WorldWideScience

Sample records for amplify high-latitude warming

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

    OpenAIRE

    Swann, Abigail L.; Fung, Inez Y.; Levis, Samuel; BONAN, GORDON B.; Doney, Scott C.

    2010-01-01

    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 ...

  2. Relocation, high-latitude warming and host genetic identity shape the foliar fungal microbiome of poplars.

    Science.gov (United States)

    Bálint, Miklós; Bartha, László; O'Hara, Robert B; Olson, Matthew S; Otte, Jürgen; Pfenninger, Markus; Robertson, Amanda L; Tiffin, Peter; Schmitt, Imke

    2015-01-01

    Micro-organisms associated with plants and animals affect host fitness, shape community structure and influence ecosystem properties. Climate change is expected to influence microbial communities, but their reactions are not well understood. Host-associated micro-organisms are influenced by the climate reactions of their hosts, which may undergo range shifts due to climatic niche tracking, or may be actively relocated to mitigate the effects of climate change. We used a common-garden experiment and rDNA metabarcoding to examine the effect of host relocation and high-latitude warming on the complex fungal endophytic microbiome associated with leaves of an ecologically dominant boreal forest tree (Populus balsamifera L.). We also considered the potential effects of poplar genetic identity in defining the reactions of the microbiome to the treatments. The relocation of hosts to the north increased the diversity of the microbiome and influenced its structure, with results indicating enemy release from plausible pathogens. High-latitude warming decreased microbiome diversity in comparison with natural northern conditions. The warming also caused structural changes, which made the fungal communities distinct in comparison with both low-latitude and high-latitude natural communities, and increased the abundance of plausible pathogens. The reactions of the microbiome to relocation and warming were strongly dependent on host genetic identity. This suggests that climate change effects on host-microbiome systems may be mediated by the interaction of environmental factors and the population genetic processes of the hosts. PMID:25443313

  3. Vegetation Feedbacks Explain Recent High-latitude Summer Warming in Alaskan Arctic and Boreal Ecosystems

    Science.gov (United States)

    Chapin, F. S.; Beringer, J.; Copass, C.; Epstein, H.; Lloyd, A.; Lynch, A.; McGuire, A. D.; Sturm, M.

    2002-12-01

    Although General Circulation Models predict the observed winter and spring warming at high latitudes, there is no obvious physical mechanism in the climate system that can account for the significant increase in summer temperatures that has occurred at high latitudes during the past 30 years. We demonstrate that vegetation-induced feedbacks in snow properties and summer energy exchange with the atmosphere explain this recent summer warming. A combination of stand-age reconstructions, repeat photography, and satellite measures of vegetation greenness demonstrate an expansion of the distribution and an infilling of shrubs in moist tundra and of trees in forest tundra. These vegetation changes increase the depth and thermal resistance of the snow pack, causing a 3oC increase in winter soil temperature and an increase in winter decomposition and nutrient mineralization, which enhance plant growth. These vegetation changes also increase summer heat transport to the atmosphere by increasing radiation absorption (lower albedo) and the proportion of absorbed energy that is transferred to the atmosphere as sensible heat. The resulting increase in atmospheric heating, on a unit-area basis, is similar to effects of a doubling of atmospheric carbon dioxide or a 2% change in solar constant, such as occurred at the last glacial-interglacial boundary. Simulations with the regional climate model ARCSyM indicate that a change from shrubless tundra to shrub-dominated tundra on the North Slope of Alaska would increase July mean temperature by 1.5 to 3.5 degrees C, with the warming effects extending south into the boreal forest of interior Alaska. If these vegetation feedbacks to regional warming are widespread, as suggested by indigenous knowledge and the satellite record, they are of sufficient magnitude to explain the summer warming that has recently been observed in northern Alaska and other regions of the circumpolar Arctic.

  4. Variable Responses of Benthic Communities to Anomalously Warm Sea Temperatures on a High-Latitude Coral Reef

    OpenAIRE

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

    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 c...

  5. 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 records from northern high-latitude forests record the effects of climate warming and pCO2 rise across the twentieth century.

  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. 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. PMID:25426718

  8. Re-evaluating high-latitude warming in the Pliocene Nordic Seas

    Science.gov (United States)

    Hill, Daniel; Smith, Yvonne; Dolan, Aisling

    2016-04-01

    The Pliocene warm period was generally been seen as stable warm climate with global temperatures of 2-3K above pre-industrial and significant polar amplification. Northern Hemisphere ice has been reconstructed to be restricted to the high altitude areas of Greenland and global reconstructions of sea surface temperatures show an especially strong warming in the Nordic Seas, most often attributed to increased ocean heat transport in the North Atlantic Ocean. Here we present climate model results that show that the strongest warming recorded in the Nordic Seas and Arctic is forced by changes in orbital forcing and palaeogeographic changes. Of particular importance is the presence of a sub-aerial landmass in the Barents Sea region, which has subsequently been eroded by Pleistocene glaciation. While climate models can produce strong warming signals in the Nordic Seas, a new iceberg modelling study showing that through much of the Pliocene the conditions in the Nordic Seas were suitable for the presence of significant quantities of icebergs. The locations of IRD records also raises the possibility of significant glaciations in places previously considered to be ice free in the Pliocene.

  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

    and the inclusion of land cover and soil type variables. Moreover, their ability to predict range shifts under climate change is limited, especially at the expanding edge. More tests with independent validations are needed to fully understand the predictive potential of SDMs across taxa and biomes.......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...... 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...

  10. Early Paleogene Arctic terrestrial ecosystems affected by the change of polar hydrology under global warming:Implications for modern climate change at high latitudes

    Institute of Scientific and Technical Information of China (English)

    Gaytha; A.; LANGLOIS

    2010-01-01

    Our understanding of both the role and impact of Arctic environmental changes under the current global warming climate is rather limited despite efforts of improved monitoring and wider assessment through remote sensing technology. Changes of Arctic ecosystems under early Paleogene warming climate provide an analogue to evaluate long-term responses of Arctic environmental alteration to global warming. This study reviews Arctic terrestrial ecosystems and their transformation under marked change of hydrological conditions during the warmest period in early Cenozoic, the Paleocene and Eocene. We describe a new approach to quantitatively reconstruct high latitudinal paleohydrology using compound-specific hydrogen isotope analysis which applies empirically derived genus-specific hydrogen isotope fractionations to in situ biomolecules from fossil plants. We propose a moisture recycling model at the Arctic to explain the reconstructed hydrogen isotope signals of ancient high latitude precipitation during early Paleogene, which bears implications to the likely change of modern Arctic ecosystems under the projected accelerated global warming.

  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. Energy feedbacks of northern high-latitude ecosystems to the climate system due to reduced snow cover during 20th century warming

    Science.gov (United States)

    Euskirchen, E.S.; McGuire, A.D.; Chapin, F.S.

    2007-01-01

    The warming associated with changes in snow cover in northern high-latitude terrestrial regions represents an important energy feedback to the climate system. Here, we simulate snow cover-climate feedbacks (i.e. changes in snow cover on atmospheric heating) across the Pan-arctic over two distinct warming periods during the 20th century, 1910-1940 and 1970-2000. We offer evidence that increases in snow cover-climate feedbacks during 1970-2000 were nearly three times larger than during 1910-1940 because the recent snow-cover change occurred in spring, when radiation load is highest, rather than in autumn. Based on linear regression analysis, we also detected a greater sensitivity of snow cover-climate feedbacks to temperature trends during the more recent time period. Pan-arctic vegetation types differed substantially in snow cover-climate feedbacks. Those with a high seasonal contrast in albedo, such as tundra, showed much larger changes in atmospheric heating than did those with a low seasonal contrast in albedo, such as forests, even if the changes in snow-cover duration were similar across the vegetation types. These changes in energy exchange warrant careful consideration in studies of climate change, particularly with respect to associated shifts in vegetation between forests, grasslands, and tundra. ?? 2007 Blackwell Publishing Ltd.

  13. The ever-increasing CO2 seasonal cycle amplitude: contributions from high latitude warming, CO2 fertilization, and the agricultural Green Revolution

    Science.gov (United States)

    Zeng, N.; Martin, C.; Zhao, F.; Collatz, G. J.; Kalnay, E.; Salawitch, R. J.; West, T. O.; Guanter, L.

    2014-12-01

    Human activities has tranformed the Earth's surface in complex ways. Here we show that not only land cover change, but also the management intensity, namely the intensification of agriculture through the Green Revolution has had a profound impact on the carbon cycle. A long-standing puzzle in the global carbon cycle is the increase in the amplitude of the seasonal cycle of atmospheric CO2. This increase likely reflects enhanced biological activity in the Northern Hemisphere (NH). It has been hypothesized that vegetation growth may have been stimulated by higher concentrations of CO2 as well as warming in recent decades, but the role of such specific mechanisms has not been quantified and they have been unable to explain the full range and magnitude of observations. Here we suggest another potential driver of the increased seasonal amplitude: the intensification of agriculture from the Green Revolution to feed a rising population, that led to a 3-fold increase in world crop production over the last 5 decades. Our analysis of CO2 data and atmospheric inversions shows a robust 15% long-term increase in CO2 seasonal amplitude from 1961 to 2010 that is punctuated by large decadal and interannual variations. The three pillars of the Green Revolution, consisting of high yield cultivars, fertilizer use, and irrigation, are represented in a terrestrial carbon cycle model. The results reveal that the long-term increase in CO2 seasonal amplitude arises from two major regions in the NH: the mid-latitude cropland between 25N-60N that encompasses the world's major agriculture zones in Asia, Europe and North America, and the high-latitude natural vegetation between 50N-70N that includes much of the Northern boreal forests, tundra and some deciduous forests. The long-term trend of seasonal amplitude is 0.3% per year, of which sensitivity experiments attribute 43% to land use change, 31% to climate variability and change, and 26% to CO2 fertilization. Our results suggest that human

  14. Qualitative models of global warming amplifiers

    NARCIS (Netherlands)

    U. Milošević; B. Bredeweg

    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. Amplified Arctic warming by phytoplankton under greenhouse warming

    OpenAIRE

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

    2015-01-01

    One of the important impacts of marine phytoplankton on climate systems is the geophysical feedback by which chlorophyll and the related pigments in phytoplankton absorb solar radiation and then change sea surface temperature. Yet such biogeophysical impact is still not considered in many climate projections by state-of-the-art climate models, nor is its impact on the future climate quantified. This study shows that, by conducting global warming simulations with and without an active marine e...

  16. Evidence for a warm ice-free environment on the high latitude Antarctic coast (78°S) during the Middle to Late Eocene

    Science.gov (United States)

    Levy, R. H.; Bohaty, S. M.; Harwood, D. M.; Sangiorgi, F.; Willmott, V.; Talarico, F.; MacLeod, K. G.

    2013-12-01

    Much of Antarctica's Cenozoic geological record is hidden beneath the thick ice sheets and fringing ice shelves that cover the continent. Glacial erratics of sedimentary rocks present in coastal moraines at Minna Bluff and Mount Discovery, McMurdo Sound, western Ross Sea, Antarctica contain middle and late Eocene plant and marine fossils that were deposited in a range of marine settings along the Antarctic coastline. This suite of sedimentary rocks were likely deposited at the margin of a narrow (c. 100 km wide), relatively deep (up to 1000 m) marine seaway that was bound by the proto-Transantarctic Mountains to the west and a topographic high to the east. Although these Eocene ';';McMurdo Erratics'' lack stratigraphic integrity, they are significant as they offer a rare glimpse into Antarctica's climate during global greenhouse conditions at high latitudes (c. 78°S). Fossils recovered from the rocks are diverse and include marine and terrestrial palynomorphs, diatoms, molluscs, wood, leaves and other macrofauna and flora. Geochemical temperature proxies derived from the sedimentary rocks include organic biomarkers (TEX86) and fish tooth δ18O that indicate coastal sea surface temperatures were at least 15°C in the late Middle Eocene. While rare lonestones occur in several sandstone erratics, we find no conclusive evidence for glaciation at the coast. The fossil-bearing coastal moraines also contain a suite of igneous and metamorphic erratics that are comparable to lithological units exposed in the Transantarctic Mountains between the Skelton and Mulock glaciers. This suggests that the Eocene erratics were eroded from the north-eastern portion of a large sub-glacial basin behind Minna Bluff and/or from grabens in a basement high immediately south-east of Minna Bluff. Importantly, the northeastward extension of this basement high is a target for stratigraphic drilling during the proposed ANDRILL Coulman High Project. Drilling on the Coulman High has an excellent

  17. A nudged chemistry-climate model simulation of chemical constituent distribution at northern high-latitude stratosphere observed by SMILES and MLS during the 2009/2010 stratospheric sudden warming

    Science.gov (United States)

    Akiyoshi, H.; Nakamura, T.; Miyasaka, T.; Shiotani, M.; Suzuki, M.

    2016-02-01

    Stratospheric sudden warming (SSW) is a dramatic phenomenon of the winter stratosphere in which the distribution of chemical constituents, associated chemical tendency, and transport of chemical constituents differ significantly inside and outside of the polar vortex. In this study, the chemical constituent distributions in the major SSW of 2009/2010 were simulated by the Model for Interdisciplinary Research on Climate 3.2-Chemistry-Climate Model (CCM) nudged toward the European Center for Medium-Range Weather Forecasts-Interim Re-Analysis data. The results were compared with Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and Microwave Limb Sounder (MLS) observations. In addition, ozone tendency due to ozone transport and chemical ozone loss in the high-latitude lower stratosphere before and after the SSW was analyzed for the period from 1 January 2010 to 11 February 2010. The evolution and distribution of ozone and HCl inside/outside the polar vortex associated with the vortex shift to the midlatitudes in January are quite similar between SMILES and MLS. Those of ClO are also similar, considering the difference in the local time for the measurement. Analyses of the nudged CCM run indicate that inside the polar vortex at 50 hPa, the ozone concentration increased moderately owing to partial cancelation between the large negative ozone tendency due to chemical ozone destruction and large positive ozone tendency due to horizontal ozone influx from outside of the vortex as well as downward advection. In the region of a high ozone concentration with the same area as that of the polar vortex at 50 hPa, the large increase in ozone was primarily due to a downward advection of ozone. SMILES and MLS observations, nudged CCM simulations, and ozone tendency analyses revealed a highly longitudinal dependent ozone tendency at high latitudes during the SSW.

  18. Sea Ice, High-Latitude Convection, and Equable Climates

    Science.gov (United States)

    Abbot, D. S.; Tziperman, E.

    2007-12-01

    It is argued that deep atmospheric convection might occur during winter in ice-free high-latitude oceans, and that the surface radiative warming effects of the clouds and water vapor associated with this winter convection could keep high-latitude oceans ice-free through polar night. In such an ice-free high-latitude ocean the annual-mean SST would be much higher and the seasonal cycle would be dramatically reduced - making potential implications for equable climates manifest. The constraints that atmospheric heat transport, ocean heat transport, and CO2 concentration place on this mechanism are established. These ideas are investigated using a column model with state-of-the-art atmospheric physics, high vertical resolution, a full seasonal cycle, a thermodynamic sea ice model, and a mixed layer ocean (the SCAM).

  19. Variability of methane fluxes over high latitude permafrost wetlands

    OpenAIRE

    Andrei Serafimovich; Hartmann, J.; Eric Larmanou; Torsten Sachs

    2013-01-01

    Atmospheric methane plays an important role in the global climate system. Due to significant amounts of organic material stored in the upper layers of high latitude permafrost wetlands and a strong Arctic warming trend, there is concern about potentially large methane emissions from Arctic and sub-Arctic areas. The quantification of methane fluxes and their variability from these regions therefore plays an important role in understanding the Arctic carbon cycle and changes in atmo...

  20. 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; McKenna-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 (> 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.

  1. Tidi Observations Relating to High Latitude Aeronomy

    Science.gov (United States)

    Gell, D.; Niciejewski, R.; Killeen, T.; Wu, Q.; Skinner, W.; Solomon, S.; Ortland, D.; Kafkalidis, J.; Gablehouse, D.; Johnson, R.

    2003-12-01

    Unique observations of the horizontal neutral winds at high latitudes in the altitude range 60 to 180 km have been performed by TIDI (Thermosphere Ionosphere Doppler Interferometer) since January 2002. The satellite orbit is such that the TIDI field of view includes latitudes to both the north pole and the south pole. Though high latitude neutral wind measurements have been obtained from space with the DE-2 satellite and the UARS satellite, TIDI is the first instrument to sample the mesosphere and the lower thermosphere up to and including both polar regions on a long-term basis. Ground based studies have previously reported a strong semi-diurnal tide in the mesosphere over Resolute, Canada. This paper will describe the climatology that has been obtained by the TIDI instrument since early 2002 for high latitudes. The precession rate of TIMED supports two month averaging of data sets in order to sample all local solar time.

  2. Electrodynamics of the high-latitude mesosphere

    Science.gov (United States)

    Goldberg, Richard A.

    1989-01-01

    The discovery of apparent large (V/m) electric fields within the mesosphere suggests that this region is more active electrically than originally suspected. High-latitude observations have been particularly productive in developing new concepts regarding mesospheric electrodynamics. Several high-latitude observations of large mesospheric fields have been made under both quiet and aurorally active conditions but always below heights where enhanced ionizing radiations could significantly penetrate. Two measurements from Andoya, Norway, have also produced an anticorrelation of horizontal electric field directions with neutral wind velocities, leading to the theoretical description of a newly defined mechanism for V/m electric field generation involving wind-induced separation of charged aerosols. Evidence for mesospheric aerosols and winds exists at all latitudes but is most evident at high latitudes during the appearance of noctilucent and/or polar mesospheric clouds.

  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, P. C. D.

    2016-09-01

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

    International Nuclear Information System (INIS)

    Observations and modeling studies indicate that enhanced vegetation activities over high latitudes under an elevated CO2 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 2xCO2 environments. The increased vegetation activities over high latitudes under a 2xCO2 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)

  5. 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 s

  6. Electrodynamics of the high latitude middle atmosphere

    Science.gov (United States)

    Goldberg, R. A.

    1987-01-01

    Atmospheric electrodynamics is reviewed. The discovery of apparent large (V/m) electric fields within the mesosphere invites the possibility for this region to be electrically active. Observations of the V/m field were made at high latitudes even under active conditions, but always below heights where significant enhancements in electrical conductivity are found to occur. Two measurements at Andoya (Norway) show anticorrelation of horizontal field directions with wind directions, suggesting a mechanism which involves mechanical separation of charged aerosols. Reported evidence for such aerosols makes this concept more viable. Noctilucent clouds and mesospheric turbulence, and their influence on the local electrical environment are mentioned.

  7. Characteristics of High Latitude Ionosphere Scintillations

    Science.gov (United States)

    Morton, Y.

    2012-12-01

    As we enter a new solar maximum period, global navigation satellite systems (GNSS) receivers, especially the ones operating in high latitude and equatorial regions, are facing an increasing threat from ionosphere scintillations. The increased solar activities, however, also offer a great opportunity to collect scintillation data to characterize scintillation signal parameters and ionosphere irregularities. While there are numerous GPS receivers deployed around the globe to monitor ionosphere scintillations, most of them are commercial receivers whose signal processing mechanisms are not designed to operate under ionosphere scintillation. As a result, they may distort scintillation signal parameters or lose lock of satellite signals under strong scintillations. Since 2008, we have established and continuously improved a unique GNSS receiver array at HAARP, Alaska. The array contains high ends commercial receivers and custom RF front ends which can be automatically triggered to collect high quality GPS and GLONASS satellite signals during controlled heating experiments and natural scintillation events. Custom designed receiver signal tracking algorithms aim to preserve true scintillation signatures are used to process the raw RF samples. Signal strength, carrier phase, and relative TEC measurements generated by the receiver array since its inception have been analyzed to characterize high latitude scintillation phenomena. Daily, seasonal, and solar events dependency of scintillation occurrence, spectral contents of scintillation activities, and plasma drifts derived from these measurements will be presented. These interesting results demonstrate the feasibility and effectiveness of our experimental data collection system in providing insightful details of ionosphere responses to active perturbations and natural disturbances.

  8. 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

  9. AIRS total precipitable water over high latitudes

    Science.gov (United States)

    Ye, H.; Fetzer, E. J.; Bromwich, D. H.; Fishbein, E.; Olsen, E. T.; Granger, S.; Lee, S.; Lambrigtsen, B.; Chen, L.

    2006-12-01

    Given the importance of atmospheric conditions over the Arctic and Antarctica to the global climate system, hydrological cycles, and cryopspheric dynamics, and the poor coverage of traditional data over these region, AIRS data will play a significant role in filling the information gaps. In this study, we examine the quality of AIRS total atmospheric precipitable water (PWV) and explore its potential applications over the Antarctica and Arctic. For Antarctica, both Level II matching files and Level III gridded products of AIRS are compared with radiosonde records at Dome C and ECMWF's analysis products during December 10, 2003 to January 26, 2004. Results will testify to the quality of AIRS moisture data over glacial surfaces. For the Arctic region, AIRS level III data are used to compare with AMSR-E data and ECMWF analysis product during September of 2004. Results will reveal the quality of AIRS data over high-latitude water, sea ice, and land surfaces. The potential of AIRS data to improve model simulation will be discussed.

  10. Magnotospheric imaging of high latitude ion outflows

    Directory of Open Access Journals (Sweden)

    D. E. Garrido

    Full Text Available High latitude ion outflows mostly consist of upward streaming O+ and He+ emanating from the ionosphere. At heights above 1000 km, these flows consist of cold and hot components which resonantly scatter solar extreme ultraviolet (EUV light, however, the ion populations respond differently to Doppler shifting resulting from the large relative velocities between the ions and the Sun. The possibility of optical detection of the Doppler effect on the scattering rate will be discussed for the O+ (83.4 nm ions. We have contrasted the EUV solar resonance images of these outflows by simulations of the 30.4 nm He+ and 83.4 nm O+ emissions for both quiet and disturbed geomagnetic conditions. Input data for the 1000 km level has been obtained from the EICS instrument aboard the Dynamics Explorer satellite. Our results show emission rates of 50 and 56 milli-Rayleighs at 30.4 nm for quiet and disturbed conditions and 65 and 75 milli-Rayleighs at 83.4 nm for quiet and disturbed conditions, respectively, obtained for a polar orbiting satellite and viewing radially outward. We also find that an imager at an equatorial distance of 9 RE or more is in a favourable position for detecting ion outflows, particularly when the plasmapause is depressed in latitude. However, an occultation disk is necessary to obscure the bright plasmaspheric emissions.

  11. Testing High Latitude Emission in GRBs

    CERN Document Server

    Genet, F

    2008-01-01

    Most gamma-ray bursts (GRBs) observed by the Swift satellite show an early rapid decay phase (RDP) in their X-ray lightcurve, which is usually a smooth continuation of the prompt gamma-ray emission, strongly suggesting that it is its tail. However, the mechanism behind it is still not clear. The most popular model for this RDP is High Latitude Emission (HLE). While HLE is expected in many models for the prompt GRB emission, such as the popular internal shocks model, there are models in which it is not expected, such as sporadic magnetic reconnection events. Therefore, testing whether the RDP is consistent with HLE can help distinguish between different prompt emission models. We address this question by modeling the prompt emission as the sum of its individual pulses with their HLE tails. Analytic expressions for the observed flux density are obtained for power-law and Band function emission spectra. For internal shocks the observed instantaneous spectrum is very close to the emitted one, and should be well d...

  12. Corotating Interaction Regions at High Latitudes

    Science.gov (United States)

    Kunow, H.; Lee, M. A.; Fisk, L. A.; Forsyth, R. J.; Heber, B.; Horbury, T. S.; Keppler, E.; Kóta, J.; Lou, Y.-Q.; McKibben, R. B.; Paizis, C.; Potgieter, M. S.; Roelof, E. C.; Sanderson, T. R.; Simnett, G. M.; von Steiger, R.; Tsurutani, B. T.; Wimmer-Schweingruber, R. F.; Jokipii, J. R.

    1999-07-01

    Ulysses observed a stable strong CIR from early 1992 through 1994 during its first journey into the southern hemisphere. After the rapid latitude scan in early 1995, Ulysses observed a weaker CIR from early 1996 to mid-1997 in the northern hemisphere as it traveled back to the ecliptic at the orbit of Jupiter. These two CIRs are the observational basis of the investigation into the latitudinal structure of CIRs. The first CIR was caused by an extension of the northern coronal hole into the southern hemisphere during declining solar activity, whereas the second CIR near solar minimum activity was caused by small warps in the streamer belt. The latitudinal structure is described through the presentation of three 26-day periods during the southern CIR. The first at ˜24°S shows the full plasma interaction region including fast and slow wind streams, the compressed shocked flows with embedded stream interface and heliospheric current sheet (HCS), and the forward and reverse shocks with associated accelerated ions and electrons. The second at 40°S exhibits only the reverse shock, accelerated particles, and the 26-day modulation of cosmic rays. The third at 60°S shows only the accelerated particles and modulated cosmic rays. The possible mechanisms for the access of the accelerated particles and the CIR-modulated cosmic rays to high latitudes above the plasma interaction region are presented. They include direct magnetic field connection across latitude due to stochastic field line weaving or to systematic weaving caused by solar differential rotation combined with non-radial expansion of the fast wind. Another possible mechanism is particle diffusion across the average magnetic field, which includes stochastic field line weaving. A constraint on connection to a distant portion of the CIR is energy loss in the solar wind, which is substantial for the relatively slow-moving accelerated ions. Finally, the weaker northern CIR is compared with the southern CIR. It is weak

  13. Vegetation controls on northern high latitude snow-albedo feedback: Observations and CMIP5 model simulations

    OpenAIRE

    Loranty, MM; Berner, LT; Goetz, SJ; Jin, Y.; Randerson, JT

    2014-01-01

    The snow-masking effect of vegetation exerts strong control on albedo in northern high latitude ecosystems. Large-scale changes in the distribution and stature of vegetation in this region will thus have important feedbacks to climate. The snow-albedo feedback is controlled largely by the contrast between snow-covered and snow-free albedo (Δα), which influences predictions of future warming in coupled climate models, despite being poorly constrained at seasonal and century time scales. Here, ...

  14. Arctic winter warming amplified by the thermal inversion and consequent low infrared cooling to space

    NARCIS (Netherlands)

    Bintanja, R.; Graversen, R.G.; Hazeleger, W.

    2011-01-01

    Pronounced warming in the Arctic region, coined Arctic amplification, is an important feature of observed and modelled climate change1, 2. Arctic amplification is generally attributed to the retreat of sea-ice3 and snow, and the associated surface-albedo feedback4, in conjunction with other processe

  15. High-latitude dust in the Earth system

    Science.gov (United States)

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

    2016-06-01

    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.

  16. Simulation studies of high-latitude magnetospheric boundary dynamics

    Institute of Scientific and Technical Information of China (English)

    PU; Zuyin; SHI; Quanqi; XIAO; Chijie; FU; Suiyan; ZHANG; Hu

    2004-01-01

    Magnetic reconnection at the high-latitude magnetopause is studied using 2.5-dimensional Hail-MHD simulation. Concentric flow vortices and magnetic islands appear when both Hall effect and sheared flow are considered. Plasma mixing across the magnetopause occurs in the presence of the flow vortices. Reconnected structure generated in the vicinity of the subsolar point changes its geometry with increasing flow shear while moving to high latitudes. In the presence of flow shear, with the Hail-MHD reconnection a higher reconnection rate than with the traditional MHD is obtained. The out-of-plane components of flow and magnetic field produced by the Hall current are redistributed under the action of the flow shear, which makes the plasma transport across the boundaries more complicated. The simulation results provide some help in understanding the dynamic processes at the high latitude magnetopause.

  17. Multistation measurements of high-latitude ionospheric convection

    Science.gov (United States)

    Heelis, R. A.; Foster, J. C.; Holt, J.; de La Beaujardiere, O.

    1983-12-01

    Satellite and ground-based observations of the ionospheric drift velocity taken during a MITHRAS campaign have been combined to determine instantaneous pictures of the high-latitude convection pattern. These data, taken when the interplanetary magnetic field has a relatively stable southward/away orientation, show the existence of an asymmetric convection pattern under these conditions. A stability in the high latitude convection geometry can also be seen and changes in response to magnetic disturbances are inferred. Changes in the convection pattern as the interplanetary field turns northward possibly provide some information about the nature of the magnetosphere-solar wind interaction.

  18. Multistation measurements of high-latitude ionospheric convection

    Energy Technology Data Exchange (ETDEWEB)

    Heelis, R.A.; Foster, J.C.; de la Beaujardiere, O.; Holt, J.

    1922-12-01

    Satellite and ground-based observations of the ionospheric drift velocity taken during a MITHRAS campaign have been combined to determine instantaneous pictures of the high-latitude convection pattern. These data, taken when the interplanetary magnetic field has a relatively stable southward/away orientation, show the existence of an asymmetric convection pattern under these conditions. A stability in the high latitude convection geometry can also be seen and changes in response to magnetic disturbances are inferred. Changes in the convection pattern as the interplanetary field turns northward possibly provide some information about the nature of the magnetosphere-solar wind interaction.

  19. Climate Effects on High Latitude Daphnia via Food Quality and Thresholds.

    Directory of Open Access Journals (Sweden)

    Anna Przytulska

    Full Text Available Climate change is proceeding rapidly at high northern latitudes and may have a variety of direct and indirect effects on aquatic food webs. One predicted effect is the potential shift in phytoplankton community structure towards increased cyanobacterial abundance. Given that cyanobacteria are known to be a nutritionally poor food source, we hypothesized that such a shift would reduce the efficiency of feeding and growth of northern zooplankton. To test this hypothesis, we first isolated a clone of Daphnia pulex from a permafrost thaw pond in subarctic Québec, and confirmed that it was triploid but otherwise genetically similar to a diploid, reference clone of the same species isolated from a freshwater pond in southern Québec. We used a controlled flow-through system to investigate the direct effect of temperature and indirect effect of subarctic picocyanobacteria (Synechococcus on threshold food concentrations and growth rate of the high latitude clone. We also compared the direct effect of temperature on both Daphnia clones feeding on eukaryotic picoplankton (Nannochloropsis. The high latitude clone had a significantly lower food threshold for growth than the temperate clone at both 18 and 26°C, implying adaptation to lower food availability even under warmer conditions. Polyunsaturated fatty acids were present in the picoeukaryote but not the cyanobacterium, confirming the large difference in food quality. The food threshold for growth of the high latitude Daphnia was 3.7 (18°C to 4.2 (26°C times higher when fed Synechococcus versus Nannochloropsis, and there was also a significant negative effect of increased temperature and cyanobacterial food on zooplankton fatty acid content and composition. The combined effect of temperature and food quality on the performance of the high latitude Daphnia was greater than their effects added separately, further indicating the potentially strong indirect effects of climate warming on aquatic food web

  20. Climate Effects on High Latitude Daphnia via Food Quality and Thresholds

    Science.gov (United States)

    Przytulska, Anna; Bartosiewicz, Maciej; Rautio, Milla; Dufresne, France; Vincent, Warwick F.

    2015-01-01

    Climate change is proceeding rapidly at high northern latitudes and may have a variety of direct and indirect effects on aquatic food webs. One predicted effect is the potential shift in phytoplankton community structure towards increased cyanobacterial abundance. Given that cyanobacteria are known to be a nutritionally poor food source, we hypothesized that such a shift would reduce the efficiency of feeding and growth of northern zooplankton. To test this hypothesis, we first isolated a clone of Daphnia pulex from a permafrost thaw pond in subarctic Québec, and confirmed that it was triploid but otherwise genetically similar to a diploid, reference clone of the same species isolated from a freshwater pond in southern Québec. We used a controlled flow-through system to investigate the direct effect of temperature and indirect effect of subarctic picocyanobacteria (Synechococcus) on threshold food concentrations and growth rate of the high latitude clone. We also compared the direct effect of temperature on both Daphnia clones feeding on eukaryotic picoplankton (Nannochloropsis). The high latitude clone had a significantly lower food threshold for growth than the temperate clone at both 18 and 26°C, implying adaptation to lower food availability even under warmer conditions. Polyunsaturated fatty acids were present in the picoeukaryote but not the cyanobacterium, confirming the large difference in food quality. The food threshold for growth of the high latitude Daphnia was 3.7 (18°C) to 4.2 (26°C) times higher when fed Synechococcus versus Nannochloropsis, and there was also a significant negative effect of increased temperature and cyanobacterial food on zooplankton fatty acid content and composition. The combined effect of temperature and food quality on the performance of the high latitude Daphnia was greater than their effects added separately, further indicating the potentially strong indirect effects of climate warming on aquatic food web processes. PMID

  1. Greater aerial moisture transport distances with warming amplify interbasin salinity contrasts

    Science.gov (United States)

    Singh, Hansi K. A.; Donohoe, Aaron; Bitz, Cecilia M.; Nusbaumer, Jesse; Noone, David C.

    2016-08-01

    The distance atmospheric moisture travels is fundamental to Earth's hydrologic cycle, governing how much evaporation is exported versus precipitated locally. The present-day tropical Atlantic is one region that exports much locally evaporated moisture away, leading to more saline surface waters in the Atlantic compared to the Indo-Pacific at similar latitudes. Here we use a state-of-the-art global climate model equipped with numerical water tracers to show that over half of the atmospheric freshwater exported from the Atlantic originates as evaporation in the northern Atlantic subtropics, primarily between 10°N and 20°N, and is transported across Central America via prevailing easterlies into the equatorial Pacific. We find enhanced moisture export from the Atlantic to Pacific with warming is due to greater distances between moisture source and sink regions, which increases moisture export from the Atlantic at the expense of local precipitation. Distance traveled increases due to longer moisture residence times, not simply Clausius-Clapeyron scaling.

  2. Soil-frost-enabled soil-moisture-precipitation feedback over northern high latitudes

    Science.gov (United States)

    Hagemann, Stefan; Blome, Tanja; Ekici, Altug; Beer, Christian

    2016-07-01

    Permafrost or perennially frozen ground is an important part of the terrestrial cryosphere; roughly one quarter of Earth's land surface is underlain by permafrost. The currently observed global warming is most pronounced in the Arctic region and is projected to persist during the coming decades due to anthropogenic CO2 input. This warming will certainly have effects on the ecosystems of the vast permafrost areas of the high northern latitudes. The quantification of such effects, however, is still an open question. This is partly due to the complexity of the system, including several feedback mechanisms between land and atmosphere. In this study we contribute to increasing our understanding of such land-atmosphere interactions using an Earth system model (ESM) which includes a representation of cold-region physical soil processes, especially the effects of freezing and thawing of soil water on thermal and hydrological states and processes. The coupled atmosphere-land models of the ESM of the Max Planck Institute for Meteorology, MPI-ESM, have been driven by prescribed observed SST and sea ice in an AMIP2-type setup with and without newly implemented cold-region soil processes. Results show a large improvement in the simulated discharge. On the one hand this is related to an improved snowmelt peak of runoff due to frozen soil in spring. On the other hand a subsequent reduction in soil moisture enables a positive feedback to precipitation over the high latitudes, which reduces the model's wet biases in precipitation and evapotranspiration during the summer. This is noteworthy as soil-moisture-atmosphere feedbacks have previously not been the focus of research on the high latitudes. These results point out the importance of high-latitude physical processes at the land surface for regional climate.

  3. Improved soil physics for simulating high latitude permafrost regions by the JSBACH terrestrial ecosystem model

    Directory of Open Access Journals (Sweden)

    A. Ekici

    2013-05-01

    Full Text Available State-of-the-art climate models postulate disproportionately large climate warming in the northern latitudes. Ground and satellite observations indicate recent warming is already altering the environment, evidenced by increasing permafrost temperature, deepening active layers, accelerating glacier melt and increasing river runoff. It is estimated that the circum-arctic regions contain vast amounts of soil organic carbon, whose fate is governed by climate; if temperature continues to rise, thawing of permafrost could release historic carbon initiating a positive climate-carbon cycle feedback. Consequently, projecting the future state of ecosystems in permafrost regions under changing environmental conditions is a major research challenge, but most of the associated processes are not yet adequately represented in current Earth system models. The new version of JSBACH incorporates phenomena specific to high latitudes: freeze/thaw processes, coupling thermal and hydrological processes in a layered soil scheme, defining a multi-layer snow representation and an insulating moss cover. Evaluations using the most comprehensive Arctic datasets show improvements at the site, basin, continental and circum-arctic scales. Such improvements highlight the need to include processes relevant to high latitude systems in order to capture the dynamics, and therefore realistically predict the evolution of this climatically critical biome.

  4. 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

  5. Star Formation in High-Latitude Molecular Clouds

    Science.gov (United States)

    Magnus McGehee, Peregrine

    2015-08-01

    Galactic star formation preferentially occurs within the dense molecular clouds that reside primarily near the disk mid-plane and are thus seen in projection against the Milky Way. A population of molecular clouds are seen at higher Galactic latitude although distance determinations are required in order to identify those that are actually in extraplanar environments.We review the known high-latitude star formation regions (MBM 12, LDN 1642, and HRK 81.4-77.8) and discuss the nature and environment of other high-latitude molecular clouds. Distances to each of these structures are deduced from optical reddening profiles derived from analysis of Sloan Digital Sky Survey photometry. In particular, we examine those molecular clouds found within the complex of intermediate and high velocity HI clouds that span the Northern 2nd Galactic Quadrant: the Draco clouds, the IVC pair at (l+b) = 135+51 and 135+54, and IREC 306.

  6. An energy principle for high-latitude electrodynamics

    Science.gov (United States)

    Barbosa, D. D.

    1984-01-01

    A theoretical model for mid- and high-latitude electric fields and currents is constructed using Fourier analysis methods. A two-dimensional planar ionosphere with an enhanced conductivity auroral belt and field-aligned currents at the edges is employed. The postulate that the electric field and currents adjust self-consistently to minimize the global Joule dissipation rate defines a theoretical relation between the primary and secondary field-aligned currents. This so-called minimal dissipation configuration is examined using several input field-aligned current models, and graphical solutions for the electric field and ionospheric current are shown. A detailed discussion and interpretation of the solutions with relation to diverse observations and high-latitude phenomenology are included.

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

    OpenAIRE

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

    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 population...

  8. High Resolution Mapping of Peatland Hydroperiod at a High-Latitude Swedish Mire

    Directory of Open Access Journals (Sweden)

    Nathan Torbick

    2012-06-01

    Full Text Available Monitoring high latitude wetlands is required to understand feedbacks between terrestrial carbon pools and climate change. Hydrological variability is a key factor driving biogeochemical processes in these ecosystems and effective assessment tools are critical for accurate characterization of surface hydrology, soil moisture, and water table fluctuations. Operational satellite platforms provide opportunities to systematically monitor hydrological variability in high latitude wetlands. The objective of this research application was to integrate high temporal frequency Synthetic Aperture Radar (SAR and high spatial resolution Light Detection and Ranging (LiDAR observations to assess hydroperiod at a mire in northern Sweden. Geostatistical and polarimetric (PLR techniques were applied to determine spatial structure of the wetland and imagery at respective scales (0.5 m to 25 m. Variogram, spatial regression, and decomposition approaches characterized the sensitivity of the two platforms (SAR and LiDAR to wetland hydrogeomorphology, scattering mechanisms, and data interrelationships. A Classification and Regression Tree (CART, based on random forest, fused multi-mode (fine-beam single, dual, quad pol Phased Array L-band Synthetic Aperture Radar (PALSAR and LiDAR-derived elevation to effectively map hydroperiod attributes at the Swedish mire across an aggregated warm season (May–September, 2006–2010. Image derived estimates of water and peat moisture were sensitive (R2 = 0.86 to field measurements of water table depth (cm. Peat areas that are underlain by permafrost were observed as areas with fluctuating soil moisture and water table changes.

  9. Electric fields and electrostatic potentials in the high latitude ionosphere

    Science.gov (United States)

    Banks, P. M.; Saint Maurice, J.-P.; Heelis, R. A.; Hanson, W. B.

    1981-01-01

    Recent interpretive studies of electric field-driven ionospheric plasma convection data from the AE-C satellite are described, where the instruments employed include an ion drift meter and an ion-retarding potential analyzer. Electrostatic potential curves are derived from ion drift velocity measurements for high-latitude segments of the satellite's orbit. The potential curves are shown to be useful in determining the character of the global electrostatic potential pattern, with emphasis on the separation of convective cells. Results are given for six orbits, with attention to the mid-day auroral region.

  10. Small-scale characteristics of extremely high latitude aurora

    Directory of Open Access Journals (Sweden)

    J. A. Cumnock

    2009-09-01

    Full Text Available We examine 14 cases of an interesting type of extremely high latitude aurora as identified in the precipitating particles measured by the DMSP F13 satellite. In particular we investigate structures within large-scale arcs for which the particle signatures are made up of a group of multiple distinct thin arcs. These cases are chosen without regard to IMF orientation and are part of a group of 87 events where DMSP F13 SSJ/4 measures emissions which occur near the noon-midnight meridian and are spatially separated from both the dawnside and duskside auroral ovals by wide regions with precipitating particles typical of the polar cap. For 73 of these events the high-latitude aurora consists of a continuous region of precipitating particles. We focus on the remaining 14 of these events where the particle signatures show multiple distinct thin arcs. These events occur during northward or weakly southward IMF conditions and follow a change in IMF By. Correlations are seen between the field-aligned currents and plasma flows associated with the arcs, implying local closure of the FACs. Strong correlations are seen only in the sunlit hemisphere. The convection associated with the multiple thin arcs is localized and has little influence on the large-scale convection. This also implies that the sunward flow along the arcs is unrelated to the overall ionospheric convection.

  11. Statistics of ionospheric scintillation occurrence over European high latitudes

    Science.gov (United States)

    Sreeja, V.; Aquino, M.

    2014-12-01

    Rapid fluctuation in the amplitude and phase of transionospheric radio signals caused by small scale ionospheric plasma density irregularities is known as scintillation. Over the high latitudes, irregularities causing scintillation are associated with large scale plasma structures and scintillation occurrence is mainly enhanced during geomagnetic storms. This paper presents a statistical analysis of scintillation occurrence on GPS L1C/A signal at a high latitude station located in Bronnoysund (geographic latitude 65.5°N, geographic longitude 12.2°E; corrected geomagnetic (CGM) latitude 62.77°N), Norway, during the periods around the peaks of solar cycles 23 (2002-2003) and 24 (2011-2013). The analysis revealed that the scintillation occurrence at Bronnoysund during both the solar maximum periods maximises close to the midnight magnetic local time (MLT) sector. A higher occurrence of scintillation is observed on geomagnetically active days during both the solar maximum periods. The seasonal pattern of scintillation occurrence indicated peaks during the summer and equinoctial months. A comparison with the interplanetary magnetic field (IMF) components By and Bz showed an association of scintillation occurrence with the southward IMF Bz conditions.

  12. Response of thermosphere density to high-latitude forcing

    Science.gov (United States)

    Yamazaki, Y.; Kosch, M. J.; Vickers, H.; Sutton, E. K.; Ogawa, Y.

    2014-12-01

    Solar wind-magnetospheric disturbances cause enhancements in the energy input to the high-latitude upper atmosphere through particle precipitation and Joule heating. As the upper atmosphere is heated and expanded during geomagnetically disturbed periods, the neutral density in the thermosphere increases at a fixed altitude. Conversely, the thermosphere contracts during the recovery phase of the disturbance, resulting in a decrease of the density. The main objectives of this study are (1) to determine the morphology of the global thermospheric density response to high-latitude forcing, and (2) to determine the recovery speed of the thermosphere density after geomagnetic disturbances. For (1), we use thermospheric density data measured by the Challenging Minisatellite Payload (CHAMP) satellite during 2000-2010. It is demonstrated that the density enhancement during disturbed periods occurs first in the dayside cusp region, and the density at other regions slowly follows it. The reverse process is observed when geomagnetic activity ceases; the density enhancement in the cusp region fades away first, then the global density slowly goes back to the quiet level. For (2), we analyze EISCAT Svalbard radar and Tromso UHF radar data to estimate thermospheric densities during the recovery phase of geomagnetic disturbances. We attempt to determine the time constant for the density recovery both inside and outside the cusp region.

  13. 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

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

    International Nuclear Information System (INIS)

    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

  15. 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.

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

    International Nuclear Information System (INIS)

    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

  17. Climatology of GNSS ionospheric scintillation at high latitudes

    Science.gov (United States)

    Spogli, L.; Alfonsi, L.; de Franceschi, G.; Romano, V.; Aquino, M.; Dodson, A.; Mitchell, C. N.

    2009-12-01

    Under perturbed conditions caused by intense solar wind magnetosphere coupling, the ionosphere may become highly turbulent and irregularities, typically enhancements or depletions of the electron density embedded in the ambient ionosphere, can form. Such irregularities cause diffraction effects, mainly due to the random fluctuations of the refractive index of the ionosphere, on the satellites signals passing through them and consequent perturbations may cause GNSS navigation errors and outages, abruptly corrupting its performance. Due to the morphology of the geomagnetic field, whose lines are almost vertical at high latitude, polar areas are characterized by the presence of significant ionospheric irregularities having scale sizes ranging from hundreds of kilometers down to a few centimeters and with highly dynamic structures. The understanding of the effect of such phenomena is important, not only in preparation for the next solar cycle (24), whose maximum is expected in 2012, but also for a deeper comprehension of the dynamics of the high-latitude ionosphere. We analyze the fluctuations in the carrier frequency of the radio waves received on the ground, commonly referred to as ionospheric amplitude and phase scintillations, to investigate the physical processes causing them. The phase scintillations on GNSS signals are likely caused by ionospheric irregularities of scale size of hundreds of meters to few kilometers. The amplitude scintillations on GNSS signals are caused by ionospheric irregularities of scale size smaller than the Fresnel radius, which is of the order of hundreds of meters for GNSS signals, typically embedded into the patches. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Institute of Engineering Surveying and Space Geodesy (IESSG) of the University of Nottingham manage the same kind of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers over the European high and mid latitude regions and over Antarctica. The

  18. Use of radio occultation to probe the high latitude ionosphere

    Directory of Open Access Journals (Sweden)

    A. J. Mannucci

    2015-02-01

    Full Text Available We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomagnetic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere-ionosphere because of the important role of conductivity on high latitude Joule heating. Two high-speed stream (HSS and two coronal mass ejection (CME storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At nighttime local times, the number of profiles with maximum electron densities in the E layer (below 200 km altitude is well correlated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are captured by the COSMIC profiles. These "E layer dominant ionosphere" (ELDI profiles have geomagnetic latitudes that are consistent with climatological models of the auroral location. For the two HSS storms, that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the southern, less sunlit, hemisphere. Stronger aurora and precipitation have been observed before in winter hemispheres, but the degree of asymmetry deserves further study. For the two CME storms, occurring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm's main phase but continuing for several days into the recovery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50° magnetic latitude for signatures of precipitation in the E region. For nine days during the July 2012 period, we find a signature of precipitation occurs nearly

  19. A Pan-Arctic Assessment of High-Latitude Lake Change ~25 Years Apart

    Science.gov (United States)

    Sheng, Y.; Smith, L. C.; Li, J.; Lyons, E. A.; Wang, J.

    2011-12-01

    The Arctic and Sub-Arctic regions are the home to the world's largest quantity of terrestrial lakes. These lakes play a preeminent role in the global water cycle and balance, are sensitive to global warming, and are vital for human and animal water supply. However, they are poorly observed, and a uniform lake inventory is unavailable at the pan-Arctic scale. Though there have been studies of Arctic lake dynamics at local scales, the general picture of Arctic lake change stays unclear. A systematic regional-scale assessment of Arctic lake change in the past ~30 years is crucial for us to address "How have Arctic lakes responded to global warming?" The presentation reports a systematic effort of high-latitude (45N and north) lake inventory using recently available high-resolution satellite imagery. Since Arctic lakes are abundant in small-size classes and their seasonality varies from region to region, pan-Arctic lake mapping requires the use of thousands of cloud-free Landsat images acquired in lake-stable seasons. Nearly eight million lakes have been mapped in various landscapes of the pan-Arctic using automated lake identification algorithms with high replicability. Lake-abundant regions are selected using a systematic sampling strategy to detect decadal lake change using the mid-1970s and circa-2000 Landsat imagery. Spatial patterns of the observed lake dynamics are analyzed at regional scales and the relationship between lake abundance and size distribution is investigated.

  20. 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...... 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...

  1. Birkeland current effects on high-latitude groundmagnetic field perturbations

    CERN Document Server

    Laundal, K M; Lehtinen, N; Gjerloev, J W; Østgaard, N; Tenfjord, P; Reistad, J P; Snekvik, K; Milan, S E; Ohtani, S; Anderson, B J

    2016-01-01

    Magnetic perturbations on ground at high latitudes are directly associated only with the divergence-free component of the height-integrated horizontal ionospheric current, $\\textbf{J}_{\\perp,df}$. Here we show how $\\textbf{J}_{\\perp,df}$ can be expressed as the total horizontal current $\\textbf{J}_\\perp$ minus its curl-free component, the latter being completely determined by the global Birkeland current pattern. Thus in regions where $\\textbf{J}_\\perp = 0$, the global Birkeland current distribution alone determines the local magnetic perturbation. We show with observations from ground and space that in the polar cap, the ground magnetic field perturbations tend to align with the Birkeland current contribution in darkness but not in sunlight. We also show that in sunlight, the magnetic perturbations are typically such that the equivalent overhead current is anti-parallel to the convection, indicating that the Hall current system dominates. Thus the ground magnetic field in the polar cap relates to different c...

  2. A Study of Steady Magnetospheric Convection Using High Latitude Magnetometers

    Science.gov (United States)

    de Silva, J. T.; Erickson, K. N.; Engebretson, M. J.; Murr, D. L.; Hughes, W. J.

    2001-05-01

    Magnetometer data from the MACCS and CANOPUS arrays in northern North America have been analyzed during two of the intervals of steady magnetospheric convection identified by the GEM community, January 29-30 and February 3-4, 1998. These intervals were characterized by extended periods of southward interplanetary magnetic field (negative IMF Bz), and by the absence of substorms. The patterns of ionospheric current flow on the dayside were found to be in general agreement with the disturbance current system, SD, originally described by Silsbee and Vestine [1942]. This indicates that during extended periods of southward IMF the convection on the dayside is the same whether or not there are substorms. When plasma flow patterns measured by the SuperDARN auroral radar network were available for comparison, these patterns agreed with the patterns inferred from magnetometers. Further study will investigate convection patterns on the nightside, and a similar study of convection for the southern high latitude region will be conducted using data from Antarctic stations.

  3. The role of superthermal electrons in high latitude ionospheric outflows

    Science.gov (United States)

    Glocer, A.; Khazanov, G. V.; Liemohn, M. W.; Toth, G.; Gombosi, T. I.

    2014-12-01

    It is well accepted that the ionosphere is a critical source of plasma for the magnetosphere, providing O+, H+, and He+ which can have wide ranging consequences for the space environment system. Changing ion composition affects magnetic reconnection in the magnetosphere, the ring current, and the wave environment which is important for high energy radiation belt electrons. Of the myriad of mechanisms that are important in determining the ionospheric outflow solution at high latitudes, we focus on the role of superthermal electron populations. It has been demonstrated in multiple studies that even small concentrations of superthermal electrons can have a dramatic effect on the outflow solution. In this presentation, we present simulation results using our Polar Wind Outflow Model (PWOM) and our SuperThermal Electron Transport (STET) code. We describe recent results on superthermal electrons role in defining the quiet time solar wind solution with comparisons to observations. We also discuss preliminary results that combine the PWOM and STET codes for a more comprehensive treatment of the impact of superthermal electrons.

  4. Environmental conditions for alternative tree cover states in high latitudes

    Science.gov (United States)

    Abis, Beniamino; Brovkin, Victor

    2016-04-01

    Previous analysis of the vegetation cover from remote sensing revealed the existence of three alternative modes in the frequency distribution of boreal tree cover: a sparsely vegetated treeless state, a savanna-like state, and a forest state. Identifying which are the regions subject to multimodality, and assessing which are the main factors underlying their existence, is important to project future change of natural vegetation cover and its effect on climate. We study the impact on the forest cover fraction distribution of seven globally-observed environmental factors: mean annual rainfall, mean minimum temperature, growing degree days above 0, permafrost distribution, soil moisture, wildfire occurrence frequency, and thawing depth. Through the use of generalised additive models, regression trees, and conditional histograms, we find that the main factors determining the forest distribution in high latitudes are: permafrost distribution, mean annual rainfall, mean minimum temperature, soil moisture, and wildfire frequency. Additionally, we find differences between regions within the boreal area, such as Eurasia, Eastern North America, and Western North America. Furthermore, using a classification based on these factors, we show the existence and location of alternative tree cover states under the same climate conditions in the boreal region. These are areas of potential interest for a more detailed analysis of land-atmosphere interactions.

  5. Tracking strategy for photovoltaic solar systems in high latitudes

    International Nuclear Information System (INIS)

    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

  6. Distance to the northern high-latitude HI shells

    CERN Document Server

    Puspitarini, Lucky

    2012-01-01

    A detailed 3D distribution of interstellar matter in the solar neighborhood is increasingly necessary. As part of a 3D mapping program, we aim at assigning a precise distance to the high-latitude HI gas in particular the northern part (b \\geq 55^{circ}) of the shell associated with the conspicuous radio continuum Loop I. This shell is thought to be the expanding boundary of an interstellar bubble inflated and recently reheated by the strong stellar winds of the nearby Scorpius-Centaurus OB. We recorded high-resolution spectra of 30 A-type target stars located at various distances in the direction of the northern part of Loop I. Interstellar NaI 5889-5895 and CaII K-H 3934-3968 {\\AA} are modeled and compared with the HI emission spectra from the LAB Survey. About two-thirds of our stellar spectra possess narrow interstellar lines. Narrow lines are located at the velocity of the main, low-velocity Loop 1 HI shell ([-6,+1] km/s in the LSR). Using Hipparcos distances to the target stars, we show that the closest ...

  7. Structure of High Latitude Currents in Magnetosphere-Ionosphere Models

    Science.gov (United States)

    Wiltberger, M.; Rigler, E. J.; Merkin, V.; Lyon, J. G.

    2016-07-01

    Using three resolutions of the Lyon-Fedder-Mobarry global magnetosphere-ionosphere model (LFM) and the Weimer 2005 empirical model we examine the structure of the high latitude field-aligned current patterns. Each resolution was run for the entire Whole Heliosphere Interval which contained two high speed solar wind streams and modest interplanetary magnetic field strengths. Average states of the field-aligned current (FAC) patterns for 8 interplanetary magnetic field clock angle directions are computed using data from these runs. Generally speaking the patterns obtained agree well with results obtained from the Weimer 2005 computing using the solar wind and IMF conditions that correspond to each bin. As the simulation resolution increases the currents become more intense and narrow. A machine learning analysis of the FAC patterns shows that the ratio of Region 1 (R1) to Region 2 (R2) currents decreases as the simulation resolution increases. This brings the simulation results into better agreement with observational predictions and the Weimer 2005 model results. The increase in R2 current strengths also results in the cross polar cap potential (CPCP) pattern being concentrated in higher latitudes. Current-voltage relationships between the R1 and CPCP are quite similar at the higher resolution indicating the simulation is converging on a common solution. We conclude that LFM simulations are capable of reproducing the statistical features of FAC patterns.

  8. Biosphere-atmosphere interactions in high-latitude regions

    Science.gov (United States)

    Teufel, B. S.; Sushama, L.

    2015-12-01

    The impact of interactive vegetation phenology on land-atmosphere interactions in high-latitude regions is assessed by comparing two pan-arctic simulations of the fifth generation Canadian Regional Climate Model (CRCM5) - one with interactive phenology and the other with prescribed phenology, both driven by ECMWF reanalysis data. Both simulations include soil organic matter and use a deep soil configuration for better representation of permafrost. Interactive phenology is represented in CRCM5 by means of the Canadian Terrestrial Ecosystem Model (CTEM), which is coupled to the Canadian Land Surface Scheme (CLASS). Previous offline simulations of CTEM coupled to CLASS, driven by reanalysis data, show that these models have significant skill in simulating carbon pools and fluxes, as well as permafrost extent and active layer thickness. The performance of the CRCM5 simulations is first assessed by comparing simulated fields, e.g. 2m temperature, precipitation, snow water equivalent, leaf area index, primary productivity, soil carbon and permafrost, to observation-based datasets. The impact of interactive phenology on the simulated land surface and climate is then assessed by focusing on the biophysical feedbacks. The differences in the representation of interannual variability are also analyzed in order to quantify the added value of interactive phenology.

  9. High-latitude circulation in giant planet magnetospheres

    Science.gov (United States)

    Southwood, D. J.; Chané, E.

    2016-06-01

    We follow-up the proposal by Cowley et al. (2004) that the plasma circulation in the magnetospheres of the giant planets is a combination of two cycles or circulation systems. The Vasyliunas cycle transports heavy material ionized deep within the magnetosphere eventually to loss in the magnetotail. The second cycle is driven by magnetic reconnection between the planetary and the solar wind magnetic fields (the Dungey cycle) and is found on flux tubes poleward of those of the Vasyliunas cycle. We examine features of the Dungey system, particularly what occurs out of the equatorial plane. The Dungey cycle requires reconnection on the dayside, and we suggest that at the giant planets the dayside reconnection occurs preferentially in the morning sector. Second, we suggest that most of the solar wind material that enters through reconnection on to open flux tubes on the dayside never gets trapped on closed field lines but makes less than one circuit of the planet and exits down tail. In its passage to the nightside, the streaming ex-solar wind material is accelerated centrifugally by the planetary rotation primarily along the field; thus, in the tail it will appear very like a planetary wind. The escaping wind will be found on the edges of the tail plasma sheet, and reports of light ion streams in the tail are likely due to this source. The paper concludes with a discussion of high-latitude circulation in the absence of reconnection between the solar wind and planetary field.

  10. Distance to northern high-latitude HI shells

    Science.gov (United States)

    Puspitarini, L.; Lallement, R.

    2012-09-01

    Context. A detailed three-dimensional (3D) distribution of interstellar matter in the solar neighborhood is increasingly necessary. It would allow a more realistic computation of photons and cosmic rays propagation, which is of prime importance for microwave and gamma-ray background emission interpretation, as well as a better understanding of the chain of phenomena that gave rise to the main local structures. Aims: As part of a 3D mapping program, we aim at assigning a precise distance to the high-latitude HI gas, in particular the northern part (b ≥ 55°) of the shell associated with the conspicuous radio continuum Loop I. This shell is thought to be the expanding boundary of an interstellar bubble inflated and recently reheated by the strong stellar winds of the nearby Scorpius-Centaurus OB associations. Methods: We recorded high-resolution spectra of 30 A-type target stars located at various distances in the direction of the northern part of Loop I. Interstellar neutral sodium and singly ionized calcium absorptions (NaI 5889-5895 and CaII K-H 3934-3968 Å) are modeled and compared with the HI emission spectra from the LAB Survey. Results: About two-thirds of our stellar spectra possess narrow interstellar lines, while the remaining spectra show no absorption at all. Narrow lines are located at the velocity of the main, low-velocity Loop 1 HI shell ([-6, +1] km s-1 in the LSR). Using Hipparcos distances to the target stars, we show that the closest boundary of the b ≥ + 70° part of this low-velocity Loop I arch is located at of 98 ± 6 pc. The corresponding interval for the lower-latitude part (55 ≤ b ≤ 70°) is 95-157 pc. However, since the two structures are apparently connected, the lower limit is more likely. At variance with this shell, the second HI structure (b ≥ +85°), which is characterized by LSR Doppler velocities centered at -30 km s-1, is NOT detected in any of the optical spectra. It is located beyond 200 parsecs or totally depleted in

  11. The impact of high latitudes on the optical design of solar systems

    OpenAIRE

    Rönnelid, Mats; Karlsson, Björn; Gordon, J. M.

    1996-01-01

    Irradiation distribution functions based on the yearly collectible energy have been derived for two locations; Sydney, Australia which represents a mid-latitude site and Stockholm, Sweden, which represents a high latitude site. The strong skewing of collectible energy toward summer solstice at high latitudes dictates optimal collector tilt angles considerably below the polar mount. The lack of winter radiation at high latitudes indicates that the optimal acceptance angle for a stationary EW-a...

  12. Two dimensional hydrodynamic modeling of a high latitude braided river

    Science.gov (United States)

    Humphries, E.; Pavelsky, T.; Bates, P. D.

    2014-12-01

    Rivers are a fundamental resource to physical, ecologic and human systems, yet quantification of river flow in high-latitude environments remains limited due to the prevalence of complex morphologies, remote locations and sparse in situ monitoring equipment. Advances in hydrodynamic modeling and remote sensing technology allow us to address questions such as: How well can two-dimensional models simulate a flood wave in a highly 3-dimensional braided river environment, and how does the structure of such a flood wave differ from flow down a similar-sized single-channel river? Here, we use the raster-based hydrodynamic model LISFLOOD-FP to simulate flood waves, discharge, water surface height, and velocity measurements over a ~70 km reach of the Tanana River in Alaska. In order to use LISFLOOD-FP a digital elevation model (DEM) fused with detailed bathymetric data is required. During summer 2013, we surveyed 220,000 bathymetric points along the study reach using an echo sounder system connected to a high-precision GPS unit. The measurements are interpolated to a smooth bathymetric surface, using Topo to Raster interpolation, and combined with an existing five meter DEM (Alaska IfSAR) to create a seamless river terrain model. Flood waves are simulated using varying complexities in model solvers, then compared to gauge records and water logger data to assess major sources of model uncertainty. Velocity and flow direction maps are also assessed and quantified for detailed analysis of braided channel flow. The most accurate model output occurs with using the full two-dimensional model structure, and major inaccuracies appear to be related to DEM quality and roughness values. Future work will intercompare model outputs with extensive ground measurements and new data from AirSWOT, an airborne analog for the Surface Water and Ocean Topography (SWOT) mission, which aims to provide high-resolution measurements of terrestrial and ocean water surface elevations globally.

  13. On the Frozen Soil Scheme for High Latitude Regions

    Science.gov (United States)

    Ganji, A.; Sushama, L.

    2014-12-01

    Regional and global climate model simulated streamflows for high-latitude regions show systematic biases, particularly in the timing and magnitude of spring peak flows. Though these biases could be related to the snow water equivalent and spring temperature biases in models, a good part of these biases is due to the unaccounted effects of non-uniform infiltration capacity of the frozen ground and other related processes. In this paper, the frozen scheme in the Canadian Land Surface Scheme (CLASS), which is used in the Canadian regional and global climate models, is modified to include fractional permeable area, supercooled liquid water and a new formulation for hydraulic conductivity. Interflow is also included in these experiments presented in this study to better explain the steamflows after snow melt season. The impact of these modifications on the regional hydrology, particularly streamflow, is assessed by comparing three simulations, performed with the original and two modified versions of CLASS, driven by atmospheric forcing data from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (ERA-Interim), for the 1990-2001 period, over a northeast Canadian domain. The two modified versions of CLASS differ in the soil hydraulic conductivity and matric potential formulations, with one version being based on formulations from a previous study and the other one is newly proposed. Results suggest statistically significant decreases in infiltration for the simulation with the new hydraulic conductivity and matric potential formulations and fractional permeable area concept, compared to the original version of CLASS, which is also reflected in the increased spring surface runoff and streamflows in this simulation with modified CLASS, over most of the study domain. The simulated spring peaks and their timing in this simulation is also in better agreement to those observed.

  14. Seymour Island/Marambio Drilling Project: Drilling 40Ma (Campanian to Eocene) of high latitude Southern Hemisphere climate history.

    Science.gov (United States)

    Viereck-Gotte, Lothar; Francis, Jane E.; Vaughan, Alan P. M.; Mohr, Barbara A. R.; Marenssi, Sergio A.; Pekar, Stephen F.

    2010-05-01

    The aim of this project is to core a key geological section in the Antarctic Peninsula region. The James Ross Basin, east of the Antarctic Peninsula, contains the best high-latitude section in the world that spans more than 40 million years of geological history from the mid-Cretaceous to the mid-Cenozoic (~80-34Ma). More than 6500m of marine and estuarine sediments were deposited during the filling of the James Ross back-arc basin. The sedimentary succession is extremely fossiliferous, yielding diverse invertebrate, vertebrate and plant fossil assemblages, allowing detailed reconstructions and integration of both terrestrial and marine systems. The sequence also contains a key global reference section for the Cretaceous-Palaeocene extinction event at high latitudes. The sequence contains key intervals that provide details about past polar climates: Mid-Late Cretaceous Thermal Maximum (~80Ma) when tropical floras grew at ~65°S and greenhouse temperatures reached their peak across the globe; a possible phase of high-latitude glaciation within greenhouse times during the latest Cretaceous; the Cretaceous-Palaeocene extinction event at 65Ma; the Palaeocene-Eocene Thermal Maximum episode of rapid global warming at 55Ma (possibly an unconformity in Seymour Island but this can be better established in a drill core); early Eocene hothouse climates; a cooling phase during the Eocene, and the first signs of global cooling in the latest Eocene. Although the sedimentary sequence is reasonably well known from surface outcrop and a stratigraphy has been established, the unconsolidated and weathered nature of the outcrop prohibits high resolution studies. Drill cores will provide more consolidated sediments that can be logged and sampled at high resolution and provide an extremely detailed picture of environmental and climate evolution through this transition from greenhouse to icehouse climates. Three drill cores are planned in this time interval using a land-based rig with

  15. Early Eocene hyperthermals record orbitally controlled changes in high latitude climates

    Science.gov (United States)

    Galeotti, S.; DeConto, R. M.; Lanci, L.; Pagani, M.; Rohl, U.; Westerhold, T.; Zachos, J. C.

    2012-04-01

    The Late Paleocene to Early Eocene records a succession of short-term (104 yr) negative carbon isotope excursions (CIEs) in marine carbonates and organic carbon. Available data indicate that at least three of these episodes, including the Paleocene Eocene Thermal Maximum (PETM) at ca. 55.5, the Eocene Thermal Maximum (ETM)2 at ca. 53.5 Ma and the ETM3 at ca. 52 Ma, were associated with rapid warming, and widespread marine carbonate dissolution forced by shoaling of the carbonate lysocline and lowering of the carbonate saturation state. Large temperature raises associated with decreased δ13C values in both terrestrial and oceanic records and concomitant acidification of oceanic waters implies that hyperthermals were caused by the addition of massive amounts of 13C-depleted greenhouse gases (CH4 and/or CO-2) into the atmosphere and subsequent sequestration by oceanic waters. Cyclostratigraphic analyses of marine sequences provided evidence that CIEs and associated carbonate dissolution episodes were linked to orbital changes in insolation. Here we show grounds that Early Eocene hyperthermals are part of a continuum of δ13C anomaly and carbonate dissolution episodes and are triggered by long-term orbitally-controlled changes in local climates at high latitudes.

  16. 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.

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

    Directory of Open Access Journals (Sweden)

    S. Haapanala

    2009-06-01

    Full Text Available Emissions of volatile organic compounds (VOCs from mountain birches were measured in Abisko, northern Sweden. Mountain birches make up majority of the tree biomass in Scandinavian high latitudes, area subject to significant climate warming. The measurements were carried out in two growing seasons. The emissions of a branch from four individual trees 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 sesquiterpene emission changed dramatically between the years. For example, the average α-farnesene emission in 2006 was almost 2000 ng gdw−1 h−1 while in 2007 the emission of α-farnesene was negligible. 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 several years.

  18. High Resolution Mapping of Peatland Hydroperiod at a High-Latitude Swedish Mire

    OpenAIRE

    Nathan Torbick; Andreas Persson; David Olefeldt; Steve Frolking; William Salas; Stephen Hagen; Patrick Crill; Changsheng Li

    2012-01-01

    Monitoring high latitude wetlands is required to understand feedbacks between terrestrial carbon pools and climate change. Hydrological variability is a key factor driving biogeochemical processes in these ecosystems and effective assessment tools are critical for accurate characterization of surface hydrology, soil moisture, and water table fluctuations. Operational satellite platforms provide opportunities to systematically monitor hydrological variability in high latitude wetlands. The obj...

  19. Uncertainty analysis of vegetation distribution in the northern high latitudes during the 21st century with a dynamic vegetation model.

    Science.gov (United States)

    Jiang, Yueyang; Zhuang, Qianlai; Schaphoff, Sibyll; Sitch, Stephen; Sokolov, Andrei; Kicklighter, David; Melillo, Jerry

    2012-03-01

    This study aims to assess how high-latitude vegetation may respond under various climate scenarios during the 21st century with a focus on analyzing model parameters induced uncertainty and how this uncertainty compares to the uncertainty induced by various climates. The analysis was based on a set of 10,000 Monte Carlo ensemble Lund-Potsdam-Jena (LPJ) simulations for the northern high latitudes (45(o)N and polewards) for the period 1900-2100. The LPJ Dynamic Global Vegetation Model (LPJ-DGVM) was run under contemporary and future climates from four Special Report Emission Scenarios (SRES), A1FI, A2, B1, and B2, based on the Hadley Centre General Circulation Model (GCM), and six climate scenarios, X901M, X902L, X903H, X904M, X905L, and X906H from the Integrated Global System Model (IGSM) at the Massachusetts Institute of Technology (MIT). In the current dynamic vegetation model, some parameters are more important than others in determining the vegetation distribution. Parameters that control plant carbon uptake and light-use efficiency have the predominant influence on the vegetation distribution of both woody and herbaceous plant functional types. The relative importance of different parameters varies temporally and spatially and is influenced by climate inputs. In addition to climate, these parameters play an important role in determining the vegetation distribution in the region. The parameter-based uncertainties contribute most to the total uncertainty. The current warming conditions lead to a complexity of vegetation responses in the region. Temperate trees will be more sensitive to climate variability, compared with boreal forest trees and C3 perennial grasses. This sensitivity would result in a unanimous northward greenness migration due to anomalous warming in the northern high latitudes. Temporally, boreal needleleaved evergreen plants are projected to decline considerably, and a large portion of C3 perennial grass is projected to disappear by the end of

  20. CO J = 3 -> 2 observations of translucent and high-latitude molecular clouds

    NARCIS (Netherlands)

    Dishoeck, van E.F.; Phillips, T.G.; Black, J.H.; Gredel, R.

    1991-01-01

    Measurements were carried out on the CO J = 3-2 emission line at 345 GHz from a number of translucent and high-latitude molecular clouds, as well as on the J = 2-1 and J = 1-0 lines of both the (C-12)O and (C-13)O. It is shown that the physical conditions in the high-latitude clouds are very similar

  1. Bringing Feedback and Resilience of High-latitude Ecosystems into the Corporate Boardroom

    OpenAIRE

    Whiteman, G; Forbes, B.C.; NiemelÀ, J.; Chapin, F. S.

    2004-01-01

    This paper discusses the role of companies in high-latitude regions, which are conceptualized as socially and economically mediated ecosystems, and identifies a number of important social actors within the business environment. We present three examples of corporate activity at high latitudes and discuss a variety of common threads. Notably, we argue that business theory and practice needs to move beyond a narrow social or economic concept of organizational resilience and embrace the ecologic...

  2. Water vapour variability in the high-latitude upper troposphere - Part 2: Impact of volcanic eruptions

    Science.gov (United States)

    Sioris, Christopher E.; Zou, Jason; McElroy, C. Thomas; Boone, Chris D.; Sheese, Patrick E.; Bernath, Peter F.

    2016-02-01

    The impact of volcanic eruptions on water vapour in the high-latitude upper troposphere is studied using deseasonalized time series based on observations by the Atmospheric Chemistry Experiment (ACE) water vapour sensors, namely MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) and the Fourier Transform Spectrometer (ACE-FTS). The two eruptions with the greatest impact on the high-latitude upper troposphere during the time frame of this satellite-based remote sensing mission are chosen. The Puyehue-Cordón Caulle volcanic eruption in June 2011 was the most explosive in the past 24 years and is shown to be able to account for the observed (50 ± 12) % increase in water vapour in the southern high-latitude upper troposphere in July 2011 after a minor adjustment for the simultaneous influence of the Antarctic oscillation. Eyjafjallajökull erupted in the spring of 2010, increasing water vapour in the upper troposphere at northern high latitudes significantly for a period of ˜ 1 month. These findings imply that extratropical volcanic eruptions in windy environments can lead to significant perturbations to high-latitude upper tropospheric humidity mostly due to entrainment of lower tropospheric moisture by wind-blown plumes. The Puyehue-Cordón Caulle eruption must be taken into account to properly determine the magnitude of the trend in southern high-latitude upper tropospheric water vapour over the last decade.

  3. BVOC ecosystem flux measurements at a high latitude wetland site

    Directory of Open Access Journals (Sweden)

    T. Holst

    2008-12-01

    responses. Long-term measurements of BVOC are still lacking for nearly all ecosystems and only a very few studies about seasonal or even interannual variation of BVOC emissions have been published so far, particularly for northern ecosystems. The results presented here will be useful for testing process understanding obtained in laboratory studies and for model evaluation, improving our understanding of biogeochemical cycles in a region which is likely to be sensitive to climate change and currently undergoes rapid changes due to global warming.

  4. Relative Contributions of Heating and Momentum Forcing to High-Latitude Lower Thermospheric Winds

    Science.gov (United States)

    Kwak, Y. S.; Richmond, A. D.

    2015-12-01

    At high latitudes the thermospheric dynamics are gov­erned by various heat and momentum sources. Recently several modeling studies have been attempt­ed to understand the physical process that control the high-latitude lower thermospheric dynamics. Kwak and Richmond [2007] and Kwak et al. [2007] studied the momentum forcing bal­ance that are mainly responsible for maintaining the high-latitude lower thermospheric wind system by using the National Center for Atmospheric Research Thermo­sphere Ionosphere Electrodynamics General Circulation Model (NCAR TIE-GCM). Kwak and Richmond [2014] analyzed the divergence and vorticity of the high-latitude neutral wind field in the lower thermosphere during the south­ern summertime. In this study, we extend previous works by Kwak and Rich­mond [2007, 2014] and Kwak et al. [2007], which helped to better understand the physical processes maintaining thermospheric dynamics at high latitudes, and here perform a "term analysis of the potential vorticity equation" for the high-latitude neu­tral wind field in the lower thermosphere, on the basis of numerical simulations using the NCAR TIE-GCM. These analyses can provide insight into the relative strength of the heating and the momentum forcing responsible for driving rotational winds at the high-latitude lower thermosphere. The heating is the net heat including the heat transfer by downward molecular and eddy heat conduction, the absorption of solar ultraviolet (UV) and extreme ultraviolet (EUV) ra­diation, auroral heating by particles, Joule dissipation of ionospheric currents, release of chemical energy by the atomic oxygen recombination, and radiative CO2, NO and O infrared emissions. The momentum forcing is associated with the viscous force and the frictional drag force from convecting ions.

  5. Green house gas flux at high latitudes - constraints and susceptibility to a changing climate

    Science.gov (United States)

    Nilsson, M. B.

    2015-12-01

    High latitude boreal forests and peatlands contribute importantly to the land-atmosphere exchange of both carbon dioxide and methane. High latitude biomes are also identified as most vulnerable to changing climate. High latitudes are characterized by a strong seasonality in incoming solar radiation, weather conditions and biogeochemical processes. The strong seasonality in incoming solar radiation, not to change in response to a changing climate, constitute firm constraints on how changes in air temperature, evapotranspiration and precipitation will affect biogeochemical processes underlying the land atmosphere exchange of green house gases. Timing of the soil frost thaw and plant phenology thus constitutes two master controls on how fluxes of both CO2 and CH4 will be affected by weather conditions. In addition also the wintertime conditions importantly affect GHG fluxes both during winter time as well as during the succeeding summer. Examples will primarily be given for peatlands and coniferous forests.

  6. Climate anomalies in the southern high latitudes associated with the Subtropical Dipole Mode

    Institute of Scientific and Technical Information of China (English)

    Liu Na; Liu Lin; Chen Hongxia; Zhang Qinghua; Pan Zengdi

    2004-01-01

    Climate anomalies in the southern high latitude associated with the Subtropical Dipole Mode (SDM) are investigated using a 23-year database consisting of SLP (sea level pressure), surface air temperature (SAT) and sea surface temperature (SST). The analysis depicts, for the first time, the spatial variability in the relationship of the above variables with the Subtropical Dipole Mode Index (SDI). It suggests that the SDM signal exists in the southern high latitudes and the correlation fields exhibit a wavenumber-3 pattern around the circumpolar Southern Ocean. Lead-lag correlation analysis used to the SLP, SAT, and SST anomalies with the SDI time series at the positive and negative correlation extremes shows that the southern-high-latitude climate responses to SDM almost instantaneously proposing the connection is by atmospheric and not by oceanic propagation.

  7. Scaling laws for the spectrum of interchange instabilities in the high-latitude ionosphere

    International Nuclear Information System (INIS)

    The Naval Research Laboratory (NRL) high-latitude ionosphere-magnetosphere mesoscale coupling model has been used to develop constraints on and scaling laws associated with the spectrum of interchange-like instabilities and processes believed to be operating in the high-latitude ionosphere. In this model, current closure in the ionosphere is given by Pedersen currents, while in the magnetosphere, closure is achieved with polarization currents. For Pedersen current-driven interchange-like instabilities with growth rate γ, the author treats the limit ν 0)2)-n/2 he shows that 1 0 is the outer scale wave number. The bounds on the spectral indices as predicted by the approach are shown to be consistent with experimental observations. Applications to mesoscale dynamics, structure, and stability of convecting inhomogeneities and large-scale plasma density structures in the high-latitude ionosphere have been made

  8. Southern high latitude climate anomalies associated with the Indian Ocean dipole mode

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Using a 23-year database consisting of sea level pressure, surface air temperature and sea surface temperature, the authors studied southern high latitude climate anomalies associated with IOD (Indian Ocean Dipole). Correlation analysis of the spatial variability regarding monthly sea level pressure, surface air temperature, and sea surface temperature anomalies with IOD index suggests that IOD signal exists in southern high latitudes. The correlation fields exhibit a wavenumber-3 pattern around the circumpolar Southern Ocean.Lead-lag correlation analysis on the strongest correlation areas with IOD index shows that IOD in the tropical Indian Ocean responses to the southern high latitude climate almost instantaneously. It is proposed in the present paper that this connection is realized through atmospheric propagation rather than through oceanic one.

  9. Water vapour variability in the high-latitude upper troposphere - Part 2: Impact of volcanic emissions

    Science.gov (United States)

    Sioris, C. E.; Zou, J.; McElroy, C. T.; Boone, C. D.; Sheese, P. E.; Bernath, P. F.

    2015-09-01

    The impact of volcanic eruptions on water vapour in the region of the high latitude tropopause is studied using deseasonalized time series based on observations by the Atmospheric Chemistry Experiment (ACE) water vapour sensors, namely MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) and the Fourier Transform Spectrometer (ACE-FTS). The three eruptions with the greatest impact on the high latitude upper troposphere during the time frame of this satellite-based remote sensing mission are chosen. The Puyehue-Cordón Caulle volcanic eruption in June 2011 was the most explosive eruption in the past 24 years and resulted in an observed (50 ± 12) % increase in water vapour in the southern high-latitude upper troposphere in July 2011 that persisted into September 2011. A pair of Northern Hemisphere volcanoes, namely Eyjafjallajökull and Nabro, erupted in 2010 and 2011 respectively, increasing water vapour in the upper troposphere at northern high latitudes significantly for a period of ~ 3 months following each eruption. Both had a volcanic explosivity index of 4. Nabro led to a statistically significant increase of ~ 1 ppm in lower stratospheric (13.5-15.5 km) water vapour at northern high-latitudes (60-90° N) in September 2011, when the brunt of its plume arrived in the Arctic. These findings imply that steam emitted into the high-latitude, upper troposphere during volcanic eruptions must be taken into account to properly determine the magnitude of the trend in water vapour over the last decade.

  10. Examining the Role of Aquatic Vegetation in Methane Production: Examples From a Shallow High Latitude Lake in Abisko, Sweden.

    Science.gov (United States)

    Horruitiner, C. D.; Varner, R. K.; Palace, M. W.; Johnson, J. E.; Wik, M.; Lundgren, D. J.; Sinclair, S. N.; Nicastro, A. J. D.; Crawford, M.

    2015-12-01

    High latitude lakes and ponds are a large source of atmospheric methane. Emissions from lakes are thought to be controlled primarily by temperature and secondarily by the availability of labile organic carbon. Aquatic plants provide insitu carbon sources to lake bottoms and therefore can potentially impact rates of methane production. We studied vegetation and lake sediment characteristics across shallow depths in Inre Harrsjön, a lake located within the Stordalen Mire in the discontinuous permafrost zone in subarctic Sweden. Vegetation surveys using a submerged quadrat with camera were performed in transects across IH to characterize bottom vegetation. Carbon and nitrogen elemental analysis was performed on vegetation samples from both the lake and surrounding mire ecosystem. Sediment cores representing each vegetation type were analyzed for CH4, δ13CH4, and elemental CHNS. In all cores but one, total organic carbon (TOC) is greatest near the surface and decreases downcore. Methane concentrations correlated with TOC indicating insitu methane production. C:N ratios in sediment cores are more reflective of aquatic than terrestrial mire vegetation indicating that organic carbon in the lake sediments is dominated by aquatic sources. δ13CH4 is relatively constant downcore, which indicates little to no methane oxidation. The methane produced in sediments is consistently within the range of hydrogenotrophic methanogenesis via CO2 reduction. We suggest the role of aquatic vegetation in the production of methane in high latitude shallow lakes may be important and will likely have a positive feedback in a warming climate with longer ice-free seasons.

  11. Coupled thermo-geophysical inversion for high-latitude permafrost monitoring

    DEFF Research Database (Denmark)

    Tomaskovicova, Sonia; Paamand, Eskild; Ingeman-Nielsen, Thomas;

    2013-01-01

    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....... 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...

  12. Are the high-latitude torsional oscillations of the sun real

    Science.gov (United States)

    Labonte, B. J.; Howard, R.

    1982-01-01

    A numerical test is made to determine if the high-latitude torsional wave is generated from the low-latitude torsional pattern as a result of reduction procedures. The results indicate that the high-latitude motions are not an artifact of the analysis, but are true solar features. It is also demonstrated that the one-wave-per-hemisphere torsional oscillation does not result from the reduction procedure. These results place the observations in conflict with the predictions of alpha-omega models of the solar cycle.

  13. Permafrost thaw and resulting soil moisture changes regulate projected high-latitude CO2 and CH4 emissions

    International Nuclear Information System (INIS)

    The fate of currently frozen permafrost carbon as high-latitude climate warms remains highly uncertain and existing models give widely varying estimates of the permafrost carbon-climate feedback. This uncertainty is due to many factors, including the role that permafrost thaw-induced transitions in soil hydrologic conditions will have on organic matter decomposition rates and the proportion of aerobic to anaerobic respiration. Large-scale permafrost thaw, as predicted by the Community Land Model (CLM) under an unmitigated greenhouse gas emissions scenario, results in significant soil drying due to increased drainage following permafrost thaw, even though permafrost domain water inputs are projected to rise (net precipitation minus evaporation >0). CLM predicts that drier soil conditions will accelerate organic matter decomposition, with concomitant increases in carbon dioxide (CO2) emissions. Soil drying, however, strongly suppresses growth in methane (CH4) emissions. Considering the global warming potential (GWP) of CO2 and CH4 emissions together, soil drying weakens the CLM projected GWP associated with carbon fluxes from the permafrost zone by more than 50% compared to a non-drying case. This high sensitivity to hydrologic change highlights the need for better understanding and modeling of landscape-scale changes in soil moisture conditions in response to permafrost thaw in order to more accurately assess the potential magnitude of the permafrost carbon-climate feedback. (letter)

  14. Synthesis of Trace Gas and Aerosol Observations and Evaluation of Modelled Short-lived Climate Pollutants Across the Pan-Eurasian High Latitudes

    Science.gov (United States)

    Arnold, S.; Nieminen, T.

    2015-12-01

    Model calculations suggest that changes in short-lived climate pollutants (SLCPs) such as ozone and aerosol may have contributed significantly to rapid Arctic warming over the past century. Arctic tropospheric budgets of SLCPs are impacted by long-range transport of trace gases and aerosols from Europe, Asia and N. America, but also by local sources such as gas flaring, shipping and boreal fires. Recently, the POLARCAT Model Intercomparison Project (POLMIP) showed that significant model biases persist through the depth of the European and North American high latitude troposphere in modelled trace-gas abundances. Evaluation of models over the Siberian high latitudes is challenging due to a severe paucity of available observations, despite the potential importance of this region as a route for European pollution export to the Arctic. Despite the existence of a number of limited datasets, which could be used for model evaluation in this region, until now no effort has been made to synthesise and exploit these observations to evaluate modelled abundances of SLCPs such as tropospheric ozone & aerosol. In this presentation, we will show evaluation of simulated aerosol, tropospheric ozone, and precursor species in several global chemical transport models, using a synthesis of available surface, aircraft and satellite observations over the high latitude pan-Eurasian region. We use models and observations to investigate source regions contributing to remote Siberian SLCP abundances over the annual cycle, and show substantial biases in simulated aerosol and trace gas concentrations that are consistent across a suite of different models. These comparisons constitute the first multi-model evaluation of tropospheric composition in the pan-Eurasin region using observations from across the broad region. Finally, we use the model simulations to determine optimum locations for the development of future monitoring activities in high latitude Eurasia with an aim of better

  15. High-latitude forcing of diatom productivity in the southern Agulhas Plateauduring the past 350kyr

    NARCIS (Netherlands)

    Romero, O.E.; Kim, J.-H.; Bárcena, M.A.; Hall, I.R.; Zahn, R.; Schneider, R.

    2015-01-01

    The hydrography of the Indian-Atlantic Ocean gateway has been connected to high-latitude climate dynamics by oceanic and atmospheric teleconnections on orbital and suborbital timescales. A wealth of sedimentary records aiming at reconstructing the late Pleistocene paleoceanography around the souther

  16. 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

    . There seems to be some hope that comparatively simple relationships between evaporation and photosynthesis and leaf area may be sufficiently robust to allow the use of remotely sensed images to investigate the areally averaged exchanges. It is suspected that high latitude regions will experience considerable...

  17. Influence of sea ice cover on high latitude precipitation: Inferences from precipitation isotope measurements and a 2D model

    Science.gov (United States)

    Posmentier, E. S.; Faiia, A.; Feng, X.; Michel, F. A.

    2009-12-01

    The most widely cited climate feedback in the Arctic region is ice cover. Warming climate reduces the sea ice extent, which causes a lower surface albedo, resulting in more absorbed insolation and further warming - a positive feedback. Conversely, warming is also likely to result in increased Arctic evaporation and precipitation, leading to increased snow cover and a higher Arctic terrestrial albedo, which would cause cooling - a negative feedback. The balance between these feedbacks must be understood and quantified in order to predict climate response to influences such as increased greenhouse gases. Here, we use measurements of high latitude precipitation isotopes and a 2D model to investigate interannual variability in the contributions of subtropical and Arctic vapor sources to Arctic precipitation. In a previous study, we used isotopic ratios alone to investigate the sources of moisture to the Arctic. We found significant positive relationships between ice area and the d-excess of precipitation on both interannual and seasonal timescales, an expected result under the assumption that sea ice prevents evaporation from the sea surface and consequently reduces the contribution of Arctic moisture with low d-excess values to Arctic precipitation. In this work, we go a step further with an attempt to estimate the influence of sea ice cover on Arctic evaporation using a 2D model and constraining it with high latitude isotopic measurements. The 2D model is a vertical-meridional mass conservation model for H2O, HDO, and H218O with prescribed atmospheric circulation and temperatures. For each isotope, the rates of surface evaporation, sublimation, precipitation, and reevaporation of falling hydrometeors are calculated, and values of the humidity and isotopic concentrations of both vapor and hydrometeors are computed interdependently with the four process rates.. The model fractionation associated with the four processes is based primarily on the work of Jouzel and

  18. 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

  19. Diffuse Galactic Gamma Rays at Intermediate and High Latitudes, Constraints on ISM Properties

    CERN Document Server

    Tavakoli, Maryam; Evoli, Carmelo; Ullio, Piero

    2011-01-01

    The spectral data on the diffuse Galactic gamma-rays, at medium and high latitudes (|b| > 10) and energies of 1-100 GeV, recently published by the Fermi Collaboration are used to produce a novel study on the gamma-ray emissivity in the Galaxy. We focus on analyzing the properties of propagation of cosmic rays (CRs), using the publicly available DRAGON code. We critically address some of the models for the interstellar HI and H2 gas distributions commonly used in the literature, as well as test a variety of propagation models. Each model assumes a distinct global profile for the diffusion and the re-acceleration of CRs. Fitting propagation parameters to well measured local CRs such as, the B/C ratio, protons, antiprotons and electron, positron fluxes, we evaluate the gamma-ray spectra at medium and high latitudes in order to place further constraints on these propagation models.

  20. 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.

  1. 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.

  2. 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.

  3. 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. PMID:26812259

  4. High-latitude ionospheric convection during strong interplanetary magnetic field B-y

    DEFF Research Database (Denmark)

    Huang, C.S.; Sofko, G.J.; Murr, D.;

    1999-01-01

    . The interplanetary magnetic field (IMF) conditions corresponding to the occurrence of the ionospheric convection were B-x approximate to 1 nT, B-y approximate to 10 nT, and B-z ...An unusual high-latitude ionospheric pattern was observed on March 23, 1995. ionospheric convection appeared as clockwise merging convection cell focused at 84 degrees magnetic latitude around 1200 MLT. No signature of the viscous convection cell in the afternoon sector was observed...

  5. Gravitational lensing as a possible explanation for some unidentified gamma-ray sources at high latitudes

    OpenAIRE

    Torres, Diego F.; Romero, Gustavo E.; Eiroa, Ernesto F.

    2001-01-01

    We propose that some of the high-latitude unidentified EGRET gamma-ray sources could be the result of gravitational lensing amplification of the innermost regions of distant, faint, active galactic nuclei. These objects have gamma-ray emitting regions small enough as to be affected by microlensing of stars in interposed galaxies. We compute the gravitational amplification taking into account effects of the host galaxy of the lens and prove that, whereas the innermost gamma-ray regions can be ...

  6. 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).

  7. Spectral characteristics of atmospheric pressure and electric field variations under severe weather conditions at high latitudes

    OpenAIRE

    Kasatkina, E. A.; Shumilov, O. I.; Vinogradov, Y. A.; Vasilyev, A. N.

    2006-01-01

    International audience The time-dependent relationships between atmospheric parameters (electric field, positive and negative conductivity, variations of atmospheric pressure) and different meteorological phenomena (rain, fogs, snowstorms, thunderstorms) were investigated through spectral analysis. These parameters were measured with help of a high-latitude computer-aided complex installed at Apatity (66.5 N, 33.4 E). The complex consists of three spaced microbarographs for measurements of...

  8. Upper-thermospheric observations and neutral-gas dynamics at high latitudes during solar maximum

    International Nuclear Information System (INIS)

    The primary objective was to understand the time-dependent dynamics of high-latitude thermospheric neutral winds. A unique 70-orbit December-solstice dataset of Dynamics Explorer 2 (DE-2) satellite data was established, with coverage of both polar caps during the same orbit. Analysis of this data led to the characterization of four basic high-latitude neutral-wind signature categories for each hemisphere under various interplanetary-magnetic-field (IMF) configurations. In addition, neutral-gas forcing simulations for the same solar-maximum December-solstice conditions using the NCAR thermospheric general circulation model (TGCM) showed that the orientation of the pressure-gradient force in the winder northern hemisphere was different from the summer southern hemisphere, explaining the differences in neutral-wind flow patterns systematically observed by DE-2 in opposite hemispheres. The variations in the pressure-gradient forces in opposite hemispheres were ascribed to density variations and temperature gradients, resulting from a superposition of solar-EUV, Joule, and cusp heating. The DE-2 dataset was then used to conduct two different time-dependent tests of the NCAR-TGCM. Finally, a technique for short-range forecasting of the high-latitude ion-convection parameters was noted

  9. Large-scale energy transformations in the high latitudes of the Northern Hemisphere

    Science.gov (United States)

    Kung, E. C.; Masters, S. E.; Corte-Real, J. A. M.

    1983-01-01

    The kinetic energy balance and kinetic energy sources are studied for high latitudes north of 55 deg N with twice daily upper air observations during a seven-year period from 1973 to 1979. Energy variables are presented for 5 deg latitudinal zones from 55 to 75 deg N and for the polar cap north of 75 deg N. Spatial distributions of important energy variables are also presented. The upper level maximum of the cross-isobaric generation in high latitudes is observed in th lower stratosphere above the tropopause level in the winter and becomes insignificant during the summer. The flux convergence of potential energy from the source in lower latitudes is identified as the single major source for kinetic energy in higher latitudes. The contribution of the baroclinic conversion is minor. Examination during the First GARP Global Experiment winter indicates that the cold air outbreaks of the Asian winter monsoon are associated with noticeable changes in the hemispherical distributions of the fields of vertical motion and energetics in the high latitudes.

  10. Status of High Latitude Precipitation Estimates: The Role of GPM in Advancing our Current Understanding

    Science.gov (United States)

    Behrangi, A.; Richardson, M.; Christensen, M.; Huffman, G. J.; Adler, R. F.; Stephens, G. L.; Lambrigtsen, B.

    2015-12-01

    This presentation reviews the current status of precipitation estimation from observation and reanalysis at high latitudes and discusses new insights gained by GPM. An intercomparison of high-latitude precipitation characteristics from observation-based and reanalysis products is performed. Precipitation products from GPM and the cloud profiling radar on the CloudSat satellite provide an independent assessment to other products which have already been widely used, these being the observationally-based GPCP, GPCC and CMAP and the reanalyses ERA-Interim, MERRA and NCEP-DOE. Seasonal and annual total precipitation in both hemispheres poleward of 55° latitude is considered in all products, and GPM and CloudSat products are used to assess frequency of precipitation occurrence by phase, defined as rain, snow or mixed phase. Estimates of snowfall over Antarctica and Greenland are compared from various products. A number of disagreements on regional or seasonal scales are identified which will be reported and discussed. These estimates from observations and reanalyses provide useful insights for diagnostic assessment of precipitation products in high latitudes, quantifying the current uncertainties among observations and reanalyses, and establishing a benchmark for assessment of climate models.

  11. A FUSE Survey of Interstellar Molecular Hydrogen toward High-Latitude AGN

    CERN Document Server

    Gillmon, K; Tumlinson, J; Danforth, C; Gillmon, Kristen; Tumlinson, Jason; Danforth, Charles

    2006-01-01

    We report results from a FUSE survey of interstellar molecular hydrogen (H2) along 45 sight lines to AGN at high Galactic latitudes (|b| > 20 degrees). Most (39 of 45) of the sight lines show detectable Galactic H2 absorption from Lyman and Werner bands between 1000 and 1126 A, with column densities ranging from N(H2) = 10^(14.17-19.82) cm^-2. In the northern Galactic hemisphere, we identify many regions of low column, N(H2) 54 degrees. These `"H2 holes" provide valuable, uncontaminated sight lines for extragalactic UV spectroscopy, and a few may be related to the "Northern Chimney" (low Na I absorption) and "Lockman Hole" with low N(HI). A comparison of high-latitude H2 with 139 OB-star sight lines surveyed in the Galactic disk suggests that high-latitude and disk H2 clouds may have different rates of heating, cooling, and UV excitation. For rotational states J = 0 and 1, the mean excitation temperature at high latitude, = 124 +/- 8 K, is somewhat above that in the Galactic disk, = 86 +/- 20 K. For J = 2-...

  12. 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

  13. Can bioenergy cropping compensate high carbon emissions from large-scale deforestation of mid to high latitudes?

    Directory of Open Access Journals (Sweden)

    P. Dass

    2013-02-01

    Full Text Available Numerous studies have concluded that deforestation of mid to high latitudes result in a global cooling. This is mainly because of the increased albedo of deforested land which dominates over other biogeophysical and biogeochemical mechanisms in the energy balance. This dominance however may be due to an underestimation of the biogeochemical response, as carbon emissions are typically at or below the lower end of estimates. Here, we use the dynamic global vegetation model LPJmL for a better estimate of the carbon cycle under such large-scale deforestation. These studies are purely academic to understand the role of vegetation in the energy balance and the earth system. They must not be mistaken as possible mitigation options, because of the devastating effects on pristine ecosystems. We show that even optimistic assumptions on the manageability of these areas and its utilization for bioenergy crops could not make up for the strong carbon losses in connection with the losses of vegetation carbon and the long-term decline of soil carbon stocks. We find that the global biophysical bioenergy potential is 78.9 ± 7.9 EJ yr−1 of primary energy at the end of the 21st century for the most plausible scenario. Due to avoided usage of fossil fuels over the time frame of this experiment, the cooling due to the biogeophysical feedback could be supplemented by an avoided warming of approximately 0.1 to 0.3 °C. However, the extensive deforestation simulated in this study causes an immediate emission of 182.3 ± 0.7 GtC followed by long term emissions. In the most plausible scenario, this carbon debt is not neutralized even if bioenergy production is assumed to be carbon-neutral other than for the land use emissions so that global temperatures would increase by ~0.2 to 0.6 °C by the end of the 21st century. The carbon dynamics in the high latitudes, especially with respect to permafrost dynamics and long-term carbon losses, require additional attention in

  14. The dynamics of the warming hiatus over the Northern Hemisphere

    Science.gov (United States)

    Huang, Jianping; Xie, Yongkun; Guan, Xiaodan; Li, Dongdong; Ji, Fei

    2016-05-01

    A warming hiatus is a period of relatively little change in global mean surface air temperatures (SAT). Many studies have attributed the current warming hiatus to internal climate variability (ICV). But there is less work on discussion of the dynamics about how these ICV modes influence cooling over land in the Northern Hemisphere (NH). Here we demonstrate the warming hiatus was more significant over the continental NH. We explored the dynamics of the warming hiatus from a global perspective and investigated the mechanisms of the reversing from accelerated warming to hiatus, and how ICV modes influence SAT change throughout the NH land. It was found that these ICV modes and Arctic amplification can excite a decadal modulated oscillation (DMO), which enhances or suppresses the long-term trend on decadal to multi-decadal timescales. When the DMO is in an upward (warming) phase, it contributes to an accelerated warming trend, as in last 20 years of twentieth-century. It appears that there is a downward swing in the DMO occurring at present, which has balanced or reduced the radiative forced warming and resulted in the recent global warming hiatus. The DMO modulates the SAT, in particular, the SAT of boreal cold months, through changes in the asymmetric meridional and zonal thermal forcing (MTF and ZTF). The MTF represents the meridional temperature gradients between the mid- and high-latitudes, and the ZTF represents the asymmetry in temperatures between the extratropical large-scale warm and cold zones in the zonal direction. Via the different performance of combined MTF and ZTF, we found that the DMO's modulation effect on SAT was strongest when both weaker (stronger) MTF and stronger (weaker) ZTF occurred simultaneously. And the current hiatus is a result of a downward DMO combined with a weaker MTF and stronger ZTF, which stimulate both a weaker polar vortex and westerly winds, along with the amplified planetary waves, thereby facilitating southward invasion of

  15. A theoretical study of the high-latitude winter F region at solar minimum for low magnetic activity

    Science.gov (United States)

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

    1981-01-01

    A simple plasma convection model is combined with an ionospheric-atmospheric composition model in order to study the high-latitude winter F region at the solar minimum for low magnetic activity. The high latitude ionospheric features, such as the main trough, the ionization hole, the tongue of ionization, the aurorally produced ionization peaks, and the universal time effects are a natural consequence of the competition between the various chemical and transport processes known to be operating in the high-latitude ionosphere. In the polar hole, the F region peak electron density is below 300 km, and the dominant process at 300 km for NO(+) ions is diffusion.

  16. Linking Sediment Microbial Communities to Carbon Cycling in High-Latitude Lakes

    Science.gov (United States)

    Emerson, J. B.; Varner, R. K.; Johnson, J. E.; Owusu-Dommey, A.; Binder, M.; Woodcroft, B. J.; Wik, M.; Freitas, N. L.; Boyd, J. A.; Crill, P. M.; Saleska, S. R.; Tyson, G. W.; Rich, V. I.

    2015-12-01

    It is well recognized that thawing permafrost peatlands are likely to provide a positive feedback to climate change via CH4 and CO2 emissions. High-latitude lakes in these landscapes have also been identified as sources of CH4 and CO2 loss to the atmosphere. To investigate microbial contributions to carbon loss from high-latitude lakes, we characterized sediment geochemistry and microbiota via cores collected from deep and shallow regions of two lakes (Inre Harrsjön and Mellersta Harrsjön) in Arctic Sweden in July, 2012. These lakes are within the Stordalen Mire long-term ecological area, a focal site for investigating the impacts of climate change-related permafrost thaw, and the lakes in this area are responsible for ~55% of the CH4 loss from this hydrologically interconnected system. Across 40 samples from 4 to 40 cm deep within four sediment cores, Illumina 16S rRNA gene sequencing revealed that the sedimentary microbiota was dominated by candidate phyla OP9 and OP8 (Atribacteria and Aminicenantes, respectively, including putative fermenters and anaerobic respirers), predicted methanotrophic Gammaproteobacteria, and predicted methanogenic archaea from the Thermoplasmata Group E2 clade. We observed some overlap in community structure with nearby peatlands, which tend to be dominated by methanogens and Acidobacteria. Sediment microbial communities differed significantly between lakes, by overlying lake depth (shallow vs. deep), and by depth within a core, with each trend corresponding to parallel differences in biogeochemical measurements. Overall, our results support the potential for significant microbial controls on carbon cycling in high-latitude lakes associated with thawing permafrost, and ongoing metagenomic analyses of focal samples will yield further insight into the functional potential of these microbial communities and their dominant members.

  17. IMF dependence of high-latitude thermospheric wind pattern derived from CHAMP cross-track measurements

    Science.gov (United States)

    Förster, M.; Rentz, S.; Köhler, W.; Liu, H.; Haaland, S. E.

    2008-06-01

    Neutral thermospheric wind pattern at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both North and South polar regions are statistically analyzed in their dependence on the Interplanetary Magnetic Field (IMF) direction in the GSM y-z plane (clock angle). We compare this dependency with magnetospheric convection pattern obtained from the Cluster EDI plasma drift measurements under the same sorting conditions. The IMF-dependency shows some similarity with the corresponding high-latitude plasma convection insofar that the larger-scale convection cells, in particular the round-shaped dusk cell for ByIMF+ (ByIMF-) conditions at the Northern (Southern) Hemisphere, leave their marks on the dominant general transpolar wind circulation from the dayside to the nightside. The direction of the transpolar circulation is generally deflected toward a duskward flow, in particular in the evening to nighttime sector. The degree of deflection correlates with the IMF clock angle. It is larger for ByIMF+ than for ByIMF- and is systematically larger (~5°) and appear less structured at the Southern Hemisphere compared with the Northern. Thermospheric cross-polar wind amplitudes are largest for BzIMF-/ByIMF- conditions at the Northern Hemisphere, but for BzIMF-/ByIMF+ conditions at the Southern because the magnetospheric convection is in favour of largest wind accelerations over the polar cap under these conditions. The overall variance of the thermospheric wind magnitude at Southern high latitudes is larger than for the Northern. This is probably due to a larger "stirring effect" at the Southern Hemisphere because of the larger distance between the geographic and geomagnetic frameworks.

  18. 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.

  19. On the solar cycle variation in the barometer coefficients of high latitude neutron monitors

    Science.gov (United States)

    Kusunose, M.; Ogita, N.

    1985-01-01

    Evaluation of barometer coefficients of neutron monitors located at high latitudes has been performed by using the results of the spherical harmonic analysis based on the records from around twenty stations for twelve years from January 1966 to December 1977. The average of data at eight stations, where continuous records are available for twelve years, show that the absolute value of barometer coefficient is in positive correlation with the cosmic ray neutron intensity. The variation rate of the barometer coefficient to the cosmic ray neutron intensity is influenced by the changes in the cutoff rigidity and in the primary spectrum.

  20. High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes

    OpenAIRE

    Wright, D. M.; Yeoman, T.K.; Chapman, P J

    1997-01-01

    A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF) waves by a high-latitude (geographic: 69.6°N 19.2°E) high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated with pulsations in ground magnetometer data, exhibit periods in the range 100–400 s and have azimuthal wave numbers in the range 3–8. They are interpreted here as local field line resonances. Phase information provided by O- and X-mode ...

  1. High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

    OpenAIRE

    Wright, D. M.; Yeoman, T.K.

    1999-01-01

    The DOPE (Doppler Pulsation Experiment) HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3) is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance...

  2. ULF wave occurrence statistics in a high-latitude HF Doppler sounder

    OpenAIRE

    Wright, D. M.; Yeoman, T.K.; T. B. Jones

    1999-01-01

    Ultra low frequency (ULF) wave activity in the high-latitude ionosphere has been observed by a high frequency (HF) Doppler sounder located at Tromsø, Norway (69.7°N, 19.2°E geographic coordinates). A statistical study of the occurrence of these waves has been undertaken from data collected between 1979 and 1984. The diurnal, seasonal, solar cycle and geomagnetic activity variations in occurrence have been investigated. The findings demonstrate that the ability of the sounder to detect ULF wav...

  3. Multi-Cell High Latitude Density Structure Induced by Ion Drag during Active Periods

    Science.gov (United States)

    Walterscheid, R. L.; Crowley, G.

    2012-12-01

    During active periods two-cell convection patterns can produce four-cell density structure in the high-latitude thermosphere. During these periods density perturbations approaching 50% are possible. The occurrence of density structures that are more complex than the forcing itself suggests that the structure is caused by a profound change in the balance of forces. Using a General Circulation Model of the thermosphere, we compare the balance of forces in the upper and lower thermosphere during active and quiet times. We also examine the thermal structure caused by the dynamical adjustment to ion-drag forcing in relation to the other terms as a balanced state is approached. Simulations reveal that where ion drag is unable to accelerate the atmosphere into rapid motion (during quiet times or at low thermospheric altitudes) the Coriolis force is the dominant inertial term, and for fixed pressure levels centers of cyclonic motion are (per the usual meteorology relations) colder and denser than the surrounding air, while centers of anticyclonic motion are warmer and less dense. At fixed heights, densities are high in the evening anticyclonic gyre, and low in the dawn cyclonic gyre. However, this situation is radically changed during active periods when the atmosphere is spun up to rapid motion and the centrifugal force resulting from curved trajectories is the dominant inertial force. When this occurs, the high latitude anticyclones and cyclones both become centers of relatively cold high density air at fixed height. Cold low-density centers are found on both the dawn and dusk sides with a trough of low density air over the pole connecting them. This intrusion of low density splits the evening high density region that exists under quiet conditions giving the four cell pattern found by Crowley et al. [1989; 1996a, b]. Crowley, G., J. Schoendorf, R. G. Roble, F. A. Marcos (1996a). Cellular structures in the high latitude lower thermosphere, J. Geophys. Res. 101, 211

  4. Saturn’s UV aurora: the (high latitude) point of view of Cassini

    OpenAIRE

    Grodent, Denis; Bonfond, Bertrand; Gustin, Jacques; Radioti, Aikaterini; Gérard, Jean-Claude; Pryor, Wayne

    2013-01-01

    The high latitude vantage point of Cassini and its short distance to Saturn give rise to a unique opportunity for obtaining exceptional spectral images of the aurorae, along with in situ observations of the associated particles and magnetic field. Cassini’s T83 flyby of Titan significantly changed the inclination of the spacecraft’s orbit and marked the beginning of the XXM inclined phase 1 which will last until March 16, 2015. We will give an overview of the auroral emissions observed so ...

  5. EISCAT Observations of Main Ionization Troughs in the High-Latitude Ionosphere

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    F-region electron density depletions associated with main ionization troughs in the high-latitude ionosphere are studied using EISCAT CP3 data of meridian scanning experiments. The troughs in our observations are found to appear mainly in dusk sector, extending from late afternoon to pre-midnight, with higher occurrence rate during equinox and winter. Simultaneous ion drift velocity in F-region shows that the main trough minimm is mostly located at the equator ward edge of the plasma convection flow, rather than in the r~ion where the largest ion flow are observed.

  6. Spatiotemporal Divergence of the Warming Hiatus over Land Based on Different Definitions of Mean Temperature

    Science.gov (United States)

    Zhou, Chunlüe; Wang, Kaicun

    2016-08-01

    Existing studies of the recent warming hiatus over land are primarily based on the average of daily minimum and maximum temperatures (T2). This study compared regional warming rates of mean temperature based on T2 and T24 calculated from hourly observations available from 1998 to 2013. Both T2 and T24 show that the warming hiatus over land is apparent in the mid-latitudes of North America and Eurasia, especially in cold seasons, which is closely associated with the negative North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) and cold air propagation by the Arctic-original northerly wind anomaly into mid-latitudes. However, the warming rates of T2 and T24 are significantly different at regional and seasonal scales because T2 only samples air temperature twice daily and cannot accurately reflect land-atmosphere and incoming radiation variations in the temperature diurnal cycle. The trend has a standard deviation of 0.43 °C/decade for T2 and 0.41 °C/decade for T24, and 0.38 °C/decade for their trend difference in 5° × 5° grids. The use of T2 amplifies the regional contrasts of the warming rate, i.e., the trend underestimation in the US and overestimation at high latitudes by T2.

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

    Directory of Open Access Journals (Sweden)

    J.-P. St.-Maurice

    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

  8. 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 (land 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.

  9. Mapping high-latitude ionospheric electrodynamics with SuperDARN and AMPERE

    Science.gov (United States)

    Cousins, E. D. P.; Matsuo, Tomoko; Richmond, A. D.

    2015-07-01

    An assimilative procedure for mapping high-latitude ionospheric electrodynamics is developed for use with plasma drift observations from the Super Dural Auroral Radar Network (SuperDARN) and magnetic perturbation observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). This procedure incorporates the observations and their errors, as well as two background models and their error covariances (estimated through empirical orthogonal function analysis) to infer complete distributions of electrostatic potential and vector magnetic potential in the high-latitude ionosphere. The assimilative technique also enables objective error analysis of the results. Various methods of specifying height-integrated ionospheric conductivity, which is required by the procedure, are implemented and evaluated quantitatively. The benefits of using both SuperDARN and AMPERE data to solve for both electrostatic and vector magnetic potentials, rather than using the data sets independently or solving for just electrostatic potential, are demonstrated. Specifically, solving for vector magnetic potential improves the specification of field-aligned currents (FACs), and using both data sets together improves the specification of features in regions lacking one type of data (SuperDARN or AMPERE). Additionally, using the data sets together results in a better correspondence between large-scale features in the electrostatic potential distribution and those in the FAC distribution, as compared to using SuperDARN data alone to infer electrostatic potential and AMPERE data alone to infer FACs. Finally, the estimated uncertainty in the results decreases by typically ˜20% when both data sets rather than just one are included.

  10. Effects of magnetospheric lobe cell convection on dayside upper thermospheric winds at high latitudes

    Science.gov (United States)

    Zhang, B.; Wang, W.; Wu, Q.; Knipp, D.; Kilcommons, L.; Brambles, O. J.; Liu, J.; Wiltberger, M.; Lyon, J. G.; Häggström, I.

    2016-08-01

    This paper investigates a possible physical mechanism of the observed dayside high-latitude upper thermospheric wind using numerical simulations from the coupled magnetosphere-ionosphere-thermosphere (CMIT) model. Results show that the CMIT model is capable of reproducing the unexpected afternoon equatorward winds in the upper thermosphere observed by the High altitude Interferometer WIND observation (HIWIND) balloon. Models that lack adequate coupling produce poleward winds. The modeling study suggests that ion drag driven by magnetospheric lobe cell convection is another possible mechanism for turning the climatologically expected dayside poleward winds to the observed equatorward direction. The simulation results are validated by HIWIND, European Incoherent Scatter, and Defense Meteorological Satellite Program. The results suggest a strong momentum coupling between high-latitude ionospheric plasma circulation and thermospheric neutral winds in the summer hemisphere during positive IMF Bz periods, through the formation of magnetospheric lobe cell convection driven by persistent positive IMF By. The CMIT simulation adds important insight into the role of dayside coupling during intervals of otherwise quiet geomagnetic activity

  11. Inorganic carbon in a high latitude estuary-fjord system in Canada's eastern Arctic

    Science.gov (United States)

    Turk, D.; Bedard, J. M.; Burt, W. J.; Vagle, S.; Thomas, H.; Azetsu-Scott, K.; McGillis, W. R.; Iverson, S. J.; Wallace, D. W. R.

    2016-09-01

    Rapidly changing conditions in the Arctic can have a significant impact on biogeochemical cycles and can be particularly important in high latitude estuary-fjord systems with abundant and diverse freshwater sources. This study provides a first look into the inorganic carbon system and its relation to freshwater sources in Cumberland Sound in the east coast of Baffin Island, Nunavut, Canada. These data contribute to the very limited set of inorganic carbon measurements in high latitude estuary-fjord systems. During the ice-free conditions in August 2011, the meteoric freshwater fractions (MW) in the upper 40 m ranged from 11 to 21% and no sea ice melt (SIM) was present in the Sound. Surface waters were undersaturated with pCO2 (260 and 300 μatm), and DIC and TA ranged between 1779 and 1966 μmol DIC kg-1, and 1922 and 2140 μmol TA kg-1, respectively. Aragonite saturation (ΩAr) state ranged from 1.9 in the surface to 1.4 in the subsurface waters. Data show decreasing TA and ΩAr with increasing MW fraction and suggest that Cumberland Sound waters would become aragonite undersaturated (ΩAr water and glacial melt. In August 2012, MW fractions at the surface were between 8 and 11.5%, and SIM between 7 and 23%. Significant interannual variability of summertime SIM could potentially result in ΩAr undersaturation.

  12. The dayside high-latitude trough under quiet geomagnetic conditions: Radio tomography and the CTIP model

    Directory of Open Access Journals (Sweden)

    S. E. Pryse

    2005-06-01

    Full Text Available The dayside high-latitude trough is a persistent feature of the post-noon wintertime auroral ionosphere. Radio tomography observations have been used to map its location and latitudinal structure under quiet geomagnetic conditions (Kp≤2 near winter solstice. The trough is also a clear feature in the ion density distribution of the Coupled Thermosphere-Ionosphere-Plasmasphere model (CTIP under similar geophysical conditions. Comparisons of the measured and modelled distributions show that the plasma production equatorward of the trough is mainly controlled by solar radiation, but there are also other processes maintaining the equatorward trough-wall that are open to debate. The poleward trough-wall is produced by particle precipitation, but the densities are significantly overestimated by the model. At the trough minimum the observed densities are consistent with low nighttime densities convecting sunward to displace the higher daytime densities, but this is not borne out by the CTIP model. The study shows the potential of combining radio tomography and modelling to interpret the balance of the physical processes responsible for large-scale structuring of the high-latitude ionosphere, and highlights the role of tomographic imaging in validating and developing physical models.

  13. Seasonal study of the micrometeor input function at high latitudes using PFISR

    Science.gov (United States)

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

    2007-12-01

    We present a seasonal study of the micrometeor input function (MIF) at high latitudes using meteor head-echo radar observations performed with the new Poker Flat Incoherent Scatter Radar (PFISR). This flux is responsible for a number of atmospheric phenomena, one of which, may be the production of meteoric smoke which would act as a condensation nuclei in the formation of ice particles in the polar mesosphere. The observations were performed during 24 hrs 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. Precise altitude and radar instantaneous line-of-sight (radial) Doppler velocity information are obtained for each of the hundreds of events detected ever day. The results to be discussed include, diurnal meteor rate curves and altitude and radial meteoroid velocity distributions. We compared observed and modeled results and find them to be in good agreement. A surprising result is that the peak of the detected meteor altitude distribution varies up to an atmospheric scale height depending on season. We will discuss if these changes are due to seasonal variability of the atmospheric temperature in the mesosphere or in the directionality of the meteoric influx.

  14. High-latitude energy input and its impact on the thermosphere

    Science.gov (United States)

    Lu, G.; Richmond, A. D.; Lühr, H.; Paxton, L.

    2016-07-01

    This paper presents a quantitative assessment of high-latitude energy input and its partitioning in the polar cap by synthesizing various space and ground-based observations during the 17 January 2005 geomagnetic storm. It was found that Joule heating is the primary form of magnetospheric energy input, especially during active times when the hemispheric-integrated Joule heating can be an order of magnitude larger than the hemispheric-integrated auroral power. Most of magnetospheric energy is dissipated in the auroral zone rather than in the polar cap. On average, only about 22-25% of the total hemispheric energy input is dissipated into the polar cap region bordered by the convection reversal boundary (CRB) and the poleward auroral flux boundary (FXB). The impact of high-latitude energy input was also investigated to unveil the causal relationship between Joule heating and the formation of polar cap mass density anomalies. Our numerical simulation demonstrated that thermosphere dynamics readily redistributes composition, temperature, and mass through upwelling and atmospheric gravity waves. The polar cap mass density anomalies observed by the CHAMP satellite during the storm were largely a result of large-scale atmospheric gravity waves. Therefore, an increase in local thermospheric mass density does not necessarily mean there is direct energy input.

  15. 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.

  16. Influences of basic flow on unstable excitation of intraseasonal oscillation in mid-high latitudes

    Institute of Scientific and Technical Information of China (English)

    李崇银; 曹文忠; 李桂龙

    1995-01-01

    The influences of basic flow fields on the unstable excitation of the intraseasonal atmosphericoscillation in the mid-high latitudes are studied by using a simple nonlinear dynamical model.The results showthat the westerly profile has an important effect on unstable modes in the atmosphere;the growth rates andspectrum distributions of the excited unstable modes are different for the different profiles.For the usualwesterly profile patterns in the real atmosphere,the most unstable mode is in the intraseasonal(30—60 d)frequency band.The local intensity and meridional gradient of the westerlies also clearly affect unstablemodes.The consistency of the results in observational data analyses with that in dynamical theory proved thecorrectness and rationalization of the above-mentioned results.

  17. Momentum transfer at the high-latitude magnetopause and boundary layers

    Directory of Open Access Journals (Sweden)

    E. J. Lund

    2008-08-01

    Full Text Available How and where momentum is transferred from the solar wind to the magnetosphere and ionosphere is one of the key problems of space physics. Much of this transfer occurs through direct reconnection on the dayside, particularly when the IMF is southward. However, momentum transfer also occurs at higher latitudes via Alfvén waves on old open field lines, even for southward IMF. This momentum is transferred to the ionosphere via field-aligned currents (FACs, and the flow channel associated with these FACs produces a Hall current which causes magnetic variations at high latitude (the Svalgaard-Mansurov effect. We show examples where such momentum transfer is observed with multiple spacecraft and ground-based instruments.

  18. The high latitude circulation and temperature structure of the thermosphere near solstice

    Science.gov (United States)

    Roble, R. G.; Dickinson, R. E.; Ridley, E. C.; Emery, B. A.; Hays, P. B.; Killeen, T. L.; Spencer, N. W.

    1983-01-01

    NCAR thermospheric-general-circulation-model (TGCM) computations of solar-maximum thermospheric neutral-gas temperature and circulation around the December solstice are presented and discussed. The TGCM uses a 5 x 5-deg grid and 24 constant-pressure layers, corresponding to altitudes of about 97-500 km. The results are mapped as electron-density contours, polar plots, cylindrical equidistant projections, meridional cross sections, and F-region polar plots comparing the TGCM predictions with DE-2 satellite observations. The significant differences between summer and winter high-latitude F-region winds are attributed to the ion drag momentum associated with magnetospheric convection. The TGCM wind predictions follow the same pattern as the satellite measurements but are too small; possible model corrections are considered.

  19. High-Latitude Molecular Clouds as (Gamma)-ray Sources for GLAST

    Energy Technology Data Exchange (ETDEWEB)

    Torres, D F; Dame, T M; Digel, S W

    2005-01-05

    For about two decades, a population of relative small and nearby molecular clouds has been known to exist at high Galactic latitudes. Lying more than 10{sup o} from the Galactic plane, these clouds have typical distances of {approx}150 pc, angular sizes of {approx}1{sup o}, and masses of order tens of solar masses. These objects are passive sources of high-energy {gamma}-rays through cosmic ray-gas interactions. Using a new wide-angle CO survey of the northern sky, we show that typical high-latitude clouds are not bright enough in {gamma}-rays to have been detected by EGRET, but that of order 100 of them will be detectable by the Large Area Telescope (LAT) on GLAST. Thus, we predict a new steady population of {gamma}-ray sources at high Galactic latitudes, perhaps the most numerous after active galactic nuclei.

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

    DEFF Research Database (Denmark)

    Kjellerup, Sanne

    2014-01-01

    -web, linking smaller and larger organisms. Research of copepod communities in the Arctic has traditionally focused on larger taxa present in the surface layers. Consequently, little is known about reproduction strategies and population dynamics of smaller copepods located deeper in the water column. The aim......, small copepod species were less dependent on the spring phytoplankton bloom, and their reproduction and population dynamics were less pulsed. Likewise, a large proportion of Oithona similis was ovigerous from March to August. Reproduction of Microsetella norvegica, another of the small key species...... diurnal and nocturnal sampling. The seasonal fjord study further identified different life strategies with respect to seasonal adaptations in reproduction and migration patterns. In contrast to the general assumption that large calanoid copepods dominate high latitude ecosystems, we find that smaller...

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

    International Nuclear Information System (INIS)

    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

  2. Geomagnetic responses in high latitudes during the storm of July 15-16, 2000

    Institute of Scientific and Technical Information of China (English)

    陈耿雄; 杜爱民; 徐文耀; 陈鸿飞; 洪明华; 彭丰林; 师恩齐

    2002-01-01

    The ionospheric equivalent currents in the high latitudes and the auroral electrojet system during the geomagnetic storm on July 15-16, 2000 are analyzed by using geomagnetic data from IMAGE chain. The large-scale vortices of equivalent currents are observed in the storm. The vortices on the dusk side of ionosphere correspond to four-celled pattern of plasma convection associated with NBZ, region I and region II field-aligned currents. Only one vortex can be found on the dawn side of ionosphere after interplanetary magnetic field (IMF) turns southward. In the initial phase of the storm, the center of eastward electrojets tends to shift equatorward. It arrives at 58.62o latitude of corrected geomagnetic coordinates (CGM). The westward electrojets are strong in the main phase. The center of westward electrojets in this period moves equatorward and may be beyond the southernmost station (56.45°) of the chain.

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

    International Nuclear Information System (INIS)

    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

  4. Middle-High Latitude N2O Distributions Related to the Arctic Vortex Breakup

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The relationship of N2O distributions with the Arctic vortex breakup is first analyzed with a probability distribution function (PDF) analysis. The N2O concentration shows different distributions between the early and late vortex breakup years. In the early breakup years, the N2O concentration shows low values and large dispersions after the vortex breakup, which is related to the inhomogeneity in the vertical advection in the middle and high latitude lower stratosphere. The horizontal diffusion coefficient (Kyy)shows a larger value accordingly. In the late breakup years, the N2O concentration shows high values and more uniform distributions than in the early years after the vortex breakup, with a smaller vertical advection and Kyy after the vortex breakup. It is found that the N2O distributions are largely affected by the Arctic vortex breakup time but the dynamically defined vortex breakup time is not the only factor.

  5. ULF wave occurrence statistics in a high-latitude HF Doppler sounder

    Science.gov (United States)

    Wright, D. M.; Yeoman, T. K.; Jones, T. B.

    1999-06-01

    Ultra low frequency (ULF) wave activity in the high-latitude ionosphere has been observed by a high frequency (HF) Doppler sounder located at Tromsø, Norway (69.7°N, 19.2°E geographic coordinates). A statistical study of the occurrence of these waves has been undertaken from data collected between 1979 and 1984. The diurnal, seasonal, solar cycle and geomagnetic activity variations in occurrence have been investigated. The findings demonstrate that the ability of the sounder to detect ULF wave signatures maximises at the equinoxes and that there is a peak in occurrence in the morning sector. The occurrence rate is fairly insensitive to changes associated with the solar cycle but increases with the level of geomagnetic activity. As a result, it has been possible to characterise the way in which prevailing ionospheric and magnetospheric conditions affect such observations of ULF waves.

  6. Birkeland current effects on high-latitude ground magnetic field perturbations

    Science.gov (United States)

    Laundal, K. M.; Haaland, S. E.; Lehtinen, N.; Gjerloev, J. W.; Østgaard, N.; Tenfjord, P.; Reistad, J. P.; Snekvik, K.; Milan, S. E.; Ohtani, S.; Anderson, B. J.

    2015-09-01

    Magnetic perturbations on ground at high latitudes are directly associated only with the divergence-free component of the height-integrated horizontal ionospheric current, J⊥,df. Here we show how J⊥,df can be expressed as the total horizontal current J⊥ minus its curl-free component, the latter being completely determined by the global Birkeland current pattern. Thus, in regions where J⊥=0, the global Birkeland current distribution alone determines the local magnetic perturbation. We show with observations from ground and space that in the polar cap, the ground magnetic field perturbations tend to align with the Birkeland current contribution in darkness but not in sunlight. We also show that in sunlight, the magnetic perturbations are typically such that the equivalent overhead current is antiparallel to the convection, indicating that the Hall current system dominates. Thus, the ground magnetic field in the polar cap relates to different current systems in sunlight and in darkness.

  7. Grounding-zone wedges (GZWs) on high-latitude continental margins

    Science.gov (United States)

    Batchelor, Christine; Dowdeswell, Julian

    2014-05-01

    The grounding-zone of marine-terminating ice sheets is the area at which the ice-sheet base ceases to be in contact with the underlying substrate. The grounding-zone is a key site at which ice, meltwater and sediment are transferred from ice sheets to the marine environment. GZWs are asymmetric sedimentary depocentres which form through the rapid accumulation of glacigenic debris along a line source at the grounding-zone largely through the delivery of deforming subglacial sediments, together with sediment remobilisation from gravity flows. The presence of GZWs in the geomorphological record indicates an episodic style of ice retreat punctuated by still-stands in the grounding-zone position. GZWs may take decades to centuries to form. Moraine ridges and ice-proximal fans may also build up at the grounding-zone during still-stands or re-advances of the ice margin, but these require either considerable vertical accommodation space or are derived from point-sourced subglacial meltwater streams. We present an inventory of GZWs which is compiled from available studies of bathymetric, shallow acoustic and reflection seismic data from high-latitude continental margins. The objectives are to present locations of and morphological data on GZWs from the Arctic and Antarctic, alongside a synthesis of their key architectural and geomorphic characteristics. We use, for example, newly-available two-dimensional seismic reflection data to show the approximate locations of GZWs off northwest and northeast Greenland. Controls on GZW formation are considered in relation to shelf topography and ice-sheet internal dynamics. A total of 129 GZWs are described from high-latitude continental shelves. GZWs are only observed within cross-shelf troughs and major fjord systems, which are the former locations of ice streams and fast-flowing outlet glaciers. Typical high-latitude GZWs are less than 15 km long and 15 to 100 m thick. A positive correlation between GZW length and thickness is

  8. Probabilistic Forecasting of Ionospheric Scintillation and GNSS Receiver Signal Tracking Performance at High Latitudes

    Science.gov (United States)

    Prikryl, P.; Sreeja, V.; Aquino, M.; Jayachandran, P. T.

    2012-12-01

    At high latitudes, phase scintillation occurs predominantly on the dayside in the ionospheric footprint of magnetospheric cusp and in the nightside auroral oval. A new technique of probabilistic forecast of phase scintillation occurrence relative to arrival time of high-speed solar wind (HSSW) from coronal holes and interplanetary coronal mass ejections (ICMEs) has recently been proposed [Prikryl et al., 2012]. Cumulative probability distribution functions for the phase scintillation occurrence that are obtained can be specified for low and high (below- and above-median) values of various solar wind plasma parameters. Recent advances in solar wind modeling of HSSW and ICMEs combined with the probabilistic forecasting of scintillation will lead to improved operational space weather forecasting applications. Scintillation forecasting and mitigation techniques need to be developed to avoid potential costly failures of Global Navigation Satellite Systems (GNSS)-based technology in the near future, in particular during the upcoming solar maximum. GNSS receiver tracking performance during severe scintillation conditions can be assessed by the analysis of receiver phase lock loop (PLL) jitter variance. Tracking jitter variance maps [Sreeja et al, 2011] offer a potentially useful tool to provide users with expected tracking conditions, if based on scintillation prediction as proposed above. Scintillation indices are obtained from L1 GPS data collected with the Canadian High Arctic Ionospheric Network (CHAIN). Combined with high rate amplitude and phase data they can be used as input to receiver tracking models to develop scintillation mitigation techniques. References Prikryl, P., P. T. Jayachandran, S. C. Mushini, and I. G. Richardson (2012), Towards the Probabilistic Forecasting of High-Latitude GPS Phase Scintillation, Space Weather, doi:10.1029/2012SW000800, in press. Sreeja, V., M. Aquino, and Z. G. Elmas (2011), Impact of ionospheric scintillation on GNSS receiver

  9. Intraseasonal variability of air temperature over the mid-high latitude Eurasia in boreal winter

    Science.gov (United States)

    Yang, Shuangyan; Li, Tim

    2016-10-01

    The intraseasonal oscillation (ISO) of air temperature over the mid- and high-latitude Eurasia in boreal winter was investigated by NCEP-NCAR reanalysis data. It is found that the intraseasonal temperature disturbances exhibit maximum variability near the surface in the region of 50°-75°N, 80°‒120°E and they propagate southeastwards at average zonal and meridional phase speeds of 3.2 and 2.5 m s-1, respectively. The low-level temperature signal is tightly coupled with upper-tropospheric height anomalies, and both propagate southeastward in a similar phase speed. A diagnosis of the temperature budget reveals that the southeastward propagation is primarily attributed to the advection of the temperature anomaly by the mean wind. A wave activity flux analysis indicates that the southeastward propagating wave train is likely a result of Rossby wave energy propagation. The source of the Rossby wave train appears at the high latitude Europe/Atlantic sector, where maximum wave activity flux convergence resides. During its southeastward journey, the ISO perturbation gains energy from the mean flow through both kinetic and potential energy conversions. A physics-based empirical model was constructed to predict the intraseasonal temperature anomaly over southeast China. The major predictability source is the southeastward-propagating ISO signal. The data for 1979‒2003 were used as a training period to construct the empirical model. A 10-yr (2004‒2013) independent forecast shows that the model attains a useful skill of up to 25 days.

  10. 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

  11. Design of ecoregional monitoring in conservation areas of high-latitude ecosystems under contemporary climate change

    Science.gov (United States)

    Beever, Erik A.; Woodward, Andrea

    2011-01-01

    Land ownership in Alaska includes a mosaic of federally managed units. Within its agency’s context, each unit has its own management strategy, authority, and resources of conservation concern, many of which are migratory animals. Though some units are geographically isolated, many are nevertheless linked by paths of abiotic and biotic flows, such as rivers, air masses, flyways, and terrestrial and aquatic migration routes. Furthermore, individual land units exist within the context of a larger landscape pattern of shifting conditions, requiring managers to understand at larger spatial scales the status and trends in the synchrony and spatial concurrence of species and associated suitable habitats. Results of these changes will determine the ability of Alaska lands to continue to: provide habitat for local and migratory species; absorb species whose ranges are shifting northward; and experience mitigation or exacerbation of climate change through positive and negative atmospheric feedbacks. We discuss the geographic and statutory contexts that influence development of ecological monitoring; argue for the inclusion of significant amounts of broad-scale monitoring; discuss the importance of defining clear programmatic and monitoring objectives; and draw from lessons learned from existing long-term, broad-scale monitoring programs to apply to the specific contexts relevant to high-latitude protected areas such as those in Alaska. Such areas are distinguished by their: marked seasonality; relatively large magnitudes of contemporary change in climatic parameters; and relative inaccessibility due to broad spatial extent, very low (or zero) road density, and steep and glaciated areas. For ecological monitoring to effectively support management decisions in high-latitude areas such as Alaska, a monitoring program ideally would be structured to address the actual spatial and temporal scales of relevant processes, rather than the artificial boundaries of individual land

  12. Inorganic carbon in a high latitude estuary-fjord system in Canada's eastern Arctic

    Science.gov (United States)

    Turk, D.; Bedard, J. M.; Burt, W. J.; Vagle, S.; Thomas, H.; Azetsu-Scott, K.; McGillis, W. R.; Iverson, S. J.; Wallace, D. W. R.

    2016-09-01

    Rapidly changing conditions in the Arctic can have a significant impact on biogeochemical cycles and can be particularly important in high latitude estuary-fjord systems with abundant and diverse freshwater sources. This study provides a first look into the inorganic carbon system and its relation to freshwater sources in Cumberland Sound in the east coast of Baffin Island, Nunavut, Canada. These data contribute to the very limited set of inorganic carbon measurements in high latitude estuary-fjord systems. During the ice-free conditions in August 2011, the meteoric freshwater fractions (MW) in the upper 40 m ranged from 11 to 21% and no sea ice melt (SIM) was present in the Sound. Surface waters were undersaturated with pCO2 (260 and 300 μatm), and DIC and TA ranged between 1779 and 1966 μmol DIC kg-1, and 1922 and 2140 μmol TA kg-1, respectively. Aragonite saturation (ΩAr) state ranged from 1.9 in the surface to 1.4 in the subsurface waters. Data show decreasing TA and ΩAr with increasing MW fraction and suggest that Cumberland Sound waters would become aragonite undersaturated (ΩAr < 1) at MW = 0.37 (95% CI: 0.29 to 0.56). Estimated local δ18O (-19.2‰) and TA (174 μmol TA kg-1) end-members indicate MW was most likely a mixture of river water and glacial melt. In August 2012, MW fractions at the surface were between 8 and 11.5%, and SIM between 7 and 23%. Significant interannual variability of summertime SIM could potentially result in ΩAr undersaturation.

  13. Small-scale fluctuations in barium drifts at high latitudes and associated Joule heating effects

    Science.gov (United States)

    Hurd, L. D.; Larsen, M. F.

    2016-01-01

    Most previous estimates of Joule heating rates, especially the contribution of small-scale structure in the high-latitude ionosphere, have been based on incoherent scatter or coherent scatter radar measurements. An alternative estimate can be found from the plasma drifts obtained from ionized barium clouds released from sounding rockets. We have used barium drift data from three experiments to estimate Joule heating rates in the high-latitude E region for different magnetic activity levels. In particular, we are interested in the contribution of small-scale plasma drift fluctuations, corresponding to equivalent electric field fluctuations, to the local Joule heating rate on scales smaller than those typically resolved by radar or other measurements. Since Joule heating is a Lagrangian quantity, the inherently Lagrangian estimates provided by the chemical tracer measurements are a full description of the effects of electric field variance and neutral winds on the heating, differing from the Eulerian estimates of the type provided by ground-based measurements. Results suggest that the small-scale contributions to the heating can be more than a factor of 2 greater than the mean field contribution regardless of geomagnetic conditions, and at times the small-scale contribution is even larger. The high-resolution barium drift measurements, moreover, show that the fine structure in the electric field can be more variable than previous studies have reported for similar conditions. The neutral winds also affect the heating, altering the height-integrated Joule heating rates by as much as 12%, for the cases studied here, and modifying the height distribution of the heating profile as well.

  14. Status of high-latitude precipitation estimates from observations and reanalyses

    Science.gov (United States)

    Behrangi, Ali; Christensen, Matthew; Richardson, Mark; Lebsock, Matthew; Stephens, Graeme; Huffman, George J.; Bolvin, David; Adler, Robert F.; Gardner, Alex; Lambrigtsen, Bjorn; Fetzer, Eric

    2016-05-01

    An intercomparison of high-latitude precipitation characteristics from observation-based and reanalysis products is performed. In particular, the precipitation products from CloudSat provide an independent assessment to other widely used products, these being the observationally based Global Precipitation Climatology Project (GPCP), Global Precipitation Climatology Centre, and Climate Prediction Center Merged Analysis of Precipitation (CMAP) products and the ERA-Interim, Modern-Era Retrospective Analysis for Research and Applications (MERRA), and National Centers for Environmental Prediction-Department of Energy Reanalysis 2 (NCEP-DOE R2) reanalyses. Seasonal and annual total precipitation in both hemispheres poleward of 55° latitude are considered in all products, and CloudSat is used to assess intensity and frequency of precipitation occurrence by phase, defined as rain, snow, or mixed phase. Furthermore, an independent estimate of snow accumulation during the cold season was calculated from the Gravity Recovery and Climate Experiment. The intercomparison is performed for the 2007-2010 period when CloudSat was fully operational. It is found that ERA-Interim and MERRA are broadly similar, agreeing more closely with CloudSat over oceans. ERA-Interim also agrees well with CloudSat estimates of snowfall over Antarctica where total snowfall from GPCP and CloudSat is almost identical. A number of disagreements on regional or seasonal scales are identified: CMAP reports much lower ocean precipitation relative to other products, NCEP-DOE R2 reports much higher summer precipitation over Northern Hemisphere land, GPCP reports much higher snowfall over Eurasia, and CloudSat overestimates precipitation over Greenland, likely due to mischaracterization of rain and mixed-phase precipitation. These outliers are likely unrealistic for these specific regions and time periods. These estimates from observations and reanalyses provide useful insights for diagnostic assessment of

  15. Polar Warming Drivers

    Science.gov (United States)

    McDunn, T. L.; Bougher, S. W.; Mischna, M. A.; Murphy, J. R.

    2012-12-01

    Polar warming is a dynamically induced temperature enhancement over mid-to-high latitudes that results in a reversed (poleward) meridional temperature gradient. This phenomenon was recently characterized over the 40-90 km altitude region [1] based on nearly three martian years of Mars Climate Sounder observations [2, 3]. Here we investigate which forcing mechanisms affect the magnitude and distribution of the observed polar warming by conducting simulations with the Mars Weather Research and Forecasting General Circulation Model [4, 5]. We present simulations confirming the influence topography [6] and dust loading [e.g., 7] have upon polar warming. We then present simulations illustrating the modulating influence gravity wave momentum deposition exerts upon polar warming, consistent with previous modeling studies [e.g., 8]. The results of this investigation suggest the magnitude and distribution of polar warming in the martian middle atmosphere is modified by gravity wave activity and that the characteristics of the gravity waves that most significantly affect polar warming vary with season. References: [1] McDunn, et al., 2012 (JGR), [2]Kleinböhl, et al., 2009 (JGR), [3] Kleinböhl, et al., 2011 (JQSRT), [4] Richardson, et al., 2007 (JGR), [5] Mischna, et al., 2011 (Planet. Space Sci.), [6] Richardson and Wilson, 2002 (Nature), [7] Haberle, et al., 1982 (Icarus), [8] Barnes, 1990 (JGR).

  16. Electrodynamics of the high-latitude trough: Its relationship with convection flows and field-aligned currents

    Science.gov (United States)

    Zou, Shasha; Moldwin, Mark B.; Nicolls, Michael J.; Ridley, Aaron J.; Coster, Anthea J.; Yizengaw, Endawoke; Lyons, Larry R.; Donovan, Eric F.

    2013-05-01

    We present a detailed case study of the electrodynamics of a high-latitude trough observed at ~ 12 UT (~1 MLT) on 8 March 2008 using multiple instruments, including incoherent scattering radar (ISR), GPS total electron content (TEC), magnetometers, and auroral imager. The electron density within the trough dropped as much as 80% within 6 minutes. This trough was collocated with a counterclockwise convection flow vortex, indicating divergent horizontal electric fields and currents. Together with a collocated dark area shown in auroral images, the observations provide strong evidence for an existence of downward field-aligned currents (FACs) collocated with the high-latitude trough. This is further supported by assimilative mapping of ionospheric electrodynamics results. In addition, the downward FACs formed at about the same time as a substorm onset and east of the Harang reversal, suggesting it is part of the substorm current wedge. It has long been a puzzle why this type of high-latitude trough predominantly occurs just east of the Harang reversal in the postmidnight sector. We suggest that the high-latitude trough is associated with the formation of downward FACs of the substorm current system, which usually occur just east of the Harang reversal. In addition, we find that the ionospheric electron temperature within the high latitude trough decreases in the F region while increasing in the E region. We discuss possible mechanisms responsible for the complex change in electron temperature, such as ion composition change and/or presence of downward FACs.

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

    International Nuclear Information System (INIS)

    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)

  18. Spatial teleconnection pattern between Indian Ocean Dipole and the southern high-latitude sea level pressure field

    Institute of Scientific and Technical Information of China (English)

    LIU Na; CHEN Hongxia; MIN Jinzhong; HUA Feng; BIAN Hongcun

    2005-01-01

    Sea level pressure (SLP) anomalies over the southern high latitudes associated with the Indian Ocean Dipole Mode(IOD) are investigated. Partial correlation and composite analysis depict, for the first time, the seasonal spatial variability in the relationship of SLP field in Southern Ocean with IOD. Results suggest that the IOD signal exists in the southern high latitudes and it is enhanced in boreal autumn, an active season of IOD. On interannual to subdecadal timescales, the spatial teleconnection pattern exhibits a wavenumber-3 pattern around the circumpolar Southern Ocean and the lead-lag correlation analysis shows that there are about 3 months of SLP anomalies in southern high latitudes lagging IOD, which indicates that the response time is almost instantaneous.

  19. Application of spherical cap harmonic analysis to plasma convection mapping at high latitudes

    Science.gov (United States)

    Fiori, Robyn A. D.

    The primary goal of this work is to develop, validate, and apply a new technique for mapping the high-latitude ionospheric plasma flow (convection pattern) from velocity measurements routinely performed by the Super Dual Auroral Radar (SuperDARN) network of high frequency (HF) radars. The currently employed FIT technique relies heavily on assumptions that are not always justifiable. A spherical cap harmonic analysis (SCHA) technique, traditionally used in handling geomagnetic field data, is introduced for mapping the high-latitude ionospheric convection pattern based on SuperDARN velocity measurements. The SCHA technique does not require contributions from a statistical model which is dependent on the magnitude and orientation of the interplanetary magnetic field (IMF), and does not confine the high-latitude flows to a specific region based on magnetic latitude. Several steps are taken to validate the SCHA convection mapping technique. First, it is demonstrated that the SCHA technique can reproduce an arbitrary pattern based on simulated data modified by a random noise component. SCHA maps of the global scale plasma flow pattern for various IMF conditions are next shown to be consistent with expectations for patterns reported in the literature. SCHA maps are compared to ion drifts measured by the Defense Meteorological Satellite Program (DMSP) satellites and with convection vectors inferred by merging SuperDARN measurements at beam crossings. The SCHA technique is shown to perform comparably to the FIT technique over regions of good data coverage. The SCHA technique provides a better representation of the ionospheric convection pattern for regions with limited data coverage and over regions of highly variable flow, particularly near the equatorward edge of the mapping region. SCHA analysis of SuperDARN data to create convection maps is expanded to include magnetometer measurements of the perturbation magnetic field. Plasma flow is determined from magnetometer data

  20. 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

  1. High-latitude plasma convection from Cluster EDI: variances and solar wind correlations

    Directory of Open Access Journals (Sweden)

    M. Förster

    2007-07-01

    Full Text Available Based on drift velocity measurements of the EDI instruments on Cluster during the years 2001–2006, we have constructed a database of high-latitude ionospheric convection velocities and associated solar wind and magnetospheric activity parameters. In an earlier paper (Haaland et al., 2007, we have described the method, consisting of an improved technique for calculating the propagation delay between the chosen solar wind monitor (ACE and Earth's magnetosphere, filtering the data for periods of sufficiently stable IMF orientations, and mapping the EDI measurements from their high-altitude positions to ionospheric altitudes. The present paper extends this study, by looking at the spatial pattern of the variances of the convection velocities as a function of IMF orientation, and by performing sortings of the data according to the IMF magnitude in the GSM y-z plane, |ByzIMF|, the estimated reconnection electric field, Er,sw, the solar wind dynamic pressure, Pdyn, the season, and indices characterizing the ring current (Dst and tail activity (ASYM-H. The variability of the high-latitude convection shows characteristic spatial patterns, which are mirror symmetric between the Northern and Southern Hemispheres with respect to the IMF By component. The latitude range of the highest variability zone varies with IMF Bz similar to the auroral oval extent. The magnitude of convection standard deviations is of the same order as, or even larger than, the convection magnitude itself. Positive correlations of polar cap activity are found with |ByzIMF| and with Er,sw, in particular. The strict linear increase for small magnitudes of Er,sw starts to deviate toward a flattened increase above about 2 mV/m. There is also a weak positive correlation with Pdyn. At

  2. 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

  3. 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

  4. 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

  5. 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

  6. Variability of the nighttime OH layer and mesospheric ozone at high latitudes during northern winter: influence of meteorology

    Directory of Open Access Journals (Sweden)

    A. Damiani

    2010-11-01

    Full Text Available Analyses of OH zonal means, recorded at boreal high latitudes by the Aura Microwave Limb Sounder (MLS in winters of 2005–2009, have shown medium- (weeks and short- (days term variability of the nighttime OH layer.

    Because of the exceptional descent of air from the mesosphere-lower thermosphere (MLT region, medium-term variability occurred during February 2006 and February/March 2009. The layer normally situated at about 82 km descended by about 5–7 km, and its density increased to more than twice January values. In these periods and location the abundance of the lowered OH layer is comparable to the OH values induced by Solar Energetic Particle (SEP forcing (e.g., SEP events of January 2005 at the same altitudes. In both years, the descent of the OH layer was coupled with increased mesospheric temperatures, elevated carbon monoxide and an almost complete disappearance of ozone at the altitude of the descended layer (which was not observed in other years. Moreover, under these exceptional atmospheric conditions, the third ozone peak, normally at about 72 km, is shown to descend about 5 km to lower altitude and increase in magnitude, with maximum values recorded during February 2009.

    Short-term variability occurred during Sudden Stratospheric Warming (SSW events, in particular in January 2006, February 2008 and January 2009, when dynamics led to a smaller abundance of the OH layer at its typical altitude. During these periods, there was an upward displacement of the OH layer coupled to changes in ozone and carbon monoxide. These perturbations were the strongest during the SSW of January 2009; coincident upper mesospheric temperatures were the lowest recorded over the late winters of 2005–2009. Finally, the series of SSW events that occurred in late January/February 2008 induced noticeable short-term variability in ozone at altitudes of both the ozone minimum and the third ozone peak.

    These phenomena, confined

  7. Probabilistic forecasting of ionospheric scintillation and GNSS receiver signal tracking performance at high latitudes

    Directory of Open Access Journals (Sweden)

    Paul Prikryl

    2013-06-01

    Full Text Available At high latitudes, phase scintillation occurs predominantly on the dayside in the ionospheric footprint of the magnetospheric cusp, and in the nightside auroral oval. A new technique of probabilistic forecasting of phase scintillation occurrence relative to the arrival time of high-speed solar wind from coronal holes and interplanetary coronal mass ejections has recently been proposed [Prikryl et al. 2012]. Cumulative probability distribution functions for the phase-scintillation occurrence that are obtained can be specified for low (below-median and high (above-median values of various solar wind plasma parameters. Recent advances in modeling of high-speed solar wind and coronal mass ejections, combined with the probabilistic forecasting of scintillation, will lead to improved operational space weather forecasting applications. Scintillation forecasting and mitigation techniques need to be developed to avoid potential costly failures of technology-based Global Navigation Satellite Systems in the near future, in particular during the upcoming solar maximum. The Global Navigation Satellite Systems receiver-tracking performance during severe scintillation conditions can be assessed by the analysis of receiver phase-locked-loop jitter. Tracking jitter maps [Sreeja et al. 2011] offers a potentially useful tool to provide users with expected tracking conditions, if based on scintillation predictions as proposed above. Scintillation indices are obtained from L1 GPS data collected with the Canadian High Arctic Ionospheric Network. Combined with high rate amplitude and phase data, they can be used as input to receiver tracking models to develop scintillation mitigation techniques.

  8. Structuring of full plasma patches in the high latitude with realistic drives-continued.

    Science.gov (United States)

    Guzdar, P. N.; Gondarenko, N. A.; Sojka, J. J.; David, M.

    2002-12-01

    The robustness of plasma patches, in spite of structuring by a combination of gradient drift and secondary Kelvin-Helmholtz (KH) instabilities, has been attributed to the strong stabilizing influence of dynamics of electrons along the field line and the break-up of the gradient drift instability driven fingers by secondary KH instabilities. Another physical effect that contributes significantly to the robustness of the patch is the variability of the convection of the patch over the polar cap region. Recently we have developed a parallel version of our 3D code, which can run on the IBM SP. We will present results of a set of runs with realistic convective drives obtained from MHD simulations of real event studies of substorms. The goal is to develop a database to provide statistical information on the nature of structuring in high latitude plasma patches. We are also developing diagnostic capabilities to compare with reconstructed images of the 3D transverse as well as parallel structure of the irregularities.

  9. Study of high-latitude ionosphere: One-year campaign over Husafell, Iceland

    Science.gov (United States)

    Bahari, S. A.; Abdullah, M.; Hasbi, A. M.; Yatim, B.; Suparta, W.; Kadokura, A.; Bjornsson, G.

    2016-07-01

    This paper reports on the effects of diurnal, seasonal, geomagnetic and solar activity on GPS Vertical Total Electron Content (VTEC) measurements at a high-latitude station in Husafell, Iceland (64.7°N, 21.0°W) from March 2009 to February 2010. According to the diurnal VTEC pattern, there was generally a build-up region at sunrise (0500-1000 LT), a daytime plateau in the afternoon (1200-1400 LT), and a decay region from evening to pre-dawn (1800-0400 LT). The month-to-month analysis showed high VTEC variability, particularly in February 2010, due to an increase in solar activity. The VTEC showed a high variability during both winter and the equinoxes, with the highest value being 90%, but showed a low variability in summer. Two abnormal peaks appeared at sunrise and sunset in winter and the equinoxes. These peaks were the result of steep density gradients caused by the onset and turnoff of solar radiation. The correlation analysis yielded almost no correlation between the VTEC and geomagnetic activity but showed a high correlation with solar activity for all the seasons, particularly at night-time.

  10. The 20 March 2015 total solar eclipse: effects in the high-latitude lower ionosphere

    Science.gov (United States)

    Cherniakov, Sergey; Tereshchenko, Valentina; Ogloblina, Olga; Vasiliev, Evgeny; Gomonov, Alexander

    2016-07-01

    The medium-wave facility of partial reflections of the Polar Geophysical Institute (observatory "Tumanny", 69 N, 35.7 E) has observed behavior of the lower high-latitude ionosphere during the 20 March 2015 total solar eclipse. There were several effects during the eclipse. Generally on the heights of the lower ionosphere the "short night" effect had shown, but at some heights local enhanced electron concentration were revealed and the behavior of the electron concentration had the wave-like form. It had seen also at the behavior of the total electron content of the lower ionosphere. The periods and behavior of the wave are considered. It can be explained by influence of acoustic-gravity waves which originated after cooling of the atmosphere by the lunar shadow during its supersonic movement along the earth surface. The periods and behavior of waves during the eclipse were also received using riometer data at the observatory "Tumanny" and the magnetometer at the observatory "Loparskaya" (68.63 N, 33.38 E).

  11. Causes of spring vegetation growth in the northern mid-high latitudes from 1982 to 2004

    Science.gov (United States)

    Mao, J.; Shi, X.; Thornton, P. E.

    2011-12-01

    The ability of a process-based ecosystem model like Version 4 of the Community Land Model (CLM4) to provide accurate estimates vegetation growth is a top priority for researchers, modelers and policy makers. Remote sensing can provide long-term and large scale products suitable for ecosystem model evaluation. Here we will describe how the CLM4 and the satellite-derived NDVI are applied to examine the spring Normalized Difference Vegetation Index (NDVI) changes in response to climate, CO2 fertilization, nitrogen deposition and land use land cover change (LULCC) effects on the inter-annual timescale over the northern mid-high latitudes (NMH) (>25 °N) for the recent decades (1982-2004). Our results show that the rising CO2 is simulated to cause a general increase of vegetation greenness. The predicted effects of nitrogen deposition on the vegetation growth are positive or negative dependent on the trend of the nitrogen change. The LULCC influence relies on the type of land management and the latitudes where the conversion happens. On the whole, the complicated impacts of multiple non-climate factors on spring NDVI variations locally alter the temperate-dominated inter-annual variations in the northern vegetation growth. Our results highlight the importance of the non-climate factors in mitigating or exacerbating the impact of temperature on spring vegetation growth, particularly across regions with intense human activity.

  12. Bird orientation at high latitudes: flight routes between Siberia and North America across the Arctic Ocean

    Science.gov (United States)

    Alerstam; Gudmundsson

    1999-12-22

    Bird migration and orientation at high latitudes are of special interest because of the difficulties associated with different compass systems in polar areas and because of the considerable differences between flight routes conforming to loxodromes (rhumblines) or orthodromes (great circle routes). Regular and widespread east-north-east migration of birds from the northern tundra of Siberia towards North America across the Arctic Ocean (without landmark influences) were recorded by ship-based tracking radar studies in July and August. Field observations indicated that waders, including species such as Phalaropusfulicarius and Calidris melanotos, dominated, but also terns and skuas may have been involved. Analysis of flight directions in relation to the wind showed that these movements are not caused by wind drift. Assuming possible orientation principles based on celestial or geomagnetic cues, different flight trajectories across the Arctic Ocean were calculated: geographical loxodromes, sun compass routes, magnetic loxodromes and magnetoclinic routes. The probabilities of these four alternatives are evaluated on the basis of both the availability of required orientation cues and the predicted flight paths. This evaluation supports orientation along sun compass routes. Because of the longitudinal time displacement sun compass routes show gradually changing compass courses in close agreement with orthodromes. It is suggested that an important migration link between Siberia and North American stopover sites 1000-2500km apart across the Arctic Ocean has evolved based on sun compass orientation along orthodrome-like routes. PMID:10693821

  13. A filament of energetic particles near the high-latitude dawn magnetopause

    Science.gov (United States)

    Lui, A. T. Y.; Williams, D. J.; Mcentire, R. W.; Christon, S. P.; Jacquey, C.; Angelopoulos, V.; Yamamoto, T.; Kokubun, S.; Frank, L. A.; Ackerson, K. L.

    1994-01-01

    The Geotail satelite detected a filament of tailward-streaming energetic particles spatially separated from the boundary layer of energetic particles at the high-latitude dawn magnetopause at a downstream distance of approximately 80 R(sub E) on October 27, 1992. During this event, the composition and charge states of energetic ions at energies above approximately 10 keV show significant intermix of ions from solar wind and ionospheric sources. Detailed analysis leads to the deduction that the filament was moving southward towards the neutral sheet at an average speed of approximately 80 km/s, implying an average duskward electric field of approximately 1 mV/m. Its north-south dimension was approximately 1 R(sub E) and it was associated with an earthward directed field-aligned current of approximately 5 mA/m. The filament was separated from the energetic particle boundary layer straddling the magnetopause by approximately 0.8 R(sub E) and was inferred to be detached from the boundary layer at downstream distance beyond approximately 70 R(sub E) in the distant tail.

  14. Measurements of the 21 centimeter Zeeman effect in high-latitude directions

    Energy Technology Data Exchange (ETDEWEB)

    Verschuur, G.L.

    1989-04-01

    A new series of measurements of the Zeeman effect at 21 cm has been launched using the 140 foot (43 m) telescope of the NRAO. The observations of high-latitude sources reveal tremendous improvement in sensitivity over measurements done in previous era. The detection of a field of + 5.5 micro G in the direction of the North Polar Spur, in the H I equivalent of CO cloud 40 of Magnani, Blitz, and Mundy, is reported. Field limits as low as a few microgauss were set in the direction of two very cold H I clouds after only 4 hr of integration. The detection of a field of the order of 7 micro G in one of the expanding H I shells observed by Troland and Heiles is confirmed, and the field varies significantly on a scale of 20 arcmin (0.6 pc at the shell). The detection of a field in the direction of the Orion region by Heiles and Troland is confirmed in one direction but not in another. 14 refs.

  15. Measurements of the 21 centimeter Zeeman effect in high-latitude directions

    International Nuclear Information System (INIS)

    A new series of measurements of the Zeeman effect at 21 cm has been launched using the 140 foot (43 m) telescope of the NRAO. The observations of high-latitude sources reveal tremendous improvement in sensitivity over measurements done in previous era. The detection of a field of + 5.5 micro G in the direction of the North Polar Spur, in the H I equivalent of CO cloud 40 of Magnani, Blitz, and Mundy, is reported. Field limits as low as a few microgauss were set in the direction of two very cold H I clouds after only 4 hr of integration. The detection of a field of the order of 7 micro G in one of the expanding H I shells observed by Troland and Heiles is confirmed, and the field varies significantly on a scale of 20 arcmin (0.6 pc at the shell). The detection of a field in the direction of the Orion region by Heiles and Troland is confirmed in one direction but not in another. 14 refs

  16. Measurements of the 21 centimeter Zeeman effect in high-latitude directions

    Science.gov (United States)

    Verschuur, Gerrit L.

    1989-04-01

    A new series of measurements of the Zeeman effect at 21 cm has been launched using the 140 foot (43 m) telescope of the NRAO. The observations of high-latitude sources reveal tremendous improvement in sensitivity over measurements done in previous era. The detection of a field of + 5.5 micro G in the direction of the North Polar Spur, in the H I equivalent of CO cloud 40 of Magnani, Blitz, and Mundy, is reported. Field limits as low as a few microgauss were set in the direction of two very cold H I clouds after only 4 hr of integration. The detection of a field of the order of 7 micro G in one of the expanding H I shells observed by Troland and Heiles is confirmed, and the field varies significantly on a scale of 20 arcmin (0.6 pc at the shell). The detection of a field in the direction of the Orion region by Heiles and Troland is confirmed in one direction but not in another.

  17. The mid-high latitude whistler mode chorus waves observed around substorm onsets

    Institute of Scientific and Technical Information of China (English)

    YANG JunYing; CAO JinBin; YAN ChunXiao; LI LiuYuan; MA YuDuan

    2008-01-01

    Using the data of LFEW/TC-2, we studied the dawn side chorus around substorm onsets during a strong geomagnetic storm in November 2004. During this storm, LFEW/TC-2 observed 14 dawnside chorus events. Nine of them were associated with substorms and occurred within 40 min around the substorm onsets. The fre-quencies of waves have a very good correlation with the half equatorial electron cyclotron frequencies. Chorus can be excited in the region near magnetic equato-rial plane and then propagate to the mid and high latitudes. When the wave fre-quencies reach the local lower hybrid frequencies, chorus can be reflected due to the lower hybrid resonance. The time delay between the chorus and its echo is about 28 min. Previous observations show that the chorus can propagate at most to the magnetic latitudes of 40°. LFEW/TC-2 found for the first time that the chorus in space could propagate to the magnetic latitude of 70°. Since most of the previous chorus observatlons are made close to the magnetic equatorial plane, our results are Important for the studies of excitation and propagation of whistler mode wave, and relevant relativistic electron acceleration in the magnetosphere.

  18. The mid-high latitude whistler mode chorus waves observed around substorm onsets

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Using the data of LFEW/TC-2, we studied the dawn side chorus around substorm onsets during a strong geomagnetic storm in November 2004. During this storm, LFEW/TC-2 observed 14 dawnside chorus events. Nine of them were associated with substorms and occurred within 40 min around the substorm onsets. The fre-quencies of waves have a very good correlation with the half equatorial electron cyclotron frequencies. Chorus can be excited in the region near magnetic equato-rial plane and then propagate to the mid and high latitudes. When the wave fre-quencies reach the local lower hybrid frequencies, chorus can be reflected due to the lower hybrid resonance. The time delay between the chorus and its echo is about 28 min. Previous observations show that the chorus can propagate at most to the magnetic latitudes of 40°. LFEW/ TC-2 found for the first time that the chorus in space could propagate to the magnetic latitude of 70°. Since most of the previous chorus observations are made close to the magnetic equatorial plane, our results are important for the studies of excitation and propagation of whistler mode wave, and relevant relativistic electron acceleration in the magnetosphere.

  19. Dust in High Latitudes in the Community Earth System Model since the Last Glacial Maximum

    Science.gov (United States)

    Albani, S.; Mahowald, N. M.

    2015-12-01

    Earth System Models are one of the main tools in modern climate research, and they provide the means to produce future climate projections. Modeling experiments of past climates is one of the pillars of the Coupled Modelling Inter-comparison Project (CMIP) / Paleoclimate Modelling Inter-comparison Project (PMIP) general strategy, aimed at understanding the climate sensitivity to varying forcings. Physical models are useful tools for studying dust transport patterns, as they allow representing the full dust cycle from sources to sinks with an internally consistent approach. Combining information from paleodust records and climate models in coherent studies can be a fruitful approach from different points of view. Based on a new quality-controlled, size- and temporally-resolved data compilation, we used the Community Earth System Model to estimate the mass balance of and variability in the global dust cycle since the Last Glacial Maximum and throughout the Holocene. We analyze the variability of the reconstructed global dust cycle at different climate equilibrium conditions since the LGM until the pre-industrial climate, and compare with palodust records, focusing on the high latitudes, and discuss the uncertainties and the implications for dust and iron deposition to the oceans.

  20. Principles and Problems of Data Assimilation for High-Latitude Ionospheric Electrodynamics

    Science.gov (United States)

    Richmond, A. D.; Matsuo, T.; Cousins, E. D. P.; Knipp, D. J.; Lu, G.; Marsal, S.

    2014-12-01

    Knowledge of the time-varying distributions of high-latitude ionospheric ionospheric electric fields and currents is needed for modeling the physics of the ionosphere and thermosphere. The patterns can also be used to investigate magnetospheric processes. The Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure was developed to estimate the distributions of electrodynamic parameters from combinations of observations of ionospheric drifts, ground- and satellite-based magnetic perturbations, and quantities related to ionospheric electrical conductivities, together with prior information about climatology and covariance of the parameters. AMIE uses optimal estimation theory to build on previous statistical studies and on an earlier mapping procedure that used only ground magnetometer data. Many of the improvements made to AMIE have been the addition of new data sets and procedures for semi-automatically processing the data. Theoretical developments have included improvements to the organization of the data in realistic magnetic coordinates, and dynamic estimation of the covariance matrices based on the data available at any given time. More recently, it has been shown that most of the large-scale variability can be represented with a relatively small number of empirical orthogonal basis functions derived from statistical analysis of large data sets. A key remaining limitation of AMIE-type estimations is the limited knowledge of auroral ionospheric conductivities, including limited understanding of nonlinear conductivities when electric fields are very strong. Neutral winds have heretofore been neglected, but they can sometimes have significant effects on the electrodynamics.

  1. Diffuse Galactic Gamma Rays at intermediate and high latitudes. I. Constraints on the ISM properties

    CERN Document Server

    Cholis, I; Evoli, C; Maccione, L; Ullio, P

    2011-01-01

    We study the high latitude (|b|>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 ~230 GV in CR proton...

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

    International Nuclear Information System (INIS)

    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

  3. Simulation of equatorial and high-latitude jets on Jupiter in a deep convection model.

    Science.gov (United States)

    Heimpel, Moritz; Aurnou, Jonathan; Wicht, Johannes

    2005-11-10

    The bands of Jupiter represent a global system of powerful winds. Broad eastward equatorial jets are flanked by smaller-scale, higher-latitude jets flowing in alternating directions. Jupiter's large thermal emission suggests that the winds are powered from within, but the zonal flow depth is limited by increasing density and electrical conductivity in the molecular hydrogen-helium atmosphere towards the centre of the planet. Two types of planetary flow models have been explored: shallow-layer models reproduce multiple high-latitude jets, but not the equatorial flow system, and deep convection models only reproduce an eastward equatorial jet with two flanking neighbours. Here we present a numerical model of three-dimensional rotating convection in a relatively thin spherical shell that generates both types of jets. The simulated flow is turbulent and quasi-two-dimensional and, as observed for the jovian jets, simulated jet widths follow Rhines' scaling theory. Our findings imply that Jupiter's latitudinal transition in jet width corresponds to a separation between the bottom-bounded flow structures in higher latitudes and the deep equatorial flows. PMID:16281029

  4. 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.)

  5. Solar Wind Electron Strahls Associated with a High-Latitude CME: Ulysses Observations

    Science.gov (United States)

    Lazar, M.; Pomoell, J.; Poedts, S.; Dumitrache, C.; Popescu, N. A.

    2014-11-01

    Counterstreaming beams of electrons are ubiquitous in coronal mass ejections (CMEs) - although their existence is not unanimously accepted as a necessary and/or sufficient signature of these events. We continue the investigation of a high-latitude CME registered by the Ulysses spacecraft on 18 - 19 January 2002 (Dumitrache, Popescu, and Oncica, Solar Phys. 272, 137, 2011), by surveying the solar-wind electron distributions associated with this event. The temporal evolution of the pitch-angle distributions reveals populations of electrons that are distinguishable through their anisotropy, with clear signatures of i) electron strahls, ii) counter-streaming in the magnetic clouds and their precursors, and iii) unidirectionality in the fast wind preceding the CME. The analysis of the counter-streams inside the CME allows us to elucidate the complexity of the magnetic-cloud structures embedded in the CME and to refine the borders of the event. Identifying such strahls in CMEs, which preserve properties of the low β [<1] coronal plasma, gives more support to the hypothesis that these populations are remnants of the hot coronal electrons that escape from the electrostatic potential of the Sun into the heliosphere.

  6. 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.

  7. Forecasts for the WFIRST High Latitude Survey using the BlueTides Simulation

    CERN Document Server

    Waters, Dacen; Feng, Yu; Wilkins, Stephen M; Croft, Rupert A C

    2016-01-01

    We use the BlueTides simulation to predict the properties of the high-$z$ galaxy and active galactic nuclei (AGN) populations for the planned 2200deg$^2$ Wide-Field Infrared Survey Telescope's (WFIRST)-AFTA High Latitude Survey (HLS). BlueTides is a cosmological hydrodynamic simulation, which incorporates a variety of baryon physics in a $(400h^{-1} \\mathrm{Mpc})^3$ volume evolved to $z=8$ with 0.7 trillion particles. The galaxy luminosity functions in the simulation show good agreement with all the current observational constraints (up to $z=11$) and predicts an enhanced number of UV bright galaxies. At the proposed depth of the HLS ($m < 26.75$), BlueTides predicts $10^6$ galaxies at $z=8$ with a few up to $z\\sim 15$ due to the enhanced bright end of the galaxy luminosity function. At $z=8$, galaxies in the mock HLS have specific star formation rates of $\\sim 10 {\\rm Gyr}^{-1}$ and ages of $\\sim 80 {\\rm Myr}$ (both evolving linearly with redshift) and a non-evolving mass-metallicity relation. BlueTides a...

  8. Relationship of solar wind parameters to continuous, dayside, high latitude traveling ionospheric convection vortices

    International Nuclear Information System (INIS)

    In a companion paper the authors have shown that many continuous, dayside, high latitude magnetic pulsations are caused by steady, traveling ionospheric convection vortices (McHenry et al. this issue). A variety of evidence indicates that these vortices are the ionospheric signatures of the Kelvin-Helmholtz instability at the inner edge of the magnetospheric boundary layer. In this paper the authors present the results of a statistical study of the occurrence of these vortices and the upstream solar wind parameters observed by the IMP 8 spacecraft. Surveying fifty days of Greenland west coast chain magnetometer data indicates this class of pulsations is most likely to be detected post local noon and when the solar wind speed is low. However, it is possible that observational factors significantly affect the detection of the vortices. the slow solar wind might create large, slow moving traveling vortices of steady strength which are easiest to identify. Little correlation is found between the average IMF and the probability of detecting the vortices. They also find a strong correlation between the frequency of dayside pulsations and the solar wind speed. This suggests that many pulsations are caused by traveling ionospheric current systems that map to the vicinity of the flows in the magnetospheric boundary layer. Periods also exist when the IMF is variable and large pulsations with 5 to 20 min period exist. These pulsations are not caused by traveling ionospheric vortices but are likely to be the result of rapid variations of the large scale field-aligned cusp currents

  9. Electronic kinetics of molecular nitrogen and molecular oxygen in high-latitude lower thermosphere and mesosphere

    Directory of Open Access Journals (Sweden)

    A. S. Kirillov

    2010-01-01

    Full Text Available Total quenching rate coefficients of Herzberg states of molecular oxygen and three triplet states of molecular nitrogen in the collisions with O2 and N2 molecules are calculated on the basis of quantum-chemical approximations. The calculated rate coefficients of electronic quenching of O2* and N2* molecules show a good agreement with available experimental data. An influence of collisional processes on vibrational populations of electronically excited N2 and O2 molecules is studied for the altitudes of high-latitude lower thermosphere and mesosphere during auroral electron precipitation. It is indicated that molecular collisions of metastable nitrogen N2(A3Σu* with O2 molecules are principal mechanism in electronic excitation of both Herzberg states c1Σu&minus, A'3Δu, A3Σu+ and high vibrational levels of singlet states a1Δg and b1Σg+ of molecular oxygen O2 at these altitudes.

  10. 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Chu, W. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather; Univ. of Chinese Academy of Sciences, Beijing (China). College of Earth Sciences; Qin, G. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather

    2016-04-01

    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.

  12. Forecasts for the WFIRST High Latitude Survey using the BLUETIDES Simulation

    Science.gov (United States)

    Waters, Dacen; Di Matteo, Tiziana; Feng, Yu; Wilkins, Stephen M.; Croft, Rupert A. C.

    2016-08-01

    We use the BLUETIDES simulation to predict the properties of the high-z galaxy and active galactic nuclei (AGN) populations for the planned 2200deg2 Wide-Field Infrared Survey Telescope's (WFIRST) High Latitude Survey (HLS). BLUETIDES is a cosmological hydrodynamic simulation, which incorporates a variety of baryon physics in a (400h-1Mpc)3 volume evolved to z = 8 with 0.7 trillion particles. The galaxy luminosity functions in the simulation show good agreement with all the current observational constraints (up to z = 11) and predicts an enhanced number of UV bright galaxies. At the proposed depth of the HLS (mUV luminosity function. At z = 8, galaxies in the mock HLS have specific star formation rates of ˜10Gyr-1 and ages of ˜80Myr (both evolving linearly with redshift) and a non-evolving mass-metallicity relation. BLUETIDES also predicts ˜104 AGN in WFIRST HLS from z = 8 out to z ˜ 14. These AGN host black holes of M ˜ 106 - 108M⊙ accreting close to their Eddington luminosity. Galaxies and AGN have host halo masses of Mhalo ˜ 1011 - 12M⊙ and a linear bias b ≈ 13 - 20. Given the expected galaxy space densities, their high bias and large volume probed we speculate that it may be feasible for WFIRST HLS detect the Baryon Acoustic Oscillation peak in the galaxy power spectrum out to z = 8 - 9.

  13. High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    Full Text Available The DOPE (Doppler Pulsation Experiment HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3 is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.

    Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions · Magnetospheric physics (MHD waves and instabilities

  14. High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes

    Science.gov (United States)

    Wright, D. M.; Yeoman, T. K.; Chapman, P. J.

    1997-12-01

    A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF) waves by a high-latitude (geographic: 69.6°N 19.2°E) high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated with pulsations in ground magnetometer data, exhibit periods in the range 100-400 s and have azimuthal wave numbers in the range 3-8. They are interpreted here as local field line resonances. Phase information provided by O- and X-mode Doppler data support the view that these are associated with field line resonances having large azimuthal scale sizes. The relative phases and amplitudes of the signatures in the Doppler and ground magnetometer data are compared with a model for the generation of Doppler signatures from incident ULF waves. The outcome suggests that the dominant mechanism involved in producing the Doppler signature is the vertical component of an E × B bulk motion of the local plasma caused by the electric field perturbation of the ULF wave.

  15. High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    Full Text Available A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF waves by a high-latitude (geographic: 69.6°N 19.2°E high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated with pulsations in ground magnetometer data, exhibit periods in the range 100–400 s and have azimuthal wave numbers in the range 3–8. They are interpreted here as local field line resonances. Phase information provided by O- and X-mode Doppler data support the view that these are associated with field line resonances having large azimuthal scale sizes. The relative phases and amplitudes of the signatures in the Doppler and ground magnetometer data are compared with a model for the generation of Doppler signatures from incident ULF waves. The outcome suggests that the dominant mechanism involved in producing the Doppler signature is the vertical component of an E × B bulk motion of the local plasma caused by the electric field perturbation of the ULF wave.

    Key words. Auroral ionosphere · Magnetosphere-ionosphere interactions · MHD waves and instabilities HF Doppler · ULF Waves

  16. ULF wave occurrence statistics in a high-latitude HF Doppler sounder

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    Full Text Available Ultra low frequency (ULF wave activity in the high-latitude ionosphere has been observed by a high frequency (HF Doppler sounder located at Tromsø, Norway (69.7°N, 19.2°E geographic coordinates. A statistical study of the occurrence of these waves has been undertaken from data collected between 1979 and 1984. The diurnal, seasonal, solar cycle and geomagnetic activity variations in occurrence have been investigated. The findings demonstrate that the ability of the sounder to detect ULF wave signatures maximises at the equinoxes and that there is a peak in occurrence in the morning sector. The occurrence rate is fairly insensitive to changes associated with the solar cycle but increases with the level of geomagnetic activity. As a result, it has been possible to characterise the way in which prevailing ionospheric and magnetospheric conditions affect such observations of ULF waves.

    Key words. Ionosphere (auroral ionosphere; ionosphere -magnetosphere interactions · Magnetospheric physics (MHD waves and instabilities

  17. High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

    Science.gov (United States)

    Wright, D. M.; Yeoman, T. K.

    1999-07-01

    The DOPE (Doppler Pulsation Experiment) HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3) is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg) pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.

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

    International Nuclear Information System (INIS)

    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.)

  19. GPS phase scintillation and proxy index at high latitudes during a moderate geomagnetic storm

    Directory of Open Access Journals (Sweden)

    P. Prikryl

    2013-05-01

    Full Text Available The amplitude and phase scintillation indices are customarily obtained by specialised GPS Ionospheric Scintillation and TEC Monitors (GISTMs from L1 signal recorded at the rate of 50 Hz. The scintillation indices S4 and σΦ are stored in real time from an array of high-rate scintillation receivers of the Canadian High Arctic Ionospheric Network (CHAIN. Ionospheric phase scintillation was observed at high latitudes during a moderate geomagnetic storm (Dst = −61 nT that was caused by a moderate solar wind plasma stream compounded with the impact of two coronal mass ejections. The most intense phase scintillation (σΦ ~ 1 rad occurred in the cusp and the polar cap where it was co-located with a strong ionospheric convection, an extended tongue of ionisation and dense polar cap patches that were observed with ionosondes and HF radars. At sub-auroral latitudes, a sub-auroral polarisation stream that was observed by mid-latitude radars was associated with weak scintillation (defined arbitrarily as σΦ Φ > 0.1 rad and DPR > 2 mm s−1, both mapped as a function of magnetic latitude and magnetic local time, are very similar.

  20. Observations of the High-Latitude Ionospheric Response to the Onset of the April 2002 Storm

    Science.gov (United States)

    Thayer, J. P.; Heinselman, C. J.; Tsunoda, R. T.; van Eyken, A. P.; Stromme, A.; McCready, M. A.

    2002-12-01

    The high-latitude incoherent scatter radars at Sondrestrom, Greenland, and Longyearbyen, Svalbard, observed detailed ionospheric behavior during the initial shock, occurring near 11:00 UT on April 17, and the onset of the geomagnetic storm. During this period, the Sondrestrom radar observed extreme electric field enhancements in excess of 120 mV/m. The direction of the electric field at Sondrestrom indicates the measurements are located in the sunward convection region of the dawn and pre-noon sector. These large electric fields subsequently produced very high levels of Joule heating rates (greater than 80 mW/m2), extreme ion heating events (in excess of 3500 K), aurorally enhanced electron temperatures and current-driven instabilities leading to extreme electron temperatures in the lower E region (in excess of 2000 K). Additionally the F-region meridional neutral wind response and E region neutral winds are inferred. Concurrent observations on Svalbard, in the post-noon and dusk sector, also indicate enhanced F- and E-region ion and electron temperatures. Though the ionospheric response observed by the radars are determined locally, electric field enhancements estimated by AMIE runs during this period of the storm suggest that these effects may, in fact, occur over a much larger region.

  1. 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. PMID:15734581

  2. 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 < 0.01), indicating that warmer summers were beneficial for growth, perhaps by increasing 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.

  3. Axial obliquity control on the greenhouse carbon budget through middle- to high-latitude reservoirs

    Science.gov (United States)

    Laurin, Jiří; Meyers, Stephen R.; Uličný, David; Jarvis, Ian; Sageman, Bradley B.

    2015-02-01

    Carbon sources and sinks are key components of the climate feedback system, yet their response to external forcing remains poorly constrained, particularly for past greenhouse climates. Carbon-isotope data indicate systematic, million-year-scale transfers of carbon between surface reservoirs during and immediately after the Late Cretaceous thermal maximum (peaking in the Cenomanian-Turonian, circa 97-91 million years, Myr, ago). Here we calibrate Albian to Campanian (108-72 Myr ago) high-resolution carbon isotope records with a refined chronology and demonstrate how net transfers between reservoirs are plausibly controlled by ~1 Myr changes in the amplitude of axial obliquity. The amplitude-modulating terms are absent from the frequency domain representation of insolation series and require a nonlinear, cumulative mechanism to become expressed in power spectra of isotope time series. Mass balance modeling suggests that the residence time of carbon in the ocean-atmosphere system is—by itself—insufficient to explain the Myr-scale variability. It is proposed that the astronomical control was imparted by a transient storage of organic matter or methane in quasi-stable reservoirs (wetlands, soils, marginal zones of marine euxinic strata, and potentially permafrost) that responded nonlinearly to obliquity-driven changes in high-latitude insolation and/or meridional insolation gradients. While these reservoirs are probably underrepresented in the geological record due to their quasi-stable character, they might have provided an important control on the dynamics and stability of the greenhouse climate.

  4. Seasonal migration to high latitudes results in major reproductive benefits in an insect.

    Science.gov (United States)

    Chapman, Jason W; Bell, James R; Burgin, Laura E; Reynolds, Donald R; Pettersson, Lars B; Hill, Jane K; Bonsall, Michael B; Thomas, Jeremy A

    2012-09-11

    Little is known of the population dynamics of long-range insect migrants, and it has been suggested that the annual journeys of billions of nonhardy insects to exploit temperate zones during summer represent a sink from which future generations seldom return (the "Pied Piper" effect). We combine data from entomological radars and ground-based light traps to show that annual migrations are highly adaptive in the noctuid moth Autographa gamma (silver Y), a major agricultural pest. We estimate that 10-240 million immigrants reach the United Kingdom each spring, but that summer breeding results in a fourfold increase in the abundance of the subsequent generation of adults, all of which emigrate southward in the fall. Trajectory simulations show that 80% of emigrants will reach regions suitable for winter breeding in the Mediterranean Basin, for which our population dynamics model predicts a winter carrying capacity only 20% of that of northern Europe during the summer. We conclude not only that poleward insect migrations in spring result in major population increases, but also that the persistence of such species is dependent on summer breeding in high-latitude regions, which requires a fundamental change in our understanding of insect migration. PMID:22927392

  5. Quantifying Climate Feedbacks from Abrupt Changes in High-Latitude Trace-Gas Emissions

    Energy Technology Data Exchange (ETDEWEB)

    Schlosser, Courtney Adam [MIT; Walter-Anthony, Katey [University of Alaska; Zhuang, Qianlai [Purdue University; Melillo, Jerry [Marine Biological Laboratory

    2013-04-26

    Our overall goal was to quantify the potential for threshold changes in natural emission rates of trace gases, particularly methane and carbon dioxide, from pan-arctic terrestrial systems under the spectrum of anthropogenically forced climate warming, and the extent to which these emissions provide a strong feedback mechanism to global climate warming. This goal is motivated under the premise that polar amplification of global climate warming will induce widespread thaw and degradation of the permafrost, and would thus cause substantial changes in the extent of wetlands and lakes, especially thermokarst (thaw) lakes, over the Arctic. Through a coordinated effort of field measurements, model development, and numerical experimentation with an integrated assessment model framework, we have investigated the following hypothesis: There exists a climate-warming threshold beyond which permafrost degradation becomes widespread and thus instigates strong and/or sharp increases in methane emissions (via thermokarst lakes and wetland expansion). These would outweigh any increased uptake of carbon (e.g. from peatlands) and would result in a strong, positive feedback to global climate warming.

  6. GPS phase scintillation at high latitudes during geomagnetic storms of 7-17 March 2012 - Part 2: Interhemispheric comparison

    Science.gov (United States)

    Prikryl, P.; Ghoddousi-Fard, R.; Spogli, L.; Mitchell, C. N.; Li, G.; Ning, B.; Cilliers, P. J.; Sreeja, V.; Aquino, M.; Terkildsen, M.; Jayachandran, P. T.; Jiao, Y.; Morton, Y. T.; Ruohoniemi, J. M.; Thomas, E. G.; Zhang, Y.; Weatherwax, A. T.; Alfonsi, L.; De Franceschi, G.; Romano, V.

    2015-06-01

    During the ascending phase of solar cycle 24, a series of interplanetary coronal mass ejections (ICMEs) in the period 7-17 March 2012 caused geomagnetic storms that strongly affected high-latitude ionosphere in the Northern and Southern Hemisphere. GPS phase scintillation was observed at northern and southern high latitudes by arrays of GPS ionospheric scintillation and TEC monitors (GISTMs) and geodetic-quality GPS receivers sampling at 1 Hz. Mapped as a function of magnetic latitude and magnetic local time (MLT), the scintillation was observed in the ionospheric cusp, the tongue of ionization fragmented into patches, sun-aligned arcs in the polar cap, and nightside auroral oval and subauroral latitudes. Complementing a companion paper (Prikryl et al., 2015a) that focuses on the high-latitude ionospheric response to variable solar wind in the North American sector, interhemispheric comparison reveals commonalities as well as differences and asymmetries between the northern and southern high latitudes, as a consequence of the coupling between the solar wind and magnetosphere. The interhemispheric asymmetries are caused by the dawn-dusk component of the interplanetary magnetic field controlling the MLT of the cusp entry of the storm-enhanced density plasma into the polar cap and the orientation relative to the noon-midnight meridian of the tongue of ionization.

  7. What do model results tell us regarding Climate Intervention (Geoengineering) strategies to counter high latitude climate change.

    Science.gov (United States)

    Rasch, P. J.

    2015-12-01

    A number of modeling studies at various levels of complexity have taken place to explore consequences of climate intervention in countering climate change. I will review results from some of those studies, cover some new analysis, and identify areas where more study is needed, with a focus on high latitude climate.

  8. 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...

  9. Transpiration of urban trees and its cooling effect in a high latitude city

    Science.gov (United States)

    Konarska, Janina; Uddling, Johan; Holmer, Björn; Lutz, Martina; Lindberg, Fredrik; Pleijel, Håkan; Thorsson, Sofia

    2016-01-01

    An important ecosystem service provided by urban trees is the cooling effect caused by their transpiration. The aim of this study was to quantify the magnitude of daytime and night-time transpiration of common urban tree species in a high latitude city (Gothenburg, Sweden), to analyse the influence of weather conditions and surface permeability on the tree transpiration, and to find out whether tree transpiration contributed to daytime or nocturnal cooling. Stomatal conductance and leaf transpiration at day and night were measured on mature street and park trees of seven common tree species in Gothenburg: Tilia europaea, Quercus robur, Betula pendula, Acer platanoides, Aesculus hippocastanum, Fagus sylvatica and Prunus serrulata. Transpiration increased with vapour pressure deficit and photosynthetically active radiation. Midday rates of sunlit leaves ranged from less than 1 mmol m-2 s-1 ( B. pendula) to over 3 mmol m-2 s-1 ( Q. robur). Daytime stomatal conductance was positively related to the fraction of permeable surfaces within the vertically projected crown area. A simple estimate of available rainwater, comprising of precipitation sum and fractional surface permeability within the crown area, was found to explain 68 % of variation in midday stomatal conductance. Night-time transpiration was observed in all studied species and amounted to 7 and 20 % of midday transpiration of sunlit and shaded leaves, respectively. With an estimated night-time latent heat flux of 24 W m-2, tree transpiration significantly increased the cooling rate around and shortly after sunset, but not later in the night. Despite a strong midday latent heat flux of 206 W m-2, a cooling effect of tree transpiration was not observed during the day.

  10. High Latitude Scintillation Monitoring at UHF with the COMMX Experiment on TACSat4

    Science.gov (United States)

    Bernhardt, P. A.; Siefring, C. L.; Akins, K.; Nurnberger, M.

    2013-12-01

    UHF Beacon Transmissions at 253 MHz have provided high latitude scintillation monitoring from Gakona Alaska using the COMMX instrument on TACSat4. TACSat4 was constructed by the Naval Research Laboratory and was launched in September 2011 as an experimental communications satellite. Ground UHF transmissions are uplinked to TACSat4 using the 4 meter diameter antenna deployed to view the earth. These signals are coherently translated to other UHF frequency to be rebroadcast to the ground. Scintillation monitoring is achieved by taking the 401.25 MHz signals from ground DORIS beacons located in Cold Bay, Alaska; Yellowknife, Canada; Kauai, Hawaii; and Soccoro Island, Mexico. These signals are translated to 253 MHz and broadcast with the 4 meter antenna pointed to the UHF receiver located at Gakona, Alaska. The satellite antenna gain is 18 dB in this UHF band and the transmitter power is 2 Watts. The satellite is in an elliptical orbit with an inclination of 63 degrees and a perigee of 12,000 km. Doppler frequency shifts allow separation of each uplink from the ground DORIS beacons. This new scintillation monitoring system has been used to detect natural and artificial field aligned irregularity effects on the amplitude and phase of UHF carriers where typical scintillation amplitudes are 2dB or less. Using the HAARP transmitter in Alaska, TACSat4 was used to discover the artificial ionization clouds produce scintillation with as much as 16 dB and amplitude indices S4 greater than unity. This is the first demonstration of significant effects on radio scintillations using high power HF radio waves to disturb the ionosphere.

  11. Evolution of high latitude ionospheric convection associated with substorms: Multiple radar observations

    Science.gov (United States)

    Zou, Shasha

    The work presented in this dissertation concerns evolution of the high latitude ionospheric convection and the relevant current systems associated with substorms, with emphasize on these features near the nightside Harang reversal region. Three different types of radars, including the Super Dual Auroral Radar Network (SuperDARN) coherent-scatter radars, the new advanced modular incoherent-scatter radar at Poker Flat (PFISR), and the Sondrestrom incoherent-scatter radar (ISR), have been utilized. Observations from those radars, together with those from complementary instruments, including satellites and other ground-based instruments, have revealed fundamental new understand of the ionospheric electrodynamic properties associated with substorms. By using the SuperDARN and the PFISR radars, we found that the auroral activity at substorm onset is located in the center of the Harang reversal, which represents a key region in the magnetospheric and ionospheric convection and is part of the Region 2 system. We have also shown that nightside convection flows exhibit repeatable, distinct variations at different locations relative to the substorm-related auroral activity. Taking advantage of the simultaneous flow and ionization measurements from PFISR, a current closure relation has been found between the Region 2 and the substorm field-aligned current systems. These observations demonstrate a strong coupling between the Region 2 system and the substorm dynamics. This study sheds new light on the substorm-related magnetosphere-ionosphere coupling and contributes to the building of a holistic picture of the substorm dynamics. The third radar has been used to study the dayside ionospheric convection response to the external soar wind and IMF driving and its role in substorm dynamics. The results have been applied to study substorm triggering and in the future could be used to study the relation between the external driving and the formation of the Harang reversal.

  12. Characteristics of satellite accelerometer measurements of thermospheric neutral winds at high latitudes

    Science.gov (United States)

    Doornbos, E.; Ridley, A. J.; Cnossen, I.; Aruliah, A. L.; Foerster, M.

    2015-12-01

    Thermospheric neutral winds play an important part in the coupled thermosphere-ionosphere system at high latitudes. Neutral wind speeds have been derived from the CHAMP and GOCE satellites, which carried precise accelerometers in low Earth orbits. Due to the need to simultaneously determine thermosphere neutral density from the accelerometer in-track measurements, only information on the wind component in the cross-track direction, perpendicular to the flight direction can be derived. However, contrary to ground-based Fabry-Perot interferometer and scanning Doppler imager observations of the thermosphere wind, these satellite-based measurements provide equally distributed coverage over both hemispheres. The sampling of seasonal and local time variations depend on the precession rate of the satellite's orbital plane, with CHAMP covering about 28 cycles of 24-hour local solar time coverage, during its 10 year mission (2000-2010), while the near sun-synchronous orbit of GOCE resulted in a much more limited local time coverage ranging from 6:20 to 8:00 (am and pm), during a science mission duration of 4 years (2009-2013). For this study, the wind data from both CHAMP and GOCE have been analysed in terms of seasonal variations and geographic and geomagnetic local solar time and latitude coordinates, in order to make statistical comparisons for both the Northern and Southern polar areas. The wind data from both satellites were studied independently and in combination, in order to investigate how the strengths and weaknesses of the instruments and orbit parameters of these missions affect investigations of interhemispheric differences. Finally, the data have been compared with results from coupled ionosphere-thermosphere models and from ground-based FPI and SDI measurements.

  13. 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

  14. 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.

  15. 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.

  16. Global High-Latitude Conductivity Modeling: New Data and Improved Methods

    Science.gov (United States)

    McGranaghan, R. M.; Knipp, D. J.; Matsuo, T.; Godinez, H. C.

    2014-12-01

    The ionospheric conductivity distribution is essential for understanding the coupling in the magnetosphere-ionosphere-thermosphere (MIT) system. Hall conductivities, which regulate ionospheric current flow in the direction perpendicular to both the background magnetic field and the electric field, exert control over magnetospheric configuration, including transport within the plasmasphere and reconnection in the magnetotail [Lotko et al., 2014]. Pedersen conductivities control electric field variability and, in turn, determine the distribution and intensity of Joule heating, a prominent source of upper atmospheric temperature and neutral density enhancement. Contemporary conductivity modeling techniques rely on limiting assumptions and are 2-dimensional by design. Typically these models assume Maxwellian incoming particle energy distributions and simplistic current closure paths within an ionospheric 'shell' located at 110 km. We have developed a method to: 1) eliminate these assumptions and 2) allow 3-dimensional conductivity analysis using particle energy spectra provided by Defense Meteorological Satellite Program (DMSP) satellites. A sequential non-linear procedure then regresses the conductivities derived from DMSP data on the same basis functions used in the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure to obtain a realistic form of the covariance model, with the goal to integrate 3-dimensional conductivity analysis into the AMIE procedure. This addresses one of the primary sources of uncertainty within AMIE, and will ultimately allow more accurate characterization of high-latitude ionospheric electrodynamics. We present 3-dimensional conductivity distributions derived from satellite observations and global maps of these conductivities for the year 2010. References:Lotko, W., et al. (2014), Ionospheric control of magnetotail reconnection, Science, 345(6193), 184-187, doi:10.1126/science.1252907.

  17. Evidence For Inputs of Allochthonous Alkenones During The Last Glacial To The North Atlantic: Shortcomings In The Use of Alkenone Proxies In High Latitudes

    Science.gov (United States)

    Rosell-Melé, A.; Kornilova, O.; Russell, M.

    The reliability of UK37 to reconstruct SST in the Northern North Atlantic during the last glacial period has been already challenged in the literature. Thus, estimates of SST in cores located in latitudes higher than 50 degrees North appear to be unexpectedly warm if the conventional approach to use UK37 is followed (i.e. the relative abun- dance of the di and tri unsaturated alkenone converted to temperature using the equa- tion proposed by Prahl et al 1988, or Müller et al 1998). One of the feasible processes postulated to explain the unexpected warm estimates is to advocate the advection to the deep sea of allochthonous alkenones reflecting SSTs much warmer than those of the last glacial in high latitudes. However, no conclusive proof to date has been of- fered to demonstrate this hypothesis. To investigate this further we have examined the biomarker content of debris flows surrounding the northern North Atlantic. The last glacial ice sheets drained through specific outlet glaciers, giving rise to a number of large submarine fans in the continental margins. Large amounts of debris which had been entrained in the ice sheets were deposited at the shelf break. These sediments were inherently unstable, failed and were deposited on the slope through gravimet- ric mass flows (i.e. debris flows). We have found that some of the major debris flows contain alkenones in significant amounts. The composition of individual deposits is also homogenous both within a lobe and between lobes from the same area. More- over, those deposits in the Eastern Atlantic contain a SST-UK37 warm signal, devoid of tetraunsaturated C37 ketone, higher than those UK37 values found in modern sur- face sediments in the Northern North Atlantic. We argue that our findings prove that the estimates of SST derived from UK37 in glacial sediments of the northern north Atlantic are biased by an input of allochthonous alkenones transported by ice rafted debris.

  18. A new paleomagnetic Paleocene-Eocene apparent polar wandering path derived from magnetostratigraphies: correlations for faunal and floral development at high latitude.

    Science.gov (United States)

    Moreau, M.; Besse, J.; Fluteau, F.

    2005-12-01

    The development of endemic warm-climate flora and fauna at high latitudes in both hemispheres attests to the global warming that affected the Earth at the end of the Paleocene and the beginning of the Eocene. Nonetheless, the presence of these species at very high latitudes is also conditional on insolation, and the presence of tropical flora and fauna at very high paleomagnetic paleolatitudes, well north of the Arctic Circle, remains intriguing. We thus reappraise paleomagnetic data in a new way, defining an apparent geomagnetic polar wander path (APWP) from the beginning of the Paleocene to the middle of the mid-Eocene (65-42Ma) using a selection of magnetostratigraphies published over the last 25 years. Six series of VGPs are sufficiently long and of high enough quality to be retained; they originate from Gubbio (Italy) and from leg 74 for the African plate; from the Aix en Provence (France) and Basque (Spain) basins for Europe; from leg 171B for North America, and from leg 121 for Australia. For each site, a VGP (virtual geomagnetic pole) is defined for each magnetic anomaly and then transferred using classical kinematic parameters onto Africa selected as the single reference frame. The successive mean geomagnetic poles for each anomaly (hence perfectly synchronous) are then calculated in order to define the APWP. This shows a loop with two cusps at anomalies 26-25 (61-56 Ma) and 24-23 (56-51 Ma); the corresponding mean poles differ according to McFadden and McElhinny (1990), whereas the end poles relating to anomalies 29-27 (65.5-61 Ma) and 22-19 (51-42.5 Ma) are identical. The plate movements inferred from this loop, possibly related to an episode of true polar wander, are shown to be in agreement with the climatic and paleoenvironmental data and suggests a migration of flora and fauna which is synchronous with migration of the pole, rather than an adaptation of these species to the polar obscurity.

  19. 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

  20. 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.

  1. Absence of 21st century warming on Antarctic Peninsula consistent with natural variability.

    Science.gov (United States)

    Turner, John; Lu, Hua; White, Ian; King, John C; Phillips, Tony; Hosking, J Scott; Bracegirdle, Thomas J; Marshall, Gareth J; Mulvaney, Robert; Deb, Pranab

    2016-07-21

    Since the 1950s, research stations on the Antarctic Peninsula have recorded some of the largest increases in near-surface air temperature in the Southern Hemisphere. This warming has contributed to the regional retreat of glaciers, disintegration of floating ice shelves and a 'greening' through the expansion in range of various flora. Several interlinked processes have been suggested as contributing to the warming, including stratospheric ozone depletion, local sea-ice loss, an increase in westerly winds, and changes in the strength and location of low-high-latitude atmospheric teleconnections. Here we use a stacked temperature record to show an absence of regional warming since the late 1990s. The annual mean temperature has decreased at a statistically significant rate, with the most rapid cooling during the Austral summer. Temperatures have decreased as a consequence of a greater frequency of cold, east-to-southeasterly winds, resulting from more cyclonic conditions in the northern Weddell Sea associated with a strengthening mid-latitude jet. These circulation changes have also increased the advection of sea ice towards the east coast of the peninsula, amplifying their effects. Our findings cover only 1% of the Antarctic continent and emphasize that decadal temperature changes in this region are not primarily associated with the drivers of global temperature change but, rather, reflect the extreme natural internal variability of the regional atmospheric circulation.

  2. Absence of 21st century warming on Antarctic Peninsula consistent with natural variability

    Science.gov (United States)

    Turner, John; Lu, Hua; White, Ian; King, John C.; Phillips, Tony; Hosking, J. Scott; Bracegirdle, Thomas J.; Marshall, Gareth J.; Mulvaney, Robert; Deb, Pranab

    2016-07-01

    Since the 1950s, research stations on the Antarctic Peninsula have recorded some of the largest increases in near-surface air temperature in the Southern Hemisphere. This warming has contributed to the regional retreat of glaciers, disintegration of floating ice shelves and a ‘greening’ through the expansion in range of various flora. Several interlinked processes have been suggested as contributing to the warming, including stratospheric ozone depletion, local sea-ice loss, an increase in westerly winds, and changes in the strength and location of low–high-latitude atmospheric teleconnections. Here we use a stacked temperature record to show an absence of regional warming since the late 1990s. The annual mean temperature has decreased at a statistically significant rate, with the most rapid cooling during the Austral summer. Temperatures have decreased as a consequence of a greater frequency of cold, east-to-southeasterly winds, resulting from more cyclonic conditions in the northern Weddell Sea associated with a strengthening mid-latitude jet. These circulation changes have also increased the advection of sea ice towards the east coast of the peninsula, amplifying their effects. Our findings cover only 1% of the Antarctic continent and emphasize that decadal temperature changes in this region are not primarily associated with the drivers of global temperature change but, rather, reflect the extreme natural internal variability of the regional atmospheric circulation.

  3. Absence of 21st century warming on Antarctic Peninsula consistent with natural variability.

    Science.gov (United States)

    Turner, John; Lu, Hua; White, Ian; King, John C; Phillips, Tony; Hosking, J Scott; Bracegirdle, Thomas J; Marshall, Gareth J; Mulvaney, Robert; Deb, Pranab

    2016-07-21

    Since the 1950s, research stations on the Antarctic Peninsula have recorded some of the largest increases in near-surface air temperature in the Southern Hemisphere. This warming has contributed to the regional retreat of glaciers, disintegration of floating ice shelves and a 'greening' through the expansion in range of various flora. Several interlinked processes have been suggested as contributing to the warming, including stratospheric ozone depletion, local sea-ice loss, an increase in westerly winds, and changes in the strength and location of low-high-latitude atmospheric teleconnections. Here we use a stacked temperature record to show an absence of regional warming since the late 1990s. The annual mean temperature has decreased at a statistically significant rate, with the most rapid cooling during the Austral summer. Temperatures have decreased as a consequence of a greater frequency of cold, east-to-southeasterly winds, resulting from more cyclonic conditions in the northern Weddell Sea associated with a strengthening mid-latitude jet. These circulation changes have also increased the advection of sea ice towards the east coast of the peninsula, amplifying their effects. Our findings cover only 1% of the Antarctic continent and emphasize that decadal temperature changes in this region are not primarily associated with the drivers of global temperature change but, rather, reflect the extreme natural internal variability of the regional atmospheric circulation. PMID:27443743

  4. 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

  5. Modeling of nitrobenzene in the river with ice process in high-latitude regions

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    To deal with the accidental release of pollutants into frozen rivers, those rivers in high-latitude regions should be treated differently. Pollutants could be stored up in the ice and released when the ice melts in spring, perhaps resulting in secondary pollution in the river. A water quality model of nitrobenzene has been developed in this paper to assess the influence on river water quality due to the freezing process. The model is made up of three modules: thermodynamic module, hydrodynamic module and water quality module. The thermodynamic module considers the complex heat exchange processes between the water body and the atmosphere, the water body and the river bed, the water body and the ice cover, and so on. The growth of the ice cover is simulated in a simplified form whilst taking consideration of heat balance. The hydrodynamic model uses the Saint-Venant equations in non-constant flow and the influence of the ice cover is measured. The degradation, diffusion, absorption and desorption, and the influence of the freezing process are incorporated in the water quality module and the concept of Con- tinuously Stirred Tanked Reactors (CSTRs) model is applied in the model construction. The model has been applied to supporting the management of accidental pollution in the Songhua River. The model was calibrated and validated with monitored data. Regional sensitivity analysis based on a task-based Hornberger-Spear-Young (HSY) algorithm was carried out to examine the model structure and the re- sult showed that the model could describe the system very well. Then the conditioned model was ap- plied to predicting the concentration of nitrobenzene in the water when the ice melted in spring. The predictive result showed that the release of pollutants in the ice could lead to an increase in the con- centration of pollutants in the water, but the increase would be very small because there was only a small amount of pollutants stored in the ice. A secondary pollution

  6. Modeling of nitrobenzene in the river with ice process in high-latitude regions

    Institute of Scientific and Technical Information of China (English)

    SUN PengCheng; ZENG SiYu; CHEN JiNing

    2009-01-01

    To deal with the accidental release of pollutants into frozen rivers,those rivers in high-latitude regions should be treated differently.Pollutants could be stored up in the ice and released when the ice melts in spring,perhaps resulting in secondary pollution in the river.A water quality model of nitrobenzene has been developed in this paper to assess the influence on river water quality due to the freezing process.The model is made up of three modules:thermodynamic module,hydrodynamic module and water quality module.The thermodynamic module considers the complex heat exchange processes between the water body and the atmosphere,the water body and the river bed,the water body and the ice cover,and so on.The growth of the ice cover is simulated in a simplified form whilst taking consideration of heat balance.The hydrodynamic model uses the Saint-Venant equations in non-constant flow and the influence of the ice cover is measured.The degradation,diffusion,absorption and desorption,and the influence of the freezing process are incorporated in the water quality module and the concept of Continuously Stirred Tanked Reactors (CSTRs) model is applied in the model construction.The model has been applied to supporting the management of accidental pollution in the Songhua River.The model was calibrated and validated with monitored data.Regional sensitivity analysis based on a task-based Hornberger-Spear-Young (HSY) algorithm was carried out to examine the model structure and the result showed that the model could describe the system very well.Then the conditioned model was applied to predicting the concentration of nitrobenzene in the water when the ice melted in spring.The predictive result showed that the release of pollutants in the ice could lead to an increase in the concentration of pollutants in the water,but the increase would be very small because there was only a small amount of pollutants stored in the ice.A secondary pollution could therefore be avoided

  7. Persistence of biological nitrogen fixation in high latitude grass-clover grasslands under different management practices

    Science.gov (United States)

    Tzanakakis, Vasileios; Sturite, Ievina; Dörsch, Peter

    2016-04-01

    Biological nitrogen fixation (BNF) can substantially contribute to N supply in permanent grasslands, improving N yield and forage quality, while reducing inorganic N inputs. Among the factors critical to the performance of BNF in grass-legume mixtures are selected grass and legume species, proportion of legumes, the soil-climatic conditions, in particular winter conditions, and management practices (e.g. fertilization and compaction). In high latitude grasslands, low temperatures can reduce the performance of BNF by hampering the legumés growth and by suppressing N2 fixation. Estimation of BNF in field experiments is not straightforward. Different methods have been developed providing different results. In the present study, we evaluated the performance of BNF, in a newly established field experiment in North Norway over four years. The grassland consisted of white clover (Trifolium repens L.) and red clover (Trifolium pretense L.) sawn in three proportions (0, 15 and 30% in total) together with timothy (Pheum pretense L.) and meadow fescue (Festuca pratensis L.). Three levels of compaction were applied each year (no tractor, light tractor, heavy tractor) together with two different N rates (110 kg N/ha as cattle slurry or 170 kg N/ha as cattle slurry and inorganic N fertilizer). We applied two different methods, the 15N natural abundance and the difference method, to estimate BNF in the first harvest of each year. Overall, the difference method overestimated BNF relative to the 15N natural abundance method. BNF in the first harvest was compared to winter survival of red and white clover plants, which decreased with increasing age of the grassland. However, winter conditions did not seem to affect the grassland's ability to fix N in spring. The fraction of N derived from the atmosphere (NdfA) in white and red clover was close to 100% in each spring, indicating no suppression of BNF. BNF increased the total N yield of the grasslands by up to 75%, mainly due to high

  8. New Terminology for the High-Latitude Field-Aligned Current Systems

    Science.gov (United States)

    Papitashvili, V.; Weimer, D.

    2003-12-01

    hours. We will discuss new terms that might be needed for the existing lexicon - to extend its old terminology in describing the modern understanding of morphology and evolution of the high-latitude field-aligned current systems.

  9. 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

  10. Tracing of high latitude magnetopause by Interball, Polar and Geotail versus MHD and gas dynamic modelling

    Science.gov (United States)

    Savin, S.; Zelenyi, L.; Amata, E.; Berchem, J.; Buechner, J.; Song, P.; Fuselier, S.; Kawano, H.; Mukai, T.; Maynard, N.

    L. Zelenyi (1), E. Amata (6), J. Berchem (5), J. Buechner (7), P. Song (3), S. Fuselier (13), H. Kawano (4), V. Lutsenko (1), T. Mukai (8), K. Maezawa (8), N. Maynard (2), Z. Nemecek (14), R. Nakamura (15), M. Fujimoto (10), A. Pedersen (9), E. Panov (1), I. Sandahl (11), J. Safrankova (14), J.A. Sauvaud (16), V. Smirnov (1), K. Stasiewicz (12) (2) MRC, Nashua, USA, (3) U. Mass., Lowell, USA, (4) Kyushu U., Japan, (5) UCLA, USA, (6) IFSI, Roma, Italy, (7) MPAe, Lindau, Germany, (8) ISAS, Japan, (9) Oslo U., Norway, (10) Tokyo U., Japan, (11) IRF, Kiruna, Sweden, (12) IRF-U, Uppsala, Sweden, (13) LMATC, USA, (14) Charles U., Czech Rep., (15) IWF, Graz, Austria, (16) CESR, Toulouse, France, We present two case studies of magnetosheath (MSH) interaction with the high latitude magnetopause (MP) on the basis of Interball-1, Polar, Geotail and other ISTP spacecraft data. On April 23-24, 1998 Interball & Polar over cusp and Geotail at the tail flank (GSM Z =10 Re) traced boundary layers (BL). The time-depended MHD modeling serves to unite the 6-point data with the global reconnection pattern, driven by strong solar wind (SW) disturbances. At the smaller scales the BL perturbations display similar kinked magnetic spectra and 3-wave phase coupling, the correlation length is less than the distance between Interball-Polar (3 RE). Strong SW disturbances, decelerated over cusp, penetrate deep into tail. For quiet SW local perturbations dominate at frequencies over few mHz. Similar spectral features are seen on June 19, 1998 both in stagnant MSH (Polar) and upstream 'plasma ball' (PB, Interball-1) - demagnetized heated plasma (ion beta ~ 2-15) of MSH origin inside MP. Comparison with SW magnetic spectra and plasma moments from Geotail using Gas Dynamic Convection Field model indicates that the patchy reconnection pulses at Polar location are modulated by the upstream BL fluctuations. The fluctuations result from direct interaction of PB with MSH flow by means of reflected from

  11. Absorption properties of high-latitude Norwegian coastal water: The impact of CDOM and particulate matter

    Science.gov (United States)

    Nima, Ciren; Frette, Øyvind; Hamre, Børge; Erga, Svein Rune; Chen, Yi-Chun; Zhao, Lu; Sørensen, Kai; Norli, Marit; Stamnes, Knut; Stamnes, Jakob J.

    2016-09-01

    We present data from measurements and analyses of the spectral absorption due to colored dissolved organic matter (CDOM), total suspended matter (TSM), phytoplankton, and non-algal particles (NAP) in high-latitude northern Norwegian coastal water based on samples taken in spring, summer, and autumn. The Chlorophyll-a (Chl-a) concentration was found to vary significantly with season, whereas regardless of season CDOM was found to be the dominant absorber for wavelengths shorter than 600 nm. The absorption spectral slope S350-500 for CDOM varied between 0.011 and 0.022 nm-1 with mean value and standard deviation given by (0.015 ± 0.002) nm-1. The absorption spectral slope was found to be strongly dependent on the wavelength interval used for fitting. On average, S280-500 was found to be 43% higher than S350-500. A linear relationship was found between the base 10 logarithm of the absorption coefficient at 440 nm [log(ag(440))] and S350-500. Regardless of season, phytoplankton were the dominant component of the TSM absorption indicating little influence from land drainage. The mean values of the Chl-a specific absorption coefficient of phytoplankton aph*(λ) at 440 nm and 676 nm were 0.052 m2 mg-1 and 0.023 m2 mg-1, respectively, and aph*(λ) was found to vary with season, being higher in summer and autumn than in spring. The absorption spectral slope SNAP, which is the spectral slope of absorption spectrum for non-algal particles, was lower than that for European coastal water in general. It varied between 0.0048 and 0.022 nm-1 with mean value and standard deviation given by (0.0083-1 ± 0.003) nm-1. Comparisons of absorption coefficients measured in situ using an ac-9 instrument with those measured in the laboratory from water samples show a good agreement.

  12. Space Weather Impact on the European Interconnected Power Transmission System at High Latitudes

    Science.gov (United States)

    Piccinelli, Roberta; Krausmann, Elisabeth

    2016-04-01

    High voltage power transmission grids can suffer outages or blackouts during geomagnetic storms (GMS). More specifically, GMS can inject geomagnetically induced currents (GICs) into the power network. Transformers were identified as the most vulnerable components of the power networks: GICs cause transformers to work in saturation regions generating voltage instabilities and eventually driving the system to collapse. Since GMS are expected to cause more pronounced disturbances at high latitudes, we addressed the effects of extreme GMS on the Scandinavian 400 kV interconnected power transmission grid, including Finland, Sweden and Norway. By applying extreme 100-year-benchmark scenarios, we analyzed potential space-weather triggered voltage instabilities in the power grid considering mono-phase transformers, which are known to be more vulnerable to GIC injection, and three-phase transformers, which are more resistant. We assumed that every node of the grid included either transformers of the mono-phase type, or three-phase transformers.Our simulations indicate that the three-phase configuration of the network is significantly more robust than the mono-phase one. Our study indicates that for a system with only three-phase transformers the likelihood of grid collapse is very low, and collapse only occurs for the worst-case scenario with extremely high geoelectric field intensities. In such a case, the increase in reactive power demand caused by transformer saturation is too high for the system to continue to provide power. Our results indicate that lines that experience higher reactive power losses during normal operation are more likely to increase losses during a GMS event. According to our study, the portion of the Scandinavian interconnected power transmission grid most vulnerable to extreme space weather is the part where the highest reactive losses in transmission lines and in voltage magnitudes are observed. This corresponds to the southern parts of Sweden and

  13. Investigatigating inter-/intra-annual variability of surface hydrology at northern high latitude from spaceborne measurements

    Science.gov (United States)

    Kang, K.; Duguay, C. R.

    2014-12-01

    Lakes encompass a large part of the surface cover in the northern boreal and tundra areas of northern Canada and are therefore a significant component of the terrestrial hydrological system. To understand the hydrologic cycle over subarctic and arctic landscapes, estimating surface parameters such as surface net radiation, soil moisture, and surface albedo is important. Although ground-based field measurements provide a good temporal resolution, these data provide a limited spatial representation and are often restricted to the summer period (from June to August), and few surface-based stations are located in high-latitude regions. In this respect, spaceborne remote sensing provides the means to monitor surface hydrology and to estimate components of the surface energy balance with reasonable spatial and temporal resolutions required for hydrological investigations, as well as for providing more spatially representative lake-relevant information than available from in situ measurements. The primary objective of this study is to quantify the sources of temporal and spatial variability in surface albedo over subarctic wetland from satellite derived albedo measurements in the Hudson Bay Lowlands near Churchill, Manitoba. The spatial variability in albedo within each land-cover type is investigated through optical satellite imagery from Landsat-5 Thematic Mapper, Landsat-7 Enhanced Thematic Mapper Plus, and Landsat-8 Operational Land Imager obtained in different seasons from spring into fall (April and October) over a 30-year period (1984-2013). These data allowed for an examination of the spatial variability of surface albedo under relatively dry and wet summer conditions (i.e. 1984, 1998 versus 1991, 2005). A detailed analysis of Landsat-derived surface albedo (ranging from 0.09 to 0.15) conducted in the Churchill region for August is inversely related to surface water fraction calculated from Landsat images. Preliminary analysis of surface albedo observed between

  14. The Soil Moisture Active Passive (SMAP): Radar Measurements at High Latitudes and of Freeze/Thaw State

    Science.gov (United States)

    Spencer, Michael; Dunbar, Scott; Chen, Curtis

    2013-01-01

    The Soil Moisture Active/Passive (SMAP) mission is scheduled for a late 2014 launch date. The mission will use both active radar and passive radiometer instruments at L-Band. In order to achieve a wide swath at sufficiently high resolution for both active and passive channels, an instrument architecture that uses a large rotating reflector is employed. In this paper, a focus will be places on the radar design and associated data products at high latitudes. The radar will employ synthetic-aperture processing to achieve a "moderate" resolution dual-pol product over a 1000 km swath. Because the radar is operating continuously, very frequent temporal coverage will be achieved at high latitudes. This data will be used, among other things, to produce a surface freeze/thaw state data product.

  15. Methane fluxes between terrestrial ecosystems and the atmosphere at northern high latitudes during the past century: A retrospective analysis with a process-based biogeochemistry model

    Science.gov (United States)

    Zhuang, Q.; Melillo, J.M.; Kicklighter, D.W.; Prinn, R.G.; McGuire, A.D.; Steudler, P.A.; Felzer, B.S.; Hu, S.

    2004-01-01

    We develop and use a new version of the Terrestrial Ecosystem Model (TEM) to study how rates of methane (CH4) emissions and consumption in high-latitude soils of the Northern Hemisphere have changed over the past century in response to observed changes in the region's climate. We estimate that the net emissions of CH4 (emissions minus consumption) from these soils have increased by an average 0.08 Tg CH4 yr-1 during the twentieth century. Our estimate of the annual net emission rate at the end of the century for the region is 51 Tg CH4 yr-1. Russia, Canada, and Alaska are the major CH4 regional sources to the atmosphere, responsible for 64%, 11%, and 7% of these net emissions, respectively. Our simulations indicate that large interannual variability in net CH4 emissions occurred over the last century. Our analyses of the responses of net CH4 emissions to the past climate change suggest that future global warming will increase net CH4 emissions from the Pan-Arctic region. The higher net CH4 emissions may increase atmospheric CH 4 concentrations to provide a major positive feedback to the climate system. Copyright 2004 by the American Geophysical Union.

  16. Early Holocene Laurentide Ice Sheet deglaciation causes cooling in the high-latitude Southern Hemisphere through oceanic teleconnection

    OpenAIRE

    H. Renssen; Goosse, H.; X. Crosta; Roche, D. M.

    2010-01-01

    The impact of the early Holocene Laurentide Ice Sheet (LIS) deglaciation on the climate at Southern Hemisphere high latitudes is studied in three transient simulations performed with a global climate model of the coupled atmosphere-ocean-vegetation system. Considering the LIS deglaciation, we quantify separately the impacts of the background meltwater fluxes and the changes in topography and surface albedo. In our model, the meltwater input into the North Atlantic results in a substantial wea...

  17. North-South differences in the Earth's high-latitude upper atmosphere dynamics: influence of solar activity and seasonal variations

    OpenAIRE

    M. Förster; I. Cnossen

    2014-01-01

    Recent observations have shown that the upper thermospheric/ionospheric response to solar wind and IMF dependent drivers of the magnetosphere-ionosphere-thermosphere (M-I-T) system can be very dissimilar in the Northern and Southern Hemisphere. We present statistical studies of the high-latitude upper thermospheric neutral wind circulation patterns obtained from almost a decade of measurements with an accelerometer on board the CHAMP spacecraft. The influence of the solar activity and the dep...

  18. Theoretical Study of the Electron Temperature in the High-Latitude Ionosphere for Solar Maximum and Winter Conditions

    OpenAIRE

    Schunk, Robert W.; Sojka, Jan Josef; Bowline, M. D.

    1986-01-01

    The electron temperature (Te) variation in the high-latitude ionosphere at altitudes between 120 and 800 km has been modeled for solar maximum, winter solstice, and strong magnetic activity conditions. The calculated electron temperatures are consistent with the plasma densities and ion temperatures computed from a time-dependent ionospheric model. Heating rates for both solar EUV and auroral precipitation were included. In general, the predicted UT variation of the electron temperature that ...

  19. Polar, Cluster and SuperDARN Evidence for High-Latitude Merging during Southward IMF: Temporal/Spatial Evolution

    Science.gov (United States)

    Maynard, N. C.; Ober, D. M.; Burke, W. J.; Scudder, J. D.; Lester, M.; Dunlap, M.; Wild, J. A.; Grocott, A.; Farrugia, C. J.; Lund, E. J.; Russell, C. T.

    2003-01-01

    Magnetic merging on the dayside magnetopause often occurs at high latitudes. Polar measured fluxes of accelerated ions and wave Poynting vectors while skimming the subsolar magnetopause. The measurements indicate that their source was located to the north of the spacecraft, well removed from expected component merging sites. This represents the first use of wave Poynting flux as a merging discriminator at the magnetopause. We argue that wave Poynting vectors, like accelerated particle fluxes and the Walen tests, are necessary, but not sufficient, conditions, for identifying merging events. The Polar data are complemented with nearly simultaneous measurements from Cluster in the northern cusp, with correlated observations from the SuperDARN radar, to show that the locations and rates of merging vary. Magnetohydrodynamic (MHD) simulations are used to place the measurements into a global context. The MHD simulations confirm the existence of a high-latitude merging site and suggest that Polar and SuperDARN observed effects are attributable to both exhaust regions of a temporally varying X-line. A survey of 13 merging events places the location at high latitudes whenever the interplanetary magnetic field (IMF) clock angle is less than approximately 150 degrees. While inferred high-latitude merging sites favor the antiparallel merging hypothesis, our data alone cannot exclude the possible existence of a guide field. Merging can even move away from equatorial latitudes when the IMF has a strong southward component. MHD simulations suggest that this happens when the dipole tilt angle increases or when IMF B(sub X) increases the effective dipole tilt.

  20. Polar, Cluster and SuperDARN evidence for high-latitude merging during southward IMF: temporal/spatial evolution

    Directory of Open Access Journals (Sweden)

    N. C. Maynard

    Full Text Available Magnetic merging on the dayside magnetopause often occurs at high latitudes. Polar measured fluxes of accelerated ions and wave Poynting vectors while skimming the subsolar magnetopause. The measurements indicate that their source was located to the north of the spacecraft, well removed from expected component merging sites. This represents the first use of wave Poynting flux as a merging discriminator at the magnetopause. We argue that wave Poynting vectors, like accelerated particle fluxes and the Walén tests, are necessary, but not sufficient, conditions for identifying merging events. The Polar data are complemented with nearly simultaneous measurements from Cluster in the northern cusp, with correlated observations from the Super-DARN radar, to show that the locations and rates of merging vary. Magnetohydrodynamic (MHD simulations are used to place the measurements into a global context. The MHD simulations confirm the existence of a high-latitude merging site and suggest that Polar and SuperDARN observed effects are attributable to both exhaust regions of a temporally varying X-line. A survey of 13 merging events places the location at high latitudes whenever the interplanetary magnetic field (IMF clock angle is less than ~150°. While inferred high-latitude merging sites favor the antiparallel merging hypothesis, our data alone cannot exclude the possible existence of a guide field. Merging can even move away from equatorial latitudes when the IMF has a strong southward component. MHD simulations suggest that this happens when the dipole ilt angle increases or when IMF BX increases the effective dipole tilt.

    Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetospheric configuration and dynamics; solar wind-magnetosphere interactions

  1. Influence of sunspot number and magnetic activity on the diurnal variation of the geomagnetic field at mid to high latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Hamilton, R.A. (British Antarctic Survey, Cambridge); Hodder, B.M. (Natural Environment Research Council, Edinburgh (UK). Inst. of Geological Sciences)

    1984-02-01

    The variations of the diurnal range of the geomagnetic field with sunspot number and with magnetic activity was studied at mid and high latitude stations in the northern hemisphere at different seasons. The effect of increasing sunspot number is small at lower latitudes and increases with geomagnetic latitude, while the effect of increasing magnetic activity is to increase the range at all latitudes, very greatly at the higher geomagnetic latitudes.

  2. Evaluating the dominant components of warming in Pliocene climate simulations

    Directory of Open Access Journals (Sweden)

    D. J. Hill

    2013-03-01

    Full Text Available The Pliocene Model Intercomparison Project 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 cloud albedo feedbacks enhancing the warming in most of the models, but by widely varying amounts. The responses to mid-Pliocene climate forcing in the Northern Hemisphere mid-latitudes 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. 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 cloud albedo feedbacks in the tropics and polar clear sky albedo, particularly in sea ice regions. These simulations show that high latitude albedo feedbacks provide the most significant enhancements to Pliocene greenhouse warming.

  3. 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.

  4. Comparison with oblique sounder data of high-latitude HF propagation predictions from RADAR C and AMBCOM computer program

    Science.gov (United States)

    Dave, Nikhil

    1988-06-01

    A study is done using two High Frequency (HF) propagation prediction programs - RADAR C and AMBCOM - to determine how well they predict median values of oblique sounder data of maximum observed frequencies (MOF) at high latitudes. The main differences between RADAR C and AMBCOM are the inclusion in the latter of high-latitude ionosphere and auroral absorption models, as well as a more sophisticated and accurate ray-tracing scheme. The data used for comparison are taken for the Winnipeg-Resolute Bay path in the year 1959 and for the Andoya-Ft. Monmouth and Andoya-College paths in 1964. The data for the Winnipeg-Resolute Bay corresponds to high sunspot number, while the others correspond to low sunspot number. Hence, this study provides information on the performance of the two programs for various high-latitude paths at both high and low sunspot number. AMBCOM was found to give generally better agreement with the above data than did RADAR C. Comparison of details of model predictions from the two computer programs for the above data-base is used to form an understanding of this improvement in prediction capability.

  5. Defining parasite biodiversity at high latitudes of North America: new host and geographic records for Onchocerca cervipedis (Nematoda: Onchocercidae in moose and caribou

    Directory of Open Access Journals (Sweden)

    Verocai Guilherme G

    2012-10-01

    Full Text Available Abstract Background Onchocerca cervipedis is a filarioid nematode of cervids reported from Central America to boreal regions of North America. It is found primarily in subcutaneous tissues of the legs, and is more commonly known as ‘legworm’. Blackflies are intermediate hosts and transmit larvae to ungulates when they blood-feed. In this article we report the first records of O. cervipedis from high latitudes of North America and its occurrence in previously unrecognized host subspecies including the Yukon-Alaska moose (Alces americanus gigas and the Grant’s caribou (Rangifer tarandus granti. Methods We examined the subcutaneous connective tissues of the metacarpi and/or metatarsi of 34 moose and one caribou for parasitic lesions. Samples were collected from animals killed by subsistence hunters or animals found dead in the Northwest Territories (NT, Canada and Alaska (AK, USA from 2005 to 2012. Genomic DNA lysate was prepared from nematode fragments collected from two moose. The nd5 region of the mitochondrial DNA was amplified by PCR and sequenced. Results Subcutaneous nodules were found in 12 moose from the NT and AK, and one caribou from AK. Nematodes dissected from the lesions were identified as Onchocerca cervipedis based on morphology of female and male specimens. Histopathological findings in moose included cavitating lesions with multifocal granulomatous cellulitis containing intralesional microfilariae and adults, often necrotic and partially mineralized. Lesions in the caribou included periosteitis with chronic cellulitis, eosinophilic and lymphoplasmacytic infiltrate, and abundant granulation associated with intralesional adult nematodes and larvae. Sequences of the nd5 region (471bp, the first generated for this species, were deposited with Genbank (JN580791 and JN580792. Representative voucher specimens were deposited in the archives of the United States National Parasite Collection. Conclusions The geographic range of O

  6. Microbial communities in high latitudes and high altitudes ecosystems%高寒生态系统微生物群落研究进展

    Institute of Scientific and Technical Information of China (English)

    褚海燕

    2013-01-01

    Climate warming is widely predicted to be largest and most rapid at high latitudes and high altitudes like Arctic tundra, alpine tundra, Tibetan plateau, etc. The impacts of climate change on these ecosystems are critical for the global C cycle because of the large amount of C stored in these cold regions. Microbes are key drivers in biogeochemical cycling, and microbial responses and feedbacks to climate change affect ecosystems functioning and stability. This paper review microbial community composition, diversity and spatial distributions in those cold ecosystems, and microbial responses to climate change (warming, nitrogen deposition, fire interference), which could provide base in expanding microbial community studies in cold ecosystems of China.%高寒生态系统分布在高纬度或高海拔、气候寒冷的地区,包括北极苔原、高山苔原、青藏高原等.高寒生态系统对气候变化非常敏感,其土壤中储存大量的有机碳,对全球的碳平衡起关键作用.微生物是生物地球化学循环的主要驱动者,微生物群落对气候变化的响应和反馈影响生态系统的功能与稳定性.本文回顾了高寒生态系统微生物群落组成、多样性与空间分布,以及微生物群落对气候变化(增温、氮沉降、火干扰)的响应,为拓展我国高寒生态系统微生物研究提供基础.

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

    Science.gov (United States)

    Kuhn, Thomas; Heymsfield, Andrew J.

    2016-06-01

    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

  8. 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

  9. 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

  10. Controls on winter ecosystem respiration at mid- and high-latitudes

    Science.gov (United States)

    Wang, T.; Ciais, P.; Piao, S.; Ottle, C.; Brender, P.; Maignan, F.; Arain, A.; Gianelle, D.; Gu, L.; Lafleur, P.; Laurila, T.; Margolis, H.; Montagnani, L.; Moors, E.; Nobuko, S.; Vesala, T.; Wohlfahrt, G.; Reichstein, M.; Migliavacca, M.; Ammann, C.; Aubinet, M.; Barr, A.; Bernacchi, C.; Bernhofer, C.; Black, T.; Davis, K.; Dellwik, E.; Dragoni, D.; Don, A.; Flanagan, L.; Foken, T.; Granier, A.; Hadley, J.; Hirata, R.; Hollinger, D.; Kato, T.; Kutsch, W.; Marek, M.; Matamala, R.; Matteucci, G.; Meyers, T.; Monson, R.; Munger, J.; Oechel, W.; Paw U, K. T.; Rebmann, C.; Tuba, Z.; Valentini, R.; Varlagin, A.; Verma, S.

    2010-09-01

    Winter CO2 fluxes represent an important component of the annual carbon budget in northern ecosystems. Understanding winter respiration processes and their responses to climate change is also central to our ability to assess terrestrial carbon cycle and climate feedbacks in the future. The factors influencing the spatial and temporal pattern of winter respiration (RECO) of northern ecosystems are poorly understood. For this reason, we analyzed eddy covariance flux data sets from 57 ecosystem sites ranging from ~35° N to ~70° N. Deciduous forests carry the highest winter RECO ratios (9.7-10.5 g C m-2 d-1), when winter is defined as the period during which air temperature remained below 0 °C. By contrast, wetland ecosystems had the lowest winter RECO (2.1-2.3 g C m-2 d-1). Evergreen needle-leaved forests, grasslands and croplands were characterized by intermediate winter RECO values of 7.4-7.9 g C m-2 d-1, 5.8-6.0 g C m-2 d-1, and 5.2-5.3 g C m-2 d-1, respectively. Cross site analysis showed that winter air or soil temperature, and the seasonal amplitude of the leaf area index inferred from satellite observation, which is a proxy for the amount of litter available for RECO in the subsequent winter, are the two main factors determining spatial pattern of daily mean winter RECO. Together, these two factors can explain 71% (Tair, ΔLAI) or 69% (Tsoil, ΔLAI) of the spatial variance of winter RECO across the 57 sites. The spatial temperature sensitivity of daily winter RECO was determined empirically by fitting an Arrhenius relationship to the data. The activation energy parameter of this relationship was found to decrease at increasing soil temperature at a rate of 83.1 KJ ° C-1 (r = -0.32, p < 0.05), which implies a possible dampening of the increase in winter RECO due to global warming. The interannual variability of winter RECO is better explained by soil temperature than by air temperature, likely due to the insulating effects of snow cover. The increase in

  11. -induced continental warming

    Science.gov (United States)

    Kamae, Youichi; Watanabe, Masahiro; Kimoto, Masahide; Shiogama, Hideo

    2014-11-01

    In this the second of a two-part study, we examine the physical mechanisms responsible for the increasing contrast of the land-sea surface air temperature (SAT) in summertime over the Far East, as observed in recent decades and revealed in future climate projections obtained from a series of transient warming and sensitivity experiments conducted under the umbrella of the Coupled Model Intercomparison Project phase 5. On a global perspective, a strengthening of land-sea SAT contrast in the transient warming simulations of coupled atmosphere-ocean general circulation models is attributed to an increase in sea surface temperature (SST). However, in boreal summer, the strengthened contrast over the Far East is reproduced only by increasing atmospheric CO2 concentration. In response to SST increase alone, the tropospheric warming over the interior of the mid- to high-latitude continents including Eurasia are weaker than those over the surrounding oceans, leading to a weakening of the land-sea SAT contrast over the Far East. Thus, the increasing contrast and associated change in atmospheric circulation over East Asia is explained by CO2-induced continental warming. The degree of strengthening of the land-sea SAT contrast varies in different transient warming scenarios, but is reproduced through a combination of the CO2-induced positive and SST-induced negative contributions to the land-sea contrast. These results imply that changes of climate patterns over the land-ocean boundary regions are sensitive to future scenarios of CO2 concentration pathways including extreme cases.

  12. Controls on winter ecosystem respiration at mid- and high-latitudes

    Directory of Open Access Journals (Sweden)

    T. Wang

    2010-09-01

    in winter RECO due to global warming. The interannual variability of winter RECO is better explained by soil temperature than by air temperature, likely due to the insulating effects of snow cover. The increase in winter RECO with a 1 °C warming based calculated from the spatial analysis was almost that double that calculated from the temporal analysis. Thus, models that calculate the effects of warming on RECO based only on spatial analyses could be over-estimating the impact.

  13. Importance of post-shock streams and sheath region as drivers of intense magnetospheric storms and high-latitude activity

    Directory of Open Access Journals (Sweden)

    K. E. J. Huttunen

    2004-04-01

    Full Text Available Magnetic disturbances in the Earth's magnetosphere can be very different depending on the type of solar wind driver. We have determined the solar wind causes for intense magnetic storms (Dst<-100nT over a 6-year period from the beginning of 1997 to the end of 2002, using observations by the WIND and ACE spacecraft. We have taken into consideration whether the storm was caused by the sheath region or by the following interplanetary coronal mass ejection (ICME. We also divided ICMEs into those having a magnetic cloud structure and those without such a structure. We found that post-shock streams and sheath regions caused the largest fraction of intense magnetic storms. We present four periods of magnetospheric activity in more detail. One of the events was caused by a magnetic cloud (10-11 August 2000 and the rest (13-14 July 2000, 8-9 June 2000 and 17-18 April 2001 by sheath regions and post-shock streams. We have used several magnetic indices to monitor the low- and high-latitude magnetospheric response to these different solar wind structures. Two of the events are interesting examples where at first strong high-latitude activity took place and the low-latitude response followed several hours later. These events demonstrate that low- and high-latitude activity do not always occur concurrently and the level of activity may be very different. According to the examples shown the evolution of the pressure-corrected Dst index was more difficult to model for a sheath region or a post-shock stream driven storm than for a storm caused by a magnetic cloud.

  14. Generation of kinetic Alfven waves in the high-latitude near-Earth magnetotail: A global hybrid simulation

    Science.gov (United States)

    Guo, Zhifang; Hong, Minghua; Lin, Yu; Du, Aimin; Wang, Xueyi; Wu, Mingyu; Lu, Quanming

    2015-02-01

    In this paper, effects of a fast flow in the tail plasma sheet on the generation of kinetic Alfven waves (KAWs) in the high-latitude of the near-Earth magnetotail are investigated by performing a two-dimensional (2-D) global-scale hybrid simulation, where the plasma flow is initialized by the E ×B drift near the equatorial plane due to the existence of the dawn-dusk convection electric field. It is found that firstly, the plasma sheet becomes thinned and the dipolarization of magnetic field appears around (x ,z ) =(-10.5 RE,0.3 RE) , where RE is the radius of the Earth. Then, shear Alfven waves are excited in the plasma sheet, and the strong earthward flow is braked by the dipole-like magnetic field. These waves propagate along the magnetic field lines toward the polar regions later. Subsequently, KAWs with k⊥≫k∥ are generated in the high-latitude magnetotail due to the existence of the non-uniformity of the magnetic field and density in the polar regions. The ratio of the electric field to the magnetic field in these waves is found to obey the relation (δEz)/(δBy )˜ω/k∥ of KAWs. Our simulation provides a mechanism for the generation of the observed low-frequency shear Alfven waves in the plasma sheet and kinetic Alfven waves in the high-latitude near-Earth magnetotail, whose source is suggested to be the flow braking in the low-latitude plasma sheet.

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

    OpenAIRE

    Luis Juanicó; Nicolás Di Lalla

    2014-01-01

    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 not...

  16. ETHOS 1: A high latitude planetary nebula with jets forged by a post common envelope binary central star

    OpenAIRE

    Miszalski, B.; Corradi, R.L.M.; Boffin, H. M. J.; Jones, D.; Sabin, L.; Santander-García, M.; Rodríguez-Gil, P.; Rubio-Díez, M. M.

    2010-01-01

    We report on the discovery of ETHOS 1 (PN G068.1+11.0), the first spectroscopically confirmed planetary nebula (PN) from a survey of the SuperCOSMOS Science Archive for high-latitude PNe. ETHOS 1 stands out as one of the few PNe to have both polar outflows (jets) travelling at $120\\pm10$ km/s and a close binary central star. The lightcurve observed with the Mercator telescope reveals an orbital period of 0.535 days and an extremely large amplitude (0.816 mag) due to irradiation of the compani...

  17. Final Report for High Latitude Climate Modeling: ARM Takes Us Beyond Case Studies

    Energy Technology Data Exchange (ETDEWEB)

    Russell, Lynn M [Scripps/UCSD; Lubin, Dan [Scripps/UCSD

    2013-06-18

    The main thrust of this project was to devise a method by which the majority of North Slope of Alaska (NSA) meteorological and radiometric data, collected on a daily basis, could be used to evaluate and improve global climate model (GCM) simulations and their parameterizations, particularly for cloud microphysics. Although the standard ARM Program sensors for a less complete suite of instruments for cloud and aerosol studies than the instruments on an intensive field program such as the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC), the advantage they offer lies in the long time base and large volume of data that covers a wide range of meteorological and climatological conditions. The challenge has been devising a method to interpret the NSA data in a practical way, so that a wide variety of meteorological conditions in all seasons can be examined with climate models. If successful, climate modelers would have a robust alternative to the usual “case study” approach (i.e., from intensive field programs only) for testing and evaluating their parameterizations’ performance. Understanding climate change on regional scales requires a broad scientific consideration of anthropogenic influences that goes beyond greenhouse gas emissions to also include aerosol-induced changes in cloud properties. For instance, it is now clear that on small scales, human-induced aerosol plumes can exert microclimatic radiative and hydrologic forcing that rivals that of greenhouse gas–forced warming. This project has made significant scientific progress by investigating what causes successive versions of climate models continue to exhibit errors in cloud amount, cloud microphysical and radiative properties, precipitation, and radiation balance, as compared with observations and, in particular, in Arctic regions. To find out what is going wrong, we have tested the models' cloud representation over the full range of meteorological conditions found in the Arctic using the

  18. A multi-diagnostic approach to understanding high-latitude plasma transport during the Halloween 2003 storm

    Directory of Open Access Journals (Sweden)

    P. Yin

    2008-09-01

    Full Text Available During the Halloween 2003 storm event, significant electron density enhancements at elevated F-layer altitudes were recorded by the EISCAT and ESR radars in northern Europe between 20:00 and 24:00 UT on 30 October. At the same time, a sequence of optical images from Qaanaaq in northern Greenland captured a series of eastward-propagating polar cap patches. In this paper, an advanced 4-D tomographic method based on the assimilation of global GPS data, coupled to a predictive Kalman filtering technique, has been used to reveal the linkage between these ionospheric structures. The combination of the various data sources has clearly established the time history of this extreme event, in which high-density plasma was uplifted in the dayside ionosphere and convected anti-sunward across the polar cap to European high latitudes at an elevated F-layer. Using this multi instrument approach, we can differentiate between those density structures observed at the ESR which occurred as a result of cross-polar transport and those more likely to have been produced by in-situ soft particle precipitation, a distinction which is supported by the ESR and EISCAT data. The multi-diagnostic approach reported here has the potential significantly to extend our current understanding of high latitude plasma transport and the origin of electron density enhancements.

  19. SuperDARN CUTLASS Finland radar observations of high-latitude magnetic reconnections under northward interplanetary magnetic field (IMF) conditions

    Institute of Scientific and Technical Information of China (English)

    ZHANG QingHe; LIU RuiYuan; YANG HuiGen; HU HongQiao; ZHANG BeiChen; DUNLOP Malcolm; LESTER Mark; BOGDANOVA Yulia; WALSH Andrew

    2012-01-01

    A number of backscatter power enhancement events with “equatorward-moving radar auroral forms” in the high-latitude ionosphere were observed by SuperDARN CUTLASS Finland radar when the IMF was northward during 09:00 -10:00 UT on 26 March 2004.These events were also associated with sunward flow enhancements at each location in the Northern Hemisphere which were shown in ionospheric convections measured by the SuperDARN radars.These are typical features of high-latitude (lobe) magnetic reconnections.The durations of the velocity enhancements imply that the evolution time of the lobe reconnections is about 8-16 min from their origin at the reconnection site to their addition to the magnetotail lobe again.In additional,the Double Star TC-1 spacecraft was moving from magnetosheath into magnetosphere,and crossing the magnetopause near the subsolar region during this interval,and observed typical low-latitude magnetic reconnection signatures.This infers that the dayside high- and low-latitude reconnections may occur simultaneously.

  20. High-Latitude Plasma Convection as a Function of Solar Wind and IMF Using a Simple Parameterization

    Science.gov (United States)

    Baker, K. B.

    2001-12-01

    A simple parameterization of high-latitude ionospheric plasma convection patterns has been developed to study the relationship of the convection patterns to the speed and density of the solar wind and the interplanetary magnetic field (IMF). The parameterization includes the overall size of the convection pattern, the total potential drop, the orientation of the pattern, and the relative sizes of the dawn and dusk convection cells. The spherical harmonic fitting analysis of Ruohoniemi and Baker [1998] was applied to two years (1999, 2000) of SuperDARN HF-Radar data from the northern hemisphere. Solar Wind and IMF data were take from the definitive ACE key parameter data. Linear regression analysis was applied to determine the relationship of the convection pattern parameters to various combinations of solar wind and IMF parameters. The polar cap potential drop was found to be most strongly correlated to vBz, but a weaker correlation to v*abs(By) was also noted. The orientation of the convection pattern was well correlated with either By alone or the IMF clock angle. Ruohoniemi, J. M., and K. B. Baker, Large-scale imaging of high-latitude convection with SuperDARN HF-radar observations, J. Geophys. Res., 103, 20,797-20,811, 1998.

  1. Precipitation of low energy electrons at high latitudes: Effects of substorms, interplanetary magnetic field and dipole tilt angle

    Science.gov (United States)

    Burch, J. L.

    1972-01-01

    Data from the auroral particles experiment on OGO-4 were used to study effects of substorm activity, interplanetary magnetic field latitutde, and dipole tilt angle on high-latitude precipitation of 700 eV electrons. It was found that: (1) The high-latitude zone of 700 eV electron precipitation in late evening and early morning hours moves equatorward by 5 to 10 deg during substorms. (2) The low-latitude boundary of polar cusp electron precipitation at 9 to 15 hours MLT also moves equatorward by several degrees during substorms and, in the absence of significant substorm activity, after a period of southward interplanetary magnetic field. (3) With times containing substorm activity or a southward interplanetary magnetic field eliminated, the low-latitude boundary of polar cusp electron precipitation is found to move by approximately 4 deg over the total yearly range of tilt angles. At maximum winter and summer conditions the invariant latitude of the boundary is shown to shift by approximately -3 deg and +1 deg respectively from its equinox location.

  2. Southern high-latitude terrestrial climate change during the Paleocene–Eocene derived from a marine pollen record (ODP Site 1172, East Tasman Plateau

    Directory of Open Access Journals (Sweden)

    L. Contreras

    2014-01-01

    Full Text Available Reconstructing the early Paleogene climate dynamics of terrestrial settings in the high southern latitudes is important to assess the role of high-latitude physical and biogeochemical processes in the global climate system. However, whereas a number of high-quality Paleogene climate records has become available for the marine realm of the high southern latitudes over the recent past, the long-term evolution of coeval terrestrial climates and ecosystems is yet poorly known. We here explore the climate and vegetation dynamics on Tasmania from the middle Paleocene to the early Eocene (60.7–54.2 Ma based on a sporomorph record from Ocean Drilling Program (ODP Site 1172 on the East Tasman Plateau. Our results show that three distinctly different vegetation types thrived on Tasmania under a high-precipitation regime during the middle Paleocene to early Eocene, with each type representing different temperature conditions: (i warm-temperate forests dominated by gymnosperms that were dominant during the middle and late Paleocene; (ii cool-temperate forests dominated by southern beech (Nothofagus and araucarians across the middle/late Paleocene transition interval (~59.5 to ~59.0 Ma; and (iii paratropical forests rich in ferns that were established during and in the wake of the Paleocene–Eocene Thermal Maximum (PETM. The transient establishment of cool-temperate forests lacking any frost-sensitive elements (i.e., palms and cycads across the middle/late Paleocene transition interval indicates markedly cooler conditions, with the occurrence of frosts in winter, on Tasmania during that time. The integration of our sporomorph data with previously published TEX86-based sea-surface temperatures from ODP Site 1172 documents that the vegetation dynamics on Tasmania were closely linked with the temperature evolution in the Tasman sector of the Southwest Pacific region. Moreover, the comparison of our season-specific climate estimates for the sporomorph

  3. Southern high-latitude terrestrial climate change during the Paleocene-Eocene derived from a marine pollen record (ODP Site 1172, East Tasman Plateau)

    Science.gov (United States)

    Contreras, L.; Pross, J.; Bijl, P. K.; O'Hara, R. B.; Raine, J. I.; Sluijs, A.; Brinkhuis, H.

    2014-01-01

    Reconstructing the early Paleogene climate dynamics of terrestrial settings in the high southern latitudes is important to assess the role of high-latitude physical and biogeochemical processes in the global climate system. However, whereas a number of high-quality Paleogene climate records has become available for the marine realm of the high southern latitudes over the recent past, the long-term evolution of coeval terrestrial climates and ecosystems is yet poorly known. We here explore the climate and vegetation dynamics on Tasmania from the middle Paleocene to the early Eocene (60.7-54.2 Ma) based on a sporomorph record from Ocean Drilling Program (ODP) Site 1172 on the East Tasman Plateau. Our results show that three distinctly different vegetation types thrived on Tasmania under a high-precipitation regime during the middle Paleocene to early Eocene, with each type representing different temperature conditions: (i) warm-temperate forests dominated by gymnosperms that were dominant during the middle and late Paleocene; (ii) cool-temperate forests dominated by southern beech (Nothofagus) and araucarians across the middle/late Paleocene transition interval (~59.5 to ~59.0 Ma); and (iii) paratropical forests rich in ferns that were established during and in the wake of the Paleocene-Eocene Thermal Maximum (PETM). The transient establishment of cool-temperate forests lacking any frost-sensitive elements (i.e., palms and cycads) across the middle/late Paleocene transition interval indicates markedly cooler conditions, with the occurrence of frosts in winter, on Tasmania during that time. The integration of our sporomorph data with previously published TEX86-based sea-surface temperatures from ODP Site 1172 documents that the vegetation dynamics on Tasmania were closely linked with the temperature evolution in the Tasman sector of the Southwest Pacific region. Moreover, the comparison of our season-specific climate estimates for the sporomorph assemblages from ODP

  4. Southern high-latitude terrestrial climate change during the Palaeocene-Eocene derived from a marine pollen record (ODP Site 1172, East Tasman Plateau)

    Science.gov (United States)

    Contreras, L.; Pross, J.; Bijl, P. K.; O'Hara, R. B.; Raine, J. I.; Sluijs, A.; Brinkhuis, H.

    2014-07-01

    Reconstructing the early Palaeogene climate dynamics of terrestrial settings in the high southern latitudes is important to assess the role of high-latitude physical and biogeochemical processes in the global climate system. However, whereas a number of high-quality Palaeogene climate records has become available for the marine realm of the high southern latitudes over the recent past, the long-term evolution of coeval terrestrial climates and ecosystems is yet poorly known. We here explore the climate and vegetation dynamics on Tasmania from the middle Palaeocene to the early Eocene (60.7-54.2 Ma) based on a sporomorph record from Ocean Drilling Program (ODP) Site 1172 on the East Tasman Plateau. Our results show that three distinctly different vegetation types thrived on Tasmania under a high-precipitation regime during the middle Palaeocene to early Eocene, with each type representing different temperature conditions: (i) warm-temperate forests dominated by gymnosperms that were dominant during the middle and late Palaeocene (excluding the middle/late Palaeocene transition); (ii) cool-temperate forests dominated by southern beech (Nothofagus) and araucarians that transiently prevailed across the middle/late Palaeocene transition interval (~ 59.5 to ~ 59.0 Ma); and (iii) paratropical forests rich in ferns that were established during and in the wake of the Palaeocene-Eocene Thermal Maximum (PETM). The transient establishment of cool-temperate forests lacking any frost-sensitive elements (i.e. palms and cycads) across the middle/late Palaeocene transition interval indicates markedly cooler conditions, with the occurrence of frosts in winter, on Tasmania during that time. The integration of our sporomorph data with previously published TEX86-based sea-surface temperatures from ODP Site 1172 documents that the vegetation dynamics on Tasmania were closely linked with the temperature evolution in the Tasman sector of the Southwest Pacific region. Moreover, the

  5. 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

  6. 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

  7. Effects of extraordinary solar cosmic ray events on variations in the atmospheric electric field at high latitudes

    Science.gov (United States)

    Shumilov, O. I.; Kasatkina, E. A.; Frank-Kamenetsky, A. V.

    2015-09-01

    Studies of variations in the atmospheric electric field vertical component ( E z ) are illustrated based on data from the Apatity high-latitude observatory (geomagnetic latitude Φ' = 63.8°) for three solar cosmic ray (SCR) events that occurred on April 15, April 18, and November 4, 2001. For the SCR event of April 15, 2001, the observed E z variations have been compared with the corresponding data from the Voeykovo midlatitude observatory and the Vostok observatory on the polar cap. It has been indicated that solar coronal mass ejections and some powerful SCR events can result in variations in the global electric circuit. Disturbances in the atmospheric electric field can be used to diagnose the development of intense processes on the Sun.

  8. 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...... from the solar cycle variation of regular geomagnetic activity, measured by indices such as aa and Dst. The spectral band power is generally at minimum just prior to solar maximum and has a strong maximum in the late declining phase associated with high-speed streams from coronal holes. We have...... compared the spectral band power with satellite observations of the solar wind velocity and find a high log-linear correlation in the range 0.7-0.8. The highest correlation is found in the 2-4 min band. Contrary to this, the correlation with Bs and upsilon Bs is very weak (similar to 0.0-0.2), except...

  9. Matching dust emission structures and magnetic field in high-latitude cloud L1642: comparing Herschel and Planck maps

    CERN Document Server

    Malinen, J; Montillaud, J; Juvela, M; Ristorcelli, I; Clark, S E; Berné, O; Bernard, J -Ph; Pelkonen, V -M; Collins, D C

    2015-01-01

    The nearby cloud L1642 is one of only two known very high latitude (|b| > 30 deg) clouds actively forming stars. It is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g., of the effect of magnetic fields. We compare Herschel dust emission structures and magnetic field orientation revealed by Planck polarization maps in L1642. The high-resolution (~18-40") Herschel data reveal a complex structure including a dense, compressed central blob with elongated extensions, low density striations, "fishbone" like structures with a spine and perpendicular striations, and a spiraling "tail". The Planck polarization data (at 10' resolution) reveal an ordered magnetic field pervading the cloud and aligned with the surrounding striations. There is a complex interplay between the cloud structure and large scale magnetic field. This suggests that magnetic field is closely linked to the formation and evolution of the cloud. CO rotational emission confirm...

  10. On the relationship between the geometrical control of scintillation indices and the data detrending problems observed at high latitudes

    Directory of Open Access Journals (Sweden)

    B. Forte

    2007-06-01

    Full Text Available The experimental estimate of radio waves scintillation, caused by plasma density irregularities in the ionosphere, is usually attempted by means of scintillation indices which are essentially standard deviations of stochasticly fluctuating parts of the received radio wave intensity and phase. At high latitudes, provided that the propagation problem may be modelled by means of the weak scattering theory, the typical scintillation indices S4 and ?? depend on a geometrical factor which introduces some amplifications on their values. Scintillation indices S4 and ?? measured at auroral latitudes are estimated by means of different boundary detrending conditions and the geometrical effect on those detrending conditions is investigated. In the case of the polar Low Earth Orbiting (LEO satellite links considered here, high phase with low intensity scintillation events do not seem to be related to geometrical effects only, but rather to misleading data detrending.

  11. Applications of NO2 Satellite Observations at High Latitudes for Monitoring Air Quality (ILMA): Objectives and First Results

    Science.gov (United States)

    Ialongo, Iolanda; Tamminen, Johanna

    2015-06-01

    The first results of ILMA project are presented in this paper. The project aims at increasing the scientific exploitation of satellite data for air quality monitoring at high latitudes. The specific focus of the project is evaluating the quality of satellite NO2 retrievals and preparing for upcoming TROPOMI mission. Satellite-based OMI (Ozone Monitoring Instrument) NO2 total columns are compared with Pandora measurements performed in Helsinki in 2012. The median relative difference for OMI standard product is 1% and -6% for clear sky and all sky conditions, respectively. Larger differences between OMI and Pandora correspond to cloudy autumn-winter days with solar zenith angles above 70° . Both satellite and ground-based data show similar weekly cycle, with lower NO2 levels during the weekend compared to the weekdays.

  12. The Soil Moisture Active Passive (SMAP) Radar: Measurements at High Latitudes and of Surface Freeze/Thaw State

    Science.gov (United States)

    Spencer, Michael; Dunbar, Scott; Chen, Curtis

    2013-01-01

    The Soil Moisture Active/Passive (SMAP) mission is scheduled for a late 2014 launch date. The mission will use both active radar and passive radiometer instruments at L-Band in order to achieve the science objectives of measuring soil moisture and land surface freeze-thaw state. To achieve requirements for a wide swath at sufficiently high resolution for both active and passive channels, an instrument architecture that uses a large rotating reflector is employed. In this paper, focus will be placed on the radar design. The radar will employ synthetic-aperture processing to achieve a "moderate" resolution dual-pol product over a 1000 km swath. Because the radar is operating continuously, very frequent temporal coverage will be achieved at high latitudes. This data will be used to produce a surface freeze/thaw state data product.

  13. HILAT a multi-experiment satellite addressing the dynamics of irregularity formation in the high-latitude ionosphere

    Science.gov (United States)

    Fremouw, E. J.

    A combined beacon, in-situ, and optical satellite mission is being prepared for definitive investigation of the formation, development, and decay of plasma-density irregularities in the high-latitude ionosphere. The satellite, named HILAT (P83-1), will carry a VHF-UHF-L-Band coherent beacon for scintillation and TEC measurements, three payloads for in-situ and ionospheric/magnetospheric coupling observations, and a vacuum-ultraviolet imager for meso-scale recording of dayside and nightside auroras and emissions from the F layer. Observations are planned at northern latitudes ranging from the plasmapause to the pole, employing beacon receiving stations which also will decode telemetry from the other payloads. Launch is planned for the boreal summer of 1983.

  14. North-South differences in the Earth's high-latitude upper atmosphere dynamics: Influence of solar activity and seasonal variations

    Science.gov (United States)

    Förster, Matthias; Cnossen, Ingrid

    2014-05-01

    Recent observations have shown that the upper thermospheric/ionospheric response to solar wind and IMF dependent drivers of the magnetosphere-ionosphere-thermosphere (M-I-T) system can be very dissimilar in the Northern and Southern Hemisphere. We present statistical studies of the high-latitude upper thermospheric neutral wind circulation patterns obtained from almost a decade of measurements with an accelerometer on board the CHAMP spacecraft. The influence of the solar activity and the dependence on seasonal variations is analysed with respect to average cross-polar wind velocities and high-latitude neutral wind vorticity values. Using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model, on the other hand, we simulated representative equinox as well as solstice intervals for low and high solar activity conditions. For the simulations, we used on the one hand side symmetric dipole and on the other realistic (IGRF) geomagnetic field configurations. The comparative survey of both the numerical simulation and the statistical observation results show some prominent asymmetries between the two hemispheres, which are caused by the different geographic-geomagnetic offsets and/or the different patterns of geomagnetic flux densities. The average cross-polar neutral wind velocities show a distinct seasonal variation with minimum values during the respective hemispheric winter solstice. The neutral wind vorticity values are generally larger in the Northern than the Southern Hemisphere, except for northern winter solstice conditions. The hemispheric differences become larger for higher solar activity and show a semidiurnal variation. In contrast, the spatial variance of the upper thermospheric neutral wind is usually considerably larger in the polar region of the Southern Hemisphere compared with the Northern, and the hemispheric difference shows a strong semidiurnal variation.

  15. Characterizing Geology and Mineralization at High Latitudes in Alaska Using Airborne and Field-Based Imaging Spectrometer Data

    Science.gov (United States)

    Hoefen, T. M.; Kokaly, R. F.; Graham, G. E.; Kelley, K. D.; Buchhorn, M.; Johnson, M. R.; Hubbard, B. E.; Goldfarb, R. J.; Prakash, A.

    2015-12-01

    Passive optical remote sensing of high latitude regions faces many challenges including a short acquisition season and poor illumination. Identification of surface minerals can be complicated by steep terrain and vegetation cover. In July 2014, the HyMap* imaging spectrometer was flown over two study areas in Alaska. Contemporaneously, field spectra and samples of geologic units were collected, including altered and unaltered parts of intrusions hosting mid-Cretaceous porphyry copper deposits at Orange Hill and Bond Creek in the eastern Alaska Range. The HyMap radiance data were converted to surface reflectance using a radiative transfer correction program and reflectance spectra of calibration sites. Reflectance data were analyzed with the Material Identification and Characterization Algorithm (MICA), a module of USGS PRISM (Processing Routines in IDL for Spectroscopic Measurements; speclab.cr.usgs.gov). Large areas of abundant epidote/chlorite, muscovite/illite, calcite, kaolinite, montmorillonite, and (or) pyrophyllite were mapped, which are minerals typically formed during alteration of host rocks surrounding porphyry copper deposits. A map showing the wavelength position of the muscovite/illite absorption feature was made. Shifts in wavelength position have been related to the aluminum composition of micas and areas of high metal concentrations in past studies. In July 2015, rock and spectral sampling was continued in areas with surface exposures of copper- and molybdenum-bearing sulfides. Also, high-spatial resolution (~6 cm pixel size) imaging spectrometer data were collected at the Orange Hill deposit using the University of Alaska, Fairbanks (UAF) HySpex imaging spectrometer (www.hyperspectral.alaska.edu). Laboratory, field, and airborne spectra are being examined to define indicators of mineralization. The study results will be used to assess the effectiveness of spectroscopic remote sensing for geologic mapping and exploration targeting in Alaska and

  16. Cluster multispacecraft observations at the high-latitude duskside magnetopause: implications for continuous and component magnetic reconnection

    Directory of Open Access Journals (Sweden)

    A. Retinò

    2005-02-01

    Full Text Available We report multispacecraft Cluster observations of magnetic reconnection at the high-latitude magnetopause/magnetospheric boundary layer (MP/BL under mainly northward interplanetary magnetic field (IMF conditions. The event we study is on 3 December 2001 when the Cluster spacecraft were skimming the high-latitude duskside MP/BL during a period of about four hours. The orbit and configuration of the spacecraft were such that at least one satellite was present in the MP/BL during most of that period. We present the evidence of reconnection in the form of tangential stress balance between the magnetosheath and the MP/BL (Walén test and in several cases in the form of transmitted magnetosheath ions in the MP/BL and incident/reflected magnetosheath ions in the magnetosheath boundary layer (MSBL . The observations are consistent with magnetic reconnection occurring tailward of the cusp and going on continuously for a period of about four hours. The observed directions of the reconnection flows are consistent with the IMF orientation, thus indicating that reconnection is globally controlled by the IMF. Observations of a few flow reversals suggest passages of the spacecraft close to the X-line. The observation of low magnetic shear across the magnetopause during a flow reversal is consistent with component merging at least in one case. The observation of reconnection flows on the duskside magnetopause irrespective of the change in the sign of the IMF BY also suggests a better agreement with the component merging model, though antiparallel merging cannot be excluded because the distance from the X-line is not known.

  17. Tuning the Mg/Ca Paleothermometer for High-Latitude Species and Insights into Intraspecific and Intrashell Variability

    Science.gov (United States)

    Davis, C. V.; Fehrenbacher, J. S.; Russell, A. D.; Spero, H. J.; Hill, T. M.

    2015-12-01

    The Mg/Ca of planktic foraminifera shells has become a widely used paleothermometer. However, culture-based calibrations have been confined primarily to low-latitude species with limited data from species growing below 12°C. Some core-top calibrations on high-latitude Neogloboquadrinids raise questions about the influence of [CO3-2] and low Mg/Ca "crusts" on shell geochemistry (e.g. 1). This study seeks to extend the low temperature range of culture-based calibrations to temperatures relevant in high-latitudes and active upwelling areas, taking into account the wide range of [CO3-2] observed in these environments. We further examine whether intrashell geochemical variability in the form of "crusting" poses a limitation to Mg/Ca paleothermometry of crust-forming species. Here we present the results of laboratory experiments with living Neogloboquadrina incompta and Neogloboquadrina pachyderma collected and cultured at UC Davis Bodega Marine Laboratory at temperatures between 6° and 12°C and a range of [CO3-2]. We use a combination of Laser Ablation Inductively Coupled Mass Spectrometry and Electron Microprobe mapping, to analyze both intraspecific and intrashell variability in Mg/Ca. We extend existing culture-based temperature calibrations to 6°C, while accounting for the effect of environmental [CO3-2]. Single-shell analyses reveal a high degree of intraspecific variability in the Mg/Ca of calcite grown under stable laboratory conditions. Intrashell analyses identify characteristic low Mg/Ca "crusts" in N. incomptagrown at constant temperature, which record chamber average Mg/Ca within the range of uncrusted conspecifics grown at the same temperature. 1. R. Kozdon et al., Reassessing Mg/Ca temperature calibrations of Neogloboquadrina pachyderma (sinistral) using paired δ44/40Ca and Mg/Ca measurements. Geochem Geophys. 10, Q03005 (2009).

  18. Solar wind transport into magnetosphere caused by magnetic reconnection at high latitude magnetopause during northward IMF: Cluster-DSP conjunction observations

    Institute of Scientific and Technical Information of China (English)

    YAN GuangQing; SHEN Chao; LIU ZhenXing; M. DUNLOP; E. LUOEK; H. REME; C. M. OARR; ZHANG TieLong

    2008-01-01

    An event of Cluster-Double Star conjunction observations of magnetic reconnec-tion at high latitude magnetopause nightside of both cusps and solar wind trans-port into magnetosphere caused by such reconnection process has been investi-gated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause night$1de of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: (1) during northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; (2) the direction of the accelerated flows, with its sunward component Vx, dawnward component Vy, northward component Vz, is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component By; (3) reconnection can heat plasma more in par-allel direction than in perpendicular direction, to a level of about 4 keV; (4) with reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; (5) by reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magneto-sphere.

  19. A satellite snow depth multi-year average derived from SSM/I for the high latitude regions

    Science.gov (United States)

    Biancamaria, S.; Mognard, N.M.; Boone, A.; Grippa, M.; Josberger, E.G.

    2008-01-01

    The hydrological cycle for high latitude regions is inherently linked with the seasonal snowpack. Thus, accurately monitoring the snow depth and the associated aerial coverage are critical issues for monitoring the global climate system. Passive microwave satellite measurements provide an optimal means to monitor the snowpack over the arctic region. While the temporal evolution of snow extent can be observed globally from microwave radiometers, the determination of the corresponding snow depth is more difficult. A dynamic algorithm that accounts for the dependence of the microwave scattering on the snow grain size has been developed to estimate snow depth from Special Sensor Microwave/Imager (SSM/I) brightness temperatures and was validated over the U.S. Great Plains and Western Siberia. The purpose of this study is to assess the dynamic algorithm performance over the entire high latitude (land) region by computing a snow depth multi-year field for the time period 1987-1995. This multi-year average is compared to the Global Soil Wetness Project-Phase2 (GSWP2) snow depth computed from several state-of-the-art land surface schemes and averaged over the same time period. The multi-year average obtained by the dynamic algorithm is in good agreement with the GSWP2 snow depth field (the correlation coefficient for January is 0.55). The static algorithm, which assumes a constant snow grain size in space and time does not correlate with the GSWP2 snow depth field (the correlation coefficient with GSWP2 data for January is - 0.03), but exhibits a very high anti-correlation with the NCEP average January air temperature field (correlation coefficient - 0.77), the deepest satellite snow pack being located in the coldest regions, where the snow grain size may be significantly larger than the average value used in the static algorithm. The dynamic algorithm performs better over Eurasia (with a correlation coefficient with GSWP2 snow depth equal to 0.65) than over North America

  20. Plasma modifications induced by an X-mode HF heater wave in the high latitude F region of the ionosphere

    Science.gov (United States)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Yeoman, T. K.; Rietveld, M. T.; Häggström, I.; Ivanova, I. M.

    2013-12-01

    We presented experimental results of strong plasma modifications induced by X-mode powerful HF radio waves injected towards the magnetic zenith into the high latitude F region of the ionosphere. The experiments were conducted in 2009-2011 using the EISCAT Heating facility, UHF incoherent scatter radar and the EISCAT ionosonde at Tromsø, Norway; and the CUTLASS SuperDARN HF coherent radar at Hankasalmi, Finland. The results showed that the X-mode HF pump wave can generate strong small-scale artificial field aligned irregularities (AFAIs) in the F region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 9-15 m, were excited when the heater frequency (fH) was above the ordinary-mode critical frequency (foF2) by 0.1-1.2 MHz. It was found that the X-mode AFAIs appeared between 10 s and 4 min after the heater is turned on. Their decay time varied over a wide range between 3 min and 30 min. The excitation of X-mode AFAIs was accompanied by electron temperature (Te) enhancements and an increase in the electron density (Ne) depending on the effective radiated power (ERP). Under ERPs of about 75-180 MW the Te enhances up to 50% above the background level and an increase in Ne of up to 30% were observed. Dramatic changes in the Te and Ne behavior occurred at effective radiated powers of about 370-840 MW, when the Ne and Te values increased up to 100% above the background ones. It was found that AFAIs, Ne and Te enhancements occurred, when the extraordinary-mode critical frequency (fxF2) lied in the frequency range fH-fce/2≤fxF2≤fH+fce/2, where fce is the electron gyrofrequency. The strong Ne enhancements were observed only in the magnetic field-aligned direction in a wide altitude range up to the upper limit of the UHF radar measurements. In addition, the maximum value of Ne is about 50 km higher than the Te enhancement peak. Such electron density enhancements (artificial ducts) cannot be explained by

  1. 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.; Kamae, Y.; Zhang, Z.; Abe-Ouchi, A.; Chandler, M. A.; Jost, A.; Lohmann, G.; Otto-Bliesner, B. L.; Ramstein, G.; Ueda, H.

    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.

  2. Theoretical study of the electron temperature in the high-latitude ionosphere for solar maximum and winter conditions

    International Nuclear Information System (INIS)

    The electron temperature (T/sub e/) variation in the high-latitude ionosphere at altitudes between 120 and 800 km has been modeled for solar maximum, winter solstice, and strong magnetic activity conditions. The calculated electron temperatures are consistent with the plasma densities and ion temperatures computed from a time-dependent ionospheric model. Heating rates for both solar EUV and auroral precipitation were included. In general, the predicted UT variation of the electron temperature that results from the displacement between the magnetic and geographic poles is only a few hundred degrees. However, in sunlit trough regions, T/sub e/ hot spots develop, and these hot spots show a marked UT variation, by as much as 2500 K. The dominant parameter controlling the T/sub e/ variation above 200 km is the magnetospheric heat flux, the maximum electron temperature ranges from 5000 to 10,000 K at 800 km. A magnetospheric heat flux is particularly effective in enhancing trough electron temperatures. In general, the electron heat flux at high altitudes is uniquely related to the electron temperature and gradient, except on auroral field lines where thermoelectric heat flow is important

  3. Turbulent high-latitude oceanic intrusions—details of non-smooth apparent isopycnal transport West of Svalbard

    Science.gov (United States)

    van Haren, Hans; Greinert, Jens

    2016-07-01

    Filament intrusions are observed in high-resolution temperature (T) measurements from a 100-m and several month-long mooring in the Fram Strait in around 400-m water depth at the continental slope West of Svalbard (Spitsbergen, Norway). In this dynamic environment, a wide variety of intrusive layers are observed with thicknesses between 5 and 80 m with warmer water between cooler waters above and below. The layers typically last from several hours up to 1 day, exceeding the local buoyancy period but not lasting as long as intrusive layers in the open ocean. The intrusions are a result of an intermingling of Arctic and North-Atlantic waters and generated in the basins interior and locally via internal wave steepening upon the sloping bottom. Freely propagating semidiurnal lunar internal tides cannot exist without background vorticity at these high latitudes. Strongly nonlinear turbulent bores are not observed at the tidal periodicity, but wave fronts occur at the sub-inertial frequency of dominant baroclinic instability. The fronts are in part associated with near-buoyancy frequency internal waves (breaking). The details of the moored T observations and their spectral content demonstrate the non-smooth, relatively turbulent development including convective overturning and shear-induced instabilities when intrusions disperse in presumably salinity-compensated isopycnal layers.

  4. 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.

  5. Five new Fast Radio Bursts from the HTRU high latitude survey: first evidence for two-component bursts

    CERN Document Server

    Champion, D J; Kramer, M; Keith, M J; Bailes, M; Barr, E D; Bates, S D; Bhat, N D R; Burgay, M; Burke-Spolaor, S; Flynn, C M L; Jameson, A; Johnston, S; Ng, C; Levin, L; Possenti, A; Stappers, B W; van Straten, W; Tiburzi, C; Lyne, A G

    2015-01-01

    The detection of five new fast radio bursts (FRBs) found in the High Time Resolution Universe high latitude survey is presented. The rate implied is 6$^{+4}_{-3}\\times~10^3$ (95%) FRBs sky$^{-1}$ day$^{-1}$ above a fluence of between 0.13 and 5.9 Jy ms for FRBs between 0.128 and 262 ms in duration. One of these FRBs has a clear two-component profile, each component is similar to the known population of single component FRBs and are separated by 2.4(4) ms. All the FRB components appear to be unresolved following deconvolution with a scattering tail and accounting for intra-channel smearing. The two-component FRB also has the highest dispersion measure (1629 pc cm$^{-3}$) of any FRB to-date. Many of the proposed models to explain FRBs use a single high energy event involving compact objects (such as neutron star mergers) and therefore cannot easily explain a two-component FRB. Models that are based on extreme versions of flaring, pulsing or orbital events however could produce multiple component profiles. The c...

  6. Site-level model intercomparison of high latitude and high altitude soil thermal dynamics in tundra and barren landscapes

    Directory of Open Access Journals (Sweden)

    A. Ekici

    2014-09-01

    Full Text Available Modelling soil thermal dynamics at high latitudes and altitudes requires representations of specific physical processes such as snow insulation, soil freezing/thawing, as well as subsurface conditions like soil water/ice content and soil texture type. We have compared six different land models (JSBACH, ORCHIDEE, JULES, COUP, HYBRID8, LPJ-GUESS at four different sites with distinct cold region landscape types (i.e. Schilthorn-Alpine, Bayelva-high Arctic, Samoylov-wet polygonal tundra, Nuuk-non permafrost Arctic to quantify the importance of physical processes in capturing observed temperature dynamics in soils. This work shows how a range of models can represent distinct soil temperature regimes in permafrost and non-permafrost soils. Snow insulation is of major importance for estimating topsoil conditions and must be combined with accurate subsoil temperature dynamics to correctly estimate active layer thicknesses. Analyses show that land models need more realistic surface processes (such as detailed snow dynamics and moss cover with changing thickness/wetness as well as better representations of subsoil thermal dynamics (i.e. soil heat transfer mechanism and correct parameterization of heat conductivity/capacities.

  7. Eocene high-latitude temperature gradients over time and space based on d18O values of fossil shark teeth

    Science.gov (United States)

    Zeichner, S. S.; Kim, S.; Colman, A. S.

    2015-12-01

    Early-Mid Eocene (56.0-33.9Mya) is characterized by a temperate Antarctic climate and shallower latitudinal temperature gradients than those in present day. The warmer waters off the coast of the Antarctic Peninsula provided suitable habitats for taxa (i.e., sharks) that live today at lower latitudes. Stable isotope analysis of Eocene shark teeth provides a proxy to understand high latitude temperature gradients. However, shark ecology, in particular migration and occupation of tidal versus pelagic habitats, must be considered in the interpretation of stable isotope data. In this study, we analyze d18OPO4 values from the enameloid of Striatolamia (synonymized with Carcharias) shark teeth from the La Meseta formation (Seymour Island, Antarctica) to estimate paleotemperature in Early-Mid Eocene Antarctica, and assess the impact of ecology versus environmental signals on d18OPO4 values. We compare the ranges and offsets between our measured shark tooth d18OPO4 and published bivalve d18OCO3 values to test whether shark teeth record signals of migration across latitudinal temperature gradients, or instead reflect seasonal and long-term temporal variation across La Meseta stratigraphic units.

  8. The evolution of high-latitude field-aligned currents and magnetospheric dynamics in response to solar wind drivers

    Science.gov (United States)

    Bogdanova, Yulia; Vennerstrøm, Susanne; Wild, James; Korth, Haje; Lühr, Hermann; Wing, Simon; Pitout, Frederic

    2016-04-01

    While the statistical behaviour of the solar wind-magnetosphere-ionosphere system is well defined by the Dungey cycle, questions remain on the behaviour of this coupled system during extreme conditions, for example during magnetic storms or periods with long lasting northward IMF, and on how, and how fast, the system reacts to abrupt changes in the solar wind driver. Field-aligned currents play a crucial role in the dynamics of this coupled system as they provide connectivity between different regions and act as channels for energy and momentum transfer. These currents have been investigated in the last decade thanks to observations from low-orbiting satellites, such as CHAMP, Ørsted, DMSP, and the Iridium constellation. However, many previous studies concentrated on the statistical behavior of the current systems or measurements from individual observatories. In this paper we will employ data from Swarm, AMPERE, DMSP, Cluster, SuperDARN and SuperMAG to perform a multi-point study of high-latitude field-aligned current systems evolution and properties and magnetospheric dynamics in response to the solar wind driver, concentrating on the intervals of changes in the IMF orientation and extreme IMF and solar wind conditions.

  9. Assessment of land influence on a high-latitude marine coastal system: Tierra del Fuego, southernmost Argentina.

    Science.gov (United States)

    Amin, Oscar; Comoglio, Laura; Spetter, Carla; Duarte, Claudia; Asteasuain, Raúl; Freije, Rubén Hugo; Marcovecchio, Jorge

    2011-04-01

    The study deals with the determination of physico-chemical parameters, inorganic nutrients, particulate organic matter, and photosynthetic pigments on a monthly basis during an annual cycle from nine sampling sites of the coastal zone of a high-latitude ecosystem (Tierra del Fuego, Argentina). Nitrites and phosphates concentrations were similar to other systems of the south Atlantic coast (median, 0.30 and 1.02 μM, respectively), while nitrates were higher in all sampling periods (median, 45.37 μM), and silicates were significantly smaller (median, 7.76 μM). Chlorophyll a and phaeopigments have shown median values of 0.38 and 0.85 mg m(-3), respectively, while saturated values of dissolved oxygen were recorded throughout the study. The analysis reflected that nutrient enrichment seems to be linked to an anthropogenic source, the presence of peatlands areas, and a sink of Nothofagus pumilio woods. The area could be characterized in three zones related to (1) high urban influence, (2) natural inputs of freshwater, and (3) mixed inputs coming from moderate urban impacts. PMID:20473562

  10. A Balloon-borne Measurement of High Latitude Atmospheric Neutrons Using a LiCAF Neutron Detector

    CERN Document Server

    Kole, Merlin; Fukuda, Kentaro; Ishizu, Sumito; Jackson, Miranda; Kamae, Tune; Kawaguchi, Noriaki; Kawano, Takafumi; Kiss, Mózsi; Moretti, Elena; Salinas, Maria Fernanda Muñoz; Pearce, Mark; Rydström, Stefan; Takahashi, Hiromitsu; Yanagida, Takayuki

    2013-01-01

    PoGOLino is a scintillator-based neutron detector. Its main purpose is to provide data on the neutron flux in the upper stratosphere at high latitudes at thermal and nonthermal energies for the PoGOLite instrument. PoGOLite is a balloon borne hard X-ray polarimeter for which the main source of background stems from high energy neutrons. No measurements of the neutron environment for the planned flight latitude and altitude exist. Furthermore this neutron environment changes with altitude, latitude and solar activity, three variables that will vary throughout the PoGOLite flight. PoGOLino was developed to study the neutron environment and the influences from these three variables upon it. PoGOLino consists of two Europium doped Lithium Calcium Aluminium Fluoride (Eu:LiCAF) scintillators, each of which is sandwiched between 2 Bismuth Germanium Oxide (BGO) scintillating crystals, which serve to veto signals produced by gamma-rays and charged particles. This allows the neutron flux to be measured even in high rad...

  11. ETHOS 1: A high latitude planetary nebula with jets forged by a post common envelope binary central star

    CERN Document Server

    Miszalski, B; Boffin, H M J; Jones, D; Sabin, L; Santander-García, M; Rodríguez-Gil, P; Rubio-Díez, M M

    2010-01-01

    We report on the discovery of ETHOS 1 (PN G068.1+11.0), the first spectroscopically confirmed planetary nebula (PN) from a survey of the SuperCOSMOS Science Archive for high-latitude PNe. ETHOS 1 stands out as one of the few PNe to have both polar outflows (jets) travelling at $120\\pm10$ km/s and a close binary central star. The lightcurve observed with the Mercator telescope reveals an orbital period of 0.535 days and an extremely large amplitude (0.816 mag) due to irradiation of the companion by a very hot pre-white dwarf. ETHOS 1 further strengthens the long suspected link between binary central stars of planetary nebulae (CSPN) and jets. INT IDS and VLT FORS spectroscopy of the CSPN reveals weak N III, C III and C IV emission lines seen in other close binary CSPN and suggests many CSPN with these weak emission lines are misclassified close binaries. We present VLT FORS imaging and Manchester Echelle Spectrometer long slit observations from which a kinematic model of the nebula is built. An unusual combina...

  12. Matching dust emission structures and magnetic field in high-latitude cloud L1642: comparing Herschel and Planck maps★

    Science.gov (United States)

    Malinen, J.; Montier, L.; Montillaud, J.; Juvela, M.; Ristorcelli, I.; Clark, S. E.; Berné, O.; Bernard, J.-Ph.; Pelkonen, V.-M.; Collins, D. C.

    2016-08-01

    The nearby cloud L1642 is one of only two known very high latitude (|b| > 30 deg) clouds actively forming stars. It is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g. of the effect of magnetic fields. We compare Herschel dust emission structures and magnetic field orientation revealed by Planck polarization maps in L1642. The high-resolution (˜20 arcsec) Herschel data reveal a complex structure including a dense, compressed central clump, and low-density striations. The Planck polarization data (at 10 arcmin resolution) reveal an ordered magnetic field pervading the cloud and aligned with the surrounding striations. There is a complex interplay between the cloud structure and large-scale magnetic field. This suggests that the magnetic field is closely linked to the formation and evolution of the cloud. CO rotational emission confirms that the striations are connected with the main clumps and likely to contain material either falling into or flowing out of the clumps. There is a clear transition from aligned to perpendicular structures approximately at a column density of NH = 1.6 × 1021 cm-2. Comparing the Herschel maps with the Planck polarization maps shows the close connection between the magnetic field and cloud structure even in the finest details of the cloud.

  13. Comparisons of high latitude E > 20 MeV proton geomagnetic cutoff observations with predictions of the SEPTR model

    Directory of Open Access Journals (Sweden)

    A. Ling

    Full Text Available Radiation effects from solar energetic proton (SEP events are a concern when the International Space Station reaches high latitudes accessible to SEPs. We use data from the 20–29 and 29–64 MeV proton channels of the Proton/Electron Telescope on the SAMPEX satellite during nine large SEP events to determine the experimental geographic cutoff latitudes for the two energy ranges. These are compared with calculated cutoff latitudes based on a computer model, SEPTR (solar energetic particle tracer. The observed cutoff latitudes are systematically equatorward of the latitudes calculated by the SEPTR program using a Tsyganenko field model, but that model produces mean values of ~ 2° for latitudinal differences with observations, DLat, which are ~ 3 times smaller than those using the 1995 International Geomagnetic Reference Field model alone. The number distributions of DLat are peaked near 0° and decline toward higher values. With the Tsyganenko model, we find no significant trend in either the DLat or their variances with increasing Kp .Key words. Interplanetary physics (energetic particles – Magnetospheric physics (polar cap phenomena – Space plasma physics (charged particle motion and acceleration

  14. The high latitudes in the International Reference Ionosphere; Meeting C4 of Commission C, COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994

    Science.gov (United States)

    Rawer, K.; Bilitza, D.; Singer, W.

    1995-01-01

    An international conference on high-latitude ionospheric modeling produced 27 papers in the areas of ionospheric mapping, electron density and distribution, ion density and distribution, ionospheric storems, ionospheric composition, and ionospheric sounding techniques. Upgrades to the International Reference Ionosphere (IRI) model were proposed in several papers.

  15. Exploring medium gravity icy planetary bodies: an opportunity in the Inner System by landing at Ceres high latitudes

    Science.gov (United States)

    Poncy, J.; Grasset, O.; Martinot, V.; Tobie, G.

    2009-04-01

    assessment of a mission to Ceres high latitudes. We present here why we think an in-situ mission to the polar areas of Ceres should be of interest in the near future. We dwell on the environmental factors and challenges for a Lander, both as specificities of Ceres and as a consequence of the high latitude targeted. Factors such as day duration, fine regolith, terrain hazards, optical contrasts, thermal gradients, planetary contamination... are reviewed. We then assess how the soft precision landing technologies being developed for other missions would apply in such an environment. We present a preliminary mission analysis and a concept for the Lander, with preliminary evaluation of mass and power resources for a fixed payload or for a mini-rover. The resulting mission design combines technological maturity and a launch mass that is found compatible with the moderate cost of a Soyuz launcher. Finally we conclude that a Ceres Polar Lander mission should be feasible, covered by automatic missions to the Moon in terms of difficulty of landing and by Dawn for the cruise. Lander missions to medium gravity bodies such as Ceres, Enceladus, Europa, Ganymede, Callisto, Iapetus, Triton… in the [0.01-0.15g] range should be accounted for in the development roadmaps of landing techniques and be considered in their return on investment. The synergies with the soft landing missions to come on Mars and Moon should then make a Ceres lander affordable for the agencies within the end of the next decade and pave the way for in-situ missions to more distant icy bodies.

  16. 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.

  17. 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

  18. Spatial distribution of spectral parameters of high latitude geomagnetic disturbances in the Pc5/Pi3 frequency range

    Directory of Open Access Journals (Sweden)

    V. A. Pilipenko

    2010-09-01

    Full Text Available We analyze spectral parameters of the geomagnetic disturbances within the 1–4 mHz (Pc5/Pi3 frequency range for 29 observatories from polar to auroral latitudes. The main object of this study is the broadband (noise background under quiet and moderately disturbed conditions. To obtain a quantitative description of background high-latitude long period ULF activity the log-log dependence of the spectral power on frequency is expanded over Legendre polynomials, and the coefficients of this expansion (spectral moments are used to describe the most common features of these spectra. Not only the spectral power, but also the spectral slope and higher spectral moments, averaged over relatively long time intervals, demonstrate a systematic dependence on corrected geomagnetic (CGM latitude, Φ, and magnetic local time, MLT. The 2-D distributions of the spectral moments in Φ-MLT coordinates are characterized by existence of structures, narrow in latitude and extended in MLT, which can be attributed to the projections of different magnetospheric domains. Spatio-temporal distributions of spectral power of elliptically (P-component and randomly (N-component polarized signal are similar, but not identical. The N-component contribution to the total signal becomes non-negligible in regions with a high local activity, such as the auroral oval and dayside polar cusp. The spectral slope indicates a larger relative contribution of higher frequencies upon the latitude decrease, probably, as a result of the resonant effects in the ULF noise. The higher spectral moments are also controlled mostly by CGM latitude and MLT and are fundamentally different for the polarized and non-polarized components. This study is a step towards the construction of an empirical model of the ULF wave power in Earth's magnetosphere.

  19. Using data assimilation to investigate the causes of Southern Hemisphere high latitude cooling from 10 to 8 ka BP

    Directory of Open Access Journals (Sweden)

    P. Mathiot

    2012-11-01

    Full Text Available Paleoclimate records show an atmospheric and oceanic cooling in the high latitudes of the Southern Hemisphere from 10 to 8 ka BP. In order to study the causes of this cooling, simulations covering the early Holocene period have been performed with the climate model of intermediate complexity LOVECLIM constrained to follow the signal recorded in climate proxies using a data assimilation method based on a particle filtering. The selected proxies represent oceanic and atmospheric surface temperature in the Southern Hemisphere derived from terrestrial, marine and glaciological records. Using our modeling framework, two mechanisms potentially explaining the 10–8 ka BP cooling pattern are investigated. The first hypothesis is a change in atmospheric circulation. The state obtained by data assimilation displays a modification of the meridional atmospheric circulation around Antarctica, producing a 0.6 °C drop in atmospheric temperatures over Antarctica from 10 to 8 ka BP without congruent cooling of the atmospheric and sea-surface temperature in the Southern Ocean. The second hypothesis is a cooling of the sea surface temperature in the Southern Ocean, simulated here as the response to a higher West Antarctic Ice Sheet melting rate. Using data assimilation, we constrain the fresh water flux to increase by 100 mSv from 10 to 8 ka BP. This perturbation leads to an oceanic cooling of 0.5 °C and a strengthening of Southern Hemisphere westerlies (+6%. However, the observed cooling in Antarctic and the Southern Ocean proxy records can only be reconciled with the combination of a modified atmospheric circulation and an enhanced freshwater flux.

  20. Trans-Tasman Sea climate variability since ad 1740 inferred from middle to high latitude tree-ring data

    Energy Technology Data Exchange (ETDEWEB)

    D' Arrigo, R.; Cook, E.; Buckley, B. [Columbia Univ., Palisades, NY (United States). Lamont-Doherty Earth Observatory; Villalba, R. [Tree-Ring Laboratory, IANIGLA-CRICYT, Mendoza (Argentina); Salinger, J. [NIWA, 269 Khyber Pass Rd, Newmarket, Auckland (New Zealand); Palmer, J. [Lincoln University, Canterbury (New Zealand); Allen, K. [Department of Geography and Environmental Studies University of Tasmania, Sandybay, Tas. (Australia)

    2000-08-01

    The limited length and spatial coverage of instrumental climate data for many areas of the Southern Hemisphere impedes the study of atmosphere-ocean dynamics prior to the past century. Such analyses are important for understanding interannual to decadal variation of the Southern Hemisphere circulation and whether recent changes are related to anthropogenic effects rather than natural variability. We use a middle- to high-latitude tree-ring width data set (from Tasmania, New Zealand and Tierra del Fuego) to reconstruct sea-level pressure (SLP) variability spanning the Tasman Sea and vicinity since ad 1740. The variables reconstructed are austral summer (November-March) SLP for Hobart, Tasmania (43 S, 147 E) and the Chatham Islands, New Zealand (44 S, 177 E), as well as a meridional circulation index (Hobart-Chatham Islands index) which measures the pressure gradient between these two stations. The three reconstructions are well verified statistically and capture between 40 and 48% of the variance in the SLP data. The instrumental and estimated SLP show similar spatial patterns of correlation with the sea surface temperature (SST) field for the Pacific. Statistically significant (above 95% level) 3-3.5 year spectral peaks are identified in the three reconstructions using multitaper spectral analysis, and a significant 4-5 year peak is found in both the Chatham Islands and Hobart-Chatham Islands SLP reconstructions. These two modes are within the bandwidth of the El Nino-southern oscillation. Although very speculative, they may also correspond to a proposed Antarctic circumpolar wave of SLP, SST, wind and sea-ice extent, believed to play a key role in atmosphere-ocean circulation for the Southern Hemisphere. (orig.)

  1. Boundary-Layer Development and Low-level Baroclinicity during High-Latitude Cold-Air Outbreaks: A Simple Model

    Science.gov (United States)

    Chechin, Dmitry G.; Lüpkes, Christof

    2016-08-01

    A new quasi-analytical mixed-layer model is formulated describing the evolution of the convective atmospheric boundary layer (ABL) during cold-air outbreaks (CAO) over polar oceans downstream of the marginal sea-ice zones. The new model is superior to previous ones since it predicts not only temperature and mixed-layer height but also the height-averaged horizontal wind components. Results of the mixed-layer model are compared with dropsonde and aircraft observations carried out during several CAOs over the Fram Strait and also with results of a 3D non-hydrostatic (NH3D) model. It is shown that the mixed-layer model reproduces well the observed ABL height, temperature, low-level baroclinicity and its influence on the ABL wind speed. The mixed-layer model underestimates the observed ABL temperature only by about 10 %, most likely due to the neglect of condensation and subsidence. The comparison of the mixed-layer and NH3D model results shows good agreement with respect to wind speed including the formation of wind-speed maxima close to the ice edge. It is concluded that baroclinicity within the ABL governs the structure of the wind field while the baroclinicity above the ABL is important in reproducing the wind speed. It is shown that the baroclinicity in the ABL is strongest close to the ice edge and slowly decays further downwind. Analytical solutions demonstrate that the e -folding distance of this decay is the same as for the decay of the difference between the surface temperature of open water and of the mixed-layer temperature. This distance characterizing cold-air mass transformation ranges from 450 to 850 km for high-latitude CAOs.

  2. On the importance of appropriate rain-gauge catch correction for hydrological modelling at mid to high latitudes

    Directory of Open Access Journals (Sweden)

    S. Stisen

    2012-03-01

    Full Text Available An existing rain gauge catch correction method addressing solid and liquid precipitation was applied both as monthly mean correction factors based on a 30 yr climatology (standard correction and as daily correction factors based on daily observations of wind speed and temperature (dynamic correction. The two methods resulted in different winter precipitation rates for the period 1990–2010. The resulting precipitation data sets were evaluated through the comprehensive Danish National Water Resources model (DK-Model revealing major differences in both model performance and optimized model parameter sets. Simulated stream discharge is improved significantly when introducing a dynamic precipitation correction, whereas the simulated hydraulic heads and multi-annual water balances performed similarly due to recalibration adjusting model parameters to compensate for input biases. The resulting optimized model parameters are much more physically plausible for the model based on dynamic correction of precipitation. A proxy-basin test where calibrated DK-Model parameters were transferred to another region without site specific calibration showed better performance for parameter values based on the dynamic correction. Similarly, the performances of the dynamic correction method were superior when considering two single years with a much dryer and a much wetter winter, respectively, as compared to the winters in the calibration period (differential split-sample tests. We conclude that dynamic 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 type (solid/liquid fluctuate significantly

  3. High-latitude environmental change during MIS 8–12: biogeochemical evidence from Lake El'gygytgyn, Far East Russia

    Directory of Open Access Journals (Sweden)

    D. B. Finkelstein

    2012-09-01

    Full Text Available Marine Isotope Stages (MIS 11 has been proposed as an analog for the present interglacial; however, terrestrial records of this time period are rare. Sediments from Lake El'gygytgyn (67°30´ N, 172°5´ E in Far East Russia contain a 3.56 Ma record of climate variability from the Arctic. Here, we present an organic geochemical reconstruction of environmental and climatic changes from MIS 8 through 12 (289 to 460 ka. Terrestrial vegetation changes, as revealed by plant leaf wax (n-alkane indices and concentrations of arborinol (a biomarker for trees, show increased tree cover around the lake during interglacial periods, with higher concentrations observed during MIS 11 as compared to MIS 9. A similar pattern is also observed in records of aquatic productivity revealed by molecular indicators from dinoflagellates (dinosterol, eustigmatophyte algae (long-chain (C28–C32 1,15 n-alkyl diols in addition to short-chain nalkanes, where aquatic productivity is highest during MIS 11. Changes recorded in these molecular proxies track relative temperature variability as recorded by the MBT/CBT paleothermometer, based on branched glycerol dialkyl glycerol tetraethers (GDGTs. Additionally, relative MBT/CBT temperature changes generally track pollen and diatom δ18O temperature estimates, compiled by other studies, which suggest glacial–interglacial temperature changes of ~ 9–12 °C. These records of environmental and climatic change indicate Arctic sensitivity to external forcings such as orbital variability and atmospheric greenhouse gas concentrations. Overall, this study indicates that organic geochemical analyses of the Lake El'gygytgyn sediment archive can provide critical insight into the response of lake ecosystems and their sensitivity in high latitude regions.

  4. Tropical Atlantic climate response to different freshwater input in high latitudes with an ocean-only general circulation model

    Science.gov (United States)

    Men, Guang; Wan, Xiuquan; Liu, Zedong

    2016-10-01

    Tropical Atlantic climate change is relevant to the variation of Atlantic meridional overturning circulation (AMOC) through different physical processes. Previous coupled climate model simulation suggested a dipole-like SST structure cooling over the North Atlantic and warming over the South Tropical Atlantic in response to the slowdown of the AMOC. Using an ocean-only global ocean model here, an attempt was made to separate the total influence of various AMOC change scenarios into an oceanic-induced component and an atmospheric-induced component. In contrast with previous freshwater-hosing experiments with coupled climate models, the ocean-only modeling presented here shows a surface warming in the whole tropical Atlantic region and the oceanic-induced processes may play an important role in the SST change in the equatorial south Atlantic. Our result shows that the warming is partly governed by oceanic process through the mechanism of oceanic gateway change, which operates in the regime where freshwater forcing is strong, exceeding 0.3 Sv. Strong AMOC change is required for the gateway mechanism to work in our model because only when the AMOC is sufficiently weak, the North Brazil Undercurrent can flow equatorward, carrying warm and salty north Atlantic subtropical gyre water into the equatorial zone. This threshold is likely to be model-dependent. An improved understanding of these issues may have help with abrupt climate change prediction later.

  5. Gain ranging amplifier

    International Nuclear Information System (INIS)

    A gain ranging amplifier system is provided for use in the acquisition of data. Voltage offset compensation is utilized to correct errors in the gain ranging amplifier system caused by thermal drift and temperature dependent voltage offsets, both of which are associated with amplifiers in the gain ranging amplifier system

  6. Global warming

    International Nuclear Information System (INIS)

    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

  7. Buffering and Amplifying Interactions among OAW (Ocean Acidification & Warming) and Nutrient Enrichment on Early Life-Stage Fucus vesiculosus L. (Phaeophyceae) and Their Carry Over Effects to Hypoxia Impact.

    Science.gov (United States)

    Al-Janabi, Balsam; Kruse, Inken; Graiff, Angelika; Winde, Vera; Lenz, Mark; Wahl, Martin

    2016-01-01

    Ocean acidification and warming (OAW) are occurring globally. Additionally, at a more local scale the spreading of hypoxic conditions is promoted by eutrophication and warming. In the semi-enclosed brackish Baltic Sea, occasional upwelling in late summer and autumn may expose even shallow-water communities including the macroalga Fucus vesiculosus to particularly acidified, nutrient-rich and oxygen-poor water bodies. During summer 2014 (July-September) sibling groups of early life-stage F. vesiculosus were exposed to OAW in the presence and absence of enhanced nutrient levels and, subsequently to a single upwelling event in a near-natural scenario which included all environmental fluctuations in the Kiel Fjord, southwestern Baltic Sea, Germany (54°27 ´N, 10°11 ´W). We strove to elucidate the single and combined impacts of these potential stressors, and how stress sensitivity varies among genetically different sibling groups. Enhanced by a circumstantial natural heat wave, warming and acidification increased mortalities and reduced growth in F. vesiculosus germlings. This impact, however, was mitigated by enhanced nutrient conditions. Survival under OAW conditions strongly varied among sibling groups hinting at a substantial adaptive potential of the natural Fucus populations in the Western Baltic. A three-day experimental upwelling caused severe mortality of Fucus germlings, which was substantially more severe in those sibling groups which previously had been exposed to OAW. Our results show that global (OAW), regional (nutrient enrichment) and local pressures (upwelling), both alone and co-occurring may have synergistic and antagonistic effects on survival and/or growth of Fucus germlings. This result emphasizes the need to consider combined stress effects.

  8. Buffering and Amplifying Interactions among OAW (Ocean Acidification & Warming) and Nutrient Enrichment on Early Life-Stage Fucus vesiculosus L. (Phaeophyceae) and Their Carry Over Effects to Hypoxia Impact

    Science.gov (United States)

    Al-Janabi, Balsam; Kruse, Inken; Graiff, Angelika; Winde, Vera; Lenz, Mark; Wahl, Martin

    2016-01-01

    Ocean acidification and warming (OAW) are occurring globally. Additionally, at a more local scale the spreading of hypoxic conditions is promoted by eutrophication and warming. In the semi-enclosed brackish Baltic Sea, occasional upwelling in late summer and autumn may expose even shallow-water communities including the macroalga Fucus vesiculosus to particularly acidified, nutrient-rich and oxygen-poor water bodies. During summer 2014 (July–September) sibling groups of early life-stage F. vesiculosus were exposed to OAW in the presence and absence of enhanced nutrient levels and, subsequently to a single upwelling event in a near-natural scenario which included all environmental fluctuations in the Kiel Fjord, southwestern Baltic Sea, Germany (54°27 ´N, 10°11 ´W). We strove to elucidate the single and combined impacts of these potential stressors, and how stress sensitivity varies among genetically different sibling groups. Enhanced by a circumstantial natural heat wave, warming and acidification increased mortalities and reduced growth in F. vesiculosus germlings. This impact, however, was mitigated by enhanced nutrient conditions. Survival under OAW conditions strongly varied among sibling groups hinting at a substantial adaptive potential of the natural Fucus populations in the Western Baltic. A three-day experimental upwelling caused severe mortality of Fucus germlings, which was substantially more severe in those sibling groups which previously had been exposed to OAW. Our results show that global (OAW), regional (nutrient enrichment) and local pressures (upwelling), both alone and co-occurring may have synergistic and antagonistic effects on survival and/or growth of Fucus germlings. This result emphasizes the need to consider combined stress effects. PMID:27043710

  9. High latitude meteoric δ18O compositions: Paleosol siderite in the Middle Cretaceous Nanushuk Formation, North Slope, Alaska

    Science.gov (United States)

    Ufnar, David F.; Ludvigson, Greg A.; Gonzalez, Luis A.; Brenner, Richard L.; Witzke, Brian J.

    2004-01-01

    paleotemperature estimates and isotope mass balance models of the hydrologic cycle and can be used in future global circulation modeling (GCM) experiments of "greenhouse-world" climates to constrain high latitude precipitation rates in simulations of ancient worlds with decreased equator-to-pole temperature gradients. ?? 2004 Geological Society of America.

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

    International Nuclear Information System (INIS)

    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 (NOx) concentrations in the boundary-layer within and immediately around an urban area. The short-time-scale photochemical processes of ozone and NOx, 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 56oN) 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 NOx 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

  11. 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.

  12. X-mode HF Pump-induced Phenomena at High Heater Frequencies in the High Latitude Ionosphere F-region

    Science.gov (United States)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Kalishin, A. S.; Yeoman, T. K.; Häggström, I.

    2015-12-01

    Experimental results concentrating on X-mode HF-induced phenomena in the high latitude ionosphere F region are discussed. Experiments have been carried out at the HF Heating facility at Tromsø with an effective radiated power of 450 - 650 MW at high heater frequencies of 6.2 - 8.0 MHz. Multi-instriment diagnostics included the European Incoherent Scatter (EISCAT) UHF radar at 931 MHz at Tromsø, the Finland CUTLASS (Co-operative UK Twin Located Auroral Sounding System) radar, the stimulated electromagnetic emission (SEE) equipment at Tromsø, and the HF receiver near St. Petersburg for the observations of narrow band SEE features. The key parameter considered is the ratio between the heater frequency and critical frequency of the F2 layer (fH/foF2). We have analyzed the behaviors of small-scale artificial field-aligned irregularities (FAIs) and HF-enhanced plasma and ion lines (HFPLs and HFILs) depending on the pump proximity to the critical frequency. It was shown that the HFPLs and HFILs coexisted with FAIs throughout the whole heater pulse when fH/foF2 > 1 as well as fH/foF2 ≤ 1. It is indicative that parametric decay instability was not quenched by fully developed FAIs. The comparison between contrasting O/X mode HF-induced phenomena, when the heater frequency is below or near the critical frequency of F2 layer, is made. It was found that an X-mode HF pumping is able to excite different narrow band spectral components in the SEE spectra (within 1 kHz of pump frequency), such as ion acoustic, electrostatic ion cyclotron, and electrostatic ion cyclotron harmonic waves (otherwise known as neutralized ion Bernstein waves) observed at a long distance from the HF Heating facility. It was suggested that these spectral component can be attributed to the stimulated Brillion scatter (SBS) process. The results obtained show that an X-polarized electromagnetic wave scattered by SBS can propagate more than one thousand km without significant attenuation.

  13. ETHOS 1: a high-latitude planetary nebula with jets forged by a post-common-envelope binary central star

    Science.gov (United States)

    Miszalski, B.; Corradi, R. L. M.; Boffin, H. M. J.; Jones, D.; Sabin, L.; Santander-García, M.; Rodríguez-Gil, P.; Rubio-Díez, M. M.

    2011-05-01

    We report on the discovery of ETHOS 1 (PN G068.1+11.0), the first spectroscopically confirmed planetary nebula (PN) from a survey of the SuperCOSMOS Science Archive for high-latitude PNe. ETHOS 1 stands out as one of the few PNe to have both polar outflows (jets) travelling at 120 ± 10 km s-1 and a close binary central star. The light curve observed with the Mercator Telescope reveals an orbital period of 0.535 d and an extremely large amplitude (0.816 mag) due to irradiation of the companion by a very hot pre-white dwarf. ETHOS 1 further strengthens the long-suspected link between binary central stars of PNe (CSPN) and jets. The Isaac Newton Telescope/Intermediate Dispersion Spectrograph and Very Large Telescope (VLT) FORS spectroscopy of the CSPN reveals weak N III, C III and C IV emission lines seen in other close binary CSPN and suggests that many CSPN with these weak emission lines are misclassified close binaries. We present VLT FORS imaging and Manchester Echelle Spectrometer long-slit observations from which a kinematic model of the nebula is built. An unusual combination of bipolar outflows and a spherical nebula conspires to produce an X-shaped appearance. The kinematic age of the jets (1750 ± 250 yr kpc-1) is found to be more than that of the inner nebula (900 ± 100 yr kpc-1), consistent with previous studies of similar PNe. Emission-line ratios of the jets are found to be consistent with that of reverse-shock models for fast low-ionization emitting regions (FLIERs) in PNe. Further large-scale surveys for close binary CSPN will be required to securely establish whether FLIERs are launched by close binaries. Based on observations made with the Flemish Mercator Telescope and Isaac Newton Telescope of the Observatorio del Roque de Los Muchachos and the VLT at the Paranal Observatory under programs 083.D-0654(A) and 085.D-0629(A).

  14. The Middle Eocene Climatic Optimum (MECO) in the high latitudes of the North Atlantic: Temperature and Biotic change

    OpenAIRE

    M. Polling; Houben, A. J. P.; Firth, J; Coxall, H.; J. S. Eldrett; Schouten, S.; Reichart, G.-J.; Brinkhuis, H.

    2011-01-01

    Increasingly high resolution isotope- and novel organic geochemical proxy records have revealed that the long-term cooling trend of the middle Eocene was interrupted by a warming phase designated the Middle Eocene Climatic Optimum (MECO). It is suggested to represent an increase in sea surface temperatures of about 4°C, lasting approximately 400 kyr. The temperature evolution of the MECO is notably well-documented in the Southern Ocean. However, records of temperature- and biotic change durin...

  15. Warm Greenland during the last interglacial: the role of sea ice

    Science.gov (United States)

    Merz, Niklaus; Born, Andreas; Raible, Christoph C.; Stocker, Thomas F.

    2016-04-01

    The last interglacial, the Eemian, is characterized by warmer than present conditions in the high latitudes and is therefore often considered as a possible analogue for the climate in the near future. Simulations of Eemian surface air temperatures (SAT) in the Northern Hemisphere (NH), however, show large variations between different climate models and it has been hypothesized that this model spread relates to diverse representations of the Eemian sea ice cover. Here we use version 3 and 4 of the Community Climate System Model (CCSM3 and CCSM4), to highlight the crucial role of sea ice and sea surface temperatures during the Eemian, in particular for SAT in the North Atlantic sector and in Greenland. A substantial reduction in NH sea ice results in an amplified atmospheric warming and, thus, a better agreement with Eemian proxy records. Sensitivity experiments with idealized lower boundary conditions reveal that warming over Greenland is mostly due to a sea ice retreat in the Nordic Seas. In contrast, sea ice changes in the Labrador Sea have a limited local impact. Changes in sea ice in either region are transferred to the overlying atmosphere through anomalous surface energy fluxes. The large-scale warming simulated for the sea ice retreat in the Nordic Seas further relates to anomalous heat advection. Diabatic processes play a secondary role, yet distinct changes in the hydrological cycle are possible. Our results imply that temperature and accumulation records from Greenland ice cores are sensitive to sea ice changes in the Nordic Seas but insensitive to sea ice changes in the Labrador Sea. Moreover, our simulations suggest that the uncertainty in the Eemian sea ice cover accounts for 1.6°C of the Eemian warming at the NEEM ice core site. The estimated Eemian warming of 5°C above present-day based on the NEEM δ15N record can be reconstructed by the CCSM4 model for the scenario that a sea ice retreat in the Nordic Seas coincided with a reduced Greenland ice

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

    OpenAIRE

    Andrew G. Carroll; Dalton, Steven J.

    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...

  17. Probing the high latitude ionosphere from ground-based observations: The state of current knowledge and capabilities during IPY (2007–2009)

    OpenAIRE

    Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Kavanagh, A. J.; Space Plasma Environment and Radio Science Group, Department of Communication Systems, InfoLab 21, Lancaster University, Lancaster LA1 4WA, UK; Amata, E.; Istituto di Fisica dello Spazio Interplanetario I.N.A.F., Via del fosso del cavaliere 100, 00133 Rome, Italy; Cilliers, P.; Hermanus Magnetic Observatory (HMO), P.O. Box 32, Hermanus, South Africa; Correia, E.; Instituto Nacional de Pesquisas Espaciais (INPE), São José dos Campos, Brazil and Centro de Rádio Astronomia e Astrofísica Mackenzie (CRAAM), Universidade Presbiteriana Mackenzie, Rua da Consolação 930, CEP: 01302-907 São Paulo, Brazil; Freeman, M.; British Antarctic Survey, High Cross Madingley Road, Cambridge, UK; Kauristie, K.; Finnish Meteorological Institute, Erik Palménin aukio 1, Helsinki, Finland; Liu, R.; Polar Research Institute of China, Shanghai 200136, China; Luntama, J.-P.; Finnish Meteorological Institute, Erik Palménin aukio 1, Helsinki, Finland; Mitchell, C. N.; Department of Electrical Engineering, University of Bath, Bath BA2 7AY, UK; Zherebtsov, G. A.; Institute of Solar-Terrestrial Physics, Siberian Branch, Russian Academy of Science, Irkutsk, Russia

    2008-01-01

    During the International Polar Year (IPY), one area of great interest is co-coordinated, multi-instrument probing of the ionosphere at high latitudes. This region is important not only for the applications that rely upon our understanding of it, but also because it contains the footprints of processes that have their origin in the interplanetary space. Many different techniques are now available for probing the ionosphere, from radar measurements to the analysis of very low frequency (V...

  18. A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

    OpenAIRE

    Villain, J.-P.; André, R; M. Pinnock; R. A. Greenwald; Hanuise, C.

    2002-01-01

    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. Perio...

  19. 高寒区玉米丰产栽培技术%Analysis of the fertility cultivation of corn in high latitude district

    Institute of Scientific and Technical Information of China (English)

    于静; 李洪; 鲁喜荣; 郭凤琴

    2015-01-01

    According to the analysis of the ecological adaptability of the corn in high latitude and cold area of Shanxi Frovince and the influencing factors of corn fertility, this article proposed the fertility cultivation of corn in high latitude district, including the anti-cold variety, deep ploughing, timely sowing, rational close planting, scientific fertilization, timely mulching, timely weeding, timely prevention and the control of plant diseases and insect pests, etc, so as to provide reference for the fertility cultivation of corn in high latitude district.%通过分析山西省高寒地区玉米的生态适应性及影响玉米丰产的因素,提出了高寒区玉米丰产栽培技术,包括选用抗寒品种、深耕整地、适时早播、合理密植、科学施肥、适时覆膜、及时除草,病虫害防治等内容,以期为高寒区玉米的丰产栽培提供参考.

  20. Comparison with oblique sounder data of high-latitude HF propagation predictions from RADAR C and AMBCOM computer programs. Professional Paper for October 1987

    Energy Technology Data Exchange (ETDEWEB)

    Dave, N.

    1988-06-01

    A study was done using two High Frequency (HF) propagation prediction programs - RADAR C and AMBCOM - to determine how well they predict median values of oblique sounder data of maximum observed frequencies (MOF) at high latitudes. The main differences between RADAR C and AMBCOM are the inclusion in the latter of high-latitude ionosphere and auroral absorption models, as well as a more-sophisticated and accurate ray-tracing scheme. The data used for comparison are taken for the Winnipeg-Resolute Bay path in the year 1959 and for the Andoya-Ft. Monmouth and Andoya-College paths in 1964. The data for the Winnipeg-Resolute Bay corresponds to high sunspot number, while the others correspond to low sunspot number. Hence, the study provides information on the performance of the two programs for various high-latitude paths at both high and low sunspot number. AMBCOM was found to give generally better agreement with the above data than did RADAR C. Comparison of details of model predictions from the two computer programs for the above data-base is used to form an understanding of this improvement in prediction capability.

  1. 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.

  2. Portable musical instrument amplifier

    Energy Technology Data Exchange (ETDEWEB)

    Christian, David E. (Danbury, CT)

    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.

  3. Extreme warm temperatures alter forest phenology and productivity in Europe.

    Science.gov (United States)

    Crabbe, Richard A; Dash, Jadu; Rodriguez-Galiano, Victor F; Janous, Dalibor; Pavelka, Marian; Marek, Michal V

    2016-09-01

    Recent climate warming has shifted the timing of spring and autumn vegetation phenological events in the temperate and boreal forest ecosystems of Europe. In many areas spring phenological events start earlier and autumn events switch between earlier and later onset. Consequently, the length of growing season in mid and high latitudes of European forest is extended. However, the lagged effects (i.e. the impact of a warm spring or autumn on the subsequent phenological events) on vegetation phenology and productivity are less explored. In this study, we have (1) characterised extreme warm spring and extreme warm autumn events in Europe during 2003-2011, and (2) investigated if direct impact on forest phenology and productivity due to a specific warm event translated to a lagged effect in subsequent phenological events. We found that warmer events in spring occurred extensively in high latitude Europe producing a significant earlier onset of greening (OG) in broadleaf deciduous forest (BLDF) and mixed forest (MF). However, this earlier OG did not show any significant lagged effects on autumnal senescence. Needleleaf evergreen forest (NLEF), BLDF and MF showed a significantly delayed end of senescence (EOS) as a result of extreme warm autumn events; and in the following year's spring phenological events, OG started significantly earlier. Extreme warm spring events directly led to significant (p=0.0189) increases in the productivity of BLDF. In order to have a complete understanding of ecosystems response to warm temperature during key phenological events, particularly autumn events, the lagged effect on the next growing season should be considered. PMID:27152990

  4. Recent Rapid Regional Climate Warming on the Antarctic Peninsula

    Science.gov (United States)

    Vaughan, D. G.; Marshall, G. J.; Connolley, W. M.; Parkinson, C.; Mulvaney, R.; Hodgson, D. A.; King, J. C.; Pudsey, C. J.; Turner, J.

    2002-12-01

    The Intergovernmental Panel on Climate Change (IPCC) confirmed that global warming was 0.6 ñ 0.2 degrees C during the 20th Century and cited increases in greenhouse gases as a likely contributor. But this average conceals the complexity of observed climate change, which is seasonally biased, decadally variable and geographically patchy. In particular, over the last 50 years three high-latitude areas have undergone recent rapid regional (RRR) warming ? substantially more rapid than the global mean. We discuss the spatial and temporal significance of RRR warming in one area, the Antarctic Peninsula. New analyses of station records show no ubiquitous polar amplification of global warming but significant RRR warming on the Antarctic Peninsula. We investigate the likelihood that this could be amplification of a global warming, and use climate-proxy data to indicate that this RRR warming on the Antarctic Peninsula is unprecedented over the last two millennia and unlikely to be a natural mode of variability. We can show a strong connection between RRR warming and reduced sea-ice duration in an area on the west of the Antarctic Peninsula, but here we cannot yet distinguish cause and effect. Thus for the present we cannot determine which process causes the RRR warming, and until the mechanism initiating and sustaining it is understood, and is convincingly reproduced in climate models, we lack a sound basis for predicting climate change in this region over the coming century.

  5. Long-term versus short-term warming effects on microbial processes

    Science.gov (United States)

    Walker, Tom; Leblans, Niki; Sigurdsson, Bjarni D.; Richter, Andreas

    2016-04-01

    Rapid warming in high latitude ecosystems is predicted to drive massive losses of carbon dioxide (CO2) from soils to the atmosphere, raising concerns that it will create a positive feedback to climate change. However, such predictions expect that temperature effects on soil microbes, as chief producers of CO2, will persist over time scales meaningful to the climate system (i.e. decades to centuries). There is increasing awareness that the soil microbial community can acclimate to temperature change over time scales from months to years, resulting in attenuating responses of CO2 release to the atmosphere. Despite this, nothing is currently known about long-term warming effects on the activity or physiology of high latitude soil microbes, and, through this, the longevity of CO2 losses from these ecosystems. We conducted a study at a unique research site that makes use of natural (geothermal) gradients in soil temperature that have been in place for over 35 years as a natural warming treatment. We determined long-term warming effects (+0.5 °C, +1.5 °C, +3 °C and +6 °C) on soil CO2 release through microbial respiration in a laboratory incubation experiment, and explored microbial carbon use efficiency and soil carbon and nitrogen pools as mechanisms. We also performed a companion experiment to compare long-term warming effects on microbial processes to those caused by six weeks of warming of ambient soil to +3 °C and +6 °C. We show that while six weeks of warming consistently increased microbial respiration by up to 30%, this effect did not persist in soils exposed to 35 years of warming. We present further data linking such long-term thermal acclimation to shifts in microbial carbon use efficiency and soil carbon and nitrogen availability, and discuss our findings in the context of warming-driven feedbacks from high latitude soils to future climate change.

  6. High voltage distributed amplifier

    Science.gov (United States)

    Willems, D.; Bahl, I.; Wirsing, K.

    1991-12-01

    A high-voltage distributed amplifier implemented in GaAs MMIC technology has demonstrated good circuit performance over at least two octave bandwidth. This technique allows for very broadband amplifier operation with good efficiency in satellite, active-aperture radar, and battery-powered systems. Also, by increasing the number of FETs, the amplifier can be designed to match different voltage rails. The circuit does require a small amount of additional chip size over conventional distributed amplifiers but does not require power dividers or additional matching networks. This circuit configuration should find great use in broadband power amplifier design.

  7. Regional Contrasts of the Warming Rate over Land Significantly Depend on the Calculation Methods of Mean Air Temperature

    OpenAIRE

    Kaicun Wang; Chunlüe Zhou

    2015-01-01

    Global analyses of surface mean air temperature (T m ) are key datasets for climate change studies and provide fundamental evidences for global warming. However, the causes of regional contrasts in the warming rate revealed by such datasets, i.e., enhanced warming rates over the northern high latitudes and the “warming hole” over the central U.S., are still under debate. Here we show these regional contrasts depend on the calculation methods of T m . Existing global analyses calculate T m fro...

  8. 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.

  9. Low- and Mid-High Latitude Components of the East Asian Winter Monsoon and Their Reflecting Variations in Winter Climate over Eastern China

    Institute of Scientific and Technical Information of China (English)

    LIU Ge; JI Li-Ren; SUN Shu-Qing; XIN Yu-Fei

    2012-01-01

    The present study defines a low-latitude component (regionally averaged winter 1000-hPa V-winds over 10 25°N, 105 135°E) and a mid-high-latitude component (regionally averaged winter 1000-hPa V-winds over 30 50°N, 110 125°E) of the East Asian winter monsoon (EAWM), which are denoted as EAWM-L and EAWM-M, respectively. The study examines the variation characteristics, reflecting variations in winter climate over eastern China, and associated atmospheric circulations corresponding to the two components. The main results are as follows: 1) the EAWM-L and EAWM-M have consistent variation in some years but opposite variations in other years; 2) the EAWM-M index mainly reflects the extensive temperature variability over eastern China, while the EAWM-L index better reflects the variation in winter precipitation over most parts of eastern China; and 3) corresponding to the variation in the EAWM-M index, anomalous winds over the mid-high latitudes of East Asia modulate the southward invasion of cold air from the high latitudes and accordingly affect temperatures over eastern China. In combination with the variation in the EAWM-L index, anomalous low-latitudinal winds regulate the water vapor transport from tropical oceans to eastern China, resulting in anomalous winter precipitation. These pronounced differences between the EAWM-L and the EAWM-M suggest that it is necessary to explore the monsoons' individual features and effects in the EAWM study.

  10. IMF Dependence of High-Latitude Thermospheric Wind Pattern Derived from CHAMP Cross-Track Accelerometer Data and the Corresponding Magnetospheric Convection from Cluster EDI Measurements

    Science.gov (United States)

    Foerster, Matthias; Haaland, Stein E.; Rentz, Stefanie; Liu, Huixin

    Neutral thermospheric wind pattern at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both North and South polar regions are statistically analyzed in their dependence on the Interplanetary Magnetic Field (IMF) direction in the GSM y-z plane (clock angle). We compare this dependency with magnetospheric convection pattern using 1-min-averages of Cluster/EDI electric drift observations and the same IMF and solar wind sorting conditions. The spatially distributed Cluster/EDI measurements are mapped to a the common reference level at ionospheric F-region heights in a magnetic latitude/MLT grid. We obtained both regular thermospheric wind and plasma drift pattern according to the various IMF conditions. The IMF-dependency shows some similarity with the corresponding high-latitude plasma convection insofar that the larger-scale convection cells, in particular the round-shaped dusk cell for IMF By+ (By-) conditions at the Northern (Southern) Hemisphere, leave their marks on the dominant general transpolar wind circulation from the dayside to the nightside. The direction of the transpolar circulation is generally deflected toward a duskward flow, in particular in the evening to nighttime sector. The degree of deflection correlates with the IMF clock angle. It is larger for IMF By+ than for Byand is systematically larger (about 5 deg) and appear less structured at the Southern Hemisphere compared with the Northern. Thermospheric cross-polar wind amplitudes are largest for IMF Bz-/Byconditions (corresponding to sector 5) at the Northern Hemisphere, but for IMF Bz-/By+ conditions (sector 3) at the Southern because the magnetospheric convection is in favour of largest wind accelerations over the polar cap under these conditions. The overall variance of the thermospheric wind magnitude at Southern high latitudes is larger than for the Northern. This is probably due to a larger "stirring effect" at the Southern Hemisphere because

  11. Testing the applicability of neural networks as a gap-filling method using CH4 flux data from high latitude wetlands

    DEFF Research Database (Denmark)

    Dengel, S.; Zona, D.; Sachs, T.;

    2013-01-01

    no consensus on CH4 gap-filling methods, and methods applied are still study-dependent and often carried out on low resolution, daily data. In the current study, we applied artificial neural networks to six distinctively different CH4 time series from high latitudes, explain the method and test its...... pressure, solar radiation, wind direction (indicator of source location) and in addition the lagged effect of water table depth and precipitation. In keeping with the principle of parsimony, we included up to five of these variables traditionally measured at CH4 flux measurement sites. Fuzzy sets were...

  12. Erosion of soil organic carbon at high latitudes and its delivery to Arctic Ocean sediments: New source to sink insight from radiocarbon dating

    Science.gov (United States)

    Hilton, Robert; Galy, Valier; Gaillardet, Jerome; Dellinger, Mathieu; Bryant, Charlotte; O'Regan, Matt; Grocke, Darren; Coxall, Helen

    2016-04-01

    Soils of the northern high latitudes store carbon over thousands of years and contain almost double the carbon stock of the atmosphere. Erosion processes can mobilise this pre-aged soil organic carbon from the landscape and supply it to rivers. If it escapes degradation during river transport and is delivered to the coastal ocean, this carbon may be sequestered for much longer periods of time (>104 yr) as a geological CO2 sink. Despite this recognition, the erosional flux and fate of particulate organic carbon (POC) in large rivers draining the high latitudes remains poorly constrained. Using radiocarbon activity, we quantify POC source, flux and fate in the Mackenzie River, the main sediment supplier to the Arctic Ocean. When combined with stable carbon isotopes and element ratios, the radiocarbon activity of POC allows us to distinguish inputs of POC from sedimentary rocks and quantify the average age of biospheric POC (from vegetation and soil) transported through the river system. We find that the eroded biospheric POC has resided in the basin for millennia, with a mean radiocarbon age of 5800±800 years. This is much older than large tropical rivers where we have equivalent data (Amazon River, Ganges River), and likely reflects the longer residence time of organic matter in cold, wet, high latitude soils. Based on the measured biospheric POC content and annual sediment flux, we calculate a biospheric POC flux of 2.2 (+1.3/-0.9) TgC yr-1 from the Mackenzie River. This is the largest input of aged organic carbon to the Arctic Ocean, more than the combined POC flux from the Eurasian Rivers. Offshore, we use a marine core to investigate organic carbon burial over the Holocene period. Radiocarbon measurements of bulk organic carbon reveal a significant offset from benthic foraminifera radiocarbon ages throughout the core, which is dependent upon the grain size of the sediments. Organic matter in sediments >63μm are offset from foraminifera by ˜ 6,000 14C years

  13. Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the Southwest Pacific

    Directory of Open Access Journals (Sweden)

    K. M. Pascher

    2015-07-01

    Full Text Available The Eocene was characterised by "greenhouse" climate conditions that were gradually terminated by a long-term cooling trend through the middle and late Eocene. This long-term trend was determined by several large-scale climate perturbations that culminated in a shift to "ice-house" climates at the Eocene–Oligocene Transition. Geochemical and micropaleontological proxies suggest that tropical-to-subtropical sea-surface temperatures persisted into the late Eocene in the high-latitude Southwest Pacific Ocean. Here, we present radiolarian microfossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP Sites 277, 280, 281 and 283 from the middle Eocene to early Oligocene (~ 40–33 Ma to identify oceanographic changes in the Southwest Pacific across this major transition in Earth's climate history. The Middle Eocene Climatic Optimum at ~ 40 Ma is characterised by a negative shift in foraminiferal oxygen isotope values and a radiolarian assemblage consisting of about 5 % of low latitude taxa Amphicraspedum prolixum group and Amphymenium murrayanum. In the early late Eocene at ~ 37 Ma, a positive oxygen isotope shift can be correlated to the Priabonian Oxygen Isotope Maximum (PrOM event – a short-lived cooling event recognized throughout the Southern Ocean. Radiolarian abundance, diversity, and preservation increase during the middle of this event at Site 277 at the same time as diatoms. The PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. These high-latitude taxa also increase in abundance during the late Eocene and early Oligocene at DSDP Sites 280, 281 and 283 and are associated with very high diatom abundance. We therefore infer a~northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau towards the end of the late Eocene. In the early Oligocene (~ 33 Ma there is an overall decrease in radiolarian abundance and diversity at

  14. Long-range dispersal and high-latitude environments influence the population structure of a "stress-tolerant" dinoflagellate endosymbiont.

    Directory of Open Access Journals (Sweden)

    D Tye Pettay

    Full Text Available The migration and dispersal of stress-tolerant symbiotic dinoflagellates (genus Symbiodinium may influence the response of symbiotic reef-building corals to a warming climate. We analyzed the genetic structure of the stress-tolerant endosymbiont, Symbiodinium glynni nomen nudum (ITS2 - D1, obtained from Pocillopora colonies that dominate eastern Pacific coral communities. Eleven microsatellite loci identified genotypically diverse populations with minimal genetic subdivision throughout the Eastern Tropical Pacific, encompassing 1000's of square kilometers from mainland Mexico to the Galapagos Islands. The lack of population differentiation over these distances corresponds with extensive regional host connectivity and indicates that Pocillopora larvae, which maternally inherit their symbionts, aid in the dispersal of this symbiont. In contrast to its host, however, subtropical populations of S. glynni in the Gulf of California (Sea of Cortez were strongly differentiated from populations in tropical eastern Pacific. Selection pressures related to large seasonal fluctuations in temperature and irradiance likely explain this abrupt genetic discontinuity. We infer that S. glynni genotypes harbored by host larvae arriving from more southern locations are rapidly replaced by genotypes adapted to more temperate environments. The strong population structure of S. glynni corresponds with fluctuating environmental conditions and suggests that these genetically diverse populations have the potential to evolve rapidly to changing environments and reveals the importance of environmental extremes in driving microbial eukaryote (e.g., plankton speciation in marine ecosystems.

  15. Oscillators and operational amplifiers

    DEFF Research Database (Denmark)

    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....

  16. Global warming

    International Nuclear Information System (INIS)

    '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

  17. 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. PMID:24386125

  18. 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.

  19. Theoretical predictions for ion composition in the high-latitude winter F-region for solar minimum and low magnetic activity

    Science.gov (United States)

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

    1981-01-01

    A simple plasma convection model is combined with an ionospheric-atmospheric density model in order to study the ion composition in the high-latitude winter F-region at solar minimum for low geomagnetic activity. The numerical study produces time-dependent, three-dimensional ion density distributions for the ions NO(+), O2(+), N2(+), O(+), N(+), and He(+). The high-latitude ionosphere above 54 deg N magnetic latitude is covered at altitudes between 160 and 800 km for one complete day. Among the conclusions are the following: the ion composition varies significantly with latitude, local time, altitude, and universal time; the variations in the ion composition with latitude and local time are in good agreement with the Atmosphere Explorer measurements both quantitatively and qualitatively; and at times and at certain locations the molecular ion density can be comparable to the O(+) density at 300 km, and at 200 km the O(+) density can be comparable to the molecular ion density.

  20. Dependence of the high-latitude plasma irregularities on the auroral activity indices: a case study of 17 March 2015 geomagnetic storm

    Science.gov (United States)

    Cherniak, Iurii; Zakharenkova, Irina

    2015-09-01

    The magnetosphere substorm plays a crucial role in the solar wind energy dissipation into the ionosphere. We report on the intensity of the high-latitude ionospheric irregularities during one of the largest storms of the current solar cycle—the St. Patrick's Day storm of 17 March 2015. The database of more than 2500 ground-based Global Positioning System (GPS) receivers was used to estimate the irregularities occurrence and dynamics over the auroral region of the Northern Hemisphere. We analyze the dependence of the GPS-detected ionospheric irregularities on the auroral activity. The development and intensity of the high-latitude irregularities during this geomagnetic storm reveal a high correlation with the auroral hemispheric power and auroral electrojet indices (0.84 and 0.79, respectively). Besides the ionospheric irregularities caused by particle precipitation inside the polar cap region, evidences of other irregularities related to the storm enhanced density (SED), formed at mid-latitudes and its further transportation in the form of tongue of ionization (TOI) towards and across the polar cap, are presented. We highlight the importance accounting contribution of ionospheric irregularities not directly related with particle precipitation in overall irregularities distribution and intensity.

  1. 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.

  2. Amazonian mid- to high-latitude glaciation on Mars: Supply-limited ice sources, ice accumulation patterns, and concentric crater fill glacial flow and ice sequestration

    Science.gov (United States)

    Fastook, James L.; Head, James W.

    2014-02-01

    Concentric crater fill (CCF) occurs in the interior of impact craters in mid- to high latitudes on Mars and is interpreted to have formed by glacial ice flow and debris covering. We use the characteristics and orientation of deposits comprising CCF, the thickness of pedestal deposits in mid- to high-latitude pedestal craters (Pd), the volumes of the current polar caps, and information about regional slopes and ice rheology to address questions about (1) the maximum thickness of regional ice deposits during the Late Amazonian, (2) the likelihood that these deposits flowed regionally, (3) the geological regions and features most likely to induce ice-flow, and (4) the locations and environments in which ice is likely to have been sequestered up to the present. We find that regional ice flow under Late Amazonian climate conditions requires ice thicknesses exceeding many hundreds of meters for slopes typical of the vast majority of the surface of Mars, a thickness for the mid-latitudes that is well in excess of the total volume available from polar ice reservoirs. This indicates that although conditions for mid- to high-latitude glaciation may have persisted for tens to hundreds of millions of years, the process is “supply limited”, with a steady state reached when the polar ice cap water ice supply becomes exhausted. Impact craters are by far the most abundant landform with associated slopes (interior wall and exterior rim) sufficiently high to induce glacial ice flow under Late Amazonian climate conditions, and topographic slope data show that Amazonian impact craters have been clearly modified, undergoing crater interior slope reduction and floor shallowing. We show that these trends are the predictable response of ice deposition and preferential accumulation and retention in mid- to high-latitude crater interiors during episodes of enhanced spin-axis obliquity. We demonstrate that flow from a single episode of an inter-crater terrain layer comparable to Pedestal

  3. Regional Contrasts of the Warming Rate over Land Significantly Depend on the Calculation Methods of Mean Air Temperature.

    Science.gov (United States)

    Wang, Kaicun; Zhou, Chunlüe

    2015-01-01

    Global analyses of surface mean air temperature (T(m)) are key datasets for climate change studies and provide fundamental evidences for global warming. However, the causes of regional contrasts in the warming rate revealed by such datasets, i.e., enhanced warming rates over the northern high latitudes and the "warming hole" over the central U.S., are still under debate. Here we show these regional contrasts depend on the calculation methods of T(m). Existing global analyses calculate T(m) from daily minimum and maximum temperatures (T2). We found that T2 has a significant standard deviation error of 0.23 °C/decade in depicting the regional warming rate from 2000 to 2013 but can be reduced by two-thirds using T(m) calculated from observations at four specific times (T4), which samples diurnal cycle of land surface air temperature more often. From 1973 to 1997, compared with T4, T2 significantly underestimated the warming rate over the central U.S. and overestimated the warming rate over the northern high latitudes. The ratio of the warming rate over China to that over the U.S. reduces from 2.3 by T2 to 1.4 by T4. This study shows that the studies of regional warming can be substantially improved by T4 instead of T2. PMID:26198976

  4. Regional Contrasts of the Warming Rate over Land Significantly Depend on the Calculation Methods of Mean Air Temperature

    Science.gov (United States)

    Wang, Kaicun; Zhou, Chunlüe

    2016-04-01

    Global analyses of surface mean air temperature (Tm) are key datasets for climate change studies and provide fundamental evidences for global warming. However, the causes of regional contrasts in the warming rate revealed by such datasets, i.e., enhanced warming rates over the northern high latitudes and the "warming hole" over the central U.S., are still under debate. Here we show these regional contrasts depends on the calculation methods of Tm. Existing global analyses calculated Tm from daily minimum and maximum temperatures (T2). We found that T2 has a significant standard deviation error of 0.23 °C/decade in depicting the regional warming rate from 2000 to 2013 but can be reduced by two-thirds using Tm calculated from observations at four specific times (T4), which samples diurnal cycle of land surface air temperature more often. From 1973 to 1997, compared with T4, T2 significantly underestimated the warming rate over the central U.S. and overestimated the warming rate over the northern high latitudes. The ratio of the warming rate over China to that over the U.S. reduces from 2.3 by T2 to 1.4 by T4. This study shows that the studies of regional warming can be substantially improved by T4 instead of T2.

  5. Enhanced seasonal CO2 exchange caused by amplified plant productivity in northern ecosystems.

    Science.gov (United States)

    Forkel, Matthias; Carvalhais, Nuno; Rödenbeck, Christian; Keeling, Ralph; Heimann, Martin; Thonicke, Kirsten; Zaehle, Sönke; Reichstein, Markus

    2016-02-12

    Atmospheric monitoring of high northern latitudes (above 40°N) has shown an enhanced seasonal cycle of carbon dioxide (CO2) since the 1960s, but the underlying mechanisms are not yet fully understood. The much stronger increase in high latitudes relative to low ones suggests that northern ecosystems are experiencing large changes in vegetation and carbon cycle dynamics. We found that the latitudinal gradient of the increasing CO2 amplitude is mainly driven by positive trends in photosynthetic carbon uptake caused by recent climate change and mediated by changing vegetation cover in northern ecosystems. Our results underscore the importance of climate-vegetation-carbon cycle feedbacks at high latitudes; moreover, they indicate that in recent decades, photosynthetic carbon uptake has reacted much more strongly to warming than have carbon release processes.

  6. Global warming and carbon dynamics in permafrost soils: methane production and oxidation

    OpenAIRE

    Dirk Wagner; Susanne Liebner;  ,

    2009-01-01

    The Arctic plays a key role in the Earths climate system, because global warming is predicted to be most pronounced at high latitudes, and one third of the global carbon pool is stored in ecosystems of the northern latitudes. The degradation of permafrost and the associated intensified release of methane, a climate-relevant trace gas, represent potential environmental hazards. The microorganisms driving methane production and oxidation in Arctic permafrost soils have remained poorly investiga...

  7. Controlled Soil Warming Powered by Alternative Energy for Remote Field Sites

    OpenAIRE

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

    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...

  8. Greenhouse warming and the Eurasian biota: are there any lessons from the past?

    Science.gov (United States)

    Velichko, A. A.; Borisova, O. K.; Zelikson, E. M.; Faure, H.; Adams, J. M.; Branchu, P.; Faure-Denard, L.

    1993-05-01

    Climate models predict a rise in global mean temperature of around 2-4°C by the end of the next century, with far greater rises in the high latitudes. Mean annual temperature rises of 6-8°C are predicted for 65°N, and as much as 10-12°C for above 70°N. There can be little doubt that such changes will have profound effects on boreal and arctic ecosystems, both through the temperature effects themselves and through associated changes in water balance. There is abundant evidence of climatic change in the high latitudes from the last 2.4 million years of the Quaternary. In a succession of glacial-interglacial cycles, high latitude temperatures seem to have fluctuated overall by about the same amount as is projected for the next century. Perhaps it is possible to use our knowledge of such past changes to understand what might happen to the high latitude ecosystems once the future greenhouse warming gets under way? There are many potential pitfalls in using data from the past to attempt to predict the future. In addition to the limitations in the data, there are also many important differences in the rate and setting of changes that should be borne in mind. With regard to climatic time-scale, the biogeographical patterns which we observe for the past are far more likely to represent equilibrium situations than those which we will observe in the future. Equilibrium data can itself be useful in that it provides indications of the distribution of climate conditions towards which the Earth will move. For example, it provides support for the notion that the climatic models are indeed correct in predicting that the strongest warming will occur in the high latitudes. Even following the relatively slow climate changes of the Quaternary high latitudes, there is abundant evidence of disequilibrium in tree species migrations, lasting for millennia in some cases. The survival of nearly all the high-latitude forms of plants and animals known from the Pleistocene fossil record

  9. 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...

  10. Global warming: Sea ice and snow cover

    International Nuclear Information System (INIS)

    In spite of differences among global climate simulations under scenarios where atmospheric CO2 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

  11. 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.

  12. 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, R. F.; Fainberg, J.; Osherovich, V. A.; Truhlik, V.; Wang, Y.; Arbacher, R. T.

    2011-12-01

    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 Web (CDAWeb). Solar-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.

  13. 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.

  14. Evidence for a very low-column density hole in the Galactic halo in the direction of the high latitude molecular cloud MBM 16

    CERN Document Server

    Liu, Wenhao; Ursino, Eugenio

    2015-01-01

    Shadow observations are the only way to observe emission from the galactic halo (GH) and/or the circumgalactic medium (CGM) free of any foreground contamination from local hot bubble (LHB) and solar wind charge exchange (SWCX). We analyzed data from a shadow observation in the direction of the high latitude, neutral hydrogen cloud MBM 16 with \\Suzaku. We found that all emission can be accounted for by foreground emission from LHB and SWCX, plus power law emission associated with unresolved point sources. The GH/CGM in the direction of MBM 16 is negligible or inexistent in our observation, with upper limits on the emission measure of 9.5x10^{-4} pc cm^{-6} (90% C.L.), at the lowest end of current estimates.

  15. Observation of Neon at mid and high latitudes in the sunlit lunar exosphere: Results from CHACE aboard MIP/Chandrayaan-1

    Science.gov (United States)

    Das, Tirtha Pratim; Thampi, Smitha V.; Bhardwaj, Anil; Ahmed, S. M.; Sridharan, R.

    2016-07-01

    The distribution of neutral Neon at the mid and high latitudes in the sunlit lunar exosphere observed by CHandra's Altitudinal Composition Explorer (CHACE) aboard the Moon Impact Probe (MIP) of the Chandrayaan-1 is reported. The CHACE observation was made when Moon was in the Earth's magnetotail. The upper limits of the surface number density are found to vary from (7-22) × 103 cm-3 at the pole, to (3-5) × 103 cm-3 in mid (50°S) latitudes and to (0.5-1.1) × 103 cm-3 in lower (20°S) latitudes. The surface number densities estimated at lower latitudes from CHACE observations are consistent with the LADEE Neutral Mass Spectrometer (NMS) observations.

  16. Energetic particle fluxes in the exterior cusp and the high-latitude dayside magnetosphere: statistical results from the Cluster/RAPID instrument

    Directory of Open Access Journals (Sweden)

    T. Asikainen

    2005-09-01

    Full Text Available In this paper we study the fluxes of energetic protons (30–4000 keV and electrons (20–400 keV in the exterior cusp and in the adjacent high-latitude dayside plasma sheet (HLPS with the Cluster/RAPID instrument. Using two sample orbits we demonstrate that the Cluster observations at high latitudes can be dramatically different because the satellite orbit traverses different plasma regions for different external conditions. We make a statistical study of energetic particles in the exterior cusp and HLPS by analysing all outbound Cluster dayside passes in February and March, 2002 and 2003. The average particle fluxes in HLPS are roughly three (protons or ten (electrons times larger than in the exterior cusp. This is also true on those Cluster orbits where both regions are visited within a short time interval. Moreover, the total electron fluxes, as well as proton fluxes above some 100 keV, in these two regions correlate with each other. This is true even for fluxes in every energy channel when considered separately. The spectral indices of electron and proton fluxes are the same in the two regions. We also examine the possible dependence of particle fluxes at different energies on the external (solar wind and IMF and internal (geomagnetic conditions. The energetic proton fluxes (but not electron fluxes in the cusp behave differently at low and high energies. At low energies (<70 keV, the fluxes increase strongly with the magnitude of IMF By. Instead, at higher energies the proton fluxes in the cusp depend on substorm/geomagnetic activity. In HLPS proton fluxes, irrespective of energy, depend strongly on the Kp and AE indices. The electron fluxes in HLPS depend both on the <Kp index and the solar wind speed. In the cusp the electron fluxes mainly depend on the solar wind speed, and are higher for northward than southward IMF. These results give strong evidence in favour of the idea that the

  17. A Case Study of Energy Deposition and Absorption by Magnetic Cloud Electrons and Protons over the High Latitude Stations: Effects on the Mesosphere and Lower Thermosphere

    Directory of Open Access Journals (Sweden)

    Olakunle Ogunjobi

    2014-01-01

    Full Text Available Several possible characteristics of magnetic clouds (MCs have been discussed in the literature, but none appears to explain all the effects from accumulated observations. MC characteristics range from low proton temperature and plasma beta, to high magnetic field magnitude, to smooth rotation in the direction of the magnetic field thus resulting in strong geomagnetic disturbances. Varied instrumentation which is located not only in SANAE IV, Antarctica, but also at Halley, a same radial distance (L ~ 4 in the southern hemisphere and in the vicinity of a conjugate location in northern hemisphere provide an opportunity to test theories applied to high latitude heating rates on the arrival of MC. The Halley riometer is used to monitor coincidences of absorption with the arrival of MC which was observed on 8 November 2004. Using the Monte Carlo Energy Transport Model (MCETM, the corresponding altitude of electron and proton energy distribution indicates the importance of MC triggered geomagnetic storms on mesosphere dynamics.

  18. Measurements of Doppler and multipath spread on oblique high-latitude HF paths and their use in characterizing data modem performance

    Science.gov (United States)

    Angling, Matthew J.; Cannon, Paul S.; Davies, Nigel C.; Willink, Tricia J.; Jodalen, Vivianne; Lundborg, Bengt

    1998-01-01

    Measurements of Doppler spread, multipath spread, and signal-to-noise ratio have been made on four high-latitude high-frequency (HF) communications paths. The measurement system and analysis techniques are outlined, and an analysis of the data pertinent to the design of robust HF data modems is presented. A summary of the spreads that are exceeded for 5% of time is presented for each path. Doppler spreads range from 2 to 55 Hz, while multipath spreads range from 1 to 11 ms. Physical interpretations of the data are made, and the data are related to the measured performance characteristics of an HF data modem to estimate the modem availability on the paths considered. When there is mode support, availabilities range from 64% to 100% for a signal-to-noise ratio of 0 dB, although the data indicate that the availabilities can generally be increased by optimizing frequency selection.

  19. 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.

  20. 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

  1. Early season lightning storms followed by vapor pressure deficit anomalies contributed to an extreme wildfire season near the high latitude treeline in Northwest Canada in 2014

    Science.gov (United States)

    Veraverbeke, S.; Worthy, D. E. J.; Chan, D.; Chan, E.; Wiggins, E. B.; Miller, C. E.; Henderson, J.; Tosca, M. G., Jr.; Randerson, J. T.

    2015-12-01

    Fires are the most important landscape disturbance in the boreal forest. Fire location and extent in boreal ecosystems highly depend on ignitions by lightning and periods of high vapor pressure deficit (VPD) that promote the spread of the fires. We show, using fire perimeter and remotely sensed burned area, that during the 2014 fire season, the Northwest Territories in Canada experienced its most severe fire season since the beginning of the fire perimeter record in 1971. Using a pyrogenic carbon consumption model driven by remotely sensed tree cover and burn severity, and meteorological reanalysis data, we estimate total carbon emissions of 136 (SE = 25) Tg for the entire territory. We also found anomalously large fires relatively close (0-300 km) to the high latitude treeline where sparse black spruce forests transition into tundra, ecosystems that are traditionally less affected by fire disturbance. This area received below-average winter precipitation and experienced an early snow melt in 2014. Using data from the Canadian Lightning Detection Network we show that many of these fires were ignited during lightning storms in May and June, and expanded during periods of anomalously high VPD in June and July. Fires that were ignited before July 1 accounted for approximately 76% of the total annual burned area. We hypothesize that the extent and northward expansion of boreal fires, driven by climatic anomalies in lightning and VPD, may accelerate northward species migration with climate change. We also show, using plume heights retrieved from the Multi-angle Imaging Spectroradiometer (MISR), that maximum plume injection heights in 2014 were on average more than 300 m higher compared to observations from other years. These high injection heights combined with the high latitude location of the fires increase the potential for northward long-range transport of black carbon emissions towards Greenland and other vulnerable components of the northern cryosphere.

  2. Electrospun Amplified Fiber Optics

    OpenAIRE

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

    2015-01-01

    A lot of research is focused on all-optical signal processing, 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 an efficient signal transmission. However, the complex fabrication methods, involving high-temperature processes performed in highly pure environment, slow down the fabrication and make amplified components expensive with respect to an ideal, ...

  3. RF Power Amplifier Analysis

    Directory of Open Access Journals (Sweden)

    M. Lokay

    1993-04-01

    Full Text Available The special program is presented for the demonstration of RF power transistor amplifiers for the purposes of the high-school education in courses of radio transmitters. The program is written in Turbo Pascal 6. 0 and enables to study the waveforms in selected points of the amplifier and to draw the trajectories of the working point in a plot of output transistor characteristics.

  4. 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....

  5. Geochemistry of groundwater in front of a warm-based glacier in Southeast Greenland

    DEFF Research Database (Denmark)

    Kristiansen, Søren Munch; Yde, Jacob Clement; Bárcena, Teresa G;

    2013-01-01

    Groundwater in front of warm-based glaciers is likely to become a more integrated part of the future proglacial hydrological system at high latitudes due to global warming. Here, we present the first monitoring results of shallow groundwater chemistry and geochemical fingerprinting of glacier...... shows that isotopic fractionation occurs in both groundwater and glacier meltwater, but fractionation due to evaporation from near-surface soil moisture prior to infiltration has the most significant effect. This study shows that groundwater in Low Arctic Greenland is likely to possess a combined...

  6. Numerical simulation of the sensitivity of the Pacific subtropical-tropical meridional cell to global warming

    Institute of Scientific and Technical Information of China (English)

    ZHOU Tianjun; YU Yongqiang; LIU Hailong; LI Wei; YU Rucong

    2006-01-01

    Sensitivity of the Pacific subtropical-tropical meridional cell to global warming is examined by using a global ocean-atmosphere coupled model developed at LASG/IAP. Results indicate that associated with the increasing of atmospheric carbon dioxide, the most prominent signals of global warming locate at high latitudes, and the change of middle and low latitudes, in particular the surface wind, is relatively weak, which leads to a weak response of the Pacific subtropical-tropical meridional cell. At the time of atmospheric carbon dioxide doubling, the change of the meridional cell strength is smaller than the amplitude of natural variability.

  7. 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.

  8. Warm World Ocean Thermohaline Circulation Model

    Science.gov (United States)

    Zimov, N.; Zimov, S. A.

    2014-12-01

    Modern day ocean circulation is dominated by thermal convection with cold waters subsiding in the Northern Atlantic, filling the ocean interior with cold and heavy water. However, ocean circulation diminished during the last glaciation and consequently the downwelling of the cold. Therefore interior ocean water temperatures must have been affected by other mechanisms which are negligible in the current state. We propose that the submergence of highly saline water from warm seas with high rates of evaporation (like the Red or Mediterranean Sea) was a major factor controlling ocean circulation during the last glaciation. Even today, waters in these poorly connected seas are the heaviest waters in the World ocean (1.029 g/cm3). The second mechanism affecting ocean temperature is the geothermal heat flux. With no heat exchange between the atmosphere and the ocean, geothermal heat flux through the ocean floor is capable of increasing ocean temperature by tens of degrees C over a 100 thousand year glacial cycle. To support these hypotheses we present an ocean box model that describes thermohaline circulation in the World Ocean. According to the model parameters, all water circulation is driven by the water density gradient. Boxes include high-latitude seas, high salinity seas, surface ocean, glaciers, and rift and lateral zones of the ocean interior. External heat sources are radiative forcing, affected by Milankovich cycles, and geothermal heat flux. Additionally this model accounts for the heat produced by organic rain decay. Taking all input parameters close to currently observed values, the model manages to recreate the glacial-interglacial cycles. During the glacial periods only haline circulation takes place, the ocean is strongly stratified, and the interior ocean accumulates heat while high-latitudes accumulate ice. 112,000 years after glaciation starts, water density on the ocean bottom becomes equal to the density of water in high-latitude seas, strong thermal

  9. Evidence for increased latent heat transport during the Cretaceous (Albian) greenhouse warming

    Science.gov (United States)

    Ufnar, David F.; Gonzalez, Luis A.; Ludvigson, Greg A.; Brenner, Richard L.; Witzke, B.J.

    2004-01-01

    Quantitative estimates of increased heat transfer by atmospheric H 2O vapor during the Albian greenhouse warming suggest that the intensified hydrologic cycle played a greater role in warming high latitudes than at present and thus represents a viable alternative to oceanic heat transport. Sphaerosiderite ??18O values in paleosols of the North American Cretaceous Western Interior Basin are a proxy for meteoric ??18O values, and mass-balance modeling results suggest that Albian precipitation rates exceeded modern rates at both mid and high latitudes. Comparison of modeled Albian and modern precipitation minus evaporation values suggests amplification of the Albian moisture deficit in the tropics and moisture surplus in the mid to high latitudes. The tropical moisture deficit represents an average heat loss of ???75 W/m2 at 10??N paleolatitude (at present, 21 W/m2). The increased precipitation at higher latitudes implies an average heat gain of ???83 W/m2 at 45??N (at present, 23 W/m2) and of 19 W/m2 at 75??N (at present, 4 W/m2). These estimates of increased poleward heat transfer by H2O vapor during the Albian may help to explain the reduced equator-to-pole temperature gradients. ?? 2004 Geological Society of America.

  10. A micropower electrocardiogram amplifier.

    Science.gov (United States)

    Fay, L; Misra, V; Sarpeshkar, R

    2009-10-01

    We introduce an electrocardiogram (EKG) preamplifier with a power consumption of 2.8 muW, 8.1 muVrms input-referred noise, and a common-mode rejection ratio of 90 dB. Compared to previously reported work, this amplifier represents a significant reduction in power with little compromise in signal quality. The improvement in performance may be attributed to many optimizations throughout the design including the use of subthreshold transistor operation to improve noise efficiency, gain-setting capacitors versus resistors, half-rail operation wherever possible, optimal power allocations among amplifier blocks, and the sizing of devices to improve matching and reduce noise. We envision that the micropower amplifier can be used as part of a wireless EKG monitoring system powered by rectified radio-frequency energy or other forms of energy harvesting like body vibration and body heat. PMID:23853270

  11. A vircator amplifier

    International Nuclear Information System (INIS)

    A cavity vircator has demonstrated that formation of a virtual cathode in a cavity can improve microwave production efficiency and narrow the radiation bandwidth. When the virtual cathode radiates the microwave fields grow from noise. For each cavity, there is only one or a limited number of allowable modes for a given frequency. In this paper, a novel device - a vircator amplifier is described. The device consists of a relativistic magnetron and a cavity vircator with both devices powered by a 1 MeV, 3 Ω, 65 ns FWHM pulser. The idea is to inject a signal from the magnetron before and during virtual cathode formation in a cavity. The injected signal should lock the frequency and enhance electron bunching and therefore improve efficiency further. Experiments underway to evaluate the amplifier operating characteristics are discussed. The applicability of vircator amplifiers to the next generation of high-power microwave devices are addressed

  12. 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....

  13. 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.

  14. 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.

  15. Ion-neutral coupling in the high-latitude F-layer from incoherent scatter and Fabry-Perot interferometer measurements

    Directory of Open Access Journals (Sweden)

    K. Cierpka

    Full Text Available Since the auroral ionosphere provides an important energy sink for the magnetosphere, ionosphere-thermosphere coupling must be investigated when considering the energy budget of the ionosphere-magnetosphere coupling. We present the first Scandinavian ground-based study of high-latitude F-region ion-neutral frictional heating where ion velocity and temperature are measured by the EISCAT incoherent scatter radar as well as neutral wind and temperature being measured simultaneously by a Fabry-Perot interferometer. A geomagnetically active period (Kp = 7 – 5 and quiet period (Kp = 0+ – 0 were studied. Neglecting the neutral wind can result in errors of frictional heating estimates of 60% or more in the F-layer. About 96% of the local ion temperature enhancement over the neutral temperature is accounted for by ion-neutral frictional heating.

    Key words: Ionosphere (auroral ionosphere; ionosphere-atmosphere interactions

  16. 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.

  17. 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.

  18. A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

    Science.gov (United States)

    Villain, J.-P.; André, R.; Pinnock, M.; Greenwald, R. A.; Hanuise, C.

    2002-11-01

    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.

  19. 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

  20. Modification of the High-Latitude Ionospheric F Region By High-Power HF Radio Waves at Frequencies Near the fifth and Sixth Electron Gyroharmonics

    Science.gov (United States)

    Borisova, T. D.; Blagoveshchenskaya, N. F.; Kalishin, A. S.; Rietveld, M. T.; Yeoman, T. K.; Hägström, I.

    2016-01-01

    We study the modification effects of the high-latitude ionospheric F region induced by a highpower O-mode HF radio wave injected towards the magnetic zenith, at frequencies near the fifth and sixth electron gyroharmonics using the EISCAT/Heating facility. Multi-instrument diagnostics with the EISCAT incoherent scatter radar (930 MHz) at Tromsø, Norway, the CUTLASS coherent radar at Hankasalmi, Finland, and stimulated electromagnetic emission (SEE) receiver at Tromsø, has been used for analysis of the observed phenomena. The behavior of the ionospheric plasma parameters (electron's density and temperature), small-scale artificial field-aligned irregularities, plasma and ion-line spectra, and ionospheric SEE are analyzed in detail. Modification effects near the fifth and sixth electron gyroharmonics have been compared. The coexistence of the thermal (resonance) parametric instability, parametric decay (striction) instability, and/or oscillating two-stream instability was found at these frequencies. The excitation of instabilities occurred at altitudes close to the reflection altitude of the HF pump wave and at the altitudes of the upper-hybrid resonance.

  1. 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.

  2. Fourier plane image amplifier

    Science.gov (United States)

    Hackel, L.A.; Hermann, M.R.; Dane, C.B.; Tiszauer, D.H.

    1995-12-12

    A solid state laser is frequency tripled to 0.3 {micro}m. A small portion of the laser is split off and generates a Stokes seed in a low power oscillator. The low power output passes through a mask with the appropriate hole pattern. Meanwhile, the bulk of the laser output is focused into a larger stimulated Brillouin scattering (SBS) amplifier. The low power beam is directed through the same cell in the opposite direction. The majority of the amplification takes place at the focus which is the fourier transform plane of the mask image. The small holes occupy large area at the focus and thus are preferentially amplified. The amplified output is now imaged onto the multichip module where the holes are drilled. Because of the fourier plane amplifier, only about 1/10th the power of a competitive system is needed. This concept allows less expensive masks to be used in the process and requires much less laser power. 1 fig.

  3. The polar Sudden Stratospheric Warming (SSW) and it's possible manifestations in the equatorial Mesosphere-Thermosphere-Ionosphere

    Science.gov (United States)

    Pant, Tarun

    In this study, the variations in daytime mesopause temperature and the Equatorial Electrojet over equator during Sudden Stratospheric Warming (SSW) events over high latitudes have been investigated. To reflect upon the stratospheric conditions NCEP-NCAR reanalysis data have also been used. This study indicates a possible dynamical coupling between the two regions through the planetary wave activity. The amplified wave signatures of quasi-16 day period are seen in the equatorial mesopause temperature and zonal mean polar stratospheric temperature (at 10 hPa) during the course of SSW. The possibility that the planetary waves over the polar stratosphere, which play an important role in the generation of SSW, could also have contribu-tion from the tropics has been indicated through numerical simulations in the past [Dunkerton, 1981], but due to the paucity of global measurements it could not be established unequivocally. These simulations also indicated the presence of a zero-wind line whose real counterparts were not observed in the atmosphere. The NCEP-NCAR reanalysis of stratospheric wind and tem-peratures clearly shows that (i) a dynamical feature similar to the zero-wind line appears over the tropics 60 days prior to the major warming and progresses poleward and, (ii) enhanced PW activity is seen almost simultaneously. This study shows that the recent SSW events had tropical associations. Further, favored occurrences of Equatorial Counter Electrojets (CEJs) with a quasi 16-day periodicity over Trivandrum (8.5oN, 76.5oE, 0.5oN diplat.) in association with the polar Stratospheric Sudden Warming (SSW) events are presented. It is seen that, the stratospheric temperature at 30 km over Trivandrum showed a sudden cooling prior to the SSW and the first bunch of CEJs occurred around this time. Stratospheric zonal mean zonal wind at 30 km exhibited a distinctly different pattern during the SSW period. These circula-tion changes are proposed to be conducive for the upward

  4. Global Warming and Energy Transition: A Public Policy Imperative

    Science.gov (United States)

    Stone, G. T.

    2006-12-01

    The historic transition from fossil fuels to alternative energy resources has begun. This development is commonly attributed to increasing energy costs and the need for energy security. Looming ever larger, however, is the issue that will soon drive the third energy revolution: global warming. A preponderance of evidence documents accelerating warming, enlarging impacts, and human causes -- principally combustion of fossil fuels. The carbon dioxide (C02) content of Earth's atmosphere has increased more than 35 percent since the beginning of the industrial revolution and is the highest in 650,000 years. This dramatic rise of C02 and attendant positive feedbacks are already forcing significant impacts worldwide. These include atmospheric warming with shifting climatic and habitat zones, spreading tropical disease, and more extreme weather events; rapid ice loss at high latitude and high altitude; ocean warming and acidification with coral reef bleaching and intensifying tropical storms; rising sea level; and accelerating extinction rates. The 2007 draft report of the Intergovernmental Panel on Climate Change (IPCC) predicts greater warming than in previous models. A tipping point to abrupt climate change may be imminent. It is incumbent upon geoscientists and geoscience educators to assume leadership in addressing this challenge through public outreach and general education. The following topics should be integrated into all appropriate courses: the evidence of global warming and its causes; observed present and predicted future impacts of global warming; mitigation and adaptation strategies; and implications for energy policies and economic opportunities. New entry-level science and general education courses -- such as Climate Change Fundamentals and Energy in Nature, Technology, and Society -- are proving to be effective should be widely developed In addition, by workshops and presentations to civic and business organizations and by demonstrated examples of

  5. Effects of Geomagnetic Storms and Sudden Stratospheric Warmings on Mesosphere and Lower Thermosphere Winds

    Science.gov (United States)

    Wu, Q.; Gablehouse, R. D.; Gell, D. A.; Johnson, R. M.; Kafkalidis, J. F.; Killeen, T. L.; Niciejewski, R. J.; Ortland, D. A.; Skinner, W. R.; Solomon, S. C.

    2003-12-01

    Neutral winds in the MLT region are affected by dynamical influences from above and below. This is particular true at high latitudes, where solar forcing of the migrating tide may be smaller but other forcings play a big role. During geomagnetic storms, MLT neutral winds can be driven by magnetospheric convection through ion-neutral interactions. This is imparted onto the ionosphere as a cross polar cap potential forming an anti-sunward two-cell ion convection pattern which in turn drives the neutral winds in the polar MLT region. The question has always been how deep into the atmosphere the ion drift can affect the neutral wind. Scarcity of high-latitude data has hampered further understanding of the problem. Also, in the winter polar regions, the stratosphere from time to time experiences sudden warming events. While it is generally understood that these warmings are caused by troposphere planetary wave activity, there are still many unknown aspects to their excitation and propagation. There are also changes in the MLT region associated with these warming events. Moreover, this phenomena, although usually confined to the northern hemisphere, occurred in the southern hemisphere in 2002. We will use TIDI data to examine MLT neutral winds during the recent geomagnetic storm events in 2002 and 2003, and present data during the recent 2002 southern hemisphere warming event.

  6. Helical Fiber Amplifier

    Science.gov (United States)

    Koplow, Jeffrey P.; Kliner, Dahy; Goldberg, Lew

    2002-12-17

    A multi-mode gain fiber is provided which affords substantial improvements in the maximum pulse energy, peak power handling capabilities, average output power, and/or pumping efficiency of fiber amplifier and laser sources while maintaining good beam quality (comparable to that of a conventional single-mode fiber source). These benefits are realized by coiling the multimode gain fiber to induce significant bend loss for all but the lowest-order mode(s).

  7. High-latitude volcanic eruptions in the Norwegian Earth System Model: the effect of different initial conditions and of the ensemble size

    Directory of Open Access Journals (Sweden)

    Francesco S. R. Pausata

    2015-06-01

    Full Text Available Large volcanic eruptions have strong impacts on both atmospheric and ocean dynamics that can last for decades. Numerical models have attempted to reproduce the effects of major volcanic eruptions on climate; however, there are remarkable inter-model disagreements related to both short-term dynamical response to volcanic forcing and long-term oceanic evolution. The lack of robust simulated behaviour is related to various aspects from model formulation to simulated background internal variability to the eruption details. Here, we use the Norwegian Earth System Model version 1 to calculate interactively the volcanic aerosol loading resulting from SO2 emissions of the second largest high-latitude volcanic eruption in historical time (the Laki eruption of 1783. We use two different approaches commonly used interchangeably in the literature to generate ensembles. The ensembles start from different background initial states, and we show that the two approaches are not identical on short-time scales (<1 yr in discerning the volcanic effects on climate, depending on the background initial state in which the simulated eruption occurred. Our results also show that volcanic eruptions alter surface climate variability (in general increasing it when aerosols are allowed to realistically interact with circulation: Simulations with fixed volcanic aerosol show no significant change in surface climate variability. Our simulations also highlight that the change in climate variability is not a linear function of the amount of the volcanic aerosol injected. We then provide a tentative estimation of the ensemble size needed to discern a given volcanic signal on surface temperature from the natural internal variability on regional scale: At least 20–25 members are necessary to significantly detect seasonally averaged anomalies of 0.5°C; however, when focusing on North America and in winter, a higher number of ensemble members (35–40 is necessary.

  8. An assemblage of mollusks associated with the high latitude scleractinian coral Alveopora japonica (Eguchi 1968) in Jeju Island, off the south coast of Korea

    Science.gov (United States)

    Noseworthy, Ronald G.; Hong, Hyun-Ki; Keshavmurthy, Shashank; Lee, Hee-Jung; Jeung, Hee-Do; Ju, Se-Jong; Kim, Jong-Bin; Jung, Sukgeun; Choi, Kwang-Sik

    2016-03-01

    Corals reefs and communities support a wide range of flora and fauna. The complete richness and abundance of faunal communities in either coral reefs or communities is not fully understood. This is especially true for high-latitude coral communities. In this work, we carried out an analysis of an Alveopora japonica associated mollusk assemblage, in Jeju Island, Korea. A. japonica is one of the major coral species present in high abundance (88-155 colonies m-2), with a high recruitment rate (7.8 juvenile corals m-2 yr-1) in Jeju Island, and may serve as a habitat for other benthic organisms. In 2012, a total number of 579 A. japonica colonies with sizes ranging between 15.1-346.7 cm2 in the surface area were collected from a 1m× 10m quadrat installed at a depth of 10 m at Keumneung, on the northwest coast of Jeju Island. Numerous benthic invertebrates were found to be associated with A. japonica colonies. Twenty-seven bivalves and gastropods were identified, including a boring mytilid, Lithophaga curta, and an arcid, Barbatia stearnsi. A zonalgeographical examination of the distribution ranges of these mollusks revealed a majority of warmer water species. Our observations also showed that A. japonica may be providing a habitat to grazing gastropod, Turbo cornutus, and encrusting Spondylidae and Chamidae bivalves. A. japonica forms a coral carpet with a distinct assemblage of bivalves. It is thought that the presence of these mollusks species in the coral indicates its use as a nursery for juvenile species, a ready food supply of organic detritus, and a refuge from predators.

  9. High Latitude Forest Dynamics - CO2 EXCHANGE Measurements and Forest Growth at the Altitudinal Forest Line in High Subarctic Finnish Lapland

    Science.gov (United States)

    Dengel, S.; Siivola, E.; Aakala, T.; Kolari, P.; Hari, P.; Back, J. K.; Grace, J.; Vesala, T.

    2015-12-01

    Forests in high subarctic fell regions of Fennoscandia belong to the most northern forests in the world, a dynamic ecosystem vulnerable under a changing climate with treelines moving further north and also higher up slopes. An ecosystem is characterised by the interaction between micrometeorology, macroecology and the underlying terrain and topography. The current study is carried out at 68° North (Värriö strict nature reserve), the most sensitive zone of the high subarctic in Finnish Lapland. As the treeline is climbing up the slopes trees and eventually forests establish along the slopes leading to a greening of the area ("Greening of the Arctic" effect) and to an increase in CO2 uptake, also as a result of rising air temperatures and Nitrogen fertilization effects. Such developments and the little grazing (in this area) are leading to an increase in photosynthesising biomass. In order to fully understand the atmosphere - forest interaction in the fell region of Finnish Lapland, several important aspects are taken in consideration: its high latitudinal location, on-going climate change, polar day, its topographic characteristic and the dynamic of the progressing tree line. All these physiognomies cumulate in the capacity and efficiency of high latitude biomes in converting energy into photosynthate and contributing to removal of CO2 from the atmosphere. Carrying out CO2 and energy exchange measurements at ecosystem level in such extreme environments are challenging in particular when trying to follow and fulfil established assumptions set out by the application of the eddy covariance technique. Results from the first four consecutive snow free growing seasons show this site to act as a sink for atmospheric CO2. We are investigating the orographic effect on the observed fluxes and evaluate the performance of the flux setup determining if the topography has any systematic effects on fluxes or whether its external properties bias the carbon balance.

  10. Localized High-Latitude Ionosphere-Thermosphere Ionization Events during the High Speed Stream Interval of 29 April - 5 May 2011

    Science.gov (United States)

    Verkhoglyadova, O. P.; Mannucci, A. J.; Tsurutani, B. T.; Mlynczak, M. G.; Hunt, L. A.; Redmon, R. J.; Green, J. C.

    2014-12-01

    We analyze localized ionospheric - thermospheric (IT) events in response to external driving by a high-speed stream (HSS) event during the ascending phase of the solar cycle 24. The HSS event occurred from 29 April to 5 May, 2011. The HSS (and not the associated co-rotating interaction region) caused a moderate geomagnetic storm with peak SYM-H = -55 nT and prolonged auroral activity. We analyze TIMED/SABER measurements of nitric oxide (NO) cooling emission during the interval as a measure of thermospheric response to auroral heating. We identify several local cooling emission (LCE) events in high- to sub-auroral latitudes that are presumed to be in response to external driving. Individual cooling emission profiles during these LCE events are enhanced at ~100 to 150 km altitude (ionospheric E layer). For the first time, we present electron density profiles in the vicinity of the LCE events using COSMIC radio-occultation measurements. Measurements at local nighttime show the formation of an enhanced E-layer (about 2.5 times increase over the undisturbed value) at the same approximate altitudes as the LCE peaks. Daytime electron density profiles show relatively smaller enhancements in the E-layer. We suggest that the IT response is due to additional ionization caused by medium energy electron (>20 keV) precipitation into the sub-auroral to high-latitude atmosphere during the HSS event. POES/MEPED electron precipitation data are presented to support this hypothesis. Consequences for space weather forecasting are discussed.

  11. High-latitude ionospheric irregularities: differences between ground- and space-based GPS measurements during the 2015 St. Patrick's Day storm

    Science.gov (United States)

    Cherniak, Iurii; Zakharenkova, Irina

    2016-07-01

    We present an analysis of ionospheric irregularities at high latitudes during the 2015 St. Patrick's Day storm. Our study used measurements from ~2700 ground-based GPS stations and GPS receivers onboard five low earth orbit (LEO) satellites—Swarm A, B and C, GRACE and TerraSAR-X—that had close orbit altitudes of ~500 km, and the Swarm in situ plasma densities. An analysis of the rate of TEC index (ROTI) derived from LEO-GPS data, together with Swarm in situ plasma probe data, allowed us to examine the topside ionospheric irregularities and to compare them to the main ionospheric storm effects observed in ground-based GPS data. We observed strong ionospheric irregularities in the topside ionosphere during the storm's main phase that were associated with storm-enhanced density (SED) formation at mid-latitudes and further evolution of the SED plume to the polar tongue of ionization (TOI). Daily ROTI maps derived from ground-based and LEO-GPS measurements show the pattern of irregularities oriented in the local noon-midnight direction, which is a signature of SED/TOI development across the polar cap region. Analysis of the Swarm in situ plasma measurements revealed that, during the storm's main phase, all events with extremely enhanced plasma densities (>106 el/cm3) in the polar cap were observed in the Southern Hemisphere. When Swarm satellites crossed these enhancements, degradation of GPS performance was observed, with a sudden decrease in the number of GPS satellites tracked. Our findings indicate that polar patches and TOI structures in the topside ionosphere were predominantly observed in the Southern Hemisphere, which had much higher plasma densities than the Northern Hemisphere, where SED/TOI structures have already been reported earlier. LEO-GPS data (ROTI and topside TEC) were consistent with these results.

  12. 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.

  13. 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.

  14. Oxygen isotopes in Indian Plate eclogites (Kaghan Valley, Pakistan): Negative δ18O values from a high latitude protolith reset by Himalayan metamorphism

    Science.gov (United States)

    Rehman, Hafiz Ur; Tanaka, Ryoji; O'Brien, Patrick J.; Kobayashi, Katsura; Tsujimori, Tatsuki; Nakamura, Eizo; Yamamoto, Hiroshi; Khan, Tahseenullah; Kaneko, Yoshiyuki

    2014-11-01

    Oxygen isotope compositions are reported for the first time for the Himalayan metabasites of the Kaghan Valley, Pakistan in this study. The highest metamorphic grades are recorded in the north of the valley, near the India-Asia collision boundary, in the form of high-pressure (HP: Group I) and ultrahigh-pressure (UHP: Group II) eclogites. The rocks show a step-wise decrease in grade from the UHP to HP eclogites and amphibolites. The protoliths of these metabasites were the Permian Panjal Trap basalts (ca. 267 ± 2.4 Ma), which were emplaced along the northern margin of India when it was part of Gondwana. After the break-up of Gondwana, India drifted northward, subducted beneath Asia and underwent UHP metamorphism during the Eocene (ca. 45 ± 1.2 Ma). At the regional scale, amphibolites, Group I and II eclogites yielded δ18O values of + 5.84 and + 5.91‰, + 1.66 to + 4.24‰, and - 2.25 to + 0.76‰, respectively, relative to VSMOW. On a more local scale, within a single eclogite body, the δ18O values were the lowest (- 2.25 to- 1.44‰) in the central, the best preserved (least retrograded) parts, and show a systematic increase outward into more retrograded rocks, reaching up to + 0.12‰. These values are significantly lower than the typical mantle values for basalts of + 5.7 ± 0.3‰. The unusually low or negative δ18O values in Group II eclogites potentially resulted from hydrothermal alteration of the protoliths by interactions with meteoric water when the Indian plate was at southern high latitudes (~ 60°S). The stepwise increase in δ18O values, among different eclogite bodies in general and at single outcrop-scales in particular, reflects differing degrees of resetting of the oxygen isotope compositions during exhumation-related retrogression.

  15. Estimation of the soil heat flux/net radiation ratio based on spectral vegetation indexes in high-latitude Arctic areas

    International Nuclear Information System (INIS)

    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)

  16. 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.

  17. Soil respiration characteristics in different land uses and response of soil organic carbon to biochar addition in high-latitude agricultural area.

    Science.gov (United States)

    Ouyang, Wei; Geng, Xiaojun; Huang, Wejia; Hao, Fanghua; Zhao, Jinbo

    2016-02-01

    The farmland tillage practices changed the soil chemical properties, which also impacted the soil respiration (R s ) process and the soil carbon conservation. Originally, the farmland in northeast China had high soil carbon content, which was decreased in the recent decades due to the tillage practices. To better understand the R s dynamics in different land use types and its relationship with soil carbon loss, soil samples at two layers (0-15 and 15-30 cm) were analyzed for organic carbon (OC), total nitrogen (TN), total phosphorus (TP), total carbon (TC), available nitrogen (AN), available phosphorus (AP), soil particle size distribution, as well as the R s rate. The R s rate of the paddy land was 0.22 (at 0-15 cm) and 3.01 (at 15-30 cm) times of the upland. The average concentrations of OC and clay content in cultivated areas were much lower than in non-cultivated areas. The partial least squares analysis suggested that the TC and TN were significantly related to the R s process in cultivated soils. The upland soil was further used to test soil CO2 emission response at different biochar addition levels during 70-days incubation. The measurement in the limited incubation period demonstrated that the addition of biochar improved the soil C content because it had high concentration of pyrogenic C, which was resistant to mineralization. The analysis showed that biochar addition can promote soil OC by mitigating carbon dioxide (CO2) emission. The biochar addition achieved the best performance for the soil carbon conservation in high-latitude agricultural area due to the originally high carbon content.

  18. Modification of the high latitude F region of the ionosphere by X-mode powerful HF radio waves: Experimental results from multi-instrument diagnostics

    Science.gov (United States)

    Blagoveshchenskaya, Nataly; Rietveld, Michael; Haggstrom, Ingemar; Borisova, Tatiana; Yeoman, Tim

    We present the experimental results for strong plasma modifications induced by the X-mode powerful HF radio waves injected towards the magnetic zenith into the high latitude F region of the ionosphere. A large number of experiments in the course of Russian EISCAT heating campaigns were conducted in 2009 - 2013 under different background conditions in a wide heater frequency range from 4 to 8 MHz. The EISCAT UHF incoherent scatter radar at Tromsø, the CUTLASS (SuperDARN) HF coherent radar in Finland, SEE receiver at Tromsø, the HF Doppler equipment near St. Petersburg, and the EISCAT ionosonde (dynasonde) were used as diagnostic instruments. The results show that the X-mode HF pump wave can generate: (1) strong small-scale artificial field aligned irregularities (AFAIs); (2) HF-induced plasma and HF-enhanced ion lines (HFPLs and HFILs) from UHF radar spectra; (3) strong electron density enhancements along magnetic field line in a wide altitude range; (4) spectral components (few tens of Hz) in the Doppler spectra of the heater signal measured at a distance of 1200 km from the Tromsø HF heating facility. The experimental results obtained points to the strong magnetic zenith effect due to self-focusing powerful HF radio wave with X-mode polarization. For heater frequencies in the range of about 4 - 6 MHz the mentioned above phenomena are generated when the heater frequency is equal or above the ordinary-mode critical frequency (foF2). Under high background electron density and the heater frequencies used of 6.5 - 8.0 MHz, the strong X-mode HF-induced phenomena were observed both when the heater frequency is equal or above the foF2 and the heater frequency is below the foF2.

  19. Metabolic balance of a plankton community in a pelagic water of a northern high latitude fjord in response to increased pCO2

    Directory of Open Access Journals (Sweden)

    J.-P. Gattuso

    2012-08-01

    Full Text Available The effect of ocean acidification on the balance between gross community production (GCP and community respiration (CR (i.e. net community production, NCP of plankton communities was investigated in summer 2010 in Kongsfjorden, West of Svalbard. Surface water, which was characterized by low concentrations of dissolved inorganic nutrients and chlorophyll, was enclosed in 9 mesocosms and subjected to 8 pCO2 levels (2 replicated controls and 7 enhanced pCO2 treatments for one month. Nutrients were added to all mesocosms on day 13 of the experiment, and thereafter increase of chlorophyll (index of phytoplankton biomass was provoked in all mesocosms. No clear trend in response to increasing pCO2 was found in the daily values of NCP, CR, and GCP. For further analysis, these parameters were cumulated for the following three periods: phase 1: end of CO2 manipulation until nutrient addition (t4 to t13; phase 2: nutrient addition until the second chlorophyll minimum (t14 to t21; phase 3: the second chlorophyll minimum until the end of this study (t22 to t28. Significant response was detected as a decrease of NCP with increasing pCO2 during phase 3. CR was relatively stable throughout the experiment in all mesocosms. As a result, the cumulative GCP significantly decreased with increasing pCO2 during phase 3. After the nutrient addition, the ratios of cumulative NCP to cumulative consumption of NO3 and PO4 showed significant decrease during phase 3 with increasing pCO2. The results suggest that elevated pCO2 influenced cumulative NCP and stoichiometric C and nutrient coupling of the plankton community in a high latitude fjord only for a limited period. However provided that there were some differences or weak correlations between NCP data based on different methods in the same experiment, this conclusion should be taken with caution.

  20. Global warming triggers the loss of a key Arctic refugium

    OpenAIRE

    K. M. Rühland; Paterson, A. M.; Keller, W; Michelutti, N.; Smol, J.P.

    2013-01-01

    We document the rapid transformation of one of the Earth's last remaining Arctic refugia, a change that is being driven by global warming. In stark contrast to the amplified warming observed throughout much of the Arctic, the Hudson Bay Lowlands (HBL) of subarctic Canada has maintained cool temperatures, largely due to the counteracting effects of persistent sea ice. However, since the mid-1990s, climate of the HBL has passed a tipping point, the pace and magnitude of which is exceptional eve...

  1. 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

    1996-01-01

    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 population

  2. Electronic amplifiers for automatic compensators

    CERN Document Server

    Polonnikov, D Ye

    1965-01-01

    Electronic Amplifiers for Automatic Compensators presents the design and operation of electronic amplifiers for use in automatic control and measuring systems. This book is composed of eight chapters that consider the problems of constructing input and output circuits of amplifiers, suppression of interference and ensuring high sensitivity.This work begins with a survey of the operating principles of electronic amplifiers in automatic compensator systems. The succeeding chapters deal with circuit selection and the calculation and determination of the principal characteristics of amplifiers, as

  3. 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

  4. 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

  5. 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

  6. 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. PMID:27330557

  7. AN ANALYSIS OF THE WINTER EXTREME PRECIPITATION EVENTS ON THE BACKGROUND OF CLIMATE WARMING IN SOUTHERN CHINA

    Institute of Scientific and Technical Information of China (English)

    ZHI Xie-fei; ZHANG Ling; PAN Jia-lu

    2010-01-01

    Based on daily precipitation and monthly temperature data in southern China, the winter extreme precipitation changes in southern China have been investigated by using the Mann-Kendall test and the return values of Generalized Pareto Distribution. The results show that a winter climate catastrophe in southern China occurred around 1991, and the intensity of winter extreme precipitation was strengthened after climate warming. The anomalous circulation characteristics before and after the climate warming was further analyzed by using the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data. It is found that the tropical winter monsoon over East Asia is negatively correlated with the precipitation in southeastern China. After climate warming the meridionality of the circulations in middle and high latitudes increases, which is favorable for the southward movement of the cold air from the north. In addition, the increase of the temperature over southern China may lead to the decrease of the differential heating between the continent and the ocean. Consequently, the tropical winter monsoon over East Asia is weakened, which is favorable for the transport of the warm and humid air to southeastern China and the formation of the anomalous convergence of the moisture flux, resulting in large precipitation over southeastern China. As a result, the interaction between the anomalous circulations in the middle and high latitudes and lower latitudes after the climate warming plays a major role in the increase of the winter precipitation intensity over southeastern China.

  8. 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.

  9. Biomass burning influence on high latitude tropospheric ozone and reactive nitrogen in summer 2008: a multi-model analysis based on POLMIP simulations

    Directory of Open Access Journals (Sweden)

    S. R. Arnold

    2014-09-01

    lead to large-scale photochemical enhancement in high latitude tropospheric ozone during summer.

  10. 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

  11. Universal Signal Conditioning Amplifier

    Science.gov (United States)

    Kinney, Frank

    1997-01-01

    The Technological Research and Development Authority (TRDA) and NASA-KSC entered into a cooperative agreement in March of 1994 to achieve the utilization and commercialization of a technology development for benefiting both the Space Program and U.S. industry on a "dual-use basis". The technology involved in this transfer is a new, unique Universal Conditioning Amplifier (USCA) used in connection with various types of transducers. The project was initiated in partnership with I-Net Corporation, Lockheed Martin Telemetry & Instrumentation (formerly Loral Test and Information Systems) and Brevard Community College. The project consists of designing, miniaturizing, manufacturing, and testing an existing prototype of USCA that was developed for NASA-KSC by the I-Net Corporation. The USCA is a rugged and field-installable self (or remotely)- programmable amplifier that works in combination with a tag random access memory (RAM) attached to various types of transducers. This summary report comprises performance evaluations, TRDA partnership tasks, a project summary, project milestones and results.

  12. DIAMOND AMPLIFIED PHOTOCATHODES.

    Energy Technology Data Exchange (ETDEWEB)

    SMEDLEY,J.; BEN-ZVI, I.; BOHON, J.; CHANG, X.; GROVER, R.; ISAKOVIC, A.; RAO, T.; WU, Q.

    2007-11-26

    High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.

  13. Radiative forcing and feedback by forests in warm climates - a sensitivity study

    Science.gov (United States)

    Port, Ulrike; Claussen, Martin; Brovkin, Victor

    2016-07-01

    We evaluate the radiative forcing of forests and the feedbacks triggered by forests in a warm, basically ice-free climate and in a cool climate with permanent high-latitude ice cover using the Max Planck Institute for Meteorology Earth System Model. As a paradigm for a warm climate, we choose the early Eocene, some 54 to 52 million years ago, and for the cool climate, the pre-industrial climate, respectively. To isolate first-order effects, we compare idealised simulations in which all continents are covered either by dense forests or by deserts with either bright or dark soil. In comparison with desert continents covered by bright soil, forested continents warm the planet for the early Eocene climate and for pre-industrial conditions. The warming can be attributed to different feedback processes, though. The lapse-rate and water-vapour feedback is stronger for the early Eocene climate than for the pre-industrial climate, but strong and negative cloud-related feedbacks nearly outweigh the positive lapse-rate and water-vapour feedback for the early Eocene climate. Subsequently, global mean warming by forests is weaker for the early Eocene climate than for pre-industrial conditions. Sea-ice related feedbacks are weak for the almost ice-free climate of the early Eocene, thereby leading to a weaker high-latitude warming by forests than for pre-industrial conditions. When the land is covered with dark soils, and hence, albedo differences between forests and soil are small, forests cool the early Eocene climate more than the pre-industrial climate because the lapse-rate and water-vapour feedbacks are stronger for the early Eocene climate. Cloud-related feedbacks are equally strong in both climates. We conclude that radiative forcing by forests varies little with the climate state, while most subsequent feedbacks depend on the climate state.

  14. 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

  15. A contribution by ice nuclei to global warming

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Xiping [Univ. of Maryland, Baltimore, MD (United States). Goddard Earth Sciences and Technology Center; NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Lab. for Atmospheres; Tao, Wei-Kuo [NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Lab. for Atmospheres; Zhang, Minghua [Stony Brook Univ., NY (United States). School of Marine and Atmospheric Sciences; Hou, Arthur Y. [NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Lab. for Atmospheres; Xie, Shaocheng [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Atmospheric Sciences Division; Lang, Stephen [Univ. of Maryland, Baltimore, MD (United States). Goddard Earth Sciences and Technology Center; NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Lab. for Atmospheres; Li, Xiaowen [Univ. of Maryland, Baltimore, MD (United States). Goddard Earth Sciences and Technology Center; NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Lab. for Atmospheres; Starr, David O' C [NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Lab. for Atmospheres; Li, Xiaofan [National Oceanic and Atmospheric Administration (NOAA), Camp Spring, MD (United States). National Environmental Satellite, Data, and Information Service

    2009-06-10

    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 becomes 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 CO2. We 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. Finally, a general match in geographic

  16. 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....... 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...

  17. Nanoscale electromechanical parametric amplifier

    Energy Technology Data Exchange (ETDEWEB)

    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.

  18. 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....

  19. Interhemispheric comparison of GPS phase scintillation at high latitudes during the magnetic-cloud-induced geomagnetic storm of 5–7 April 2010

    Directory of Open Access Journals (Sweden)

    P. Prikryl

    2011-12-01

    Full Text Available Arrays of GPS Ionospheric Scintillation and TEC Monitors (GISTMs are used in a comparative scintillation study focusing on quasi-conjugate pairs of GPS receivers in the Arctic and Antarctic. Intense GPS phase scintillation and rapid variations in ionospheric total electron content (TEC that can result in cycle slips were observed at high latitudes with dual-frequency GPS receivers during the first significant geomagnetic storm of solar cycle 24 on 5–7 April 2010. The impact of a bipolar magnetic cloud of north-south (NS type embedded in high speed solar wind from a coronal hole caused a geomagnetic storm with maximum 3-hourly Kp = 8- and hourly ring current Dst = −73 nT. The interhemispheric comparison of phase scintillation reveals similarities but also asymmetries of the ionospheric response in the northern and southern auroral zones, cusps and polar caps. In the nightside auroral oval and in the cusp/cleft sectors the phase scintillation was observed in both hemispheres at about the same times and was correlated with geomagnetic activity. The scintillation level was very similar in approximately conjugate locations in Qiqiktarjuaq (75.4° N; 23.4° E CGM lat. and lon. and South Pole (74.1° S; 18.9° E, in Longyearbyen (75.3° N; 111.2° E and Zhongshan (74.7° S; 96.7° E, while it was significantly higher in Cambridge Bay (77.0° N; 310.1° E than at Mario Zucchelli (80.0° S; 307.7° E. In the polar cap, when the interplanetary magnetic field (IMF was strongly northward, the ionization due to energetic particle precipitation was a likely cause of scintillation that was stronger at Concordia (88.8° S; 54.4° E in the dark ionosphere than in the sunlit ionosphere over Eureka (88.1° N; 333.4° E, due to a difference in ionospheric conductivity. When the IMF tilted southward, weak or no significant scintillation was detected in the northern polar cap, while in the southern polar cap rapidly varying TEC and strong phase scintillation

  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. 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

  2. Keeping Warm Without Coal

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Heat-pump technology offers a clean heating alternative to coal With no air conditioning or indoor heating, families in southeast Beijing’s Fangzhuang neighbor-hood still enjoy refreshing warm air all year round. The secret is in the pump technology. Heat pumps cool the homes in summer and warm them in winter just like a central air-conditioning system.

  3. On Global Warming

    Institute of Scientific and Technical Information of China (English)

    Brad Franklin

    2010-01-01

    @@ There is a huge argument going on in the world these days and it is centered on the notion that our planet is warming up. It's celled global warming and it postulates1 that our use of fossil fuels such as coal and oil and our destruction of large areas of forest across the world have combined to create so-celled greenhouse gases.

  4. 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.

  5. Onset of deglacial warming in West Antarctica driven by local orbital forcing

    Science.gov (United States)

    WAIS Divide Project Members,; Steig, Eric J.; Markle, Bradley R.; Schoenemann, Spruce W.; Ding, Qinghua; Taylor, Kendrick C.; McConnell, Joseph R.; Brook, Edward J.; Sowers, Todd; White, James W. C.; Alley, Richard B.; Chen, Hai; Clow, Gary D.; Cole-Dai, Jihong; Conway, Howard; Fitzpatrick, Joan J.; Hargreaves, Geoffrey; ,

    2013-01-01

    The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.

  6. Tundra soil carbon is vulnerable to rapid microbial decomposition under climate warming

    Science.gov (United States)

    Xue, Kai; M. Yuan, Mengting; J. Shi, Zhou; Qin, Yujia; Deng, Ye; Cheng, Lei; Wu, Liyou; He, Zhili; van Nostrand, Joy D.; Bracho, Rosvel; Natali, Susan; Schuur, Edward. A. G.; Luo, Chengwei; Konstantinidis, Konstantinos T.; Wang, Qiong; Cole, James R.; Tiedje, James M.; Luo, Yiqi; Zhou, Jizhong

    2016-06-01

    Microbial decomposition of soil carbon in high-latitude tundra underlain with permafrost is one of the most important, but poorly understood, potential positive feedbacks of greenhouse gas emissions from terrestrial ecosystems into the atmosphere in a warmer world. Using integrated metagenomic technologies, we showed that the microbial functional community structure in the active layer of tundra soil was significantly altered after only 1.5 years of warming, a rapid response demonstrating the high sensitivity of this ecosystem to warming. The abundances of microbial functional genes involved in both aerobic and anaerobic carbon decomposition were also markedly increased by this short-term warming. Consistent with this, ecosystem respiration (Reco) increased up to 38%. In addition, warming enhanced genes involved in nutrient cycling, which very likely contributed to an observed increase (30%) in gross primary productivity (GPP). However, the GPP increase did not offset the extra Reco, resulting in significantly more net carbon loss in warmed plots compared with control plots. Altogether, our results demonstrate the vulnerability of active-layer soil carbon in this permafrost-based tundra ecosystem to climate warming and the importance of microbial communities in mediating such vulnerability.

  7. 高原高寒地域适应性训练卫勤保障实践%Practice on Implementing Adaptive Training of Medical Support under High Latitude and Cold Environment

    Institute of Scientific and Technical Information of China (English)

    徐承金; 李思睿

    2013-01-01

    2012年8-9月,某部组织部分官兵首次远程机动至高原高寒地域进行适应性训练。针对演练时间长、机动距离远、演习规格高、保障任务重的实际,克服缺氧环境、复杂地域、恶劣气候的影响,充分检测内陆部队进驻高原参训官兵生理指标变化特点和适应能力,深入探索研究未来内陆部队赴高原地区遂行机动支援卫勤保障面临的问题和对策。%Certain unit organized firstly a long -range mobile to implement adaptive training in the high latitude and cold area from August to September 2012 .In the process , the personnel should face the following diffi-culties, such as long time drill, long distance mobility, high requirements and heavy task .The personnel overcame the difficulties of hypoxia , complex terrain and bad weather .The military operation fully tested the changing char-acteristic of physiological index and adaptability of the soldiers to high latitude and cold area for training .It ex-plored the question and countermeasures for interior troops implementing combat mission of medical support in high latitude and cold area .

  8. International Standardization Activities for Optical Amplifiers

    Institute of Scientific and Technical Information of China (English)

    Haruo Okamura

    2003-01-01

    International standardization activities for Optical Amplifiers at IECTC86 and ITU-T SG15 are reviewed. Current discussions include Optical Amplifier safety guideline, Reliability standard, Rest methods of Noise and PMD, Definitions of Raman amplifier parameters and OA classification.

  9. Climate variability of the mid- and high-latitudes of the Southern Hemisphere in ensemble simulations from 1500 to 2000 AD

    Directory of Open Access Journals (Sweden)

    S. B. Wilmes

    2011-10-01

    Full Text Available To increase the sparse knowledge of long-term Southern Hemisphere (SH climate variability we assess an ensemble of 4 transient simulations over the last 500 yr performed with a state-of-the-art atmosphere ocean general circulation model. The model is forced with reconstructions of solar irradiance, greenhouse gas (GHG and volcanic aerosol concentrations. A 1990 control simulation shows that the model is able to represent the Southern Annular Mode (SAM, and to some extent the South Pacific Dipole (SPD and the Zonal Wave 3 (ZW3. During the past 500 yr we find that SPD and ZW3 variability remain stable, whereas SAM shows a significant shift towards its positive state during the 20th century. Regional temperatures over South America are strongly influenced by changing both GHG concentrations and volcanic eruptions whereas precipitation shows no significant response to the varying external forcing. For temperature this stands in contrast to proxy records suggesting that SH climate is dominated by internal variability rather than external forcing. The underlying dynamics of the temperature changes generally point to a combination of several modes, thus, hampering the possibilities regional reconstructions of the modes from proxy records. The linear imprint of the external forcing is as expected, i.e. a warming for increase in the combined solar and GHG forcing and a cooling after volcanic eruptions. Dynamically only the increase in SAM with increased combined forcing is simulated.

  10. Distribution and respiration of the high-latitude pelagic amphipod Themisto gaudichaudi in the Benguela Current in relation to upwelling intensity

    Science.gov (United States)

    Auel, Holger; Ekau, Werner

    2009-12-01

    The cold and highly productive waters of coastal upwelling areas provide habitats for marine species usually occurring at higher latitudes and allow those species to extend their distribution ranges towards the equator into regions otherwise characterised by warm and oligotrophic sub-tropical waters. The pelagic hyperiid amphipod Themisto gaudichaudi has a circum-Antarctic epipelagic distribution pattern generally south of 35°S and plays an important role in Antarctic food webs as effective link from zooplankton secondary production to higher trophic levels including seabirds and marine mammals. In the cold and productive waters of the Benguela Current coastal upwelling system, the distribution range of the species extents far northward into the subtropics. The present study focuses on the distribution of T. gaudichaudi at the northernmost limit of its range in the Benguela upwelling system in relation to upwelling intensity and hydrographic conditions (sea surface temperature) based on time-series data from 2002 to 2008. Moreover, field data on life-history traits and respiration rates in relation to water temperature are combined to elucidate the environmental and physiological factors limiting the distribution range. Compared to Themisto populations from higher latitudes, the relatively higher water temperatures in the coastal upwelling region lead to higher respiration rates, faster growth, earlier sexual maturity and smaller body size.

  11. 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.

  12. 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.

  13. A Transformer Class E Amplifier

    Directory of Open Access Journals (Sweden)

    Mikolajewski Miroslaw

    2014-12-01

    Full Text Available In a high-efficiency Class E ZVS resonant amplifier a matching and isolation transformer can replace some or even all inductive components of the amplifier thus simplifying the circuit and reducing its cost. In the paper a theoretical analysis, a design example and its experimental verification for a transformer Class E amplifier are presented. In the experimental amplifier with a transformer as the only inductive component in the circuit high efficiency ηMAX = 0.95 was achieved for supply voltage VI = 36 V, maximum output power POMAX = 100 W and the switching frequency f = 300 kHz. Measured parameters and waveforms showed a good agreement with theoretical predictions. Moreover, the relative bandwidth of the switching frequency was only 19% to obtain output power control from 4.8 W to POMAX with efficiency not less than 0.9 in the regulation range.

  14. A KIND OF NEW AMPLIFIER

    Institute of Scientific and Technical Information of China (English)

    YIN XUN-HE; FENG RU-PENG; REN YONG

    2000-01-01

    Chaotic characteristics in the iteration of logistic map (one-dimensional discrete dynamic system) are simulatedand analyzed. The circuit implementation of a kind of chaotic amplifier model is based on the chaotic characteristicsthat chaos is sensitively dependent on its initial conditions, and the circuit simulation result is given using simulationprogram with integrated circuit emphasis for personal computer (PSPICE), and is compared with linear amplifier.Advantages and disadvantages of such a model are indicated.

  15. Long-term community changes on a high-latitude coral reef in the Greater St Lucia Wetland Park, South Africa.

    Science.gov (United States)

    Schleyer, Michael H; Kruger, Alke; Celliers, Louis

    2008-03-01

    South African coral reefs are limited in size but, being marginal, provide a model for the study of many of the stresses to which these valuable systems are being subjected globally. Soft coral cover, comprising relatively few species, exceeds that of scleractinians over much of the reefs. The coral communities nevertheless attain a high biodiversity at this latitude on the East African coast. A long-term monitoring programme was initiated in 1993, entailing temperature logging and image analysis of high resolution photographs of fixed quadrats on representative reef. Sea temperatures rose by 0.15 degrees C p.a. at the site up to 2000 but have subsequently been decreasing by 0.07 degrees C p.a. Insignificant bleaching was encountered in the region during the 1998 El Nino Southern Oscillation (ENSO) event, unlike elsewhere in East Africa, but quantifiable bleaching occurred during an extended period of warming in 2000. Peak temperatures on the South African reefs thus appear to have attained the coral bleaching threshold. While this has resulted in relatively little bleaching thus far, the increased temperatures appear to have had a deleterious effect on coral recruitment success as other anthropogenic influences on the reefs are minimal. Recruitment success diminished remarkably up to 2004 but appears again to be improving. Throughout, the corals have also manifested changes in community structure, involving an increase in hard coral cover and reduction in that of soft corals, resulting in a 5.5% drop in overall coral cover. These "silent" effects of temperature increase do not appear to have been reported elsewhere in the literature.

  16. 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.

  17. 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.

  18. Proxy Constraints on a Warm, Fresh Late Cretaceous Arctic Ocean

    Science.gov (United States)

    Super, J. R.; Li, H.; Pagani, M.; Chin, K.

    2015-12-01

    The warm Late Cretaceous is thought to have been characterized by open Arctic Ocean temperatures upwards of 15°C (Jenkyns et al., 2004). The high temperatures and low equator-to-pole temperature gradient have proven difficult to reproduce in paleoclimate models, with the role of the atmospheric hydrologic cycle in heat transport being particularly uncertain. Here, sediments, coprolites and fish teeth of Santonian-Campanian age from two high-latitude mixed terrestrial and marine sections on Devon Island in the Canadian High Arctic (Chin et al., 2008) were analyzed using a suite of organic and inorganic proxies to evaluate the temperature and salinity of Arctic seawater. Surface temperature estimates were derived from TEX86 estimates of near-shore, shallow (~100 meters depth) marine sediments (Witkowski et al., 2011) and MBT-CBT estimates from terrestrial intervals and both suggest mean annual temperatures of ~20°C, consistent with previous estimates considering the more southerly location of Devon Island. The oxygen isotope composition of non-diagenetic phosphate from vertebrate coprolites and bony fish teeth were then measured, giving values ranging from +13‰ to +19‰. Assuming the TEX86 temperatures are valid and using the temperature calibration of Puceat 2010, the δ18O values of coprolites imply Arctic Ocean seawater δ18O values between -4‰ and -10‰, implying very fresh conditions. Lastly, the δD of precipitation will be estimated from the hydrogen isotope composition of higher plant leaf waxes (C-25, C-27, C-29 and C-31 n-alkanes) from both terrestrial and marine intervals. Data are used to model the salinity of seawater and the meteoric relationship between δD and δ18O, thereby helping to evaluate the northern high-latitude meteoric water line of the Late Cretaceous.

  19. Projections of 2.0°C Warming over the Globe and China under RCP4.5

    Institute of Scientific and Technical Information of China (English)

    Zhang Ying

    2012-01-01

    The outputs of 17 models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are employed to investigate the temporal and spatial features of 2.0°C warming of the surface temperature over the globe and China under the Representative Concentration Pathways (RCP) 4.5 scenario. The simulations of the period 1860–1899 in the "historical" experiment are chosen as the baseline. The simulations for the 21st century in the RCP4.5 experiment are chosen as the future project. The multi-model ensemble mean (MME) shows that the global mean temperature would cross the 2.0°C warming threshold in 2047. Warming in most of the models would cross the threshold during 2030–2060. For local warming, high-latitude areas in the Northern Hemisphere show the fastest warming over the globe. Land areas warm substantially faster than the oceans. Most of the southern oceans would not exceed the 2.0°C warming threshold within the 21st century. Over China, surface warming is substantially faster than the global mean. The area-averaged warming would cross the 2.0°C threshold in 2034. Locally, Northwest China shows the fastest warming trend, followed by Central North China and Northeast China. Central China, East China, and South China are the last to cross the 2.0°C warming threshold. The diversity of the models is also estimated in this study. Generally, the spread among the models increases with time, and there is smaller spread among the models for the areas with the faster warming.

  20. Reconciling Warming Trends

    Science.gov (United States)

    Schmidt, Gavin A.; Shindell, Drew T.; Tsigaridis, Konstantinos

    2014-01-01

    Climate models projected stronger warming over the past 15 years than has been seen in observations. Conspiring factors of errors in volcanic and solar inputs, representations of aerosols, and El NiNo evolution, may explain most of the discrepancy.

  1. 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.

  2. 2002: The extra-strong warm winter event in North Asia and its accompanying anomalous atmospheric circulation

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Features of an extra-strong warm winter event in North Asia in 2002 and its accompanying anomalous atmospheric circulation were studied through diagnosis on the atmospheric reanalysis data set. Results show that the winter of 2002 is of the warmest in the recent 54 years in North Asia, which was caused by both decadal scale and interannual scale variability. The interannual variability is proved to be as the main cause for the event, and it is related to the global scale atmospheric circulation anomalies, with the strongest of them in the Eastern Hemisphere and in the middle and high latitude region of the Southern Hemisphere.

  3. 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)

    Estimates of the seasonal and interannual exchanges of carbon dioxide (CO2) and methane (CH4) 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 CH4 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 CH4 yr−1). In contrast, consideration of interannual changes of wetland inundation extent result in regional estimates of the net CO2 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 CO2 sink responds with only 7–9% changes to the changes in wetland inundation extent. Seasonally, the inundated area changes result in higher summer CH4 emissions, but lower summer CO2 sinks, leading to lower summer negative greenhouse gas forcing. Our analysis further indicates that wetlands

  4. Patterns of cold-air drainage and microclimate in mid-latitude versus high-latitude mountains: contrasts and implications for climate change (Invited)

    Science.gov (United States)

    Pepin, N. C.

    2009-12-01

    Predictions of current spatial patterns of climate are difficult in areas of complex relief in all parts of the world, because of the interweaving influences of topography, elevation and aspect. These influences vary temporally as a result of the seasonal and diurnal cycles in radiation balance. In periods of negative energy balance, surface decoupling can occur as cold air drainage develops low-level temperature inversions, and the surface temperature regime beneath the inversion becomes divorced from free atmospheric forcing. Both the spatial scale and temporal persistence of this decoupling vary according to latitude, and although the physical processes that influence inversion formation are similar in polar areas and mid-latitude mountains, the contrasting seasonal and diurnal forcings make the end results very different. Examples are contrasted from detailed field temperature measurements (~50 sites per field area) taken over several years in areas of complex relief in the eastern Pyrenees (~42.5 deg N), the Oregon Cascades (also ~42.5 deg N) and Finnish Lapland (70 deg N and above the Arctic circle). In the former two locations decoupling is mostly diurnally driven, and small-scale topography is important in mediating the effects. Summer decoupling is brief and spatially limited, whereas winter decoupling can be more spatially extensive. There are strong relationships between synoptic conditions, as measured by objective flow indices at the 700 mb level (derived from NCEP/NCAR reanalysis fields) and the patterns of decoupling, which allow us to assess the effects of past and potential future circulation change on spatial patterns of future climate warming. In Finnish Lapland the decoupling regime most clearly approaches the mid-latitude pattern around the equinoxes when there are clear day and night periods. In winter and summer however (the polar night and polar day) with the muting of the diurnal cycle, processes are more poorly understood. Winter cold

  5. A comparison of general circulation models and their application to temperature change assessments in a high-latitude agricultural area in northeastern China

    Science.gov (United States)

    Ouyang, Wei; Shi, Yandan; Hao, Fanghua; Jiao, Wei

    2016-07-01

    The two main focuses of this study are a comparison of the general circulation models (GCMs) from Phase 5 of the Coupled Model Inter-Comparison Project (CMIP5) and an assessment of the surface air temperature under multiple climate scenarios in a high middle latitude area of China. In the past 55 years temperatures in this area have shown an obvious upward trend (a rise of 1.50 °C), and another important change during this time period was a significant alteration in tillage practices that occurred in 1986. Using methods and tools such as average deviation, the Taylor figure and the space techniques rating (SS), time sequence related coefficient, and the M2 index, a comprehensive spatial-temporal assessment was performed based on the CMIP5 models. The simulations provided by the models had certain common features, but there were also significant differences. The three best models (CanCM4, INMCM4, and IPSL-CM5A-MR) have a common characteristic: the institutions where they were developed are located at latitudes that are similar to or higher than the latitude of the study area. Future climate changes were analyzed by simulating a representative concentration pathway 4.5/8.5 (RCP4.5/RCP8.5) of emission scenarios with a multi-model ensemble. The temperatures under the RCP4.5 and RCP8.5 scenarios have a certain upward trend, with increases of 2.24 and 5.44 °C, respectively. From a spatial perspective, the distributions of the temperature change trend showed a southwest to northeast step increase under both scenarios, but the warming trend in the area of each lattice point under the RCP4.5 scenario is much lower than that of the RCP8.5 scenario. There are no obvious changes in the spatial distribution of the accumulated intensity and frequency of the regional air temperature in the three periods (2016-2035, 2036-2065, and 2066-2095) under the two scenarios.

  6. 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. PMID:26662380

  7. EMI-resilient amplifier circuits

    CERN Document Server

    van der Horst, Marcel J; Linnenbank, André C

    2014-01-01

    This book enables circuit designers to reduce the errors introduced by the fundamental limitations and electromagnetic interference (EMI) in negative-feedback amplifiers.  The authors describe a systematic design approach for application specific negative-feedback amplifiers, with specified signal-to-error ratio (SER).  This approach enables designers to calculate noise, bandwidth, EMI, and the required bias parameters of the transistors used in  application specific amplifiers in order to meet the SER requirements.   ·         Describes design methods that incorporate electromagnetic interference (EMI) in the design of application specific negative-feedback amplifiers; ·         Provides designers with a structured methodology to avoid the use of trial and error in meeting signal-to-error ratio (SER) requirements; ·         Equips designers to increase EMI immunity of the amplifier itself, thus avoiding filtering at the input, reducing the number of components and avoiding detr...

  8. Low-Noise Band-Pass Amplifier

    Science.gov (United States)

    Kleinberg, L.

    1982-01-01

    Circuit uses standard components to overcome common limitation of JFET amplifiers. Low-noise band-pass amplifier employs JFET and operational amplifier. High gain and band-pass characteristics are achieved with suitable choice of resistances and capacitances. Circuit should find use as low-noise amplifier, for example as first stage instrumentation systems.

  9. Ecosystems response and restitution time across the K/Pg boundary transition at high-latitudes, Southern Hemisphere, New Zealand - a palynological approach

    Science.gov (United States)

    Willumsen, Pi; Vajda, Vivi

    2010-05-01

    terrestrial record e.g. "Fern-spike" interval (Vajda et al. 2001; Vajda and Raine 2003; Vajda and McLoughlin 2004). Interestingly, the dinocyst Trithyrodinium evittii has first occurrence immediately above the K/Pg boundary horizon in the southwest Pacific (Helby et al., 1987; Wilson 1987, 1988; Williams et al. 2004; Willumsen 2000, 2006). This dinocyst pattern is interpreted to reflect an invasion of this species into the southwest Pacific, in the aftermath of the Chicxulub impact. In the New Zealand sections, two earliest Paleocene intervals with dominance of T. evittii are separated by an acme interval of Paleoperidinium pyrophorum (Willumsen 2000, 2006; Willumsen et al., 2004a; 2004b). The sudden acme of P. pyrophorum ca. 0.5 Ma after the K/Pg boundary event is interpreted to reflect a regional cold water pulse taking place after a period with relatively warmer sea-surface e.g. T. evittii dominated dinocyst assemblages. A second period with warm-surface water is observed c. 0.8-1.5 Ma after the event. The end of the main marine recovery period is marked by a gradual arrival of new suite of dinocyst species and oligotrophic conditions. The timing of these early Paleocene events in New Zealand aligns well with D'Hondt et al. (1998, 2005) who propose that the marine ecosystem was radically altered due to the K/Pg boundary event and that the post-K/Pg boundary is divided into several recovery steps before the open-ocean ecosystem was fully recovered c. 3 Ma after the event.

  10. 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

  11. Gaussian amplifier for nuclear spectrometry

    International Nuclear Information System (INIS)

    One of the major goals of nuclear spectrometry is the determination of the energy spectrum of a radioactive source. To measure this spectrum with electronic instrumentation one need to use a nuclear spectrometry chain of which the amplifier is part of, and whose filter shaping considerably influences the final energy resolution achieved. The amplifier released accomplishes a 7th order Gaussian filter shape with Taylor series approximation synthesized by the Shifted Companion Form and mounted using only electronic components availablein Brazil. The final version has been tested and the results showed a very good performance and the energy resolution achieved was equivalent to the imported models. (Author)

  12. Dielectric waveguide amplifiers and lasers

    NARCIS (Netherlands)

    Pollnau, M.

    2014-01-01

    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 o

  13. Thermal recovery of NIF amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Sutton, S.; Marshall, C.; Petty, C.; Smith, L.; van Wonterghem, B.; Mills, S.

    1997-02-01

    The issue of thermal recovery of the NIF amplifiers has taken on increased emphasis as program goals move toward increasing the shot rate to once every four hours. This paper addresses the technical issues associated with achieving thermal recovery in the NIF amplifiers. We identify two temperature related thermal recovery quantities: (1) the difference between the average slab temperature and the temperature of other surfaces in the amplifier cavity, and (2) the temperature difference in the slab over the aperture. The first quantity relates to optical disturbances in the gas column in the system, while the second quantity is associated with optical aberrations in the laser media itself. Calculations and experiments are used to quantify recovery criteria, and develop cooling approaches. The cooling approaches discussed are (1) active cooling of the flashlamps with ambient gas and chilled gas, and (2) active cooling of the slab edge cladding. Calculations indicate that the NIF baseline cooling approach of 20 cfm per lamp ambient temperature gas flow in both the central and side flashlamp cassettes is capable of meeting thermal recovery requirements for an 8 hour shot period, while to achieve a 4 hour shot period requires use of chilled gas and edge cladding cooling. In addition, the effect of changing the amplifier cavity and beamtube fill gas from nitrogen to helium is addressed, showing that a factor of 8 reduction in the sensitivity to thermal disturbances is possible. 6 refs., 9 figs., 1 tab.

  14. A wideband dc-coupled amplifier

    International Nuclear Information System (INIS)

    A method is described whereby an ac-coupled high-frequency amplifier and a dc-coupled low-frequency amplifier are connected in parallel in order to obtain a dc-coupled wideband amplifier. By using an operational amplifier which compares the output voltage with the input voltage, the low-frequency amplifier contributes to the overall gain only when the gain of the ac-coupled amplifier droops at low frequencies. Thus, no frequency splitting networks are necessary and the excellent low-frequency features of an operational amplifier are added to those of the ac-coupled wideband amplifier. As an example, a low noise amplifier is described which exhibits a hundredfold gain, a bandwidth from dc to 550 MHz, an input bias current of less than 1 nA, and an output voltage range of ±1 V

  15. Northern hemisphere glaciation during the globally warm early Late Pliocene.

    Directory of Open Access Journals (Sweden)

    Stijn De Schepper

    Full Text Available The early Late Pliocene (3.6 to ∼3.0 million years ago is the last extended interval in Earth's history when atmospheric CO2 concentrations were comparable to today's and global climate was warmer. Yet a severe global glaciation during marine isotope stage (MIS M2 interrupted this phase of global warmth ∼3.30 million years ago, and is seen as a premature attempt of the climate system to establish an ice-age world. Here we propose a conceptual model for the glaciation and deglaciation of MIS M2 based on geochemical and palynological records from five marine sediment cores along a Caribbean to eastern North Atlantic transect. Our records show that increased Pacific-to-Atlantic flow via the Central American Seaway weakened the North Atlantic Current and attendant northward heat transport prior to MIS M2. The consequent cooling of the northern high latitude oceans permitted expansion of the continental ice sheets during MIS M2, despite near-modern atmospheric CO2 concentrations. Sea level drop during this glaciation halted the inflow of Pacific water to the Atlantic via the Central American Seaway, allowing the build-up of a Caribbean Warm Pool. Once this warm pool was large enough, the Gulf Stream-North Atlantic Current system was reinvigorated, leading to significant northward heat transport that terminated the glaciation. Before and after MIS M2, heat transport via the North Atlantic Current was crucial in maintaining warm climates comparable to those predicted for the end of this century.

  16. Reality of Global Warming

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Global warming is today heard in the international arena as frequently and with the same brooding concern as terrorism, nuclear weapons and the Iraq war. Zou Ji, Vice Dean of the School of Environment, Renmin University of China in Beijing, has been a me

  17. Susceptibility to a metal under global warming is shaped by thermal adaptation along a latitudinal gradient.

    Science.gov (United States)

    Dinh Van, Khuong; Janssens, Lizanne; Debecker, Sara; De Jonge, Maarten; Lambret, Philippe; Nilsson-Örtman, Viktor; Bervoets, Lieven; Stoks, Robby

    2013-09-01

    Global warming and contamination represent two major threats to biodiversity that have the potential to interact synergistically. There is the potential for gradual local thermal adaptation and dispersal to higher latitudes to mitigate the susceptibility of organisms to contaminants and global warming at high latitudes. Here, we applied a space-for-time substitution approach to study the thermal dependence of the susceptibility of Ischnura elegans damselfly larvae to zinc in a common garden warming experiment (20 and 24 °C) with replicated populations from three latitudes spanning >1500 km in Europe. We observed a striking latitude-specific effect of temperature on the zinc-induced mortality pattern; local thermal adaptation along the latitudinal gradient made Swedish, but not French, damselfly larvae more susceptible to zinc at 24 °C. Latitude- and temperature-specific differences in zinc susceptibility may be related to the amount of energy available to defend against and repair damage since Swedish larvae showed a much stronger zinc-induced reduction of food intake at 24 °C. The pattern of local thermal adaptation indicates that the predicted temperature increase of 4 °C by 2100 will strongly magnify the impact of a contaminant such as zinc at higher latitudes unless there is thermal evolution and/or migration of lower latitude genotypes. Our results underscore the critical importance of studying the susceptibility to contaminants under realistic warming scenarios taking into account local thermal adaptation across natural temperature gradients.

  18. Arctic lakes are continuous methane sources to the atmosphere under warming conditions

    International Nuclear Information System (INIS)

    Methane is the second most powerful carbon-based greenhouse gas in the atmosphere and its production in the natural environment through methanogenesis is positively correlated with temperature. Recent field studies showed that methane emissions from Arctic thermokarst lakes are significant and could increase by two- to four-fold due to global warming. But the estimates of this source are still poorly constrained. By using a process-based climate-sensitive lake biogeochemical model, we estimated that the total amount of methane emissions from Arctic lakes is 11.86 Tg yr−1, which is in the range of recent estimates of 7.1–17.3 Tg yr−1 and is on the same order of methane emissions from northern high-latitude wetlands. The methane emission rate varies spatially over high latitudes from 110.8 mg CH4 m−2 day−1 in Alaska to 12.7 mg CH4 m−2 day−1 in northern Europe. Under Representative Concentration Pathways (RCP) 2.6 and 8.5 future climate scenarios, methane emissions from Arctic lakes will increase by 10.3 and 16.2 Tg CH4 yr−1, respectively, by the end of the 21st century. (letter)

  19. Arctic lakes are continuous methane sources to the atmosphere under warming conditions

    Science.gov (United States)

    Tan, Zeli; Zhuang, Qianlai

    2015-05-01

    Methane is the second most powerful carbon-based greenhouse gas in the atmosphere and its production in the natural environment through methanogenesis is positively correlated with temperature. Recent field studies showed that methane emissions from Arctic thermokarst lakes are significant and could increase by two- to four-fold due to global warming. But the estimates of this source are still poorly constrained. By using a process-based climate-sensitive lake biogeochemical model, we estimated that the total amount of methane emissions from Arctic lakes is 11.86 Tg yr-1, which is in the range of recent estimates of 7.1-17.3 Tg yr-1 and is on the same order of methane emissions from northern high-latitude wetlands. The methane emission rate varies spatially over high latitudes from 110.8 mg CH4 m-2 day-1 in Alaska to 12.7 mg CH4 m-2 day-1 in northern Europe. Under Representative Concentration Pathways (RCP) 2.6 and 8.5 future climate scenarios, methane emissions from Arctic lakes will increase by 10.3 and 16.2 Tg CH4 yr-1, respectively, by the end of the 21st century.

  20. 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.

  1. The long-term fate of permafrost peatlands under rapid climate warming

    Science.gov (United States)

    Swindles, Graeme T.; Morris, Paul J.

    2016-04-01

    High-latitude permafrost peatlands contain globally important amounts of soil organic carbon, owing to cold conditions which suppress anaerobic decomposition. However, there is much concern that climate warming and subsequent permafrost thaw threaten the stability of this carbon store. The ultimate fate of permafrost peatlands and their carbon stores is unclear because of complex feedbacks between peat accumulation, hydrology and vegetation. Unfortunately, field monitoring campaigns only span the last few decades and therefore provide an incomplete picture of permafrost peatland response to rapid warming in the twentieth century. Here we use a high-resolution palaeoecological approach to understand the longer-term response of peatlands in Subarctic Sweden in contrasting states of permafrost degradation to recent rapid warming. At all sites we identify a drying trend until the late-twentieth century; however, two sites subsequently experienced a rapid shift to wetter conditions as permafrost thawed in response to climatic warming, culminating in collapse of the peat domes. Commonalities between study sites lead us to propose a five-phase model for permafrost peatland response to climatic warming. This model suggests a shared ecohydrological trajectory towards a common end point: inundated Arctic fen. Although carbon accumulation is rapid in such sites, and thus peatland ecosystem services are resumed, saturated soil conditions are likely to cause elevated methane emissions that have implications for climate-feedback mechanisms. We outline our plans to test the model published in Swindles et al. (2015) using the same methodological approach in other high-latitude locations, including zones of continuous and discontinuous permafrost. Reference: Swindles, G.T., Morris, P.J., Mullan, D., Watson, E.J., Turner, T.E., Roland, T., Amesbury, M.J., Kokfelt, U., Schoning, K., Pratte, S., Gallego-Sala, A., Charman, D.J., Sanderson, N., Garneau, M., Carrivick, J.L., Woulds, C

  2. Wintertime ecosystem respiration shifts tundra from carbon sink to carbon source at tundra warming experiment

    Science.gov (United States)

    Webb, E.; Schuur, E. A.; Natali, S.; Bracho, R.

    2013-12-01

    Northern latitude ecosystems play a significant role in the global carbon (C) budget due to the roughly 1700 Pg of C stored in permafrost soils. As high latitudes warm, previously frozen C is expected to decompose, thereby increasing CO2 fluxes to the atmosphere and potentially creating a positive feedback to climate warming. While warming has been shown to increase plant C uptake during the growing season, these seasonal C gains may be offset on an annual basis by ecosystem respiration (Reco) during the remaining seven months of the year. Here we present research from the Carbon in Permafrost Experimental Heating Research (CiPEHR) project, a tundra ecosystem warming experiment in interior Alaska. We partitioned the non-growing season into three segments: fall (October 1 until first snow), winter (snow-covered period until spring), and spring (snow depth less than 30cm until melt out). During fall, we measured net ecosystem exchange and Reco using a static flux chamber. In winter, we measured Reco using chamber measurements and soda lime. For spring, we modeled fluxes based on known relationships between snow depth and photosynthetic rate of arctic evergreen species. We found that ecosystem warming caused plants to photosynthesize later in fall and increased C uptake during spring but also enhanced respiration during the long winter. We combined these off-season estimates with measurements from growing season auto-chamber data and found that despite the C gained during the growing season, ecosystem warming resulted in net annual C loss for the two years measured. This annual C loss was dependent on the magnitude of wintertime Reco. Our results indicate that snow depth, soil temperature, and day of season are the major determinants of wintertime Reco. Some climate models predict that arctic ecosystems will experience warmer winters with more snow. Thus, despite increased plant productivity during the growing season, we document that increased wintertime temperatures

  3. 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

  4. Seeing the risks of multiple Arctic amplifying feedbacks.

    Science.gov (United States)

    Carter, P.

    2014-12-01

    There are several potentially very large sources of Arctic amplifying feedbacks that have been identified. They present a great risk to the future as they could become self and inter-reinforcing with uncontrollable knock-on, or cascading risks. This has been called a domino effect risk by Carlos Duarte. Because of already committed global warming and the millennial duration of global warming, these are highly policy relevant. These Arctic feedback processes are now all operant with emissions of carbon dioxide methane and nitrous oxide detected. The extent of the risks from these feedback sources are not obvious or easy to understand by policy makers and the public. They are recorded in the IPCC AR5 as potential tipping points, as is the irreversibility of permafrost thaw. Some of them are not accounted for in the IPCC AR5 global warming projections because of quantitative uncertainty. UNEP issued a 2012 report (Policy Implications of Thawing Permafrost) advising that by omitting carbon feedback emissions from permafrost, carbon budget calculations by err on the low side. There is the other unassessed issue of a global warming safety limit for preventing uncontrollable increasing Arctic feedback emissions. Along with our paper, we provide illustrations of the Arctic feedback sources and processes from satellite imagery and flow charts that allows for their qualitative consideration. We rely on the IPCC assessments, the 2012 paper Possible role of wetlands permafrost can methane hydrates in the methane cycle under future climate change; a review, by Fiona M. O'Connor et al., and build on the WWF 2009 Arctic Climate Feedbacks: Global Implications. The potential sources of Arctic feedback processes identified include: Arctic and Far North snow albedo decline, Arctic summer sea ice albedo decline, Greenland summer ice surface melting albedo loss, albedo decline by replacement of Arctic tundra with forest, tundra fires, Boreal forest fires, Boreal forest die

  5. 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....

  6. 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.

  7. 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...

  8. Quantum Theory of Laser Amplifiers.

    Science.gov (United States)

    Mander, Gillian Linda

    Available from UMI in association with The British Library. Requires signed TDF. We calculate the input-output characteristics of a below threshold laser amplifier. Expressions are derived for the output second- and fourth-order spectral and temporal correlation functions in terms of the corresponding input quantities, and for the photocount first and second factorial moments for both homodyne and direct detection. The general results are applied to several cases of practical interest, including specific non-classical input states. We show that a maximum of twofold amplification is permitted if squeezing in the input is to survive at the output. Similarly, for preservation of photon antibunching in amplification we show that only very small gains are allowed. The model treated here provides a detailed example of the amplifier noise limitations imposed by quantum mechanics. In particular, we show that minimum noise occurs in a cavity that is asymmetric with respect to the mirror reflectivities. The latter part of this work treats the above threshold laser amplifier. The laser output is back-scattered from a moving target to provide a weak Doppler-shifted signal which re-enters the laser cavity and is amplified. We show that the three-level atomic lasing medium is equivalent to a two-level medium pumped by an inverted bath. We use the methods of quantum statistical analysis to obtain time -evolution equations for the c-number amplitudes of the laser and signal fields. We show that the results may be applied to the below threshold regime for appropriate values of the pump parameter. By considering the amplitude differential gain we show explicitly that the behaviour of the laser around threshold is characteristic of a second -order phase transition. We calculate the output intensity gain appropriate to a heterodyne detection process, and find good agreement between the predicted gain profiles and measured data for both carbon dioxide and argon-ion lasers.

  9. 338-GHz Semiconductor Amplifier Module

    Science.gov (United States)

    Samoska, Lorene A.; Gaier, Todd C.; Soria, Mary M.; Fung, King Man; Rasisic, Vesna; Deal, William; Leong, Kevin; Mei, Xiao Bing; Yoshida, Wayne; Liu, Po-Hsin; Uyeda, Jansen; Lai, Richard

    2010-01-01

    Research findings were reported from an investigation of new gallium nitride (GaN) monolithic millimeter-wave integrated circuit (MMIC) power amplifiers (PAs) targeting the highest output power and the highest efficiency for class-A operation in W-band (75-110 GHz). W-band PAs are a major component of many frequency multiplied submillimeter-wave LO signal sources. For spectrometer arrays, substantial W-band power is required due to the passive lossy frequency multipliers.

  10. High power regenerative laser amplifier

    Science.gov (United States)

    Miller, J.L.; Hackel, L.A.; Dane, C.B.; Zapata, L.E.

    1994-02-08

    A regenerative amplifier design capable of operating at high energy per pulse, for instance, from 20-100 Joules, at moderate repetition rates, for instance from 5-20 Hertz is provided. The laser amplifier comprises a gain medium and source of pump energy coupled with the gain medium; a Pockels cell, which rotates an incident beam in response to application of a control signal; an optical relay system defining a first relay plane near the gain medium and a second relay plane near the rotator; and a plurality of reflectors configured to define an optical path through the gain medium, optical relay and Pockels cell, such that each transit of the optical path includes at least one pass through the gain medium and only one pass through the Pockels cell. An input coupler, and an output coupler are provided, implemented by a single polarizer. A control circuit coupled to the Pockels cell generates the control signal in timed relationship with the input pulse so that the input pulse is captured by the input coupler and proceeds through at least one transit of the optical path, and then the control signal is applied to cause rotation of the pulse to a polarization reflected by the polarizer, after which the captured pulse passes through the gain medium at least once more and is reflected out of the optical path by the polarizer before passing through the rotator again to provide an amplified pulse. 7 figures.

  11. 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.

  12. Warm Springs pupfish recovery plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This document gives a history of pupfish and focuses on the warm springs pupfish. The warm springs pupfish is endangered, and this is a plan to help recover the...

  13. Quaternary climate - Terrestrial Biosphere Interaction: amplifying or stabilizing?

    Science.gov (United States)

    Claussen, Martin

    2016-04-01

    According to the Gaia hypothesis, interaction between climate and biological processes tend to homeostatically maintain, on a global scale, conditions favourable for life. Does the idea of homeostatic interaction between terrestrial biosphere and climate hold for the Quaternary glacial - interglacial changes? Interpretation of palaeoclimate and palaeobotanic evidence by using climate and Earth system models yields an interesting picture. The synergy between the sea-ice albedo - climate feedback and the taiga-tundra - climate feedback is suggested to amplify the orbitally forced climatic precession. This effect seems to be strong at regional scale, but small at global scale. Various simulations indicate that biogeophysical processes amplify the difference of some 4 to 6 K in global mean temperature between glacial and interglacial climate by some 10 percent. The combined effect of biogeophysical and biogeochemical processes, i.e. processes with involve carbon stored in biomass and soil, is less clear. Theoretical studies suggest that in pre-industrial, interglacial climate, a reduction in boreal and extratropical forests tend to cool the climate and a reduction in tropical forest, to warm the climate. Recent estimates in changes in organic carbon stored under ice sheets and in permafrost point at the possibility that the sum of all terrestrial biogeochemical processes might almost "carbon neutral" to the climate system. If corroborated, this observation would favour the assumption of a dominance of biogeophysical processes amplifying orbitally forced Quaternary climate variations.

  14. Improved charge amplifier using hybrid hysteresis compensation

    Science.gov (United States)

    Amin-Shahidi, Darya; Trumper, David L.

    2013-08-01

    We present a novel charge amplifier, with a robust feedback circuit and a method for compensating piezoelectric actuator's hysteresis at low frequencies. The amplifier uses a modified feedback circuit which improves robustness to the addition of series load impedance such as in cabling. We also describe a hybrid hysteresis compensation method for enabling the charge amplifier to reduce hysteresis at low frequencies. Experimental results demonstrate the utility of the new amplifier design.

  15. Thinking About Global Warming

    Energy Technology Data Exchange (ETDEWEB)

    Baron, J. [Department of Psychology, University of Pennsylvania, 3720 Walnut St., Philadelphia, 19104-6241, PA (United States)

    2006-07-15

    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.

  16. Warm Little Inflaton

    CERN Document Server

    Bastero-Gil, Mar; Ramos, Rudnei O; Rosa, Joao G

    2016-01-01

    We show that inflation can naturally occur at a finite temperature T>H that is sustained by dissipative effects, when the inflaton field corresponds to a pseudo-Nambu Goldstone boson of a broken gauge symmetry. Similarly to "Little Higgs" scenarios for electroweak symmetry breaking, the flatness of the inflaton potential is protected against both quadratic divergences and the leading thermal corrections. We show that, nevertheless, non-local dissipative effects are naturally present and are able to sustain a nearly-thermal bath of light particles despite the accelerated expansion of the Universe. As an example, we discuss the dynamics of chaotic warm inflation with a quartic potential and show that the associated observational predictions are in very good agreement with the latest Planck results. This model constitutes the first realization of warm inflation where the inflaton is directly coupled to only two light fields.

  17. Climate change - global warming

    International Nuclear Information System (INIS)

    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)

  18. Spontaneous emission from saturated parametric amplifiers

    DEFF Research Database (Denmark)

    Rottwitt, Karsten; Ott, Johan Raunkjær; Steffensen, Henrik;

    2009-01-01

    Noise performance of parametric amplifiers is typically calculated assuming un-depleted operation. However, in many applications especially when applied as regenerative amplifiers in systems based on phase shift keyed modulation schemes, this assumption is not valid. Here we show the impact on ac...... on accumulated spontaneous emission for a parametric amplifier operated in saturation....

  19. 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 Eu...

  20. A High-performance Small Signal Amplifier

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    According to questions in the design of high quality small signal amplifier, this paper gave a new-type high performance small signal amplifier. The paper selected the operational amplifier of ICL Company and designed a new-type circuit with simple, low cost and excellent performance.

  1. Radio frequency amplifier with effective decoupling

    NARCIS (Netherlands)

    Besling, W.F.A.; Bakker, T.W.; Lamy, Y.; Kochupurackal, J.; Roozeboom, F.

    2011-01-01

    A variety of circuits, methods and devices are implemented for radiofrequency amplifiers. According to one such implementation, a radiofrequency amplifier circuit is implemented in a SMD package. The circuit amplifies a radiofrequency signal having a base-band portion and a plurality of carrier sign

  2. low pump power photonic crystal fibre amplifiers

    DEFF Research Database (Denmark)

    Hougaard, Kristian G.; Broeng, Jes; Bjarklev, Anders Overgaard

    2003-01-01

    Designs of low pump power optical amplifiers, based on photonic crystal fibres are presented. The potential of these fibre amplifiers is investigated, and it is demonstrated that such amplifiers may deliver gains of more than 15 dB at 1550 nm with less than 1 mW of optical pump power....

  3. Enhanced seasonal CO2 exchange caused by amplified plant productivity in northern ecosystems

    Science.gov (United States)

    Forkel, Matthias; Carvalhais, Nuno; Rödenbeck, Christian; Keeling, Ralph; Heimann, Martin; Thonicke, Kirsten; Zaehle, Sönke; Reichstein, Markus

    2016-04-01

    Atmospheric monitoring has shown an increase in the seasonal cycle of carbon dioxide (CO2) in high northern latitudes (> 40°N) since the 1960s. The much stronger increase of the seasonal CO2 amplitude in high latitudes compared to low latitudes suggests that northern ecosystems are experiencing large changes in carbon cycle dynamics. However the underlying mechanisms are not yet fully understood and current climate/carbon cycle models under-estimate observed changes in the seasonal CO2 amplitude. Here we aim to explain the observed latitudinal gradient of seasonal CO2 amplitude trends by contrasting observations from long-term monitoring sites of atmospheric CO2 concentration, satellite observation of vegetation greenness, and global observation-based datasets of gross primary production and net biome productivity, with results from the LPJmL dynamic global vegetation model coupled to the TM3 atmospheric transport model. Our results demonstrate that the latitudinal gradient of the enhanced seasonal CO2 amplitude is mainly driven by positive trends in photosynthetic carbon uptake caused by recent climate change and mediated by changing vegetation cover in boreal and arctic ecosystems. Climate change affects processes such as plant physiology, phenology, water availability, and vegetation dynamics, ultimately leading to increased plant productivity and vegetation cover in northern ecosystems in the last decades. Thereby photosynthetic carbon uptake has reacted much more strongly to warming than respiratory carbon release processes. Continued long-term observation of atmospheric CO2 together with ground and satellite observations of land surface and vegetation dynamics will be the key to detect, model, and better predict changes in high-latitude land/carbon cycle dynamics.

  4. 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

  5. Time-dependent convection at high latitudes

    Directory of Open Access Journals (Sweden)

    D. W. Idenden

    Full Text Available A fully time-dependent ionospheric convection model, in which electric potentials are derived by an analytic solution of Laplace's equation, is described. This model has been developed to replace the empirically derived average convection patterns currently used routinely in the Sheffield/SEL/UCL coupled thermosphere/ionosphere/plasmasphere model (CTIP for modelling disturbed periods. Illustrative studies of such periods indicate that, for the electric field pulsation periods imposed, long-term averages of parameters such as Joule heating and plasma density have significantly different values in a time-dependent model compared to those derived under the same mean conditions in a steady-state model. These differences are indicative of the highly non-linear nature of the processes involved.

  6. Ozone Profile Comparisons at High Latitudes

    Science.gov (United States)

    McPeters, R. D.; Bojkov, B. R.; Deland, M.

    2008-05-01

    Ozone profiles measured by both satellite and ground based instruments at a site at 67.4 N were compared. The measurements were made during the Sodankyla Total Column Ozone Intercomparison (SAUNA) which was held in Sodankyla, Finland in March-April 2006 in support of Aura validation. Measurements by the NOAA 16 SBUV/2 and the Aura MLS instrument were compared with lidar and sonde profiles measured in Sodankyla. Profiles from the satellite instruments generally agreed with profiles from the ground-based instruments to within about 10%. The total column ozone comparisons showed that SBUV/2 and the Aura OMI instrument agreed well with the double Brewer instruments provided the scenes were carefully matched.

  7. Response to CO2 Transient Increase in the GISS Coupled Model: Regional Coolings in a Warming Climate

    Science.gov (United States)

    Russell, Gary L.; Rind, David

    1999-01-01

    The (GISS) Goddard Institute for Space Studies coupled atmosphere-ocean model is used to investigate the effect of increased atmospheric CO2 by comparing a compounded 1 percent CO2 increase experiment with a control simulation. After 70 years of integration, the global surface air temperature in the 1 percent CO2 experiment is 1.43 C warmer. In spite of this global warming, there are two distinct regions, the northern Atlantic Ocean and the southern Pacific Ocean, where the surface air temperature is up to 4 C cooler. This situation is maintained by two positive feedbacks: a local effect on convection in the South Pacific and a non-local impact on the meridional circulation in the North Atlantic. The poleward transport of latent energy and dry static energy by the atmosphere is greater in the 1 percent CO2 experiment, caused by warming and therefore increased water vapor and greater greenhouse capacity at lower latitudes. The larger atmospheric transports tend to reduce upward vertical fluxes of heat and moisture from the ocean surface at high latitudes, which has the effect of stabilizing the ocean, reducing both convection and the thermohaline circulation. With less convection, less warm water is brought up from below, and with a reduced North Atlantic thermohaline circulation (by 30 percent at time of CO2 doubling), the poleward energy transport by the oceans decreases. The colder water then leads to further reductions in evaporation, decreases of salinity at high latitudes, continued stabilization of the ocean, and maintenance of reduced convection and meridional overturning. Although sea ice decreases globally, it increases in the cooling regions which reduces the overall climate sensitivity; its effect is most pronounced in the Southern Hemisphere. Tropical warming has been observed over the past several decades; if modeling studies such as this and others which have produced similar effects are valid, these processes may already be beginning.

  8. Effect of high latitude on tea quality of southern tea cultivated at northern area%南茶高纬度北引对茶叶品质的影响

    Institute of Scientific and Technical Information of China (English)

    汪曙晖; 汪东风; 李晓东; 彭正云; 姜星; 张续周

    2015-01-01

    目的:研究南茶高纬度北引后对茶类适制性及绿茶品质产生的影响。方法通过理化方法,分析同一品种茶树在高纬度北引后对其叶片厚度、鲜叶成分、不同茶类感官品质、绿茶成分及感官品质所产生的变化。结果随着纬度的增加,绿茶品质较好,而红茶品质较差;随着南茶高纬度北引,叶片厚度、氨基酸、水溶性糖、水浸出物和芳香物质(精油)总量等含量随纬度增大而增加;茶多酚含量则相反;对精油中各成分分析显示,北方茶烃类成分较多,醇类成分较少。结论本研究明确了南茶高纬度北引后茶叶品质特点及化学成分基础。%Objective To study the effect of high latitude on suitability for processing different teas and green tea quality of southern tea cultivated at northern area.Methods The tea fresh leaves from the tea plant, which was introduced from southern area and cultivated at high latitude of northern area, were made into black tea (full fermentation tea), oolong tea (semi-fermentation tea) and green tea (no fermentation tea). The main component content and quality of the tea fresh leaves and the teas were analyzed by the methods about physicochemical analysis. Results The sensory quality of green tea was the most one in the three teas with latitude increasing; the leaf thickness, amino acid, soluble sugar, water extract and total aromatic compounds (essential oils) content increased with latitude increasing, but tea polyphenol content showed the opposite. Analysis of each component of the essential oil showed that hydrocarbon constituents were much more and alcohol content was less in northern tea.Conclusion The above changes of tea functional components content are the basis of chemical composition of north tea quality characteristics from south tea cultivated at high north latitude.

  9. Log amplifier with pole-zero compensation

    Science.gov (United States)

    Brookshier, William

    1987-01-01

    A logarithmic amplifier circuit provides pole-zero compensation for improved stability and response time over 6-8 decades of input signal frequency. The amplifier circuit includes a first operational amplifier with a first feedback loop which includes a second, inverting operational amplifier in a second feedback loop. The compensated output signal is provided by the second operational amplifier with the log elements, i.e., resistors, and the compensating capacitors in each of the feedback loops having equal values so that each break point or pole is offset by a compensating break point or zero.

  10. 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...

  11. The tropical Pacific as a key pacemaker of the variable rates of global warming

    Science.gov (United States)

    Kosaka, Yu; Xie, Shang-Ping

    2016-09-01

    Global mean surface temperature change over the past 120 years resembles a rising staircase: the overall warming trend was interrupted by the mid-twentieth-century big hiatus and the warming slowdown since about 1998. The Interdecadal Pacific Oscillation has been implicated in modulations of global mean surface temperatures, but which part of the mode drives the variability in warming rates is unclear. Here we present a successful simulation of the global warming staircase since 1900 with a global ocean-atmosphere coupled model where tropical Pacific sea surface temperatures are forced to follow the observed evolution. Without prescribed tropical Pacific variability, the same model, on average, produces a continual warming trend that accelerates after the 1960s. We identify four events where the tropical Pacific decadal cooling markedly slowed down the warming trend. Matching the observed spatial and seasonal fingerprints we identify the tropical Pacific as a key pacemaker of the warming staircase, with radiative forcing driving the overall warming trend. Specifically, tropical Pacific variability amplifies the first warming epoch of the 1910s-1940s and determines the timing when the big hiatus starts and ends. Our method of removing internal variability from the observed record can be used for real-time monitoring of anthropogenic warming.

  12. A cascade of warming impacts brings bluefin tuna to Greenland waters

    DEFF Research Database (Denmark)

    MacKenzie, Brian; Payne, Mark; Boje, Jesper;

    in ecological isolation from others. Here we show that a large highly migratory top predator fish species has entered a high latitude sub-polar area. Bluefin tuna, Thunnus thynnus Linnaeus 1758, were captured in waters east of Greenland (65o N) in August 2012 during exploratory fishing for Atlantic mackerel......Rising ocean temperatures are causing marine fish species to shift spatial distributions and ranges, and are altering predator-prey dynamics in food-webs. Most documented cases of species shifts so far involve relatively small species at lower trophic levels, and consider individual species......, Scomber scombrus Linnaeus 1758. The bluefin tuna were captured in a single net-haul in 9-11o C water together with 6 tonnes of mackerel, which is a preferred prey species and itself a new immigrant to the area. Regional temperatures in August 2012 were historically high and contributed to a warming trend...

  13. HIGH AVERAGE POWER OPTICAL FEL AMPLIFIERS

    International Nuclear Information System (INIS)

    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

  14. High temperature charge amplifier for geothermal applications

    Science.gov (United States)

    Lindblom, Scott C.; Maldonado, Frank J.; Henfling, Joseph A.

    2015-12-08

    An amplifier circuit in a multi-chip module includes a charge to voltage converter circuit, a voltage amplifier a low pass filter and a voltage to current converter. The charge to voltage converter receives a signal representing an electrical charge and generates a voltage signal proportional to the input signal. The voltage amplifier receives the voltage signal from the charge to voltage converter, then amplifies the voltage signal by the gain factor to output an amplified voltage signal. The lowpass filter passes low frequency components of the amplified voltage signal and attenuates frequency components greater than a cutoff frequency. The voltage to current converter receives the output signal of the lowpass filter and converts the output signal to a current output signal; wherein an amplifier circuit output is selectable between the output signal of the lowpass filter and the current output signal.

  15. 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

  16. Cathode-follower power amplifier

    International Nuclear Information System (INIS)

    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

  17. Climatologies of nighttime upper thermospheric winds measured by ground-based Fabry-Perot interferometers during geomagnetically quiet conditions: 2. High-latitude circulation and interplanetary magnetic field dependence

    DEFF Research Database (Denmark)

    Emmert, J.T.; Hernandez, G.; Jarvis, M.J.;

    2006-01-01

    We analyze upper thermospheric (similar to 250 km) nighttime horizontal neutral wind patterns, during geomagnetically quiet (Kp <3) conditions, over the following locations: South Pole (90 degrees S), Halley (76 degrees S, 27 degrees W), Millstone Hill (43 degrees N, 72 degrees W), Sondre Stromfj...... at latitudes as low as that of Millstone Hill ( magnetic latitude 53 degrees N). Quiet time Bz effects are negligible except over the magnetic polar cap station of Thule....... Stromfjord (67 degrees N, 51 degrees W), and Thule (77 degrees N, 68 degrees W). We examine the wind patterns as a function of magnetic local time and latitude, solar cycle, day of year, and the dawn-dusk and north-south components of the interplanetary magnetic field (IMF B-y and B-z). In magnetic...... coordinates, the quiet time high-latitude wind patterns are dominated by antisunward flow over the polar cap, with wind speeds that generally increase with increasing solar extreme ultraviolet (EUV) irradiation. The winds are generally stronger during equinox than during winter, particularly over the South...

  18. Introduction Experiment of Extremely Early Maturing Corn in High-latitude and High-altitude Awusiqi%高纬度高海拔阿吾斯奇地区极早熟玉米引种试验

    Institute of Scientific and Technical Information of China (English)

    刘彦; 付强; 刘军; 刘雪芹

    2016-01-01

    此试验是在特殊的高纬度高海拔,≥10℃年积温只有2088℃的阿吾斯奇地区进行的极早熟玉米引种试验,试验品种九个,分别引自内蒙古、新疆本地和黑龙江。试验表明,阿吾斯奇地区不能种植收籽玉米,可种植青贮玉米,但只能是收无穗的青玉米秆。最适宜的品种是丰早304。%The experiment related to introduction of extremely early maturing corn is carried out in particular high-latitude and high-altitude Awusqi, where ≥10℃accumulated temperature is 2 088℃every year. Nine varieties are respectively introduced from Inner Mongolia, Xinjiang and Heilongjiang. It indicates that Awusqi region can not be suitable for seeding corn but silage corn, and only the green corn stover without spikes can be collected. The most suitable variety is fengzao-304.

  19. 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)

  20. 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.