output ports. Many famous designs are evaluated in depth, using a carefully structured approach enhanced by numerous figures. In order to reinforce the concepts introduced and facilitate self-evaluation of design skills, the author includes problems with detailed solutions, as well as simulation exercises. Provides te...

  9. TARC: Carlo Rubbia's Energy Amplifier

    CERN Multimedia

    Laurent Guiraud

    1997-01-01

    Transmutation by Adiabatic Resonance Crossing (TARC) is Carlo Rubbia's energy amplifier. This CERN experiment demonstrated that long-lived fission fragments, such as 99-TC, can be efficiently destroyed.

  10. Enhanced performance CCD output amplifier

    Science.gov (United States)

    Dunham, Mark E.; Morley, David W.

    1996-01-01

    A low-noise FET amplifier is connected to amplify output charge from a che coupled device (CCD). The FET has its gate connected to the CCD in common source configuration for receiving the output charge signal from the CCD and output an intermediate signal at a drain of the FET. An intermediate amplifier is connected to the drain of the FET for receiving the intermediate signal and outputting a low-noise signal functionally related to the output charge signal from the CCD. The amplifier is preferably connected as a virtual ground to the FET drain. The inherent shunt capacitance of the FET is selected to be at least equal to the sum of the remaining capacitances.

  11. Global warming: it's not only size that matters

    Science.gov (United States)

    Hegerl, Gabriele C.

    2011-09-01

    Observed and model simulated warming is particularly large in high latitudes, and hence the Arctic is often seen as the posterchild of vulnerability to global warming. However, Mahlstein et al (2011) point out that the signal of climate change is emerging locally from that of climate variability earliest in regions of low climate variability, based on climate model data, and in agreement with observations. This is because high latitude regions are not only regions of strong feedbacks that enhance the global warming signal, but also regions of substantial climate variability, driven by strong dynamics and enhanced by feedbacks (Hall 2004). Hence the spatial pattern of both observed warming and simulated warming for the 20th century shows strong warming in high latitudes, but this warming occurs against a backdrop of strong variability. Thus, the ratio of the warming to internal variability is not necessarily highest in the regions that warm fastest—and Mahlstein et al illustrate that it is actually the low-variability regions where the signal of local warming emerges first from that of climate variability. Thus, regions with strongest warming are neither the most important to diagnose that forcing changes climate, nor are they the regions which will necessarily experience the strongest impact. The importance of the signal-to-noise ratio has been known to the detection and attribution community, but has been buried in technical 'optimal fingerprinting' literature (e.g., Hasselmann 1979, Allen and Tett 1999), where it was used for an earlier detection of climate change by emphasizing aspects of the fingerprint of global warming associated with low variability in estimates of the observed warming. What, however, was not discussed was that the local signal-to-noise ratio is of interest also for local climate change: where temperatures emerge from the range visited by internal climate variability, it is reasonable to assume that changes in climate will also cause more

  12. Warming of the Global Ocean: Spatial Structure and Water-Mass Trends

    Science.gov (United States)

    Hakkinen, Sirpa; Rhines, Peter B.; Worthen, Denise L.

    2016-01-01

    This study investigates the multidecadal warming and interannual-to-decadal heat content changes in the upper ocean (0-700 m), focusing on vertical and horizontal patterns of variability. These results support a nearly monotonic warming over much of the World Ocean, with a shift toward Southern Hemisphere warming during the well-observed past decade. This is based on objectively analyzed gridded observational datasets and on a modeled state estimate. Besides the surface warming, a warming climate also has a subsurface effect manifesting as a strong deepening of the midthermocline isopycnals, which can be diagnosed directly from hydrographic data. This deepening appears to be a result of heat entering via subduction and spreading laterally from the high-latitude ventilation regions of subtropical mode waters. The basin-average multidecadal warming mainly expands the subtropical mode water volume, with weak changes in the temperature-salinity (u-S) relationship (known as ''spice'' variability). However, the spice contribution to the heat content can be locally large, for example in Southern Hemisphere. Multidecadal isopycnal sinking has been strongest over the southern basins and weaker elsewhere with the exception of the Gulf Stream/North Atlantic Current/subtropical recirculation gyre. At interannual to decadal time scales, wind-driven sinking and shoaling of density surfaces still dominate ocean heat content changes, while the contribution from temperature changes along density surfaces tends to decrease as time scales shorten.

  13. Strong Delayed Interactive Effects of Metal Exposure and Warming: Latitude-Dependent Synergisms Persist Across Metamorphosis.

    Science.gov (United States)

    Debecker, Sara; Dinh, Khuong V; Stoks, Robby

    2017-02-21

    As contaminants are often more toxic at higher temperatures, predicting their impact under global warming remains a key challenge for ecological risk assessment. Ignoring delayed effects, synergistic interactions between contaminants and warming, and differences in sensitivity across species' ranges could lead to an important underestimation of the risks. We addressed all three mechanisms by studying effects of larval exposure to zinc and warming before, during, and after metamorphosis in Ischnura elegans damselflies from high- and low-latitude populations. By integrating these mechanisms into a single study, we could identify two novel patterns. First, during exposure zinc did not affect survival, whereas it induced mild to moderate postexposure mortality in the larval stage and at metamorphosis, and very strongly reduced adult lifespan. This severe delayed effect across metamorphosis was especially remarkable in high-latitude animals, as they appeared almost insensitive to zinc during the larval stage. Second, the well-known synergism between metals and warming was manifested not only during the larval stage but also after metamorphosis, yet notably only in low-latitude damselflies. These results highlight that a more complete life-cycle approach that incorporates the possibility of delayed interactions between contaminants and warming in a geographical context is crucial for a more realistic risk assessment in a warming world.

  14. Low-high latitude interaction forcing on the evolution of the 400 kyr cycle in East Asian winter monsoon records during the last 2.8 Myr

    Science.gov (United States)

    Li, Dawei; Zhao, Meixun; Tian, Jun

    2017-09-01

    Variability of the East Asian winter monsoon (EAWM), stronger during glacials and weaker during interglacials, has been tightly linked to the wax and wane of the Northern Hemisphere ice sheets (NHIS) via the Siberian High over the last 2.8 million years (Myr). However, the long eccentricity cycle (ca. 400 kyr) in the EAWM record from the late Pliocene to early-Pleistocene (2.8-1.2 Ma) could not be linked to NHIS changes, which lacked the long eccentricity cycle in the Pleistocene. Here, we present the first low latitude EAWM record of the last 2.8 Myr using surface and subsurface temperature difference from the northern South China Sea to evaluate interactions between tropical ocean and EAWM changes. The results show that the EAWM variability displayed significant 400 kyr cycle between 2.8 Ma and 1.2 Ma, with weak (strong) EAWM during high (low) earth orbital eccentricity state. A super El Niño-Southern Oscillation (ENSO) proxy record, calculated using west-east equatorial Pacific sea surface temperature differences, revealed 400 kyr cycles throughout the last 2.8 Myr with warm phase during high eccentricity state. Thus, we propose that super ENSO mean state strongly modulated the EAWM strength through remote forcing to generate the 400 kyr cycle between 2.8 Ma and 1.2 Ma, while low NHIS volume was not sufficient to dominate the EAWM variation as it did over the last 0.9 Myr with 100 kyr cycles in dominance.

  15. Warm Mix Asphalt

    Science.gov (United States)

    2009-04-17

    State of Alaska State of Alaska - Warm Mix Project Warm Mix Project: Location - Petersburg, Alaska which is Petersburg, Alaska which is located in the heart of Southeast Alaska located in the heart of Southeast Alaska's Inside Passage at the tip of M...

  16. Spectroscopic amplifier for pin diode

    International Nuclear Information System (INIS)

    Alonso M, M. S.; Hernandez D, V. M.; Vega C, H. R.

    2014-10-01

    The photodiode remains the basic choice for the photo-detection and is widely used in optical communications, medical diagnostics and field of corpuscular radiation. In detecting radiation it has been used for monitoring radon and its progeny and inexpensive spectrometric systems. The development of a spectroscopic amplifier for Pin diode is presented which has the following characteristics: canceler Pole-Zero (P/Z) with a time constant of 8 μs; constant gain of 57, suitable for the acquisition system; 4th integrator Gaussian order to waveform change of exponential input to semi-Gaussian output and finally a stage of baseline restorer which prevents Dc signal contribution to the next stage. The operational amplifier used is the TLE2074 of BiFET technology of Texas Instruments with 10 MHz bandwidth, 25 V/μs of slew rate and a noise floor of 17 nv/(Hz)1/2. The integrated circuit has 4 operational amplifiers and in is contained the total of spectroscopic amplifier that is the goal of electronic design. The results show like the exponential input signal is converted to semi-Gaussian, modifying only the amplitude according to the specifications in the design. The total system is formed by the detector, which is the Pin diode, a sensitive preamplifier to the load, the spectroscopic amplifier that is what is presented and finally a pulse height analyzer (Mca) which is where the spectrum is shown. (Author)

  17. Influence of changes in wetland inundation extent on net fluxes of carbon dioxide and methane in northern high latitudes from 1993 to 2004

    International Nuclear Information System (INIS)

    Zhuang, Qianlai; Zhu, Xudong; He, Yujie; Prigent, Catherine; Melillo, Jerry M; Kicklighter, David W; David McGuire, A; Prinn, Ronald G

    2015-01-01

    Estimates of the seasonal and interannual exchanges of carbon dioxide (CO 2 ) and methane (CH 4 ) between land ecosystems north of 45°N and the atmosphere are poorly constrained, in part, because of uncertainty in the temporal variability of water-inundated land area. Here we apply a process-based biogeochemistry model to evaluate how interannual changes in wetland inundation extent might have influenced the overall carbon dynamics of the region during the time period 1993–2004. We find that consideration by our model of these interannual variations between 1993 and 2004, on average, results in regional estimates of net methane sources of 67.8 ± 6.2 Tg CH 4 yr −1 , which is intermediate to model estimates that use two static inundation extent datasets (51.3 ± 2.6 and 73.0 ± 3.6 Tg CH 4 yr −1 ). In contrast, consideration of interannual changes of wetland inundation extent result in regional estimates of the net CO 2 sink of −1.28 ± 0.03 Pg C yr −1 with a persistent wetland carbon sink from −0.38 to −0.41 Pg C yr −1 and a upland sink from −0.82 to −0.98 Pg C yr −1 . Taken together, despite the large methane emissions from wetlands, the region is a consistent greenhouse gas sink per global warming potential (GWP) calculations irrespective of the type of wetland datasets being used. However, the use of satellite-detected wetland inundation extent estimates a smaller regional GWP sink than that estimated using static wetland datasets. Our sensitivity analysis indicates that if wetland inundation extent increases or decreases by 10% in each wetland grid cell, the regional source of methane increases 13% or decreases 12%, respectively. In contrast, the regional CO 2 sink responds with only 7–9% changes to the changes in wetland inundation extent. Seasonally, the inundated area changes result in higher summer CH 4 emissions, but lower summer CO 2 sinks, leading to lower summer negative greenhouse gas forcing. Our analysis further

  18. Effects of Warming Hiatuses on Vegetation Growth in the Northern Hemisphere

    Directory of Open Access Journals (Sweden)

    Hong Wei

    2018-04-01

    Full Text Available There have been hiatuses in global warming since the 1990s, and their potential impacts have attracted extensive attention and discussion. Changes in temperature not only directly affect the greening of vegetation but can also indirectly alter both the growth state and the growth tendency of vegetation by altering other climatic elements. The middle-high latitudes of the Northern Hemisphere (NH constitute the region that has experienced the most warming in recent decades; therefore, identifying the effects of warming hiatuses on the vegetation greening in that region is of great importance. Using satellite-derived Normalized Difference Vegetation Index (NDVI data and climatological observation data from 1982–2013, we investigated hiatuses in warming trends and their impact on vegetation greenness in the NH. Our results show that the regions with warming hiatuses in the NH accounted for 50.1% of the total area and were concentrated in Mongolia, central China, and other areas. Among these regions, 18.8% of the vegetation greenness was inhibited in the warming hiatus areas, but 31.3% of the vegetation grew faster. Because temperature was the main positive climatic factor in central China, the warming hiatuses caused the slow vegetation greening rate. However, precipitation was the main positive climatic factor affecting vegetation greenness in Mongolia; an increase in precipitation accelerated vegetation greening. The regions without a warming hiatus, which were mainly distributed in northern Russia, northern central Asia, and other areas, accounted for 49.9% of the total area. Among these regions, 21.4% of the vegetation grew faster over time, but 28.5% of the vegetation was inhibited. Temperature was the main positive factor affecting vegetation greenness in northern Russia; an increase in temperature promoted vegetation greening. However, radiation was the main positive climatic factor in northern central Asia; reductions in radiation

  19. Climate warming feedback from mountain birch forest expansion: reduced albedo dominates carbon uptake.

    Science.gov (United States)

    de Wit, Heleen A; Bryn, Anders; Hofgaard, Annika; Karstensen, Jonas; Kvalevåg, Maria M; Peters, Glen P

    2014-07-01

    Expanding high-elevation and high-latitude forest has contrasting climate feedbacks through carbon sequestration (cooling) and reduced surface reflectance (warming), which are yet poorly quantified. Here, we present an empirically based projection of mountain birch forest expansion in south-central Norway under climate change and absence of land use. Climate effects of carbon sequestration and albedo change are compared using four emission metrics. Forest expansion was modeled for a projected 2.6 °C increase in summer temperature in 2100, with associated reduced snow cover. We find that the current (year 2000) forest line of the region is circa 100 m lower than its climatic potential due to land-use history. In the future scenarios, forest cover increased from 12% to 27% between 2000 and 2100, resulting in a 59% increase in biomass carbon storage and an albedo change from 0.46 to 0.30. Forest expansion in 2100 was behind its climatic potential, forest migration rates being the primary limiting factor. In 2100, the warming caused by lower albedo from expanding forest was 10 to 17 times stronger than the cooling effect from carbon sequestration for all emission metrics considered. Reduced snow cover further exacerbated the net warming feedback. The warming effect is considerably stronger than previously reported for boreal forest cover, because of the typically low biomass density in mountain forests and the large changes in albedo of snow-covered tundra areas. The positive climate feedback of high-latitude and high-elevation expanding forests with seasonal snow cover exceeds those of afforestation at lower elevation, and calls for further attention of both modelers and empiricists. The inclusion and upscaling of these climate feedbacks from mountain forests into global models is warranted to assess the potential global impacts. © 2013 John Wiley & Sons Ltd.

  20. Warm and Saline Events Embedded in the Meridional Circulation of the Northern North Atlantic

    Science.gov (United States)

    Hakkinen, Sirpa; Rhines, Peter B.; Worthen, Denise L.

    2011-01-01

    Ocean state estimates from 1958 to 2005 from the Simple Ocean Assimilation System (SODA) system are analyzed to understand circulation between subtropical and subpolar Atlantic and their connection with atmospheric forcing. This analysis shows three periods (1960s, around 1980, and 2000s) with enhanced warm, saline waters reaching high latitudes, alternating with freshwater events originating at high latitudes. It complements surface drifter and altimetry data showing the subtropical -subpolar exchange leading to a significant temperature and salinity increase in the northeast Atlantic after 2001. The warm water limb of the Atlantic meridional overturning cell represented by SODA expanded in density/salinity space during these warm events. Tracer simulations using SODA velocities also show decadal variation of the Gulf Stream waters reaching the subpolar gyre and Nordic seas. The negative phase of the North Atlantic Oscillation index, usually invoked in such variability, fails to predict the warming and salinization in the early 2000s, with salinities not seen since the 1960s. Wind stress curl variability provided a linkage to this subtropical/subpolar gyre exchange as illustrated using an idealized two ]layer circulation model. The ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal. In this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax; hence, the polar front moves westward, opening an enhanced northward access of the subtropical waters in the eastern boundary current.

  1. Dielectric waveguide amplifiers and lasers

    NARCIS (Netherlands)

    Pollnau, Markus

    The performance of semiconductor amplifiers and lasers has made them the preferred choice for optical gain on a micro-chip. In the past few years, we have demonstrated that also rare-earth-ion-doped dielectric waveguides show remarkable performance, ranging from a small-signal gain per unit length

  2. Global Warming: A Myth?

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 6; Issue 7. Global Warming: A Myth? - Credibility of Climate Scenarios Predicted by Systems Simulations. Deepanjan Majumdar. General Article Volume 6 Issue 7 July 2001 pp 13-21 ...

  3. Warm and Cool Dinosaurs.

    Science.gov (United States)

    Mannlein, Sally

    2001-01-01

    Presents an art activity in which first grade students draw dinosaurs in order to learn about the concept of warm and cool colors. Explains how the activity also helped the students learn about the concept of distance when drawing. (CMK)

  4. Global warming yearbook: 1998

    Energy Technology Data Exchange (ETDEWEB)

    Arris, L. [ed.

    1999-02-01

    The report brings together a year`s worth of global warming stories - over 280 in all - in one convenient volume. It provides a one-stop report on the scientific, political and industrial implications of global warming. The report includes: detailed coverage of negotiations on the Kyoto Protocol; scientific findings on carbon sources and sinks, coral bleaching, Antarctic ice shelves, plankton, wildlife and tree growth; new developments on fuel economy, wind power, fuel cells, cogeneration, energy labelling and emissions trading.

  5. Media Pembelajaran Global Warming

    OpenAIRE

    Tham, Fikri Jufri; Liliana, Liliana; Purba, Kristo Radion

    2016-01-01

    Computer based learning media is one of the media has an important role in learning. Learning media will be attractive when packaged through interactive media , such as interactive media created in paper manufacture " instructional media global warming" . The advantage gained is that it can increase knowledge, generally educate people to be more concerned about the environment , and also can be a means of entertainment. This application is focused to learn about global warming and packaged in...

  6. Refrigeration and global warming

    International Nuclear Information System (INIS)

    Anon.

    1997-01-01

    Some aspects of global warming in general, and the implications for refrigerants and refrigerator efficiency in particular, are briefly considered in a question and answer format. The concepts of Global Warming Potential (GWP) and Total Equivalent Warming Impact (TEWI) are explained. GWP is an index which allows a simple comparison to be make between the warming effects of different gases on a kg to kg basis relative to carbon. The GWP depends both on the lifetime of a substance in the atmosphere and its infra-red absorption capacity. The overall warming effect of operating a refrigeration system for its entire life is measured by its TEWI. Chloroflourocarbons (CFCs) which have been widely used as refrigerants are powerful greenhouse gases with high GWPs. Because of the bank of CFCs in refrigerating systems, their levels in the atmosphere are still increasing and it will be some time before refrigerant changes will be effective in reducing the warming effects of refrigerant releases. Hydrocarbons, hydroflourocarbons and ammonia all have a part to play as substitute refrigerants. Refrigerator efficiency is very important in terms of reducing CO 2 emissions. (UK)

  7. Compensatory mechanisms mitigate the effect of warming and drought on wood formation.

    Science.gov (United States)

    Balducci, Lorena; Cuny, Henri E; Rathgeber, Cyrille B K; Deslauriers, Annie; Giovannelli, Alessio; Rossi, Sergio

    2016-06-01

    Because of global warming, high-latitude ecosystems are expected to experience increases in temperature and drought events. Wood formation will have to adjust to these new climatic constraints to maintain tree mechanical stability and long-distance water transport. The aim of this study is to understand the dynamic processes involved in wood formation under warming and drought. Xylogenesis, gas exchange, water relations and wood anatomy of black spruce [Picea mariana (Mill.) B.S.P.] saplings were monitored during a greenhouse experiment where temperature was increased during daytime or night-time (+6 °C) combined with a drought period. The kinetics of tracheid development expressed as rate and duration of the xylogenesis sub-processes were quantified using generalized additive models. Drought and warming had a strong influence on cell production, but little effect on wood anatomy. The increase in cell production rate under warmer temperatures, and especially during the night-time warming at the end of the growing season, resulted in wider tree-rings. However, the strong compensation between rates and durations of cell differentiation processes mitigates warming and drought effects on tree-ring structure. Our results allowed quantification of how wood formation kinetics is regulated when water and heat stress increase, allowing trees to adapt to future environmental conditions. © 2015 John Wiley & Sons Ltd.

  8. Experimental warming effects on the bacterial community structure and diversity

    Science.gov (United States)

    Kim, W.; Han, S.; Adams, J.; Son, Y.

    2014-12-01

    The objective of this study is to investigate the responses of soil bacterial community to future temperature increase by conducting open-field warming experiment. We conducted an open-field experimental warming system using infra-red heater in 2011 and regulated the temperature of warmed plots by 3oC higher than that of control plots constantly. The seeds of Pinus densiflora, Abies holophylla, Abies koreana, Betula costata, Quercus variabilis, Fraxinus rhynchophylla, and Zelkova serrata were planted in each 1 m × 1 m plot (n=3) in April, 2012. We collected soil samples from the rhizosphere of 7 tree species. DNA was extracted and PCR-amplified for the bacterial 16S gene targeting V1-V3 region. The paired-end sequencing was performed at Beijing Genome Institute (BGI, Hong Kong, China) using 2× 100 bp Hiseq2000 (Illumina). This study aimed to answer the following prediction/hypothesis: 1) Experimental warming will change the structure of soil bacterial community, 2) There will be distinct 'indicator group' which response to warming treatment relatively more sensitive than other groups. 3) Warming treatment will enhance the microbial activity in terms of soil respiration. 4) The rhizoplane bacterial communities for each of 7 tree species will show different response pattern to warming treatment. Since the sequence data does not arrive before the submission deadline, therefore, we would like to present the results and discussions on December 2014, AGU Fall Meeting.

  9. Autumn photosynthetic decline and growth cessation in seedlings of white spruce are decoupled under warming and photoperiod manipulations.

    Science.gov (United States)

    Stinziano, Joseph R; Way, Danielle A

    2017-08-01

    Climate warming is expected to increase the seasonal duration of photosynthetic carbon fixation and tree growth in high-latitude forests. However, photoperiod, a crucial cue for seasonality, will remain constant, which may constrain tree responses to warming. We investigated the effects of temperature and photoperiod on weekly changes in photosynthetic capacity, leaf biochemistry and growth in seedlings of a boreal evergreen conifer, white spruce [Picea glauca (Moench) Voss]. Warming delayed autumn declines in photosynthetic capacity, extending the period when seedlings had high carbon uptake. While photoperiod was correlated with photosynthetic capacity, short photoperiods did not constrain the maintenance of high photosynthetic capacity under warming. Rubisco concentration dynamics were affected by temperature but not photoperiod, while leaf pigment concentrations were unaffected by treatments. Respiration rates at 25 °C were stimulated by photoperiod, although respiration at the growth temperatures was increased in warming treatments. Seedling growth was stimulated by increased photoperiod and suppressed by warming. We demonstrate that temperature is a stronger control on the seasonal timing of photosynthetic down-regulation than is photoperiod. Thus, while warming can stimulate carbon uptake in boreal conifers, the extra carbon may be directed towards respiration rather than biomass, potentially limiting carbon sequestration under climate change. © 2017 John Wiley & Sons Ltd.

  10. CMOS Current-mode Operational Amplifier

    DEFF Research Database (Denmark)

    Kaulberg, Thomas

    1992-01-01

    current-mode feedback amplifier or a constant bandwidth in a transimpedance feedback amplifier. The amplifier is found to have a gain bandwidth product of 8 MHz, an offset current of 0.8 ¿A (signal-range ±700¿A) and a (theoretically) unlimited slew-rate. The amplifier is realized in a standard CMOS 2......A fully differential-input differential-output current-mode operational amplifier (COA) is described. The amplifier utilizes three second generation current-conveyors (CCII) as the basic building blocks. It can be configured to provide either a constant gain-bandwidth product in a fully balanced...

  11. A CMOS current-mode operational amplifier

    DEFF Research Database (Denmark)

    Kaulberg, Thomas

    1993-01-01

    current-mode feedback amplifier or a constant bandwidth in a transimpedance feedback amplifier. The amplifier is found to have a gain-bandwidth product of 3 MHz, an offset current of 0.8 μA (signal range ±700 μA), and a (theoretically) unlimited slew rate. The amplifier is realized in a standard CMOS 2......A fully differential-input, differential-output, current-mode operational amplifier (COA) is described. The amplifier utilizes three second-generation current conveyors (CCIIs) as the basic building blocks. It can be configured to provide either a constant gain-bandwidth product in a fully balanced...

  12. Amplified spontaneous emissions in a high-gain laser amplifier

    International Nuclear Information System (INIS)

    Osada, Hidenori; Gamo, Hideya.

    1978-01-01

    The gain and line-narrowing of the amplified spontaneous emissions(ASE) in a partially homogeneous high-gain Xe 3.51 μm laser amplifier were studied theoretically and experimentally with emphasis of saturation effect. The unidirectionally travelling ASE was generated by conveniently using optical isolators and used as a broadband radiation source. It has properties of 10 μW/mm 2 in intensity with fluctuation of less than 1% in 5 hours, 43.5 MHz of the linewidth and 1.0 x 10 -3 radians of beam divergence. The measured saturation intensity was 4.85 μW/mm 2 and a small signal gain was 0.1 cm -1 . The theoretical prediction of the line-narrowing shows reasonablly good agreement with the measured one. (author)

  13. Global warming on trial

    International Nuclear Information System (INIS)

    Broeker, W.S.

    1992-01-01

    Jim Hansen, a climatologist at NASA's Goddard Space Institute, is convinced that the earth's temperature is rising and places the blame on the buildup of greenhouse gases in the atmosphere. Unconvinced, John Sununu, former White House chief of staff, doubts that the warming will be great enough to produce serious threat and fears that measures to reduce the emissions would throw a wrench into the gears that drive the Unites States' troubled economy. During his three years at the White House, Sununu's view prevailed, and although his role in the debate has diminished, others continue to cast doubt on the reality of global warming. A new lobbying group called the Climate Council has been created to do just this. Burning fossil fuels is not the only problem; a fifth of emissions of carbon dioxide now come from clearing and burning forests. Scientists are also tracking a host of other greenhouse gases that emanate from a variety of human activities; the warming effect of methane, chlorofluorocarbons and nitrous oxide combined equals that of carbon dioxide. Although the current warming from these gases may be difficult to detect against the background noise of natural climate variation, most climatologists are certain that as the gases continue to accumulate, increases in the earth's temperature will become evident even to skeptics. If the reality of global warming were put on trial, each side would have trouble making its case. Jim Hansen's side could not prove beyond a reasonable doubt that carbon dioxide and other greenhouse gases have warmed the planet. But neither could John Sununu's side prove beyond a reasonable doubt that the warming expected from greenhouse gases has not occurred. To see why each side would have difficulty proving its case, this article reviews the arguments that might be presented in such a hearing

  14. Long range global warming

    International Nuclear Information System (INIS)

    Rolle, K.C.; Pulkrabek, W.W.; Fiedler, R.A.

    1995-01-01

    This paper explores one of the causes of global warming that is often overlooked, the direct heating of the environment by engineering systems. Most research and studies of global warming concentrate on the modification that is occurring to atmospheric air as a result of pollution gases being added by various systems; i.e., refrigerants, nitrogen oxides, ozone, hydrocarbons, halon, and others. This modification affects the thermal radiation balance between earth, sun and space, resulting in a decrease of radiation outflow and a slow rise in the earth's steady state temperature. For this reason the solution to the problem is perceived as one of cleaning up the processes and effluents that are discharged into the environment. In this paper arguments are presented that suggest, that there is a far more serious cause for global warming that will manifest itself in the next two or three centuries; direct heating from the exponential growth of energy usage by humankind. Because this is a minor contributor to the global warming problem at present, it is overlooked or ignored. Energy use from the combustion of fuels and from the output of nuclear reactions eventually is manifest as warming of the surroundings. Thus, as energy is used at an ever increasing rate the consequent global warming also increases at an ever increasing rate. Eventually this rate will become equal to a few percent of solar radiation. When this happens the earth's temperature will have risen by several degrees with catastrophic results. The trends in world energy use are reviewed and some mathematical models are presented to suggest future scenarios. These models can be used to predict when the global warming problem will become undeniably apparent, when it will become critical, and when it will become catastrophic

  15. Global Warming and 21st Century Drying

    Science.gov (United States)

    Cook, Benjamin I.; Smerdun, Jason E.; Seager, Richard; Coats, Sloan

    2014-01-01

    Global warming is expected to increase the frequency and intensity of droughts in the twenty-first century, but the relative contributions from changes in moisture supply (precipitation) versus evaporative demand (potential evapotranspiration; PET) have not been comprehensively assessed. Using output from a suite of general circulation model (GCM) simulations from phase 5 of the Coupled Model Intercomparison Project, projected twentyfirst century drying and wetting trends are investigated using two offline indices of surface moisture balance: the Palmer Drought Severity Index (PDSI) and the Standardized Precipitation Evapotranspiration Index (SPEI). PDSI and SPEI projections using precipitation and Penman- Monteith based PET changes from the GCMs generally agree, showing robust cross-model drying in western North America, Central America, the Mediterranean, southern Africa, and the Amazon and robust wetting occurring in the Northern Hemisphere high latitudes and east Africa (PDSI only). The SPEI is more sensitive to PET changes than the PDSI, especially in arid regions such as the Sahara and Middle East. Regional drying and wetting patterns largely mirror the spatially heterogeneous response of precipitation in the models, although drying in the PDSI and SPEI calculations extends beyond the regions of reduced precipitation. This expansion of drying areas is attributed to globally widespread increases in PET, caused by increases in surface net radiation and the vapor pressure deficit. Increased PET not only intensifies drying in areas where precipitation is already reduced, it also drives areas into drought that would otherwise experience little drying or even wetting from precipitation trends alone. This PET amplification effect is largest in the Northern Hemisphere mid-latitudes, and is especially pronounced in western North America, Europe, and southeast China. Compared to PDSI projections using precipitation changes only, the projections incorporating both

  16. Single conversion stage amplifier - SICAM

    Energy Technology Data Exchange (ETDEWEB)

    Ljusev, P.

    2005-12-15

    This Ph.D. thesis presents a thorough analysis of the so called SICAM - SIngle Converter stage AMplifier approach to building direct energy conversion audio power amplifiers. The mainstream approach for building isolated audio power amplifiers today consists of isolated DC power supply and Class D amplifier, which essentially represents a two stage solution, where each of the components can be viewed as separate and independent part. The proposed SICAM solution strives for direct energy conversion from the mains to the audio output, by dedicating the operation of the components one to another and integrating their functions, so that the final audio power amplifier represents a single-stage topology with higher efficiency, lower volume, less board space, lower component count and subsequently lower cost. The SICAM approach is both applicable to non-isolated and isolated audio power amplifiers, but the problems encountered in these two cases are different. Non-isolated SICAM solutions are intended for both AC mains-connected and battery-powered devices. In non-isolated mains-connected SICAMs the main idea is to simplify the power supply or even provide integrated power factor correction (PFC) functions, while still maintaining low component stress and good audio performance by generally decreasing the input voltage level to the Class D audio power amplifier. On the other hand, non-isolated battery-powered SICAMs have to cope with the ever changing battery voltage and provide output voltage levels which are both lower and higher than the battery voltage, while still being simple and single-stage energy conversion solutions. In isolated SICAMs the isolation transformer adjusts the voltage level on the secondary side to the desired level, so the main challenges here are decreasing the size of the magnetic core and reducing the number and size of bulky reactive components as much as possible. The main focus of this thesis is directed towards the isolated SICAMs and

  17. Analog circuit design designing high performance amplifiers

    CERN Document Server

    Feucht, Dennis

    2010-01-01

    The third volume Designing High Performance Amplifiers applies the concepts from the first two volumes. It is an advanced treatment of amplifier design/analysis emphasizing both wideband and precision amplification.

  18. Higher order mode optical fiber Raman amplifiers

    DEFF Research Database (Denmark)

    Rottwitt, Karsten; Friis, Søren Michael Mørk; Usuga Castaneda, Mario A.

    2016-01-01

    We review higher order mode Raman amplifiers and discuss recent theoretical as well as experimental results including system demonstrations.......We review higher order mode Raman amplifiers and discuss recent theoretical as well as experimental results including system demonstrations....

  19. SPS RF System Amplifier plant

    CERN Multimedia

    1977-01-01

    The picture shows a 2 MW, 200 MHz amplifier plant with feeder lines. The main RF-system of the SPS comprises four cavities: two of 20 m length and two of 16.5 m length. They are all installed in one long straight section (LSS 3). These cavities are of the travelling-wave type operating at a centre frequency of 200.2 MHz. They are wideband, filling time about 700 ns and untuned. The power amplifiers, using tetrodes are installed in a surface building 200 m from the cavities. Initially only two cavities were installed, a third cavity was installed in 1978 and a forth one in 1979. The number of power amplifiers was also increased: to the first 2 MW plant a second 2 MW plant was added and by end 1979 there were 8 500 kW units combined in pairs to feed each of the 4 cavities with up to about 1 MW RF power, resulting in a total accelerating voltage of about 8 MV. See also 7412016X, 7412017X, 7411048X.

  20. Challenges in higher order mode Raman amplifiers

    DEFF Research Database (Denmark)

    Rottwitt, Karsten; Nielsen, Kristian; Friis, Søren Michael Mørk

    2015-01-01

    A higher order Raman amplifier model that take random mode coupling into account ispresented. Mode dependent gain and signal power fluctuations at the output of the higher order modeRaman amplifier are discussed......A higher order Raman amplifier model that take random mode coupling into account ispresented. Mode dependent gain and signal power fluctuations at the output of the higher order modeRaman amplifier are discussed...

  1. European Research on THz Vacuum Amplifiers

    DEFF Research Database (Denmark)

    Brunetti, F.; Cojocarua, C.-S.; de Rossi, A.

    2010-01-01

    The OPTHER (OPtically Driven TeraHertz AmplifiERs) project represents a considerable advancement in the field of high frequency amplification. The design and realization of a THz amplifier within this project is a consolidation of efforts at the international level from the main players...... of the European research, academy and industry in vacuum electronics. This paper describes the status of the project and progress towards the THz amplifier realization....

  2. Integrated amplifying circuit with MOS transistors

    Energy Technology Data Exchange (ETDEWEB)

    Baylac, B; Merckel, G; Meunier, P

    1974-01-25

    The invention relates to a feedback-pass-band amplifier with MOS-transistors. The differential stage of conventional amplifiers is changed into an adding state, whereas the differential amplification stages are changed into amplifier inverter stages. All MOS transistors used in that amplifier are of similar configuration and are interdigitized, whereby the operating speed dispersion is reduced. This can be applied to obtaining a measurement channel for proportional chambers.

  3. G-warm inflation

    Energy Technology Data Exchange (ETDEWEB)

    Herrera, Ramón, E-mail: ramon.herrera@pucv.cl [Instituto de Física, Pontificia Universidad Católica de Valparaíso, Avenida Brasil 2950, Casilla 4059, Valparaíso (Chile)

    2017-05-01

    A warm inflationary universe in the context of Galileon model or G-model is studied. Under a general formalism we study the inflationary dynamics and the cosmological perturbations considering a coupling of the form G (φ, X )= g (φ) X . As a concrete example, we consider an exponential potential together with the cases in which the dissipation and Galilean coefficients are constants. Also, we study the weak regime given by the condition R <1+3 gH φ-dot , and the strong regime in which 1< R +3 gH φ-dot . Additionally, we obtain constraints on the parameters during the evolution of G-warm inflation, assuming the condition for warm inflation in which the temperature T > H , the conditions or the weak and strong regimes, together with the consistency relation r = r ( n {sub s} ) from Planck data.

  4. G-warm inflation

    Science.gov (United States)

    Herrera, Ramón

    2017-05-01

    A warm inflationary universe in the context of Galileon model or G-model is studied. Under a general formalism we study the inflationary dynamics and the cosmological perturbations considering a coupling of the form G(phi,X)=g(phi) X. As a concrete example, we consider an exponential potential together with the cases in which the dissipation and Galilean coefficients are constants. Also, we study the weak regime given by the condition RR+3gHdot phi. Additionally, we obtain constraints on the parameters during the evolution of G-warm inflation, assuming the condition for warm inflation in which the temperature T>H, the conditions or the weak and strong regimes, together with the consistency relation r=r(ns) from Planck data.

  5. The global warming problem

    International Nuclear Information System (INIS)

    Anon.

    1990-01-01

    In this chapter, a discussion is presented of the global warming problem and activities contributing to the formation of acid rain, urban smog and to the depletion of the ozone layer. Globally, about two-thirds of anthropogenic carbon dioxide emissions arise from fossil-fuel burning; the rest arise primarily from deforestation. Chlorofluorocarbons are the second largest contributor to global warming, accounting for about 20% of the total. The third largest contributor is methane, followed by ozone and nitrous oxide. A study of current activities in the US that contribute to global warming shows the following: electric power plants account for about 33% of carbon dioxide emissions; motor vehicles, planes and ships (31%); industrial plants (24%); commercial and residential buildings (11%)

  6. NASA developments in solid state power amplifiers

    Science.gov (United States)

    Leonard, Regis F.

    1990-01-01

    Over the last ten years, NASA has undertaken an extensive program aimed at development of solid state power amplifiers for space applications. Historically, the program may be divided into three phases. The first efforts were carried out in support of the advanced communications technology satellite (ACTS) program, which is developing an experimental version of a Ka-band commercial communications system. These first amplifiers attempted to use hybrid technology. The second phase was still targeted at ACTS frequencies, but concentrated on monolithic implementations, while the current, third phase, is a monolithic effort that focusses on frequencies appropriate for other NASA programs and stresses amplifier efficiency. The topics covered include: (1) 20 GHz hybrid amplifiers; (2) 20 GHz monolithic MESFET power amplifiers; (3) Texas Instruments' (TI) 20 GHz variable power amplifier; (4) TI 20 GHz high power amplifier; (5) high efficiency monolithic power amplifiers; (6) GHz high efficiency variable power amplifier; (7) TI 32 GHz monolithic power amplifier performance; (8) design goals for Hughes' 32 GHz variable power amplifier; and (9) performance goals for Hughes' pseudomorphic 60 GHz power amplifier.

  7. A pulse amplifier for nuclear instrumentation

    International Nuclear Information System (INIS)

    Martin, D.; Cliff, P.

    1987-01-01

    A Class-A 1 Watt amplifier has been designed and optimized for nanosecond pulses. Spanning .01MHz to 1300Mhz, signal gain is 26dB with gain flatness of 1dB. The amplifier drive +- 10 volts across 500 with 350ps risetime. Each amplifier is housed in a 2-wide NIM

  8. Remote Acquisition Amplifier For 50-Ohm Cable

    Science.gov (United States)

    Amador, Jose J.

    1995-01-01

    Buffer-amplifier unit designed to drive 50-Ohm cables up to 100 ft. (30 m) long, compensating for attenuation in cables and enabling remote operation of oscilloscopes. Variable resistor provides for adjustment of gain of amplifier, such that overall gain from input terminals of amplifier to output end of cable set to unity.

  9. Greenhouse Warming Research

    DEFF Research Database (Denmark)

    Sørensen, Bent Erik

    2016-01-01

    The changing greenhouse effect caused by natural and anthropogenic causes is explained and efforts to model the behavior of the near-surface constituents of the Earth's land, ocean and atmosphere are discussed. Emissions of various substances and other aspects of human activity influence...... the greenhouse warming, and the impacts of the warming may again impact the wellbeing of human societies. Thus physical modeling of the near-surface ocean-soil-atmosphere system cannot be carried out without an idea of the development of human activities, which is done by scenario analysis. The interactive...

  10. Regional seasonal warming anomalies and land-surface feedbacks

    Science.gov (United States)

    Coffel, E.; Horton, R. M.

    2017-12-01

    Significant seasonal variations in warming are projected in some regions, especially central Europe, the southeastern U.S., and central South America. Europe in particular may experience up to 2°C more warming during June, July, and August than in the annual mean, enhancing the risk of extreme summertime heat. Previous research has shown that heat waves in Europe and other regions are tied to seasonal soil moisture variations, and that in general land-surface feedbacks have a strong effect on seasonal temperature anomalies. In this study, we show that the seasonal anomalies in warming are also due in part to land-surface feedbacks. We find that in regions with amplified warming during the hot season, surface soil moisture levels generally decline and Bowen ratios increase as a result of a preferential partitioning of incoming energy into sensible vs. latent. The CMIP5 model suite shows significant variability in the strength of land-atmosphere coupling and in projections of future precipitation and soil moisture. Due to the dependence of seasonal warming on land-surface processes, these inter-model variations influence the projected summertime warming amplification and contribute to the uncertainty in projections of future extreme heat.

  11. An Implantable CMOS Amplifier for Nerve Signals

    DEFF Research Database (Denmark)

    Nielsen, Jannik Hammel; Lehmann, Torsten

    2003-01-01

    In this paper, a low noise high gain CMOS amplifier for minute nerve signals is presented. The amplifier is constructed in a fully differential topology to maximize noise rejection. By using a mixture of weak- and strong inversion transistors, optimal noise suppression in the amplifier is achieved....... A continuous-time current-steering offset-compensation technique is utilized in order to minimize the noise contribution and to minimize dynamic impact on the amplifier input nodes. The method for signal recovery from noisy nerve signals is presented. A prototype amplifier is realized in a standard digital 0...

  12. Semiconductor quantum-dot lasers and amplifiers

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Borri, Paola; Ledentsov, N. N.

    2002-01-01

    -power surface emitting VCSELs. We investigated the ultrafast dynamics of quantum-dot semiconductor optical amplifiers. The dephasing time at room temperature of the ground-state transition in semiconductor quantum dots is around 250 fs in an unbiased amplifier, decreasing to below 50 fs when the amplifier...... is biased to positive net gain. We have further measured gain recovery times in quantum dot amplifiers that are significantly lower than in bulk and quantum-well semiconductor optical amplifiers. This is promising for future demonstration of quantum dot devices with high modulation bandwidth...

  13. CMOS Current-mode Operational Amplifier

    OpenAIRE

    Kaulberg, Thomas

    1992-01-01

    A fully differential-input differential-output current-mode operational amplifier (COA) is described. The amplifier utilizes three second generation current-conveyors (CCII) as the basic building blocks. It can be configured to provide either a constant gain-bandwidth product in a fully balanced current-mode feedback amplifier or a constant bandwidth in a transimpedance feedback amplifier. The amplifier is found to have a gain bandwidth product of 8 MHz, an offset current of 0.8 ¿A (signal-r...

  14. NIF/LMJ prototype amplifier mechanical design

    International Nuclear Information System (INIS)

    Horvath, J.

    1996-10-01

    Amplifier prototypes for the National Ignition Facility and the Laser Megajoule will be tested at Lawrence Livermore National Laboratory. The prototype amplifier, which is an ensemble of modules from LLNL and Centre d'Etudes de Limeil-Valenton, is cassette-based with bottom access for maintenance. A sealed maintenance transfer vehicle which moves optical cassettes between the amplifier and the assembly cleanroom, and a vacuum gripper which holds laser slabs during cassette assembly will also be tested. The prototype amplifier will be used to verify amplifier optical performance, thermal recovery time, and cleanliness of mechanical operations

  15. Warm pre-stressing

    International Nuclear Information System (INIS)

    Hedner, G.

    1983-01-01

    Literature survey and critical evaluation of the phenomenon of warm pre-stressing (WPS) is presented. It is found that the cause of it is not clear and a calculated control is missing. The effect of irradiation is unknown, and the influence of WPS on the behaviour of reactor vessels is discussed. (G.B.)

  16. Being Warm-Hearted

    Institute of Scientific and Technical Information of China (English)

    李函; 任汉鼎

    2017-01-01

    Good morning,ladies and gentlemen.It’s my honor to address[向……致辞] you.My English name is Isabella.I’m a high school student of 17.I have some good personality traits[特点],including being warm-hearted.So here comes my topic:Being

  17. Warm and Cool Cityscapes

    Science.gov (United States)

    Jubelirer, Shelly

    2012-01-01

    Painting cityscapes is a great way to teach first-grade students about warm and cool colors. Before the painting begins, the author and her class have an in-depth discussion about big cities and what types of buildings or structures that might be seen in them. They talk about large apartment and condo buildings, skyscrapers, art museums,…

  18. The global warming scare

    International Nuclear Information System (INIS)

    Sunavala, P.D.

    1992-01-01

    It is argued that the present propaganda about the global warming with its disastrous consequences is a scare spread by some First World countries, especially the United States, to prevent the rapid industrialization of developing third world countries. (author). 6 refs., 1 tab

  19. Paralyzed warming world

    Czech Academy of Sciences Publication Activity Database

    Ač, Alexander

    2010-01-01

    Roč. 2, č. 2 (2010), s. 81-86 ISSN 1876-8156 Institutional research plan: CEZ:AV0Z60870520 Keywords : global warming * climate Subject RIV: EH - Ecology, Behaviour http://ojs.ubvu.vu.nl/alf/article/view/134/250

  20. Asymmetric responses to simulated global warming by populations of Colobanthus quitensis along a latitudinal gradient

    Directory of Open Access Journals (Sweden)

    Ian S. Acuña-Rodríguez

    2017-09-01

    high latitudes could increase in their ecophysiological performance, enhancing the size of populations or their spread.

  1. Asymmetric responses to simulated global warming by populations of Colobanthus quitensis along a latitudinal gradient.

    Science.gov (United States)

    Acuña-Rodríguez, Ian S; Torres-Díaz, Cristian; Hereme, Rasme; Molina-Montenegro, Marco A

    2017-01-01

    The increase in temperature as consequence of the recent global warming has been reported to generate new ice-free areas in the Antarctic continent, facilitating the colonization and spread of plant populations. Consequently, Antarctic vascular plants have been observed extending their southern distribution. But as the environmental conditions toward southern localities become progressively more departed from the species' physiological optimum, the ecophysiological responses and survival to the expected global warming could be reduced. However, if processes of local adaptation are the main cause of the observed southern expansion, those populations could appear constrained to respond positively to the expected global warming. Using individuals from the southern tip of South America, the South Shetland Islands and the Antarctic Peninsula, we assess with a long term experiment (three years) under controlled conditions if the responsiveness of Colobanthus quitensis populations to the expected global warming, is related with their different foliar traits and photoprotective mechanisms along the latitudinal gradient. In addition, we tested if the release of the stress condition by the global warming in these cold environments increases the ecophysiological performance. For this, we describe the latitudinal pattern of net photosynthetic capacity, biomass accumulation, and number of flowers under current and future temperatures respective to each site of origin after three growing seasons. Overall, was found a clinal trend was found in the foliar traits and photoprotective mechanisms in the evaluated C. quitensis populations. On the other hand, an asymmetric response to warming was observed for southern populations in all ecophysiological traits evaluated, suggesting that low temperature is limiting the performance of C. quitensis populations. Our results suggest that under a global warming scenario, plant populations that inhabiting cold zones at high latitudes could

  2. HIGH AVERAGE POWER OPTICAL FEL AMPLIFIERS

    International Nuclear Information System (INIS)

    2005-01-01

    Historically, the first demonstration of the optical FEL was in an amplifier configuration at Stanford University [l]. There were other notable instances of amplifying a seed laser, such as the LLNL PALADIN amplifier [2] and the BNL ATF High-Gain Harmonic Generation FEL [3]. However, for the most part FELs are operated as oscillators or self amplified spontaneous emission devices. Yet, in wavelength regimes where a conventional laser seed can be used, the FEL can be used as an amplifier. One promising application is for very high average power generation, for instance FEL's with average power of 100 kW or more. The high electron beam power, high brightness and high efficiency that can be achieved with photoinjectors and superconducting Energy Recovery Linacs (ERL) combine well with the high-gain FEL amplifier to produce unprecedented average power FELs. This combination has a number of advantages. In particular, we show that for a given FEL power, an FEL amplifier can introduce lower energy spread in the beam as compared to a traditional oscillator. This properly gives the ERL based FEL amplifier a great wall-plug to optical power efficiency advantage. The optics for an amplifier is simple and compact. In addition to the general features of the high average power FEL amplifier, we will look at a 100 kW class FEL amplifier is being designed to operate on the 0.5 ampere Energy Recovery Linac which is under construction at Brookhaven National Laboratory's Collider-Accelerator Department

  3. High-Latitude Neutral Mass Density Maxima

    Science.gov (United States)

    Huang, C. Y.; Huang, Y.; Su, Y.-J.; Huang, T.; Sutton, E. K.

    2017-10-01

    Recent studies have reported that thermospheric effects due to solar wind driving can be observed poleward of auroral latitudes. In these papers, the measured neutral mass density perturbations appear as narrow, localized maxima in the cusp and polar cap. They conclude that Joule heating below the spacecraft is the cause of the mass density increases, which are sometimes associated with local field-aligned current structures, but not always. In this paper we investigate neutral mass densities measured by accelerometers on the CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) spacecraft from launch until years 2010 (CHAMP) and 2012 (GRACE), approximately 10 years of observations from each satellite. We extract local maxima in neutral mass densities over the background using a smoothing window with size of one quarter of the orbit. The maxima have been analyzed for each year and also for the duration of each set of satellite observations. We show where they occur, under what solar wind conditions, and their relation to magnetic activity. The region with the highest frequency of occurrence coincides approximately with the cusp and mantle, with little direct evidence of an auroral zone source. Our conclusions agree with the "hot polar cap" observations that have been reported and studied in the past.

  4. Striking Seasonality in the Secular Warming of the Northern Continents: Structure and Mechanisms

    Science.gov (United States)

    Nigam, S.; Thomas, N. P.

    2017-12-01

    The linear trend in twentieth-century surface air temperature (SAT)—a key secular warming signal— exhibits striking seasonal variations over Northern Hemisphere continents; SAT trends are pronounced in winter and spring but notably weaker in summer and fall. The SAT trends in historical twentieth-century climate simulations informing the Intergovernmental Panel for Climate Change's Fifth Assessment show varied (and often unrealistic) strength and structure, and markedly weaker seasonal variation. The large intra-ensemble spread of winter SAT trends in some historical simulations was surprising, especially in the context of century-long linear trends, with implications for the detection of the secular warming signal. The striking seasonality of observed secular warming over northern continents warrants an explanation and the representation of related processes in climate models. Here, the seasonality of SAT trends over North America is shown to result from land surface-hydroclimate interactions and, to an extent, also from the secular change in low-level atmospheric circulation and related thermal advection. It is argued that the winter dormancy and summer vigor of the hydrologic cycle over middle- to high-latitude continents permit different responses to the additional incident radiative energy from increasing greenhouse gas concentrations. The seasonal cycle of climate, despite its monotony, provides an expanded phase space for the exposition of the dynamical and thermodynamical processes generating secular warming, and an exceptional cost-effective opportunity for benchmarking climate projection models.

  5. A 400-year ice core melt layer record of summertime warming in the Alaska Range

    Science.gov (United States)

    Winski, D.; Osterberg, E. C.; Kreutz, K. J.; Wake, C. P.; Ferris, D. G.; Campbell, S. W.; Baum, M.; Raudzens Bailey, A.; Birkel, S. D.; Introne, D.; Handley, M.

    2017-12-01

    Warming in high-elevation regions has socially relevant impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high-elevation temperature records exist from the middle or high latitudes. While many terrestrial paleoclimate records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually-resolved temperature records from high elevations. We present a 400-year temperature record based on the melt-layer stratigraphy in two ice cores collected from Mt. Hunter in the Central Alaska Range. The ice core record shows a 60-fold increase in melt frequency and water equivalent melt thickness between the pre-industrial period (before 1850) and present day. We calibrate the melt record to summer temperatures based on local and regional weather station analyses, and find that the increase in melt production represents a summer warming of at least 2° C, exceeding rates of temperature increase at most low elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p<0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby-wave like pattern that induces high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century, and that conditions in the tropical oceans contribute to this warming.

  6. Linking carbon and iron cycles by investigating transport, fate and mineralogy of iron-bearing colloids from peat-draining rivers - Scotland as model for high-latitude rivers

    Science.gov (United States)

    Wood, Deborah; Crocket, Kirsty; Brand, Tim; Stutter, Marc; Wilson, Clare; Schröder, Christian

    2016-04-01

    Linking carbon and iron cycles by investigating transport, fate and mineralogy of iron-bearing colloids from peat-draining rivers - Scotland as model for high-latitude rivers Wood, D.A¹, Crocket, K², Brand, T², Stutter, M³, Wilson, C¹ & Schröder, C¹ ¹Biological and Environmental Sciences, University of Stirling, Stirling, FK9 4LA ²Scottish Association for Marine Science, University of the Highlands and Islands, Dunbeg, Oban, PA37 1QA ³James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH The biogeochemical iron cycle exerts significant control on the carbon cycle¹. Iron is a limiting nutrient in large areas of the world's oceans and its bioavailability controls CO2 uptake by marine photosynthesizing microorganisms. While atmospheric iron inputs to the open ocean have been extensively measured, global river inputs have likely been underestimated because most major world rivers exhibit extensive iron removal by flocculation and sedimentation during seawater mixing. Iron minerals and organic matter mutually stabilise each other², which results in a 'rusty carbon sink' in sediments³ on the one hand but may also enhance transport beyond the salinity gradient on the other. Humic-rich, high latitude rivers have a higher iron-carrying capacity⁴-⁶ but are underrepresented in iron flux calculations. The West Coast sea lochs in Scotland are fed by predominantly peatland drainage catchments, and the rivers entering the sea lochs carry a high load of organic matter. The short distance between many of these catchments and the coastal ocean facilitates source-to-sea research investigating transport, fate and mineralogy of iron-bearing colloids providing a good analogue for similar high latitude fjordic systems. We use SeaFAST+ICP-MS and Mössbauer spectroscopy to survey trace metal concentrations, with emphasis on iron concentrations, speciation and mineralogy, across salinity gradients. In combination with ultra-filtration techniques, this allows

  7. Audio power amplifier design handbook

    CERN Document Server

    Self, Douglas

    2013-01-01

    This book is essential for audio power amplifier designers and engineers for one simple reason...it enables you as a professional to develop reliable, high-performance circuits. The Author Douglas Self covers the major issues of distortion and linearity, power supplies, overload, DC-protection and reactive loading. He also tackles unusual forms of compensation and distortion produced by capacitors and fuses. This completely updated fifth edition includes four NEW chapters including one on The XD Principle, invented by the author, and used by Cambridge Audio. Cro

  8. Cathode-follower power amplifier

    International Nuclear Information System (INIS)

    Giordano, S.; Puglisi, M.

    1983-01-01

    In circular accelerators and particularly in storage rings it is essential that the total impedance, as seen by the beam, be kept below some critical value. A model of the accelerating system was built using a single-ended cathode-follower amplifier driving a ferrite-loaded cavity. The system operated at 234.5 kHz with a peak output voltage of +-10 kV on the gap. The dynamic output impedance, as measured on the gap, was < 15 ohms

  9. Variabilities of mesospheric tides and equatorial electrojet strength during major stratospheric warming events

    Directory of Open Access Journals (Sweden)

    S. Sridharan

    2009-11-01

    Full Text Available The present study demonstrates the relationship between the high latitude northern hemispheric major sudden stratospheric warming (SSW events and the reversal in the afternoon equatorial electrojet (EEJ, often called the counter-electrojet (CEJ, during the winter months of 1998–1999, 2001–2002, 2003–2004 and 2005–2006. As the EEJ current system is driven by tidal winds, an investigation of tidal variabilities in the MF radar observed zonal winds during the winters of 1998–1999 and 2005–2006 at 88 km over Tirunelveli, a site close to the magnetic equator, shows that there is an enhancement of semi-diurnal tidal amplitude during the days of a major SSW event and a suppression of the same immediately after the event. The significance of the present results lies in demonstrating the latitudinal coupling between the high latitude SSW phenomenon and the equatorial ionospheric current system with clear evidence for major SSW events influencing the day-to-day variability of the CEJ.

  10. Asian climate change under 1.5–4 °C warming targets

    Directory of Open Access Journals (Sweden)

    Ying Xu

    2017-06-01

    Full Text Available Based on simulations of 18 CMIP5 models under three RCP scenarios, this article investigates changes in mean temperature and precipitation and their extremes over Asia in the context of global warming targets of 1.5–4 °C, and further compares the differences between 1.5 °C and 2 °C targets. Results show that relative to the pre-industrial era, the mean temperature over Asia increases by 2.3 °C, 3.0 °C, 4.6 °C, and 6.0 °C at warming targets of 1.5 °C, 2 °C, 3 °C, and 4 °C, respectively, with stronger warming in high latitudes than in low latitudes. The corresponding enhancement in mean precipitation over the entire Asian region is 4.4%, 5.8%, 10.2%, and 13.0%, with significant regional differences. In addition, an increase in warm extremes, a decrease in cold extremes, and a strengthening in the variability of amounts of extreme precipitation are projected. Under the 1.5 °C target, compared with the climate under the 2 °C target, the mean temperature will be lower by 0.5–1 °C over Asia; the mean precipitation will be less by 5%–20% over most of Asia, but will be greater by about 10%–15% over West Asia and western South Asia; extreme high temperatures will be uniformly cooler throughout the Asian region, and the warming in extreme low temperatures will decrease significantly in high latitudes of Asia; extreme precipitation will be weaker over most of Asia but will be stronger over West Asia and western South Asia. Under the 1.5 °C and 2 °C warming targets, the probability of very hot weather (anomalies greater than 1σ, σ is standard deviation, extremely hot weather (anomalies greater than 3σ, and extremely heavy precipitation (anomalies greater than 3σ occurring will increase by at least once, 10%, and 10%, respectively, compared to the reference period (1861–1900.

  11. Global water cycle amplifying at less than the Clausius-Clapeyron rate

    OpenAIRE

    Skliris, Nikolaos; Zika, Jan D.; Nurser, George; Josey, Simon A.; Marsh, Robert

    2016-01-01

    A change in the cycle of water from dry to wet regions of the globe would have far reaching impact on humanity. As air warms, its capacity to hold water increases at the Clausius-Clapeyron rate (CC, approximately 7%?°C?1). Surface ocean salinity observations have suggested the water cycle has amplified at close to CC following recent global warming, a result that was found to be at odds with state-of the art climate models. Here we employ a method based on water mass transformation theory for...

  12. Change of the high-latitude ionosphere during heating by a powerful short radio wave of the EISCAT/Heating complex according to signals of the GLONASS satellite and the incoherent scattering radar

    Directory of Open Access Journals (Sweden)

    Tereshchenko E. D.

    2018-03-01

    Full Text Available Results of observations of variations of temperature, electron concentration and total electron content of the high-latitude region of the ionosphere during its modification by powerful short radio waves of the heating complex EISCAT/Heating (Tromsø, Norway according to signals of the GLONASS satellites and the incoherent scattering UHF EISCAT radar (Tromsø, Norway have been provided. The geometry of passes of the GLONASS and GPS satellites for operating conditions of the heating complex in Tromsø has been considered. It has been shown that during the experiments on the EISCAT/Heating complex for the study of the modified structure of the high-latitude ionosphere it is more convenient to use the GLONASS satellites. Parameters of orbits of these satellites allow researching changes of total electron content in the direction along the geomagnetic field line at the place of observation. It has been shown that during heating of the ionosphere by powerful short radio waves its structure is becoming an irregular one. Operation of the heating complex in the mode "switched on – switched off" has caused appearance of wavy variations of total electron content with the periods close to the heating period. The main features of behavior of the total electron content in the case of the continuous heating of the ionosphere in the direction of the magnetic zenith according to the GLONASS satellite are: reduction of total electron content in the central zone of the antenna diagram, i. e. in the direction of the magnetic zenith, and presence of the increased values of total electron content at the edges of the heating zone. According to the incoherent scattering radar the heating of the ionosphere by the powerful short radio wave has created the region of the increased electron temperature and electron concentration along the direction of the magnetic zenith. The behavior of total electron content according to the GLONASS satellite and the radar of

  13. Reconstructing warm inflation

    Science.gov (United States)

    Herrera, Ramón

    2018-03-01

    The reconstruction of a warm inflationary universe model from the scalar spectral index n_S(N) and the tensor to scalar ratio r( N) as a function of the number of e-folds N is studied. Under a general formalism we find the effective potential and the dissipative coefficient in terms of the cosmological parameters n_S and r considering the weak and strong dissipative stages under the slow roll approximation. As a specific example, we study the attractors for the index n_S given by nS-1∝ N^{-1} and for the ratio r∝ N^{-2}, in order to reconstruct the model of warm inflation. Here, expressions for the effective potential V(φ ) and the dissipation coefficient Γ (φ ) are obtained.

  14. Thinking About Global Warming

    International Nuclear Information System (INIS)

    Baron, J.

    2006-01-01

    Attitudes toward global warming are influenced by various heuristics, which may distort policy away from what is optimal for the well-being of people. These possible distortions, or biases, include: a focus on harms that we cause, as opposed to those that we can remedy more easily; a feeling that those who cause a problem should fix it; a desire to undo a problem rather than compensate for its presence; parochial concern with one's own group (nation); and neglect of risks that are not available. Although most of these biases tend to make us attend relatively too much to global warming, other biases, such as wishful thinking, cause us to attend too little. I discuss these possible effects and illustrate some of them with an experiment conducted on the World Wide Web

  15. Climate change - global warming

    International Nuclear Information System (INIS)

    Ciconkov, Risto

    2001-01-01

    An explanation about climate, weather, climate changes. What is a greenhouse effect, i.e. global warming and reasons which contribute to this effect. Greenhouse gases (GHG) and GWP (Global Warming Potential) as a factor for estimating their influence on the greenhouse effect. Indicators of the climate changes in the previous period by known international institutions, higher concentrations of global average temperature. Projecting of likely scenarios for the future climate changes and consequences of them on the environment and human activities: industry, energy, agriculture, water resources. The main points of the Kyoto Protocol and problems in its realization. The need of preparing a country strategy concerning the acts of the Kyoto Protocol, suggestions which could contribute in the preparation of the strategy. A special attention is pointed to the energy, its resources, the structure of energy consumption and the energy efficiency. (Author)

  16. Warm natural inflation

    International Nuclear Information System (INIS)

    Mishra, Hiranmaya; Mohanty, Subhendra; Nautiyal, Akhilesh

    2012-01-01

    In warm inflation models there is the requirement of generating large dissipative couplings of the inflaton with radiation, while at the same time, not de-stabilising the flatness of the inflaton potential due to radiative corrections. One way to achieve this without fine tuning unrelated couplings is by supersymmetry. In this Letter we show that if the inflaton and other light fields are pseudo-Nambu-Goldstone bosons then the radiative corrections to the potential are suppressed and the thermal corrections are small as long as the temperature is below the symmetry breaking scale. In such models it is possible to fulfil the contrary requirements of an inflaton potential which is stable under radiative corrections and the generation of a large dissipative coupling of the inflaton field with other light fields. We construct a warm inflation model which gives the observed CMB-anisotropy amplitude and spectral index where the symmetry breaking is at the GUT scale.

  17. Slowing global warming

    International Nuclear Information System (INIS)

    Flavin, C.

    1990-01-01

    According to the authors, global warming promises to be one of the central environmental issues of the nineties. After a decade of scientific concern but popular neglect, the eighties ended with a growing political as well as scientific consensus that the world can no longer afford to procrastinate about this issue. This paper reports on coping with global warming which, according to the author, will force societies to move rapidly into uncharted terrain, reversing powerful trends that have dominated the industrial age. This challenge cannot be met without a strong commitment on the part of both individual consumers and governments. In terms of the earth's carbon balance, the unprecedented policy changes that have now become urgent include a new commitment to greater energy efficiency and renewable energy sources, a carbon tax on fossil fuels, a reversal of deforestation in tropical countries, and the rapid elimination of CFCs

  18. Military Implications of Global Warming.

    Science.gov (United States)

    1999-05-20

    U.S. environmental issues also have important global implications. This paper analyzes current U.S. Policy as it pertains to global warming and climate...for military involvement to reduce global warming . Global warming and other environmental issues are important to the U.S. military. As the United

  19. UV-B absorbing pigments in spores: biochemical responses to shade in a high-latitude birch forest and implications for sporopollenin-based proxies of past environmental change

    Directory of Open Access Journals (Sweden)

    Terry V. Callaghan

    2011-08-01

    Full Text Available Current attempts to develop a proxy for Earth's surface ultraviolet-B (UV-B flux focus on the organic chemistry of pollen and spores because their constituent biopolymer, sporopollenin, contains UV-B absorbing pigments whose relative abundance may respond to the ambient UV-B flux. Fourier transform infrared (FTIR microspectroscopy provides a useful tool for rapidly determining the pigment content of spores. In this paper, we use FTIR to detect a chemical response of spore wall UV-B absorbing pigments that correspond with levels of shade beneath the canopy of a high-latitude Swedish birch forest. A 27% reduction in UV-B flux beneath the canopy leads to a significant (p<0.05 7.3% reduction in concentration of UV-B absorbing compounds in sporopollenin. The field data from this natural flux gradient in UV-B further support our earlier work on sporopollenin-based proxies derived from sedimentary records and herbaria collections.

  20. Second workshop of I.A.G./A.I.G. SEDIBUD - Sediment Budgets in Cold Environments: Sediment fluxes and sediment budgets in changing high-latitude and high-altitude cold environments

    Energy Technology Data Exchange (ETDEWEB)

    Beylich, Achim A; Lamoureux, Scott F; Decaulne, Armelle

    2007-07-01

    This Second Workshop of the I.A.G./A.I.G. Working Group SEDIBUD (Sediment Budgets in Cold Environments) builds on four previous ESF SEDIFLUX Science Meetings held in Saudarkrokur (Iceland) in June 2004, Clermont-Ferrand (France) in January 2005, Durham (UK) in December 2005 and Trondheim (Norway) in the end of October/beginning of November 2006. A first kick-off Meeting of the new I.A.G./A.I.G. SEDIBUD Workshop. The theme of this Second I.A.G./A.I.G. SEDIBUD Workshop is Sediment FLuxes and Sediment Budgets in Changing High-Latitude Cold Environments. The Workshop is split between scientific paper and poster presentations, presentation and discussion of SEDIBUD key test sites, discussions within defined work groups and guided field trip to Kaerkevagge. This workshop will address the key aim of SEDIBUD to discuss Source-to-Sink-Fluxes and Sediment Budgets in Changing Cold Environments. Major emphasis will be given to consequences of climate change, scaling issues and source-to-sink correlations. Central issues will be presentation and discussion of the SEDIFLUX Manual (First Edition), the selection of SEDIBUD key test sites, the discussion and development of further ideas to extend the scientific activities within SEDIBUD in a global framework.(auth)

  1. EFFECTS OF GLOBAL WARMING

    OpenAIRE

    Dr. Basanti Jain

    2017-01-01

    The abnormal increase in the concentration of the greenhouse gases is resulting in higher temperatures. We call this effect is global warming. The average temperature around the world has increased about 1'c over 140 years, 75% of this has risen just over the past 30 years. The solar radiation, as it reaches the earth, produces "greenhouse effect" in the atmosphere. The thick atmospheric layers over the earth behaves as a glass surface, as it permits short wave radiations from coming in, but ...

  2. Warm natural inflation

    International Nuclear Information System (INIS)

    Mishra, Hiranmaya; Mohanty, Subhendra; Nautiyal, Akhilesh

    2013-01-01

    In warm inflation models there is the requirement of generating large dissipative couplings of the inflation with radiation, while at the same Âătime, not de-stabilising the flatness of the inflation potential due to radiative corrections. One way to achieve this without fine tuning unrelated couplings is by supersymmetry. In this talk we will discuss warm inflation with Pseudo-Nambu-Goldstone Bosons (PNGB). In this case inflation and other light fields are PNGB. So, the radiative corrections to the potential are suppressed and the thermal Âăcorrections are small as long as the temperature is below the symmetry breaking scale. In such models it is possible to fulfill the contrary requirements of an inflation potential which is stable under radiative corrections and the generation of a large dissipative coupling of the inflation field with other light fields. This warm inflation model with PNGB gives the observed CMB-anisotropy amplitude and spectral index having the symmetry breaking scale at the GUT scale. (author)

  3. A system for biasing a differential amplifier

    International Nuclear Information System (INIS)

    Barbier, Daniel; Ittel, J.M.; Poujois, Robert

    1975-01-01

    This invention concerns a system for biasing a differential amplifier. It particularly applies to the integrated differential amplifiers designed with MOS field effect transistors. Variations in the technological parameters may well cause the amplifying transistors to work outside their usual operational area, in other words outside the linear part of the transfer characteristic. To ensure that these transistors function correctly, it is necessary that the value of the voltage difference at the output be equally null. To do this and to centre on the so called 'rest' point of the amplifier transfer charateristic, the condition will be set that the output potentials of each amplifier transistor should have a zero value or a constant value as sum. With this in view, the bias on the source (generally a transistor powered by its grid bias voltage) supplying current to the two amplifying transistors fitted in parallel, is permanently adjusted in a suitable manner [fr

  4. Enhanced Gain in Photonic Crystal Amplifiers

    DEFF Research Database (Denmark)

    Ek, Sara; Semenova, Elizaveta; Hansen, Per Lunnemann

    2012-01-01

    We experimentally demonstrate enhanced gain in the slow-light regime of quantum well photonic crystal amplifiers. A strong gain enhancement is observed with the increase of the group refractive index, due to light slow-down. The slow light enhancement is shown in a amplified spontaneous emission....... These results are promising for short and efficient semiconductor optical amplifiers. This effect will also benefit other devices, such as mode locked lasers....

  5. Very broad bandwidth klystron amplifiers

    Science.gov (United States)

    Faillon, G.; Egloff, G.; Farvet, C.

    Large surveillance radars use transmitters at peak power levels of around one MW and average levels of a few kW, and possibly several tens of kW, in S band, or even C band. In general, the amplification stage of these transmitters is a microwave power tube, frequently a klystron. Although designers often turn to klystrons because of their good peak and average power capabilities, they still see them as narrow band amplifiers, undoubtedly because of their resonant cavities which, at first sight, would seem highly selective. But, with the progress of recent years, it has now become quite feasible to use these tubes in installations requiring bandwidths in excess of 10 - 12 percent, and even 15 percent, at 1 MW peak for example, in S-band.

  6. Hydraulically amplified PZT mems actuator

    Science.gov (United States)

    Miles, Robin R.

    2004-11-02

    A hydraulically amplified microelectromechanical systems actuator. A piece of piezoelectric material or stacked piezo bimorph is bonded or deposited as a thin film. The piece is operatively connected to a primary membrane. A reservoir is operatively connected to the primary membrane. The reservoir contains a fluid. A membrane is operatively connected to the reservoir. In operation, energizing the piezoelectric material causing the piezoelectric material to bow. Bowing of the piezoelectric material causes movement of the primary membrane. Movement of the primary membrane results in a force in being transmitted to the liquid in the reservoir. The force in the liquid causes movement of the membrane. Movement of the membrane results in an operating actuator.

  7. Transverse pumped laser amplifier architecture

    Science.gov (United States)

    Bayramian, Andrew James; Manes, Kenneth; Deri, Robert; Erlandson, Al; Caird, John; Spaeth, Mary

    2013-07-09

    An optical gain architecture includes a pump source and a pump aperture. The architecture also includes a gain region including a gain element operable to amplify light at a laser wavelength. The gain region is characterized by a first side intersecting an optical path, a second side opposing the first side, a third side adjacent the first and second sides, and a fourth side opposing the third side. The architecture further includes a dichroic section disposed between the pump aperture and the first side of the gain region. The dichroic section is characterized by low reflectance at a pump wavelength and high reflectance at the laser wavelength. The architecture additionally includes a first cladding section proximate to the third side of the gain region and a second cladding section proximate to the fourth side of the gain region.

  8. Long-Term Warming Trends in Korea and Contribution of Urbanization: An Updated Assessment

    Science.gov (United States)

    Park, Bo-Joung; Kim, Yeon-Hee; Min, Seung-Ki; Kim, Maeng-Ki; Choi, Youngeun; Boo, Kyung-On; Shim, Sungbo

    2017-10-01

    This study conducted an updated analysis of the long-term temperature trends over South Korea and reassessed the contribution of the urbanization effect to the local warming trends. Linear trends were analyzed for three different periods over South Korea in order to consider possible inhomogeneity due to changes in the number of available stations: recent 103 years (1912-2014), 61 years (1954-2014), and 42 years (1973-2014). The local temperature has increased by 1.90°C, 1.35°C, and 0.99°C during the three periods, respectively, which are found 1.4-2.6 times larger than the global land mean trends. The countries located in the northern middle and high latitudes exhibit similar warming trends (about 1.5 times stronger than the global mean), suggesting a weak influence of urbanization on the local warming over South Korea. Urbanization contribution is assessed using two methods. First, results from "city minus rural" methods showed that 30-45% of the local warming trends during recent four decades are likely due to the urbanization effect, depending on station classification methods and analysis periods. Results from an "observation minus reanalysis" method using the Twentieth Century Reanalysis (20CR) data sets (v2 and v2c) indicated about 25-30% contribution of the urbanization effect to the local warming trend during the recent six decades. However, the urbanization contribution was estimated as low as 3-11% when considering the century-long period. Our results confirm large uncertainties in the estimation of urbanization contribution when using shorter-term periods and suggest that the urbanization contribution to the century-long warming trends could be much lower.

  9. Design of an 1800nm Raman amplifier

    DEFF Research Database (Denmark)

    Svane, Ask Sebastian; Rottwitt, Karsten

    2013-01-01

    We present the experimental results for a Raman amplifier that operates at 1810 nm and is pumped by a Raman fiber laser at 1680 nm. Both the pump laser and the Raman amplifier is polarization maintaining. A challenge when scaling Raman amplifiers to longer wavelengths is the increase...... in transmission loss, but also the reduction in the Raman gain coefficient as the amplifier wavelength is increased. Both polarization components of the Raman gain is characterized, initially for linearly co-polarized signal and pump, subsequently linearly polarized orthogonal signal and pump. The noise...

  10. Reflection amplifiers in self-regulated learning

    NARCIS (Netherlands)

    Verpoorten, Dominique

    2012-01-01

    Verpoorten, D. (2012). Reflection amplifiers in self-regulated learning. Doctoral thesis. November, 9, 2012, Heerlen, The Netherlands: Open Universiteit (CELSTEC). Datawyse / Universitaire Pers Maastricht.

  11. Competition between global warming and an abrupt collapse of the AMOC in Earth's energy imbalance.

    Science.gov (United States)

    Drijfhout, Sybren

    2015-10-06

    A collapse of the Atlantic Meridional Overturning Circulation (AMOC) leads to global cooling through fast feedbacks that selectively amplify the response in the Northern Hemisphere (NH). How such cooling competes with global warming has long been a topic for speculation, but was never addressed using a climate model. Here it is shown that global cooling due to a collapsing AMOC obliterates global warming for a period of 15-20 years. Thereafter, the global mean temperature trend is reversed and becomes similar to a simulation without an AMOC collapse. The resulting surface warming hiatus lasts for 40-50 years. Global warming and AMOC-induced NH cooling are governed by similar feedbacks, giving rise to a global net radiative imbalance of similar sign, although the former is associated with surface warming, the latter with cooling. Their footprints in outgoing longwave and absorbed shortwave radiation are very distinct, making attribution possible.

  12. Tuning the climate sensitivity of a global model to match 20th Century warming

    Science.gov (United States)

    Mauritsen, T.; Roeckner, E.

    2015-12-01

    A climate models ability to reproduce observed historical warming is sometimes viewed as a measure of quality. Yet, for practical reasons historical warming cannot be considered a purely empirical result of the modelling efforts because the desired result is known in advance and so is a potential target of tuning. Here we explain how the latest edition of the Max Planck Institute for Meteorology Earth System Model (MPI-ESM1.2) atmospheric model (ECHAM6.3) had its climate sensitivity systematically tuned to about 3 K; the MPI model to be used during CMIP6. This was deliberately done in order to improve the match to observed 20th Century warming over the previous model generation (MPI-ESM, ECHAM6.1) which warmed too much and had a sensitivity of 3.5 K. In the process we identified several controls on model cloud feedback that confirm recently proposed hypotheses concerning trade-wind cumulus and high-latitude mixed-phase clouds. We then evaluate the model fidelity with centennial global warming and discuss the relative importance of climate sensitivity, forcing and ocean heat uptake efficiency in determining the response as well as possible systematic biases. The activity of targeting historical warming during model development is polarizing the modeling community with 35 percent of modelers stating that 20th Century warming was rated very important to decisive, whereas 30 percent would not consider it at all. Likewise, opinions diverge as to which measures are legitimate means for improving the model match to observed warming. These results are from a survey conducted in conjunction with the first WCRP Workshop on Model Tuning in fall 2014 answered by 23 modelers. We argue that tuning or constructing models to match observed warming to some extent is practically unavoidable, and as such, in many cases might as well be done explicitly. For modeling groups that have the capability to tune both their aerosol forcing and climate sensitivity there is now a unique

  13. Distributed feedback laser amplifiers combining the functions of amplifiers and channel filters

    DEFF Research Database (Denmark)

    Wang, Z.; Durhuus, T.; Mikkelsen, Benny

    1994-01-01

    A dynamic model for distributed feedback amplifiers, including the mode coupled equations and the carrier rate equation, is established. The presented mode coupled equations have taken into account the interaction between fast changing optical signal and the waveguide with corrugations. By showin...... the possibility of amplifying 100 ps pulses without pulse broadening, we anticipate that a distributed feedback amplifier can be used as a combined amplifier and channel filter in high bit rate transmission systems....

  14. Global warning, global warming

    International Nuclear Information System (INIS)

    Benarde, M.A.

    1992-01-01

    This book provides insights into the formidable array of issues which, in a warmer world, could impinge upon every facet of readers lives. It examines climatic change and long-term implications of global warming for the ecosystem. Topics include the ozone layer and how it works; the greenhouse effect; the dangers of imbalance and its effects on human and animal life; disruptions to the basic ecology of the planet; and the real scientific evidence for and against aberrant climatic shifts. The author also examines workable social and political programs and changes that must be instituted to avoid ecological disaster

  15. Self-pulsation in Raman fiber amplifiers

    DEFF Research Database (Denmark)

    Pedersen, Martin Erland Vestergaard; Ott, Johan Raunkjær; Rottwitt, Karsten

    2009-01-01

    Dynamic behavior caused by Brillouin scattering in Raman fiber amplifiers is studied. Modes of self-pulsation steady state oscillations are found. Their dependence on amplification scheme is demonstrated.......Dynamic behavior caused by Brillouin scattering in Raman fiber amplifiers is studied. Modes of self-pulsation steady state oscillations are found. Their dependence on amplification scheme is demonstrated....

  16. Pulse amplifier with high 'common mode rejection'

    International Nuclear Information System (INIS)

    Ijlst, P.

    1987-01-01

    The input signal of a pulse amplifier contains large 'common-mode' signals which have to be suppressed. A transformer, especially constructed for this purpose, is described. It has been tried to optimize the signal to noise ratio of the pulse amplifier by means of noise analysis. (Auth.)

  17. BROADBAND TRAVELLING WAVE SEMICONDUCTOR OPTICAL AMPLIFIER

    DEFF Research Database (Denmark)

    2010-01-01

    Broadband travelling wave semiconductor optical amplifier (100, 200, 300, 400, 800) for amplification of light, wherein the amplifier (100, 200, 300, 400, 800) comprises a waveguide region (101, 201, 301, 401, 801) for providing confinement of the light in transverse directions and adapted...

  18. Bevalac injector final stage RF amplifier upgrades

    International Nuclear Information System (INIS)

    Howard, D.; Calvert, J.; Dwinell, R.; Lax, J.; Lindner, A.; Richter, R.; Ridgeway, W.

    1991-01-01

    With the assistance of the DOE In-house Energy Management Program, the Bevalac injector final stage RF amplifier systems have been successfully upgraded to reduce energy consumption and operating costs. This recently completed project removed the energy-inefficient plate voltage modulator circuits that were used in conjunction with the final stage RF amplifiers. Construction, design, and operating parameters are described in detail

  19. Method for reducing snap in magnetic amplifiers

    Science.gov (United States)

    Fischer, R. L. E.; Word, J. L.

    1968-01-01

    Method of reducing snap in magnetic amplifiers uses a degenerative feedback circuit consisting of a resistor and a separate winding on a magnetic core. The feedback circuit extends amplifier range by allowing it to be used at lower values of output current.

  20. 500-year climate cycles stacking of recent centennial warming documented in an East Asian pollen record

    Science.gov (United States)

    Xu, Deke; Lu, Houyuan; Chu, Guoqiang; Wu, Naiqin; Shen, Caiming; Wang, Can; Mao, Limi

    2014-01-01

    Here we presented a high-resolution 5350-year pollen record from a maar annually laminated lake in East Asia (EA). Pollen record reflected the dynamics of vertical vegetation zones and temperature change. Spectral analysis on pollen percentages/concentrations of Pinus and Quercus, and a temperature proxy, revealed ~500-year quasi-periodic cold-warm fluctuations during the past 5350 years. This ~500-year cyclic climate change occurred in EA during the mid-late Holocene and even the last 150 years dominated by anthropogenic forcing. It was almost in phase with a ~500-year periodic change in solar activity and Greenland temperature change, suggesting that ~500-year small variations in solar output played a prominent role in the mid-late Holocene climate dynamics in EA, linked to high latitude climate system. Its last warm phase might terminate in the next several decades to enter another ~250-year cool phase, and thus this future centennial cyclic temperature minimum could partially slow down man-made global warming. PMID:24402348

  1. Increased ventilation of Antarctic deep water during the warm mid-Pliocene.

    Science.gov (United States)

    Zhang, Zhongshi; Nisancioglu, Kerim H; Ninnemann, Ulysses S

    2013-01-01

    The mid-Pliocene warm period is a recent warm geological period that shares similarities with predictions of future climate. It is generally held the mid-Pliocene Atlantic Meridional Overturning Circulation must have been stronger, to explain a weak Atlantic meridional δ(13)C gradient and large northern high-latitude warming. However, climate models do not simulate such stronger Atlantic Meridional Overturning Circulation, when forced with mid-Pliocene boundary conditions. Proxy reconstructions allow for an alternative scenario that the weak δ(13)C gradient can be explained by increased ventilation and reduced stratification in the Southern Ocean. Here this alternative scenario is supported by simulations with the Norwegian Earth System Model (NorESM-L), which simulate an intensified and slightly poleward shifted wind field off Antarctica, giving enhanced ventilation and reduced stratification in the Southern Ocean. Our findings challenge the prevailing theory and show how increased Southern Ocean ventilation can reconcile existing model-data discrepancies about Atlantic Meridional Overturning Circulation while explaining fundamental ocean features.

  2. Antarctica: Cooling or Warming?

    Science.gov (United States)

    Bunde, Armin; Ludescher, Josef; Franzke, Christian

    2013-04-01

    We consider the 14 longest instrumental monthly mean temperature records from the Antarctica and analyse their correlation properties by wavelet and detrended fluctuation analysis. We show that the stations in the western and the eastern part of the Antarctica show significant long-term memory governed by Hurst exponents close to 0.8 and 0.65, respectively. In contrast, the temperature records at the inner part of the continent (South Pole and Vostok), resemble white noise. We use linear regression to estimate the respective temperature differences in the records per decade (i) for the annual data, (ii) for the summer and (iii) for the winter season. Using a recent approach by Lennartz and Bunde [1] we estimate the respective probabilities that these temperature differences can be exceeded naturally without inferring an external (anthropogenic) trend. We find that the warming in the western part of the continent and the cooling at the South Pole is due to a gradually changes in the cold extremes. For the winter months, both cooling and warming are well outside the 95 percent confidence interval, pointing to an anthropogenic origin. In the eastern Antarctica, the temperature increases and decreases are modest and well within the 95 percent confidence interval. [1] S. Lennartz and A. Bunde, Phys. Rev. E 84, 021129 (2011)

  3. A fluidic/pneumatic interface amplifier

    Science.gov (United States)

    Limbert, D. E.; Kegel, T. M.

    The development of a low cost, reliable, linear pressure amplifier to interface Laminar Proportional Amplifiers (LPA) to pneumatic controllers is presented. The amplifier consists of an LPA input stage and an output stage consisting of a venturi in series with a bellows nozzle valve. The LPA output drives the bellows nozzle valve thereby altering the flowrate through the venturi. The pressure within the venturi throat region, which is the amplifier output, changes with the flowrate. Non-linear characteristics, due to supersonic flow within the venturi, are altered through the use of feedback to the LPA input. A computer based model, to aid in optimizing the amplifier design, is developed. This model incorporates the effects of shock waves and boundary layers within the venturi. Good correspondence between the model and an experimental prototype is shown.

  4. Amplified OTDR Systems for Multipoint Corrosion Monitoring

    Science.gov (United States)

    Nascimento, Jehan F.; Silva, Marcionilo J.; Coêlho, Isnaldo J. S.; Cipriano, Eliel; Martins-Filho, Joaquim F.

    2012-01-01

    We present two configurations of an amplified fiber-optic-based corrosion sensor using the optical time domain reflectometry (OTDR) technique as the interrogation method. The sensor system is multipoint, self-referenced, has no moving parts and can measure the corrosion rate several kilometers away from the OTDR equipment. The first OTDR monitoring system employs a remotely pumped in-line EDFA and it is used to evaluate the increase in system reach compared to a non-amplified configuration. The other amplified monitoring system uses an EDFA in booster configuration and we perform corrosion measurements and evaluations of system sensitivity to amplifier gain variations. Our experimental results obtained under controlled laboratory conditions show the advantages of the amplified system in terms of longer system reach with better spatial resolution, and also that the corrosion measurements obtained from our system are not sensitive to 3 dB gain variations. PMID:22737017

  5. An Implantable CMOS Amplifier for Nerve Signals

    DEFF Research Database (Denmark)

    Nielsen, Jannik Hammel; Lehmann, Torsten

    2001-01-01

    In this paper, a low noise high gain CMOS amplifier for minute nerve signals is presented. By using a mixture of weak- and strong inversion transistors, optimal noise suppression in the amplifier is achieved. A continuous-time offset-compensation technique is utilized in order to minimize impact...... on the amplifier input nodes. The method for signal recovery from noisy nerve signals is presented. A prototype amplifier is realized in a standard digital 0.5 μm CMOS single poly, n-well process. The prototype amplifier features a gain of 80 dB over a 3.6 kHz bandwidth, a CMRR of more than 87 dB and a PSRR...

  6. Bandwidth tunable amplifier for recording biopotential signals.

    Science.gov (United States)

    Hwang, Sungkil; Aninakwa, Kofi; Sonkusale, Sameer

    2010-01-01

    This paper presents a low noise, low power, bandwidth tunable amplifier for bio-potential signal recording applications. By employing depletion-mode pMOS transistor in diode configuration as a tunable sub pA current source to adjust the resistivity of MOS-Bipolar pseudo-resistor, the bandwidth is adjusted without any need for a separate band-pass filter stage. For high CMRR, PSRR and dynamic range, a fully differential structure is used in the design of the amplifier. The amplifier achieves a midband gain of 39.8dB with a tunable high-pass cutoff frequency ranging from 0.1Hz to 300Hz. The amplifier is fabricated in 0.18εm CMOS process and occupies 0.14mm(2) of chip area. A three electrode ECG measurement is performed using the proposed amplifier to show its feasibility for low power, compact wearable ECG monitoring application.

  7. Dual-range linearized transimpedance amplifier system

    Science.gov (United States)

    Wessendorf, Kurt O.

    2010-11-02

    A transimpedance amplifier system is disclosed which simultaneously generates a low-gain output signal and a high-gain output signal from an input current signal using a single transimpedance amplifier having two different feedback loops with different amplification factors to generate two different output voltage signals. One of the feedback loops includes a resistor, and the other feedback loop includes another resistor in series with one or more diodes. The transimpedance amplifier system includes a signal linearizer to linearize one or both of the low- and high-gain output signals by scaling and adding the two output voltage signals from the transimpedance amplifier. The signal linearizer can be formed either as an analog device using one or two summing amplifiers, or alternately can be formed as a digital device using two analog-to-digital converters and a digital signal processor (e.g. a microprocessor or a computer).

  8. Detection of Non-Amplified Genomic DNA

    CERN Document Server

    Corradini, Roberto

    2012-01-01

    This book offers a state-of-the-art overview on non amplified DNA detection methods and provides chemists, biochemists, biotechnologists and material scientists with an introduction to these methods. In fact all these fields have dedicated resources to the problem of nucleic acid detection, each contributing with their own specific methods and concepts. This book will explain the basic principles of the different non amplified DNA detection methods available, highlighting their respective advantages and limitations. The importance of non-amplified DNA sequencing technologies will be also discussed. Non-amplified DNA detection can be achieved by adopting different techniques. Such techniques have allowed the commercialization of innovative platforms for DNA detection that are expected to break into the DNA diagnostics market. The enhanced sensitivity required for the detection of non amplified genomic DNA has prompted new strategies that can achieve ultrasensitivity by combining specific materials with specifi...

  9. Ultrafast disk lasers and amplifiers

    Science.gov (United States)

    Sutter, Dirk H.; Kleinbauer, Jochen; Bauer, Dominik; Wolf, Martin; Tan, Chuong; Gebs, Raphael; Budnicki, Aleksander; Wagenblast, Philipp; Weiler, Sascha

    2012-03-01

    Disk lasers with multi-kW continuous wave (CW) output power are widely used in manufacturing, primarily for cutting and welding applications, notably in the automotive industry. The ytterbium disk technology combines high power (average and/or peak power), excellent beam quality, high efficiency, and high reliability with low investment and operating costs. Fundamental mode picosecond disk lasers are well established in micro machining at high throughput and perfect precision. Following the world's first market introduction of industrial grade 50 W picosecond lasers (TruMicro 5050) at the Photonics West 2008, the second generation of the TruMicro series 5000 now provides twice the average power (100 W at 1030 nm, or 60 W frequency doubled, green output) at a significantly reduced footprint. Mode-locked disk oscillators achieve by far the highest average power of any unamplified lasers, significantly exceeding the 100 W level in laboratory set-ups. With robust long resonators their multi-microjoule pulse energies begin to compete with typical ultrafast amplifiers. In addition, significant interest in disk technology has recently come from the extreme light laser community, aiming for ultra-high peak powers of petawatts and beyond.

  10. The effects of the Indo-Pacific warm pool on the stratosphere

    Science.gov (United States)

    Zhou, Xin; Li, Jianping; Xie, Fei; Ding, Ruiqiang; Li, Yanjie; Zhao, Sen; Zhang, Jiankai; Li, Yang

    2017-03-01

    Sea surface temperature (SST) in the Indo-Pacific warm pool (IPWP) plays a key role in influencing East Asian climate, and even affects global-scale climate change. This study defines IPWP Niño and IPWP Niña events to represent the warm and cold phases of IPWP SST anomalies, respectively, and investigates the effects of these events on stratospheric circulation and temperature. Results from simulations forced by observed SST anomalies during IPWP Niño and Niña events show that the tropical lower stratosphere tends to cool during IPWP Niño events and warm during IPWP Niña events. The responses of the northern and southern polar vortices to IPWP Niño events are fairly symmetric, as both vortices are significantly warmed and weakened. However, the responses of the two polar vortices to IPWP Niña events are of opposite sign: the northern polar vortex is warmed and weakened, but the southern polar vortex is cooled and strengthened. These features are further confirmed by composite analysis using reanalysis data. A possible dynamical mechanism connecting IPWP SST to the stratosphere is suggested, in which IPWP Niño and Niña events excite teleconnections, one similar to the Pacific-North America pattern in the Northern Hemisphere and a Rossby wave train in the Southern Hemisphere, which project onto the climatological wave in the mid-high latitudes, intensifying the upward propagation of planetary waves into the stratosphere and, in turn, affecting the polar vortex.

  11. Climate change under a scenario near 1.5 °C of global warming: monsoon intensification, ocean warming and steric sea level rise

    Directory of Open Access Journals (Sweden)

    J. Schewe

    2011-03-01

    Full Text Available We present climatic consequences of the Representative Concentration Pathways (RCPs using the coupled climate model CLIMBER-3α, which contains a statistical-dynamical atmosphere and a three-dimensional ocean model. We compare those with emulations of 19 state-of-the-art atmosphere-ocean general circulation models (AOGCM using MAGICC6. The RCPs are designed as standard scenarios for the forthcoming IPCC Fifth Assessment Report to span the full range of future greenhouse gas (GHG concentrations pathways currently discussed. The lowest of the RCP scenarios, RCP3-PD, is projected in CLIMBER-3α to imply a maximal warming by the middle of the 21st century slightly above 1.5 °C and a slow decline of temperatures thereafter, approaching today's level by 2500. We identify two mechanisms that slow down global cooling after GHG concentrations peak: The known inertia induced by mixing-related oceanic heat uptake; and a change in oceanic convection that enhances ocean heat loss in high latitudes, reducing the surface cooling rate by almost 50%. Steric sea level rise under the RCP3-PD scenario continues for 200 years after the peak in surface air temperatures, stabilizing around 2250 at 30 cm. This contrasts with around 1.3 m of steric sea level rise by 2250, and 2 m by 2500, under the highest scenario, RCP8.5. Maximum oceanic warming at intermediate depth (300–800 m is found to exceed that of the sea surface by the second half of the 21st century under RCP3-PD. This intermediate-depth warming persists for centuries even after surface temperatures have returned to present-day values, with potential consequences for marine ecosystems, oceanic methane hydrates, and ice-shelf stability. Due to an enhanced land-ocean temperature contrast, all scenarios yield an intensification of monsoon rainfall under global warming.

  12. Scientists' Views about Attribution of Global Warming

    Science.gov (United States)

    Verheggen, Bart; Strengers, Bart; Cook, John; van Dorland, Rob; Vringer, Kees; Peters, Jeroen; Visser, Hans; Meyer, Leo

    2015-04-01

    What do scientists think? That is an important question when engaging in science communication, in which an attempt is made to communicate the scientific understanding to a lay audience. To address this question we undertook a large and detailed survey among scientists studying various aspects of climate change , dubbed "perhaps the most thorough survey of climate scientists ever" by well-known climate scientist and science communicator Gavin Schmidt. Among more than 1800 respondents we found widespread agreement that global warming is predominantly caused by human greenhouse gases. This consensus strengthens with increased expertise, as defined by the number of self-reported articles in the peer-reviewed literature. 90% of respondents with more than 10 climate-related peer-reviewed publications (about half of all respondents), agreed that anthropogenic greenhouse gases are the dominant cause of recent global warming, i.e. having contributed more than half of the observed warming. With this survey we specified what the consensus position entails with much greater specificity than previous studies. The relevance of this consensus for science communication will be discussed. Another important result from our survey is that the main attribution statement in IPCC's fourth assessment report (AR4) may lead to an underestimate of the greenhouse gas contribution to warming, because it implicitly includes the lesser known masking effect of cooling aerosols. This shows the importance of the exact wording in high-profile reports such as those from IPCC in how the statement is perceived, even by fellow scientists. The phrasing was improved in the most recent assessment report (AR5). Respondents who characterized the human influence on climate as insignificant, reported having the most frequent media coverage regarding their views on climate change. This shows that contrarian opinions are amplified in the media in relation to their prevalence in the scientific community. This

  13. Daytime warming has stronger negative effects on soil nematodes than night-time warming

    OpenAIRE

    Yan, Xiumin; Wang, Kehong; Song, Lihong; Wang, Xuefeng; Wu, Donghui

    2017-01-01

    Warming of the climate system is unequivocal, that is, stronger warming during night-time than during daytime. Here we focus on how soil nematodes respond to the current asymmetric warming. A field infrared heating experiment was performed in the western of the Songnen Plain, Northeast China. Three warming modes, i.e. daytime warming, night-time warming and diurnal warming, were taken to perform the asymmetric warming condition. Our results showed that the daytime and diurnal warming treatmen...

  14. Trends in continental temperature and humidity directly linked to ocean warming.

    Science.gov (United States)

    Byrne, Michael P; O'Gorman, Paul A

    2018-05-08

    In recent decades, the land surface has warmed substantially more