WorldWideScience

Sample records for high-latitude northern hemisphere

  1. 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

  2. Holocene temperature evolution in the Northern Hemisphere high latitudes - Model-data comparisons

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    Zhang, Yurui; Renssen, Hans; Seppä, Heikki; Valdes, Paul J.

    2017-10-01

    Heterogeneous Holocene climate evolutions in the Northern Hemisphere high latitudes are primarily determined by orbital-scale insolation variations and melting ice sheets. Previous inter-model comparisons have revealed that multi-simulation consistencies vary spatially. We, therefore, compared multiple model results with proxy-based reconstructions in Fennoscandia, Greenland, north Canada, Alaska and Siberia. Our model-data comparisons reveal that data and models generally agree in Fennoscandia, Greenland and Canada, with the early-Holocene warming and subsequent gradual decrease to 0 ka BP (hereinafter referred as ka). In Fennoscandia, simulations and pollen data suggest a 2 °C warming by 8 ka, but this is less expressed in chironomid data. In Canada, a strong early-Holocene warming is suggested by both the simulations and pollen results. In Greenland, the magnitude of early-Holocene warming ranges from 6 °C in simulations to 8 °C in δ18O-based temperatures. Simulated and reconstructed temperatures are mismatched in Alaska. Pollen data suggest strong early-Holocene warming, while the simulations indicate constant Holocene cooling, and chironomid data show a stable trend. Meanwhile, a high frequency of Alaskan peatland initiation before 9 ka can reflect a either high temperature, high soil moisture or large seasonality. In high-latitude Siberia, although simulations and proxy data depict high Holocene temperatures, these signals are noisy owing to a large spread in the simulations and between pollen and chironomid results. On the whole, the Holocene climate evolutions in most regions (Fennoscandia, Greenland and Canada) are well established and understood, but important questions regarding the Holocene temperature trend and mechanisms remain for Alaska and Siberia.

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

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

    2009-04-01

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

  4. Precipitation Mediates the Response of Carbon Cycle to Rising Temperature in the Mid-to-High Latitudes of the Northern Hemisphere.

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    Xin Lin

    Full Text Available Over the past decades, rising air temperature has been accompanied by changes in precipitation. Despite relatively robust literature on the temperature sensitivity of carbon cycle at continental to global scales, less is known about the way this sensitivity is affected by precipitation. In this study we investigate how precipitation mediates the response of the carbon cycle to warming over the mid-to-high latitudes in the Northern Hemisphere (north of 30 °N. Based on atmospheric CO2 observations at Point Barrow (BRW in Alaska, satellite-derived NDVI (a proxy of vegetation productivity, and temperature and precipitation data, we analyzed the responses of carbon cycle to temperature change in wet and dry years (with precipitation above or below the multiyear average. The results suggest that, over the past three decades, the net seasonal atmospheric CO2 changes at BRW were significantly correlated with temperature in spring and autumn, yet only weakly correlated with temperature and precipitation during the growing season. We further found that responses of the net CO2 changes to warming in spring and autumn vary with precipitation levels, with the absolute temperature sensitivity in wet years roughly twice that in dry years. The analyses of NDVI and climate data also identify higher sensitivity of vegetation growth to warming in wet years for the growing season, spring and summer. The different temperature sensitivities in wet versus dry years probably result from differences in soil moisture and/or nutrient availability, which may enhance (inhibit the responsiveness of carbon assimilation and/or decomposition to warming under high (low precipitation levels. The precipitation-mediated response of the terrestrial carbon cycle to warming reported here emphasizes the important role of precipitation in assessing the temporal variations of carbon budgets in the past as well as in the future. More efforts are required to reduce uncertainty in future

  5. Precipitation Mediates the Response of Carbon Cycle to Rising Temperature in the Mid-to-High Latitudes of the Northern Hemisphere.

    Science.gov (United States)

    Lin, Xin; Li, Junsheng; Luo, Jianwu; Wu, Xiaopu; Tian, Yu; Wang, Wei

    2015-01-01

    Over the past decades, rising air temperature has been accompanied by changes in precipitation. Despite relatively robust literature on the temperature sensitivity of carbon cycle at continental to global scales, less is known about the way this sensitivity is affected by precipitation. In this study we investigate how precipitation mediates the response of the carbon cycle to warming over the mid-to-high latitudes in the Northern Hemisphere (north of 30 °N). Based on atmospheric CO2 observations at Point Barrow (BRW) in Alaska, satellite-derived NDVI (a proxy of vegetation productivity), and temperature and precipitation data, we analyzed the responses of carbon cycle to temperature change in wet and dry years (with precipitation above or below the multiyear average). The results suggest that, over the past three decades, the net seasonal atmospheric CO2 changes at BRW were significantly correlated with temperature in spring and autumn, yet only weakly correlated with temperature and precipitation during the growing season. We further found that responses of the net CO2 changes to warming in spring and autumn vary with precipitation levels, with the absolute temperature sensitivity in wet years roughly twice that in dry years. The analyses of NDVI and climate data also identify higher sensitivity of vegetation growth to warming in wet years for the growing season, spring and summer. The different temperature sensitivities in wet versus dry years probably result from differences in soil moisture and/or nutrient availability, which may enhance (inhibit) the responsiveness of carbon assimilation and/or decomposition to warming under high (low) precipitation levels. The precipitation-mediated response of the terrestrial carbon cycle to warming reported here emphasizes the important role of precipitation in assessing the temporal variations of carbon budgets in the past as well as in the future. More efforts are required to reduce uncertainty in future precipitation

  6. Stratospheric warming in Southern Hemisphere high latitudes since 1979

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    Y. Hu

    2009-07-01

    Full Text Available In the present study, we show evidence of significant stratospheric warming over Southern Hemisphere high latitudes and large portions of the Antarctic polar region in winter and spring seasons, with a maximum warming of 7–8°C in September and October, using satellite Microwave Sounding Unit observations for 1979–2006. It is found that this warming is associated with increasing wave activity from the troposphere into the stratosphere, suggesting that the warming is caused by enhanced wave-driven adiabatic heating. We show that the stratospheric warming in Southern Hemisphere high latitudes has close correlations with sea surface temperature (SST increases, and that general circulation model simulations forced with observed time-varying SSTs reproduce similar warming trend patterns in the Antarctic stratosphere. The simulated stratospheric warming is closely related to increasing wave activity in the Southern Hemisphere. These findings suggest that the stratospheric warming is likely induced by SST warming. As SST warming continues as a consequence of greenhouse gas increases due to anthropogenic activity, the stratospheric warming would also continue, which has important implications to the recovery of the Antarctic ozone hole.

  7. Summertime low-ozone episodes at northern high latitudes

    OpenAIRE

    Orsolini, Y. J.; Eskes, H.; Hansen, G.; Hoppe, U.-P.; Kylling, A.; Kyrö, E.; Notholt, Justus; Van der A, R.; von der Gathen, Peter

    2003-01-01

    A pool of low-ozone air resides in the Arctic stratosphere in summer. Its formation and maintenance arise from a combination of chemical ozone-destruction and transport processes. The summertime ozone destruction is induced by gas-phase chemistry dominated by nitrogen and hydrogen catalytic cycles, which are efficient due to long summertime insolation at high latitudes. It is shown that, during events referred to as low-ozone episodes (LOEs), column ozone can locally decrease to values compar...

  8. Environmental and physical controls on northern high latitude methane fluxes across permafrost zones

    Science.gov (United States)

    D. Olefeldt; M.R. Turetsky; P.M. Crill; A.D. McGuire

    2013-01-01

    Methane (CH4) emissions from the northern high-latitude region represent potentially significant biogeochemical feedbacks to the climate system. We compiled a database of growing-season CH4 emissions from terrestrial ecosystems located across permafrost zones, including 303 sites described in 65 studies. Data on...

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

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    N. R. P. Harris

    2008-05-01

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

  10. 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, ...

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

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

    2015-12-01

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

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

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    Loranty, Michael M; Berner, Logan T; Goetz, Scott J; Jin, Yufang; Randerson, James T

    2014-02-01

    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, we compare satellite observations and coupled climate model representations of albedo and tree cover for the boreal and Arctic region. Our analyses reveal consistent declines in albedo with increasing tree cover, occurring south of latitudinal tree line, that are poorly represented in coupled climate models. Observed relationships between albedo and tree cover differ substantially between snow-covered and snow-free periods, and among plant functional type. Tree cover in models varies widely but surprisingly does not correlate well with model albedo. Furthermore, our results demonstrate a relationship between tree cover and snow-albedo feedback that may be used to accurately constrain high latitude albedo feedbacks in coupled climate models under current and future vegetation distributions. © 2013 John Wiley & Sons Ltd.

  13. Northern Hemisphere forcing of Southern Hemisphere climate during the last deglaciation.

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    He, Feng; Shakun, Jeremy D; Clark, Peter U; Carlson, Anders E; Liu, Zhengyu; Otto-Bliesner, Bette L; Kutzbach, John E

    2013-02-07

    According to the Milankovitch theory, changes in summer insolation in the high-latitude Northern Hemisphere caused glacial cycles through their impact on ice-sheet mass balance. Statistical analyses of long climate records supported this theory, but they also posed a substantial challenge by showing that changes in Southern Hemisphere climate were in phase with or led those in the north. Although an orbitally forced Northern Hemisphere signal may have been transmitted to the Southern Hemisphere, insolation forcing can also directly influence local Southern Hemisphere climate, potentially intensified by sea-ice feedback, suggesting that the hemispheres may have responded independently to different aspects of orbital forcing. Signal processing of climate records cannot distinguish between these conditions, however, because the proposed insolation forcings share essentially identical variability. Here we use transient simulations with a coupled atmosphere-ocean general circulation model to identify the impacts of forcing from changes in orbits, atmospheric CO(2) concentration, ice sheets and the Atlantic meridional overturning circulation (AMOC) on hemispheric temperatures during the first half of the last deglaciation (22-14.3 kyr BP). Although based on a single model, our transient simulation with only orbital changes supports the Milankovitch theory in showing that the last deglaciation was initiated by rising insolation during spring and summer in the mid-latitude to high-latitude Northern Hemisphere and by terrestrial snow-albedo feedback. The simulation with all forcings best reproduces the timing and magnitude of surface temperature evolution in the Southern Hemisphere in deglacial proxy records. AMOC changes associated with an orbitally induced retreat of Northern Hemisphere ice sheets is the most plausible explanation for the early Southern Hemisphere deglacial warming and its lead over Northern Hemisphere temperature; the ensuing rise in atmospheric CO(2

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

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

    2018-01-01

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

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

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    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

  16. 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

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

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    Annett Bartsch

    2016-11-01

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

  18. High Latitude Dust in the Earth System

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

    2016-01-01

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

  19. Tropical and high latitude forcing of enhanced megadroughts in Northern China during the last four terminations

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    Tang, Changyan; Yang, Huan; Pancost, Richard D.; Griffiths, Michael L.; Xiao, Guoqiao; Dang, Xinyue; Xie, Shucheng

    2017-12-01

    Understanding the origin and evolutionary history of drought events is of great significance, providing critical insight into future hydrological conditions under the changing climate. Due to the scarcity of drought proxies from northern China, the occurrence and underlying mechanisms of the drought events remains enigmatic on longer timescales. Here we utilize microbial lipid proxies to reconstruct significant drought events over the last four ice age terminations in the southernmost section (Weinan section) of the Chinese Loess Plateau. The abundance of archaeal isoprenoid GDGTs (glycerol dialkyl glycerol tetraethers) relative to bacterial branched GDGTs, measured by Ri/b and BIT indices, is diagnostic of enhanced drought conditions. The Ri/b (and BIT) indices are stable and low (high) throughout most of the loess section spanning the last 350 thousand years, but they do exhibit sharp transient peaks (valleys) during the intervals associated with the four ice age terminations, and especially Terminations II and IV. These enhanced drought events are, non-intuitively, associated with a significant decrease in the relative abundance of C4 plants, inferred by a decrease in the carbon isotope composition of bulk organic matter. Although the microbial records show some consistency with the Weinan grain size profiles, indicative of Eastern Asian winter monsoon variability, they also show some apparent difference. In fact, some features of the microbial records exhibit strong similarities with marine sediment planktonic foraminiferal δ13C records from the western Pacific warm pool, which reflect ENSO-like changes during glacial terminations. Therefore, enhanced droughts immediately before the interglacial warming in northern China could be explained, at least in part, by teleconnections in tropical ocean-atmosphere circulation via shifts in the Intertropical Convergence Zone (ITCZ) and associated Jet Stream over the Asian continent. According to our microbial biomarker

  20. Different responses of northern and southern high latitude ionospheric convection to IMF rotations: a case study based on SuperDARN observations

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    D. Ambrosino

    2009-06-01

    Full Text Available We use SuperDARN data to study high-latitude ionospheric convection over a three hour period (starting at 22:00 UT on 2 January 2003, during which the Interplanetary Magnetic Field (IMF flipped between two states, one with By>>|Bz| and one with Bz>0, both with negative Bx. We find, as expected from previous works, that day side ionospheric convection is controlled by the IMF in both hemispheres. For strongly northward IMF, we observed signatures of two reverse cells, both in the Northern Hemisphere (NH and in the Southern Hemisphere (SH, due to lobe reconnection. On one occasion, we also observed in the NH two viscous cells at the sides of the reverse cell pair. For duskward IMF, we observed in the NH a large dusk clockwise cell, accompanied by a smaller dawn cell, and the signature of a corresponding pattern in the SH. On two occasions, a three cell pattern, composed of a large clockwise cell and two viscous cells, was observed in the NH. As regards the timings of the NH and SH convection reconfigurations, we find that the convection reconfiguration from a positive Bz dominated to a positive By dominated pattern occurred almost simultaneously (i.e. within a few minutes in the two hemispheres. On the contrary, the reconfiguration from a By dominated to a northward IMF pattern started in the NH 8–13 min earlier than in the SH. We suggest that part of such a delay can be due to the following mechanism: as IMF Bx<0, the northward-tailward magnetosheath magnetic field reconnects with the magnetospheric field first tailward of the northern cusp and later on tailward of the southern cusp, due to the IMF draping around the magnetopause.

  1. Methane emission estimates at northern high latitudes for 2004-2014 from CarbonTracker Europe-CH4

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    Tsuruta, Aki; Aalto, Tuula; Backman, Leif; van der Laan-Luijkx, Ingrid T.; Krol, Maarten; Houweling, Sander; Spahni, Renato; Lienert, Sebastian; Dlugokencky, Edward; Laurila, Tuomas; Hatakka, Juha; Worthy, Doug; Sasakawa, Motoki; Peltola, Olli; Mauranen, Aleksateri; Heiman, Martin; Kozlova, Lena; Crotwell, Andrew; Peters, Wouter

    2017-04-01

    Northern high latitudes (NHL) are covered by permafrost and peatlands, and store much of global soil carbon. As global warming proceeds, methane (CH4) emissions from the Arctic and northern boreal regions are assumed to increase due to thawing of permafrost and shortening of soil freeze and snow cover periods. In addition, several large cities and industrial areas including oil and gas fields also contribute significantly to CH4 emissions from NHL. Together, both biospheric and anthropogenic activities contribute to changes in atmospheric CH4, but current understanding is still insufficient to quantify their contributions to the NHL and global CH4 budget. In this study, we present CH4 emission estimates for NHL for 2004-2014 from the CarbonTracker Europe-CH4 (CTE-CH4) data assimilation system. CTE-CH4 is based on ensemble Kalman filter, and optimises biospheric and anthropogenic emissions simultaneously, constrained by global atmospheric CH4 observations, which includes newly assimilated sites from NHL. The inversion results show that the contribution from NHL to global CH4 emissions is higher than previously thought. Posterior total CH4 emissions from 50°N-90°N are higher than prior estimates mainly from the EDGAR v4.2 FT2010 inventory and LPX-Bern dyptop ecosystem model. Much of the increase from the prior is found in anthropogenic emissions from central Russia, and in biospheric emissions from both North American and Eurasian boreal regions. In addition, the increase in the biospheric emissions resulted in stronger dependency of the CH4 emissions to temperature than in prior, particularly in autumn. For northern Europe, anthropogenic emissions are estimated to be smaller than the EDGAR inventory, and the inversions suggest that the emission distribution may need to be revised.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-01-01

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

  3. Seasonal dependence of northern high-latitude upper thermospheric winds : A quiet time climatological study based on ground-based and space-based measurements

    NARCIS (Netherlands)

    Dhadly, Manbharat; Emmert, John; Drob, Douglas; Conde, Mark; Doornbos, E.N.; Shepherd, Gordon; Makela, Jonathan; Wu, Qian; Niciejewski, Rick; Ridley, Aaron J.

    2017-01-01

    This paper investigates the large-scale seasonal dependence of geomagnetically quiet time, northern high-latitude F region thermospheric winds by combining extensive observations from eight ground-based (optical remote sensing) and three space-based (optical remote sensing and in situ)

  4. Simulation of northern hemisphere high latitude ocean/ sea ice variability 1948-2001

    Science.gov (United States)

    Haak, H.; Jungclaus, J.; Mikolajewicz, U.; Latif, M.

    2003-04-01

    North Atlantic/Arctic variability for the period 1948-2001 is studied using a global Ocean General Circulation Model coupled to a dynamic/thermodynamic sea ice model forced by daily NCEP/NCAR reanalysis data. Variability of Artic sea ice properties is analysed, in particular the formation and propagation of sea ice thickness anomalies that led to the Great Salinity Anomalies (GSA) in the 1970s, 1980s, 1990s in the Labrador Sea (LS). Anomalies are tracked to the West European Basin, but vanish before reentering the Nordic Seas. Experiments indicate only a minor impact of a single GSA event on the North Atlantic Thermohaline Circulation (THC).

  5. Satellite observed salinity distributions at high latitudes in the Northern Hemisphere: A comparison of four products

    Science.gov (United States)

    Garcia-Eidell, Cynthia; Comiso, Josefino C.; Dinnat, Emmanuel; Brucker, Ludovic

    2017-09-01

    Global surface ocean salinity measurements have been available since the launch of SMOS in 2009 and coverage was further enhanced with the launch of Aquarius in 2011. In the polar regions where spatial and temporal changes in sea surface salinity (SSS) are deemed important, the data have not been as robustly validated because of the paucity of in situ measurements. This study presents a comparison of four SSS products in the ice-free Arctic region, three using Aquarius data and one using SMOS data. The accuracy of each product is assessed through comparative analysis with ship and other in situ measurements. Results indicate RMS errors ranging between 0.33 and 0.89 psu. Overall, the four products show generally good consistency in spatial distribution with the Atlantic side being more saline than the Pacific side. A good agreement between the ship and satellite measurements was also observed in the low salinity regions in the Arctic Ocean, where SSS in situ measurements are usually sparse, at the end of summer melt seasons. Some discrepancies including biases of about 1 psu between the products in spatial and temporal distribution are observed. These are due in part to differences in retrieval techniques, geophysical filtering, and sea ice and land masks. The monthly SSS retrievals in the Arctic from 2011 to 2015 showed variations (within ˜1 psu) consistent with effects of sea ice seasonal cycles. This study indicates that spaceborne observations capture the seasonality and interannual variability of SSS in the Arctic with reasonably good accuracy.

  6. High latitude ionospheric structure.

    Science.gov (United States)

    Ossakow, S. L.; Burke, W.; Carlson, H. C.; Gary, P.; Heelis, R.; Keskinen, M.; Maynard, N.; Meng, C.; Szuszczewicz, E.; Vickrey, J.

    Contents: 1. Introduction: Ionospheric structure in general. Equatorial spread-F irregularities - a success story and a guide for high latitudes. Focus on high-latitude structure. 2. Sources and observations of high-latitude structure: Electron precipitation structures. Electric fields. Field-aligned currents. Plasma density structure. 3. Plasma instability theory: Macroinstabilities and high latitude structure. Microinstabilities and high latitude structure. 4. An emerging picture. 5. Future studies: Theoretical thrusts. Experimental emphasis.

  7. Amplified Late Pliocene terrestrial warmth in northern high latitudes from greater radiative forcing and closed Arctic Ocean gateways

    Science.gov (United States)

    Feng, Ran; Otto-Bliesner, Bette L.; Fletcher, Tamara L.; Tabor, Clay R.; Ballantyne, Ashley P.; Brady, Esther C.

    2017-05-01

    Proxy reconstructions of the mid-Piacenzian warm period (mPWP, between 3.264 and 3.025 Ma) suggest terrestrial temperatures were much warmer in the northern high latitudes (55°-90°N, referred to as NHL) than present-day. Climate models participating in the Pliocene Model Intercomparison Project Phase 1 (PlioMIP1) tend to underestimate this warmth. For instance, the underestimate is ∼10 °C on average across NHL and up to 17 °C in the Canadian Arctic region in the Community Climate System Model version 4 (CCSM4). Here, we explore potential mPWP climate forcings that might contribute to this mPWP mismatch. We carry out seven experiments to assess terrestrial temperature responses to Pliocene Arctic gateway closure, variations in CO2 level, and orbital forcing at millennial time scale. To better compare the full range of simulated terrestrial temperatures with sparse proxy data, we introduce a pattern recognition technique that simplifies the model surface temperatures to a few representative patterns that can be validate with the limited terrestrial proxy data. The pattern recognition technique reveals two prominent features of simulated Pliocene surface temperature responses. First, distinctive patterns of amplified warming occur in the NHL, which can be explained by lowered surface elevation of Greenland, pattern and amount of Arctic sea ice loss, and changing strength of Atlantic meridional overturning circulation. Second, patterns of surface temperature response are similar among experiments with different forcing mechanisms. This similarity is due to strong feedbacks from responses in surface albedo and troposphere water vapor content to sea ice changes, which overwhelm distinctions in forcings from changes in insolation, CO2 forcing, and Arctic gateway closure. By comparing CCSM4 simulations with proxy records, we demonstrate that both model and proxy records show similar patterns of mPWP NHL terrestrial warmth, but the model underestimates the magnitude

  8. Changing Temperature Gradients Linked to Holocene Moisture Trends in the Northern Hemisphere

    Science.gov (United States)

    Routson, C.; McKay, N.; Kaufman, D. S.; Ault, T.; Rodysill, J. R.

    2016-12-01

    We hypothesize that latitudinal differences in Northern Hemisphere radiative energy balance led to both enhanced hemispheric monsoon strength and mid-latitude aridity during the early-to-mid-Holocene. The width of the Hadley cell and mean position of the subtropical jet stream are influenced by the temperature gradient between the equator and the pole. Climate change is expected to strengthen Hadley circulation while weakening the equator-to-pole temperature gradient, thus shifting the mean position of the subtropical jet northward and causing the sub-tropics to become drier. We analyzed the evolution of Northern Hemisphere latitudinal temperature gradients with moisture in a new compilation of Holocene-length paleoclimate records spanning from 10°S to 90°N latitude. The primary trends in the paleoclimate records agree with future projections showing that weaker early-to-mid Holocene Northern Hemisphere latitudinal temperature gradients (increased warming of the Arctic relative to the equator) are linked to substantial increases in zonally averaged mid-latitude (30°N-55°N) aridity, and simultaneous increases in Northern Hemisphere monsoon strength. These results are significant for current warming, as northern high latitudes are warming faster than the equator, decreasing the equator-to-pole temperature gradient to values comparable with the early Holocene. Our results support model-based projections of increased drought risk in the Northern Hemisphere mid-latitudes in the coming decades.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-09-14

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

  10. Forest carbon sinks in the Northern Hemisphere

    Science.gov (United States)

    Christine L. Goodale; Michael J. Apps; Richard A. Birdsey; Christopher B. Field; Linda S. Heath; Richard A. Houghton; Jennifer C. Jenkins; Gundolf H. Kohlmaier; Werner Kurz; Shirong Liu; Gert-Jan Nabuurs; Sten Nilsson; Anatoly Z. Shvidenko

    2002-01-01

    There is general agreement that terrestrial systems in the Northern Hemisphere provide a significant sink for atmospheric CO2; however, estimates of the magnitude and distribution of this sink vary greatly. National forest inventories provide strong, measurement-based constraints on the magnitude of net forest carbon uptake. We brought together...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-06-01

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

  12. HUBBLE SPOTS NORTHERN HEMISPHERIC CLOUDS ON URANUS

    Science.gov (United States)

    2002-01-01

    Using visible light, astronomers for the first time this century have detected clouds in the northern hemisphere of Uranus. The newest images, taken July 31 and Aug. 1, 1997 with NASA Hubble Space Telescope's Wide Field and Planetary Camera 2, show banded structure and multiple clouds. Using these images, Dr. Heidi Hammel (Massachusetts Institute of Technology) and colleagues Wes Lockwood (Lowell Observatory) and Kathy Rages (NASA Ames Research Center) plan to measure the wind speeds in the northern hemisphere for the first time. Uranus is sometimes called the 'sideways' planet, because its rotation axis is tipped more than 90 degrees from the planet's orbit around the Sun. The 'year' on Uranus lasts 84 Earth years, which creates extremely long seasons - winter in the northern hemisphere has lasted for nearly 20 years. Uranus has also been called bland and boring, because no clouds have been detectable in ground-based images of the planet. Even to the cameras of the Voyager spacecraft in 1986, Uranus presented a nearly uniform blank disk, and discrete clouds were detectable only in the southern hemisphere. Voyager flew over the planet's cloud tops near the dead of northern winter (when the northern hemisphere was completely shrouded in darkness). Spring has finally come to the northern hemisphere of Uranus. The newest images, both the visible-wavelength ones described here and those taken a few days earlier with the Near Infrared and Multi-Object Spectrometer (NICMOS) by Erich Karkoschka (University of Arizona), show a planet with banded structure and detectable clouds. Two images are shown here. The 'aqua' image (on the left) is taken at 5,470 Angstroms, which is near the human eye's peak response to wavelength. Color has been added to the image to show what a person on a spacecraft near Uranus might see. Little structure is evident at this wavelength, though with image-processing techniques, a small cloud can be seen near the planet's northern limb (rightmost

  13. Tracking Snow Variations in the Northern Hemisphere Using Multi-Source Remote Sensing Data (2000–2015

    Directory of Open Access Journals (Sweden)

    Yunlong Wang

    2018-01-01

    Full Text Available Multi-source remote sensing data were used to generate 500-m resolution cloud-free daily snow cover images for the Northern Hemisphere. Simultaneously, the spatial and temporal dynamic variations of snow in the Northern Hemisphere were evaluated from 2000 to 2015. The results indicated that (1 the maximum, minimum, and annual average snow-covered area (SCA in the Northern Hemisphere exhibited a fluctuating downward trend; the variation of snow cover in the Northern Hemisphere had well-defined inter-annual and regional differences; (2 the average SCA in the Northern Hemisphere was the largest in January and the smallest in August; the SCA exhibited a downward trend for the monthly variations from February to April; and the seasonal variation in the SCA exhibited a downward trend in the spring, summer, and fall in the Northern Hemisphere (no pronounced variation trend in the winter was observed during the 2000–2015 period; (3 the spatial distribution of the annual average snow-covered day (SCD was related to the latitudinal zonality, and the areas exhibiting an upward trend were mainly at the mid to low latitudes with unstable SCA variations; and (4 the snow reduction was significant in the perennial SCA in the Northern Hemisphere, including high-latitude and high-elevation mountainous regions (between 35° and 50°N, such as the Tibetan Plateau, the Tianshan Mountains, the Pamir Plateau in Asia, the Alps in Europe, the Caucasus Mountains, and the Cordillera Mountains in North America.

  14. 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.

  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; Gasso, Santiago; Gisladottir, Gudrun; Hodgkins, Richard; McCulloch, Robert; NcKenna Neuman, Cheryl; Mockford, Tom; Stewart, Helena; Thorsteinsson, Throstur

    2016-01-01

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

  16. Electrodynamic coupling between ionospheric convection patterns in the northern and southern hemispheres

    Directory of Open Access Journals (Sweden)

    V. E. Zakharov

    Full Text Available A numerical model of the high-latitude ionospheric electric field is presented. To perform the calculations, a model of the field-aligned current source is proposed. The electric field patterns are calculated consistently both in the northern and southern hemispheres. Effects of season, universal time, solar and geomagnetic activity, the neutral atmosphere winds, and of the IMF sector structure are considered. In particular, dynamics of the parameters of convection cells are investigated that depend on the action of these factors. Comparison of the results with experimental data is carried out.

  17. A short circuit in thermohaline circulation: A cause for northern hemisphere glaciation?

    Science.gov (United States)

    Driscoll; Haug

    1998-10-16

    The cause of Northern Hemisphere glaciation about 3 million years ago remains uncertain. Closing the Panamanian Isthmus increased thermohaline circulation and enhanced moisture supply to high latitudes, but the accompanying heat would have inhibited ice growth. One possible solution is that enhanced moisture transported to Eurasia also enhanced freshwater delivery to the Arctic via Siberian rivers. Freshwater input to the Arctic would facilitate sea ice formation, increase the albedo, and isolate the high heat capacity of the ocean from the atmosphere. It would also act as a negative feedback on the efficiency of the "conveyor belt" heat pump.

  18. Lunar impact basins: New data for the nearside northern high latitudes and eastern limb from the second Galileo flyby

    Science.gov (United States)

    Head, J. W.; Belton, M.; Greeley, R.; Pieters, C.; Fischer, E.; Sunshine, J.; Klaasen, K.; Mcewen, A.; Becker, T.; Neukum, G.

    1993-01-01

    During the December 1992 Galileo Earth/Moon encounter the northern half of the nearside, the eastern limb, and parts of the western farside of the Moon were illuminated and in view, a geometry that was complementary to the first lunar encounter in December, 1990, which obtained images of the western limb and eastern farside. The Galileo Solid State Imaging System (SSI) obtained multispectral images for these regions during the second encounter and color ratio composite images were compiled using combinations of band ratios chosen on the basis of telescopic spectra and laboratory spectra of lunar samples. Ratios of images taken at 0.41 and 0.76 micron are sensitive to changes in the slope in the visible portion of the spectrum, and ratios of 0.99 and 0.76 micron relate to the strength of near-infrared absorptions due to iron-rich mafic minerals (0.76/0.99 ratio) such as olivine and pyroxene. Results of the analyses of the compositional diversity of the crust, maria, and Copernican craters are presented elsewhere. Primary objectives for lunar basin analysis for the second encounter include analysis of: the north polar region and the Humboldtianum basin; the characteristics of the Imbrium basin along its northern border and the symmetry of associated deposits; the origin of light plains north of Mare Frigoris and associated with several other basins; the nature and significance of pre-basin substrate; the utilization of the stereo capability to assess subtle basis structure; the identification of previously unrecognized ancient basins; basin deposits and structure for limb and farside basins; and assessment of evidence for proposed ancient basins. These data and results will be applied to addressing general problems of evaluation of the nature and origin of basin deposits, investigation of mode of ejecta emplacement and ejecta mixing, analysis of the origin of light plains deposits, analysis of basin deposit symmetry/asymmetry, investigation of basin depth of

  19. Environmental constraints on plant transpiration and the hydrological implications in a northern high latitude upland headwater catchment

    Science.gov (United States)

    Wang, H.; Tetzlaff, D.; Soulsby, C.

    2016-12-01

    Vegetation affects water, carbon and energy transfer in the soil-plant-atmosphere system and mediates land-atmosphere interactions by altering surface albedo, roughness and soil macro-porosity, intercepting rainfall and transpiring water from soil layers. Vegetation water use (Ec) is regulated by stomata behaviour which is constrained by environmental variables including radiation, temperature, vapour pressure deficit, and soil water content. The relative influences of these variables on Ec are usually site specific reflecting climate and species differences. At a catchment scale, Ec can account for a large proportion of total evapotranspiration, and hence regulates water storage and fluxes in the soils, groundwater reservoirs and streams. In this study, we estimated transpiration from short vegetation (Calluna vulgaris) using the Maximum Entropy Production model (MEP), and measured sap flow of two forest plantations, together with meteorological variables, soil moisture and streamflow in an upland headwater catchment in northern Scotland. Our objectives were to investigate the environmental constraints on Ec in this wet humid and cool summer climate, and the hydrological responses and regulations of Ec in terms of rainfall and streamflow. Results will assist the assessment of hydrological implications of land management in terms of afforestation/deforestation.

  20. Atmospheric Blocking in the Northern Hemisphere.

    Science.gov (United States)

    Knox, John Lewis

    Blocking is generally understood as the obstruction on a large scale of the normal west - to - east motion of mid-latitude pressure systems. It is a persistent phenomenon lasting from one to several weeks and the resulting prolonged weather regimes may have serious economic and social consequences. The recent Northern Hemisphere winters, starting with 1976 -77, featured unusually large circulation anomalies, many of which can be directly related to prolonged episodes of large scale blocking. The intent of this study is to investigate the statistics and certain diagnostics of blocking in the Northern Hemisphere. The first of the three primary objectives is to present and interpret the spatial and temporal distribution of blocking during the past 33 years. We develop objective identification criteria, adaptable to machine processing methods, by relating the blocking anticyclone to its associated positive anomaly of 5-day mean 500MB height. Anomalies meeting the criteria are called 'blocking signatures.' We present the seasonal frequency of occurrence of these signatures by longitude and by area. The results are in good agreement with published studies for the oceans, but they also reveal a high frequency of blocking signatures over the Northeastern Canadian Archipelago. This result, dubbed the 'Baffin Island Paradox' is further investigated and rationalized. A catalogue has been prepared which identifies the date, centre location and magnitude of every blocking signature which occurred from January 1, 1946 to December 31, 1978. A supplementary Catalogue identifies sequences of these signatures corresponding to actual blocking episodes. The second objective is to investigate whether regions with high incidence of blocking, in either the developing or the mature stage, features non-Gaussian distributions of 5-day mean geopotential. During winter, fields of significantly low kurtosis are found in certain mid-latitude regions where the genesis and amplification of

  1. 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.

  2. The evolution of the high-latitude blocked anticyclone during the 2012 winter in the Northern hemisphere

    Science.gov (United States)

    Sokolikhina, Natalia; Kislov, Alexander; Surkova, Galina; Semenov, Eugeny

    2017-04-01

    At present time on the Department of Meteorology and Climatology of the Faculty of Geography of MSU by Lomonosov, the topic, concerned to the dangerous hydrometeorologic events over the Russia, is investigated. A great deal of attention is given to the study of the extremely strong warming in Arctic. Earlier the processes of the synoptic scale during the 2011-2012 winter, which was the most warmest in Arctic for the whole history of meteorologic observations, were investigated. It was shown, that the reason of such an event was the situation of the westerly wind blocking. At present study the method of the analysis of the vortex as of the united formation was used. And the factors, influencing on its evolution, were obtained. Keywords: dangerous hydrometeorologic events, warming in Arctic, westerly wind blocking, analysis of the vortex as of the united formation

  3. Multisensor Analyzed Sea Ice Extent - Northern Hemisphere (MASIE-NH)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Multisensor Analyzed Sea Ice Extent Northern Hemisphere (MASIE-NH) products provide measurements of daily sea ice extent and sea ice edge boundary for the...

  4. ISLSCP II Northern Hemisphere Monthly Snow Cover Extent

    Data.gov (United States)

    National Aeronautics and Space Administration — This ISLSCP data set is derived from the National Snow and Ice Data Center (NSIDC) Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent product which...

  5. Prediction Center (CPC) Tropical/ Northern Hemisphere Teleconnection Pattern Index

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Monthly tabulated index of the Tropical/ Northern Hemisphere teleconnection pattern. The data spans the period 1950 to present. The index is derived from a rotated...

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

    Science.gov (United States)

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

    2017-01-01

    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

  7. Northern Hemisphere Gullies on Mars: Analysis of Spacecraft Data and Implications for Formation Mechanisms

    Science.gov (United States)

    Heldmann, J. L.; Johansson, H.; Carlsson, E.; Mellon, M. T.

    2005-01-01

    The origin of geologically recent gullies on Mars has remained controversial since the discovery of these features by Malin and Edgett in 2000. Numerous models have been proposed which invoke various physical processes as well as various agents of erosion to explain the origin of the Martian gullies. Hypotheses to explain the formation of the gullies invoke shallow liquid water aquifers, deep liquid water aquifers, melting ground ice, snowmelt, dry landslides, and carbon dioxide aquifers. We test the validity of such gully formation mechanisms by analyzing data from the Mars Global Surveyor and Mars Odyssey spacecrafts to uncover trends in the dimensional and physical properties of the gullies and their surrounding terrain. A similar study has previously been completed for gullies located in the southern hemisphere of Mars. The work presented here focuses exclusively on gullies in the northern hemisphere based on the identification of 136 Mars Orbiter Camera (MOC) images containing clear evidence of gully landforms, distributed in the northern mid and high latitudes. These sites have been analyzed in combination with Mars Orbiter Laser Altimeter (MOLA), Thermal Emission Spectrometer (TES), and Gamma Ray Spectrometer (GRS) data to provide quantitative measurements of numerous gully characteristics. Parameters measured include apparent source depth and distribution, vertical and horizontal dimensions, slopes, compass orientations, near-surface ice content, and factors controlling present-day climatic conditions.

  8. Atmospheric circulation in northern hemisphere and north atlantic oscillation

    Directory of Open Access Journals (Sweden)

    Александр Вадимович Холопцев

    2015-08-01

    Full Text Available Conditions under which statistical connections of interannual changes of repitition duration periods in Northern hemisphere of elementary circulation mechanisms associated to meridional northern and meridional southern groups with variations of North Atlantic oscillation are significant were revealed. It is shown, that the characteristics changes of these connections taking place in modern period can be caused by distribution changes of distribution of sea surface temperatures

  9. Pathways of high-latitude dust in the North Atlantic

    Science.gov (United States)

    Baddock, Matthew C.; Mockford, Tom; Bullard, Joanna E.; Thorsteinsson, Throstur

    2017-02-01

    The contribution of mineral dust from high-latitude sources has remained an under-examined feature of the global dust cycle. Dust events originating at high latitudes can provide inputs of aeolian sediment to regions lying well outside the subtropical dust belt. Constraining the seasonal variability and preferential pathways of dust from high-latitude sources is important for understanding the potential impacts that the dust may have on wider environmental systems, such as nearby marine or cryospheric domains. This study quantifies dust pathways from two areas exhibiting different emission dynamics in the north and south of Iceland, which is a prominent Northern Hemisphere dust source. The analysis uses air parcel trajectory modelling, and for the first time for high-latitude sources, explicitly links all trajectory simulations to time-specific (meteorological) observations of suspended dust. This approach maximises the potential for trajectories to represent dust, and illustrates that trajectory climatologies not limited to dust can grossly overestimate the potential for dust transport. Preferential pathways emerge that demonstrate the role of Iceland in supplying dust to the Northern Atlantic and sub-Arctic oceans. For dust emitted from northern sources, a dominant route exists to the northeast, into the Norwegian, Greenland and Barents Seas, although there is also potential for delivery to the North Atlantic in summer months. From the southern sources, the primary pathway extends into the North Atlantic, with a high density of trajectories extending as far south as 50°N, particularly in spring and summer. Common to both southern and northern sources is a pathway to the west-southwest of Iceland into the Denmark Strait and towards Greenland. For trajectories simulated at ≤500 m, the vertical development of dust plumes from Iceland is limited, likely due to the stable air masses of the region suppressing the potential for vertical motion. Trajectories rarely

  10. Species boundaries in non-tropical Northern Hemisphere Owls

    NARCIS (Netherlands)

    Voous, K.H.

    1990-01-01

    A survey is presented of the status of species boundaries in nontropical Northern Hemisphere owls in order to investigate the reality of the biological and geographical species concept applied to these owls in current handbooks. At the same time the practicability of evolutionary systematics as

  11. Ecology of beech forests in the northern hemisphere

    NARCIS (Netherlands)

    Peters, R.

    1992-01-01

    Beech forests are dominated or codominated by at least one Fagus species. The beeches are a homogeneous group of 11 deciduous tree species growing in the Northern Hemisphere (Figure 1.1). They often dominate forest ecosystems throughout their ranges. The optimum for

  12. Climatology of semidiurnal lunar and solar tides at middle and high latitudes: Interhemispheric comparison

    Science.gov (United States)

    Conte, J. Federico; Chau, Jorge L.; Stober, Gunter; Pedatella, Nicholas; Maute, Astrid; Hoffmann, Peter; Janches, Diego; Fritts, David; Murphy, Damian J.

    2017-07-01

    The semidiurnal lunar and solar tides obtained from meteor radar measurements spanning from 2009 to 2013 observed at Davis (69°S) and Rio Grande (54°S) are presented and compared to the Northern Hemisphere ones at Andenes (69°N) and Juliusruh (54°N). Mean tidal differences for both intrahemispheric and interhemispheric scenarios are analyzed. Tidal behavior is also compared against numerical simulations during 2009 and 2013 sudden stratospheric warming (SSW) time periods. Possible influences in the Southern Hemisphere from the local stratosphere are also investigated using Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA 2) data sets. The main features of the mean zonal wind are similar in both hemispheres, i.e., stronger amplitudes over midlatitude locations, eastward winds during winter and westward below 90 km with eastward higher up during corresponding summer times. On the other hand, the semidiurnal solar tides observed in the Southern Hemisphere show clear differences when compared to the Northern Hemisphere and between middle- and high-latitude locations at the same hemisphere. These differences are even larger for the semidiurnal lunar tide, which shows stronger amplitudes from October to March and March to October, over Davis and Rio Grande, respectively. Our results indicate that the lunar tides over the Southern Hemisphere midlatitudes are more prone to react to the Northern Hemisphere stratospheric polar vortex influences, in agreement with numerical simulations, particularly for the time of the 2013 SSW.

  13. An overview of Fukushima radionuclides measured in the northern hemisphere.

    Science.gov (United States)

    Thakur, P; Ballard, S; Nelson, R

    2013-08-01

    The Great East Japan Earthquake and tsunami on March 11, 2011 resulted in the tragic accident at the Fukushima Nuclear Power Plant (NPP) and subsequently uncontrolled release of radioactive contaminants into the atmosphere. This review article attempts to compile and interpret data collected by various national and international monitoring networks in response to the Fukushima releases across the northern hemisphere. The majority of the releases occurred during the period March 12-22 with a maximum release phase from March 14-17, 2011. The radioactivity released was dominated by volatile fission products including isotopes of the noble gases (xenon and krypton), iodine, cesium, and tellurium. The radioactive gases and particles released in the accident were dispersed over the middle latitudes of the entire northern hemisphere and for the first time also measured in the southern Hemisphere. Isotopes of iodine and cesium were detected in air, water, milk and food samples collected across the entire northern hemisphere. Elevated levels of fission products were detected from March to May 2011 at many locations over the northern hemisphere. This article focuses on the most prevalent cesium and iodine isotopes, but other secondary isotopes are also discussed. Spatial and temporal patterns and differences are contrasted. The activity ratios of (131)I/(137)Cs and (134)Cs/(137)Cs measured at several locations are evaluated to gain an insight into the fuel burn-up, the inventory of radionuclides in the reactor and the isotopic signature of the accident. It is important to note that all of the radiation levels detected outside of Japan have been very low and are well below any level of public and environmental hazard. Published by Elsevier B.V.

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

    Directory of Open Access Journals (Sweden)

    M. Förster

    2008-06-01

    Full Text Available 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.

  15. The Western Equatorial Pacific Thermal Evolution During the Onset of the Northern Hemisphere Glaciation

    Science.gov (United States)

    Medina-Elizalde, M. A.; Lea, D. W.

    2006-12-01

    During the late Pliocene, between 3 Ma and 2.5 Ma before present (B.P.), the climate of the Earth underwent profound changes which ultimately led to the onset of the Northern Hemisphere Glaciation (NHG). A number of hypotheses have been proposed to explain the secular cooling in high latitude and eastern boundary upwelling regions, suggested by foraminiferal oxygen isotopic and sea surface temperature proxy records, associated to the onset of the NHG. We present a sea surface temperature (SST) record (1.8 kyr resolution) based on planktonic foraminiferal Mg/Ca from the western equatorial Pacific (WEP) warm pool ODP Hole 806B, which spans ~500,000 years from 2.3 to 2.8 Ma B.P. Foraminiferal oxygen isotopic features are apparent in the Mg/Ca-SST record. Preliminary cross spectral analyses results between ODP Hole 806B G. ruber o18 and Mg/Ca-SS indicate that these signals are coherent with each other in the 41 kyr periodicity band, and that SSTs lead o18 changes by 1.6 +-1.2 kyrs. The largest SST range in the record is observed between marine isotope stage 99 and 98 (3 degC). Absolute SSTs and the glacial-interglacial (G-I) SST range are similar to those observed during the Pleistocene. The suggestion that warm pool SSTs were similar during the Pleistocene is intriguing in light of the evidence that indicates that high latitude and eastern boundary upwelling regions were significantly warmer during the Pliocene (Wara et al., 2005, Fedorov et al., 2006). We consider the possibility that other factors could affect the absolute calibration of Mg/Ca-based SSTs in the Pliocene.

  16. 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).

  17. Changes in autumn senescence in northern hemisphere deciduous trees: a meta-analysis of autumn phenology studies.

    Science.gov (United States)

    Gill, Allison L; Gallinat, Amanda S; Sanders-DeMott, Rebecca; Rigden, Angela J; Short Gianotti, Daniel J; Mantooth, Joshua A; Templer, Pamela H

    2015-11-01

    Many individual studies have shown that the timing of leaf senescence in boreal and temperate deciduous forests in the northern hemisphere is influenced by rising temperatures, but there is limited consensus on the magnitude, direction and spatial extent of this relationship. A meta-analysis was conducted of published studies from the peer-reviewed literature that reported autumn senescence dates for deciduous trees in the northern hemisphere, encompassing 64 publications with observations ranging from 1931 to 2010. Among the meteorological measurements examined, October temperatures were the strongest predictors of date of senescence, followed by cooling degree-days, latitude, photoperiod and, lastly, total monthly precipitation, although the strength of the relationships differed between high- and low-latitude sites. Autumn leaf senescence has been significantly more delayed at low (25° to 49°N) than high (50° to 70°N) latitudes across the northern hemisphere, with senescence across high-latitude sites more sensitive to the effects of photoperiod and low-latitude sites more sensitive to the effects of temperature. Delays in leaf senescence over time were stronger in North America compared with Europe and Asia. The results indicate that leaf senescence has been delayed over time and in response to temperature, although low-latitude sites show significantly stronger delays in senescence over time than high-latitude sites. While temperature alone may be a reasonable predictor of the date of leaf senescence when examining a broad suite of sites, it is important to consider that temperature-induced changes in senescence at high-latitude sites are likely to be constrained by the influence of photoperiod. Ecosystem-level differences in the mechanisms that control the timing of leaf senescence may affect both plant community interactions and ecosystem carbon storage as global temperatures increase over the next century. © The Author 2015. Published by Oxford

  18. Peatmoss (Sphagnum) diversification associated with Miocene Northern Hemisphere climatic cooling?

    Science.gov (United States)

    Shaw, A Jonathan; Devos, Nicolas; Cox, Cymon J; Boles, Sandra B; Shaw, Blanka; Buchanan, Alex M; Cave, Lynette; Seppelt, Rodney

    2010-06-01

    Global climate changes sometimes spark biological radiations that can feed back to effect significant ecological impacts. Northern Hemisphere peatlands dominated by living and dead peatmosses (Sphagnum) harbor almost 30% of the global soil carbon pool and have functioned as a net carbon sink throughout the Holocene, and probably since the late Tertiary. Before that time, northern latitudes were dominated by tropical and temperate plant groups and ecosystems. Phylogenetic analyses of mosses (phylum Bryophyta) based on nucleotide sequences from the plastid, mitochondrial, and nuclear genomes indicate that most species of Sphagnum are of recent origin (ca. Sphagnum species are not only well-adapted to boreal peatlands, they create the conditions that promote development of peatlands. The recent radiation that gave rise to extant diversity of peatmosses is temporally associated with Miocene climatic cooling in the Northern Hemisphere. The evolution of Sphagnum has had profound influences on global biogeochemistry because of the unique biochemical, physiological, and morphological features of these plants, both while alive and after death. 2010 Elsevier Inc. All rights reserved.

  19. Highest treeline in the Northern Hemisphere found in Southern Tibet

    OpenAIRE

    Miehe, Georg; Miehe, Sabine; Vogel, Jonas; Co, Sonam; Duo, La

    2007-01-01

    This article was first published in "Mountain Research and Development" (MRD), vol 27 no 2, pp 169-173. The rights of reproduction remain with the co-copyright holders: The International Mountain Society (IMS) and the United Nations University (UNU), c/o MRD Editorial Office, Bern, Switzerland (www.mrd-journal.org). Three new records of the highest treelines in the northern hemisphere are presented here, based on the definition of a “tree.” The tree species with the highest tre...

  20. Temporal Changes in Coupled Vegetation Phenology and Productivity are Biome-Specific in the Northern Hemisphere

    Directory of Open Access Journals (Sweden)

    Lanhui Wang

    2017-12-01

    Full Text Available Global warming has greatly stimulated vegetation growth through both extending the growing season and promoting photosynthesis in the Northern Hemisphere (NH. Analyzing the combined dynamics of such trends can potentially improve our current understanding on changes in vegetation functioning and the complex relationship between anthropogenic and climatic drivers. This study aims to analyze the relationships (long-term trends and correlations of length of vegetation growing season (LOS and vegetation productivity assessed by the growing season NDVI integral (GSI in the NH (>30°N to study any dependency of major biomes that are characterized by different imprint from anthropogenic influence. Spatial patterns of converging/diverging trends in LOS and GSI and temporal changes in the coupling between LOS and GSI are analyzed for major biomes at hemispheric and continental scales from the third generation Global Inventory Monitoring and Modeling Studies (GIMMS Normalized Difference Vegetation Index (NDVI dataset for a 32-year period (1982–2013. A quarter area of the NH is covered by converging trends (consistent significant trends in LOS and GSI, whereas diverging trends (opposing significant trends in LOS and GSI cover about 6% of the region. Diverging trends are observed mainly in high latitudes and arid/semi-arid areas of non-forest biomes (shrublands, savannas, and grasslands, whereas forest biomes and croplands are primarily characterized by converging trends. The study shows spatially-distinct and biome-specific patterns between the continental land masses of Eurasia (EA and North America (NA. Finally, areas of high positive correlation between LOS and GSI showed to increase during the period of analysis, with areas of significant positive trends in correlation being more widespread in NA as compared to EA. The temporal changes in the coupled vegetation phenology and productivity suggest complex relationships and interactions that are induced

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

    Directory of Open Access Journals (Sweden)

    P. Prikryl

    2015-06-01

    Full Text Available 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.

  2. Seasonal vegetation response to climate change in the Northern Hemisphere (1982-2013)

    Science.gov (United States)

    Kong, Dongdong; Zhang, Qiang; Singh, Vijay P.; Shi, Peijun

    2017-01-01

    This study investigated vegetation response to climate change exhibited by temperature, soil moisture, and solar radiation at Northern Hemisphere (NH) scale during the growing season and seasonal periods by analyzing satellite observations of vegetation activity and climatic data for a period of 1982-2013. Generally, About 75.8% of NH was dominated by increasing NDVI3g during growing season in 1982-2013, and 50.7% significantly increase. Autumn NDVI3g is the main cause, with 77.7% increase (45.0% significantly increase). The increasing tendency of greenness was stalled and even shifted to vegetation browning after 1994-1997 specifically in Central Europe, Northern North America, and Central Siberia. NDVI3g increase during the growing season shifts from 0.017 year- 1 to 0.006 year- 1, which mainly due to decreased spring NDVI3g and slowdown of summer NDVI3g increase. Specifically, three time intervals were identified with relatively peak NDVI3g, i.e., 1990, 1997 and 2010, and three time intervals with trough NDVI3g, i.e., 1983, 1992-1994, 2002-2005. The factors potentially influencing vegetation growth in different parts of NH are complex and varied. Temperature is recognized as the critical factor behind vegetation greenness in high latitudes especially for spring and autumn temperature, in North America and Siberia. Soil moisture is the key factor influencing vegetation growth in central Canada, eastern USA and western Africa. And solar radiation is corresponding to vegetation trend in North part of North America, eastern China. This study helps identify key factors for vegetation changes and understand vegetation response to climate change at NH scale.

  3. 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.

  4. Evaluation of coupled ocean-atmosphere simulations of the mid-Holocene using palaeovegetation data from the northern hemisphere extratropics

    Energy Technology Data Exchange (ETDEWEB)

    Wohlfahrt, J.; Harrison, S.P. [University of Bristol, School of Geographical Sciences, Bristol (United Kingdom); Max Planck Institute for Biogeochemistry, PO Box 10 01 64, Jena (Germany); Braconnot, P. [Lab. CNRS-CEA, Lab. des Sciences du Climat et de l' Environnement, CEA/Saclay Gif sur Yvette (France); Hewitt, C.D. [Hadley Centre for Climate Prediction and Research, Met Office, Devon (United Kingdom); Kitoh, A. [Meteorological Research Institute, Climate Research Department, Tsukuba, Ibaraki (Japan); Mikolajewicz, U. [Max-Planck-Institute for Meteorologie, Hamburg (Germany); Otto-Bliesner, B.L. [National Control for Atmospheric Research, Climate and Global Dynamics Division, Boulder, CO (United States); Weber, S.L. [Royal Netherlands Meteorological Institute, P.O. Box 201, DeBilt (Netherlands)

    2008-12-15

    We have used the BIOME4 biogeography-biochemistry model and comparison with palaeovegetation data to evaluate the response of six ocean-atmosphere general circulation models to mid-Holocene changes in orbital forcing in the mid- to high-latitudes of the northern hemisphere. All the models produce: (a) a northward shift of the northern limit of boreal forest, in response to simulated summer warming in high-latitudes. The northward shift is markedly asymmetric, with larger shifts in Eurasia than in North America; (b) an expansion of xerophytic vegetation in mid-continental North America and Eurasia, in response to increased temperatures during the growing season; (c) a northward expansion of temperate forests in eastern North America, in response to simulated winter warming. The northward shift of the northern limit of boreal forest and the northward expansion of temperate forests in North America are supported by palaeovegetation data. The expansion of xerophytic vegetation in mid-continental North America is consistent with palaeodata, although the extent may be over-estimated. The simulated expansion of xerophytic vegetation in Eurasia is not supported by the data. Analysis of an asynchronous coupling of one model to an equilibrium-vegetation model suggests vegetation feedback exacerbates this mid-continental drying and produces conditions more unlike the observations. Not all features of the simulations are robust: some models produce winter warming over Europe while others produce winter cooling. As a result, some models show a northward shift of temperate forests (consistent with, though less marked than, the expansion shown by data) and others produce a reduction in temperate forests. Elucidation of the cause of such differences is a focus of the current phase of the Palaeoclimate Modelling Intercomparison Project. (orig.)

  5. Tracing Fukushima Radionuclides in the Northern Hemisphere -An Overview

    Science.gov (United States)

    Thakur, Punam; Ballard, Sally; Nelson, Roger

    2013-04-01

    A massive 9.0 earthquake and ensuing tsunami struck the northern coast of the Honshu-island, Japan on March 11, 2011 and severely damaged the electric system of the Fukushima- Daiichi Nuclear Power Plant (NPP). The structural damage to the plant disabled the reactor's cooling systems. Subsequent fires, a hydrogen explosion and possible partial core meltdowns released radioactive fission products into the atmosphere. The atmospheric release from the crippled Fukushima NPP started on March 12, 2011 with a maximum release phase from March 14 to 17. The radioactivity released was dominated by volatile fission products including isotopes of the noble gases xenon (Xe-133) and krypton (Kr-85); iodine (I-131,I-132); cesium (Cs-134,Cs-136,Cs-137); and tellurium (Te-132). The non-volatile radionuclides such as isotopes of strontium and plutonium are believed to have remained largely inside the reactor, although there is evidence of plutonium release into the environment. Global air monitoring across the northern hemisphere was increased following the first reports of atmospheric releases. According to the source term, declared by the Nuclear and Industrial Safety Agency (NISA) of Japan), approximately 160 PBq (1 PBq (Peta Becquerel = 10^15 Bq)) of I-131 and 15 PBq of Cs-137 (or 770 PBq "iodine-131 equivalent"), were released into the atmosphere. The 770 PBq figure is about 15% of the Chernobyl release of 5200 PBq of "iodine-131 equivalent". For the assessment of contamination after the accident and to track the transport time of the contaminated air mass released from the Fukushima NPP across the globe, several model calculations were performed by various research groups. All model calculations suggested long-range transport of radionuclides from the damaged Fukushima NPP towards the North American Continent to Europe and to Central Asia. As a result, an elevated level of Fukushima radionuclides were detected in air, rain, milk, and vegetation samples across the northern

  6. Observations on nivation and its geomorphological effects in mountains at high latitude (with Mt. Njulla Massif in Northern Sweden as example

    Directory of Open Access Journals (Sweden)

    Raczkowska, Zofia

    1990-12-01

    Full Text Available This paper presents the geomorphological role of snow patches In the remodeling of mountain slopes in the periglacial zone based on the results of morphological mapping of Mt. Njulla region, Northern Sweden. Effectiveness of nivation is strongly controlled by geological structure. On the Eastern slope, at the foot of the hillside, nivation processes play a critical role in the creation of numerous transverse nival hollows and cryoplanation terraces. On the western slope, meltwater, originating from snow patches, facilitates weathering and transportation of wastes downslope. Vegetation of the studied region is influenced by nivation. Effects of nivation are limited to reshaping of the relief.

    [es] Este trabajo presenta el papel de las manchas de nieve en la evolución de laderas de montaña de la zona periglaciar, apoyándose en los resultados de cartografía geomorfológica de la región de Mt. Njulla, Norte de Suecia. La eficacia de la nivación está fuertemente controlada por la estructura geológica. En la vertiente oriental, al pie de la ladera, los procesos de nivación juegan un papel crítico en la creación de nichos nivales transversales y de terrazas de crioplanación. En la vertiente occidental, el agua de fusión, que surge de las manchas de nieve, facilita la meteorización y el transporte de materiales ladera abajo. La vegetación de la región estudiada también se halla Influida por la vegetación. Sin embargo, los efectos de la nivación se limitan a retoques en el relieve.
    [fr] Dans cette étude on a discuté le rôle géomorphologique des taches de neige dans la transformation du relief dans la zone périglaciére, à la base de l'analyse de la carte morphologique de la région de Njulla, au nord de la Suède. On a constaté un rapport évident entre les effets des processus de nivation et la structure géologique. Sur le versant est formé sur le front de l'escarpement structural, les processus de nivation

  7. Impacts of four northern-hemisphere teleconnection patterns on atmospheric circulations over Eurasia and the Pacific

    Science.gov (United States)

    Gao, Tao; Yu, Jin-yi; Paek, Houk

    2017-08-01

    The impacts of four teleconnection patterns on atmospheric circulation components over Eurasia and the Pacific region, from low to high latitudes in the Northern Hemisphere (NH), were investigated comprehensively in this study. The patterns, as identified by the Climate Prediction Center (USA), were the East Atlantic (EA), East Atlantic/Western Russia (EAWR), Polar/Eurasia (POLEUR), and Scandinavian (SCAND) teleconnections. Results indicate that the EA pattern is closely related to the intensity of the subtropical high over different sectors of the NH in all seasons, especially boreal winter. The wave train associated with this pattern serves as an atmospheric bridge that transfers Atlantic influence into the low-latitude region of the Pacific. In addition, the amplitudes of the EAWR, SCAND, and POLEUR patterns were found to have considerable control on the "Vangengeim-Girs" circulation that forms over the Atlantic-Eurasian region in winter or spring. The EA and EAWR mainly affect the westerlies in winter and spring and the POLEUR and SCAND, respectively, in summer and winter. Strong westerlies confine the extension of the North Polar vortex, which generally results in a small weak vortex and a shallow East Asian trough located in a position further east than normal. Furthermore, the North Polar vortex presents significant connections with the patterns during winter and summer. Analyses in this work suggest that the teleconnection patterns in summer could be driven, at least partly, by the Atlantic Multidecadal Oscillation, which to some degree might transmit the influence of the Atlantic Ocean to Eurasia and the Pacific region.

  8. Madden-Julian Oscillation Teleconnections and Their Influence on Northern Hemisphere Winter Blocking

    Science.gov (United States)

    Henderson, Stephanie A.

    Winter blocking events are characterized by persistent and quasi-stationary patterns that re-direct precipitation and air masses, leading to long-lasting extreme winter weather. Studies have shown that the teleconnection patterns forced by the primary mode of tropical intraseasonal variability, the Madden-Julian Oscillation (MJO), influence extratropical factors associated with blocking, such as the North Atlantic Oscillation. However, the influence of the MJO on winter blocking is not well understood. Understanding this relationship may improve the mid-range forecasting of winter blocking and the associated weather extremes. The impact of the MJO on Northern Hemisphere winter blocking is examined using a two-dimensional blocking index. Results suggest that all MJO phases demonstrate significant changes in west and central Pacific high-latitude blocking. East Pacific and Atlantic blocking are significantly suppressed following phase 3 of the MJO, characterized by anomalous convection in the tropical East Indian Ocean and suppressed convection in the west Pacific. A significant increase in east Pacific and Atlantic blocking follows the opposite-signed MJO heating during MJO phase 7. Over Europe, blocking is suppressed following MJO phase 4 and significantly increased after MJO phase 6. Results suggest that the European blocking increase may be due to two precursors: 1) a pre-existing anomalous Atlantic anticyclone, and 2) a negative Pacific North American (PNA) pattern triggered by the MJO. The influence of the MJO on winter blocking may be different if a change occurs to the basic state and/or MJO heating, such as during El Nino - Southern Oscillation (ENSO) events. MJO teleconnections during ENSO events are examined using composite analysis and a nonlinear baroclinic model and their influence of winter high-latitude blocking is discussed. Results demonstrate that the ENSO-altered MJO teleconnection patterns significantly influence Pacific and Atlantic blocking and

  9. Multigene Phylogeography of Bactrocera caudata (Insecta: Tephritidae): Distinct Genetic Lineages in Northern and Southern Hemispheres.

    Science.gov (United States)

    Yong, Hoi-Sen; Lim, Phaik-Eem; Tan, Ji; Song, Sze-Looi; Suana, I Wayan; Eamsobhana, Praphathip

    2015-01-01

    Bactrocera caudata is a pest of pumpkin flower. Specimens of B. caudata from the northern hemisphere (mainland Asia) and southern hemisphere (Indonesia) were analysed using the partial DNA sequences of the nuclear 28S rRNA and internal transcribed spacer region 2 (ITS-2) genes, and the mitochondrial cytochrome c oxidase subunit I (COI), cytochrome c oxidase subunit II (COII) and 16S rRNA genes. The COI, COII, 16S rDNA and concatenated COI+COII+16S and COI+COII+16S+28S+ITS-2 nucleotide sequences revealed that B. caudata from the northern hemisphere (Peninsular Malaysia, East Malaysia, Thailand) was distinctly different from the southern hemisphere (Indonesia: Java, Bali and Lombok), without common haplotype between them. Phylogenetic analysis revealed two distinct clades (northern and southern hemispheres), indicating distinct genetic lineage. The uncorrected 'p' distance for the concatenated COI+COII+16S nucleotide sequences between the taxa from the northern and southern hemispheres ('p' = 4.46-4.94%) was several folds higher than the 'p' distance for the taxa in the northern hemisphere ('p' = 0.00-0.77%) and the southern hemisphere ('p' = 0.00%). This distinct difference was also reflected by concatenated COI+COII+16S+28S+ITS-2 nucleotide sequences with an uncorrected 'p' distance of 2.34-2.69% between the taxa of northern and southern hemispheres. In accordance with the type locality the Indonesian taxa belong to the nominal species. Thus the taxa from the northern hemisphere, if they were to constitute a cryptic species of the B. caudata species complex based on molecular data, need to be formally described as a new species. The Thailand and Malaysian B. caudata populations in the northern hemisphere showed distinct genetic structure and phylogeographic pattern.

  10. Isotopic source signatures for atmospheric lead: the Northern Hemisphere

    Science.gov (United States)

    Bollhöfer, A.; Rosman, K. J. R.

    2001-06-01

    Aerosols collected between 1994 and 1999 at more than 80 different sites affecting the atmospheric composition of the Northern Hemisphere have been measured for their 206Pb/ 207Pb, 208Pb/ 207Pb and 206Pb/ 204Pb ratios and Pb concentrations. The ratios are potentially useful for tracing sources of pollution and the movement of air-masses on a global scale. A change in isotopic composition compared to earlier measurements could be detected in the Western United States and parts of Europe, most probably due to long range transport of Pb pollution from China and Russia, respectively, and an increasing relative contribution of industrial Pb. The geographical variations found in the Pb isotopic composition of the aerosols made it possible to broadly characterize different regions via the 206Pb/ 207Pb ( 208Pb/ 207Pb) isotope ratios of the aerosols sampled: Eastern United States 1.173-1.231 (2.438-2.470); Western United States 1.159-1.188 (2.426-2.455); Canada 1.094-1.177 (2.365-2.438); Mexico 1.188-1.197 (2.452-2.463); Japan 1.153-1.162 (2.435-2.443); China 1.141-1.177 (2.435-2.465); Germany 1.133-1.165 (2.405-2.440); Spain & France 1.097-1.142 (2.372-2.410); Northern Italy 1.148-1.160 (2.419 -2.430); Southern Italy 1.108-1.121 (2.376-2.387); Eastern Europe and Russia 1.112-1.164 (2.388-2.446); North Africa & Arabian Peninsula 1.096-1.153 (2.361-2.431).

  11. Jupiter's Northern Hemisphere in False Color (Time Set 1)

    Science.gov (United States)

    1997-01-01

    Mosaic of Jupiter's northern hemisphere between 10 and 50 degrees latitude. Jupiter's atmospheric circulation is dominated by alternating eastward and westward jets from equatorial to polar latitudes. The direction and speed of these jets in part determine the color and texture of the clouds seen in this mosaic. Also visible are several other common Jovian cloud features, including large white ovals, bright spots, dark spots, interacting vortices, and turbulent chaotic systems. The north-south dimension of each of the two interacting vortices in the upper half of the mosaic is about 3500 kilometers.This mosaic uses the Galileo imaging camera's three near-infrared wavelengths (756 nanometers, 727 nanometers, and 889 nanometers displayed in red, green, and blue) to show variations in cloud height and thickness. Light blue clouds are high and thin, reddish clouds are deep, and white clouds are high and thick. The clouds and haze over the ovals are high, extending into Jupiter's stratosphere. Dark purple most likely represents a high haze overlying a clear deep atmosphere. Galileo is the first spacecraft to distinguish cloud layers on Jupiter.The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  12. Polar vortex evolution during Northern Hemispheric winter 2004/05

    Directory of Open Access Journals (Sweden)

    T. Chshyolkova

    2007-06-01

    Full Text Available As a part of the project "Atmospheric Wave Influences upon the Winter Polar Vortices (0–100 km" of the CAWSES program, data from meteor and Medium Frequency radars at 12 locations and MetO (UK Meteorological Office global assimilated fields have been analyzed for the first campaign during the Northern Hemispheric winter of 2004/05. The stratospheric state has been described using the conventional zonal mean parameters as well as Q-diagnostic, which allows consideration of the longitudinal variability. The stratosphere was cold during winter of 2004/05, and the polar vortex was relatively strong during most of the winter with relatively weak disturbances occurring at the end of December and the end of January. For this winter the strongest deformation with the splitting of the polar vortex in the lower stratosphere was observed at the end of February. Here the results show strong latitudinal and longitudinal differences that are evident in the stratospheric and mesospheric data sets at different stations. Eastward winds are weaker and oscillations with planetary wave periods have smaller amplitudes at more poleward stations. Accordingly, the occurrence, time and magnitude of the observed reversal of the zonal mesospheric winds associated with stratospheric disturbances depend on the local stratospheric conditions. In general, compared to previous years, the winter of 2004/05 could be characterized by weak planetary wave activity at stratospheric and mesospheric heights.

  13. Predicting weather regime transitions in Northern Hemisphere datasets

    Energy Technology Data Exchange (ETDEWEB)

    Kondrashov, D. [University of California, Department of Atmospheric and Oceanic Sciences and Institute of Geophysics and Planetary Physics, Los Angeles, CA (United States); Shen, J. [UCLA, Department of Statistics, Los Angeles, CA (United States); Berk, R. [UCLA, Department of Statistics, Los Angeles, CA (United States); University of Pennsylvania, Department of Criminology, Philadelphia, PA (United States); D' Andrea, F.; Ghil, M. [Ecole Normale Superieure, Departement Terre-Atmosphere-Ocean and Laboratoire de Meteorologie Dynamique (CNRS and IPSL), Paris Cedex 05 (France)

    2007-10-15

    A statistical learning method called random forests is applied to the prediction of transitions between weather regimes of wintertime Northern Hemisphere (NH) atmospheric low-frequency variability. A dataset composed of 55 winters of NH 700-mb geopotential height anomalies is used in the present study. A mixture model finds that the three Gaussian components that were statistically significant in earlier work are robust; they are the Pacific-North American (PNA) regime, its approximate reverse (the reverse PNA, or RNA), and the blocked phase of the North Atlantic Oscillation (BNAO). The most significant and robust transitions in the Markov chain generated by these regimes are PNA {yields} BNAO, PNA {yields} RNA and BNAO {yields} PNA. The break of a regime and subsequent onset of another one is forecast for these three transitions. Taking the relative costs of false positives and false negatives into account, the random-forests method shows useful forecasting skill. The calculations are carried out in the phase space spanned by a few leading empirical orthogonal functions of dataset variability. Plots of estimated response functions to a given predictor confirm the crucial influence of the exit angle on a preferred transition path. This result points to the dynamic origin of the transitions. (orig.)

  14. Late-season nitrogen applications in high-latitude strawberry ...

    African Journals Online (AJOL)

    USER

    2010-02-15

    Feb 15, 2010 ... The influence of late-season nitrogen (N) applications on the fruiting pattern of strawberry runner plants of 'Camarosa' was determined over three growing seasons. Experiments were carried out in high- latitude nurseries in northern California and fruit production trials were established in southern.

  15. Jupiter's Northern Hemisphere in False Color (Time Set 2)

    Science.gov (United States)

    1997-01-01

    Mosaic of Jupiter's northern hemisphere between 10 and 50 degrees latitude. Jupiter's atmospheric circulation is dominated by alternating eastward and westward jets from equatorial to polar latitudes. The direction and speed of these jets in part determine the color and texture of the clouds seen in this mosaic. Also visible are several other common Jovian cloud features, including large white ovals, bright spots, dark spots, interacting vortices, and turbulent chaotic systems. The north-south dimension of each of the two interacting vortices in the upper half of the mosaic is about 3500 kilometers.This mosaic uses the Galileo imaging camera's three near-infrared wavelengths (756 nanometers, 727 nanometers, and 889 nanometers displayed in red, green, and blue) to show variations in cloud height and thickness. Light blue clouds are high and thin, reddish clouds are deep, and white clouds are high and thick. The clouds and haze over the ovals are high, extending into Jupiter's stratosphere. Dark purple most likely represents a high haze overlying a clear deep atmosphere. Galileo is the first spacecraft to distinguish cloud layers on Jupiter.North is at the top. The images are projected on a sphere, with features being foreshortened towards the north. The smallest resolved features are tens of kilometers in size. These images were taken on April 3, 1997, at a range of 1.4 million kilometers by the Solid State Imaging system (CCD) on NASA's Galileo spacecraft.The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  16. Jupiter's Northern Hemisphere in False Color (Time Set 3)

    Science.gov (United States)

    1997-01-01

    Mosaic of Jupiter's northern hemisphere between 10 and 50 degrees latitude. Jupiter's atmospheric circulation is dominated by alternating eastward and westward jets from equatorial to polar latitudes. The direction and speed of these jets in part determine the color and texture of the clouds seen in this mosaic. Also visible are several other common Jovian cloud features, including large white ovals, bright spots, dark spots, interacting vortices, and turbulent chaotic systems. The north-south dimension of each of the two interacting vortices in the upper half of the mosaic is about 3500 kilometers.This mosaic uses the Galileo imaging camera's three near-infrared wavelengths (756 nanometers, 727 nanometers, and 889 nanometers displayed in red, green, and blue) to show variations in cloud height and thickness. Light blue clouds are high and thin, reddish clouds are deep, and white clouds are high and thick. The clouds and haze over the ovals are high, extending into Jupiter's stratosphere. Dark purple most likely represents a high haze overlying a clear deep atmosphere. Galileo is the first spacecraft to distinguish cloud layers on Jupiter.North is at the top. The images are projected on a sphere, with features being foreshortened towards the north. The planetary limb runs along the right edge of the mosaic. Cloud patterns appear foreshortened as they approach the limb. The smallest resolved features are tens of kilometers in size. These images were taken on April 3, 1997, at a range of 1.4 million kilometers by the Solid State Imaging system (CCD) on NASA's Galileo spacecraft.The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  17. Clusters of interannual sea ice variability in the northern hemisphere

    Science.gov (United States)

    Fučkar, Neven S.; Guemas, Virginie; Johnson, Nathaniel C.; Massonnet, François; Doblas-Reyes, Francisco J.

    2016-09-01

    We determine robust modes of the northern hemisphere (NH) sea ice variability on interannual timescales disentangled from the long-term climate change. This study focuses on sea ice thickness (SIT), reconstructed with an ocean-sea-ice general circulation model, because SIT has a potential to contain most of the interannual memory and predictability of the NH sea ice system. We use the K-means cluster analysis—one of clustering methods that partition data into groups or clusters based on their distances in the physical space without the typical constraints of other unsupervised learning statistical methods such as the widely-used principal component analysis. To adequately filter out climate change signal in the Arctic from 1958 to 2013 we have to approximate it with a 2nd degree polynomial. Using 2nd degree residuals of SIT leads to robust K-means cluster patterns, i.e. invariant to further increase of the polynomial degree. A set of clustering validity indices yields K = 3 as the optimal number of SIT clusters for all considered months and seasons with strong similarities in their cluster patterns. The associated time series of cluster occurrences exhibit predominant interannual persistence with mean timescale of about 2 years. Compositing analysis of the NH surface climate conditions associated with each cluster indicates that wind forcing seem to be the key factor driving the formation of interannual SIT cluster patterns during the winter. Climate memory in SIT with such interannual persistence could lead to increased predictability of the Artic sea ice cover beyond seasonal timescales.

  18. Was the extreme Northern Hemisphere greening in 2015 predictable?

    Science.gov (United States)

    Bastos, Ana; Ciais, Philippe; Park, Taejin; Zscheischler, Jakob; Yue, Chao; Barichivich, Jonathan; Myneni, Ranga B.; Peng, Shushi; Piao, Shilong; Zhu, Zaichun

    2017-04-01

    The year 2015 was, at the time, the warmest since 1880, and many regions in the Northern Hemisphere (NH) registered record breaking annual temperatures. Simultaneously, a remarkable and widespread growing season greening was observed over most of the NH in the record from the Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI). While the response of vegetation to climate change (i.e. the long term trend) is assumed to be predictable, it is still unclear whether it is also possible to predict the interannual variability in vegetation activity. Here, we evaluate whether the unprecedented magnitude and extent of the greening observed in 2015 corresponds to an expected response to the 2015 climate anomaly, or to a change in the sensitivity of NH vegetation to climate. We decompose NDVI into the long-term and interannual variability components, and find that the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) explain about half of NDVI interannual variability. This response is in addition to the long-term temperature and human-induced greening trend. We use a simple statistical approach to predict the NDVI anomaly in 2015, using the PDO and AMO states as predictors for interannual variability, and temperature and precipitation trends for the long-term component. We show that the 2015 anomaly can be predicted as an expected vegetation response to temperature and water-availability associated with the very strong state of the PDO in 2015. The link found between climate variability patterns and vegetation activity should contribute to increase the predictability of carbon-cycle processes at interannual time-scales, which may be relevant, for instance, for optimizing land-management strategies.

  19. Jupiter's Northern Hemisphere in Violet Light (Time Set 3)

    Science.gov (United States)

    1997-01-01

    Mosaic of Jupiter's northern hemisphere between 10 and 50 degrees latitude. Jupiter's atmospheric circulation is dominated by alternating eastward and westward jets from equatorial to polar latitudes. The direction and speed of these jets in part determine the color and texture of the clouds seen in this mosaic. Also visible are several other common Jovian cloud features, including large white ovals, bright spots, dark spots, interacting vortices, and turbulent chaotic systems. The north-south dimension of each of the two interacting vortices in the upper half of the mosaic is about 3500 kilometers. Light at 410 nanometers is affected by the sizes and compositions of cloud particles, as well as the trace chemicals that give Jupiter's clouds their colors. This mosaic shows the features of Jupiter's main visible cloud deck and the hazy cloud layer above it.North is at the top. The images are projected on a sphere, with features being foreshortened towards the north. The planetary limb runs along the right edge of the mosaic. Cloud patterns appear foreshortened as they approach the limb. The smallest resolved features are tens of kilometers in size. These images were taken on April 3, 1997, at a range of 1.4 million kilometers by the Solid State Imaging system (CCD) on NASA's Galileo spacecraft.The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  20. Jupiter's Northern Hemisphere in Violet Light (Time Set 1)

    Science.gov (United States)

    1997-01-01

    Mosaic of Jupiter's northern hemisphere between 10 and 50 degrees latitude. Jupiter's atmospheric circulation is dominated by alternating eastward and westward jets from equatorial to polar latitudes. The direction and speed of these jets in part determine the color and texture of the clouds seen in this mosaic. Also visible are several other common Jovian cloud features, including large white ovals, bright spots, dark spots, interacting vortices, and turbulent chaotic systems. The north-south dimension of each of the two interacting vortices in the upper half of the mosaic is about 3500 kilometers. Light at 410 nanometers is affected by the sizes and compositions of cloud particles, as well as the trace chemicals that give Jupiter's clouds their colors. This mosaic shows the features of Jupiter's main visible cloud deck and the hazy cloud layer above it.North is at the top. The images are projected on a sphere, with features being foreshortened towards the north. The smallest resolved features are tens of kilometers in size. These images were taken on April 3, 1997, at a range of 1.4 million kilometers by the Solid State Imaging system on NASA's Galileo spacecraft.The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  1. Jupiter's Northern Hemisphere in Violet Light (Time Set 2)

    Science.gov (United States)

    1997-01-01

    Mosaic of Jupiter's northern hemisphere between 10 and 50 degrees latitude. Jupiter's atmospheric circulation is dominated by alternating eastward and westward jets from equatorial to polar latitudes. The direction and speed of these jets in part determine the color and texture of the clouds seen in this mosaic. Also visible are several other common Jovian cloud features, including large white ovals, bright spots, dark spots, interacting vortices, and turbulent chaotic systems. The north-south dimension of each of the two interacting vortices in the upper half of the mosaic is about 3500 kilometers. Light at 410 nanometers is affected by the sizes and compositions of cloud particles, as well as the trace chemicals that give Jupiter's clouds their colors. This mosaic shows the features of Jupiter's main visible cloud deck and the hazy cloud layer above it.North is at the top. The images are projected on a sphere, with features being foreshortened towards the north. The smallest resolved features are tens of kilometers in size. These images were taken on April 3, 1997, at a range of 1.4 million kilometers by the Solid State Imaging system on NASA's Galileo spacecraft.The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  2. Synchronous marine pelagic regime shifts in the Northern Hemisphere

    Science.gov (United States)

    Beaugrand, G.; Conversi, A.; Chiba, S.; Edwards, M.; Fonda-Umani, S.; Greene, C.; Mantua, N.; Otto, S. A.; Reid, P. C.; Stachura, M. M.; Stemmann, L.; Sugisaki, H.

    2015-01-01

    Regime shifts are characterized by sudden, substantial and temporally persistent changes in the state of an ecosystem. They involve major biological modifications and often have important implications for exploited living resources. In this study, we examine whether regime shifts observed in 11 marine systems from two oceans and three regional seas in the Northern Hemisphere (NH) are synchronous, applying the same methodology to all. We primarily infer marine pelagic regime shifts from abrupt shifts in zooplankton assemblages, with the exception of the East Pacific where ecosystem changes are inferred from fish. Our analyses provide evidence for quasi-synchronicity of marine pelagic regime shifts both within and between ocean basins, although these shifts lie embedded within considerable regional variability at both year-to-year and lower-frequency time scales. In particular, a regime shift was detected in the late 1980s in many studied marine regions, although the exact year of the observed shift varied somewhat from one basin to another. Another regime shift was also identified in the mid- to late 1970s but concerned less marine regions. We subsequently analyse the main biological signals in relation to changes in NH temperature and pressure anomalies. The results suggest that the main factor synchronizing regime shifts on large scales is NH temperature; however, changes in atmospheric circulation also appear important. We propose that this quasi-synchronous shift could represent the variably lagged biological response in each ecosystem to a large-scale, NH change of the climatic system, involving both an increase in NH temperature and a strongly positive phase of the Arctic Oscillation. Further investigation is needed to determine the relative roles of changes in temperature and atmospheric pressure patterns and their resultant teleconnections in synchronizing regime shifts at large scales.

  3. Reconstructed North American, Eurasian, and Northern Hemisphere Snow Cover Extent, 1915-1997

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains time series of monthly snow cover extent (SCE) for North America, Eurasia, and the Northern Hemisphere from 1915 to 1997, based on snow cover...

  4. Northern Hemisphere EASE-Grid 2.0 Weekly Snow Cover and Sea Ice Extent

    Data.gov (United States)

    National Aeronautics and Space Administration — The Northern Hemisphere EASE-Grid 2.0 Weekly Snow Cover and Sea Ice Extent Version 4 product combine snow cover and sea ice extent at weekly intervals from 23...

  5. Northern Hemisphere Cyclone Locations and Characteristics from NCEP/NCAR Reanalysis Data

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set comprises a 50-year record of daily extratropical cyclone statistics computed for the Northern Hemisphere. Cyclone locations and characteristics were...

  6. NOAA Climate Data Record (CDR) of Northern Hemisphere (NH) Snow Cover Extent (SCE), Version 1

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This NOAA Climate Data Record (CDR) is a record for the Northern Hemisphere (NH) Snow Cover Extent (SCE) spanning from October 4, 1966 to present, updated monthly...

  7. Warm Season Subseasonal Variability and Climate Extremes in the Northern Hemisphere: The Role of Stationary Rossby Waves

    Science.gov (United States)

    Schubert, Siegfried; Wang, Hailan; Suarez, Max

    2010-01-01

    This study examines the nature of boreal summer subseasonal atmospheric variability based on the new NASA Modern-Era Retrospective analysis for Research and Applications (MERRA) for the period 1979-2010. An analysis of the June, July and August subseasonal 250hPa v-wind anomalies shows distinct Rossby wave-like structures that appear to be guided by the mean jets. On monthly subseasonal time scales, the leading waves (the first 10 rotated empirical orthogonal functions or REOFs of the 250hPa v-wind) explain about 50% of the Northern Hemisphere vwind variability, and account for more than 30% (60%) of the precipitation (surface temperature) variability over a number of regions of the northern middle and high latitudes, including the U.S. northern Great Plains, parts of Canada, Europe, and Russia. The first REOF in particular, consists of a Rossby wave that extends across northern Eurasia where it is a dominant contributor to monthly surface temperature and precipitation variability, and played an important role in the 2003 European and 2010 Russian heat waves. While primarily subseasonal in nature, the Rossby waves can at times have a substantial seasonal mean component. This is exemplified by REOF 4 which played a major role in the development of the most intense anomalies of the U.S. 1988 drought (during June) and the 1993 flooding (during July), though differed in the latter event by also making an important contribution to the seasonal mean anomalies. A stationary wave model (SWM) is used to reproduce some of the basic features of the observed waves and provide insight into the nature of the forcing. In particular, the responses to a set of idealized forcing functions are used to map the optimal forcing patterns of the leading waves. Also, experiments to reproduce the observed waves with the SWM using MERRA-based estimates of the forcing indicate that the wave forcing is dominated by sub-monthly vorticity transients.

  8. Relationship between variability of the semidiurnal tide in the Northern Hemisphere mesosphere and quasi-stationary planetary waves throughout the global middle atmosphere

    Directory of Open Access Journals (Sweden)

    X. Xu

    2009-11-01

    Full Text Available To investigate possible couplings between planetary waves and the semidiurnal tide (SDT, this work examines the statistical correlations between the SDT amplitudes observed in the Northern Hemisphere (NH mesosphere and stationary planetary wave (SPW with wavenumber S=1 (SPW1 amplitudes throughout the global stratosphere and mesosphere. The latter are derived from the Aura-MLS temperature measurements. During NH summer-fall (July–October, the mesospheric SDT amplitudes observed at Svalbard (78° N and Eureka (80° N usually do not show persistent correlations with the SPW1 amplitudes in the opposite hemisphere. Although the SDT amplitudes observed at lower latitudes (~50–70° N, especially at Saskatoon (52° N, are often shown to be highly and positively correlated with the SPW1 amplitudes in high southern latitudes, these correlations cannot be sufficiently explained as evidence for a direct physical link between the Southern Hemisphere (SH winter-early spring SPW and NH summer-early fall mesospheric SDT. This is because the migrating tide's contribution is usually dominant in the mid-high latitude (~50–70° N NH mesosphere during the local late summer-early fall (July–September. The numerical correlation is dominated by similar low-frequency variability or trends between the amplitudes of the NH SDT and SH SPW1 during the respective equinoctial transitions. In contradistinction, during NH winter (November–February, the mesospheric SDT amplitudes at northern mid-high latitudes (~50–80° N are observed to be significantly and positively correlated with the SPW1 amplitudes in the same hemisphere in most cases. Because both the SPW and migrating SDT are large in the NH during the local winter, a non-linear interaction between SPW and migrating SDT probably occurs, thus providing a global non-migrating SDT. This is consistent with observations of SDT in Antarctica that are large in summer than in winter. It is suggested that

  9. Relationship between variability of the semidiurnal tide in the Northern Hemisphere mesosphere and quasi-stationary planetary waves throughout the global middle atmosphere

    Directory of Open Access Journals (Sweden)

    X. Xu

    2009-11-01

    Full Text Available To investigate possible couplings between planetary waves and the semidiurnal tide (SDT, this work examines the statistical correlations between the SDT amplitudes observed in the Northern Hemisphere (NH mesosphere and stationary planetary wave (SPW with wavenumber S=1 (SPW1 amplitudes throughout the global stratosphere and mesosphere. The latter are derived from the Aura-MLS temperature measurements. During NH summer-fall (July–October, the mesospheric SDT amplitudes observed at Svalbard (78° N and Eureka (80° N usually do not show persistent correlations with the SPW1 amplitudes in the opposite hemisphere. Although the SDT amplitudes observed at lower latitudes (~50–70° N, especially at Saskatoon (52° N, are often shown to be highly and positively correlated with the SPW1 amplitudes in high southern latitudes, these correlations cannot be sufficiently explained as evidence for a direct physical link between the Southern Hemisphere (SH winter-early spring SPW and NH summer-early fall mesospheric SDT. This is because the migrating tide's contribution is usually dominant in the mid-high latitude (~50–70° N NH mesosphere during the local late summer-early fall (July–September. The numerical correlation is dominated by similar low-frequency variability or trends between the amplitudes of the NH SDT and SH SPW1 during the respective equinoctial transitions. In contradistinction, during NH winter (November–February, the mesospheric SDT amplitudes at northern mid-high latitudes (~50–80° N are observed to be significantly and positively correlated with the SPW1 amplitudes in the same hemisphere in most cases. Because both the SPW and migrating SDT are large in the NH during the local winter, a non-linear interaction between SPW and migrating SDT probably occurs, thus providing a global non-migrating SDT. This is consistent with observations of SDT in Antarctica that are large in summer than in winter. It is suggested that

  10. The star book stargazing throughout the seasons in the Northern hemisphere

    CERN Document Server

    Grego, Peter

    2012-01-01

    Stargazing Throughout the Seasons in the Northern Hemisphere is an excerpt from The Star Book that guides you through the night skies in the Northern Hemisphere, through wide-angle star charts. Looking at the main constellations, stars and celestial showpieces of the northern celestial sphere, beginning with constellations around the north pole and then taking a season by season view. Most northern constellations are as familiar to today's stargazers as they were to the ancient Greeks. Everyone is interested in the stars and on a clear night astonished by them. Stargazing Throughout the Seasons in the Northern Hemisphere will answer any questions you may have when you look up into the night sky.

  11. A model of high-latitude thermospheric density

    Science.gov (United States)

    Yamazaki, Yosuke; Kosch, Michael J.; Sutton, Eric K.

    2015-09-01

    We present an empirical model of the high-latitude air density at 450 km, derived from accelerometer measurements by the CHAllenging Minisatellite Payload and Gravity Recovery and Climate Experiment satellites during 2002-2006, which we call HANDY (High-Latitude Atmospheric Neutral DensitY). HANDY consists of a quiet model and disturbance model. The quiet model represents the background thermospheric density for "zero geomagnetic activity" conditions. The disturbance model represents the response of the thermospheric density to solar wind forcing at high latitudes. The solar wind inputs used are the following: (1) solar wind electric field ESW, (2) interplanetary magnetic field (IMF) clock angle CSW, and (3) solar wind dynamic pressure PSW. Both quiet and disturbance models are constructed on the basis of spherical harmonic function fitting to the data. Magnetic coordinates are used for the disturbance model, while geographical coordinates are used for the quiet model. HANDY reproduces main features of the solar wind influence on the high-latitude thermospheric density, such as the IMF By effect that produces a hemispheric asymmetry in the density distribution.

  12. Northern Hemisphere hydroclimate patterns in the last 12 centuries

    Science.gov (United States)

    Charpentier Ljungqvist, Fredrik; Krusic, Paul J.; Sundqvist, Hanna S.; Zorita, Eduardo; Brattström, Gudrun; Frank, David

    2015-04-01

    Variations in local to continental-scale hydroclimate have a strong impact on ecosystem functioning, crop yields, and society's water resources. Consequently, the ability to model and predict with reasonable certainty the dynamic and spatial response of precipitation to global warming is essential. The uncertainty in hydroclimate projections from model simulations remains large as a consequence of significant gaps in our knowledge of preindustrial boundary conditions due to the short length of instrumental measurements of precipitation. In this study, we assembled an unprecedentedly large network of 196 records hydroclimatic records from the Northern Hemisphere (NH) to place recent hydrological changes and future precipitation scenarios in the context of spatially resolved and temporally persistent hydroclimatic variations over the last twelve centuries. The data from grid cells corresponding to the proxy locations were obtained from six CMIP5 last millennium simulations and treated in a similar way as the proxy data in order to facilitate a model-proxy comparison. The most extensive areas of low moisture availability are found during the 12th and 15th centuries. It is notable that the intensification of wet and dry anomalies during the 20th century shown in coupled atmosphere-ocean model simulations is not supported by empirical evidence. Our results reveals that prominent hydroclimatic see-saw patterns, also observed in instrumental data, of alternating moisture regimes between the east and west Mediterranean, southwest vs. northwest United States, east vs. west China have been operating consistently during the past millennium. Key findings: - Dry as well as wet conditions can prevail under both warm and cold climate states in most regions. - In some regions a tendency can be seen for either increased aridity or wetness with increasing or decreasing temperatures. - Such changes can be expressed in localized wet-dry seesaw patterns that climate models seems unable

  13. 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 warming and pCO2 rise across the twentieth century. © 2015 John Wiley & Sons Ltd.

  14. Widespread land surface wind decline in the Northern Hemisphere

    Science.gov (United States)

    Vautard, R.; Cattiaux, J.; Yiou, P.; Thépaut, J.-N.; Ciais, P.

    2010-09-01

    The decline of surface wind observed in many regions of the world is a potential source of concern for wind power electricity generation. It is also suggested as the main cause of decreasing pan evaporation. In China, a persistent and significant decrease of monsoon winds was observed in all seasons. Surface wind declines were also evidenced in several regions of the world (U.S., Australia, several European countries). Except over China, no clear explanation was given for the wind decrease in the regions studied. Whether surface winds decrease is due to changes in the global atmospheric circulation or its variability, in surface processes or to observational trends has therefore not been elucidated. The identification of the drivers of such a decline requires a global investigation of available surface and upper-air wind data, which has not been conducted so far. Here we use global datasets of in-situ wind measurements that contain surface weather stations wind data (hourly or three-hourly data acquisition time step) and rawinsonde vertical wind data profiles (monthly time step) prepared by the NCAR. A set of 822 worldwide surface stations with continuous wind records was selected after a careful elimination of stations with obvious breaks and large gaps. This dataset mostly covers the Northern mid latitudes over the period 1979-2008. Using this data set, we found that annual mean wind speeds have declined at 73% of the surface stations over the past 30 years. In the Northern Hemisphere, positive wind trends are found only in a few places. In Europe, Central Asia, Eastern Asia and in North America the annual mean surface wind speed has decreased on average at a rate of -2.9, -5.9, -4.2, and -1.8 %/decade respectively, i.e. a decrease of about 10% in 30 years and up to about 20% in Central Asia. These results are robust to changes in the station selection method and parameters. By contrast, upper-air winds observed from rawinsondes, geostrophic winds deduced from

  15. Respective roles of direct GHG radiative forcing and induced Arctic sea ice loss on the Northern Hemisphere atmospheric circulation

    Science.gov (United States)

    Oudar, Thomas; Sanchez-Gomez, Emilia; Chauvin, Fabrice; Cattiaux, Julien; Terray, Laurent; Cassou, Christophe

    2017-12-01

    The large-scale and synoptic-scale Northern Hemisphere atmospheric circulation responses to projected late twenty-first century Arctic sea ice decline induced by increasing Greenhouse Gases (GHGs) concentrations are investigated using the CNRM-CM5 coupled model. An original protocol, based on a flux correction technique, allows isolating the respective roles of GHG direct radiative effect and induced Arctic sea ice loss under RCP8.5 scenario. In winter, the surface atmospheric response clearly exhibits opposing effects between GHGs increase and Arctic sea ice loss, leading to no significant pattern in the total response (particularly in the North Atlantic region). An analysis based on Eady growth rate shows that Arctic sea ice loss drives the weakening in the low-level meridional temperature gradient, causing a general decrease of the baroclinicity in the mid and high latitudes, whereas the direct impact of GHGs increase is more located in the mid-to-high troposphere. Changes in the flow waviness, evaluated from sinuosity and blocking frequency metrics, are found to be small relative to inter-annual variability.

  16. Observational Analysis of Cloud and Precipitation in Midlatitude Cyclones: Northern Versus Southern Hemisphere Warm Fronts

    Science.gov (United States)

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

    2012-01-01

    Extratropical cyclones are responsible for most of the precipitation and wind damage in the midlatitudes during the cold season, but there are still uncertainties on how they will change in a warming climate. An ubiquitous problem amongst General Circulation Models (GCMs) is a lack of cloudiness over the southern oceans that may be in part caused by a lack of clouds in cyclones. We analyze CloudSat, CALIPSO and AMSR-E observations for 3 austral and boreal cold seasons and composite cloud frequency of occurrence and precipitation at the warm fronts for northern and southern hemisphere oceanic cyclones. We find that cloud frequency of occurrence and precipitation rate are similar in the early stage of the cyclone life cycle in both northern and southern hemispheres. As cyclones evolve and reach their mature stage, cloudiness and precipitation at the warm front increase in the northern hemisphere but decrease in the southern hemisphere. This is partly caused by lower amounts of precipitable water being available to southern hemisphere cyclones, and smaller increases in wind speed as the cyclones evolve. Southern hemisphere cloud occurrence at the warm front is found to be more sensitive to the amount of moisture in the warm sector than to wind speeds. This suggests that cloudiness in southern hemisphere storms may be more susceptible to changes in atmospheric water vapor content, and thus to changes in surface temperature than their northern hemisphere counterparts. These differences between northern and southern hemisphere cyclones are statistically robust, indicating A-Train-based analyses as useful tools for evaluation of GCMs in the next IPCC report.

  17. A Comparative Analysis between GIMSS NDVIg and NDVI3g for Monitoring Vegetation Activity Change in the Northern Hemisphere during 1982–2008

    Directory of Open Access Journals (Sweden)

    Deqin Fan

    2013-08-01

    Full Text Available The long-term Normalized Difference Vegetation Index (NDVI time-series data set generated from the Advanced Very High Resolution Radiometers (AVHRR has been widely used to monitor vegetation activity change. The third version of NDVI (NDVI3g produced by the Global Inventory Modeling and Mapping Studies (GIMMS group was released recently. The comparisons between the new and old versions should be conducted for linking existing studies with future applications of NDVI3g in monitoring vegetation activity change. Based on simple and piecewise linear regression methods, this study made a comparative analysis between NDVIg and NDVI3g for monitoring vegetation activity change and its responses to climate change in the middle and high latitudes of the Northern Hemisphere during 1982–2008. Our results indicated that there were large differences between NDVIg and NDVI3g in the spatial patterns for both the overall changing trends and the timing of Turning Points (TP in NDVI time series, which spread over almost the entire study region. The average NDVI trend from NDVI3g was almost twice as great as that from NDVIg and the detected average timing of TP from NDVI3g was about one year later. Although the general spatial patterns were consistent between two data sets for detecting the responses of growing-season NDVI to temperature and precipitation changes, there were large differences in the response magnitude, with a higher response magnitude to temperature in NDVI3g and an opposite response to precipitation change for the two data sets. These results demonstrated that the NDVIg data set may underestimate the vegetation activity change trend and its response to climate change in the middle and high latitudes of the Northern Hemisphere during the past three decades.

  18. The importance of wave break events for synoptic-scale buildups of Northern Hemisphere zonal available potential energy

    Science.gov (United States)

    Bowley, Kevin; Atallah, Eyad; Gyakum, John

    2017-04-01

    Zonal available potential energy (ZAPE) is an estimate of the amount of potential energy in the atmosphere available for conversion to kinetic energy, providing a good proxy for the overall strength of the general circulation. Previous studies have estimated total hemispheric ZAPE, ZAPE generation, and conversion to kinetic energy, and proposed physical mechanisms to describe the annual ZAPE cycle as well as short term (sub-seasonal to synoptic) APE depletion events. Large, short term modulations of ZAPE have been shown to be associated with impactful weather events in the mid- and high-latitudes, including severe cyclones and high-amplitude ridging and blocking events In this study, we examine the association of significant synoptic time-scale increases in ZAPE with dynamic tropopause wave break events. ZAPE buildup events are determined using a 1979-2011 daily Northern Hemisphere (20˚ -85˚ N) ZAPE climatology calculated from the National Centers for Environmental Prediction (NCEP) Department of Energy (DOE) Reanalysis 2 global reanalysis dataset in an isobaric framework. To diagnose the importance of wave breaks in the troposphere, we objectively identify wave breaks using potential temperature on the dynamic tropopause, identifying and tracking both anti-cyclonic (LC1) and cyclonic (LC2) wave breaks during the 1979-2011 period. Our results indicate that LC1 wave break events in the equatorward jet exit regions appear to play an important role in ZAPE buildup events. The formation of these anti-cyclonic wave break events result in the development of statistically significant warm-core high pressure anomalies in these regions, acting to reduce baroclinic conversions. We will further demonstrate that changes in LC2 wave break activity in the climatological storm track during ZAPE buildup events are indicative of notable changes to the regions of significant cyclone activity, which are occurring in response to shifts and elongations of the jet stream.

  19. Thermal Contraction Crack Polygon Classification and Distribution: Morphological Variations in Northern Hemisphere Patterned Ground

    Science.gov (United States)

    Levy, J.; Head, J.; Marchant, D.

    2008-09-01

    Polygonally patterned ground has been identified on Mars since the Viking era [1], and has long been interpreted as a signal of the presence of subsurface ice deposits [2-4]. The origin of ice in the shallow martian subsurface, whether by cyclical vapour diffusion or primary deposition, remains an area of active inquiry [5- 9]. Recent modelling suggests that high-latitude terrains on Mars may support buried ice sheets and glaciers, produced by direct atmospheric deposition within the past 5 My [5], overlain by a sublimation lag deposit ranging in thickness from 10s to 100s of cm [8]. These results are consistent with coarse-resolution (100s of km per pixel) neutron-spectrometer results correlating highlatitude patterned ground with subsurface water [4, 10, 11], as well as a suite of geomorphological observations linking young terrains to recently deposited, ice-rich units [5-7]. Polygon classification in terrestrial polar environments is based on morphology, structure, and origin processes. On Earth, thermal contraction crack polygons can be divided into three types: ice-wedge, sand-wedge, and sublimation polygons; each of which forms under a unique set of climate and substrate-composition conditions [12-14]. Although the thermal contraction cracking process under martian conditions is well understood [15], classification systems for polygonally patterned ground on Mars have until now relied primarily on imaging data at resolutions comparable to the scale of the polygons of interest [3]. We build on the identification of sublimation polygons in the NASA Phoenix landing area [16], and preliminary classification of polygons into morphological species (groups distinguishable by characteristic surface morphologies) [17] across the northern hemisphere of Mars. We present an integrated assessment of martian polygon morphological variation as a function of latitude, and suggest links between polygon morphology, origin timing, and global climate conditions. This analysis

  20. High-resolution record of Northern Hemisphere climate extending into the last interglacial period

    DEFF Research Database (Denmark)

    North Greenland Ice Core Project members; Andersen, Katrine K.; Azuma, N.

    2004-01-01

    Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from......-saw between the hemispheres (which dominated the last glacial period) was not operating at this time....

  1. High latitude temperature evolution across the Last Interglacial: a model-data comparison

    Science.gov (United States)

    Capron, Emilie; Stone, Emma; Govin, Aline; Loutre, Marie-France; Masson-Delmotte, Valerie; Mulitza, Stefan; Otto-Bliesner, Betty; Sime, Louise; Waelbroeck, Claire; Wolff, Eric W.

    2014-05-01

    The Last Interglacial (LIG, 129-116 thousand of years, ka) represents an interesting test bed for climate model feedbacks for warmer-than-present high latitudes. However, mainly because synchronising different paleoclimatic archives from different parts of the world is not trivial, a global picture of LIG temperature changes is difficult to obtain. In the framework of the UK iGlass consortium and the European Past4Future project, we have selected 49 polar ice core and sub-polar marine sediment records and developed a strategy to synchronise them onto the recent AICC2012 ice core chronology. This new synthesis enables us to describe the spatial and temporal climatic patterns over polar ice sheets (surface air temperature) and around the ice margins (sea surface temperatures) at a pluri-centennial to millennial-scale. Major features highlighted are (i) non synchronous maximum temperature change between the two hemispheres with the Southern Ocean and Antarctica records showing an early warming compared to North Atlantic records and (ii) Southern hemisphere records exhibiting warm conditions for a longer time period compared to records from the Northern Hemisphere and smaller temperature amplitude changes. Our compiled records are compared with recent snapshot and transient model experiments performed with three state of the art General Circulation Models (HADCM3, CCSM3, FAMOUS) and an Earth Model of Intermediary Complexity (LOVECLIM). Such an exercise enables us to investigate the climate feedbacks which causes the most apparent model-data differences.

  2. Biology and conservation of owls of the Northern Hemisphere: 2nd International symposium

    Science.gov (United States)

    James R. Duncan; David H. Johnson; Thomas H. Nicholls

    1997-01-01

    The proceeding contains 91 papers authored by 143 people from 13 countries covering biology, ecology, monitoring, habitat-use, status conservation, education, genetics, toxicology, diet, migration, mortality and related topics concerning owls of the Northern Hemisphere. Thirty-three owl species are discussed. Information presented will be useful in owl conservation,...

  3. 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

  4. Quasi-biennial oscillation modulation of the middle- and high-latitude mesospheric semidiurnal tides during August-September

    Science.gov (United States)

    Laskar, Fazlul I.; Chau, Jorge L.; Stober, Gunter; Hoffmann, Peter; Hall, Chris M.; Tsutsumi, M.

    2016-05-01

    The seasonal and interannual variabilities of mesospheric semidiurnal tides (SDT) are investigated using specular meteor radar-based winds. The horizontal wind observations during 2003 to 2014 from a high-latitude station, Andenes (69°N, 16°E), and during 2008 to 2014 from a midlatitude station, Juliusruh (54°N, 13°E), are used. It has been observed that the amplitudes of mesospheric SDTs are enhanced at both stations during August-September of all the years. These enhancements show a systematic behavior with that of the low-latitude stratospheric quasi-biennial oscillation (QBO), which is characterized based on winds from radiosonde data. The SDT amplitude values during enhancement are below/above mean level for those years in which the QBO wind at 50 hPa is westward/eastward (QBOw/QBOe). The average SDT amplitudes during the August-September enhancement duration are found to vary hand in hand with the low-latitude QBO wind, suggesting QBO modulation of SDT. Stratospheric and lower mesospheric zonal wind perturbations from MERRA reanalysis data show weak local forcing in the Northern Hemisphere and indication of enhanced quasi-stationary planetary waves (SPW) in the Southern Hemisphere. Based on these observations and some earlier results, we hypothesize that the QBOw/QBOe wind damp/enhance the southern hemispheric SPW of wave number 1 (SPW1). This modulated SPW1 then interacts with the northern midlatitude and high-latitude SDTs to imprint the signature of QBO on them.

  5. Mechanism of secular increasing of mean gravity in Northern hemisphere and secular decreasing of mean gravity in Southern hemisphere

    Science.gov (United States)

    Barkin, Yu. V.; Ferrandiz, J. M.

    2009-04-01

    phenomena as cyclicity and synchronism of planetary natural processes, inversion of activity of natural processes in opposite hemispheres. Numerous confirmations give the extensive data of every possible geophysical observations. The phenomenon of synchronism in annual variations of activity of various natural processes is rather brightly expressed - their phases are precisely synchronized, and the periods of extreme activity (or passivity) fall to February - March or August - September. In daily variations of natural processes similar laws are observed. Here we speak about modern processes, but similar laws take place in various time scales, including geological. In the given report we shall concentrate on the analysis of possible secular variations of a gravity at displacement of an external core (of its centre of mass) relatively to the elastic mantle. The analysis has shown, that gravitational influence of displaced superfluous mass of the core are a major factor of secular variations of a gravity. However the displaced core causes directed redistribution of atmospheric masses from a southern hemisphere in northern, and also complex slow redistribution of oceanic masses. Increase of loading of atmospheric and oceanic masses on an elastic crust of northern hemisphere results in its slow lowering. Return processes should observed in a southern hemisphere. All listed factors, certainly, directly influence variations of a gravity. In a more comprehensive sense redistribution of all fluid masses, including climatic character also result in changes of a gravity. Hemispheres mean secular trends of gravity. For an estimation of a role of factors of redistribution of air and fluid masses in variations of a gravity the point model of redistribution of masses of the Earth (Barkin, 2001), obtained very effective applications at studying of fundamental problems of geodynamics, has been used. Let's emphasize, that the Earth is active dynamic object at which activity in the certain

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

    Science.gov (United States)

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

    2017-12-01

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

  7. Quasiresonant amplification of planetary waves and recent Northern Hemisphere weather extremes.

    Science.gov (United States)

    Petoukhov, Vladimir; Rahmstorf, Stefan; Petri, Stefan; Schellnhuber, Hans Joachim

    2013-04-02

    In recent years, the Northern Hemisphere has suffered several devastating regional summer weather extremes, such as the European heat wave in 2003, the Russian heat wave and the Indus river flood in Pakistan in 2010, and the heat wave in the United States in 2011. Here, we propose a common mechanism for the generation of persistent longitudinal planetary-scale high-amplitude patterns of the atmospheric circulation in the Northern Hemisphere midlatitudes. Those patterns--with zonal wave numbers m = 6, 7, or 8--are characteristic of the above extremes. We show that these patterns might result from trapping within midlatitude waveguides of free synoptic waves with zonal wave numbers k ≈ m. Usually, the quasistationary dynamical response with the above wave numbers m to climatological mean thermal and orographic forcing is weak. Such midlatitude waveguides, however, may favor a strong magnification of that response through quasiresonance.

  8. Last millennium northern hemisphere summer temperatures from tree rings: Part I: The long term context

    Czech Academy of Sciences Publication Activity Database

    Wilson, R.; Anchukaitis, K.; Briffa, K. R.; Büntgen, Ulf; Cook, E.; D'Arrigo, R.; Davi, N.; Esper, J.; Frank, D.; Gunnarson, B.; Hegerl, G.; Helama, S.; Klesse, S.; Krusic, P. J.; Linderholm, H. W.; Myglan, V. S.; Osborn, T. J.; Rydval, M.; Schneider, L.; Schurer, A.; Wiles, G.; Zhang, P.; Zorita, E.

    2016-01-01

    Roč. 134, FEB (2016), s. 1-18 ISSN 0277-3791 Institutional support: RVO:67179843 Keywords : high-resolution paleoclimatology * stable carbon isotopes * medieval warm period * past 600 years * blue intensity * volcanic-eruptions * density data * ice-age * dendroclimatic reconstruction * cambium phenology * Tree-rings * Northern hemisphere * Last millennium * Summer temperatures * Reconstruction * CMIP5 models Subject RIV: EH - Ecology, Behaviour Impact factor: 4.797, year: 2016

  9. Coupled Northern Hemisphere permafrost-ice sheet evolution over the last glacial cycle

    OpenAIRE

    M. Willeit; A. Ganopolski

    2015-01-01

    Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2 and the coupled Northern Hemisphere (NH) permafrost-ice sheet evolution over the last glacial cycle is explor...

  10. Coupled Northern Hemisphere permafrost–ice-sheet evolution over the last glacial cycle

    OpenAIRE

    Willeit, M.; Ganopolski, A.

    2015-01-01

    Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH) permafrost–ice-sheet evolution over the last glacial cycle is explo...

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

    Directory of Open Access Journals (Sweden)

    G. Provan

    2004-11-01

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

  12. Investigating the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle

    Directory of Open Access Journals (Sweden)

    S. Bonelli

    2009-07-01

    Full Text Available A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREMLINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets.
    A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.

  13. Prediction and explanation of increases of mean sea levels in northern hemisphere, in southern hemisphere and all ocean of the Earth

    Science.gov (United States)

    Barkin, Yu. V.

    2009-04-01

    The phenomenon of contrast secular changes of sea levels in the southern and northern hemispheres, predicted on the basis of geodynamic model about the forced relative oscillations and displacements of the Earth shells, has obtained theoretical explanation. In northern hemisphere the mean sea level of ocean increases with velocity about 2.45±0.32 mm/yr, and in a southern hemisphere the mean sea level increases with velocity about 0.67±0.30 mm/yr. Theoretical values of velocity of increase of global mean sea level thus has been estimated in 1.61±0.36 mm/yr. 1 Introduction. The slow (secular) drift of the centre of mass of the Earth in the direction of North Pole with velocity about 12-20 mm/yr has been predicted by author in 1995, and now has confirmed with methods of space geodesy. The DORIS data in period 1999-2008 let us to estimate velocity of polar drift in 5.24 ± 0.29 mm/yr. To explain this fundamental planetary phenomenon it is possible only, having admitted, that similar northern drift tests the centre of mass of the liquid core relatively to the centre of mass of viscous-elastic and thermodynamically changeable mantle with velocity about 2-3 cm/yr [1]. Naturally, a drift of the core is accompanied by the global changes (deformations) of all layers of the mantle and the core, by inversion changes of their tension states when in one hemisphere the tension increases and opposite on the contrary - decreases. Also it is possible that thermodynamical mechanism actively works with inversion properties of molting and solidification of materials at core-mantle boundary in opposite (northern - southern) hemispheres. 2 Atmospheric and oceanic inversion tides. The gravitational attraction of superfluous mass of the drifting to the North core (in 17 masses of the Moon) causes a planetary inversion tide of air masses of the Earth and its oceanic masses, from the southern hemisphere - to the northern hemisphere [2, 3]. As consequence the phenomenon of increasing of

  14. Historical Trends in Pm2.5-Related Premature Mortality During 1990-2010 Across the Northern Hemisphere

    Science.gov (United States)

    Background: Air quality across the northern hemisphere over the past two decades has witnessed dramatic changes, with continuous improvement in developed countries in North America and Europe, but a contrasting sharp deterioration in developing regions of Asia. Objective: This s...

  15. Timing and Statistics of Autumn and Spring Annual Snow Cover for the Northern Hemisphere, 1972 to 2000

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The National Snow and Ice Data Center hosts a time-series data set comprising annual snow cover data for the Northern Hemisphere (covering land primarily over 45...

  16. MEaSUREs Northern Hemisphere State of Cryosphere Daily 25km EASE-Grid 2.0

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set reports the location of Northern Hemisphere snow cover and sea ice extent, the status of melt onset across Greenland and Artic sea ice, and the level...

  17. IMS Daily Northern Hemisphere Snow and Ice Analysis at 1 km, 4 km, and 24 km Resolutions

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data set provides snow and ice cover maps for the Northern Hemisphere from February 1997 to the present from the National Ice Center's Interactive Multisensor...

  18. Detection and attribution of Spring Snow Water Equivalent (SWE) Changes over the Northern Hemisphere

    Science.gov (United States)

    Jeong, Dae Il; Sushama, Laxmi

    2017-04-01

    Snow is an important component of the cryosphere and it has a direct and important influence on water storage and supply in snowmelt-dominated regions. This study evaluates the temporal evolution of snow water equivalent (SWE) for the February to April spring period using the GlobSnow observation dataset for the 1980-2012 period. The analysis is performed for different regions of hemispherical to sub-continental scales for the Northern Hemisphere. The detection-attribution (D-A) analysis is then performed to demonstrate anthropogenic and natural effects on spring SWE changes for different regions, by comparing observations with six CMIP5 model simulations for three different external forcings: all major anthropogenic and natural (ALL) forcings, greenhouse gas (GHG) forcing only, and natural forcing only. The observed spring SWE generally displays a decreasing trend, due to increasing spring temperatures. However, it exhibits a remarkable increasing trend for the southern parts of East Eurasia. The six CMIP5 models with ALL forcings reproduce well the observed spring SWE decreases at the hemispherical scale and continental scales, whereas important differences are noted for smaller regions such as southern and northern parts of East Eurasia and northern part of North America. The effects of ALL and GHG forcings are clearly detected for the spring SWE decline at the hemispherical scale, based on multi-model ensemble signals. The effects of ALL and GHG forcings, however, are less clear for the smaller regions or with single-model signals, indicating the large uncertainty in regional SWE changes, possibly due to stronger influence of natural climate variability.

  19. Attribution of spring snow water equivalent (SWE) changes over the northern hemisphere to anthropogenic effects

    Science.gov (United States)

    Jeong, Dae Il; Sushama, Laxmi; Naveed Khaliq, M.

    2017-06-01

    Snow is an important component of the cryosphere and it has a direct and important influence on water storage and supply in snowmelt-dominated regions. This study evaluates the temporal evolution of snow water equivalent (SWE) for the February-April spring period using the GlobSnow observation dataset for the 1980-2012 period. The analysis is performed for different regions of hemispherical to sub-continental scales for the Northern Hemisphere. The detection-attribution analysis is then performed to demonstrate anthropogenic and natural effects on spring SWE changes for different regions, by comparing observations with six CMIP5 model simulations for three different external forcings: all major anthropogenic and natural (ALL) forcings, greenhouse gas (GHG) forcing only, and natural forcing only. The observed spring SWE generally displays a decreasing trend, due to increasing spring temperatures. However, it exhibits a remarkable increasing trend for the southern parts of East Eurasia. The six CMIP5 models with ALL forcings reproduce well the observed spring SWE decreases at the hemispherical scale and continental scales, whereas important differences are noted for smaller regions such as southern and northern parts of East Eurasia and northern part of North America. The effects of ALL and GHG forcings are clearly detected for the spring SWE decline at the hemispherical scale, based on multi-model ensemble signals. The effects of ALL and GHG forcings, however, are less clear for the smaller regions or with single-model signals, indicating the large uncertainty in regional SWE changes, possibly due to stronger influence of natural climate variability.

  20. The initial dispersal and radiative forcing of a Northern Hemisphere mid-latitude super volcano: a model study

    OpenAIRE

    Timmreck, C.; H.-F. Graf

    2006-01-01

    The chemistry climate model MAECHAM4/ CHEM with interactive and prognostic volcanic aerosol and ozone was used to study the initial dispersal and radiative forcing of a possible Northern Hemisphere mid-latitude super eruption. Tropospheric climate anomalies are not analysed since sea surface temperatures are kept fixed. Our experiments show that the global dispersal of a super eruption located at Yellowstone, Wy. is strongly dependent on the season of the eruption. In Northern Hemisphere sum...

  1. Climate links and recent extremes in antarctic sea ice, high-latitude cyclones, Southern Annular Mode and ENSO

    Energy Technology Data Exchange (ETDEWEB)

    Pezza, Alexandre Bernardes; Simmonds, Ian [The University of Melbourne, School of Earth Sciences, Parkville, VIC (Australia); Rashid, Harun A. [Centre for Australian Weather and Climate Research (A partnership between CSIRO and the Bureau of Meteorology), Private Bag 1, Melbourne, VIC (Australia)

    2012-01-15

    In this article, we study the climate link between the Southern Annular Mode (SAM) and the southern sea-ice extent (SIE), and discuss the possible role of stationary waves and synoptic eddies in establishing this link. In doing so, we have used a combination of techniques involving spatial correlations of SIE, eddy streamfunction and wind anomalies, and statistics of high-latitude cyclone strength. It is suggested that stationary waves may be amplified by eddy anomalies associated with high latitude cyclones, resulting in more sea ice when the SAM is in its positive phase for most, but not all, longitudes. A similar association is observed during ENSO (La Nina years). Although this synergy in the SAM/ENSO response may partially reflect preferential areas for wave amplification around Antarctica, the short extent of the climate records does not allow for a definite causality connection to be established with SIE. Stronger polar cyclones are observed over the areas where the stationary waves are amplified. These deeper cyclones will break up and export ice equatorward more efficiently, but the near-coastal regions are cold enough to allow for a rapid re-freeze of the resulting ice break-up. We speculate that if global warming continues this same effect could help reverse the current (positive) Antarctic SIE trends once the ice gets thinner, similarly to what has been observed in the Northern Hemisphere. (orig.)

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

    Science.gov (United States)

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

    2018-01-01

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

  3. Simulated Historical (1901-2010) Changes in the Permafrost Extent and Active Layer Thickness in the Northern Hemisphere

    Science.gov (United States)

    Guo, Donglin; Wang, Huijun

    2017-11-01

    A growing body of simulation research has considered the dynamics of permafrost, which has an important role in the climate system of a warming world. Previous studies have concentrated on the future degradation of permafrost based on global climate models (GCMs) or data from GCMs. An accurate estimation of historical changes in permafrost is required to understand the relations between changes in permafrost and the Earth's climate and to validate the results from GCMs. Using the Community Land Model 4.5 driven by the Climate Research Unit -National Centers for Environmental Prediction (CRUNCEP) atmospheric data set and observations of changes in soil temperature and active layer thickness and present-day areal extent of permafrost, this study investigated the changes in permafrost in the Northern Hemisphere from 1901 to 2010. The results showed that the model can reproduce the interannual variations in the observed soil temperature and active layer thickness. The simulated area of present-day permafrost fits well with observations, with a bias of 2.02 × 106 km2. The area of permafrost decreased by 0.06 (0.62) × 106 km2 decade-1 from 1901 to 2009 (1979 to 2009). A clear decrease in the area of permafrost was found in response to increases in air temperatures during the period from about the 1930s to the 1940s, indicating that permafrost is sensitive to even a temporary increase in temperature. From a regional perspective, high-elevation permafrost decreases at a faster rate than high-latitude permafrost; permafrost in China shows the fastest rate of decrease, followed by Alaska, Russia, and Canada. Discrepancies in the rate of decrease in the extent of permafrost among different regions were mostly linked to the sensitivity of permafrost in the regions to increases in air temperatures rather than to the amplitude of the increase in air temperatures. An increase in the active layer thickness of 0.009 (0.071) m decade-1 was shown during the period of 1901

  4. High latitude electromagnetic plasma wave emissions

    Science.gov (United States)

    Gurnett, D. A.

    1983-01-01

    The principal types of electromagnetic plasma wave emission produced in the high latitude auroral regions are reviewed. Three types of radiation are described: auroral kilometric radiation, auroral hiss, and Z mode radiation. Auroral kilometric radiation is a very intense radio emission generated in the free space R-X mode by electrons associated with the formation of discrete auroral arcs in the local evening. Theories suggest that this radiation is an electron cyclotron resonance instability driven by an enhanced loss cone in the auroral acceleration region at altitudes of about 1 to 2 R sub E. Auroral hiss is a somewhat weaker whistler mode emission generated by low energy (100 eV to 10 keV) auroral electrons. The auroral hiss usually has a V shaped frequency time spectrum caused by a freqency dependent beaming of the whistler mode into a conical beam directed upward or downward along the magnetic field.

  5. Variability in winter mass balance of Northern Hemisphere glaciers and relations with atmospheric circulation

    Science.gov (United States)

    McCabe, G.J.; Fountain, A.G.; Dyurgerov, M.

    2000-01-01

    An analysis of variability in the winter mass balance (WMB) of 22 glaciers in the Northern Hemisphere indicates two primary modes of variability that explain 46% of the variability among all glaciers. The first mode of variability characterizes WMB variability in Northern and Central Europe and the second mode primarily represents WMB variability in northwestern North America, but also is related to variability in WMB of one glacier in Europe and one in Central Asia. These two modes of WMB variability are explained by variations in mesoscale atmospheric circulation which are driving forces of variations in surface temperature and precipitation. The first mode is highly correlated with the Arctic Oscillation Index, whereas the second mode is highly correlated with the Southern Oscillation Index. In addition, the second mode of WMB variability is highly correlated with variability in global winter temperatures. This result suggests some connection between global temperature trends and WMB for some glaciers.

  6. Simultaneous observation of traveling ionospheric disturbances in the Northern and Southern Hemispheres

    Directory of Open Access Journals (Sweden)

    C. E. Valladares

    2009-04-01

    Full Text Available Measurements of total electron content (TEC using 263 GPS receivers located in the North and South America continents are presented to demonstrate the simultaneous existence of traveling ionospheric disturbances (TID at high, mid, and low latitudes, and in both Northern and Southern Hemispheres. The TID observations pertain to the magnetically disturbed period of 29–30 October 2003 also known as the Halloween storm. The excellent quality of the TEC measurements makes it possible to calculate and remove the diurnal variability of TEC and then estimate the amplitude, wavelength, spectral characteristics of the perturbations, and the approximate velocity of the AGW. On 29 October 2003 between 17:00 and 19:00 UT, there existed a sequence of TEC perturbations (TECP, which were associated with the transit of atmospheric gravity waves (AGW propagating from both auroral regions toward the geographic equator. A marked difference was found between the northern and southern perturbations. In the Northern Hemisphere, the preferred horizontal wavelength varies between 1500 and 1800 km; the propagation velocity is near 700 m/s and the perturbation amplitude about 1 TEC unit (TECu. South of the geographic equator the wavelength of the TECP is as large as 2700 km, the velocity is about 550 m/s, and the TECP amplitude is 3 TECu. Concurrently with our observations, the Jicamarca digisonde observed virtual height traces that exhibited typical features that are associated with TIDs. Here, it is suggested that differences in the local conductivity between northern and southern auroral ovals create a different Joule heating energy term. The quality of these observations illustrates the merits of GPS receivers to probe the ionosphere and thermosphere.

  7. Earliest and first Northern Hemispheric hoatzin fossils substantiate Old World origin of a "Neotropic endemic".

    Science.gov (United States)

    Mayr, Gerald; De Pietri, Vanesa L

    2014-02-01

    The recent identification of hoatzins (Opisthocomiformes) in the Miocene of Africa showed part of the evolution of these birds, which are now only found in South America, to have taken place outside the Neotropic region. Here, we describe a new fossil species from the late Eocene of France, which constitutes the earliest fossil record of hoatzins and the first one from the Northern Hemisphere. Protoazin parisiensis gen. et sp. nov. is more closely related to South American Opisthocomiformes than the African taxon Namibiavis and substantiates an Old World origin of hoatzins, as well as a relictual distribution of the single extant species. Although recognition of hoatzins in Europe may challenge their presumed transatlantic dispersal, there are still no North American fossils in support of an alternative, Northern Hemispheric, dispersal route. In addition to Opisthocomiformes, other avian taxa are known from the Cenozoic of Europe, the extant representatives of which are only found in South America. Recognition of hoatzins in the early Cenozoic of Europe is of particular significance because Opisthocomiformes have a fossil record in sub-Saharan Africa, which supports the hypothesis that extinction of at least some of these "South American" groups outside the Neotropic region was not primarily due to climatic factors.

  8. Objective determination of the extratropical transition of tropical cyclones in the Northern Hemisphere

    Directory of Open Access Journals (Sweden)

    Joshua Studholme

    2015-05-01

    Full Text Available Extratropical transition (ET has eluded objective identification since the realisation of its existence in the 1970s. Recent advances in numerical, computational models have provided data of higher resolution than previously available. In conjunction with this, an objective characterisation of the structure of a storm has now become widely accepted in the literature. Here we present a method of combining these two advances to provide an objective method for defining ET. The approach involves applying K-means clustering to isolate different life-cycle stages of cyclones and then analysing the progression through these stages. This methodology is then tested by applying it to five recent years from the European Centre of Medium-Range Weather Forecasting operational analyses. It is found that this method is able to determine the general characteristics for ET in the Northern Hemisphere. Between 2008 and 2012, 54% (±7, 32 of 59 of Northern Hemisphere tropical storms are estimated to undergo ET. There is great variability across basins and time of year. To fully capture all the instances of ET is necessary to introduce and characterise multiple pathways through transition. Only one of the three transition types needed has been previously well-studied. A brief description of the alternate types of transitions is given, along with illustrative storms, to assist with further study.

  9. Observational evidence of preferred flow regimes in the Northern Hemisphere winter stratosphere

    Science.gov (United States)

    Pierce, R. B.; Fairlie, T. D. A.

    1993-01-01

    Ten years of stratospheric geopotential height data are analyzed in an attempt to determine whether there are preferred flow regimes in the Northern Hemisphere winter stratosphere. The data are taken from Stratospheric Sounding Units on board NOAA satellites. The probability density estimate of the amplitude of the wavenumber 1 10-mb height is found to be bimodal. The density distribution is composed of a dominant large-amplitude mode and a less frequent low-amplitude mode. When the wavenumber 1 10-mb height data are projected onto the phase plane defined by the 10-mb zonal-mean winds and wavenumber 1 100-mb heights, three preferred regimes are evident. The small-amplitude mode separates into a strong zonal wind-weak wave regime and a weak zonal wind-weak wave regime. The large-amplitude mode is an intermediate zonal wind-strong wave regime. Transitions between the large-amplitude regime and the weak zonal wind-weak wave regime are found to be associated with major stratospheric warmings. The clustering of the stratospheric data into the preferred flow regimes is interpreted in light of the bifurcation properties of the Holton and Mass model. The interannual variability of the Northern Hemisphere winter stratosphere is interpreted in terms of the relative frequency of the observed preferred regimes.

  10. Multiple flow regimes in the Northern Hemisphere winter. I - Methodology and hemispheric regimes. II - Sectorial regimes and preferred transitions

    Science.gov (United States)

    Kimoto, Masahide; Ghil, Michael

    1993-01-01

    Multivariate pdfs in the phase space of large-scale atmospheric motions are examined in order to identify recurrent and persistent flow patterns. The extent to which intraseasonal variablity can be described and understood in terms of multiple flow regimes is clarified. It is shown that the synoptically intriguing and statistically significant inhomogeneities exhibited by the 2D phase plane on the periphery of the distribution are due to the existence of persistent and recurrent anomaly patterns. It is argued that these inhomgeneities are obscured when PDFs are examined in a smaller-dimensional subspace than dynamically desired. A synoptic characterization of onsets and breaks for the flow regimes is given by compositing. In situ evolutions of anomaly patterns, slow westward shifts of high-latitude anomaly centers, and successive downstream increase of anomaly magnitudes are the typical signatures of such events.

  11. Research on wind and solar energy transmission economic of Asia and Europe under Northern-hemisphere energy connection

    Science.gov (United States)

    Wei, Xiaoxia; Ding, Jian; Liu, Jie; Wei, Tiezhong

    2017-01-01

    Relying on the northern-hemisphere energy connection, considering the energy implementation of Asia and Europe, carrying out clean energy alternative is mainly to use the clean energy to take place of fossil energy. Under the green development scenario, this research gives the northern-hemisphere energy interconnection development model, makes the Artic as the connection points, gives the Northern hemisphere interconnection model unite the whole world energy. This research also identifies the factors effecting the transmission changes cost, including generation cost, transmission cost and landing cost. And estimate these two continents cost benefit, its economic and variable power-jointed scheme cost competitiveness. It showed that the trans-continent mode had better benefit, and can solve the pollution and energy restriction.

  12. Alternating Southern and Northern Hemisphere climate response to astronomical forcing during the past 35 m.y.

    Science.gov (United States)

    De Vleeschouwer, David; Vahlenkamp, Maximilian; Crucifix, Michel; Pälike, Heiko

    2017-04-01

    Earth's climate has undergone different intervals of gradual change as well as abrupt shifts between climate states. Here we aim to characterize the corresponding changes in climate response to astronomical forcing in the icehouse portion of the Cenozoic, from the latest Eocene to the present. As a tool, we use a 35-m.y.-long δ18Obenthic record compiled from different high-resolution benthic isotope records spliced together (what we refer to as a megasplice). An important feature of the evolutive spectrum of the megasplice is the sustained power at the frequency of the 405-kyr long eccentricity cycle throughout the Oligocene and early to middle Miocene. That power disappears after the mid-Miocene Climatic Transition, along with a weakening of the power of the 100-kyr short eccentricity cycles. While this general feature has been previously recognized, this is the first long record where this significant transition is clearly observed. We analyze the climate response to astronomical forcing during four 800-k.y.-long time windows. During the mid-Miocene Climatic Optimum (ca. 15.5 Ma), global climate variability was mainly dependent on Southern Hemisphere summer insolation, amplified by a dynamic Antarctic ice sheet; 2.5 m.y. later, relatively warm global climate states occurred during maxima in both Southern Hemisphere and Northern Hemisphere summer insolation. At that point, the Antarctic ice sheet grew too big to pulse on the beat of precession, and the Southern Hemisphere lost its overwhelming influence on the global climate state. Likewise, we juxtapose response regimes of the Miocene (ca. 19 Ma) and Oligocene (ca. 25.5 Ma) warming periods. Despite the similarity in δ18Obenthic values and variability, we find different responses to precession forcing. While Miocene warmth occurs during summer insolation maxima in both hemispheres, Oligocene global warmth is consistently triggered when Earth reaches perihelion in the Northern Hemisphere summer. The presence of a

  13. Energy-Efficient Office Buildings at High Latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Lerum, V.

    1996-12-31

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

  14. Linear Contrail Coverage and Cloud Property Retrievals from 2012 MODIS Imagery over the Northern Hemisphere

    Science.gov (United States)

    Duda, D. P.; Minnis, P.; Chee, T.; Khlopenkov, K. V.; Bedka, S. T.

    2015-12-01

    Observation of linear contrail cirrus coverage and retrieval of their optical properties are valuable data for validating atmospheric climate models that represent contrail formation explicitly. These data can reduce our uncertainty of the regional effects of contrail-generated cirrus on global radiative forcing, and thus improve our estimation of the impact of aviation on climate change. We continue our work to create a multi-year climatology of the physical properties of linear contrails from multi-spectral satellite observations. We use an automated contrail detection algorithm (CDA) to determine the coverage of linear persistent contrails over the Northern Hemisphere during 2012. The contrail detection algorithm is a modified form of the Mannstein et al. (1999) method, and uses several channels from thermal infrared MODIS data to reduce the occurrence of false positive detections. Global aircraft emissions waypoint data provided by FAA allow comparison of detected contrails with commercial aircraft flight tracks. A pixel-level product based on the advected flight tracks defined by the waypoint data and U-V wind component profiles from the NASA GMAO MERRA reanalyses has been developed to assign a confidence of contrail detection for the contrail mask. To account for possible contrail cirrus missed by the CDA, a post-processing method based on the assumption that pixels adjacent to detected linear contrails will have radiative signatures similar to those of the detected contrails is applied to the Northern Hemisphere data. Results from MODIS measurements during 2012 will be presented, representing a near-global climatology of contrail coverage. Linear contrail coverage will be compared with coverage estimates determined previously from 2006 MODIS data and with maps of potential persistent contrail formation derived from MERRA reanalysis data for both 2006 and 2012. In addition, contrail physical properties such as optical depth and particle size derived from the

  15. Increased Ocean Heat Convergence Into the High Latitudes With CO2 Doubling Enhances Polar-Amplified Warming

    Science.gov (United States)

    Singh, H. A.; Rasch, P. J.; Rose, B. E. J.

    2017-10-01

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

  16. Is plant migration restrained by available nitrogen supply in high latitudes?

    Science.gov (United States)

    Lee, E.; Schlosser, C. A.; Felzer, B.; Kicklighter, D.; Cronin, T.; Melillo, J.; Prinn, R. G.

    2008-12-01

    Recent studies suggest that growth and distribution of natural vegetation in high latitudes may be controlled by the amount of available nitrogen. Yet few studies have examined the role of available nitrogen on plant migration in response to anticipated climate change. We use a modeling approach to explore this issue. With a projected climate dataset (GFDL CM 2.0) from the IPCC AR4 archive, we first estimate net nitrogen mineralization values for natural plant functional types in high latitudes (north of 52N), using the Terrestrial Ecosystem Model (TEM). Previous work with TEM indicates that warming increases the rates of net nitrogen mineralization in high latitudes (e.g. 10 percent increase in boreal forests), which may help support a pattern of increased woodiness in northern systems such as boreal woodlands filling in with trees and tundra becoming more shrubby. Constrained with the available nitrogen for each vegetation type, a simple rule- based model, which describes the migration process and adopts processes of climatic tolerances of trees from the BIOME biogeography model, is used to generate a newly projected vegetation map for high latitudes. Our study emphasizes the significance of the role of nitrogen in the high latitude plant distribution. We also investigate the climatic consequences of the changing albedo, resulting from shifts in the vegetation distribution.

  17. Adder bite: an uncommon cause of compartment syndrome in northern hemisphere

    Directory of Open Access Journals (Sweden)

    Evers Lars H

    2010-09-01

    Full Text Available Abstract Snakebite envenomation is an uncommon condition in the northern hemisphere, but requires high vigilance with regard to both the systemic effects of the venom and the locoregional impact on the soft tissues. Bites from the adder, Vipera Berus, may have serious clinical consequences due to systemic effects. A case of a 44-year-old man is reported. The patient was bitten in the right hand. He developed fasciotomy-requiring compartment syndrome of the upper limb. Recognition of this most seldom complication of an adder bite is vital to save the limb. We recommend that the classical signs and symptoms of compartment syndrome serve as indication for surgical decompression.

  18. Aerosol Optical Depth Distribution in Extratropical Cyclones over the Northern Hemisphere Oceans

    Science.gov (United States)

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

    2016-01-01

    Using Moderate Resolution Imaging Spectroradiometer and an extratropical cyclone database,the climatological distribution of aerosol optical depth (AOD) in extratropical cyclones is explored based solely on observations. Cyclone-centered composites of aerosol optical depth are constructed for the Northern Hemisphere mid-latitude ocean regions, and their seasonal variations are examined. These composites are found to be qualitatively stable when the impact of clouds and surface insolation or brightness is tested. The larger AODs occur in spring and summer and are preferentially found in the warm frontal and in the post-cold frontal regions in all seasons. The fine mode aerosols dominate the cold sector AODs, but the coarse mode aerosols display large AODs in the warm sector. These differences between the aerosol modes are related to the varying source regions of the aerosols and could potentially have different impacts on cloud and precipitation within the cyclones.

  19. Long-term measurements of H*(10) at aviation altitudes in the northern hemisphere.

    Science.gov (United States)

    Wissmann, F

    2006-01-01

    Monitoring the radiation field at aviation altitudes is achieved by the dosemeter system piDOS installed in a passenger aircraft. The basic detector is a 2 in. tissue-equivalent proportional counter (TEPC) mounted in a cabin-baggage-sized aluminium suitcase. The entire system was characterised in neutron and photon reference fields from which two calibration factors were determined according to the splitting of the measured dose deposition spectrum yd(y) into low-LET and high-LET regions. A total of 255 flights in the northern hemisphere was analysed. The dependencies of the ambient dose equivalent rates on altitude, latitude and solar activity have been determined. These new data extend the data base used in Germany for the validation of program codes to calculate the radiation exposure of air crew members.

  20. Asymmetric effects of daytime and night-time warming on Northern Hemisphere vegetation.

    Science.gov (United States)

    Peng, Shushi; Piao, Shilong; Ciais, Philippe; Myneni, Ranga B; Chen, Anping; Chevallier, Frédéric; Dolman, Albertus J; Janssens, Ivan A; Peñuelas, Josep; Zhang, Gengxin; Vicca, Sara; Wan, Shiqiang; Wang, Shiping; Zeng, Hui

    2013-09-05

    Temperature data over the past five decades show faster warming of the global land surface during the night than during the day. This asymmetric warming is expected to affect carbon assimilation and consumption in plants, because photosynthesis in most plants occurs during daytime and is more sensitive to the maximum daily temperature, Tmax, whereas plant respiration occurs throughout the day and is therefore influenced by both Tmax and the minimum daily temperature, Tmin. Most studies of the response of terrestrial ecosystems to climate warming, however, ignore this asymmetric forcing effect on vegetation growth and carbon dioxide (CO2) fluxes. Here we analyse the interannual covariations of the satellite-derived normalized difference vegetation index (NDVI, an indicator of vegetation greenness) with Tmax and Tmin over the Northern Hemisphere. After removing the correlation between Tmax and Tmin, we find that the partial correlation between Tmax and NDVI is positive in most wet and cool ecosystems over boreal regions, but negative in dry temperate regions. In contrast, the partial correlation between Tmin and NDVI is negative in boreal regions, and exhibits a more complex behaviour in dry temperate regions. We detect similar patterns in terrestrial net CO2 exchange maps obtained from a global atmospheric inversion model. Additional analysis of the long-term atmospheric CO2 concentration record of the station Point Barrow in Alaska suggests that the peak-to-peak amplitude of CO2 increased by 23 ± 11% for a +1 °C anomaly in Tmax from May to September over lands north of 51° N, but decreased by 28 ± 14% for a +1 °C anomaly in Tmin. These lines of evidence suggest that asymmetric diurnal warming, a process that is currently not taken into account in many global carbon cycle models, leads to a divergent response of Northern Hemisphere vegetation growth and carbon sequestration to rising temperatures.

  1. Radio optical reference frame. 6: Additional source positions in the northern hemisphere

    Science.gov (United States)

    Fey, A. L.; Russell, J. L.; de Vegt, C.; Zacharias, N.; Johnston, K. J.; Ma, C.; Hall, D. M.; Holdenried, E. R.

    1994-01-01

    Radio and optical positions for northern hemisphere extragalactic sources are reported. Milliarcsecond (mas) accurate radio positions of 106 sources north of -2 deg declination are derived from Mark III Very Long Baseline Interferometry (VLBI) observations taken during ten experiments from 1990 January through 1990 October. The results presented supplement an ongoing project to define and maintain an all-sky radio/optical reference frame of 400 or more extragalactic sources with mas accurate radio and optical positions. Radio positions for 34 new sources are presented along with improved radio positions for 72 sources already in the reference frame catalog. An additional nine sources have been determined to be unsuitable reference frame objects. Radio observations of nine calibration sources tie the new positions to the existing catalogue. The radio positions of the new sources have formal mean errors of approximately 0.7 mas in right ascension and approximately 1.0 mas in declination. Sources for which we report improved radio positions now have formal mean errors of approximately 0.5 mas in both coordinates, an improvement in some cases by as much as 75%. Positions in the FK5 system have also been obtained for the optical counterparts of an additional five northern hemisphere radio sources using prime focus plates from the Kitt Peak National Observatory's 4 m telescope and a Ritchey-Chretien focus plate from the Calar Alto 2.2 m telescope. The optical positions have internal accuracies of about 0.03 sec and differ from the radio positions by about 0.07 sec on the average.

  2. Properties of Linear Contrails Detected in 2012 Northern Hemisphere MODIS Imagery

    Science.gov (United States)

    Duda, David P.; Chee, Thad; Khlopenkov, Konstantin; Bedka, Sarah; Spangenberg, Doug; Minnis, Patrick

    2015-01-01

    Observation of linear contrail cirrus coverage and retrieval of their optical properties are valuable data for validating atmospheric climate models that represent contrail formation explicitly. These data can reduce our uncertainty of the regional effects of contrail-generated cirrus on global radiative forcing, and thus improve our estimation of the impact of commercial aviation on climate change. We use an automated contrail detection algorithm (CDA) to determine the coverage of linear persistent contrails over the Northern Hemisphere during 2012. The contrail detection algorithm is a modified form of the Mannstein et al. (1999) method, and uses several channels from thermal infrared MODIS data to reduce the occurrence of false positive detections. A set of contrail masks of varying sensitivity is produced to define the potential range of uncertainty in contrail coverage estimated by the CDA. Global aircraft emissions waypoint data provided by FAA allow comparison of detected contrails with commercial aircraft flight tracks. A pixel-level product based on the advected flight tracks defined by the waypoint data and U-V wind component profiles from the NASA GMAO GEOS-4 reanalysis has been developed to assign a confidence of contrail detection for the contrail mask. To account for possible contrail cirrus missed by the CDA, a post-processing method based on the assumption that pixels adjacent to detected linear contrails will have radiative signatures similar to those of the detected contrails is applied to the Northern Hemisphere data. Results from several months of MODIS observations during 2012 will be presented, representing a near-global climatology of contrail coverage. Linear contrail coverage will be compared with coverage estimates determined previously from 2006 MODIS data.

  3. Freshwater fluxes from the Northern Hemisphere ice sheets during the Last Deglaciation

    Science.gov (United States)

    Nemec, J.; Janssens, I.; Goelzer, H.; Huybrechts, P.

    2009-04-01

    The disintegration of the Northern Hemisphere Ice Sheets during the Last Deglaciation is thought to have significantly influenced the global climate through oceanic and atmospheric feedbacks. Besides changes in topography and albedo over the large continental ice sheets, freshwater fluxes probably had large effects on the ocean circulation and on the global temperature evolution. To study possible changes in the ocean circulation, it is crucial to track both the intensity and location of meltwater runoff and iceberg calving into the ocean. We have simulated the northern hemisphere ice sheets with a 3D thermomechanical ice sheet model forced with output from a coupled atmosphere-ocean model (ECBilt-Clio) with prescribed ice sheets (extent, elevation, and albedo) for the Last Deglacation. The ice sheet model calculates changes in topography as well as the evolution of the freshwater fluxes, resulting from iceberg calving, basal melt and surface ablation. The ice sheet melt fluxes are routed through a continental runoff scheme that provides the runoff paths over the continents and gives for each continental grid point a corresponding drainage location in the ocean. The results are very dependent on the climate forcing that serves as input for the ice sheet model. Taking GRIP (Greenland Ice Core Project) scaled temperature and precipitation input, we find three major freshwater pulses during the Last Deglaciation. The first meltwater peak occurred at approximately 17 kyr BP, with an amplitude of 0.45 Sverdrup. The second, with the highest intensity of 0.8 Sverdrup, occurred around 14 kyr BP. Large parts of this meltwater is channeled to the North Atlantic, where it might have triggered the Younger Dryas cold period. The third and last meltwater peak happened about 10 kyr BP, corresponding to a switch in the freshwater routing from the North Atlantic to the Artic Ocean.

  4. Dynamical properties and extremes of Northern Hemisphere climate fields over the past 60 years

    Science.gov (United States)

    Faranda, Davide; Messori, Gabriele; Alvarez-Castro, M. Carmen; Yiou, Pascal

    2017-12-01

    Atmospheric dynamics are described by a set of partial differential equations yielding an infinite-dimensional phase space. However, the actual trajectories followed by the system appear to be constrained to a finite-dimensional phase space, i.e. a strange attractor. The dynamical properties of this attractor are difficult to determine due to the complex nature of atmospheric motions. A first step to simplify the problem is to focus on observables which affect - or are linked to phenomena which affect - human welfare and activities, such as sea-level pressure, 2 m temperature, and precipitation frequency. We make use of recent advances in dynamical systems theory to estimate two instantaneous dynamical properties of the above fields for the Northern Hemisphere: local dimension and persistence. We then use these metrics to characterize the seasonality of the different fields and their interplay. We further analyse the large-scale anomaly patterns corresponding to phase-space extremes - namely time steps at which the fields display extremes in their instantaneous dynamical properties. The analysis is based on the NCEP/NCAR reanalysis data, over the period 1948-2013. The results show that (i) despite the high dimensionality of atmospheric dynamics, the Northern Hemisphere sea-level pressure and temperature fields can on average be described by roughly 20 degrees of freedom; (ii) the precipitation field has a higher dimensionality; and (iii) the seasonal forcing modulates the variability of the dynamical indicators and affects the occurrence of phase-space extremes. We further identify a number of robust correlations between the dynamical properties of the different variables.

  5. Trend and Self Organizing Map Analysis of Snow Data of Northern Hemisphere for 1979-2014

    Science.gov (United States)

    Gan, T. Y. Y.; Scheepers, H.

    2016-12-01

    The 1979-2014, 25km-resolution snow water equivalent (SWE) monthly dataset of the Globsnow project of the European Space Agency prepared from combining Nimbus-7 SMMR, DMSP SSM/I-SSMIS SWE data with observations of ground-based synoptic weather stations was analyzed. The dataset covers the terrestrial non-mountainous regions of Northern Hemisphere except the Greenland. The monthly SWE dataset of October-May was analyzed for monotonic trends using the non-parametric Mann-Kendall test at 0.05 significant levels. Based on the total number of snow covered pixels analyzed, up to 15.5% (7.7%) of the pixels show statistically significant decreasing (increasing) trends. December has the largest snow cover extent and the greatest percentage of statistically significant decreasing trends, of which the majority are located north of 55° latitude which may reflect the effect of polar warming. April exhibits the greatest percentage of statistically significant positive trends and most of these are located in Asia. The mean trend magnitudes detected for October-May range from 0.18 to 1.42 mm/yr. Principle component analyses was performed on the SWE dataset and the leading components were correlated with temperature, precipitation, and climate indices such as El Niño Southern Oscillation (ENSO), Pacific Decadal (PDO), North Atlantic Oscillation (NAO), and others. The methods of self-organizing map and k-means clustering were also applied to delineate 20 regions in the Northern Hemisphere that exhibit similar SWE patterns.

  6. Mass balance investigation of perfluorooctanoic acid PFOA environmental levels, emissions and sinks in the northern hemisphere

    Energy Technology Data Exchange (ETDEWEB)

    Cousins, I.T.; Prevedouros, K. [Stockholm Univ., Stockholm (Sweden); Buck, R.C.; Korzeniowski, S.H. [Dupont Chemical Solutions, Wilmington, DE (United States)

    2005-07-01

    Perfluoroalkyl sulfonic acids (PFAS) and perfluoroalkyl carboxylic acids (PFCAs) and their precursors are found in a wide array of environmental samples, and have no known degradation mechanisms. PFCAs have been used for over 50 years as processing aids in the manufacture of fluoropolymers. PFASs and fluorotelomer products are used in a wide variety of products and industrial processes. This study provided a detailed account of direct and indirect sources of perfluorooctanoic acid (PFOA) in the environment. A mass balance investigation between sources and amounts residing in the northern hemisphere was conducted, and the magnitude of historical removal processes was estimated. It was hypothesized that the majority of historical PFOA production use, and emissions occurred in the northern hemisphere. The study considered both direct and indirect sources. Production and emissions were calculated from a number of published and unpublished chemical industry data. A mass balance computation was performed to estimate historical PFOA emissions with existing environmental levels and historical losses. A literature search was used to estimate representative PFOA levels in sediments and biota. The study confirmed the importance of surface water compartments for PFOA storage. Important sink processes included physical mixing and sedimentation to the deep oceans and sediment burial. Maximum and minimum ranges of the sum of the total environmental inventory and historical sink processes overlapped the ranges of emission estimates. It was concluded that a quantitative comparison of the atmospheric transport of PFOA precursors and the aquatic transport of the substances showed that ocean transport is the most significant transport routes of PFOAs. 13 refs., 1 tab., 1 fig.

  7. Dissipation of four forest-use herbicides at high latitudes.

    Science.gov (United States)

    Newton, Mike; Cole, Elizabeth C; Tinsley, Ian J

    2008-10-01

    hexazinone. These products dissipate during summer in high latitudes much as they would in temperate climates. Winter changes are small, but are not unlike some changes reported elsewhere under freezing conditions. Unlike many other studies, soil water did not influence dissipation heavily, but the high latitude and semi-arid climate also did not create severely droughty soils. Residues in plants were much higher than those in soils, but denatured the vegetation quickly, leading to unsuitability for forage in any case. Low toxicity of these products and their metabolites combined with consistent dissipation and low mobility suggest that toxic hazard of their use at high latitudes need not be a matter of serious concern to humans, terrestrial wildlife, or aquatic systems. They are safe for use in management and rehabilitation of boreal forests when used properly. Dissipation at rates approaching those in warmer climates offer a hypothesis that microflora native to high latitudes may be adapted to destruction of such molecules at lower temperatures than may be indicated by experiments with microflora adapted to warmer climates. Residues pose no observable risk to wildlife or humans in the area of use when products are applied properly.

  8. On the wintertime low bias of Northern Hemisphere carbon monoxide in global model studies

    Science.gov (United States)

    Stein, O.; Schultz, M. G.; Bouarar, I.; Clark, H.; Huijnen, V.; Gaudel, A.; George, M.; Clerbaux, C.

    2014-01-01

    The uncertainties in the global budget of carbon monoxide (CO) are assessed to explain causes for the long-standing issue of Northern Hemispheric wintertime underestimation of CO concentrations in global models. With a series of MOZART sensitivity simulations for the year 2008, the impacts from changing a variety of surface sources and sinks were analyzed. The model results were evaluated with monthly averages of surface station observations from the global CO monitoring network as well as with total columns observed from satellites and with vertical profiles from measurements on passenger aircraft. Our basic simulation using MACCity anthropogenic emissions underestimated Northern Hemispheric near-surface CO concentrations on average by more than 20 ppb from December to April with the largest bias over Europe of up to 75 ppb in January. An increase in global biomass burning or biogenic emissions of CO or volatile organic compounds (VOC) is not able to reduce the annual course of the model bias and yields too high concentrations over the Southern Hemisphere. Raising global annual anthropogenic emissions results in overestimations of surface concentrations in most regions all-year-round. Instead, our results indicate that anthropogenic emissions in the MACCity inventory are too low for the industrialized countries during winter and spring. Thus we found it necessary to adjust emissions seasonally with regionally varying scaling factors. Moreover, exchanging the original resistance-type dry deposition scheme with a parameterization for CO uptake by oxidation from soil bacteria and microbes reduced the boreal winter dry deposition fluxes and could partly correct for the model bias. When combining the modified dry deposition scheme with increased wintertime road traffic emissions over Europe and North America (factors up to 4.5 and 2, respectively) we were able to optimize the match to surface observations and to reduce the model bias significantly with respect to the

  9. The Last Permafrost Maximum (LPM) map of the northern hemisphere: permafrost extent and mean annual air temperatures, 25-17 ka BP

    NARCIS (Netherlands)

    Vandenberghe, J.; French, H.M.; Gorbunov, A.; Velichko, A.A.; Jin, H.; Cui, Z.; Zhang, T.; Wan, X.

    2014-01-01

    This paper accompanies a map that shows the extent of permafrost in the Northern Hemisphere between 25 and 17 thousand years ago. The map is based upon existing archival data, common throughout the Northern Hemisphere, that include ice-wedge pseudomorphs, sand wedges and large cryoturbations. Where

  10. Can a coupled meteorology–chemistry model reproduce the historical trend in aerosol direct radiative effects over the Northern Hemisphere?

    Science.gov (United States)

    The ability of a coupled meteorology–chemistry model, i.e., Weather Research and Forecast and Community Multiscale Air Quality (WRF-CMAQ), to reproduce the historical trend in aerosol optical depth (AOD) and clear-sky shortwave radiation (SWR) over the Northern Hemisphere h...

  11. Depth of Faulting in Mercury's Northern Hemisphere from Lobate Scarp Morphology

    Science.gov (United States)

    Peterson, G.; Johnson, C.; Byrne, P. K.; Phillips, R. J.; Neumann, G. A.

    2016-12-01

    Lobate scarps on the surface of Mercury are interpreted to be a fault-induced anticlines atop blind or surface-breaking thrust faults, attributed to shortening of the lithosphere as the planet's interior cooled and contracted. In cross section, lobate scarps are characterized by a steeply rising scarp face and a gently sloping back limb. COULOMB dislocation modelling of an elastic half space can be used to investigate the relationship between fault-related topography and the properties of the underlying thrust fault. Using mapped shortening features and topography derived from the Mercury Laser Altimeter (MLA) instrument on the MESSENGER spacecraft, six lobate scarps across Mercury's northern smooth plains and cratered terrain were examined. For each scarp, topographic profiles were taken perpendicular to strike, and the average profile and its standard deviation generated for each scarp. COULOMB modelling incorporated a rectangular homoclinal fault. By varying the fault displacement and dip angle, as well as the minimum (Zu) and maximum (Zm) depths of faulting, best-fit parameters and their uncertainties were determined for each averaged profile. Assuming that lobate scarps deform the entire lithosphere to the brittle-ductile transition depth, estimations of faulting depth provide constraints on Mercury's elastic thickness at the time of faulting. This, in turn, provides constraints on the planet's thermal history. Our results suggest that across the northern hemisphere, the smooth terrain surrounding the northern rise has Zm = 19(+9,-7)km to 28(+10,-8)km, compared to the Carnegie-Victoria region for which Zm = 33(+15,-10) km to 53(+5,-5) km. Best-fit values for Zu are 3-9 km. Comparison of Zm with crustal thickness (Tc) values derived from Mercury's gravity field indicates that faulting typically extends at least 50% of the way through the crust, and in some case through the entire crust.

  12. Geodiversity of high-latitude landscapes in northern Finland

    Science.gov (United States)

    Hjort, Jan; Luoto, Miska

    2010-02-01

    Geodiversity is a rather new, emerging topic in earth science. There is now increased awareness of our need to understand patterns of geodiversity in different landscapes facing global change. In this study, we systematically inventoried geodiversity and topographical parameters in an area of 285 km 2 in subarctic Finland. We quantified the spatial variation of geodiversity using four different measures and analysed the relationship between geodiversity and topography using a spatial grid system at a landscape scale (the size of the analysis window was 500 × 500 m). The number of different elements of geodiversity (total geodiversity) varied from 2 to 22 per grid cell. The spatial pattern of the total geodiversity, geomorphological process variability and geodiversity index were fairly similar, whereas of the other geodiversity measures, the measure of temporal diversity differed the most. Topographically, the high-diversity sites occurred in rather steep-sided valleys. Areas of high geodiversity reflect heterogeneous abiotic conditions where both erosion and accumulation processes play a major role in landscape development. The mapping of geodiversity may be indicative not only in the context of geomorphology, but also provide a focus for conservation initiatives. From a conservation point of view, the lack of wider knowledge of the distribution of geodiversity and its relationship to biodiversity hinders the protection of ecologically and geomorphologically valuable regions. Thus, we recommend that further studies focus on: (1) quantifying spatial patterns of geodiversity in different regions, (2) determining the key drivers that control the variability of geodiversity and (3) exploring the linkage between geodiversity and biodiversity.

  13. Northern Hemisphere ice sheets and planetary waves: a strong feedback mechanism

    NARCIS (Netherlands)

    Lindeman, M.; Oerlemans, J.

    1987-01-01

    We carried out a statistical analysis orihe relation between the net mass balance of high-latitude glaciers and 500 mb height deviations of the seasonal mean atmosphere. Mass-balance series of 23 glaciers and ice caps were used, ranging in length from 8 to`30 yr. Considering the sample as a whole,

  14. Minimizing the wintertime low bias of Northern Hemisphere carbon monoxide in global model simulations

    Science.gov (United States)

    Stein, Olaf; Schultz, Martin G.; Bouarar, Idir; Clark, Hannah; Huijnen, Vincent; Gaudel, Audrey; George, Maya; Clerbaux, Cathy

    2015-04-01

    Carbon monoxide (CO) is a product of incomplete combustion and is also produced from oxidation of volatile organic compounds (VOC) in the atmosphere. It is of interest as an indirect greenhouse gas and an air pollutant causing health effects and is thus subject to emission restrictions. CO acts as a major sink for the OH radical and as a precursor for tropospheric ozone and affects the oxidizing capacity of the atmosphere as well as regional air quality. Despite the developments in the global modelling of chemistry and of the parameterization of the physical processes, CO concentrations remain underestimated during NH winter by most state-of-the-art chemical transport models. The resulting model bias can in principle originate from either an underestimation of CO sources or an overestimation of its sinks. We address both the role of sources and sinks with a series of MOZART chemistry transport model sensitivity simulations for the year 2008 and compare our results to observational data from ground-based stations, satellite observations, and from MOZAIC tropospheric profile measurements on passenger aircraft. Our base case simulation using the MACCity emission inventory (Granier et al. 2011) underestimates the near-surface Northern Hemispheric CO mixing ratios by more than 20 ppb from December to April with a maximal bias of 40 ppb in January. The bias is strongest for the European region (up to 75 ppb in January). From our sensitivity studies the mismatch between observed and modelled atmospheric CO concentrations can be explained by a combination of the following emission inventory shortcuts: (i) missing anthropogenic wintertime CO emissions from traffic or other combustion processes, (ii) missing anthropogenic VOC emissions, (iii) an exaggerated downward trend in the RCP8.5 scenario underlying the MACCity inventory, (iv) a lack of knowledge about the seasonality of emissions. Deficiencies in the parameterization of the dry deposition velocities can also lead to

  15. Using data assimilation to study extratropical Northern Hemisphere climate over the last millennium

    Directory of Open Access Journals (Sweden)

    M. Widmann

    2010-09-01

    Full Text Available Climate proxy data provide noisy, and spatially incomplete information on some aspects of past climate states, whereas palaeosimulations with climate models provide global, multi-variable states, which may however differ from the true states due to unpredictable internal variability not related to climate forcings, as well as due to model deficiencies. Using data assimilation for combining the empirical information from proxy data with the physical understanding of the climate system represented by the equations in a climate model is in principle a promising way to obtain better estimates for the climate of the past.

    Data assimilation has been used for a long time in weather forecasting and atmospheric analyses to control the states in atmospheric General Circulation Models such that they are in agreement with observation from surface, upper air, and satellite measurements. Here we discuss the similarities and the differences between the data assimilation problem in palaeoclimatology and in weather forecasting, and present and conceptually compare three data assimilation methods that have been developed in recent years for applications in palaeoclimatology. All three methods (selection of ensemble members, Forcing Singular Vectors, and Pattern Nudging are illustrated by examples that are related to climate variability over the extratropical Northern Hemisphere during the last millennium. In particular it is shown that all three methods suggest that the cold period over Scandinavia during 1790–1820 is linked to anomalous northerly or easterly atmospheric flow, which in turn is related to a pressure anomaly that resembles a negative state of the Northern Annular Mode.

  16. On the wintertime low bias of Northern Hemisphere carbon monoxide found in global model simulations

    Science.gov (United States)

    Stein, O.; Schultz, M. G.; Bouarar, I.; Clark, H.; Huijnen, V.; Gaudel, A.; George, M.; Clerbaux, C.

    2014-09-01

    Despite the developments in the global modelling of chemistry and of the parameterization of the physical processes, carbon monoxide (CO) concentrations remain underestimated during Northern Hemisphere (NH) winter by most state-of-the-art chemistry transport models. The consequential model bias can in principle originate from either an underestimation of CO sources or an overestimation of its sinks. We address both the role of surface sources and sinks with a series of MOZART (Model for Ozone And Related Tracers) model sensitivity studies for the year 2008 and compare our results to observational data from ground-based stations, satellite observations, and vertical profiles from measurements on passenger aircraft. In our base case simulation using MACCity (Monitoring Atmospheric Composition and Climate project) anthropogenic emissions, the near-surface CO mixing ratios are underestimated in the Northern Hemisphere by more than 20 ppb from December to April, with the largest bias of up to 75 ppb over Europe in January. An increase in global biomass burning or biogenic emissions of CO or volatile organic compounds (VOCs) is not able to reduce the annual course of the model bias and yields concentrations over the Southern Hemisphere which are too high. Raising global annual anthropogenic emissions with a simple scaling factor results in overestimations of surface mixing ratios in most regions all year round. Instead, our results indicate that anthropogenic CO and, possibly, VOC emissions in the MACCity inventory are too low for the industrialized countries only during winter and spring. Reasonable agreement with observations can only be achieved if the CO emissions are adjusted seasonally with regionally varying scaling factors. A part of the model bias could also be eliminated by exchanging the original resistance-type dry deposition scheme with a parameterization for CO uptake by oxidation from soil bacteria and microbes, which reduces the boreal winter dry

  17. Enhancement of the summer North Atlantic Oscillation influence on Northern Hemisphere air temperature

    Science.gov (United States)

    Yuan, Wei; Sun, Jianqi

    2009-11-01

    This study investigates the relationship between the summer North Atlantic Oscillation (SNAO) and the simultaneous Northern Hemisphere (NH) land surface air temperature (SAT) by using the Climate Research Unit (CRU) data. The results show that the SNAO is related to NH land SAT, but this linkage has varied on decadal timescales over the last 52 years, with a strong connection appearing after the late 1970s, but a weak connection before. The mechanism governing the relationship between the SNAO and NH land SAT is discussed based on the NCEP/NCAR reanalysis data. The results indicate that such a variable relationship may result from changes of the SNAO mode around the late 1970s. The SNAO pattern was centered mainly over the North Atlantic before the late 1970s, and thus had a weak influence on the NH land SAT. But after the late 1970s, the SNAO pattern shifted eastward and its southern center was enhanced in magnitude and extent, which transported the SNAO signal to the North Atlantic surrounding continents and even to central East Asia via an upper level wave train along the Asian jet.

  18. Nitrous oxide emissions from temperate grassland ecosystems in the Northern and Southern Hemispheres

    Science.gov (United States)

    Müller, Christoph; Sherlock, Robert R.

    2004-03-01

    Nitrogen (N) fertilized or grazed grasslands in temperate regions of the Northern and Southern Hemisphere are important sources for atmospheric nitrous oxide (N2O). Following synthetic urine applications in a New Zealand grassland ecosystem, and ammonium (NH4+) and nitrate (NO3-) applications to a German grassland ecosystem, approximately 31, 16, and 5%, respectively, of the total emitted N2O (N2Otot) was produced by nitrification (N2Onit) with the rest being produced by denitrification (N2Oden). Analyses of the combined data set showed that 75% of all N2O emissions occurred above 60% water filled porosity (WFPS) and that more than 80% of all N2O emissions occurred at soil temperatures between 10° and 15°C. N2Oden emissions were associated with a WFPS value at around 80% at relatively low NO3- concentrations, while N2Onit emissions only occurred at high NH4+ levels shortly after N application at soil temperatures around 10°C. To increase the accuracy of predictions with simple mathematical models, such as the "hole-in-the-pipe-model," long-term validation data sets are needed where driving variables are related to measured N2Onit and N2Oden data.

  19. Seasonal divergence in the interannual responses of Northern Hemisphere vegetation activity to variations in diurnal climate.

    Science.gov (United States)

    Wu, Xiuchen; Liu, Hongyan; Li, Xiaoyan; Liang, Eryuan; Beck, Pieter S A; Huang, Yongmei

    2016-01-11

    Seasonal asymmetry in the interannual variations in the daytime and nighttime climate in the Northern Hemisphere (NH) is well documented, but its consequences for vegetation activity remain poorly understood. Here, we investigate the interannual responses of vegetation activity to variations of seasonal mean daytime and nighttime climate in NH (>30 °N) during the past decades using remote sensing retrievals, FLUXNET and tree ring data. Despite a generally significant and positive response of vegetation activity to seasonal mean maximum temperature (Tmax) in ~22-25% of the boreal (>50 °N) NH between spring and autumn, spring-summer progressive water limitations appear to decouple vegetation activity from the mean summer Tmax, particularly in climate zones with dry summers. Drought alleviation during autumn results in vegetation recovery from the marked warming-induced drought limitations observed in spring and summer across 24-26% of the temperate NH. Vegetation activity exhibits a pervasively negative correlation with the autumn mean minimum temperature, which is in contrast to the ambiguous patterns observed in spring and summer. Our findings provide new insights into how seasonal asymmetry in the interannual variations in the mean daytime and nighttime climate interacts with water limitations to produce spatiotemporally variable responses of vegetation growth.

  20. Biodiversity and Complexity Influence Seagrass Functioning: A Comparative-Experimental Approach Across the Northern Hemisphere

    Science.gov (United States)

    Reynolds, P. L.

    2016-02-01

    Coastal ecosystems are mediated by interactions between resource supply, consumer pressure, and community composition, with the balance shifting along environmental gradients. Comparative-experimental approaches, including observational and experimental networks, are a promising way forward to organizing this complexity into predictive models and to quantify the role of biodiversity on ocean processes. Through the Zostera Experimental Network we utilize this approach to study the community ecology of eelgrass (Zostera marina), the most widespread marine plant and foundation of important but threatened coastal ecosystems throughout the northern hemisphere. In 2014, parallel field surveys and experiments were conducted at 50 field sites to measure correlations between mesograzer species diversity, eelgrass genetic diversity, predation pressure, and seagrass dynamics. Biodiversity was positively correlated with plant and grazer biomass across sites. Predation pressure in these systems decreased with grazer biomass and latitude. In subsequent experiments in 2015, habitat complexity influenced the grazer community. These results suggest that the impacts of biodiversity loss on ecosystems will be of comparable magnitude to those of other global change factors and should be accounted for in relevant monitoring and restoration activities.

  1. PROBING THE LOCAL BUBBLE WITH DIFFUSE INTERSTELLAR BANDS. II. THE DIB PROPERTIES IN THE NORTHERN HEMISPHERE

    Energy Technology Data Exchange (ETDEWEB)

    Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh; Molaeinezhad, Alireza; Tavasoli, Saeed; Habibi, Farhang; Kourkchi, Ehsan; Rezaei, Sara; Saberi, Maryam [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5746 Tehran (Iran, Islamic Republic of); Van Loon, Jacco Th.; Bailey, Mandy [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom); Hardy, Liam, E-mail: a.farhang@ipm.ir [Isaac Newton Group, Apartado 321, E-38700 Santa Cruz de La Palma (Spain)

    2015-02-10

    We present a new high signal-to-noise ratio spectroscopic survey of the Northern hemisphere to probe the Local Bubble and its surroundings using the λ5780 Å and λ5797 Å diffuse interstellar bands (DIBs). We observed 432 sightlines to a distance of 200 pc over a duration of three years. In this study, we establish the λ5780 and λ5797 correlations with Na I, Ca II and E {sub B-V}, for both inside and outside the Local Bubble. The correlations show that among all neutral and ionized atoms, the correlation between Ca II and λ5780 is stronger than its correlation with λ5797, suggesting that λ5780 is more associated with regions where Ca{sup +} is more abundant. We study the λ5780 correlation with λ5797, which shows a tight correlation within and outside the Local Bubble. In addition, we investigate the DIB properties in UV irradiated and UV shielded regions. We find that, within and beyond the Local Bubble, λ5797 is located in denser parts of clouds, protected from UV irradiation, while λ5780 is located in the low-density regions of clouds.

  2. Variability in seasonal forecast skill of Northern Hemisphere winters over the twentieth century

    Science.gov (United States)

    O'Reilly, Christopher H.; Heatley, James; MacLeod, Dave; Weisheimer, Antje; Palmer, Tim N.; Schaller, Nathalie; Woollings, Tim

    2017-06-01

    Seasonal hindcast experiments, using prescribed sea surface temperatures (SSTs), are analyzed for Northern Hemisphere winters from 1900 to 2010. Ensemble mean Pacific/North American index (PNA) skill varies dramatically, dropping toward zero during the mid-twentieth century, with similar variability in North Atlantic Oscillation (NAO) hindcast skill. The PNA skill closely follows the correlation between the observed PNA index and tropical Pacific SST anomalies. During the mid-century period the PNA and NAO hindcast errors are closely related. The drop in PNA predictability is due to mid-century negative PNA events, which were not forced in a predictable manner by tropical Pacific SST anomalies. Overall, negative PNA events are less predictable and seem likely to arise more from internal atmospheric variability than positive PNA events. Our results suggest that seasonal forecasting systems assessed over the recent 30 year period may be less skillful in periods, such as the mid-twentieth century, with relatively weak forcing from tropical Pacific SST anomalies.

  3. Higher temperature variability reduces temperature sensitivity of vegetation growth in Northern Hemisphere

    Science.gov (United States)

    Wu, Xiuchen; Liu, Hongyan; Li, Xiaoyan; Piao, Shilong; Ciais, Philippe; Guo, Weichao; Yin, Yi; Poulter, Ben; Peng, Changhui; Viovy, Nicolas; Vuichard, Nicolas; Wang, Pei; Huang, Yongmei

    2017-06-01

    Interannual air temperature variability has changed over some regions in Northern Hemisphere (NH), accompanying with climate warming. However, whether and to what extent it regulates the interannual sensitivity of vegetation growth to temperature variability (i.e., interannual temperature sensitivity)—one central issue in understanding and predicting the responses of vegetation growth to changing climate—still remains poorly quantified and understood. Here we quantify the relationships between the interannual temperature sensitivity of mean growing-season (April-October) normalized difference vegetation index (NDVI) and ecosystem model simulations of gross primary productivity (GPP), and variability in mean growing-season temperature for forest, shrub, and grass over NH. We find that higher interannual variability in mean growing-season temperature leads to consistent decrease in interannual temperature sensitivity of mean growing-season NDVI among all vegetation types but not in model simulations of GPP. Drier condition associates with 130 ± 150% further decrease in interannual temperature sensitivity of mean growing-season NDVI by temperature variability in forest and shrub. These results illustrate that varying temperature variability can significantly regulate the interannual temperature sensitivity of vegetation growth over NH, interacted with drought variability and nonlinear responses of photosynthesis to temperature. Our findings call for an improved characterization of the nonlinear effects of temperature variability on vegetation growth within global ecosystem models.

  4. Proxy-based Northern Hemisphere temperature reconstruction for the mid-to-late Holocene

    Science.gov (United States)

    Pei, Qing; Zhang, David D.; Li, Jinbao; Lee, Harry F.

    2017-11-01

    The observed late twentieth century warming must be assessed in relation to natural long-term variations of the climatic system. Here, we present a Northern Hemisphere (NH) temperature reconstruction for the mid-to-late Holocene of the past 6000 years, based on a synthesis of existing paleo-temperature proxies that are capable of revealing centennial-scale variability. This includes 56 published temperature records across the NH land areas, with a sampling resolution ranging from 1 to 100 years and a time span of at least 1000 years. The composite plus scale (CPS) method is adopted with spatial weighting to develop the NH temperature reconstruction. Our reconstruction reveals abrupt cold epochs that match well the Bond events during the past 6000 years. The study further reveals two prominent cycles in NH temperature: 1700-2000-year cycle during the mid-to-late Holocene and 1200-1500-year cycle during the past 3500 years. Our reconstruction indicates that the late twentieth century NH temperature and its rate of warming are both unprecedentedly high over the past 5000 years. By comparing our reconstruction with the projected temperature increase scenarios, we find that temperature by the end of the twenty-first century would likely exceed any peaks during the mid-to-late Holocene.

  5. Impact of maximum borehole depths on ground warming patterns: A spatial analysis over the Northern Hemisphere

    Science.gov (United States)

    Beltrami, Hugo; Matharoo, Gurpreet S.; Smerdon, Jason E.

    2013-04-01

    Past variations in the Earth's surface energy balance are preserved in the terrestrial subsurface and can be inferred from borehole temperature-depth profiles. These profiles are used to reconstruct past ground surface temperature (GST) histories. Recent work by Beltrami et al. (2011) has shown that estimated GST histories can be significantly impacted by the maximum depth of the borehole temperature measurement. In the present study, we use temperature-depth profiles measured at 558 sites distributed between 30o N and 60o N in the Northern Hemisphere. For each site, the background steady-state temperature profile is estimated using progressively deeper maximum depths of truncation. Additionally, GST histories are reconstructed using multiple maximum depth truncations. In order to control on the influence of the geographical sampling, shallow boreholes are dropped from the analysis once their depth is surpassed. The estimated temperature changes over 50-yr intervals are evaluated in these reconstructions as a function of the maximum truncation depth in the database. Similarly, the total terrestrial heat gain is also estimated using progressive depths of truncations. All calculations show a significant dependence on the maximum depths of the borehole profiles and further indicate the importance of this factor in estimates of past temperature and heat content histories derived from geothermal data. Further, calculations also show that the ground has warmed by 0.5o over last 100 years consistent with the earlier studies by Beltrami and Bourlon (2004).

  6. Quantification of temperature persistence over the Northern Hemisphere land-area

    Science.gov (United States)

    Pfleiderer, Peter; Coumou, Dim

    2017-10-01

    Extreme weather events such as heat waves and floods are damaging to society and their contribution to future climate impacts is expected to be large. Such extremes are often related to persistent local weather conditions. Weather persistence is linked to sea surface temperatures, soil-moisture (especially in summer) and large-scale circulation patterns and these factors can alter under past and future climate change. Though persistence is a key characteristic for extreme weather events, to date the climatology and potential changes in persistence have only been poorly documented. Here, we present a systematic analysis of temperature persistence for the northern hemisphere land area. We define persistence as the length of consecutive warm or cold days and use spatial clustering techniques to create regional persistence distributions. We find that persistence is longest in the Arctic and shortest in the mid-latitudes. Parameterizations of the regional persistence distributions show that they are characterized by an exponential decay with a drop in the decay rate for very persistent events, implying that feedback mechanisms are important in prolonging these events. For the mid-latitudes, we find that persistence in summer has increased over the past 60 years. The changes are particularly pronounced for prolonged events suggesting a lengthening in the duration of heat waves.

  7. Uniform Temperature Dependency in the Phenology of a Keystone Herbivore in Lakes of the Northern Hemisphere

    Science.gov (United States)

    Straile, Dietmar; Adrian, Rita; Schindler, Daniel E.

    2012-01-01

    Spring phenologies are advancing in many ecosystems associated with climate warming causing unpredictable changes in ecosystem functioning. Here we establish a phenological model for Daphnia, an aquatic keystone herbivore based on decadal data on water temperatures and the timing of Daphnia population maxima from Lake Constance, a large European lake. We tested this model with long-term time-series data from two lakes (Müggelsee, Germany; Lake Washington, USA), and with observations from a diverse set of 49 lakes/sites distributed widely across the Northern Hemisphere (NH). The model successfully captured the observed temporal variation of Daphnia phenology in the two case study sites (r2 = 0.25 and 0.39 for Müggelsee and Lake Washington, respectively) and large-scale spatial variation in the NH (R2 = 0.57). These results suggest that Daphnia phenology follows a uniform temperature dependency in NH lakes. Our approach – based on temperature phenologies – has large potential to study and predict phenologies of animal and plant populations across large latitudinal gradients in other ecosystems. PMID:23071520

  8. Robust signal of Northern Hemisphere summer monsoon variability during recent warming period

    Science.gov (United States)

    Kim, Hyung Jin

    2013-04-01

    Coupled global climate models (CGCMs) predict the overall weakening of tropical circulations in an anthropogenically warmed climate in accordance with a simple thermodynamic theory. However, the actual response of the climate systems, in particular, over the recent decades of unprecedented warming still remains a topic of debate. Here, we show that in a suite of cutting-edge atmospheric GCMs (AGCMs), the simulated Northern Hemisphere summer monsoon (NHSM) variability, measured by vertical wind shear of zonal winds, is in excellent agreement with observations on both interannual and inter-decadal timescales during 1979-2008. Furthermore, the trend of the NHSM variability is nearly unanimously enhanced among the AGCMs. The overriding factors in determining the simulated NHSM variations are El Niño on year-to-year timescale, and Mega-ENSO (defined as a leading mode of internal sea surface temperature variability over the Pacific) and Atlantic Multi-decadal Oscillation on decadal timescale and beyond, which ascertains the findings of a recent observational study. These results suggest that in contrast to the pivotal role of green-house gas forcing in the simulated future warmer climate, the basin-wide natural SST variability has exerted significant impacts on Earth's climate during the recent 30-year period.

  9. A long-term Northern Hemisphere snow cover extent data record for climate studies and monitoring

    Science.gov (United States)

    Estilow, T. W.; Young, A. H.; Robinson, D. A.

    2015-06-01

    This paper describes the long-term, satellite-based visible snow cover extent National Oceanic and Atmospheric Administration (NOAA) climate data record (CDR) currently available for climate studies, monitoring, and model validation. This environmental data product is developed from weekly Northern Hemisphere snow cover extent data that have been digitized from snow cover maps onto a Cartesian grid draped over a polar stereographic projection. The data have a spatial resolution of 190.6 km at 60° latitude, are updated monthly, and span the period from 4 October 1966 to the present. The data comprise the longest satellite-based CDR of any environmental variable. Access to the data is provided in Network Common Data Form (netCDF) and archived by NOAA's National Climatic Data Center (NCDC) under the satellite Climate Data Record Program (doi:10.7289/V5N014G9). The basic characteristics, history, and evolution of the data set are presented herein. In general, the CDR provides similar spatial and temporal variability to its widely used predecessor product. Key refinements included in the CDR improve the product's grid accuracy and documentation and bring metadata into compliance with current standards for climate data records.

  10. Changes in precipitation recycling over arid regions in the Northern Hemisphere

    Science.gov (United States)

    Li, Ruolin; Wang, Chenghai; Wu, Di

    2018-01-01

    Changes of precipitation recycling (PR) in Northern Hemisphere from 1981 to 2010 are investigated using a water recycling model. The temporal and spatial characteristics of recycling in arid regions are analyzed. The results show that the regional precipitation recycling ratio (PRR) in arid regions is larger than in wet regions. PRR in arid regions has obvious seasonal variation, ranging from more than 25 % to less than 1 %. Furthermore, in arid regions, PRR is significantly negatively correlated with precipitation (correlation coefficient r = -0.5, exceeding the 99 % significance level). Moreover, the trend of PRR is related to changes in precipitation in two ways. PRR decreases with increasing precipitation in North Africa, which implies that less locally evaporated vapor converts into actual precipitation. However, in Asian arid regions, the PRR increases as precipitation reduces, which implies that more locally evaporated vapor converts into rainfall. Further, as PRR mainly depends on evapotranspiration, the PRR trend in Asian arid regions develops as temperature increases and more evaporated vapor enters the atmosphere to offset the reduced rainfall.

  11. Adaptation of Circadian Neuronal Network to Photoperiod in High-Latitude European Drosophilids.

    Science.gov (United States)

    Menegazzi, Pamela; Dalla Benetta, Elena; Beauchamp, Marta; Schlichting, Matthias; Steffan-Dewenter, Ingolf; Helfrich-Förster, Charlotte

    2017-03-20

    The genus Drosophila contains over 2,000 species that, stemming from a common ancestor in the Old World Tropics, populate today very different environments [1, 2] (reviewed in [3]). We found significant differences in the activity pattern of Drosophila species belonging to the holarctic virilis group, i.e., D. ezoana and D. littoralis, collected in Northern Europe, compared to that of the cosmopolitan D. melanogaster, collected close to the equator. These behavioral differences might have been of adaptive significance for colonizing high-latitude habitats and hence adjust to long photoperiods. Most interestingly, the flies' locomotor activity correlates with the neurochemistry of their circadian clock network, which differs between low and high latitude for the expression pattern of the blue light photopigment cryptochrome (CRY) and the neuropeptide Pigment-dispersing factor (PDF) [4-6]. In D. melanogaster, CRY and PDF are known to modulate the timing of activity and to maintain robust rhythmicity under constant conditions [7-11]. We could partly simulate the rhythmic behavior of the high-latitude virilis group species by mimicking their CRY/PDF expression patterns in a laboratory strain of D. melanogaster. We therefore suggest that these alterations in the CRY/PDF clock neurochemistry might have allowed the virilis group species to colonize high-latitude environments. Copyright © 2017 The Author(s). Published by Elsevier Ltd.. All rights reserved.

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

    Directory of Open Access Journals (Sweden)

    M. Guimberteau

    2018-01-01

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

  13. Historical record of nuclear activities from 129I in corals from the northern hemisphere (Philippines).

    Science.gov (United States)

    Bautista, Angel T; Matsuzaki, Hiroyuki; Siringan, Fernando P

    2016-11-01

    Iodine-129 is a long-lived fission product that is majorly released in human nuclear activities (HNA) such as nuclear bomb testing, nuclear fuel reprocessing, and nuclear accidents. It is a good environmental tracer and former measurements of 129I in corals from the southern hemisphere show the increasing trend of 129I concentrations in the marine environment caused by HNA. Here we show time series of 129I/127(stable)I isotopic ratios in two coral cores from the northern hemisphere (Philippines) and how these record 129I released from HNA in even greater, unprecedented detail. Corals were taken from the Pacific Ocean (Baler) and South China Sea (Parola) sides of the Philippines. We observed nearly identical peaks (129I/127I ∼ 31.5 × 10-12) in both the Baler and Parola records, each attributed to the year 1962 - the year with the highest recorded amount of 129I release from nuclear bomb testing. This 1962 129I bomb signal offers a new time marker that can be used to establish or confirm age models of corals, comparable to or possibly better than the well-known coral 14C bomb peak. We also observed nuclear fuel reprocessing and Chernobyl accident 129I signals in years 1977, 1980, and 1986, concurrently in Parola and with 9 to 11-year lags in Baler. This discrepancy in timing suggests that 129I was transported to the South China Sea and Pacific Ocean sides of the Philippines directly from the atmosphere and through prevailing ocean currents, respectively. Lastly, we observed surprisingly high 129I/127I isotopic ratios (i.e., 22.8 to 38.9 × 10-12) in the Parola record after the year 1996, which is in contrast to the decreasing trend observed in the Baler record and in published 129I releases of different HNA. These results possibly indicate the presence of unknown sources of 129I in the South China Sea region. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. A very deep ozone minihole in the Northern Hemisphere stratosphere at mid-latitudes during the winter of 2000

    OpenAIRE

    Semane, N.; Teitelbaum, H.; Basdevant, C.

    2011-01-01

    Ozone miniholes appear on total ozone maps as localized ozone minima with horizontal extentsof a few hundreds of kilometres. They are characterized by a rapid and small-scale appearanceof a columnar ozone decrease with an equally rapid recovery after a few days. They are frequentlyobserved at Northern Hemisphere mid-latitudes in winter. Evolving too rapidly to be the resultof an ozone chemical destruction, miniholes should be the result of meteorological processes.According to some authors, m...

  15. The initial dispersal and radiative forcing of a Northern Hemisphere mid latitude super volcano: a Yellowstone case study

    OpenAIRE

    Timmreck, C.; Graf, H.-F.

    2005-01-01

    International audience; The chemistry climate model MAECHAM4/CHEM with interactive and prognostic volcanic aerosol and ozone, was used to study the initial dispersal and radiative forcing of a possible Yellowstone super eruption. Tropospheric climate anomalies are not analysed since sea surface temperatures are kept fix. Our experiments show that the global dispersal of a Yellowstone super eruption is strongly dependent on the season of the eruption. In Northern Hemisphere summer the volcanic...

  16. CLIMATE ANOMALIES AND EXTREME EVENTS IN AFRICA IN 2003, INCLUDING HEAVY RAINS AND FLOODS THAT OCCURRED DURING NORTHERN HEMISPHERE SUMMER

    OpenAIRE

    Kadomura, Hiroshi

    2005-01-01

    The climate of 2003, particularly during Northern Hemisphere summer, was marked by exceptionally abnormal events throughout the world, and Africa was no exception. As record heat waves prevailed over Europe, heavy rains and floods occurred over the west-central Sahara, across the Sudano-Sahelian region and western Kenya, while drought conditions gripped the Guinea Coast and southeastern Southern Africa, and cold waves hit southern South Africa. Among the most remarkable events were record rai...

  17. Seasonally different response of photosynthetic activity to daytime and night-time warming in the Northern Hemisphere.

    Science.gov (United States)

    Tan, Jianguang; Piao, Shilong; Chen, Anping; Zeng, Zhenzhong; Ciais, Philippe; Janssens, Ivan A; Mao, Jiafu; Myneni, Ranga B; Peng, Shushi; Peñuelas, Josep; Shi, Xiaoying; Vicca, Sara

    2015-01-01

    Over the last century the Northern Hemisphere has experienced rapid climate warming, but this warming has not been evenly distributed seasonally, as well as diurnally. The implications of such seasonal and diurnal heterogeneous warming on regional and global vegetation photosynthetic activity, however, are still poorly understood. Here, we investigated for different seasons how photosynthetic activity of vegetation correlates with changes in seasonal daytime and night-time temperature across the Northern Hemisphere (>30°N), using Normalized Difference Vegetation Index (NDVI) data from 1982 to 2011 obtained from the Advanced Very High Resolution Radiometer (AVHRR). Our analysis revealed some striking seasonal differences in the response of NDVI to changes in day- vs. night-time temperatures. For instance, while higher daytime temperature (Tmax) is generally associated with higher NDVI values across the boreal zone, the area exhibiting a statistically significant positive correlation between Tmax and NDVI is much larger in spring (41% of area in boreal zone--total area 12.6×10(6) km2) than in summer and autumn (14% and 9%, respectively). In contrast to the predominantly positive response of boreal ecosystems to changes in Tmax, increases in Tmax tended to negatively influence vegetation growth in temperate dry regions, particularly during summer. Changes in night-time temperature (Tmin) correlated negatively with autumnal NDVI in most of the Northern Hemisphere, but had a positive effect on spring and summer NDVI in most temperate regions (e.g., Central North America and Central Asia). Such divergent covariance between the photosynthetic activity of Northern Hemispheric vegetation and day- and night-time temperature changes among different seasons and climate zones suggests a changing dominance of ecophysiological processes across time and space. Understanding the seasonally different responses of vegetation photosynthetic activity to diurnal temperature changes

  18. Upper tropospheric water vapour variability at high latitudes – Part 1: Influence of the annular modes

    Directory of Open Access Journals (Sweden)

    C. E. Sioris

    2016-03-01

    Full Text Available Seasonal and monthly zonal medians of water vapour in the upper troposphere and lower stratosphere (UTLS are calculated for both Atmospheric Chemistry Experiment (ACE instruments for the northern and southern high-latitude regions (60–90° N and 60–90° S. Chosen for the purpose of observing high-latitude processes, the ACE orbit provides sampling of both regions in 8 of 12 months of the year, with coverage in all seasons. The 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 are currently the only satellite instruments that can probe from the lower stratosphere down to the mid-troposphere to study the vertical profile of the response of UTLS water vapour to the annular modes. The Arctic oscillation (AO, also known as the northern annular mode (NAM, explains 64 % (r = −0.80 of the monthly variability in water vapour at northern high latitudes observed by ACE-MAESTRO between 5 and 7 km using only winter months (January to March, 2004–2013. Using a seasonal time step and all seasons, 45 % of the variability is explained by the AO at 6.5 ± 0.5 km, similar to the 46 % value obtained for southern high latitudes at 7.5 ± 0.5 km explained by the Antarctic oscillation or southern annular mode (SAM. A large negative AO event in March 2013 produced the largest relative water vapour anomaly at 5.5 km (+70 % over the ACE record. A similarly large event in the 2010 boreal winter, which was the largest negative AO event in the record (1950–2015, led to > 50 % increases in water vapour observed by MAESTRO and ACE-FTS at 7.5 km.

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

    Directory of Open Access Journals (Sweden)

    C. E. Sioris

    2016-02-01

    Full Text Available 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.

  20. An assessment of the atmospheric centers of action in the northern hemisphere winter

    Science.gov (United States)

    Sun, X. J.; Wang, P. X.; Wang, J. X. L.

    2017-02-01

    In the northern hemisphere, there are six permanent or semi-permanent atmospheric activity centers, namely the Icelandic Low, Aleutian Low, India Low, Mongolia High, North Pacific High, and North Atlantic High. The first four are semi-permanent action centers and the last two are permanent circulation systems. The India Low exists only during the summer. By using 160 years (1850-2009) of monthly mean sea level pressure data from the Hadley Centre in the UK, we conduct a comprehensive study of the five boreal winter atmospheric centers of action (ACAs). Based on a unified definition and a method determined in previous studies, we calculate the indices of areal coverage (S), intensity (P), and position of action center ( λ c, φ c) for each of these five ACAs. Through an in-depth analysis of these indices and their relationships with climate variables, we evaluate the indices by describing and explaining areal climate anomalies, particularly precipitation and temperature anomalies in China. We show that (1) ACAs significantly influence the climate anomalies of surrounding areas (2) the influences of oceanic ACAs are larger and the intensity anomalies of ACAs have a greater impact than their location displacement, and (3) ACAs exert more control on temperature than they do on precipitation. For the two ACAs over the north Atlantic, the impacts of their intensities on the anomalies of temperature and precipitation are similar. For the two ACAs over the north Pacific, their influences are almost the opposite. The most influential ACA for climate anomalies in China during the boreal winter is HMO. When HMO is stronger, China has a colder winter and it is wetter in the north. With stronger ACAs in the upstream, i.e., the Icelandic Low and North Atlantic High, northern China has a warmer winter. The ACAs over the north Pacific exert little influence on climate anomalies in China during winter. The analyses presented in this paper provide a set of useful indices for

  1. Impacts of global warming on Northern Hemisphere winter storm tracks in the CMIP5 model suite

    Science.gov (United States)

    Eichler, Timothy Paul; Gaggini, Natalie; Pan, Zaitao

    2013-05-01

    key question in assessing how global warming may affect climate is how it may impact day-to-day weather. To help answer this question, we evaluate the frequency and intensity of northern hemisphere storm tracks in the National Center for Climate Prediction reanalysis I dataset, and the historical, RCP4.5, and RCP8.5 climate scenarios featured in the CMIP5 simulations. We found that a warmer climate resulted in a general decrease in storm frequency in midlatitudes, especially in RCP8.5. In contrast, frequency trends in the reanalysis data reflected an increase in the North Pacific consistent with a shift towards a positive Pacific Decadal Oscillation and more frequent El Niño events post mid-1970s. An examination of frequency and intensity trends in the active storm track regions of the North Pacific and North Atlantic showed that a significant decrease in storm track frequency was evident for RCP8.5. In contrast, intensity trends were dichotomous, with RCP8.5 exhibiting an increase in intensity in the North Atlantic active storm track region and a decrease in intensity in the North Pacific active storm track region. Poleward of these regions, a significant decrease in storm intensity in the North Atlantic and a significant increase in intensity in the North Pacific in RCP8.5 occurred. We also examined the intensity distribution of storms in the active storm track regions of the North Atlantic and North Pacific and determined that the models produced weaker storms with reduced variability relative to reanalysis data regardless of external climate forcing.

  2. Biogeochemical cycling in the Bering Sea over the onset of major Northern Hemisphere Glaciation

    Science.gov (United States)

    Swann, George E. A.; Snelling, Andrea M.; Pike, Jennifer

    2016-09-01

    The Bering Sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the Arctic Ocean and into the subarctic North Pacific Ocean. Cores from Integrated Ocean Drilling Program (IODP) Expedition 323 to the Bering Sea provide the first opportunity to obtain reconstructions from the region that extend back to the Pliocene. Previous research at Bowers Ridge, south Bering Sea, has revealed stable levels of siliceous productivity over the onset of major Northern Hemisphere Glaciation (NHG) (circa 2.85-2.73 Ma). However, diatom silica isotope records of oxygen (δ18Odiatom) and silicon (δ30Sidiatom) presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region, superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice. This concluded at 2.58 Ma with a sharp increase in diatom productivity, further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions. These transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest Pacific Ocean, with increases in productivity further aided by increased sea ice- and wind-driven mixing in the Bering Sea. In suggesting a linkage in biogeochemical cycling between the south Bering Sea and subarctic Northwest Pacific Ocean, mainly via the Kamchatka Strait, this work highlights the need to consider the interconnectivity of these two systems when future reconstructions are carried out in the region.

  3. Source-Receptor Relationships for East Asian Sulfur Dioxide Emissions and Northern Hemisphere Sulfate Concentrations

    Science.gov (United States)

    Liu, J.; Mauzerall, D. L.; Horowitz, L. W.

    2007-12-01

    We analyze the effect of varying East Asian (EA) sulfur emissions on sulfate concentrations in the northern hemisphere based on a global coupled oxidant-aerosol model (MOZART-2) driven with NCEP reanalysis meteorology for 1991. We conduct a base and several sensitivity simulations, in which sulfur emissions from each continent are tagged, to establish the source-receptor (S-R) relationship between EA sulfur emissions and sulfate concentrations over the source and downwind regions. We find that reducing EA SO2 emissions will significantly decrease the spatial extent of the EA sulfate influence over the North Pacific, but raising EA SO2 emissions will not significantly increase the spatial extent of influence. We define a linearity index and find the S-R relationship between EA SO2 emissions and EA sulfate concentrations to be nearly linear over most downwind regions, but to be non-linear over the EA source region, particularly at the surface and in winter. In addition, we find that besides the direct transport of EA sulfate to North America (NA) and Europe (EU), the indirect response of locally-produced NA or EU sulfate to changes in EA SO2 emissions is negative (i.e., offsetting the direct effect) in winter, spring and fall, but becomes positive in summer. In summer the indirect response is as important as direct transport of EA sulfate over the southeastern U.S. and southern EU. This summertime positive indirect effect largely results from induced changes in H2O2 oxidant concentrations over these regions.

  4. The quasi-two-day wave studied using the Northern Hemisphere SuperDARN HF radars

    Directory of Open Access Journals (Sweden)

    S. B. Malinga

    2007-08-01

    Full Text Available Data from the Super Dual Radar Network (SuperDARN radars for 2002 were used to study the behaviour of the quasi-two-day wave (QTDW in the Northern Hemisphere auroral zone. The period of the QTDW is observed to vary in the range of ~42–56 h, with the most dominant period being ~48 h and secondary peaks at ~42- and ~52-h. The spectral power shows a seasonal variation with a peak power (max~70 in summer. The power shows variations of several days and there is also evidence of changes in wave strength with longitude. The 42-h and the 48-h components tend to be strongly correlated in summer. The onset of enhanced wave activity tends to coincide with the westward acceleration of the zonal mean flow and occurs at a time of strong southward meridional flow. The most frequent instantaneous hourly period is in the 40 to 50 h period band, in line with the simultaneous dominance of the 42-h and the 48-h components. The wave numbers are less variable and are around −2 to −4 during times of strong wave activity. For a period of ~48 h, the zonal wave number is about −3 to −4, using a negative value to indicate westward propagating waves. The 42-h and the 52-h components cover a wider band in the −4 to 1 range. The wide zonal wave number spectrum in our results may account for the observed longitudinal variation in the spectral power of the wave.

  5. Coupled Northern Hemisphere permafrost–ice-sheet evolution over the last glacial cycle

    Directory of Open Access Journals (Sweden)

    M. Willeit

    2015-09-01

    Full Text Available Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH permafrost–ice-sheet evolution over the last glacial cycle is explored. The model performs generally well at reproducing present-day permafrost extent and thickness. Modeled permafrost thickness is sensitive to the values of ground porosity, thermal conductivity and geothermal heat flux. Permafrost extent at the Last Glacial Maximum (LGM agrees well with reconstructions and previous modeling estimates. Present-day permafrost thickness is far from equilibrium over deep permafrost regions. Over central Siberia and the Arctic Archipelago permafrost is presently up to 200–500 m thicker than it would be at equilibrium. In these areas, present-day permafrost depth strongly depends on the past climate history and simulations indicate that deep permafrost has a memory of surface temperature variations going back to at least 800 ka. Over the last glacial cycle permafrost has a relatively modest impact on simulated NH ice sheet volume except at LGM, when including permafrost increases ice volume by about 15 m sea level equivalent in our model. This is explained by a delayed melting of the ice base from below by the geothermal heat flux when the ice sheet sits on a porous sediment layer and permafrost has to be melted first. Permafrost affects ice sheet dynamics only when ice extends over areas covered by thick sediments, which is the case at LGM.

  6. Molecular phylogenetics and evolutionary history of sect. Quinquefoliae (Pinus): implications for Northern Hemisphere biogeography.

    Science.gov (United States)

    Hao, Zhen-Zhen; Liu, Yan-Yan; Nazaire, Mare; Wei, Xiao-Xin; Wang, Xiao-Quan

    2015-06-01

    Climatic changes and tectonic events in the Cenozoic have greatly influenced the evolution and geographic distribution of the temperate flora. Such consequences should be most evident in plant groups that are ancient, widespread, and diverse. As one of the most widespread genera of trees, Pinus provides a good model for investigating the history of species diversification and biogeographic disjunction in the Northern Hemisphere. In this study, we reconstructed the phylogeny and investigated the evolutionary and biogeographic history of sect. Quinquefoliae (Pinus), a species-rich lineage disjunctly distributed in Asia, Europe and North America, based on complete taxon sampling and by using nine DNA fragments from chloroplast (cp), mitochondrial (mt) and nuclear genomes. The monophyly of the three subsections, Krempfianae, Gerardianae, and Strobus, is well-supported by cpDNA and nuclear gene phylogenies. However, neither subsect. Gerardianae nor subsect. Strobus forms a monophyletic group in the mtDNA phylogeny, in which sect. Quinquefoliae was divided into two major clades, one consisting of the North American and northeastern Asian species as well as the European P. peuce of subsect. Strobus, and the other comprising the remaining Eurasian species belonging to three subsections. The significant topological incongruence among the gene trees, in conjunction with divergence time estimation and ancestral area reconstruction, indicates that both ancient and relatively recent introgressive hybridization events occurred in the evolution of sect. Quinquefoliae, particularly in northeastern Asia and northwestern North America. In addition, the phylogenetic analysis suggests that the species of subsect. Strobus from subtropical eastern Asia and neighboring areas may have a single origin, although species non-monophyly is very widespread in the nuclear gene trees. Moreover, our study seems to support a Tethyan origin of sect. Quinquefoliae given the distributions and

  7. Skill and predictability in multimodel ensemble forecasts for Northern Hemisphere regions with dominant winter precipitation

    Science.gov (United States)

    Ehsan, Muhammad Azhar; Tippett, Michael K.; Almazroui, Mansour; Ismail, Muhammad; Yousef, Ahmed; Kucharski, Fred; Omar, Mohamed; Hussein, Mahmoud; Alkhalaf, Abdulrahman A.

    2017-05-01

    Northern Hemisphere winter precipitation reforecasts from the European Centre for Medium Range Weather Forecast System-4 and six of the models in the North American Multi-Model Ensemble are evaluated, focusing on two regions (Region-A: 20°N-45°N, 10°E-65°E and Region-B: 20°N-55°N, 205°E-255°E) where winter precipitation is a dominant fraction of the annual total and where precipitation from mid-latitude storms is important. Predictability and skill (deterministic and probabilistic) are assessed for 1983-2013 by the multimodel composite (MME) of seven prediction models. The MME climatological mean and variability over the two regions is comparable to observation with some regional differences. The statistically significant decreasing trend observed in Region-B precipitation is captured well by the MME and most of the individual models. El Niño Southern Oscillation is a source of forecast skill, and the correlation coefficient between the Niño3.4 index and precipitation over region A and B is 0.46 and 0.35, statistically significant at the 95 % level. The MME reforecasts weakly reproduce the observed teleconnection. Signal, noise and signal to noise ratio analysis show that the signal variance over two regions is very small as compared to noise variance which tends to reduce the prediction skill. The MME ranked probability skill score is higher than that of individual models, showing the advantage of a multimodel ensemble. Observed Region-A rainfall anomalies are strongly associated with the North Atlantic Oscillation, but none of the models reproduce this relation, which may explain the low skill over Region-A. The superior quality of multimodel ensemble compared with individual models is mainly due to larger ensemble size.

  8. The initial dispersal and radiative forcing of a Northern Hemisphere mid-latitude super volcano: a model study

    Directory of Open Access Journals (Sweden)

    C. Timmreck

    2006-01-01

    Full Text Available The chemistry climate model MAECHAM4/ CHEM with interactive and prognostic volcanic aerosol and ozone was used to study the initial dispersal and radiative forcing of a possible Northern Hemisphere mid-latitude super eruption. Tropospheric climate anomalies are not analysed since sea surface temperatures are kept fixed. Our experiments show that the global dispersal of a super eruption located at Yellowstone, Wy. is strongly dependent on the season of the eruption. In Northern Hemisphere summer the volcanic cloud is transported westward and preferentially southward, while in Northern Hemisphere winter the cloud is transported eastward and more northward compared to the summer case. Aerosol induced heating leads to a more global spreading with a pronounced cross equatorial transport. For a summer eruption aerosol is transported much further to the Southern Hemisphere than for a winter eruption. In contrast to Pinatubo case studies, strong cooling tendencies appear with maximum peak values of less than −1.6 K/day three months after the eruption in the upper tropical stratosphere. This strong cooling effect weakens with decreasing aerosol density over time and initially prevents the aerosol laden air from further active rising. All-sky net radiative flux changes of less than −32 W/m2 at the surface are about a factor of 6 larger than for the Pinatubo eruption. Large positive flux anomalies of more than 16 W/m2 are found in the first months in the tropics and sub tropics. These strong forcings call for a fully coupled ocean/atmosphere/chemistry model to study climate sensitivity to such a super-eruption.

  9. Northern Hemisphere atmospheric influence of the solar proton events and ground level enhancement in January 2005

    Directory of Open Access Journals (Sweden)

    C. H. Jackman

    2011-07-01

    ppbv during the SPE period due to the small loss rates during winter. Computed NOx increases, which were statistically significant at the 95 % level, lasted about a month past the SPEs. The SCISAT-1 Atmospheric Chemistry Experiment Fourier Transform Spectrometer NOx measurements and MIPAS NO2 measurements for the polar Northern Hemisphere are in reasonable agreement with these predictions. An extremely large ground level enhancement (GLE occurred during the SPE period on 20 January 2005. We find that protons of energies 300 to 20 000 MeV, associated with this GLE, led to very small enhanced lower stratospheric odd nitrogen concentrations of less than 0.1 % and ozone decreases of less than 0.01 %.

  10. Northern Hemisphere Atmospheric Influence of the Solar Proton Events and Ground Level Enhancement in January 2005

    Science.gov (United States)

    Jackman, C. H.; Marsh, D. R.; Vitt, F. M.; Roble, R. G.; Randall, C. E.; Bernath, P. F.; Funke, B.; Lopez-Puertas, M.; Versick, S.; Stiller, G. P.; hide

    2011-01-01

    (x)increases, which were statistically significant at the 95% level, lasted about a month past the SPEs. The SCISAT-I Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) NO(x) measurements and MIPAS NO, measurements for the polar Northern Hemisphere are in reasonable agreement with these predictions. An extremely large ground level enhancement (GLE) occurred during the SPE period on January 20, 2005. We find that protons of energies 300 to 20,000 MeV, not normally included in our computations, led to enhanced lower stratospheric odd nitrogen concentrations of less than 0.1% as a result of this GLE.

  11. 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

  12. DMSP observations of high latitude Poynting flux during magnetic storms

    Science.gov (United States)

    Huang, Cheryl Y.; Huang, Yanshi; Su, Yi-Jiun; Hairston, Marc R.; Sotirelis, Thomas

    2017-11-01

    Previous studies have demonstrated that energy can enter the high-latitude regions of the Ionosphere-Thermosphere (IT) system on open field lines. To assess the extent of high-latitude energy input, we have carried out a study of Poynting flux measured by the Defense Meteorological Satellite Program (DMSP) satellites during magnetic storms. We report sporadic intense Poynting fluxes measured by four DMSP satellites at polar latitudes during two moderate magnetic storms which occurred in August and September 2011. Comparisons with a widely used empirical model for energy input to the IT system show that the model does not adequately capture electromagnetic (EM) energy at very high latitudes during storms. We have extended this study to include more than 30 storm events and find that intense EM energy is frequently detected poleward of 75° magnetic latitude.

  13. Pattern of birth in anorexia nervosa. II: A comparison of early-onset cases in the southern and northern hemispheres.

    Science.gov (United States)

    Willoughby, Kate; Watkins, Beth; Beumont, Pierre; Maguire, Sarah; Lask, Bryan; Waller, Glenn

    2002-07-01

    In the northern hemisphere, people with anorexia nervosa are more likely to be born in the spring and early summer, particularly when environmental temperature at assumed time of conception is warmer. This study investigates whether there is a comparable effect in the southern hemisphere (Australia), where seasonal and temperature patterns are reversed. Date of birth and temperature at assumed time of conception were collected for 199 Australian and 259 UK patients with early-onset anorexia nervosa. Analyses determined patterns of birth and links to temperature at conception. There was little change across the year in the birth patterns of young people with anorexia nervosa in the southern hemisphere. However, there was a significant link between temperature at assumed time of conception and diagnostic subtype. Compared with anorexics of the binge/purge subtype, restrictive anorexics from the southern hemisphere were less likely to be conceived in relatively cool weather. The findings support a temperature at conception hypothesis (modified for local temperature ranges), rather than suggesting a simple seasonal pattern of birth.

  14. Energy sources of the high latitude upper atmosphere

    Science.gov (United States)

    Banks, P. M.

    1981-01-01

    Electrodynamic (Joule) dissipation and plasma wave heating are reviewed as sources of energy for the upper atmosphere at high latitudes. Electrodynamic heating in the thermosphere is described by a generalized energy balance equation taking into account a variety of inelastic processes and energy losses, and the use of height-integrated values of the Joule heating rate to estimate the importance of electrodynamic heating at high latitudes is discussed. Observations of electrons between 95 and 115 km altitude that are up to 1000 K hotter than the neutral atmosphere is presented as evidence for atmospheric heating due to unstable plasma waves arising from the Farley-Buneman modified two-stream instability.

  15. Source-receptor relationships between East Asian sulfur dioxide emissions and Northern Hemisphere sulfate concentrations

    Science.gov (United States)

    Liu, J.; Mauzerall, D. L.; Horowitz, L. W.

    2008-07-01

    We analyze the effect of varying East Asian (EA) sulfur emissions on sulfate concentrations in the Northern Hemisphere, using a global coupled oxidant-aerosol model (MOZART-2). We conduct a base and five sensitivity simulations, in which sulfur emissions from each continent are tagged, to establish the source-receptor (S-R) relationship between EA sulfur emissions and sulfate concentrations over source and downwind regions. We find that from west to east across the North Pacific, EA sulfate contributes approximately 80% 20% of sulfate at the surface, but at least 50% at 500 hPa. Surface sulfate concentrations are dominated by local anthropogenic sources. Of the sulfate produced from sources other than local anthropogenic emissions (defined here as "background" sulfate), EA sources account for approximately 30% 50% (over the Western US) and 10% 20% (over the Eastern US). The surface concentrations of sulfate from EA sources over the Western US are highest in MAM (up to 0.15 μg/m3), and lowest in DJF (less than 0.06 μg/m3). Reducing EA SO2 emissions will significantly decrease the spatial extent of the EA sulfate influence (represented by the areas where at least 0.1 μg m-3 of sulfate originates from EA) over the North Pacific both at the surface and at 500 hPa in all seasons, but the extent of influence is insensitive to emission increases, particularly in DJF and JJA. We find that EA sulfate concentrations over most downwind regions respond nearly linearly to changes in EA SO2 emissions, but sulfate concentrations over the EA source region increase more slowly than SO2 emissions, particularly at the surface and in winter, due to limited availability of oxidants (in particular of H2O2, which oxidizes SO2 to sulfate in the aqueous phase). We find that similar estimates of the S-R relationship for trans-Pacific transport of EA sulfate would be obtained using either sensitivity (i.e., varying emissions from a region to examine the effects on downwind concentrations

  16. Source-receptor relationships between East Asian sulfur dioxide emissions and Northern Hemisphere sulfate concentrations

    Directory of Open Access Journals (Sweden)

    J. Liu

    2008-07-01

    Full Text Available We analyze the effect of varying East Asian (EA sulfur emissions on sulfate concentrations in the Northern Hemisphere, using a global coupled oxidant-aerosol model (MOZART-2. We conduct a base and five sensitivity simulations, in which sulfur emissions from each continent are tagged, to establish the source-receptor (S-R relationship between EA sulfur emissions and sulfate concentrations over source and downwind regions. We find that from west to east across the North Pacific, EA sulfate contributes approximately 80%–20% of sulfate at the surface, but at least 50% at 500 hPa. Surface sulfate concentrations are dominated by local anthropogenic sources. Of the sulfate produced from sources other than local anthropogenic emissions (defined here as "background" sulfate, EA sources account for approximately 30%–50% (over the Western US and 10%–20% (over the Eastern US. The surface concentrations of sulfate from EA sources over the Western US are highest in MAM (up to 0.15 μg/m3, and lowest in DJF (less than 0.06 μg/m3. Reducing EA SO2 emissions will significantly decrease the spatial extent of the EA sulfate influence (represented by the areas where at least 0.1 μg m−3 of sulfate originates from EA over the North Pacific both at the surface and at 500 hPa in all seasons, but the extent of influence is insensitive to emission increases, particularly in DJF and JJA. We find that EA sulfate concentrations over most downwind regions respond nearly linearly to changes in EA SO2 emissions, but sulfate concentrations over the EA source region increase more slowly than SO2 emissions, particularly at the surface and in winter, due to limited availability of oxidants (in particular of H2O2, which oxidizes SO2 to sulfate in the aqueous phase. We find that similar estimates of the S-R relationship for trans-Pacific transport of EA sulfate would be

  17. Assessment of atmosphere-ocean general circulation model simulations of winter northern hemisphere atmospheric blocking

    Energy Technology Data Exchange (ETDEWEB)

    Vial, Jessica; Osborn, Tim J. [University of East Anglia, Climatic Research Unit, School of Environmental Sciences, Norwich (United Kingdom)

    2012-07-15

    An assessment of six coupled Atmosphere-Ocean General Circulation Models (AOGCMs) is undertaken in order to evaluate their ability in simulating winter atmospheric blocking highs in the northern hemisphere. The poor representation of atmospheric blocking in climate models is a long-standing problem (e.g. D'Andrea et al. in Clim Dyn 4:385-407, 1998), and despite considerable effort in model development, there is only a moderate improvement in blocking simulation. A modified version of the Tibaldi and Molteni (in Tellus A 42:343-365, 1990) blocking index is applied to daily averaged 500 hPa geopotential fields, from the ERA-40 reanalysis and as simulated by the climate models, during the winter periods from 1957 to 1999. The two preferred regions of blocking development, in the Euro-Atlantic and North Pacific, are relatively well captured by most of the models. However, the prominent error in blocking simulations consists of an underestimation of the total frequency of blocking episodes over both regions. A more detailed analysis revealed that this error was due to an insufficient number of medium spells and long-lasting episodes, and a shift in blocking lifetime distributions towards shorter blocks in the Euro-Atlantic sector. In the Pacific, results are more diverse; the models are equally likely to overestimate or underestimate the frequency at different spell lengths. Blocking spatial signatures are relatively well simulated in the Euro-Atlantic sector, while errors in the intensity and geographical location of the blocks emerge in the Pacific. The impact of models' systematic errors on blocking simulation has also been analysed. The time-mean atmospheric circulation biases affect the frequency of blocking episodes, and the maximum event duration in the Euro-Atlantic region, while they sometimes cause geographical mislocations in the Pacific sector. The analysis of the systematic error in time-variability has revealed a negative relationship between the

  18. Probabilistic evaluation of decadal prediction skill regarding Northern Hemisphere winter storms

    Directory of Open Access Journals (Sweden)

    Tim Kruschke

    2016-12-01

    Full Text Available Winter wind storms related to intense extra-tropical cyclones are meteorological extreme events, often with major impacts on economy and human life, especially for Europe and the mid-latitudes. Hence, skillful decadal predictions regarding the frequency of their occurrence would be of great socio-economic value. The present paper extends the study of Kruschke et al. (2014 in several aspects. First, this study is situated in a more impact oriented context by analyzing the frequency of potentially damaging wind storm events instead of targeting at cyclones as general meteorological features which was done by Kruschke et al. (2014. Second, this study incorporates more data sets by analyzing five decadal hindcast experiments – 41 annual (1961–2001 initializations integrated for ten years each – set up with different initialization strategies. However, all experiments are based on the Max-Planck-Institute Earth System Model in a low-resolution configuration (MPI-ESM-LR. Differing combinations of these five experiments allow for more robust estimates of predictive skill (due to considerably larger ensemble size and systematic comparisons of the underlying initialization strategies. Third, the hindcast experiments are corrected for model bias and potential drifts over lead time by means of a novel parametric approach, accounting for non-stationary model drifts. We analyze whether skillful probabilistic three-category forecasts (enhanced, normal or decreased can be provided regarding winter (ONDJFM wind storm frequencies over the Northern Hemisphere (NH. Skill is assessed by using climatological probabilities and uninitialized transient simulations as reference forecasts. It is shown that forecasts of average winter wind storm frequencies for winters 2–5 and winters 2–9 are skillful over large parts of the NH. However, most of this skill is associated with external forcing from transient greenhouse gas and aerosol concentrations

  19. Cassini limb images of hazes in Saturn’s northern hemisphere

    Science.gov (United States)

    Sanchez-Lavega, Agustin M.; Garcia, Daniel; del Rio-Gaztelurrutia, Teresa; Garcia-Muñoz, Antonio; Perez-Hoyos, Santiago; Hueso, Ricardo

    2017-10-01

    We have used high resolution Cassini ISS images of the limb of Saturn to study the vertical distribution, altitude location, thickness and optical properties of the haze layers in the northern hemisphere (1°S to 82°N) in 2013 and 2015. The images cover an ample spectral range from the ultraviolet (UV1 filter, 264 nm) to the near infrared (CB3 filter, 938 nm) including methane absorption bands at 619 nm, 724 nm and 890 nm. Spatial resolution ranges from 1.6 to 13 km/pixel depending on wavelength and latitude. Three latitude bands were selected for the analysis according to the background zonal wind profile measured at cloud level and known dynamical activity: (a) North Polar Region encompassing the Hexagon latitude (74°N) (b) Mid-latitudes (45°N-52°N), and (3) Equator (1°N-3°S). The best defined haze structures and most extended haze layers were found at the latitude of the Hexagon. Up to 6-8 haze layers extending up to 400 km in altitude above clouds (in the pressure range from about 0.7 bar to 0.1 mbar) were detected. The vertical thickness of the layers is in the range 3-15 km compared to the scale height which is about 40 km. The spectral reflectivity is relatively uniform between the layers in the blue and red continuum wavelengths coming from the backward light scattering from the haze particles, while the brightness in the methane bands (relative to red continuum) and in the ultraviolet shows the effects of methane absorption and Rayleigh scattering by the gas, respectively. At mid-latitudes 3-4 haze layers are found spanning up to altitudes 200 km above the clouds. At the Equator 5-6 layers are found extending up to altitudes 250 km above the clouds (up to 2 mbar in pressure level) in a region of great dynamical interest because of the particular structure of the zonal winds and their known oscillations. We comment on the possible nature of the haze layers on the basis of condensing species and photochemistry.

  20. How predictable is the northern hemisphere summer upper-tropospheric circulation?

    Energy Technology Data Exchange (ETDEWEB)

    Lee, June-Yi; Wang, Bin [University of Hawaii/IPRC, International Pacific Research Center, Honolulu, HI (United States); Ding, Q. [University of Washington, Department of Earth and Space Sciences and Quaternary Research Center, Seattle, WA (United States); Ha, K.J.; Ahn, J.B. [Pusan National University, Division of Earth Environmental System, Busan (Korea, Republic of); Kumar, A. [NCEP/CPC, Camp Springs, MD (United States); Stern, B. [Princeton University, NOAA/GFDL, Princeton, NJ (United States); Alves, O. [Bureau of Meteorology, Centre for Australia Weather and Climate Research (CAWCR), Melbourne, VIC (Australia)

    2011-09-15

    The retrospective forecast skill of three coupled climate models (NCEP CFS, GFDL CM2.1, and CAWCR POAMA 1.5) and their multi-model ensemble (MME) is evaluated, focusing on the Northern Hemisphere (NH) summer upper-tropospheric circulation along with surface temperature and precipitation for the 25-year period of 1981-2005. The seasonal prediction skill for the NH 200-hPa geopotential height basically comes from the coupled models' ability in predicting the first two empirical orthogonal function (EOF) modes of interannual variability, because the models cannot replicate the residual higher modes. The first two leading EOF modes of the summer 200-hPa circulation account for about 84% (35.4%) of the total variability over the NH tropics (extratropics) and offer a hint of realizable potential predictability. The MME is able to predict both spatial and temporal characteristics of the first EOF mode (EOF1) even at a 5-month lead (January initial condition) with a pattern correlation coefficient (PCC) skill of 0.96 and a temporal correlation coefficient (TCC) skill of 0.62. This long-lead predictability of the EOF1 comes mainly from the prolonged impacts of El Nino-Southern Oscillation (ENSO) as the EOF1 tends to occur during the summer after the mature phase of ENSO. The second EOF mode (EOF2), on the other hand, is related to the developing ENSO and also the interdecadal variability of the sea surface temperature over the North Pacific and North Atlantic Ocean. The MME also captures the EOF2 at a 5-month lead with a PCC skill of 0.87 and a TCC skill of 0.67, but these skills are mainly obtained from the zonally symmetric component of the EOF2, not the prominent wavelike structure, the so-called circumglobal teleconnection (CGT) pattern. In both observation and the 1-month lead MME prediction, the first two leading modes are accompanied by significant rainfall and surface air temperature anomalies in the continental regions of the NH extratropics. The MME

  1. Responses of surface ozone air quality to anthropogenic nitrogen deposition in the Northern Hemisphere

    Science.gov (United States)

    Zhao, Yuanhong; Zhang, Lin; Tai, Amos P. K.; Chen, Youfan; Pan, Yuepeng

    2017-08-01

    Human activities have substantially increased atmospheric deposition of reactive nitrogen to the Earth's surface, inducing unintentional effects on ecosystems with complex environmental and climate consequences. One consequence remaining unexplored is how surface air quality might respond to the enhanced nitrogen deposition through surface-atmosphere exchange. Here we combine a chemical transport model (GEOS-Chem) and a global land model (Community Land Model, CLM) to address this issue with a focus on ozone pollution in the Northern Hemisphere. We consider three processes that are important for surface ozone and can be perturbed by the addition of atmospheric deposited nitrogen - namely, emissions of biogenic volatile organic compounds (VOCs), ozone dry deposition, and soil nitrogen oxide (NOx) emissions. We find that present-day anthropogenic nitrogen deposition (65 Tg N a-1 to the land), through enhancing plant growth (represented as increases in vegetation leaf area index, LAI, in the model), could increase surface ozone from increased biogenic VOC emissions (e.g., a 6.6 Tg increase in isoprene emission), but it could also decrease ozone due to higher ozone dry deposition velocities (up to 0.02-0.04 cm s-1 increases). Meanwhile, deposited anthropogenic nitrogen to soil enhances soil NOx emissions. The overall effect on summer mean surface ozone concentrations shows general increases over the globe (up to 1.5-2.3 ppbv over the western US and South Asia), except for some regions with high anthropogenic NOx emissions (0.5-1.0 ppbv decreases over the eastern US, western Europe, and North China). We compare the surface ozone changes with those driven by the past 20-year climate and historical land use changes. We find that the impacts from anthropogenic nitrogen deposition can be comparable to the climate- and land-use-driven surface ozone changes at regional scales and partly offset the surface ozone reductions due to land use changes reported in previous studies

  2. Climatic Change and Dynamics of Northern Hemisphere Storm-tracks: Changes in Transient Eddies Behavior

    Science.gov (United States)

    Martynova, Yuliya; Krupchatnikov, Vladimir

    2013-04-01

    An evidence of our understanding of the general circulation is whether we can predict changes in the general circulation that might be associated with past or future climate changes. Changes in the location, intensity or seasonality of major climatological features of the general circulation could be more important than average temperature changes, particularly where these changes could affect local hydrology, energy balances, etc. Under these major climatological features we assume the poleward expansion of the tropical circulation (Hadley circulation), static stability (changes in the vertical temperature structure of the atmosphere), role of SST forcing, sea ice extension, extratropical eddies behavior. We have a question: would the climate change significantly affect the location and intensity of midlatitude storm-tracks and associated jets? Mean-flow interaction in midlatitudes produces low-frequency variations in the latitude of the jets. It is reasonable to think that a modest climate change might significantly affects the jets location and their associated storm tracks. The storm-tracks are defined as the region of strong baroclinicity (maximum meridional temperature gradient), which are determined on the basis of eddy statistics like eddy fluxes of angular momentum, energy, and water (with the use of high-bandpass filter). In the Northern Hemisphere, there are two major storms: in the region of Atlantic and Pacific. The storm-tracks play important role in the dynamics of weather and climate. They affect the global energy cycle and the hydrological cycle, and as a result they bring heavy rains and other hazardous weather phenomena in the middle latitudes. The recent increase in global tropopause heights is closely associated with systematic temperature changes below and above the tropopause. Temperature increases in the troposphere and decreases in the stratosphere. The pattern of warming and cooling also affects the zonal wind structure in the region of

  3. The Role of Eolian Dust Fertilization in Biogeochemical Cycles in The sub-Arctic Northwest Pacific During the Late Pliocene Intensification of Northern Hemisphere Glaciation

    Science.gov (United States)

    Bailey, I.; Liu, Q.; Swann, G.; Jiang, Z.; Sun, Y.; Zhao, X.; Roberts, A.

    2010-12-01

    Marine sediments recovered during Ocean Drilling Program (ODP) Leg 145 have improved our knowledge of climatic and oceanographic change in the North Pacific Ocean and surrounding landmasses during the last several million years. Of particular importance has been the analysis of high-latitude terrigenous sedimentary components sourced from the Asian continental interior via eolian deposition and from the circum-North Pacific landmasses via ice rafting. Teasing apart the relative contribution of eolian dust and ice-rafted debris (IRD) to deep sea sediments in the sub-Arctic Pacific is important for developing our understanding of late Pliocene ice-sheet evolution and the potential role of iron fertilization in biogeochemical cycles in the North Pacific Ocean. The magnetic properties of both eolian dust and IRD often have distinctive magnetic signatures, making environmental magnetism useful for investigating the relative importance of these sediment sources to bulk terrigenous inputs. Enhancements of the low-field volume magnetic susceptibility and the terrigenous sediment component from ODP Site 882 (~45°N) are classically interpreted to indicate a major onset of ice rafting to the sub-Arctic northwest Pacific Ocean during the late Pliocene (from ca MIS G6). On the other hand, studies of the eolian dust content of sediments from ODP Site 885, cored downwind of Site 882, indicate that dust deposition in the sub-Arctic Pacific increased markedly during MIS G6. This suggests that the classic interpretation of the magnetic susceptibility record at Site 882 requires reappraisal. To investigate the relative contribution of dust versus ice rafting to the Pliocene North Pacific, we present new high-resolution environmental magnetic and IRD records from ODP sites 882 and 885. We find that terrigenous inputs to both sites across MIS G6 were dominated by eolian dust (not IRD). Our findings call into question the reliability of magnetic susceptibility as a simple proxy for IRD

  4. Importance of tropospheric ClNO2 chemistry across the Northern Hemisphere

    Science.gov (United States)

    Laboratory and field experiments have revealed that the heterogeneous hydrolysis of dinitrogen pentoxide produces nitryl chloride and nitric acid in the presence of particulate chloride. We incorporate the heterogeneous chemistry of nitryl chloride into the hemispheric Community ...

  5. Five-year records of mercury wet deposition flux at GMOS sites in the Northern and Southern hemispheres

    Science.gov (United States)

    Sprovieri, Francesca; Pirrone, Nicola; Bencardino, Mariantonia; D'Amore, Francesco; Angot, Helene; Barbante, Carlo; Brunke, Ernst-Günther; Arcega-Cabrera, Flor; Cairns, Warren; Comero, Sara; Diéguez, María del Carmen; Dommergue, Aurélien; Ebinghaus, Ralf; Feng, Xin Bin; Fu, Xuewu; Garcia, Patricia Elizabeth; Gawlik, Bernd Manfred; Hageström, Ulla; Hansson, Katarina; Horvat, Milena; Kotnik, Jože; Labuschagne, Casper; Magand, Olivier; Martin, Lynwill; Mashyanov, Nikolay; Mkololo, Thumeka; Munthe, John; Obolkin, Vladimir; Ramirez Islas, Martha; Sena, Fabrizio; Somerset, Vernon; Spandow, Pia; Vardè, Massimiliano; Walters, Chavon; Wängberg, Ingvar; Weigelt, Andreas; Yang, Xu; Zhang, Hui

    2017-02-01

    The atmospheric deposition of mercury (Hg) occurs via several mechanisms, including dry and wet scavenging by precipitation events. In an effort to understand the atmospheric cycling and seasonal depositional characteristics of Hg, wet deposition samples were collected for approximately 5 years at 17 selected GMOS monitoring sites located in the Northern and Southern hemispheres in the framework of the Global Mercury Observation System (GMOS) project. Total mercury (THg) exhibited annual and seasonal patterns in Hg wet deposition samples. Interannual differences in total wet deposition are mostly linked with precipitation volume, with the greatest deposition flux occurring in the wettest years. This data set provides a new insight into baseline concentrations of THg concentrations in precipitation worldwide, particularly in regions such as the Southern Hemisphere and tropical areas where wet deposition as well as atmospheric Hg species were not investigated before, opening the way for future and additional simultaneous measurements across the GMOS network as well as new findings in future modeling studies.

  6. Widespread land surface wind decline in the Northern Hemisphere partly attributed to land surface changes

    Science.gov (United States)

    Thepaut, J.; Vautard, R.; Cattiaux, J.; Yiou, P.; Ciais, P.

    2010-12-01

    The decline of surface wind observed in many regions of the world is a potential source of concern for wind power electricity generation. It is also suggested as the main cause of decreasing pan evaporation. In China, a persistent and significant decrease of monsoon winds was observed in all seasons. Surface wind declines were also evidenced in several regions of the world (U.S., Australia, several European countries). Except over China, no clear explanation was given for the wind decrease in the regions studied. Whether surface winds decrease is due to changes in the global atmospheric circulation or its variability, in surface processes or to observational trends has therefore not been elucidated. The identification of the drivers of such a decline requires a global investigation of available surface and upper-air wind data, which has not been conducted so far. Here we use global datasets of in-situ wind measurements that contain surface weather stations wind data (hourly or three-hourly data acquisition time step) and rawinsonde vertical wind data profiles (monthly time step) prepared by the NCAR. A set of 822 worldwide surface stations with continuous wind records was selected after a careful elimination of stations with obvious breaks and large gaps. This dataset mostly covers the Northern mid latitudes over the period 1979-2008. Using this data set, we found that annual mean wind speeds have declined at 73% of the surface stations over the past 30 years. In the Northern Hemisphere, positive wind trends are found only in a few places. In Europe, Central Asia, Eastern Asia and in North America the annual mean surface wind speed has decreased on average at a rate of -2.9, -5.9, -4.2, and -1.8 %/decade respectively, i.e. a decrease of about 10% in 30 years and up to about 20% in Central Asia. These results are robust to changes in the station selection method and parameters. By contrast, upper-air winds observed from rawinsondes, geostrophic winds deduced from

  7. Relationship Between the Northern Hemisphere Polar Vortext ,North Pacific Storm Track and the West Wind Drift

    Science.gov (United States)

    Lian, Y.; Li, S.; Liu, Z.; Shen, B.; Yang, Q.

    2007-12-01

    : For this study, we use the daily and the monthly data from the National Centers for Environmental Prediction- National Centers for Atmospheric Research(NCEP-NCAR) reanalysis. In addition, we employ the monthly sea surface temperature data and the area index of the polar vortex in the Pacific sector from Beijing Climate Center. The time of the data set covers from 1951 to 2002.We study the relationship between the polar area in the northern hemisphere and the sea surface temperature in the west wind drift( we also do the same work between the storm track and the polar area) in the spring, the result shows that: (1) In the Pacific sector (150° E - 120° W), there is obvious negative correlation between the area index of the polar vortex and the index of sea surface temperature in west wind drift area in spring. Moreover, we also find the same phenomenon between the Pacific sector polar vortex area index and the storm track in the spring. With respect to the definition of the storm track index and the index of the west wind drift area sea surface temperature, we will give some explanation at the end of the paper. (2)By using the M-K(Mann-Kendall) test method, we found that the spring polar area index in the Pacific sector and the spring storm track index all have an abrupt change in 1969. The value of the spring polar area index is smaller than that of the average throughout the 1950s and 1960's,but during the 1970s and 1980s it is on the contrary. Analysing the index variety we can conclude that the location of the Pacific storm track is more northward throughout the 1950's and 1960's but more southward during the 1970s and 1980s.Using the M-K(Mann-Kendall) test method ,we also found the spring index of the sea surface temperature in the west wind drift area have an abrupt change in 1973.It means that the sea surface temperature of the west wind drift is colder during the 1950s and 1960's,but during the 1970s and 1980s it is warmer. (3)During the 1950s and 1960s

  8. 30,000-Year Record of Climate From the Galapagos Islands and Links With High Latitudes

    Science.gov (United States)

    Koutavas, A.; Lynch-Stieglitz, J.; Sachs, J. P.; Marchitto, T. M.

    2001-12-01

    The eastern equatorial Pacific (EEP) upwelling system influences climate on a global scale as manifested by the far-reaching teleconnections of El Nino-Southern Oscillation (ENSO). It is postulated that this system has played a primary role in orbital and millennial scale climate variability of the late Quaternary, but a test of this hypothesis has been hampered by a lack of high-resolution regional climate records. New tools for sea-surface temperature (SST) reconstruction, including Mg/Ca ratios in foraminifera and alkenone unsaturation ratios in bulk sediment, offer the potential for deconvolving the sea-surface temperature signal from oxygen-isotope records dominated by the isotopic composition of seawater. Application of these methods in the EEP upwelling region is beginning to place important constraints on past SST variability, nevertheless a detailed history of regional SST evolution during the last deglaciation has been lacking due to a virtual absence of high-resolution records from the core of the EEP upwelling tongue. We present a radiocarbon-dated, millennial resolution climate record of the last 30,000 years from a sediment core near the Galapagos Islands. This site is unique in its combination of (a) a high sedimentation rate (13 cm/ky), (b) a shallow depth (617 m), and (c) a southern equatorial position (1.2° S). Collectively these characteristics help circumvent bioturbation and dissolution problems in a site proximal to the core of the upwelling tongue that develops primarily south of the equator. Despite a modest glacial-interglacial SST amplitude of \\sim1.5oC based on alkenones and δ 18O, millennial-scale oscillations in SST as well as in foraminiferal δ 18O and δ 13C suggest links with Northern Hemisphere climate involving EEP upwelling variability. However, SST is decoupled from upwelling during parts of the record, which calls for the opposing influence of some other mechanism(s). A key candidate for this role may be advection of climate

  9. Recent increase of ethane detected in the remote atmosphere of the Northern Hemisphere

    Science.gov (United States)

    Franco, Bruno; Bader, Whitney; Bovy, Benoît; Mahieu, Emmanuel; Fischer, Emily V.; Strong, Kimberly; Conway, Stephanie; Hannigan, James W.; Nussbaumer, Eric; Bernath, Peter F.; Boone, Chris D.; Walker, Kaley A.

    2015-04-01

    Ethane (C2H6) has a large impact on tropospheric composition and air quality because of its involvement in the global VOC (volatile organic compound) - HOx - NOx chemistry responsible for generating and destroying tropospheric ozone. By acting as a major sink for tropospheric OH radicals, the abundance of C2H6 influences the atmospheric content of carbon monoxide and impacts the lifetime of methane. Moreover, it is an important source of PAN, a thermally unstable reservoir for NOx radicals. On a global scale, the main sources of C2H6 are leakage from the production, transport of natural gas loss, biofuel consumption and biomass burning, mainly located in the Northern Hemisphere. Due to its relatively long lifetime of approximately two months, C2H6 is a sensitive indicator of tropospheric pollution and transport. Using an optimized retrieval strategy (see Franco et al., 2014), we present here a 20-year long-term time series of C2H6 column abundance retrieved from ground-based Fourier Transform InfraRed (FTIR) solar spectra recorded from 1994 onwards at the high-altitude station of Jungfraujoch (Swiss Alps, 46.5° N, 3580 m a.s.l.), part of the Network for the Detection of Atmospheric Composition Change (NDACC, see http://www.ndacc.org). After a regular 1994 - 2008 decrease of the C2H6 amounts, which is very consistent with prior major studies (e.g., Aydin et al., 2011; Simpson et al., 2012) and our understanding of global C2H6 emissions, trend analysis using a bootstrap resampling tool reveals a C2H6 upturn and a statistically-significant sharp burden increase from 2009 onwards (Franco et al., 2014). We hypothesize that this observed recent increase in C2H6 could affect the whole Northern Hemisphere and may be related to the recent massive growth in the exploitation of shale gas and tight oil reservoirs. This hypothesis is supported by measurements derived from solar occultation observations performed since 2004 by the Atmospheric Chemistry Experiment - Fourier

  10. Poleward Transport Variability in the Northern Hemisphere during Final Stratospheric Warmings simulated by CESM(WACCM)

    Science.gov (United States)

    Thiéblemont, Rémi; Matthes, Katja; Orsolini, Yvan; Hauchecorne, Alain; Huret, Nathalie

    2017-04-01

    Observational studies of Arctic stratospheric final warmings have shown that tropical/subtropical air masses can be advected to high latitudes and remain confined within a long-lived "frozen-in" anticyclone (FrIAC) for several months. It was suggested that the frequency of FrIACs may have increased since 2000 and that their interannual variability may be modulated by (i) the occurrence of major stratospheric warmings (mSSWs) in the preceding winter and (ii) the phase of the Quasi-Biennial Oscillation (QBO). In this study, we tested these observational-based hypotheses for the first time using a chemistry-climate model. Three 145-year sensitivity experiments were performed with the National Center of Atmospheric Research's Community Earth System Model (CESM): one control experiment including only natural variability, one with an extreme greenhouse gas emission scenario, and one without the QBO in the tropical stratosphere. In comparison with reanalysis, the model simulates a realistic frequency and characteristics of FrIACs, which occur under an abrupt and early winter-to-summer stratospheric circulation transition, driven by enhanced planetary wave activity. Furthermore, the model results support the suggestion that the development of FrIACs is favored by an easterly QBO in the middle stratosphere and by the absence of mSSWs during the preceding winter. The lower stratospheric persistence of background dynamical state anomalies induced by deep mSSWs leads to less favorable conditions for planetary waves to enter the high-latitude stratosphere in April, which in turn decreases the probability of FrIAC development. Our model results do not suggest that climate change conditions (RCP8.5 scenario) influence FrIAC occurrences.

  11. The potential for regime shifts in high latitude terrestrial ecosystems

    Science.gov (United States)

    Beck, P. S.; Goetz, S. J.

    2011-12-01

    Climate constrains the extent of the two major terrestrial biomes at high latitudes: boreal forests and arctic tundra. Model simulations provide considerable evidence that physical and biogeochemical feedbacks from these regions to the climate system act to maintain a status quo of climate and biome distribution. Ongoing anthropogenically driven changes in climate are particularly pronounced in high latitude regions, and empirical evidence for their influence on tundra and boreal ecosystems is mounting. Global vegetation models project changes to accelerate in coming decades, culminating in profound shifts in high latitude biomes by the end of this century. Regime shifts are surprisingly large changes in a system that occur when a it moves between alternative stable states ('attractors'), without the equivalent large shift of an external driver. In association with climate change, regime shifts in ecosystems could theoretically generate significant modifications to ecosystem-climate feedbacks, in the Arctic for example through the respiration or combustion of large amounts of soil carbon. Here we review evidence for historical regime shifts in terrestrial ecosystems at high latitudes, including shifts in species dominance and distribution. We describe ongoing changes in characteristics of these ecosystems, including vegetation productivity, composition, and the fire regime, and discuss whether they can be indicators of impeding regime shifts. Finally, we discuss the potential of exploiting regime shifts in tundra and boreal systems for climate change mitigation or resource management by forcing ecosystems to shift towards a more desirable stable state.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-10-18

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

  13. Organic aerosol components observed in Northern Hemispheric datasets from Aerosol Mass Spectrometry

    Directory of Open Access Journals (Sweden)

    N. L. Ng

    2010-05-01

    Full Text Available In this study we compile and present results from the factor analysis of 43 Aerosol Mass Spectrometer (AMS datasets (27 of the datasets are reanalyzed in this work. The components from all sites, when taken together, provide a holistic overview of Northern Hemisphere organic aerosol (OA and its evolution in the atmosphere. At most sites, the OA can be separated into oxygenated OA (OOA, hydrocarbon-like OA (HOA, and sometimes other components such as biomass burning OA (BBOA. We focus on the OOA components in this work. In many analyses, the OOA can be further deconvolved into low-volatility OOA (LV-OOA and semi-volatile OOA (SV-OOA. Differences in the mass spectra of these components are characterized in terms of the two main ions m/z 44 (CO2+ and m/z 43 (mostly C2H3O+, which are used to develop a new mass spectral diagnostic for following the aging of OA components in the atmosphere. The LV-OOA component spectra have higher f44 (ratio of m/z 44 to total signal in the component mass spectrum and lower f43 (ratio of m/z 43 to total signal in the component mass spectrum than SV-OOA. A wide range of f44 and O:C ratios are observed for both LV-OOA (0.17±0.04, 0.73±0.14 and SV-OOA (0.07±0.04, 0.35±0.14 components, reflecting the fact that there is a continuum of OOA properties in ambient aerosol. The OOA components (OOA, LV-OOA, and SV-OOA from all sites cluster within a well-defined triangular region in the f44 vs. f43 space, which can be used as a standardized means for comparing and characterizing any OOA components (laboratory or ambient observed with the AMS. Examination of the OOA components in this triangular space indicates that OOA component spectra become increasingly similar to each other and to fulvic acid and HULIS sample spectra as f44 (a

  14. Derivation of a northern-hemispheric biomass map for use in global carbon cycle models

    Science.gov (United States)

    Thurner, Martin; Beer, Christian; Santoro, Maurizio; Carvalhais, Nuno; Wutzler, Thomas; Schepaschenko, Dmitry; Shvidenko, Anatoly; Kompter, Elisabeth; Levick, Shaun; Schmullius, Christiane

    2013-04-01

    (C)/ha(Forest)) and broadleaf/mixed forests (58.0 ± 22.1 Mg(C)/ha(Forest)), whereas boreal forests have a carbon density of only 40.0 ± 15.4 Mg(C)/ha(Forest). While European forest carbon stocks are relatively small, the carbon density is higher compared to the other continents. The derived biomass map substantially improves the knowledge on the current carbon stocks of the northern-hemispheric boreal and temperate forests, serving as a new benchmark for spatially explicit and consistent biomass mapping with moderate spatial resolution. This product can be of great value for global carbon cycle models as well as national carbon monitoring systems. Further investigations concentrate on improving biomass parameterizations and representations in such kind of models. The presented map will help to improve the simulation of biomass spatial patterns and variability and enables identifying the dominant influential factors like climatic conditions and disturbances.

  15. Observation of polar mesosphere summer echoes with calibrated VHF radars at 69° in the Northern and Southern hemispheres

    Science.gov (United States)

    Latteck, R.; Singer, W.; Morris, R. J.; Holdsworth, D. A.; Murphy, D. J.

    2007-07-01

    Polar Mesosphere Summer Echoes (PMSE) observed in the northern and southern hemisphere were studied using continuous measurements obtained by calibrated VHF radars located at Andenes (69.3°N) and Davis (68.6°S) during the boreal summer 2004 and the austral summer 2004/2005. The PMSE observed at Davis have a lower peak volume reflectivity of approximately 4 . 10-11 m-1 compared with their counterparts (7 . 10-10 m-1) observed at Andenes. The duration of the PMSE season is correlated with the dynamical and thermal state of the mesopause region supported by recent studies using meridional winds and temperatures. PMSE occurred less frequently but with greater variability above Davis. The diurnal variation of PMSE occurrence has a maximum around 11-16 LT in both hemispheres, and a minimum occurs during late evening with a longer duration in the southern hemisphere. The mean PMSE season at both sites started around 34 days before solstice, but the duration of the Davis PMSE season is about 9 days shorter than at Andenes. The maximum occurrence height of PMSE at Davis is 86 km which is about 1 km higher than at Andenes.

  16. Seasonal variability in Northern Hemisphere atmospheric circulation during the Medieval Climate Anomaly and the Little Ice Age

    Science.gov (United States)

    Edwards, Thomas W. D.; Hammarlund, Dan; Newton, Brandi W.; Sjolte, Jesper; Linderson, Hans; Sturm, Christophe; St. Amour, Natalie A.; Bailey, Joscelyn N.-L.; Nilsson, Anders L.

    2017-06-01

    Here we report new reconstructions of winter temperature and summer moisture during the past millennium in southeastern Sweden, based on stable-isotope data from a composite tree-ring sequence, that further enhances our knowledge and understanding of seasonal climate variability in the Northern Hemisphere over the past millennium. Key features of these new climate proxy records include evidence for distinctive fluctuations in winter temperature in SE Sweden, superimposed upon the general pattern of cooling between the so-called Medieval Climate Anomaly (MCA) of the early millennium and the Little Ice Age (LIA) of the late millennium, as well as evidence for sustained summer wetness during the MCA, followed by drier and less variable conditions during the LIA. We also explore these new records within a circumpolar spatial context by employing self-organizing map analysis of meteorological reanalysis data to identify potential modern analogues of mid-tropospheric synoptic circulation types in the Northern Hemisphere extratropics that can reconcile varying seasonal climate states during the MCA and LIA in SE Sweden with less variable conditions in southwestern Canada, as portrayed by paleoclimate records developed in the same manner in an earlier study.

  17. Dispersion of sulphur in the northern hemisphere. A study with a 3-dimensional time-resolved model

    Energy Technology Data Exchange (ETDEWEB)

    Tarrason, L.

    1995-12-31

    This thesis on atmospheric dispersion of sulphur presents a calculation of intercontinental transport of oxidized sulphur and allocates different contributions to sulphur background levels over Europe. It is found that a significant fraction of anthropogenic sulphur (AS) is transported out of continental boundaries thus affecting the background levels over major parts of the northern hemisphere. Over Europe, the contribution of AS from North America is similar in amount to that of Asian AS and natural sources from the North Atlantic Ocean. Although the yearly contribution of intercontinental transport to deposition of sulphur over Europe is quite small, it can be much more important over certain areas and seasons and is comparable to the contributions from individual European countries. The calculations are based on a three-dimensional Eulerian time-resolved model that describes sulphur dispersion in the atmosphere in connection with large-scale synoptic flows and agree well with observations. The thesis emphasizes the role of synoptic scale atmospheric motions in determining intercontinental transport of sulphur. It indicates the need to resolve individual cyclones and anticyclones in order to describe the dispersion and distribution of atmospheric sulphur in the northern hemisphere and stresses the value of comparing model calculations with observations, both in atmospheric chemistry studies and in climate applications. 260 refs., 50 figs., 17 tabs.

  18. Effects of Climate Warming, North Atlantic Oscillation, and El Niño-Southern Oscillation on Thermal Conditions and Plankton Dynamics in Northern Hemispheric Lakes

    OpenAIRE

    Dieter Gerten; Rita Adrian

    2002-01-01

    Impacts of climate warming on freshwater ecosystems have been documented recently for a variety of sites around the globe. Here we provide a review of studies that report long-term (multidecadal) effects of warming trends on thermal properties and plankton dynamics in northern hemispheric lakes. We show that higher lake temperatures, shorter periods with ice cover, and shorter stagnation periods were common trends for lakes across the hemisphere in response to the warmer conditions. Only for ...

  19. Long-term active-layer dynamics: results of 22 years of field observations in Northern Hemisphere permafrost regions.

    Science.gov (United States)

    Shiklomanov, N. I.; Nelson, F. E.; Streletskiy, D. A.; Klene, A. E.; Biskaborn, B. K.

    2016-12-01

    The uppermost layer of seasonal thawing above permafrost (the active layer) is an important regulator of energy and mass fluxes between the surface and the atmosphere in the polar regions. Active layer monitoring is an important component of efforts to assess the effects of global change in permafrost environments. The Circumpolar Active Layer Monitoring (CALM) program, established in the early 1990s, is designed to observe temporal and spatial variability of the active layer and its response to changes and variations in climatic conditions. The CALM network is an integral part of the Global Terrestrial Network for Permafrost (GTN-P), operating under the auspices of the Global Terrestrial Observing System (GTOS) /Global Climate Observing System (GCOS). Standardized thaw depth observations in the Northern Hemisphere are available for more than 200 GTN-P/CALM sites in the Northern Hemisphere. At each of the sites spatially distributed ALT measurements have been conducted annually by mechanical probing. The locations of sites represent generalized surface and subsurface conditions characteristic of broader regions. The data are assimilated and distributed though the CALM (www.gwu.edu/ calm) and GTN-P (gtnpdatabase.org) online databases. In this presentation we use data from approximately 20 years of continuous observations to examine temporal trends in active-layer thickness for several representative Arctic regions. Results indicate substantial interannual fluctuations in active-layer thickness, primarily in response to variations in air temperature. Decadal trends in ALT vary by region. A progressive increase in ALT has been observed in the Nordic countries, the Russian European North, West Siberia, East Siberia, the Russian Far East, and the Interior of Alaska. North American Arctic sites show no apparent thaw depth trend over 22-years of record. However, combined active layer, ground temperature and heave/subsidence observations conducted in northern Alaska

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

    Science.gov (United States)

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

    2017-12-01

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

  1. CO2 snow depth and subsurface water-ice abundance in the northern hemisphere of Mars.

    Science.gov (United States)

    Mitrofanov, I G; Zuber, M T; Litvak, M L; Boynton, W V; Smith, D E; Drake, D; Hamara, D; Kozyrev, A S; Sanin, A B; Shinohara, C; Saunders, R S; Tretyakov, V

    2003-06-27

    Observations of seasonal variations of neutron flux from the high-energy neutron detector (HEND) on Mars Odyssey combined with direct measurements of the thickness of condensed carbon dioxide by the Mars Orbiter Laser Altimeter (MOLA) on Mars Global Surveyor show a latitudinal dependence of northern winter deposition of carbon dioxide. The observations are also consistent with a shallow substrate consisting of a layer with water ice overlain by a layer of drier soil. The lower ice-rich layer contains between 50 and 75 weight % water, indicating that the shallow subsurface at northern polar latitudes on Mars is even more water rich than that in the south.

  2. Observation and characterization of an astrophysical muon neutrino flux from the Northern Hemisphere with IceCube

    Energy Technology Data Exchange (ETDEWEB)

    Haack, Christian; Raedel, Leif; Reimann, Rene; Schoenen, Sebastian; Wiebusch, Christopher [3. Physikalisches Institut B, RWTH Aachen (Germany); Collaboration: IceCube-Collaboration

    2016-07-01

    IceCube has observed a high-energy astrophysical neutrino flux based on neutrinos of all flavors interacting within the instrumented volume. Here, a complementary measurement based on muon neutrinos where the interaction vertex can be outside the instrumented volume is presented. Due to the large muon range the effective area is significantly larger but the field of view is limited to the Northern Hemisphere. IceCube data from 2009 through 2015 have been analyzed by a likelihood approach with reconstructed muon energy and zenith angle as observables. The analyzed data consist of about 340,000 muon neutrinos with a negligible background of atmospheric muons. The majority of these events are atmospheric neutrinos. However, this analysis finds a significant astrophysical contribution, excluding the atmospheric-only hypothesis at the level of 6 standard deviations. In this talk we present the analysis results including the characterization of the astrophysical flux properties.

  3. Why does the north-south gradient of incidence of multiple sclerosis seem to have disappeared on the Northern hemisphere?

    DEFF Research Database (Denmark)

    Koch-Henriksen, Nils; Sorensen, Per Soelberg

    2011-01-01

    in environmental factors, levelling out differences in habits of life across Europe and North America, and, not least, that the interpretation of a latitudinal gradient in Europe was based primarily on prevalence studies and reviews. In addition, we observed in most regions a profound increase in female incidence......The traditional view, based on numerous early studies and reviews, is that MS is particularly prevalent in temperate zones both on the northern and southern hemisphere. This uneven distribution of MS can be attributed to differences in genes and environment and their interaction. Diagnostic...... accuracy and case ascertainment are sources of error and have their shares in the geographical and temporal variations, and improvements in diagnostic accuracy and case ascertainment influence incidence- and prevalence rates. In addition the prevalence also depends on survival. With this meta-analysis we...

  4. Why does the north-south gradient of incidence of multiple sclerosis seem to have disappeared on the northern hemisphere?

    DEFF Research Database (Denmark)

    Koch-Henriksen, Nils; Sorensen, Per Soelberg

    2011-01-01

    in environmental factors, levelling out differences in habits of life across Europe and North America, and, not least, that the interpretation of a latitudinal gradient in Europe was based primarily on prevalence studies and reviews. In addition, we observed in most regions a profound increase in female incidence......The traditional view, based on numerous early studies and reviews, is that MS is particularly prevalent in temperate zones both on the northern and southern hemisphere. This uneven distribution of MS can be attributed to differences in genes and environment and their interaction. Diagnostic...... accuracy and case ascertainment are sources of error and have their shares in the geographical and temporal variations, and improvements in diagnostic accuracy and case ascertainment influence incidence- and prevalence rates. In addition the prevalence also depends on survival. With this meta-analysis we...

  5. Roles of climate, vegetation and soil in regulating the spatial variations in ecosystem carbon dioxide fluxes in the Northern Hemisphere.

    Science.gov (United States)

    Chen, Zhi; Yu, Guirui; Ge, Jianping; Wang, Qiufeng; Zhu, Xianjin; Xu, Zhiwei

    2015-01-01

    Climate, vegetation, and soil characteristics play important roles in regulating the spatial variation in carbon dioxide fluxes, but their relative influence is still uncertain. In this study, we compiled data from 241 eddy covariance flux sites in the Northern Hemisphere and used Classification and Regression Trees and Redundancy Analysis to assess how climate, vegetation, and soil affect the spatial variations in three carbon dioxide fluxes (annual gross primary production (AGPP), annual ecosystem respiration (ARE), and annual net ecosystem production (ANEP)). Our results showed that the spatial variations in AGPP, ARE, and ANEP were significantly related to the climate and vegetation factors (correlation coefficients, R = 0.22 to 0.69, P 0.05) in the Northern Hemisphere. The climate and vegetation together explained 60% and 58% of the spatial variations in AGPP and ARE, respectively. Climate factors (mean annual temperature and precipitation) could account for 45-47% of the spatial variations in AGPP and ARE, but the climate constraint on the vegetation index explained approximately 75%. Our findings suggest that climate factors affect the spatial variations in AGPP and ARE mainly by regulating vegetation properties, while soil factors exert a minor effect. To more accurately assess global carbon balance and predict ecosystem responses to climate change, these discrepant roles of climate, vegetation, and soil are required to be fully considered in the future land surface models. Moreover, our results showed that climate and vegetation factors failed to capture the spatial variation in ANEP and suggest that to reveal the underlying mechanism for variation in ANEP, taking into account the effects of other factors (such as climate change and disturbances) is necessary.

  6. Roles of climate, vegetation and soil in regulating the spatial variations in ecosystem carbon dioxide fluxes in the Northern Hemisphere.

    Directory of Open Access Journals (Sweden)

    Zhi Chen

    Full Text Available Climate, vegetation, and soil characteristics play important roles in regulating the spatial variation in carbon dioxide fluxes, but their relative influence is still uncertain. In this study, we compiled data from 241 eddy covariance flux sites in the Northern Hemisphere and used Classification and Regression Trees and Redundancy Analysis to assess how climate, vegetation, and soil affect the spatial variations in three carbon dioxide fluxes (annual gross primary production (AGPP, annual ecosystem respiration (ARE, and annual net ecosystem production (ANEP. Our results showed that the spatial variations in AGPP, ARE, and ANEP were significantly related to the climate and vegetation factors (correlation coefficients, R = 0.22 to 0.69, P 0.05 in the Northern Hemisphere. The climate and vegetation together explained 60% and 58% of the spatial variations in AGPP and ARE, respectively. Climate factors (mean annual temperature and precipitation could account for 45-47% of the spatial variations in AGPP and ARE, but the climate constraint on the vegetation index explained approximately 75%. Our findings suggest that climate factors affect the spatial variations in AGPP and ARE mainly by regulating vegetation properties, while soil factors exert a minor effect. To more accurately assess global carbon balance and predict ecosystem responses to climate change, these discrepant roles of climate, vegetation, and soil are required to be fully considered in the future land surface models. Moreover, our results showed that climate and vegetation factors failed to capture the spatial variation in ANEP and suggest that to reveal the underlying mechanism for variation in ANEP, taking into account the effects of other factors (such as climate change and disturbances is necessary.

  7. Parametrization of the precipitation in the Northern Hemisphere and its verification in Mexico

    Directory of Open Access Journals (Sweden)

    V. M. Mendoza

    Full Text Available To improve results in monthly rainfall prediction, a parametrization of precipitation has been developed. The thermodynamic energy equation used in the Adem thermodynamic model (ATM and the Clausius and Clapeyron equation, were used to obtain a linear parametrization of the precipitation anomalies as a function of the surface temperature and the 700 mb temperature anomalies. The observed rainfall in Mexico over 36 months, from January 1981 to December 1983, was compared with the results obtained of the heat released by condensation, which is proportional to precipitation, using our theoretical formula, and those obtained using a statistical formula, which was derived for the ATM using 12 years of hemispheric real data. The verification using our formula in Mexico, showed better results than the one using the statistical formula.

    Key words. Meteorology and atmospheric dynamics (climatology; convective processes; general circulation.

  8. Parametrization of the precipitation in the Northern Hemisphere and its verification in Mexico

    Directory of Open Access Journals (Sweden)

    V. M. Mendoza

    1998-07-01

    Full Text Available To improve results in monthly rainfall prediction, a parametrization of precipitation has been developed. The thermodynamic energy equation used in the Adem thermodynamic model (ATM and the Clausius and Clapeyron equation, were used to obtain a linear parametrization of the precipitation anomalies as a function of the surface temperature and the 700 mb temperature anomalies. The observed rainfall in Mexico over 36 months, from January 1981 to December 1983, was compared with the results obtained of the heat released by condensation, which is proportional to precipitation, using our theoretical formula, and those obtained using a statistical formula, which was derived for the ATM using 12 years of hemispheric real data. The verification using our formula in Mexico, showed better results than the one using the statistical formula.Key words. Meteorology and atmospheric dynamics (climatology; convective processes; general circulation.

  9. Evapotranspiration Cycles in a High Latitude Agroecosystem: Potential Warming Role

    Science.gov (United States)

    Ruairuen, Watcharee

    2015-01-01

    As the acreages of agricultural lands increase, changes in surface energetics and evapotranspiration (ET) rates may arise consequently affecting regional climate regimes. The objective of this study was to evaluate summertime ET dynamics and surface energy processes in a subarctic agricultural farm in Interior Alaska. The study includes micrometeorological and hydrological data. Results covering the period from June to September 2012 and 2013 indicated consistent energy fractions: LE/Rnet (67%), G/Rnet (6%), H/Rnet (27%) where LE is latent heat flux, Rnet is the surface net radiation, G is ground heat flux and H is the sensible heat flux. Additionally actual surface evapotranspiration from potential evaporation was found to be in the range of 59 to 66%. After comparing these rates with those of most prominent high latitude ecosystems it is argued here that if agroecosystem in high latitudes become an emerging feature in the land-use, the regional surface energy balance will significantly shift in comparison to existing Arctic natural ecosystems. PMID:26368123

  10. Formation and detection of high latitude ionospheric irregularities

    Science.gov (United States)

    Lee, M. C.; Buchau, J.; Carlson, H. C., Jr.; Klobuchar, J. A.; Weber, E. J.

    1985-01-01

    Measurements of Total Electron Content (TEC) and airglow variations show that large scale plasma patches appearing in the high-latitude ionsophere have irregular structures evidenced by the satellite phase and amplitude scintillations. Whistler waves, intense quasi-DC electric field, and atmospheric gravity waves can become potential sources of various plamsa instabilities. The role of thermal effects in generating ionospheric irregularities by these sources is discussed. Meter-scale irregularities in the ionospheric E and F regions can be excited parametrically with lower hybrid waves by intense whistler waves. Ohmic dissipation of Pedersen current in the electron gas is able to create ionospheric F region irregularities in plasma blobs or plasma patches (i.e., high ambient plasma density environment) with broad scale lengths ranging from tens of meters to a few kilometers. Through the neutral-charged particle collisions, gravity waves can excite large-scale (less than tens of kilometers) ionospheric irregularities simultaneously with forced ion acoustic modes in the E region. The large-scale ionospheric density fluctuations produced in the E region can extend subsequently alogn the earth's magnetic field to the F region and the topside ionospheric regions. These mechanisms characterized by various thermal effects can contribute additively with other processes to the formation of ionospheric irregularities in the high latitude region.

  11. 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

  12. Wavelet-based analogous phase scintillation index for high latitudes

    Science.gov (United States)

    Ahmed, A.; Tiwari, R.; Strangeways, H. J.; Dlay, S.; Johnsen, M. G.

    2015-08-01

    The Global Positioning System (GPS) performance at high latitudes can be severely affected by the ionospheric scintillation due to the presence of small-scale time-varying electron density irregularities. In this paper, an improved analogous phase scintillation index derived using the wavelet-transform-based filtering technique is presented to represent the effects of scintillation regionally at European high latitudes. The improved analogous phase index is then compared with the original analogous phase index and the phase scintillation index for performance comparison using 1 year of data from Trondheim, Norway (63.41°N, 10.4°E). This index provides samples at a 1 min rate using raw total electron content (TEC) data at 1 Hz for the prediction of phase scintillation compared to the scintillation monitoring receivers (such as NovAtel Global Navigation Satellite Systems Ionospheric Scintillation and TEC Monitor receivers) which operate at 50 Hz rate and are thus rather computationally intensive. The estimation of phase scintillation effects using high sample rate data makes the improved analogous phase index a suitable candidate which can be used in regional geodetic dual-frequency-based GPS receivers to efficiently update the tracking loop parameters based on tracking jitter variance.

  13. Tropospheric ozone over a tropical Atlantic station in the Northern Hemisphere: Paramaribo, Surinam (6°N, 55°W)

    NARCIS (Netherlands)

    Peters, W.; Krol, M. C.; Fortuin, J. P. F.; Kelder, H. M.; Thompson, A. M.; Becker, C. R.; Lelieveld, J.; Crutzen, P. J.

    2004-01-01

    We present an analysis of 2.5 yr of weekly ozone soundings conducted at a new monitoring station in Paramaribo, Surinam (6°N, 55°W). This is currently one of only three ozone sounding stations in the Northern Hemisphere (NH) tropics, and the only one in the equatorial Atlantic region. Paramaribo is

  14. Contributions of Icelandic and other high-latitude sources to mineral dust in the Arctic

    Science.gov (United States)

    Groot Zwaaftink, Christine; Grythe, Henrik; Arnalds, Olafur; Dagsson-Waldhauserova, Pavla; Skov, Henrik; Jóhannsson, Thorsteinn; Eckhardt, Sabine; Stohl, Andreas

    2017-04-01

    Impurities in the Arctic atmosphere and cryosphere, such as mineral dust, can strongly affect the atmospheric radiation- and surface energy balance. Mineral dust can be transported into the Arctic from remote regions, but is also generated at high latitudes, for instance Iceland. With the dust mobilization scheme FLEXDUST and the Lagrangian atmospheric dispersion model FLEXPART we investigate sources of mineral dust at northern high latitudes. FLEXDUST simulations over three years indicate that about 3% of global dust emission originate from northern high-latitude (>60°N) dust sources. About 10% thereof comes from Iceland. Due to limited up-lifting of this dust and relatively small transport distances, dust from nothern high-latitude sources contributes strongly to dust deposition ( 90%) and dust surface concentrations ( 85%) in the Arctic, according to our simulations. With increasing altitude, remote sources become more important for dust concentrations, thus influencing total atmospheric dust load rather than surface concentrations and contributing to dust deposition at higher altitude locations. Total atmospheric dust loads in the Arctic are strongly influenced by Asian ( 38%) and African ( 32%) dust. Only at higher altitudes, such as on the Greenland Ice Sheet, larger fractions of deposited dust originate from remote sources. At lower altitudes, deposited dust appears to originate mostly from northern high-latitude sources. Dust mobilization from these sources is, however, rarely studied in detail. With some adaptations to FLEXDUST, we study dust emission, transport and deposition of Icelandic dust at high resolution for one year. We used a high-resolution map of soil types in Iceland and threshold friction velocity in dust sources was based on previous observations. Snow cover and precipitation were included as factors limiting dust mobilization. In a one-year high-resolution simulation for 2012, driven with hourly meteorological data from the European

  15. Lake records of Northern Hemisphere South American summer monsoon variability from the Cordillera Oriental, Colombia: Initial results from Lago de Tota and Laguna de Ubaque

    Science.gov (United States)

    Escobar, J.; Rudloff, O.; Bird, B. W.

    2013-12-01

    The lack of terrestrial paleoclimate records from the Northern Hemisphere Andes with decadal resolution has meant that our understanding of abrupt South American summer monsoon (SASM) variability during the Holocene is almost exclusively based on data from Southern Hemisphere sites. In order to develop a more integrated and complete picture of the SASM as a system and its response during rapid climate changes, high-resolution paleoclimate records are needed from the Northern Hemisphere Andes. We present initial results from analysis of lake sediment cores that were collected from Lago de Tota (N 5.554, W 72.916) and Laguna de Ubaque (N 4.500, W 73.935) in the Eastern Cordillera of the Colombian Andes. These sediment cores were collected in July 2013 as part on an ongoing paleoclimate research initiative in Colombia. Located in the Boyacá Provence, Lago de Tota is the largest high-altitude lake (3010 masl) in the Northern Hemisphere Andes and the second largest Andean lake in South America. As such, hydrologic changes recorded in the lake's sediment record reflect regional climate responses. Lago de Ubaque (2070 masl) is a small east facing moraine-dammed lake near the capital of Bogotá that contains finely laminated clastic sediments. The initial sedimentological and chronological results demonstrate that Lago de Tota and Laguna de Ubaque have excellent potential for resolving Northern Hemisphere SASM variability at decadal time scales or better. Such records will provide important counterparts to high-resolution paleoclimate records from the Southern Hemisphere Andes.

  16. Detection of Wetland Dynamics with Envisat ASAR in Support of Methane Modelling in High Latitudes

    Science.gov (United States)

    Bartsch, A.; Sabel, D.; Schlaffer, S.; Naeimi, V.; Wagner, W.

    2011-01-01

    Wetland dynamics play an important role for methane release in high latitudes. Inundation as well as changes in surface wetness at local to regional scale can be detected using especially SAR (Synthetic Aperture Radar) data. Acquisitions available from ENVISAT ASAR are assessed for their potential for regular wetland monitoring at high latitudes within the ESA STSE project ’ALANIS - Methane’. Open water surfaces larger than approximately two ha can be identified using a simple threshold-based classification applied to the normalized ENVISAT ASAR wide swath (WS) data. Specular reflection from calm water surfaces which results in low backscatter enables a straight forward identification of inundation in areas with limited vegetation coverage. Open peatland can also be identified with SAR due to their higher moisture content and thus higher backscatter. Both backscatter mechanisms are exploited for intra-seasonal wetland monitoring in Northern Eurasia for ALANIS Methane. Inter-annual variations of inundation are also derived at selected sites in boreal/arctic environment as part of the ESA DUE Permafrost project. This paper especially discusses limitations due to sampling frequency and the potential for improvements of regional scale wetland detection approaches.

  17. 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.

  18. Millennial-scale northern Hemisphere Atlantic-Pacific climate teleconnections in the earliest Middle Pleistocene.

    Science.gov (United States)

    Hyodo, Masayuki; Bradák, Balázs; Okada, Makoto; Katoh, Shigehiro; Kitaba, Ikuko; Dettman, David L; Hayashi, Hiroki; Kumazawa, Koyo; Hirose, Kotaro; Kazaoka, Osamu; Shikoku, Kizuku; Kitamura, Akihisa

    2017-08-30

    Suborbital-scale climate variations, possibly caused by solar activity, are observed in the Holocene and last-glacial climates. Recently published bicentennial-resolution paleoceanic environmental records reveal millennial-scale high-amplitude oscillations postdating the last geomagnetic reversal in the Marine Isotope Stage (MIS) 19 interglacial. These oscillations, together with decoupling of post-reversal warming from maximum sea-level highstand in mid-latitudes, are key features for understanding the climate system of MIS 19 and the following Middle Pleistocene. It is unclear whether the oscillations are synchronous, or have the same driver as Holocene cycles. Here we present a high resolution record of western North Pacific submarine anoxia and sea surface bioproductivity from the Chiba Section, central Japan. The record reveals many oxic events in MIS 19, coincident with cold intervals, or with combined cold and sea-level fall events. This allows detailed correlations with paleoceanic records from the mid-latitude North Atlantic and Osaka Bay, southwest Japan. We find that the millennial-scale oscillations are synchronous between East and West hemispheres. In addition, during the two warmest intervals, bioproductivity follows the same pattern of change modulated by bicentennial cycles that are possibly related to solar activity.

  19. Spaceborne microwave remote sensing of seasonal freeze-thaw processes in the terrestrial high latitudes: relationships with land-atmosphere CO2 exchange

    Science.gov (United States)

    McDonald, Kyle C.; Kimball, John S.; Zhao, Maosheng; Njoku, Eni; Zimmermann, Reiner; Running, Steven W.

    2004-12-01

    Landscape transitions between seasonally frozen and thawed conditions occur each year over roughly 50 million square kilometers of Earth's Northern Hemisphere. These realtively abrupt transitions represent the closest analog to a biospheric and hydrologic on/off switch existing in nature, affecting surface meteorological conditions, ecological trace gas dynamics, energy exchange and hydrologic activity profoundly. We utilize time series satellite-borne microwave remote sensing measurements from the Special Sensor Microwave Imager (SSM/I) to examine spatial and temporal variability in seasonal freeze/thaw cycles for the pan-Arctic basin and Alaska. Regional measurements of spring thaw timing are derived using daily brightness temperature measurements from the 19 GHz, horizontally polarized channel, spearately for overpasses with 6 AM and 6 PM equatorial crossing times. Spatial and temporal patterns in regional freeze/thaw dynamics show distinct differences between North Americ and Eurasia, and boreal forest and Arctic tundra biomes. Annual anomalies in the timing of thawing in spring also correspond closely to seasonal atmospheric CO2 concentration anomalies derived from NOAA CMDL arctic and subarctic monitoring stations. Classification differences between AM and PM overpass data average approximately 5 days for the region, through both appear to be effective surrogates for monitoring annual growing seasons at high latitudes.

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

    Directory of Open Access Journals (Sweden)

    J.-P. Villain

    2002-11-01

    Full Text Available The HF radars of the Super Dual Auroral Radar Network (SuperDARN provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. We have conducted a statistical study of the associated Doppler spectral width of ionospheric F-region echoes. The study has been conducted with all available radars from the Northern Hemisphere for 2 specific periods of time. Period 1 corresponds to the winter months of 1994, while period 2 covers October 1996 to March 1997. The distributions of data points and average spectral width are presented as a function of Magnetic Latitude and Magnetic Local Time. The databases are very consistent and exhibit the same features. The most stringent features are: a region of very high spectral width, collocated with the ionospheric LLBL/cusp/mantle region; an oval shaped region of high spectral width, whose equator-ward boundary matches the poleward limit of the Holzworth and Meng auroral oval. A simulation has been conducted to evaluate the geometrical and instrumental effects on the spectral width. It shows that these effects cannot account for the observed spectral features. It is then concluded that these specific spectral width characteristics are the signature of ionospheric/magnetospheric coupling phenomena.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; ionospheric irregularities

  1. 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

  2. Elevated Ozone in the Troposphere over the Atlantic and Pacific Oceans in the Northern Hemisphere

    Science.gov (United States)

    Chandra, S.; Ziemke, J. R.; Tie, Xuexi

    2003-01-01

    Tropospheric column ozone (TCO) is derived from differential measurements of total column ozone from Nimus-7 and Earth Probe TOMS, and stratospheric column ozone from the Microwave Limb Sounder instrument on the Upper Atmospheric Research Satellite. It is shown that TCO during summer months over the Atlantic and Pacific Oceans at northern mid-latitudes is about the same (50-60 Dobson Units) as over the continents of North America, Europe and Asia, where surface emissions of nitrogen oxides from industrial sources, biomass and biofuel burning and biogenic emissions are significantly larger. This nearly uniform zonal variation in TCO is modulated by surface topography of the Rocky and Himalayan mountains and Tibetan Plateau where TCO is reduced by 20-30 Dobson Units. The zonal characteristics of TCO derived from satellite measurements are well simulated by a global chemical transport model called MOZART-2 (Model of Ozone and Related Chemical Tracers, version 2). The model results are analyzed to delineate the relative importance of various processes contributing to observed zonal characteristics of TCO, and they are shown that the surface emission of NOx contributes about 50% of the TCO at northern mid-latitudes, especially over the continents of North America, Europe and Asia. The result of TCO derived from TOMS and the analysis from MOZART-2 indicate that TCO is a very useful tool to study tropospheric O3 pollution resulting from surface emissions of pollutants.

  3. Hemispheric Differences in the Response of the Upper Atmosphere to the August 2011 Geomagnetic Storm: A Simulation Study

    CERN Document Server

    Yiğit, Erdal; Moldwin, Mark B; Immel, Thomas J; Ridley, Aaron J

    2015-01-01

    Using a three-dimensional nonhydrostatic general circulation model, we investigate the response of the thermosphere-ionosphere system to the 5-6 August 2011 major geomagnetic storm. The model is driven by measured storm-time input data of the Interplanetary Magnetic Field (IMF), solar activity, and auroral activity. Simulations for quiet steady conditions over the same period are performed as well in order to assess the response of the neutral and plasma parameters to the storm. During the storm, the high-latitude mean ion flows are enhanced by up to 150-180%. Largest ion flows are found in the main phase of the storm. Overall, the global mean neutral temperature increases by up to 15%, while the maximum thermal response is higher in the winter Southern Hemisphere at high-latitudes than the summer Northern Hemisphere: 40% vs. 20%increase in high-latitude mean temperature, respectively. The global mean Joule heating increases by more than a factor of three. There are distinct hemispheric differences in the mag...

  4. Preliminary prediction model for the ROTI index at high latitude

    Science.gov (United States)

    Rochel Grimald, Sandrine; Boscher, Daniel; Fabbro, Vincent; Rougerie, Sébastien

    2017-04-01

    The variation of electron density can be described by the ROTI index (i.e. the Rate of change of Total electron content Index). This index is indicative of the electron density gradients which can be responsible of loss of satellite communications or loss of lock of GNSS system.. At high latitude, the ionosphere is connected to the magnetosphere through the magnetic field lines. When the magnetic activity increases, particles from the magnetosphere are injected in the ionosphere along the magnetic field lines. They disturb the ionospheric layer and are responsible of changes in the ROTI index. In this paper, we will use the NOAA POES satellites data to study the link between the ROTI index value and the particles flux in the inner magnetosphere. Then we will use the results to developp a preliminary ROTI model.

  5. 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.

  6. Evidence for Northern Hemisphere Glaciation Back to 44 Ma From Ice-Rafted Debris in the Greenland Sea

    Science.gov (United States)

    Shorttle, O.; Tripati, A.; Eagle, R. A.; Dawber, C.; Morton, A.; Dowdeswell, J.; Atkinson, K.; Bahe, Y.; Shaw, R.; Thanabalasundaram, L.; Khadun, E.

    2007-12-01

    The widely accepted age estimate for the onset of glaciation in the Northern Hemisphere ranges between 2 and 15 million years ago (Ma). However, recent studies indicate the date for N. Hemisphere glacial onset may be significantly older [1,2,3]. We report the presence of ice-rafted debris (IRD) in ~44 to 39 Ma sediments from the Greenland Sea, evidence for glaciation in the North Atlantic during the Middle Eocene to Late Eocene. We also have developed a high-resolution record of ice-rafting for the late Eocene through early Oligocene (39-30 Ma). Detailed sedimentological evidence indicates that glaciers extended to sea level in the region during part of the study interval, allowing icebergs to be produced. Peaks in IRD accumulation are observed at ~40-42 Ma, IRD may have been sourced from tidewater glaciers, small ice caps, and/or a continental ice sheet. Foraminiferal records from the deep Pacific show that several shifts in seawater δ18O of greater than 0.6‰ occurred during these intervals, consistent with the build-up of ice in both hemispheres [1,4]. [1] Tripati, A., Backman, J., Elderfield, H. and Ferretti, P. Eocene bipolar glaciation associated with global carbon cycle changes. Nature 436, 341-346 (2005). [2] Moran, K., Backman, J., Brinkhuis, H., Clemens, S.C., Cronin, T., Dickens, G.R., Eynaud, F., Gattacceca, J., Jakobsson, M., Jordan, R.W., Makinski, M., King, J., Koc, N., Krylov, A., Martinez, N., Matthiessen, J., McInroy, D., Moore, T.C., Onodera, J., O'Regan, M., Plike, H., Rea, B., Rio, D., Sakamoto, T., Smith, D.C., Stein, R., St. John, K., Suto, I., Suzuki, N., Takahashi, K., Watanabe, M., Yamamoto, M., Farrell, J., Frank, M., Kubik, P., Jokat, W., and Kristoffersen, Y., 2006, The Cenozoic palaeoenvironment of the Arctic Ocean, Nature, 441, 601-605. [3] Eldrett, J., Harding, I., Wilson, P., Butler, E. and Roberts, A., 2007, Continental ice in Greenland during the Eocene and Oligocene, Nature, 446, 176-179. [4] Dawber, C. and Tripati, A., 2007

  7. The effects of an interplanetary shock on the high-latitude ionospheric convection during an IMF By-dominated period

    Directory of Open Access Journals (Sweden)

    C. Hanuise

    2008-09-01

    Full Text Available On 6 January 1998 an interplanetary shock hit the magnetosphere around 14:15 UT and caused a reconfiguration of the northern high-latitude ionospheric convection. We use SuperDARN, spacecraft and ground magnetometer data to study such reconfiguration. We find that the shock front was tilted towards the morning flank of the magnetosphere, while the Interplanetary Magnetic Field (IMF was By-dominated, with By<0, IMF Bz>0 and |By|>>Bz. As expected, the magnetospheric compression started at the first impact point of the shock on the magnetopause causing an increase of the Chapman-Ferraro current from dawn to dusk and yielding an increase of the geomagnetic field at the geostationary orbit and on the ground. Moreover, the high-latitude magnetometer data show vortical structures clearly related to the interaction of the shock with the magnetosphere-ionosphere system. In this context, the SuperDARN convection maps show that at very high latitudes above the northern Cusp and in the morning sector, intense sunward convection fluxes appear, well correlated in time with the SI arrival, having a signature typical for Bz>0 dominated lobe reconnection. We suggest that in this case the dynamic pressure increase associated to the shock plays a role in favouring the setting up of a new lobe merging line albeit |By|>>Bz≥0.

  8. Response of the global surface ozone distribution to Northern Hemisphere sea surface temperature changes: implications for long-range transport

    Science.gov (United States)

    Yi, Kan; Liu, Junfeng; Ban-Weiss, George; Zhang, Jiachen; Tao, Wei; Cheng, Yanli; Tao, Shu

    2017-07-01

    The response of surface ozone (O3) concentrations to basin-scale warming and cooling of Northern Hemisphere oceans is investigated using the Community Earth System Model (CESM). Idealized, spatially uniform sea surface temperature (SST) anomalies of ±1 °C are individually superimposed onto the North Pacific, North Atlantic, and North Indian oceans. Our simulations suggest large seasonal and regional variability in surface O3 in response to SST anomalies, especially in the boreal summer. The responses of surface O3 associated with basin-scale SST warming and cooling have similar magnitude but are opposite in sign. Increasing the SST by 1 °C in one of the oceans generally decreases the surface O3 concentrations from 1 to 5 ppbv. With fixed emissions, SST increases in a specific ocean basin in the Northern Hemisphere tend to increase the summertime surface O3 concentrations over upwind regions, accompanied by a widespread reduction over downwind continents. We implement the integrated process rate (IPR) analysis in CESM and find that meteorological O3 transport in response to SST changes is the key process causing surface O3 perturbations in most cases. During the boreal summer, basin-scale SST warming facilitates the vertical transport of O3 to the surface over upwind regions while significantly reducing the vertical transport over downwind continents. This process, as confirmed by tagged CO-like tracers, indicates a considerable suppression of intercontinental O3 transport due to increased tropospheric stability at lower midlatitudes induced by SST changes. Conversely, the responses of chemical O3 production to regional SST warming can exert positive effects on surface O3 levels over highly polluted continents, except South Asia, where intensified cloud loading in response to North Indian SST warming depresses both the surface air temperature and solar radiation, and thus photochemical O3 production. Our findings indicate a robust linkage between basin-scale SST

  9. Palaeoceanographic Variability of the Benguela Upwelling System Depending on the Northern Hemisphere Glaciation (NHG) - Indicated by Organic-Walled Dinoflagellates

    Science.gov (United States)

    Bork, M.

    2003-12-01

    The causes and effects of the intensification of growth of the northern Hemisphere ice caps at around 3.2 and 2.74 Ma BP are still unclear. Possible causes are changes in the global ocean circulation and the global carbon cycle, which might have resulted from tectonic processes, solar insolation changes, or the interaction between both processes. The Benguela upwelling area forms a key area within the global ocean system. Here, warm and saline Indian Ocean waters enter the South Atlantic Ocean and are transported to the north. Variability of this inflow may thus result in changes in deep-water production in the North Atlantic, thereby influencing the global thermohaline circulation. Furthermore, the Benguela area is characterized by extremely high bioproductivity in surface waters as a result of year-round upwelling. Variations in the upwelling intensity might lead to changes in atmospheric ¤CO2. To study the changes in the circulation and the upwelling intensity, within this region organic-walled dinoflagellate cysts from two high-resolution cores (ODP 1084 and1082) covering the time interval from 3.3 to 2.5 Ma BP were investigated. Due to their sensitiveness to ecological parameters, organic-walled dinoflagellates reflect oceanographic characteristics keenly. The analyses discover clear distribution differences of individual species, especially of those that are sensible or resistant against aerobic decay. The sensible species, (Protoperidinium and Echinidinium), have their highest abundance from 2.76 to 2.73 Ma BP, a time interval in which the resistant species show no significant changes in their abundance. This implies that during this time interval the oxygen was reduced in the deep- and porewater suggesting that the global ocean deepwater circulation was weakened. Comparing these results with the known intensification of the NHG at around 2.74 Ma BP leads to the speculation that the increasing of ice caps in the northern hemisphere is highly associated with

  10. Response of the global surface ozone distribution to Northern Hemisphere sea surface temperature changes: implications for long-range transport

    Directory of Open Access Journals (Sweden)

    K. Yi

    2017-07-01

    Full Text Available The response of surface ozone (O3 concentrations to basin-scale warming and cooling of Northern Hemisphere oceans is investigated using the Community Earth System Model (CESM. Idealized, spatially uniform sea surface temperature (SST anomalies of ±1 °C are individually superimposed onto the North Pacific, North Atlantic, and North Indian oceans. Our simulations suggest large seasonal and regional variability in surface O3 in response to SST anomalies, especially in the boreal summer. The responses of surface O3 associated with basin-scale SST warming and cooling have similar magnitude but are opposite in sign. Increasing the SST by 1 °C in one of the oceans generally decreases the surface O3 concentrations from 1 to 5 ppbv. With fixed emissions, SST increases in a specific ocean basin in the Northern Hemisphere tend to increase the summertime surface O3 concentrations over upwind regions, accompanied by a widespread reduction over downwind continents. We implement the integrated process rate (IPR analysis in CESM and find that meteorological O3 transport in response to SST changes is the key process causing surface O3 perturbations in most cases. During the boreal summer, basin-scale SST warming facilitates the vertical transport of O3 to the surface over upwind regions while significantly reducing the vertical transport over downwind continents. This process, as confirmed by tagged CO-like tracers, indicates a considerable suppression of intercontinental O3 transport due to increased tropospheric stability at lower midlatitudes induced by SST changes. Conversely, the responses of chemical O3 production to regional SST warming can exert positive effects on surface O3 levels over highly polluted continents, except South Asia, where intensified cloud loading in response to North Indian SST warming depresses both the surface air temperature and solar radiation, and thus photochemical O3 production. Our findings indicate a robust linkage

  11. Quantifying the trade-off between carbon sequestration and albedo in midlatitude and high-latitude North American forests

    Science.gov (United States)

    Mykleby, P. M.; Snyder, P. K.; Twine, T. E.

    2017-03-01

    Afforestation is a viable and widely practiced method of sequestering carbon dioxide from the atmosphere. However, because of a change in surface albedo, placement of less reflective forests can cause an increase in net-absorbed radiation and localized surface warming. This effect is enhanced in northern high latitudes where the presence of snow cover exacerbates the albedo difference. Regions where afforestation could provide a climate benefit are determined by comparing net ecosystem production and net radiation differences from afforestation in midlatitude and high latitude of North America. Using the dynamic vegetation model Integrated Biosphere Simulator, agricultural version (Agro-IBIS), we find a boundary through North America where afforestation results in a positive equivalent carbon balance (cooling) to the south, and a negative equivalent carbon balance (warming) to the north. Including the effects of stand age and fraction cover affect whether a site contributes to mitigating global warming.

  12. Interannual Variability of Northern Hemisphere Storm Tracks in Coarse-Gridded Datasets

    Directory of Open Access Journals (Sweden)

    Timothy Paul Eichler

    2013-01-01

    Full Text Available Extratropical cyclones exert a large socioeconomic impact. It is therefore important to assess their interannual variability. We generate cyclone tracks from the National Center for Environmental Prediction’s Reanalysis I and the European Centre for Medium Range Prediction ERA-40 reanalysis datasets. To investigate the interannual variability of cyclone tracks, we compare the effects of El Niño, the North Atlantic Oscillation (NAO, the Indian Ocean Dipole (IOD, and the Pacific North American Pattern (PNA on cyclone tracks. Composite analysis shows similar results for the impacts of El Niño, NAO, and the PNA on NH storm tracks. Although it is encouraging, we also found regional differences when comparing reanalysis datasets. The results for the IOD suggested a wave-like alteration of cyclone frequency across the northern US/Canada possibly related to Rossby wave propagation. Partial correlation demonstrates that although El Niño affects cyclone frequency in the North Pacific and along the US east coast, its impact on the North Pacific is accomplished via the PNA. Similarly, the PNA’s impact on US east coast storms is modulated via El Niño. In contrast, the impacts of the NAO extend as far west as the North Pacific and are not influenced by either the PNA or El Niño.

  13. Trend and variability of Northern Hemisphere Teleconnection Indices simulated with CMIP3

    Science.gov (United States)

    Gonzalez-Reviriego, N.; Rodriguez-Puebla, C.

    2010-09-01

    Teleconnection patterns and their links with regional climate could be modified under warmer conditions. Therefore, it is of great interest to investigate how global climate models are able to simulate the teleconnection indices. In particular, we will show results for the following teleconnection indices: North Atlantic Oscillation (NAO), East Atlantic (EA), East Atlantic/Western Russia (EA/WR) and the Escandinavia (SCAND), that affect climate variations over Europe as demonstrated in previous work. The first step in this investigation is to determine the teleconnection indices (TI) from the geopotential at 500 hPa dataset of Global Climate Models of the World Climate Research Program Coupled Model Intercomparison Project phase 3 (WCRP CMIP3). Among the different methods to derive the TI, we used the procedure followed in the Climate Prediction Center (CPC). This method is based on partial least squares regression, where predictor variables are the Northern Teleconnection Patterns, calculated by CPC using Rotated Empirical Orthogonal Functions, and the response variables are monthly mean standardized 500 hPa geopotential anomalies of model data. The regression coefficients associated with predictor variables correspond to the TI. Then, we compare these patterns derived from different models and two experiments, 20th century (20C3M) and 21st (A1B), with ones provided by CPC. The comparison of the NAO, EA, EWR and SCA simulated and observed is performed by computing the spatial correlation, spectral analysis and trends. We also obtain the probability density functions to determine if there are preferred regimes in the simulated indices against the observed ones.

  14. Uncertainty Quantification of Extratropical Forest Biomass in CMIP5 Models over the Northern Hemisphere

    Science.gov (United States)

    Yang, C. E.; Mao, J.; Hoffman, F. M.; Ricciuto, D. M.; Fu, J. S.

    2016-12-01

    Simplified representations of processes driving global forest biomass in Earth system models contribute to large uncertainty and variability among climate predictions, in particular for the simulations of biomass magnitude, allocation, and the responses of biomass to changing climatic conditions. In this study, we evaluated forest biomass from the historical runs of eight coupled Earth system models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) archive, using a recent data product synthesized from remote sensing and ground-based observations across northern extratropical latitudes (30°N-80°N). Compared to this data product, all models excluding two Hadley Centre's models overpredicted global forest biomass in wood by 166%±153% whereas biomass in roots was underestimated by -82%∓2% in all models except the IPSL models (133%±46%). In addition, the IPSL models had the largest biases in total forest carbon mass estimates (154%±51%), which was attributed mainly to the overestimated wood component (163%±56%). Nevertheless, the allocation of modeled forest biomass in roots (21%) and in wood (76%-77%) found in the IPSL models was more consistent with observations (22% for roots and 73% for wood). Our results also demonstrated that both observed and modeled forest biomass was positively correlated with precipitation variations in most regions, while surface temperature was as important as precipitation at higher latitudes. Moreover, small differences in forest biomass between the pre-industrial period and the modern time period implied that the biases in forest biomass may have been introduced at the beginning of the simulations. Our work suggests that caution should be exercised for (1) allocating carbon mass to forest components, (2) apportioning vegetation types within modeled gridcells, and (3) reducing the uncertainty in vegetation inputs for Earth system models with correct vegetation parameterizations during the spin-up processes.

  15. The isotopic record of Northern Hemisphere atmospheric carbon monoxide since 1950: implications for the CO budget

    Directory of Open Access Journals (Sweden)

    Z. Wang

    2012-05-01

    Full Text Available We present a 60-year record of the stable isotopes of atmospheric carbon monoxide (CO from firn air samples collected under the framework of the North Greenland Eemian Ice Drilling (NEEM project. CO concentration, δ13C, and δ18O of CO were measured by gas chromatography/isotope ratio mass spectrometry (gc-IRMS from trapped gases in the firn. We applied LGGE-GIPSA firn air models (Witrant et al., 2011 to correlate gas age with firn air depth and then reconstructed the trend of atmospheric CO and its stable isotopic composition at high northern latitudes since 1950. The most probable firn air model scenarios show that δ13C decreased slightly from −25.8‰ in 1950 to −26.4‰ in 2000, then decreased more significantly to −27.2‰ in 2008. δ18O decreased more regularly from 9.8‰ in 1950 to 7.1‰ in 2008. Those same scenarios show CO concentration increased gradually from 1950 and peaked in the late 1970s, followed by a gradual decrease to present day values (Petrenko et al., 2012. Results from an isotope mass balance model indicate that a slight increase, followed by a large reduction, in CO derived from fossil fuel combustion has occurred since 1950. The reduction of CO emission from fossil fuel combustion after the mid-1970s is the most plausible mechanism for the drop of CO concentration during this time. Fossil fuel CO emissions decreased as a result of the implementation of catalytic converters and the relative growth of diesel engines, in spite of the global vehicle fleet size having grown several fold over the same time period.

  16. Water vapor increase in the northern hemispheric lower stratosphere by the Asian monsoon anticyclone observed during TACTS campaign in 2012

    Science.gov (United States)

    Rolf, Christian; Vogel, Bärbel; Hoor, Peter; Günther, Gebhard; Krämer, Martina; Müller, Rolf; Müller, Stephan; Riese, Martin

    2017-04-01

    Water vapor plays a key role in determining the radiative balance in the upper troposphere and lower stratosphere (UTLS) and thus the climate of the Earth (Forster and Shine, 2002; Riese et al., 2012). Therefore a detailed knowledge about transport pathways and exchange processes between troposphere and stratosphere is required to understand the variability of water vapor in this region. The Asian monsoon anticyclone caused by deep convection over and India and east Asia is able to transport air masses from the troposphere into the nothern extra-tropical stratosphere (Müller et al. 2016, Vogel et al. 2016). These air masses contain pollution but also higher amounts of water vapor. An increase in water vapor of about 0.5 ppmv in the extra-tropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 by in-situ instrumentation above the European northern hemisphere during the HALO aircraft mission TACTS. Here, we investigated the origin of this water vapor increase with the help of the 3D Lagrangian chemistry transport model CLaMS (McKenna et al., 2002). We can assign an origin of the moist air masses in the Asian region (North and South India and East China) with the help of model origin tracers. Additionally, back trajectories of these air masses with enriched water vapor are used to differentiate between transport from the Asia monsoon anticyclone and the upwelling of moister air in the tropics particularly from the Pacific and Southeast Asia.

  17. The role of dynamics in total ozone deviations from their long-term mean over the Northern Hemisphere

    Directory of Open Access Journals (Sweden)

    K. Petzoldt

    1999-02-01

    Full Text Available Total ozone anomalies (deviation from the long-term mean are created by anomalous circulation patterns. The dynamically produced ozone anomalies can be estimated from known circulation parameters in the layer between the tropopause and the middle stratosphere by means of statistics. Satellite observations of ozone anomalies can be compared with those expected from dynamics. Residual negative anomalies may be due to chemical ozone destruction. The statistics are derived from a 14 year data set of TOMS (Total Ozone Mapping Spectrometer January 1979-Dec. 1992 and corresponding 300 hPa geopotential (for the tropopause height together with 30 hPa temperature (for stratospheric waves at 60°N. The correlation coefficient for the linear multiple regression between total ozone (dependent variable and the dynamical parameters (independent variables is 0.88 for the zonal deviations in the winter of the Northern Hemisphere. Zonal means are also significantly dependent on circulation parameters, besides showing the known negative trend function of total ozone observed by TOMS. The significant linear trend for 60°N is \\sim3 DU/year in the winter months taking into account the dependence on the dynamics between the tropopause region and the mid-stratosphere. The highest correlation coefficient for the monthly mean total ozone anomalies is reached in November with 0.94.Key words. Atmospheric composition and structure (middle atmosphere · composition and chemistry · Meteorology and atmospheric dynamics (middle atmosphere dynamics.

  18. The role of dynamics in total ozone deviations from their long-term mean over the Northern Hemisphere

    Directory of Open Access Journals (Sweden)

    K. Petzoldt

    Full Text Available Total ozone anomalies (deviation from the long-term mean are created by anomalous circulation patterns. The dynamically produced ozone anomalies can be estimated from known circulation parameters in the layer between the tropopause and the middle stratosphere by means of statistics. Satellite observations of ozone anomalies can be compared with those expected from dynamics. Residual negative anomalies may be due to chemical ozone destruction. The statistics are derived from a 14 year data set of TOMS (Total Ozone Mapping Spectrometer January 1979-Dec. 1992 and corresponding 300 hPa geopotential (for the tropopause height together with 30 hPa temperature (for stratospheric waves at 60°N. The correlation coefficient for the linear multiple regression between total ozone (dependent variable and the dynamical parameters (independent variables is 0.88 for the zonal deviations in the winter of the Northern Hemisphere. Zonal means are also significantly dependent on circulation parameters, besides showing the known negative trend function of total ozone observed by TOMS. The significant linear trend for 60°N is sim3 DU/year in the winter months taking into account the dependence on the dynamics between the tropopause region and the mid-stratosphere. The highest correlation coefficient for the monthly mean total ozone anomalies is reached in November with 0.94.

    Key words. Atmospheric composition and structure (middle atmosphere · composition and chemistry · Meteorology and atmospheric dynamics (middle atmosphere dynamics.

  19. Changes to Saturn's zonal-mean tropospheric thermal structure after the 2010-2011 northern hemisphere storm

    Energy Technology Data Exchange (ETDEWEB)

    Achterberg, R. K.; Hesman, B. E. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Gierasch, P. J.; Conrath, B. J. [Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States); Fletcher, L. N. [Atmospheric Oceanic and Planetary Physics, University of Oxford, Clarenden Laboratory, Parks Road, Oxford OX1 3PU (United Kingdom); Bjoraker, G. L.; Flasar, F. M., E-mail: Richard.K.Achterberg@nasa.gov [Planetary Systems Laboratory NASA/GSFC, Greenbelt, MD 20771 (United States)

    2014-05-10

    We use far-infrared (20-200 μm) data from the Composite Infrared Spectrometer on the Cassini spacecraft to determine the zonal-mean temperature and hydrogen para-fraction in Saturn's upper troposphere from observations taken before and after the large northern hemisphere storm in 2010-2011. During the storm, zonal mean temperatures in the latitude band between approximately 25°N and 45°N (planetographic latitude) increased by about 3 K, while the zonal mean hydrogen para-fraction decreased by about 0.04 over the same latitudes, at pressures greater than about 300 mbar. These changes occurred over the same latitude range as the disturbed cloud band seen in visible images. The observations are consistent with low para-fraction gas being brought up from the level of the water cloud by the strong convective plume associated with the storm, while being heated by condensation of water vapor, and then advected zonally by the winds near the plume tops in the upper troposphere.

  20. Links of the significant wave height distribution in the Mediterranean sea with the Northern Hemisphere teleconnection patterns

    Directory of Open Access Journals (Sweden)

    P. Lionello

    2008-06-01

    Full Text Available This study analyzes the link between the SWH (Significant Wave Height distribution in the Mediterranean Sea during the second half of the 20th century and the Northern Hemisphere SLP (Sea Level Pressure teleconnection patterns.

    The SWH distribution is computed using the WAM (WAve Model forced by the surface wind fields provided by the ERA-40 reanalysis for the period 1958–2001. The time series of mid-latitude teleconnection patterns are downloaded from the NOAA web site. This study shows that several mid-latitude patterns are linked to the SWH field in the Mediterranean, especially in its western part during the cold season: East Atlantic Pattern (EA, Scandinavian Pattern (SCA, North Atlantic Oscillation (NAO, East Atlantic/West Russia Pattern (EA/WR and East Pacific/ North Pacific Pattern (EP/NP. Though the East Atlantic pattern exerts the largest influence, it is not sufficient to characterize the dominant variability. NAO, though relevant, has an effect smaller than EA and comparable to other patterns. Some link results from possibly spurious structures. Patterns which have a very different global structure are associated to similar spatial features of the wave variability in the Mediterranean Sea. These two problems are, admittedly, shortcomings of this analysis, which shows the complexity of the response of the Mediterranean SWH to global scale SLP teleconnection patterns.

  1. Cell size and wall dimensions drive distinct variability of earlywood and latewood density in Northern Hemisphere conifers.

    Science.gov (United States)

    Björklund, Jesper; Seftigen, Kristina; Schweingruber, Fritz; Fonti, Patrick; von Arx, Georg; Bryukhanova, Marina V; Cuny, Henri E; Carrer, Marco; Castagneri, Daniele; Frank, David C

    2017-11-01

    Interannual variability of wood density - an important plant functional trait and environmental proxy - in conifers is poorly understood. We therefore explored the anatomical basis of density. We hypothesized that earlywood density is determined by tracheid size and latewood density by wall dimensions, reflecting their different functional tasks. To determine general patterns of variability, density parameters from 27 species and 349 sites across the Northern Hemisphere were correlated to tree-ring width parameters and local climate. We performed the same analyses with density and width derived from anatomical data comprising two species and eight sites. The contributions of tracheid size and wall dimensions to density were disentangled with sensitivity analyses. Notably, correlations between density and width shifted from negative to positive moving from earlywood to latewood. Temperature responses of density varied intraseasonally in strength and sign. The sensitivity analyses revealed tracheid size as the main determinant of earlywood density, while wall dimensions become more influential for latewood density. Our novel approach of integrating detailed anatomical data with large-scale tree-ring data allowed us to contribute to an improved understanding of interannual variations of conifer growth and to illustrate how conifers balance investments in the competing xylem functions of hydraulics and mechanical support. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

  2. Balloon-borne radiometer measurements of Northern Hemisphere mid-latitude stratospheric HNO3 profiles spanning 12 years

    Directory of Open Access Journals (Sweden)

    K. A. Walker

    2007-12-01

    Full Text Available Low-resolution atmospheric thermal emission spectra collected by balloon-borne radiometers over the time span of 1990–2002 are used to retrieve vertical profiles of HNO3, CFC-11 and CFC-12 volume mixing ratios between approximately 10 and 35 km altitude. All of the data analyzed have been collected from launches from a Northern Hemisphere mid-latitude site, during late summer, when stratospheric dynamic variability is at a minimum. The retrieval technique incorporates detailed forward modeling of the instrument and the radiative properties of the atmosphere, and obtains a best fit between modeled and measured spectra through a combination of onion-peeling and optimization steps. The retrieved HNO3 profiles are consistent over the 12-year period, and are consistent with recent measurements by the Atmospheric Chemistry Experiment-Fourier transform spectrometer satellite instrument. We therefore find no evidence of long-term changes in the HNO3 summer mid-latitude profile, although the uncertainty of our measurements precludes a conclusive trend analysis.

  3. Are greenhouse gas signals of Northern Hemisphere winter extra-tropical cyclone activity dependent on the identification and tracking algorithm?

    Energy Technology Data Exchange (ETDEWEB)

    Ulbrich, Uwe; Grieger, Jens [Freie Univ. Berlin (Germany). Inst. of Meteorology; Leckebusch, Gregor C. [Birmingham Univ. (United Kingdom). School of Geography, Earth and Environmental Sciences] [and others

    2013-02-15

    For Northern Hemisphere extra-tropical cyclone activity, the dependency of a potential anthropogenic climate change signal on the identification method applied is analysed. This study investigates the impact of the used algorithm on the changing signal, not the robustness of the climate change signal itself. Using one single transient AOGCM simulation as standard input for eleven state-of-the-art identification methods, the patterns of model simulated present day climatologies are found to be close to those computed from re-analysis, independent of the method applied. Although differences in the total number of cyclones identified exist, the climate change signals (IPCC SRES A1B) in the model run considered are largely similar between methods for all cyclones. Taking into account all tracks, decreasing numbers are found in the Mediterranean, the Arctic in the Barents and Greenland Seas, the mid-latitude Pacific and North America. Changing patterns are even more similar, if only the most severe systems are considered: the methods reveal a coherent statistically significant increase in frequency over the eastern North Atlantic and North Pacific. We found that the differences between the methods considered are largely due to the different role of weaker systems in the specific methods. (orig.)

  4. Patterns of bird migration phenology in South Africa suggest northern hemisphere climate as the most consistent driver of change.

    Science.gov (United States)

    Bussière, Elsa M S; Underhill, Les G; Altwegg, Res

    2015-06-01

    Current knowledge of phenological shifts in Palearctic bird migration is largely based on data collected on migrants at their breeding grounds; little is known about the phenology of these birds at their nonbreeding grounds, and even less about that of intra-African migrants. Because climate change patterns are not uniform across the globe, we can expect regional disparities in bird phenological responses. It is also likely that they vary across species, as species show differences in the strength of affinities they have with particular habitats and environments. Here, we examine the arrival and departure of nine Palearctic and seven intra-African migratory species in the central Highveld of South Africa, where the former spend their nonbreeding season and the latter their breeding season. Using novel analytical methods based on bird atlas data, we show phenological shifts in migration of five species - red-backed shrike, spotted flycatcher, common sandpiper, white-winged tern (Palearctic migrants), and diederik cuckoo (intra-African migrant) - between two atlas periods: 1987-1991 and 2007-2012. During this time period, Palearctic migrants advanced their departure from their South African nonbreeding grounds. This trend was mainly driven by waterbirds. No consistent changes were observed for intra-African migrants. Our results suggest that the most consistent drivers of migration phenological shifts act in the northern hemisphere, probably at the breeding grounds. © 2015 John Wiley & Sons Ltd.

  5. Study of the seasonal ozone variations at European high latitudes

    Science.gov (United States)

    Werner, R.; Stebel, K.; Hansen, H. G.; Hoppe, U.-P.; Gausa, M.; Kivi, R.; von der Gathen, P.; Orsolini, Y.; Kilifarska, N.

    2011-02-01

    The geographic area at high latitudes beyond the polar circle is characterized with long darkness during the winter (polar night) and with a long summertime insolation (polar day). Consequentially, the polar vortex is formed and the surrounding strong polar jet is characterized by a strong potential vorticity gradient representing a horizontal transport barrier. The ozone dynamics of the lower and middle stratosphere is controlled both by chemical destruction processes and transport processes.To study the seasonal ozone variation at high latitudes, ozone vertical distributions are examined, collected from the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) (69.3°N, 16.0°E,) station at Andenes and from the stations at Sodankylä (67.4°N, 26.6°E) and at Ny-Ålesund (78.9°N, 11.9°E). The data sets cover the time period from 1994 until 2004. We find a second ozone maximum near 13-15 km, between the tropopause and the absolute ozone maximum near 17-20 km. The maximum is built up by the combination of air mass transport and chemical ozone destruction, mainly caused by the NOx catalytic cycle, which begins after the polar night and intensifies with the increasing day length. Formation of a troposphere inversion layer is observed. The inversion layer is thicker and reaches higher altitudes in winter rather than in summer. However, the temperature inversion during summer is stronger. The formation of an enhanced ozone number density is observed during the spring-summer period. The ozone is accumulated or becomes poor by synoptic weather patterns just above the tropopause from spring to summer. In seasonal average an ozone enhancement above the tropopause is obtained.The stronger temperature inversion during the summer period inhibits the vertical stratosphere-troposphere exchange. The horizontal advection in the upper troposphere and lower stratosphere is enforced during summer. The combination of these mechanisms generates a layer with a very low

  6. Autonomous, continuously recording broadband seismic stations at high-latitude

    Science.gov (United States)

    Beaudoin, B.; Parker, T.; Bonnett, B.; Tytgat, G.; Anderson, K.; Fowler, J.

    2009-04-01

    IRIS PASSCAL is in the third year of an NSF funded development and acquisition effort to establish a pool of cold-hardened seismic stations specifically for high-latitude broadband deployments. We have two complete years of field trials and have successfully recorded continuous seismic data during both years with data recovery rates of ~90%. Our design is premised on a 2W autonomous system recording to local media, capable of lasting two years without service. The system is composed of four new design elements: a heavily insulated station enclosure; a state-of-health (SOH) Iridium modem; a light weight, easily deployed solar panel mount; and a power system that includes power switching between primary (Lithium Thionyl Chloride) and secondary batteries. The station enclosures have proved most critical in keeping our data acquisition systems operating within manufacturer specifications and primary batteries within a 50-70% efficiency range. Enclosures with 2.5cm-thick vacuum panels and 5cm of foam insulation have kept interior enclosure temperatures 25-30°C above background (typically below -50°C). This austral summer we are deploying version three of our enclosures. Significant changes in the design include thicker vacuum panels (5cm), more robust construction, and simplified cable routing. An important aspect of our station design is easy installation and minimal weight. To simplify installation our station enclosures are packed with datalogger, SOH communications and batteries in the lab or base camp, so that access to the internal components is not necessary at the remote site. Bulkhead connectors allow a user to fully interact with the system without ever having to open the enclosure. Solar panel mounts are also fully constructed prior to deployment. Once on site, digging two large holes (one for the enclosure and one for the broadband seismometer) and constructing the site takes roughly 2 hours. A station designed to record continuously for 12-14 months is

  7. Effects of melting ice sheets and orbital forcing on the early Holocene warming in the extratropical Northern Hemisphere

    Science.gov (United States)

    Zhang, Yurui; Renssen, Hans; Seppä, Heikki

    2016-05-01

    The early Holocene is marked by the final transition from the last deglaciation to the relatively warm Holocene. Proxy-based temperature reconstructions suggest a Northern Hemisphere warming, but also indicate important regional differences. Model studies have analyzed the influence of diminishing ice sheets and other forcings on the climate system during the Holocene. The climate response to forcings before 9 kyr BP (referred to hereafter as kyr), however, remains not fully comprehended. We therefore studied, by employing the LOVECLIM climate model, how orbital and ice-sheet forcings contributed to climate change and to these regional differences during the earliest part of the Holocene (11.5-7 kyr). Our equilibrium experiment for 11.5 kyr suggests lower annual mean temperatures at the onset of the Holocene than in the preindustrial era with the exception of Alaska. The magnitude of this cool anomaly varied regionally, and these spatial patterns are broadly consistent with proxy-based reconstructions. Temperatures throughout the whole year in northern Canada and northwestern Europe for 11.5 kyr were 2-5 °C lower than those of the preindustrial era as the climate was strongly influenced by the cooling effect of the ice sheets, which was caused by enhanced surface albedo and ice-sheet orography. In contrast, temperatures in Alaska for all seasons for the same period were 0.5-3 °C higher than the control run, which were caused by a combination of orbital forcing and stronger southerly winds that advected warm air from the south in response to prevailing high air pressure over the Laurentide Ice Sheet (LIS). The transient experiments indicate a highly inhomogeneous early Holocene temperature warming over different regions. The climate in Alaska was constantly cooling over the whole Holocene, whereas there was an overall fast early Holocene warming in northern Canada by more than 1 °C kyr-1 as a consequence of progressive LIS decay. Comparisons of simulated

  8. Effects of melting ice sheets and orbital forcing on the early Holocene warming in extratropical Northern Hemisphere

    Science.gov (United States)

    Zhang, Y.; Renssen, H.; Seppä, H.

    2015-11-01

    The early Holocene is a critical period for climate change, as it marked the final transition from the last deglaciation to the relatively warm and stable Holocene. It is characterized by a warming trend that has been registered in numerous proxy records. This climatic warming was accompanied by major adjustments in different climate components, including the decaying of ice sheets in cryosphere, the perturbation of circulation in the ocean, the expansion of vegetation (over the high latitude) in biosphere. Previous studies have analyzed the influence of the demise of the ice sheets and other forcings on climate system. However, the climate response to the forcings together with the internal feedbacks before 9 ka remains not fully comprehended. In this study, we therefore disentangle how these forcings contributed to climate change during the earliest part of Holocene (11.5-7 ka) by employing the LOVECLIM climate model for both equilibrium and transient experiments. The results of our equilibrium experiments for 11.5 ka reveal that the annual mean temperature at the onset of the Holocene was lower than in the preindustrial era in the Northern extratropics, except in Alaska. The magnitude of this cool anomaly varies regionally as a response to varying climate forcings and diverse mechanisms. In eastern N America and NW Europe the temperatures throughout the whole year were 2-5 °C lower than in the preindustrial control, reaching the maximum cooling as here the climate was strongly influenced by the cooling effects of the ice sheets. This cooling of the ice-sheet surface was caused both by the enhanced surface albedo and by the orography of the ice sheets. For Siberia, a small deviation (-0.5-1.5 °C) in summer temperature and 0.5-1.5 °C cooler annual climate compared to the preindustrial run were caused by the counteraction of the high albedo associated with the tundra vegetation which was more southward extended at 11.5 ka than in the preindustrial period and the

  9. Late Pliocene millennial-scale climate variability in the northern North Atlantic prior to and after the onset of Northern Hemisphere glaciation

    Science.gov (United States)

    Bartoli, G.; Sarnthein, M.; Weinelt, M.

    2006-12-01

    Sediments recovered at Ocean Drilling Program Site 984 on the Reykjanes Ridge provided multicentennial-scale records of late Pliocene climate change over the onset of Northern Hemisphere glaciation (NHG), 2.95-2.82 Ma. Short-term climate variations prior to and after the onset of continent-wide glaciation were compared to test the hypothesis of whether Dansgaard-Oeschger (DO) cycles may have been triggered by continental ice breakouts. During two selected interglacial stages prior to and after NHG (G15 and G1), climate variability resembled that found in the Holocene and the mid-Pliocene warm period. In contrast, DO-like periodicities of 1470, 2900, and 4400 years indeed only occurred in glacial stages after the onset of NHG (G14, G6, and 104) but not in stage G20 prior to the onset. These results suggest a causal link between DO cycles and the late Pliocene onset of major NHG and ice breakouts in the North Atlantic.

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

    Science.gov (United States)

    Livermore, Phil; Hollerbach, Rainer; Finlay, Chris

    2017-04-01

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

  11. Seasonal dynamics of meroplankton in a high-latitude fjord

    Science.gov (United States)

    Michelsen, Helena Kling; Svensen, Camilla; Reigstad, Marit; Nilssen, Einar Magnus; Pedersen, Torstein

    2017-04-01

    Knowledge on the seasonal timing and composition of pelagic larvae of many benthic invertebrates, referred to as meroplankton, is limited for high-latitude fjords and coastal areas. We investigated the seasonal dynamics of meroplankton in the sub-Arctic Porsangerfjord (70°N), Norway, by examining their seasonal changes in relation to temperature, chlorophyll a and salinity. Samples were collected at two stations between February 2013 and August 2014. We identified 41 meroplanktonic taxa belonging to eight phyla. Multivariate analysis indicated different meroplankton compositions in winter, spring, early summer and late summer. More larvae appeared during spring and summer, forming two peaks in meroplankton abundance. The spring peak was dominated by cirripede nauplii, and late summer peak was dominated by bivalve veligers. Moreover, spring meroplankton were the dominant component in the zooplankton community this season. In winter, low abundances and few meroplanktonic taxa were observed. Timing for a majority of meroplankton correlated with primary production and temperature. The presence of meroplankton in the water column through the whole year and at times dominant in the zooplankton community, suggests that they, in addition to being important for benthic recruitment, may play a role in the pelagic ecosystem as grazers on phytoplankton and as prey for other organisms.

  12. Observed currents on the earth's high-latitude magnetopause

    Science.gov (United States)

    Van Allen, J. A.; Adnan, J.

    1992-01-01

    A survey of electrical currents of the earth's magnetosphere, principally at high latitudes, as inferred from magnetic vector data acquired by the Hawkeye 1 satellite, is reported. A total of 536 candidate crossings of the magnetopause were examined. A reduced data set of 139 selected cases was analyzed in detail though solar wind dynamic pressure data were available for only 117 of these cases. Inferred values of the lineal current densities on the magnetopause are in the range 5.5 to 157.5 mA/m over a wide range of solar wind dynamic pressure from 1.17 to 16.1 nPa. The apparent normal thickness of the magnetopause current sheet ranges from 30 to 850 km with mean and median values of 185 and 158 km, respectively. It is argued that the radial rate of motion of the magnetopause is of the order of 2 km/s and hence that its true thickness is of similar magnitude. The relationship of these results to models of the geomagnetic field and to other related work is discussed.

  13. Geosynchronous inclined orbits for high-latitude communications

    Science.gov (United States)

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

    2017-11-01

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

  14. DISCOVERY OF AN APPARENT HIGH LATITUDE GALACTIC SUPERNOVA REMNANT

    Energy Technology Data Exchange (ETDEWEB)

    Fesen, Robert A.; Neustadt, Jack M. M.; Black, Christine S.; Koeppel, Ari H. D. [6127 Wilder Lab, Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States)

    2015-10-10

    Deep Hα images of a faint emission complex 4.°0 × 5.°5 in angular extent and located far off the Galactic plane at l = 70.°0, b = −21.°5 reveal numerous thin filaments suggestive of a supernova remnant’s (SNR’s) shock emission. Low dispersion optical spectra covering the wavelength range 4500–7500 Å show only Balmer line emissions for one filament while three others show a Balmer dominated spectrum along with weak [N i] 5198, 5200 Å, [O i] 6300, 6364 Å, [N ii] 6583 Å, [S ii] 6716, 6731 Å, and in one case [O iii] 5007 Å line emission. Many of the brighter Hα filaments are visible in near-UV GALEX images presumably due to C iii] 1909 Å line emission. ROSAT All Sky Survey images of this region show a faint crescent-shaped X-ray emission nebula coincident with the portion of the Hα nebulosity closest to the Galactic plane. The presence of long, thin Balmer dominated emission filaments with associated UV emission and coincident X-ray emission suggests this nebula is a high latitude Galactic SNR despite a lack of known associated nonthermal radio emission. Relative line intensities of the optical lines in some filaments differ from commonly observed [S ii]/Hα ≥ 0.4 radiative shocked filaments and typical Balmer filaments in SNRs. We discuss possible causes for the unusual optical SNR spectra.

  15. 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...

  16. Azimuthal expansion of high-latitude auroral arcs

    Directory of Open Access Journals (Sweden)

    V. V. Safargaleev

    Full Text Available We used the TV auroral observations in Barentsburg (78.05° N 14.12° E in Spitsbergen archipelago, together with the data of the CUTLASS HF radars and the POLAR satellite images to study azimuthal (in the east-west direction expansion of the high-latitude auroral arcs. It is shown that the east or west edge of the arc moved in the same direction as the convection flow, westward in the pre-midnight sector and eastward in the post-midnight sector. The velocity of arc expansion was of the order of 2.5 km/s, which is 2–3 times larger than the convection velocity measured in the arc vicinity and 2–3 times smaller than the velocity of the bright patches propagating along the arc. The arc expanded from the active auroras seen from the POLAR satellite around midnight as a region of enhanced luminosity, which might be the auroral bulge or WTS. The pole- or equatorward drift of the arcs occurred at the velocity of the order of 100 m/s that was close to the convection velocity in the same direction. These experimental results can be well explained in terms of the interchange (or flute instability.

    Key words. Ionosphere (plasma convection – Magnetospheric physics (auroral phenomena; magnetospheric configuration and dynamics

  17. Accelerating carbon uptake in the Northern Hemisphere - Evidence from the interhemispheric difference of atmospheric CO{sub 2} concentrations

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yuxuan [Ministry of Education Key Lab. for Earth System Modeling, Center for Earth System Science, Tsinghua Univ., Beijing (China); Dept. of Marine Sciences, Texas A and M Univ. at Galveston, Galveston (United States)], e-mail: yxw@tsinghua.edu.cn; Li, Mingwei; Shen, Lulu [Ministry of Education Key Lab. for Earth System Modeling, Center for Earth System Science, Tsinghua Univ., Beijing (China)

    2013-11-15

    Previous studies have indicated that the regression slope between the interhemispheric difference (IHD) of CO{sub 2} mixing ratios and fossil fuel (FF) CO{sub 2} emissions was rather constant at about 0.5 ppm/Pg C yr{sup -1} during 1957 - 2003. In this study, we found that the average regression slopes between the IHD of CO{sub 2} mixing ratios and IHD of FF emissions for 16 sites in the Northern Hemisphere (NH) decreased from 0.69{+-}0.12 ppm/Pg C yr{sup -1} during 1982 - 1991 to 0.37{+-}0.06 ppm/Pg C yr{sup -1} during 1996 - 2008 (IHD of CO{sub 2} defined as the differences between each site and the South Pole, SPO). The largest difference was found in summer and autumn. The change in the spatial distribution of FF emissions driven by fast increasing Asian emissions may explain the slope change at three sites located north of 60 deg N but not at the other sites. A 30-yr SF{sub 6} simulation with time-varying meteorology and constant emissions suggests no significant difference in the decadal average and seasonal variation of interhemispheric exchange time{sub (}t{sub ex)} between the two periods. Based on the hemispheric net carbon fluxes derived from a two-box model, we attributed 75 % of the regression slope decrease at NH sites south of 60 deg N to the acceleration of net carbon sink increase in the NH and 25 % to the weakening of net carbon sink increase in the SH during 1996 - 2008. The growth rate of net carbon sink in the NH has increased by a factor of about three from 0.028{+-}0.023 [mean{+-}2{sigma}] Pg C yr{sup -2} during 1982 - 1991 to 0.093{+-}0.033 Pg C yr{sup -2} during 1996 - 2008, exceeding the percentage increase in the growth rate of IHD of FF emissions between the two periods (45%). The growth rate of net carbon sink in the SH has reduced 62 % from 0.058{+-}0.018 Pg C yr{sup -2} during 1982 - 1991 to 0.022{+-}0.012 Pg C yr{sup -2} during 1996 - 2008.

  18. Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres: the importance of nitric oxide

    Science.gov (United States)

    Kirkwood, S.; Belova, E.; Dalin, P.; Mihalikova, M.; Mikhaylova, D.; Murtagh, D.; Nilsson, H.; Satheesan, K.; Urban, J.; Wolf, I.

    2013-02-01

    The relationship between polar mesosphere summer echoes (PMSE) and geomagnetic disturbances (represented by magnetic K indices) is examined. Calibrated PMSE reflectivities for the period May 2006-February 2012 are used from two 52.0/54.5 MHz radars located in Arctic Sweden (68° N, geomagnetic latitude 65°) and at two different sites in Queen Maud Land, Antarctica (73°/72° S, geomagnetic latitudes 62°/63°). In both the Northern Hemisphere (NH) and the Southern Hemisphere (SH) there is a strong increase in mean PMSE reflectivity between quiet and disturbed geomagnetic conditions. Mean volume reflectivities are slightly lower at the SH locations compared to the NH, but the position of the peak in the lognormal distribution of PMSE reflectivities is close to the same at both NH and SH locations, and varies only slightly with magnetic disturbance level. Differences between the sites, and between geomagnetic disturbance levels, are primarily due to differences in the high-reflectivity tail of the distribution. PMSE occurrence rates are essentially the same at both NH and SH locations during most of the PMSE season when a sufficiently low detection threshold is used so that the peak in the lognormal distribution is included. When the local-time dependence of the PMSE response to geomagnetic disturbance level is considered, the response in the NH is found to be immediate at most local times, but delayed by several hours in the afternoon sector and absent in the early evening. At the SH sites, at lower magnetic latitude, there is a delayed response (by several hours) at almost all local times. At the NH (auroral zone) site, the dependence on magnetic disturbance is highest during evening-to-morning hours. At the SH (sub-auroral) sites the response to magnetic disturbance is weaker but persists throughout the day. While the immediate response to magnetic activity can be qualitatively explained by changes in electron density resulting from energetic particle

  19. Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres: the importance of nitric oxide

    Directory of Open Access Journals (Sweden)

    S. Kirkwood

    2013-02-01

    Full Text Available The relationship between polar mesosphere summer echoes (PMSE and geomagnetic disturbances (represented by magnetic K indices is examined. Calibrated PMSE reflectivities for the period May 2006–February 2012 are used from two 52.0/54.5 MHz radars located in Arctic Sweden (68° N, geomagnetic latitude 65° and at two different sites in Queen Maud Land, Antarctica (73°/72° S, geomagnetic latitudes 62°/63°. In both the Northern Hemisphere (NH and the Southern Hemisphere (SH there is a strong increase in mean PMSE reflectivity between quiet and disturbed geomagnetic conditions. Mean volume reflectivities are slightly lower at the SH locations compared to the NH, but the position of the peak in the lognormal distribution of PMSE reflectivities is close to the same at both NH and SH locations, and varies only slightly with magnetic disturbance level. Differences between the sites, and between geomagnetic disturbance levels, are primarily due to differences in the high-reflectivity tail of the distribution. PMSE occurrence rates are essentially the same at both NH and SH locations during most of the PMSE season when a sufficiently low detection threshold is used so that the peak in the lognormal distribution is included. When the local-time dependence of the PMSE response to geomagnetic disturbance level is considered, the response in the NH is found to be immediate at most local times, but delayed by several hours in the afternoon sector and absent in the early evening. At the SH sites, at lower magnetic latitude, there is a delayed response (by several hours at almost all local times. At the NH (auroral zone site, the dependence on magnetic disturbance is highest during evening-to-morning hours. At the SH (sub-auroral sites the response to magnetic disturbance is weaker but persists throughout the day. While the immediate response to magnetic activity can be qualitatively explained by changes in electron density resulting from energetic

  20. Size Variations and Long-Wave Circulation within the January Northern Hemisphere Circumpolar Vortex: 1946-89.

    Science.gov (United States)

    Burnett, Adam W.

    1993-10-01

    The close association between size variations in the Northern Hemisphere circumpolar vortex and surface and middle-troposheric thermal characteristics makes vortex measurement a valuable tool in monitoring and understanding climate change. Unfortunately, as with most hemispheric circulation indices, measures of total vortex size offer little insight into regional changes in the vortex. Traditional approaches to vortex size calculation, which are based upon planimeter measurements on a polar stereographic projection, limit the ability to examine regional contributions to the total vortex and cannot be used to assess specific linkages between vortex expansion and contraction and the broader class of long wave circulation phenomena. Furthermore, because the scale of the polar stereographic projection varies from one latitude to another, interannual variations in planimeter vortex size measurements are influenced somewhat by the position of the vortex relative to the North Pole.Many of these problems are avoided if digital data sources are used to calculate vortex size. Digital data enable the calculation of actual earth surface area within longitudinal sectors of the vortex and provide a regional decomposition of total vortex that can he linked with variations in long wave circulation. In this study, digital 500-mb geopotential height data interpolated to a 5° latitude by 5° longitude grid were used to examine size variations in the January circumpolar vortex for the period 1946-89. Total January vortices were smaller than the 44-year average during the period 1946-64, after which larger than average vortices became more common. The last few years of the data record indicate that January vortices may be becoming more contracted again. These patterns of contraction and expansion are not reflective of all sectors of the vortex. Much of the vortex expansion after 1964 occurred in association with amplified troughing over the central Pacific Ocean and eastern North

  1. Accelerating carbon uptake in the Northern Hemisphere: evidence from the interhemispheric difference of atmospheric CO2 concentrations

    Directory of Open Access Journals (Sweden)

    Yuxuan Wang

    2013-11-01

    Full Text Available Previous studies have indicated that the regression slope between the interhemispheric difference (IHD of CO2 mixing ratios and fossil fuel (FF CO2 emissions was rather constant at about 0.5 ppm/Pg C yr−1 during 1957–2003. In this study, we found that the average regression slopes between the IHD of CO2 mixing ratios and IHD of FF emissions for 16 sites in the Northern Hemisphere (NH decreased from 0.69±0.12 ppm/Pg C yr−1 during 1982–1991 to 0.37±0.06 ppm/Pg C yr−1 during 1996–2008 (IHD of CO2 defined as the differences between each site and the South Pole, SPO. The largest difference was found in summer and autumn. The change in the spatial distribution of FF emissions driven by fast increasing Asian emissions may explain the slope change at three sites located north of 60°N but not at the other sites. A 30-yr SF6 simulation with time-varying meteorology and constant emissions suggests no significant difference in the decadal average and seasonal variation of interhemispheric exchange time (τ ex between the two periods. Based on the hemispheric net carbon fluxes derived from a two-box model, we attributed 75% of the regression slope decrease at NH sites south of 60°N to the acceleration of net carbon sink increase in the NH and 25% to the weakening of net carbon sink increase in the SH during 1996–2008. The growth rate of net carbon sink in the NH has increased by a factor of about three from 0.028±0.023 [mean±2σ] Pg C yr−2 during 1982–1991 to 0.093±0.033 Pg C yr−2 during 1996–2008, exceeding the percentage increase in the growth rate of IHD of FF emissions between the two periods (45%. The growth rate of net carbon sink in the SH has reduced 62% from 0.058±0.018 Pg C yr−2 during 1982–1991 to 0.022±0.012 Pg C yr−2 during 1996–2008.

  2. NKS NordRisk. Atlas of long-range atmospheric dispersion and deposition of radionuclides from selected risk sites in the Northern Hemisphere

    Energy Technology Data Exchange (ETDEWEB)

    Havskov Soerensen, J.; Baklanov, A.; Mahura, A. (Danish Meteorological Institute, Copenhagen (Denmark)); Lauritzen, Bent; Mikkelsen, Torben (Technical Univ. of Denmark, Risoe National Lab. for Sustainable Energy, Roskilde (Denmark))

    2008-07-15

    Within the NKS NordRisk project, 'Nuclear risk from atmospheric dispersion in Northern Europe', the NKS NordRisk Atlas has been developed. The atlas describes risks from hypothetical long-range atmospheric dispersion and deposition of radionuclides from selected nuclear risk sites in the Northern Hemisphere. A number of case studies of long-term long-range atmospheric transport and deposition of radionuclides has been developed, based on two years of meteorological data. Radionuclide concentrations in air and radionuclide depositions have been evaluated and examples of long-term averages of the dispersion and deposition and of the variability around these mean values are provided. (au)

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

    OpenAIRE

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

    2005-01-01

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

  4. Occurrence of polar mesosphere summer echoes at very high latitudes

    Directory of Open Access Journals (Sweden)

    M. Zecha

    2009-03-01

    Full Text Available Observations of polar mesosphere summer echoes (PMSE have been carried out during the summer periodes 1999–2001 and 2003–2004 at the very high latitude of 78° N using the SOUSY Svalbard Radar (53.5 MHz at Longyearbyen. Although the measurements could not be done continuously in these seasons, PMSE have been detected over more than 6600 h of 9300 h of observation time overall. Using this data base, particular PMSE occurrence characteristics have been determined. PMSE at Svalbard appear from the middle of May to the end of August with an almost permanent total occurrence in June and July. Diurnal variations are observable in the height-depend occurrence rates and in PMSE thickness, they show a maximum around 09:00–10:00 UTC and a minimum around 21:00–22:00 UTC. PMSE occur nearly exclusively between a height of 80 km and 92 km with a maximum near 85 km. However, PMSE appear not simultaneously over the entire height range, the mean vertical PMSE extension is around 4–6 km in June and July. Furthermore, typically PMSE are separated into several layers, and only 30% of all PMSE are single layers. The probability of multiple layers is greater in June and July than at the beginning and the end of the PMSE season and shows a marked 5-day-variation. The same variation is noticeable in the seasonal dependence of the PMSE occurrence and the PMSE thickness. We finally discuss potential geophysical processes to explain our observational results.

  5. The longevity of broadleaf deciduous trees in Northern Hemisphere temperate forests: insights from tree-ring series

    Directory of Open Access Journals (Sweden)

    Alfredo eDi Filippo

    2015-05-01

    Full Text Available Understanding the factors controlling the expression of longevity in trees is still an outstanding challenge for tree biologists and forest ecologists. We gathered tree-ring data and literature for broadleaf deciduous (BD temperate trees growing in closed-canopy old-growth forests in the Northern Hemisphere to explore the role of geographic patterns, climate variability, and growth rates on longevity. Our pan-continental analysis, covering 32 species from 12 genera, showed that 300-400 years can be considered a baseline threshold for maximum tree lifespan in many temperate deciduous forests. Maximum age varies greatly in relation to environmental features, even within the same species. Tree longevity is generally promoted by reduced growth rates across large genetic differences and environmental gradients. We argue that slower growth rates, and the associated smaller size, provide trees with an advantage against biotic and abiotic disturbance agents, supporting the idea that size, not age, is the main constraint to tree longevity. The oldest trees were living most of their life in subordinate canopy conditions and/or within primary forests in cool temperate environments and outside major storm tracks. Very old trees are thus characterized by slow growth and often live in forests with harsh site conditions and infrequent disturbance events that kill much of the trees. Temperature inversely controls the expression of longevity in mesophilous species (Fagus spp., but its role in Quercus spp. is more complex and warrants further research in disturbance ecology. Biological, ecological and historical drivers must be considered to understand the constraints imposed to longevity within different forest landscapes.

  6. Changes to the chemical state of the Northern Hemisphere atmosphere during the second half of the twentieth century

    Science.gov (United States)

    Newland, Mike J.; Martinerie, Patricia; Witrant, Emmanuel; Helmig, Detlev; Worton, David R.; Hogan, Chris; Sturges, William T.; Reeves, Claire E.

    2017-07-01

    The NOx (NO and NO2) and HOx (OH and HO2) budgets of the atmosphere exert a major influence on atmospheric composition, controlling removal of primary pollutants and formation of a wide range of secondary products, including ozone, that can influence human health and climate. However, there remain large uncertainties in the changes to these budgets over recent decades. Due to their short atmospheric lifetimes, NOx and HOx are highly variable in space and time, and so the measurements of these species are of limited value for examining long-term, large-scale changes to their budgets. Here, we take an alternative approach by examining long-term atmospheric trends of alkyl nitrates, the production efficiency of which is dependent on the atmospheric [NO] / [HO2] ratio. We derive long-term trends in the alkyl nitrates from measurements in firn air from the NEEM site, Greenland. Their mixing ratios increased by a factor of 3-5 between the 1970s and 1990s. This was followed by a steep decline to the sampling date of 2008. Moreover, we examine how the trends in the alkyl nitrates compare to similarly derived trends in their parent alkanes (i.e. the alkanes which, when oxidised in the presence of NOx, lead to the formation of the alkyl nitrates). The ratios of the alkyl nitrates to their parent alkanes increased from around 1970 to the late 1990s. This is consistent with large changes to the [NO] / [HO2] ratio in the Northern Hemisphere atmosphere during this period. Alternatively, they could represent changes to concentrations of the hydroxyl radical, OH, or to the transport time of the air masses from source regions to the Arctic.

  7. The Biogeographic South-North Divide of Polygonatum (Asparagaceae Tribe Polygonateae) within Eastern Asia and Its Recent Dispersals in the Northern Hemisphere.

    Science.gov (United States)

    Wang, Jia-Jian; Yang, Yong-Ping; Sun, Hang; Wen, Jun; Deng, Tao; Nie, Ze-Long; Meng, Ying

    2016-01-01

    Eastern Asia (EA) is a key region for the diversification of flowering plants in the Northern Hemisphere, but few studies have focused on the biogeographic history within EA in the context of the other northern continents. Polygonatum is an important medicinal genus widely distributed in the Northern Hemisphere with its highest species richness in EA, and it represents an excellent model for studying the evolution of biogeographic patterns in this region. Divergence time estimation was used to examine the biogeographic history of Polygonatum based on nuclear ITS and four plastid sequences (rbcL, matK, psbA-trnH and trnC-petN) from 30 Polygonatum species and 35 outgroup taxa. The ancestral area of Polygonatum and subsequent dispersal routes were inferred using Bayes-Lagrange. Polygonatum was estimated to have originated in southern EA during the middle Miocene (14.34-13.57 Ma) with subsequent south-to-north expansion in the late Miocene. Multiple intercontinental dispersal events were inferred between EA and Europe or North America, and all of them have occurred recently in the late Miocene to Pliocene. The separation of Polygonatum into the south and north lineages and their subsequent diversifications in the late Miocene supports the existence of a biogeographic divide between the northern and southern parts of EA that also coincides with the retreat and redevelopment of the arid zone in EA in the Neogene. Our results demonstrate the complexity of biogeographic history of Polygonatum in the Northern Hemisphere including early vicariance followed by frequent and recent dispersals in the Neogene.

  8. Five-day planetary waves in the middle atmosphere from Odin satellite data and ground-based instruments in Northern Hemisphere summer 2003, 2004, 2005 and 2007

    Directory of Open Access Journals (Sweden)

    A. Belova

    2008-11-01

    Full Text Available A number of studies have shown that 5-day planetary waves modulate noctilucent clouds and the closely related Polar Mesosphere Summer Echoes (PMSE at the summer mesopause. Summer stratospheric winds should inhibit wave propagation through the stratosphere and, although some numerical models (Geisler and Dickinson, 1976 do show a possibility for upward wave propagation, it has also been suggested that the upward propagation may in practice be confined to the winter hemisphere with horizontal propagation of the wave from the winter to the summer hemisphere at mesosphere heights causing the effects observed at the summer mesopause. It has further been proposed (Garcia et al., 2005 that 5-day planetary waves observed in the summer mesosphere could be excited in-situ by baroclinic instability in the upper mesosphere. In this study, we first extract and analyze 5-day planetary wave characteristics on a global scale in the middle atmosphere (up to 54 km in temperature, and up to 68 km in ozone concentration using measurements by the Odin satellite for selected days during northern hemisphere summer from 2003, 2004, 2005 and 2007. Second, we show that 5-day temperature fluctuations consistent with westward-traveling 5-day waves are present at the summer mesopause, using local ground-based meteor-radar observations. Finally we examine whether any of three possible sources of the detected temperature fluctuations at the summer mesopause can be excluded: upward propagation from the stratosphere in the summer-hemisphere, horizontal propagation from the winter-hemisphere or in-situ excitation as a result of the baroclinic instability. We find that in one case, far from solstice, the baroclinic instability is unlikely to be involved. In one further case, close to solstice, upward propagation in the same hemisphere seems to be ruled out. In all other cases, all or any of the three proposed mechanisms are consistent with the observations.

  9. Late-season nitrogen applications in high-latitude strawberry ...

    African Journals Online (AJOL)

    The influence of late-season nitrogen (N) applications on the fruiting pattern of strawberry runner plants of 'Camarosa' was determined over three growing seasons. Experiments were carried out in highlatitude nurseries in northern California and fruit production trials were established in southern California. A total of 80 ...

  10. Effects of melting ice sheets and orbital forcing on the early Holocene warming in extratropical Northern Hemisphere

    Science.gov (United States)

    zhang, yurui; Renssen, Hans; Seppä, Heikki

    2016-04-01

    The early Holocene is an important climatological period, as it marked the final transition from the last deglaciation to the relatively warm and stable Holocene. Previous studies have analyzed the influence of the demise of the ice sheets and other forcings on the climate system during the Holocene. However, the climate response to the forcings together with the internal feedbacks before 9 ka remains not fully comprehended. In this study, we therefore disentangle how these forcings contributed to climate change during the earliest part of Holocene (11.5-7 ka) by employing the LOVECLIM climate model for both equilibrium and transient experiments. The results of our equilibrium experiments for 11.5 ka reveal that the annual mean temperature at the onset of the Holocene was lower than in the preindustrial era over most of the extratropical Northern Hemisphere. The magnitude of this cooler climate varies regionally and this spatial pattern is suggested by the biologically based proxies as well. In eastern N America and NW Europe the temperatures were 2-5 °C lower than in the preindustrial era as the climate was strongly influenced by the cooling effects of the ice sheets at here. This cooling of the ice-sheet surface was caused both by the enhanced surface albedo and by the orography of the ice sheets. In contrast, in Alaska, temperatures in all seasons were 0.5-3 °C higher than in the control run primarily due to the orbitally induced positive insolation anomaly and the enhanced southerly winds which advected warm air from the South as a response to the high air pressure over the Laurentide Ice Sheet (LIS). Our transient experiments indicate that the Holocene temperature evolution and the early Holocene warming were also geographically heterogeneous. In Alaska, the climate is constantly cooling over the whole Holocene. In contrast, in N Canada, there was an overall warming during the early Holocene up to 1.88 °C ka-1 in summer as a consequence of the progressive

  11. Variability of large-scale atmospheric circulation indices for the northern hemisphere during the past 100 years

    Energy Technology Data Exchange (ETDEWEB)

    Broennimann, Stefan; Stickler, Alexander [Inst. for Atmospheric and Climate Science, ETH Zurich (Switzerland); Griesser, Thomas; Fischer, Andreas M.; Grant, Andrea; Ewen, Tracy; Zhou Tianjun; Schraner, Martin; Peter, Thomas [LASG, Inst. of Atmospheric Physics, Chinese Academy of Sciences, BJ (China); Rozanov, Eugene [Inst. for Atmospheric and Climate Science, ETH Zurich (Switzerland); PMOD/WRC, Davos (Switzerland)

    2009-08-15

    We present an analysis of the large-scale atmospheric circulation variability since 1900 based on various circulation indices. They represent the main features of the zonal mean circulation in the northern hemisphere in boreal winter (such as the Hadley circulation, the subtropical jet, and the polar vortex in the lower stratosphere) as well as aspects of the regional and large-scale circulation (the Pacific Walker Circulation, the Indian monsoon, the North Atlantic Oscillation, NAO, and the Pacific North American pattern, PNA). For the past decades we calculate the indices from different reanalyses (NCEP/NCAR, ERA-40, JRA-25, ERA-Interim). For the first half of the 20{sup th} century the indices are statistically reconstructed based on historical upper-air and surface data as well as calculated from the Twentieth Century Reanalysis. The indices from all these observation-based data sets are compared to indices calculated from a 9-member ensemble of ''all forcings'' simulations performed with the chemistry-climate model SOCOL. After discussing the agreement among different data products, we analyse the interannual-to-decadal variability of the indices in the context of possible driving factors, such as El Nino/Southern Oscillation (ENSO), volcanic eruptions, and solar activity. The interannual variability of the Hadley cell strength, the subtropical jet strength, or the PNA is well reproduced by the model ensemble mean, i.e., it is predictable in the context of the specified forcings. The source of this predictability is mainly related to ENSO (or more generally, tropical sea-surface temperatures). For other indices such as the strength of the stratospheric polar vortex, the NAO, or the poleward extent of the Hadley cell the correlations between observations and model ensemble mean are much lower, but so are the correlations within the model ensemble. Multidecadal variability and trends in the individual series are discussed in the context of

  12. 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...

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

    NARCIS (Netherlands)

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

    2016-01-01

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

  14. High latitude hydrological changes during the Eocene Thermal Maximum 2

    Science.gov (United States)

    Krishnan, Srinath; Pagani, Mark; Huber, Matthew; Sluijs, Appy

    2014-10-01

    -enriched signals at the base of the event, including (1) intense local drying and cooling leading to evaporative 2H-enrichment; (2) changes in frequency/intensity of storm events and its impact on high latitude amount effects; and (3) changes in low-latitude temperatures. Evidence for hydrological shifts at the base of both hyperthermals suggests that hydrological change or the factors promoting hydrological change played a role in triggering the release of greenhouse gases. Generation of similar high-resolution isotopic- and temperature records at other latitudes is crucial for understanding the causal links between temperature and hydrological changes and may help constrain the source and mechanism of carbon release that triggered the early Eocene hyperthermals.

  15. 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.

  16. High-latitude regions of Siberia and Northeast Russia in the Paleogene: Stratigraphy, flora, climate, coal accumulation

    Science.gov (United States)

    Akhmetiev, M. A.

    2015-07-01

    The geological structure and development history of superposed depressions on the Arctic coast of East Siberia and Bering Sea region (Chukotka, Koryakiya, northern Kamchatka) in the Early Paleogene are considered with the analysis of their flora and climatic parameters. The paleofloral analysis revealed thermophilic assemblages that reflect phases of maximum warming at the Paleocene-Eocene transition and in the Early Eocene. The appearance of thermophilic plants (Magnoliaceae, Myrtaceae, Lauraceae, Araliaceae, Loranthaceae, and others) in the Siberian segment of the Arctic region is explained by the stable atmospheric heat transfer from the Tethys to higher latitudes and absence of the latitudinal orographic barrier (Alpine-Himalayan belt). The plants migrated to high latitudes also along the meridional seaway that connected the Tethys with the Arctic Ocean via marine basins of the Eastern Paratethys, Turgai Strait, and West Siberia. The migration from the American continent was realized along the southern coast of Beringia under influence of a warm current flowing from low latitudes along the western coast of North America. The palm genus Sabal migrated to northern Kamchatka and Koryakiya precisely in this way via southern Alaska. In the Oligocene, shallow-water marine sediments in high-latitude regions were replaced by terrestrial facies. The Late Oligocene was marked by maximum cooling. Coal accumulation in Northeast Russia through the Paleogene is reviewed.

  17. The Hiccup: a dynamical coupling process during the autumn transition in the Northern Hemisphere - similarities and differences to sudden stratospheric warmings

    Science.gov (United States)

    Matthias, V.; Shepherd, T. G.; Hoffmann, P.; Rapp, M.

    2015-02-01

    Sudden stratospheric warmings (SSWs) are the most prominent vertical coupling process in the middle atmosphere, which occur during winter and are caused by the interaction of planetary waves (PWs) with the zonal mean flow. Vertical coupling has also been identified during the equinox transitions, and is similarly associated with PWs. We argue that there is a characteristic aspect of the autumn transition in northern high latitudes, which we call the "hiccup", and which acts like a "mini SSW", i.e. like a small minor warming. We study the average characteristics of the hiccup based on a superimposed epoch analysis using a nudged version of the Canadian Middle Atmosphere Model, representing 30 years of historical data. Hiccups can be identified in about half the years studied. The mesospheric zonal wind results are compared to radar observations over Andenes (69° N, 16° E) for the years 2000-2013. A comparison of the average characteristics of hiccups and SSWs shows both similarities and differences between the two vertical coupling processes.

  18. The Hiccup: a dynamical coupling process during the autumn transition in the Northern Hemisphere – similarities and differences to sudden stratospheric warmings

    Directory of Open Access Journals (Sweden)

    V. Matthias

    2015-02-01

    Full Text Available Sudden stratospheric warmings (SSWs are the most prominent vertical coupling process in the middle atmosphere, which occur during winter and are caused by the interaction of planetary waves (PWs with the zonal mean flow. Vertical coupling has also been identified during the equinox transitions, and is similarly associated with PWs. We argue that there is a characteristic aspect of the autumn transition in northern high latitudes, which we call the "hiccup", and which acts like a "mini SSW", i.e. like a small minor warming. We study the average characteristics of the hiccup based on a superimposed epoch analysis using a nudged version of the Canadian Middle Atmosphere Model, representing 30 years of historical data. Hiccups can be identified in about half the years studied. The mesospheric zonal wind results are compared to radar observations over Andenes (69° N, 16° E for the years 2000–2013. A comparison of the average characteristics of hiccups and SSWs shows both similarities and differences between the two vertical coupling processes.

  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. Behavioral and metabolic contributions to thermoregulation in freely swimming leatherback turtles at high latitudes.

    Science.gov (United States)

    Casey, James P; James, Michael C; Williard, Amanda S

    2014-07-01

    Leatherback turtles in the Northwest Atlantic Ocean have a broad geographic range that extends from nesting beaches near the equator to seasonal foraging grounds as far north as Canada. The ability of leatherbacks to maintain core body temperature (Tb) higher than that of the surrounding water is thought to be a key element of their biology that permits them to exploit productive waters at high latitudes. We provide the first recordings of Tb from freely swimming leatherbacks at a northern foraging ground, and use these data to assess the importance of behavioral adjustments and metabolic sources of heat for maintenance of the thermal gradient (Tg). The mean Tb for individual leatherbacks ranged from 25.4 ± 1.7 to 27.3 ± 0.3 °C, and Tg ranged from 10.7 ± 2.4 to 12.1 ± 1.7 °C. Variation in mean Tb was best explained by the amount of time that turtles spent in the relatively warm surface waters. A diel trend in Tb was apparent, with daytime cooling suggestive of prey ingestion and night-time warming attributable to endogenous heat production. We estimate that metabolic rates necessary to support the observed Tg are ~3 times higher than resting metabolic rate, and that specific dynamic action is an important source of heat for foraging leatherbacks. © 2014. Published by The Company of Biologists Ltd.

  1. 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.

  2. Scaling Features of High-Latitude Geomagnetic Field Fluctuations at Swarm Altitude: Impact of IMF Orientation

    Science.gov (United States)

    De Michelis, Paola; Consolini, Giuseppe; Tozzi, Roberta; Marcucci, Maria Federica

    2017-10-01

    This paper attempts to explore the statistical scaling features of high-latitude geomagnetic field fluctuations at Swarm altitude. Data for this study are low-resolution (1 Hz) magnetic data recorded by the vector field magnetometer on board Swarm A satellite over 1 year (from 15 April 2014 to 15 April 2015). The first- and second-order structure function scaling exponents and the degree of intermittency of the fluctuations of the intensity of the horizontal component of the magnetic field at high northern latitudes have been evaluated for different interplanetary magnetic field orientations in the GSM Y-Z plane and seasons. In the case of the first-order structure function scaling exponent, a comparison between the average spatial distributions of the obtained values and the statistical convection patterns obtained using a Super Dual Auroral Radar Network dynamic model (CS10 model) has been also considered. The obtained results support the idea that the knowledge of the scaling features of the geomagnetic field fluctuations can help in the characterization of the different ionospheric turbulence regimes of the medium crossed by Swarm A satellite. This study shows that different turbulent regimes of the geomagnetic field fluctuations exist in the regions characterized by a double-cell convection pattern and in those regions near the border of the convective structures.

  3. Does the correlation between solar cycle lengths and Northern Hemisphere land temperatures rule out any significant global warming from greenhouse gases?

    DEFF Research Database (Denmark)

    Laut, Peter; Gundermann, Jesper

    1998-01-01

    Since the discovery of a striking correlation between solar cycle lengths and Northern Hemisphere land temperatures there have been widespread speculations as to whether these findings would rule out any significant contributions to global warming from the enhanced concentrations of greenhouse...... gases. The present analysis shows that a similar degree of correlation is obtained when testing the solar data against a couple of fictitious temperature series representing different global warming trends. Therefore, the correlation cannot be used to estimate the magnitude of a possible contribution...... to global warming from human activities, nor to rule out a sizable contribution from that source....

  4. Light limitation of primary production in high latitude reservoirs

    Directory of Open Access Journals (Sweden)

    J. Sahlberg

    2005-01-01

    Full Text Available To explore the effects of vertical mixing on the primary production in a northern reservoir, a Lagrangian particle dispersion model was coupled to a 1-D reservoir model where the vertical mixing was calculated using a k-ε model together with an empirically-based deep-water eddy viscosity. The primary production of each phytoplankton cell is assumed to be a function of the ambient light and not to be nutrient limited. The photoadaption follows first-order kinetics where the photoadaptive variables, a, b, and Pm, describe the coefficients of the photosynthesis-irradiance curve. The model is applied to the northern reservoir Akkajaure, which is strongly regulated with a mean and maximum depth of 30 m and 100 m respectively. Based on the release of 1000 particles (plankton, the model calculated the mean primary production of each plankton, during four different growing seasons. Vertical mixing has a substantial effect on the vertical distribution of phytoplankton and, thus, on the primary production in a reservoir. It was found that primary production was greater in a cold summer with weak stratification than in a warm summer when the reservoir was more stratified.

  5. NKS NordRisk II: Atlas of long-range atmospheric dispersion and deposition of radionuclides from selected risk sites in the Northern Hemisphere

    Energy Technology Data Exchange (ETDEWEB)

    Smith Korsholm, U.; Havskov Soerensen, J. (Danish Meteorological Institute (DMI), Copenhagen (Denmark)); Astrup, P.; Lauritzen, B. (Technical Univ. of Denmark, Risoe National Lab. for Sustainable Energy. Radiation Research Div., Roskilde (Denmark))

    2011-04-15

    The present atlas has been developed within the NKS/NordRisk-II project 'Nuclear risk from atmospheric dispersion in Northern Europe'. The atlas describes risks from hypothetical long-range dispersion and deposition of radionuclides from 16 nuclear risk sites on the Northern Hemisphere. The atmospheric dispersion model calculations cover a period of 30 days following each release to ensure almost complete deposition of the dispersed material. The atlas contains maps showing the total deposition and time-integrated air concentration of Cs-137 and I-131 based on three years of meteorological data spanning the climate variability associated with the North Atlantic Oscillation, and corresponding time evolution of the ensemble mean atmospheric dispersion. (Author)

  6. Changes of reanalysis-derived Northern Hemisphere summer warm extreme indices during 1948-2006 and links with climate variability

    Science.gov (United States)

    Fang, Xingqin; Wang, Anyu; Fong, Soi-kun; Lin, Wenshi; Liu, Ji

    2008-08-01

    Using1948-2006 surface 2 m daily temperature, daily maximum temperature and daily minimum temperature of National Centers for Environmental Prediction (NCEP) reanalysis dataset, summer warm extreme indices, warm days (TG90P), warm-spell days (WSFI), warm day-times (TX90P) and warm nights (TN90P) are calculated for Gaussian grids, a complete Northern Hemisphere (NH) picture of changes of summer warm extremes is presented, and their links with El Niño/La Niña & Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and North Atlantic Oscillation (NAO) are also examined in this paper. The results on the NH summer seasonal basis are as follows. Warm days, warm-spell days, warm day-times and warm nights increase at rates of 2.18, 1.23, 2.31 and 2.00 days/decade respectively during 1948-2006. A broader area is exposed to frequent occurrence of warm extremes in the recent 30 years than in the last 30 years. The 59-year long-term upward trend is characterized by a positive trend reversion in the late 1970s, with a slight downward trend in the last 30 years and a rapid upward trend in the recent 30 years, representing the main form of interdecadal variance of NH warm extremes. Warm days, warm-spell days, warm day-times and warm nights increase at rates of 4.53, 3.36, 4.44 and 4.21 days/decade respectively during 1977-2006. During 1948-2006, the largest increasing rate is at central tropical Atlantic and the largest decreasing rate in Mongolia and north China. Significant (level of 0.05) upward trends cover about half of the NH during 1948-2006 and about a third of the NH during 1977-2006 with the very significant upward trends more focused, while very sparse regions have significant downward trends during these two periods. In the recent 30 years, although NH-land summer warms at a faster rate than NH-water, warm extremes on NH-water increase much faster than those on NH-land, the average warm extreme indices and their increasing trends on NH are most modulated by

  7. On contributing factors to the winter record low of the northern hemisphere sea ice extent in 2015

    Science.gov (United States)

    Fuckar, Neven-Stjepan; Massonnet, Francois; Guemas, Virginie; Garcia-Serrano, Javier; Bellprat, Omar; Doblas-Reyes, Francisco; Acosta, Mario

    2017-04-01

    The northern hemisphere (NH) sea ice extent (SIE) has reached the record low in the satellite era (since November 1978) in March 2015. Would the 2014/15 fall-winter atmosphere yield this sea ice extreme if we reversed in time the long-term change in the ocean and sea ice state? We examine the contributions of the atmosphere and the long-term memory of the ocean and sea ice to the March 2015 record low of the NH SIE with a state-of-the-art ocean-sea-ice general circulation model (OGCM: NEMOv3.3). First, we perform a set of 5-month-long retrospective control simulations initialized on 1 November from 1979 to 2014 to assess the model skill in predicting the NH March SIE. We produce ERA-Interim-forced five ensemble members initialized from the five members of the ORAS4 ocean reanalysis and the associated five-member sea ice reconstruction. A climate variable can be decomposed into the sum of the background state represented as a linear fit over the period of interest and an interannual anomaly with respect to this fit: var(t) = [at + b] + var'(t). More specifically, initial conditions (IC) and surface forcing fields contain: (i) linear-fit background state of IC, (ii) interannual anomaly in IC with respect to factor (i), (iii) linear-fit background state of surface forcing fields, and (iv) interannual anomaly in surface forcing fields with respect to factor (iii). Next, we conduct two sets of sensitivity experiments with IC and surface forcing fields modified in such manner so that one set examine the influence of 2014/15 fall-winter atmospheric conditions, while the other focuses on the influence of change in linear-fit background state of the ocean and sea ice cover. Our forced experiments indicate that the most important factor driving the NH SIE to the record low in March 2015 was surface atmospheric conditions on average contributing at least 54% to the change from the past March states to 2015. The 1 November 2014 interannual anomaly of IC, which on average

  8. The influence of different El Nino types on the northern hemisphere stratosphere simulated by the MPI-ESM

    Science.gov (United States)

    Bittner, Matthias; Timmreck, Claudia; Schmidt, Hauke

    2013-04-01

    It is known that the El Nino Southern Oscillation (ENSO), although it is mainly a tropospheric phenomenon, has an impact on the polar winter stratosphere [e.g. van Loon and Labitzke, 1987: Camp and Tung, 2007]. This has also been shown in simulations with general circulation models (GCM) [Sassi,et al. 2004, Manzini et al. 2006]. For a couple of years there are discussions about two different "flavors" of the the El Nino, the central Pacific (or Modoki) El Nino and the east Pacific El Nino [e.g. Wang and Weisberg, 2000; Yu and Kao, 2007; Ashok et al. 2007]. An observational study [Graf and Zanchettin, 2012] indicate that the polar vortex is more disturbed during EP El Ninos. Here we to investigate the influence of the equatorial sea surface temperatures on the stratosphere-troposphere coupling in the northern hemisphere winter season in a fully coupled atmosphere-ocean-land GCM. We use two versions of the Max-Planck-Institute for Meteorology model MPI-ESM, namely MPI-ESM-LR with lower T63 L47 atmosphere and GR15 ocean resolution and the MPI-ESM-MR with the same horizontal resolution in the atmosphere but a higher resolution in the vertical (L95) and in the ocean (TP04). To exclude effects of natural and anthropogenic forcing, we analyze a 1000 year coupled control simulation with pre-industrial greenhouse gas concentration and constant solar forcing (piControl). For comparison with reananlyis data we also analyze uncoupled atmosphere-only simulations with observed sea surface temperatures from 1979 until 2008 (AMIP). We compare three ways of defining El Nino: the central Pacific (CP), the east Pacific (EP) and the canonical Nino3.4 El Nino. We show to what extent the MPI-ESM is able to simulate these different types of El Nino and how they affect the polar stratosphere. The MPI-ESM model is in both versions capable of producing CP and EP El Ninos. However, the CP El Nino is dominant one in terms of magnitude and the EP El Nino has a relative small impact on global

  9. The influence on the radioxenon background during the temporary suspension of operations of three major medical isotope production facilities in the Northern Hemisphere and during the start-up of another facility in the Southern Hemisphere.

    Science.gov (United States)

    Saey, Paul R J; Auer, Matthias; Becker, Andreas; Hoffmann, Emmy; Nikkinen, Mika; Ringbom, Anders; Tinker, Rick; Schlosser, Clemens; Sonck, Michel

    2010-09-01

    Medical isotope production facilities (MIPF) have recently been identified to emit the major part of the environmental radioxenon measured at many globally distributed monitoring sites deployed to strengthen the radionuclide component of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) verification regime. Efforts to raise a global radioxenon emission inventory revealed that the yearly global total emission from MIPF's is around 15 times higher than the total radioxenon emission from nuclear power plants (NPP's). Given that situation, from mid 2008 until early 2009 two out of the ordinary hemisphere-specific events occured: 1) In the Northern hemisphere, a joint temporary suspension of operations of the three largest MIPF's made it possible to quantify the effects of the emissions related to NPP's. The average activity concentrations of (133)Xe measured at a monitoring station close to Freiburg, Germany, went down significantly from 4.5 +/- 0.5 mBq/m(3) to 1.1 +/- 0.1 mBq/m(3) and in Stockholm, Sweden, from 2.0 +/- 0.4 mBq/m(3) to 1.05 +/- 0.15 mBq/m(3). 2) In the Southern hemisphere the only radioxenon-emitting MIPF in Australia started up test production in late November 2008. During eight test runs, up to 6.2 +/- 0.2 mBq/m(3) of (133)Xe was measured at the station in Melbourne, 700 km south-west from the facility, where no radioxenon had been observed before, originating from the isotopic production process. This paper clearly confirms the hypothesis that medical isotope production facility are at present the major emitters of radioxenon to the atmosphere. Suspension of operations of these facilities indicates the scale of their normal contribution to the European radioxenon background, which decreased two to four fold. This also gives a unique opportunity to detect and investigate the influence of other local and long distance sources on the radioxenon background. Finally the opposing effect was studied: the contribution of the start-up of a renewed

  10. Modelling turbulent energy dissipation in the high-latitude mesosphere

    Science.gov (United States)

    Hall, C. M.; Brekke, A.; Martynenko, O. V.; Namgaladze, A. A.

    1998-02-01

    The global numerical model of the Earth's thermosphere, ionosphere and protonosphere constructed at the Kaliningrad Observatory of IZMIRAN and Polar Geophysical Institute in Murmansk, (Namgaladze et al., 1991), hereafter referred to as PGI97, is being extended to encompass modelling of the mesosphere. Here we report the first predictions of turbulent intensities in the height regime 80 to 90 km. Recently, Hall (1997) reported estimates of the turbulent energy dissipation rate, ɛ, using the EISCAT VHF radar located in Northern Norway (69°N, 19°E), which has, in turn, been compared to in situ measurements. Thus initial testing of PGI97 has concentrated on the same region. The agreements between PGI97 and EISCAT results for summer and winter solstice mesospheres are good. The general seasonal variation has been investigated, again showing good agreement with the EISCAT results. However, when examining the average energy dissipation in the 80-90 km height regime, the model shows less variability than the observations.

  11. Recent Very Hot Summers in Northern Hemispheric Land Areas Measured by Wet Bulb Globe Temperature Will Be the Norm Within 20 Years

    Science.gov (United States)

    Li, Chao; Zhang, Xuebin; Zwiers, Francis; Fang, Yuanyuan; Michalak, Anna M.

    2017-12-01

    Wet bulb globe temperature (WBGT) accounts for the effect of environmental temperature and humidity on thermal comfort, and can be directly related to the ability of the human body to dissipate excess metabolic heat and thus avoid heat stress. Using WBGT as a measure of environmental conditions conducive to heat stress, we show that anthropogenic influence has very substantially increased the likelihood of extreme high summer mean WBGT in northern hemispheric land areas relative to the climate that would have prevailed in the absence of anthropogenic forcing. We estimate that the likelihood of summer mean WGBT exceeding the observed historical record value has increased by a factor of at least 70 at regional scales due to anthropogenic influence on the climate. We further estimate that, in most northern hemispheric regions, these changes in the likelihood of extreme summer mean WBGT are roughly an order of magnitude larger than the corresponding changes in the likelihood of extreme hot summers as simply measured by surface air temperature. Projections of future summer mean WBGT under the RCP8.5 emissions scenario that are constrained by observations indicate that by 2030s at least 50% of the summers will have mean WBGT higher than the observed historical record value in all the analyzed regions, and that this frequency of occurrence will increase to 95% by mid-century.

  12. On the Feasibility of Monitoring Carbon Monoxide in the Lower Troposphere from a Constellation of Northern Hemisphere Geostationary Satellites: Global Scale Assimilation Experiments (Part II)

    Science.gov (United States)

    Barre, Jerome; Edwards, David; Worden, Helen; Arellano, Avelino; Gaubert, Benjamin; Da Silva, Arlindo; Lahoz, William; Anderson, Jeffrey

    2016-01-01

    This paper describes the second phase of an Observing System Simulation Experiment (OSSE) that utilizes the synthetic measurements from a constellation of satellites measuring atmospheric composition from geostationary (GEO) Earth orbit presented in part I of the study. Our OSSE is focused on carbon monoxide observations over North America, East Asia and Europe where most of the anthropogenic sources are located. Here we assess the impact of a potential GEO constellation on constraining northern hemisphere (NH) carbon monoxide (CO) using data assimilation. We show how cloud cover affects the GEO constellation data density with the largest cloud cover (i.e., lowest data density) occurring during Asian summer. We compare the modeled state of the atmosphere (Control Run), before CO data assimilation, with the known 'true' state of the atmosphere (Nature Run) and show that our setup provides realistic atmospheric CO fields and emission budgets. Overall, the Control Run underestimates CO concentrations in the northern hemisphere, especially in areas close to CO sources. Assimilation experiments show that constraining CO close to the main anthropogenic sources significantly reduces errors in NH CO compared to the Control Run. We assess the changes in error reduction when only single satellite instruments are available as compared to the full constellation. We find large differences in how measurements for each continental scale observation system affect the hemispherical improvement in long-range transport patterns, especially due to seasonal cloud cover. A GEO constellation will provide the most efficient constraint on NH CO during winter when CO lifetime is longer and increments from data assimilation associated with source regions are advected further around the globe.

  13. Measurements of the movement of the jet streams at mid-latitudes, in the Northern and Southern Hemispheres, 1979 to 2010

    Directory of Open Access Journals (Sweden)

    R. D. Hudson

    2012-08-01

    Full Text Available Previous studies have shown that the mean latitude of the sub-tropical jet streams in both hemispheres have shifted toward the poles over the last few decades. This paper presents a study of the movement of both the subtropical and Polar fronts, the location of the respective jet streams, between 1979 and 2010 at mid-latitudes, using total ozone measurements to identify the sharp horizontal boundary that occurs at the position of the fronts. Previous studies have shown that the two fronts are the boundaries of three distinct regimes in the stratosphere, corresponding to the Hadley, Ferrel, and polar meridionally overturning circulation cells in the troposphere. Over the period of study the horizontal area of the Hadley cell has increased at latitudes between 20 and 60 degrees while the area of the Polar cell has decreased. A linear regression analysis was performed to identify the major factors associated with the movement of the subtropical jet streams. These were: (1 changes in the Tropical land plus ocean temperature, (2 direct radiative forcing from greenhouse gases in the troposphere, (3 changes in the temperature of the lower tropical stratosphere, (4 the Quasi-Biennial Oscillation, and (5 volcanic eruptions. The dominant mechanism was the direct radiative forcing from greenhouse gases. Between 1979 and 2010 the poleward movement of the subtropical jet streams was 3.7 ± 0.3 degrees in the Northern Hemisphere and 6.5 ± 0.2 degrees in the Southern Hemisphere. Previous studies have shown that weather systems tend to follow the jet streams. The observed poleward movement in both hemispheres over the past thirty years represents a significant change in the position of the sub-tropical jet streams, which should lead to significant latitudinal shifts in the global weather patterns and the hydrologic cycle.

  14. Mass spawning of corals on a high latitude coral reef

    Science.gov (United States)

    Babcock, R. C.; Wills, B. L.; Simpson, C. J.

    1994-07-01

    Evidence is presented that at least 60% of the 184 species of scleractinian corals found on reefs surrounding the Houtman Abrolhos Islands (Western Australia) participate in a late summer mass spawning. These populations are thus reproductively active, despite most species being at the extreme southern limit of their latitudinal range (28° 29°S). In the present study, coral mass spawning occurred in the same month on both temperate (Houtman-Abrolhos) and tropical (Ningaloo) reefs of Western Australia, despite more than two months difference in the timing of seasonal temperture minima between the two regions. This concurrence in the month of spawning suggests that temperature does not operate as a simple direct proximate cue for seasonal spawning synchrony in these populations. Seasonal variation in photoperiod may provide a similar and more reliable signal in the two regions, and thus might be more likely to synchronize the seasonal reproductive rhythms of these corals. Also there is overlap in the nights of mass spawning on the Houtman Abrolhos and tropical reefs of Western Australia, despite significant differences in tidal phase and amplitude between the two regions. This indicates that tidal cycle does not synchronize with the night(s) of spawning on these reefs. Spawning is more likely to be synchronised by lunar cycles. The co-occurrence of the mass spawning with spring tides in Houtman Abrolhos coral populations may be evidence of a genetic legacy inherited from northern, tropical ancestors. Micro-tidal regimes in the Houtman Abrolhos region may have exerted insufficient selective pressure to counteract this legacy.

  15. PROBLEM ANALYSIS USING NAVIGATION SYSTEMS OF UNMANNED AERIAL VEHICLES AT HIGH LATITUDES

    Directory of Open Access Journals (Sweden)

    S. V. Korevanov

    2014-01-01

    Full Text Available The article is an analysis of operation of navigation systems of unmanned aerial vehicles (UAVs in the high latitudes, considered the requirements of navigation and security drones impact of the environment on the UAV navigation equipment.

  16. 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

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

    Directory of Open Access Journals (Sweden)

    T. Holst

    2010-02-01

    Full Text Available In this study, we present summertime concentrations and fluxes of biogenic volatile organic compounds (BVOCs measured at a sub-arctic wetland in northern Sweden using a disjunct eddy-covariance (DEC technique based on a proton transfer reaction mass spectrometer (PTR-MS. The vegetation at the site was dominated by Sphagnum, Carex and extit{Eriophorum} spp. The measurements reported here cover a period of 50 days (1 August to 19 September 2006, approximately one half of the growing season at the site, and allowed to investigate the effect of day-to-day variation in weather as well as of vegetation senescence on daily BVOC fluxes, and on their temperature and light responses. The sensitivity drift of the DEC system was assessed by comparing H3O+-ion cluster formed with water molecules (H3O+(H2O at m37 with water vapour concentration measurements made using an adjacent humidity sensor, and the applicability of the DEC method was analysed by a comparison of sensible heat fluxes for high frequency and DEC data obtained from the sonic anemometer. These analyses showed no significant PTR-MS sensor drift over a period of several weeks and only a small flux-loss due to high-frequency spectrum omissions. This loss was within the range expected from other studies and the theoretical considerations.

    Standardised (20 °C and 1000 μmol m−2 s−1 PAR summer isoprene emission rates found in this study of 329 μg C m−2 (ground area h−1 were comparable with findings from more southern boreal forests, and fen-like ecosystems. On a diel scale, measured fluxes indicated a stronger temperature dependence than emissions from temperate or (subtropical ecosystems. For the first time, to our knowledge, we report ecosystem methanol fluxes from a sub-arctic ecosystem. Maximum daytime emission fluxes were around 270 μg m−2 h−1

  18. Can evolutionary constraints explain the rarity of nitrogen-fixing trees in high-latitude forests?

    Science.gov (United States)

    Menge, Duncan N L; Crews, Timothy E

    2016-09-01

    Contents 1195 I. 1195 II. 1196 III. 1196 IV. 1200 1200 References 1200 SUMMARY: The rarity of symbiotic nitrogen (N)-fixing trees in temperate and boreal ('high-latitude') forests is curious. One explanation - the evolutionary constraints hypothesis - posits that high-latitude N-fixing trees are rare because few have evolved. Here, we consider traits necessary for high-latitude N-fixing trees. We then use recent developments in trait evolution to estimate that > 2000 and > 500 species could have evolved from low-latitude N-fixing trees and high-latitude N-fixing herbs, respectively. Evolution of N-fixing from nonfixing trees is an unlikely source of diversity. Dispersal limitation seems unlikely to limit high-latitude N-fixer diversity. The greater number of N-fixing species predicted to evolve than currently inhabit high-latitude forests suggests a greater role for ecological than evolutionary constraints. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

  19. 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

  20. Green Mountains and White Plains: the effect of Northern Hemisphere ice sheets on the global energy budget

    Science.gov (United States)

    Roberts, William; Valdes, Paul

    2016-04-01

    There are two physical features of a large ice sheet that can fundamentally change the global climate: the topography and albedo. Using a series of climate model experiments we shall show how the climate responds to these features, acting alone and in concert. We shall focus on the global energy budget. We shall use as a tool the HadCM3 climate model. We shall examine three suites of experiments in which we impose the albedo, topography or both of the Laurentide Ice Sheet. In each suite we vary the size of the ice sheet in order that we may examine how the climate's response varies with ice sheet size. Understanding the effect of ice sheets at a size below their maximum is important because, during any glacial period the ice sheets exist at these lesser extents for the majority of the time. We shall show that the albedo of the ice sheet causes a reduction in the incoming shortwave radiation over the ice sheet and that this is balanced by a compensating incoming energy flux into the Southern Hemisphere. The topography of the ice sheet causes an increase in the incoming shortwave radiation over the ice sheet that is balanced by an outgoing energy flux to the south of the ice sheet, with little change in the Southern Hemisphere. The topography and albedo of the ice sheet cause an increase in the outgoing shortwave radiation over the icesheet that is balanced by incoming fluxes to the south of the ice sheet and in the Southern Hemisphere. The magnitude of the cross equatorial atmospheric heat flux shall be related to the position of the ITCZ. We shall show there is a close correlation between the position of the ITCZ and the cross equatorial heat flux, if there is no change in the ice sheet. Changing the ice sheet topography causes this relationship to breakdown.

  1. Characterizing an outperforming pea cultivar for intercropping with oat at high latitudes

    Directory of Open Access Journals (Sweden)

    Pirjo Peltonen-Sainio

    2017-10-01

    Full Text Available The cereal often dominates the grain legume in intercrops, especially when sown in larger amounts. This study assessed yield formation of pea (Pisum sativum L. and oat (Avena sativa L. in an intercropping system in high-latitude conditions. Three pea cultivars (Hulda, Karita and Perttu and one oat cultivar (Roope were grown as sole crops and intercrops with shares of either 7.5% or 15% of oat (as weight of sown seed mixture. Experiments were organized in three (southern, western and northern locations of Finland for three years. Yield and vegetative above-ground biomass, their land equivalent ratio (LER, i.e., the yield in intercrop compared to that of the component yields in pure stands, and a number of yield components were measured prior to harvest at crop-stand and single-plant levels. The share of oat in the intercrop did not have any impact on variation in LERyield. Oat yield and yield components generally benefitted from a pea companion crop. The pea cultivar Perttu was superior in intercrops: it had a LERyield>1 in seven out of eight experiments (mean LERyield=1.06, while Karita had a LERyield>1 in four (mean LERyield=1.00 and Hulda only in one experiment (mean LERyield=0.98. Perttu proved to be a compatible pea companion for a pea-oat intercrop, likely because it was successful in overcompensating for decline in relative yield (RGY of oat in intercrops, contrary to Hulda. However, none of the measured yield components of Perttu were associated with LERyield, suggesting compensation ability between them, while in Karita and Hulda, e.g., higher grain yield and number of grains and pods per square meter were associated with decline in LERyield. It was concluded that the success of Perttu as a companion for oat in intercrops is likely attributable to its flexibility in building yield through a variable combination of yield components rather than being outperformed due to some superior traits. Such flexibility, likely attributable to long

  2. Northern hemisphere extratropical tropospheric planetary waves and their low-frequency variability: Their vertical structure and interaction with transient eddies and surface thermal contrasts

    Science.gov (United States)

    Nakamura, Hisashi; Miyasaka, Takafumi; Kosaka, Yu; Takaya, Koutarou; Honda, Meiji

    Structure and dynamics of the Northern Hemisphere planetary waves, which cause geographically fixed longitudinal dependence to the climate, are examined through dynamical diagnoses applied to modern global data sets. Summertime planetary wave signature in the Western Hemisphere includes surface maritime subtropical anticyclones, for which pronounced land-sea thermal contrasts across the west coasts of subtropical continents are important as thermal forcing. Its Eastern Hemisphere counterpart is dominated by continental-scale cyclone and anticyclone in the lower and upper troposphere, respectively, associated with Asian monsoon. Wintertime planetary waves are forced orographically and thermally in middle/subpolar latitudes, with pronounced land-sea thermal contrasts, including a contribution from diabatic heating along oceanic "storm tracks." Wave activity thus generated propagates southeastward, maintaining an upper-level vorticity dipole over the Atlantic with an eddy-driven polar-front jet (PFJ) separated from a subtropical jet (STJ). Its Pacific counterpart is in the opposite sense with a predominant single jet with PFJ-STJ hybrid characteristics. Stationary circulation anomaly patterns that cause regional climate variability are strong in winter over the midlatitude ocean basins, extracting kinetic energy effectively from diffluent westerly jets and with feedback forcing by transient eddies along storm tracks. In the summertime Asian STJ exit, a stationary baroclinic anomaly pattern is dominant, maintaining itself by extracting potential energy from the jet and negating it by anomalous cumulus activity. Each of these patterns thus bears characteristics of a dynamical mode. Generation of shallow, cold surface anticyclones is discussed from a viewpoint of interaction of stationary Rossby waves with surface baroclinic zones.

  3. 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.)

  4. Effects of Climate Warming, North Atlantic Oscillation, and El Niño-Southern Oscillation on Thermal Conditions and Plankton Dynamics in Northern Hemispheric Lakes

    Directory of Open Access Journals (Sweden)

    Dieter Gerten

    2002-01-01

    Full Text Available Impacts of climate warming on freshwater ecosystems have been documented recently for a variety of sites around the globe. Here we provide a review of studies that report long-term (multidecadal effects of warming trends on thermal properties and plankton dynamics in northern hemispheric lakes. We show that higher lake temperatures, shorter periods with ice cover, and shorter stagnation periods were common trends for lakes across the hemisphere in response to the warmer conditions. Only for shallow dimictic lakes was it observed that deep-water temperatures decreased. Moreover, it became evident that phytoplankton dynamics and primary productivity altered in conjunction with changes in lake physics. Algal spring blooms developed early and were more pronounced in several European lakes after mild winters with short ice cover periods, and primary productivity increased in North American lakes. Effects of elevated temperatures on zooplankton communities were seen in an early development of various species and groups, as is documented for cladocerans, copepods, and rotifers in European lakes. Furthermore, thermophile species reached higher abundance in warmer years.

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

    Science.gov (United States)

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

    2012-04-01

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

  6. Age of the Mt. Ortles ice cores, the Tyrolean Iceman and glaciation of the highest summit of South Tyrol since the Northern Hemisphere Climatic Optimum

    Science.gov (United States)

    Gabrielli, Paolo; Barbante, Carlo; Bertagna, Giuliano; Bertó, Michele; Binder, Daniel; Carton, Alberto; Carturan, Luca; Cazorzi, Federico; Cozzi, Giulio; Dalla Fontana, Giancarlo; Davis, Mary; De Blasi, Fabrizio; Dinale, Roberto; Dragà, Gianfranco; Dreossi, Giuliano; Festi, Daniela; Frezzotti, Massimo; Gabrieli, Jacopo; Galos, Stephan P.; Ginot, Patrick; Heidenwolf, Petra; Jenk, Theo M.; Kehrwald, Natalie; Kenny, Donald; Magand, Olivier; Mair, Volkmar; Mikhalenko, Vladimir; Lin, Ping Nan; Oeggl, Klaus; Piffer, Gianni; Rinaldi, Mirko; Schotterer, Ulrich; Schwikowski, Margit; Seppi, Roberto; Spolaor, Andrea; Stenni, Barbara; Tonidandel, David; Uglietti, Chiara; Zagorodnov, Victor; Zanoner, Thomas; Zennaro, Piero

    2016-11-01

    In 2011 four ice cores were extracted from the summit of Alto dell'Ortles (3859 m), the highest glacier of South Tyrol in the Italian Alps. This drilling site is located only 37 km southwest from where the Tyrolean Iceman, ˜ 5.3 kyrs old, was discovered emerging from the ablating ice field of Tisenjoch (3210 m, near the Italian-Austrian border) in 1991. The excellent preservation of this mummy suggested that the Tyrolean Iceman was continuously embedded in prehistoric ice and that additional ancient ice was likely preserved elsewhere in South Tyrol. Dating of the ice cores from Alto dell'Ortles based on 210Pb, tritium, beta activity and 14C determinations, combined with an empirical model (COPRA), provides evidence for a chronologically ordered ice stratigraphy from the modern glacier surface down to the bottom ice layers with an age of ˜ 7 kyrs, which confirms the hypothesis. Our results indicate that the drilling site has continuously been glaciated on frozen bedrock since ˜ 7 kyrs BP. Absence of older ice on the highest glacier of South Tyrol is consistent with the removal of basal ice from bedrock during the Northern Hemisphere Climatic Optimum (6-9 kyrs BP), the warmest interval in the European Alps during the Holocene. Borehole inclinometric measurements of the current glacier flow combined with surface ground penetration radar (GPR) measurements indicate that, due to the sustained atmospheric warming since the 1980s, an acceleration of the glacier Alto dell'Ortles flow has just recently begun. Given the stratigraphic-chronological continuity of the Mt. Ortles cores over millennia, it can be argued that this behaviour has been unprecedented at this location since the Northern Hemisphere Climatic Optimum.

  7. Does the Arcto-Tertiary biogeographic hypothesis explain the disjunct distribution of Northern Hemisphere herbaceous plants? The case of Meehania (Lamiaceae).

    Science.gov (United States)

    Deng, Tao; Nie, Ze-Long; Drew, Bryan T; Volis, Sergei; Kim, Changkyun; Xiang, Chun-Lei; Zhang, Jian-Wen; Wang, Yue-Hua; Sun, Hang

    2015-01-01

    Despite considerable progress, many details regarding the evolution of the Arcto-Tertiary flora, including the timing, direction, and relative importance of migration routes in the evolution of woody and herbaceous taxa of the Northern Hemisphere, remain poorly understood. Meehania (Lamiaceae) comprises seven species and five subspecies of annual or perennial herbs, and is one of the few Lamiaceae genera known to have an exclusively disjunct distribution between eastern Asia and eastern North America. We analyzed the phylogeny and biogeographical history of Meehania to explore how the Arcto-Tertiary biogeographic hypothesis and two possible migration routes explain the disjunct distribution of Northern Hemisphere herbaceous plants. Parsimony and Bayesian inference were used for phylogenetic analyses based on five plastid sequences (rbcL, rps16, rpl32-trnH, psbA-trnH, and trnL-F) and two nuclear (ITS and ETS) gene regions. Divergence times and biogeographic inferences were performed using Bayesian methods as implemented in BEAST and S-DIVA, respectively. Analyses including 11 of the 12 known Meehania taxa revealed incongruence between the chloroplast and nuclear trees, particularly in the positions of Glechoma and Meehania cordata, possibly indicating allopolyploidy with chloroplast capture in the late Miocene. Based on nrDNA, Meehania is monophyletic, and the North American species M. cordata is sister to a clade containing the eastern Asian species. The divergence time between the North American M. cordata and the eastern Asian species occurred about 9.81 Mya according to the Bayesian relaxed clock methods applied to the combined nuclear data. Biogeographic analyses suggest a primary role of the Arcto-Tertiary flora in the study taxa distribution, with a northeast Asian origin of Meehania. Our results suggest an Arcto-Tertiary origin of Meehania, with its present distribution most probably being a result of vicariance and southward migrations of populations during

  8. Seasonal variation of mesospheric waves at northern middle and high latitudes

    Science.gov (United States)

    Hoffmann, Peter; Becker, Erich; Singer, Werner; Placke, Manja

    2010-09-01

    The seasonal variation of the wave activity in the mesosphere/lower thermosphere is investigated using wind measurements with meteor and MF radars at Juliusruh (55°N, 13°E) and Andenes (69°N, 16°E), as well as on the basis of the simulated annual cycle using a gravity-wave resolving mechanistic general circulation model. For the observations, proxies for the activity of gravity waves (GWs) and waves with longer periods are computed from wind variances for defined bandwidths. Our corresponding proxy for the simulated GWs is the non-rotational kinetic energy due to the resolved mesoscales. Both observational and computational results show the strongest GW energy during winter and a secondary maximum during summer. Additional observational analysis of short-period GWs yields a more pronounced summer maximum. The semi-annual variation is consistent with the selective filtering of westward and eastward GWs by the mean zonal wind. The latitudinal dependence during summer is characterized by stronger GW energy between 65 and 85 km at middle latitudes than at polar latitudes, and a corresponding upward shift of the wind reversal towards the pole which is also reflected by the simulated GW drag. Also the observed oscillations with periods from 2 to 4 days show a latitudinal dependence and a clear seasonal cycle which is related to the mean zonal wind shear.

  9. Characteristics of Atmospheric Waves Observed From Airglow Measurements in the Northern High-Latitude

    Directory of Open Access Journals (Sweden)

    Young-In Won

    2004-06-01

    Full Text Available The terrestrial nightglow emission in near infrared region were obtained using a Fourier Transform Spectrometer (FTS at Esrange, Sweden (67.90°N, 21.10°E and the OH(4-2 bands were used to derive temperature and airglow emission rate of the upper mesosphere. For this study, we analyzed data taken during winter of 2001/2002 and performed spectral analysis to retrieve wave information. From the Lomb-Scargle spectral analysis to the measured temperatures, dominant oscillations at various periods near tidal frequency are found. Most commonly observed waves are 4, 6, and 8 hour oscillations. Because of periods and persistence, the observed oscillations are most likely of tidal origin, i.e. zonally symmetric tides which are known to have their maximum amplitudes at the pole.

  10. Climatology of GPS phase scintillation at northern high latitudes for the period from 2008 to 2013

    Directory of Open Access Journals (Sweden)

    P. Prikryl

    2015-05-01

    Full Text Available Global positioning system scintillation and total electron content (TEC data have been collected by ten specialized GPS Ionospheric Scintillation and TEC Monitors (GISTMs of the Canadian High Arctic Ionospheric Network (CHAIN. The phase scintillation index σΦ is obtained from the phase of the L1 signal sampled at 50 Hz. Maps of phase scintillation occurrence as a function of the altitude-adjusted corrected geomagnetic (AACGM latitude and magnetic local time (MLT are computed for the period from 2008 to 2013. Enhanced phase scintillation is collocated with regions that are known as ionospheric signatures of the coupling between the solar wind and magnetosphere. The phase scintillation mainly occurs on the dayside in the cusp where ionospheric irregularities convect at high speed, in the nightside auroral oval where energetic particle precipitation causes field-aligned irregularities with steep electron density gradients and in the polar cap where electron density patches that are formed from a tongue of ionization. Dependences of scintillation occurrence on season, solar and geomagnetic activity, and the interplanetary magnetic field (IMF orientation are investigated. The auroral phase scintillation shows semiannual variation with equinoctial maxima known to be associated with auroras, while in the cusp and polar cap the scintillation occurrence is highest in the autumn and winter months and lowest in summer. With rising solar and geomagnetic activity from the solar minimum to solar maximum, yearly maps of mean phase scintillation occurrence show gradual increase and expansion of enhanced scintillation regions both poleward and equatorward from the statistical auroral oval. The dependence of scintillation occurrence on the IMF orientation is dominated by increased scintillation in the cusp, expanded auroral oval and at subauroral latitudes for strongly southward IMF. In the polar cap, the IMF BY polarity controls dawn–dusk asymmetries in scintillation occurrence collocated with a tongue of ionization for southward IMF and with sun-aligned arcs for northward IMF. In investigating the shape of scintillation-causing irregularities, the distributions of scintillation occurrence as a function of "off-meridian" and "off-shell" angles that are computed for the receiver–satellite ray at the ionospheric pierce point are found to suggest predominantly field-aligned irregularities in the auroral oval and L-shell-aligned irregularities in the cusp.

  11. North-South Asymmetries in Earth's Magnetic Field. Effects on High-Latitude Geospace

    Science.gov (United States)

    Laundal, K. M.; Cnossen, I.; Milan, S. E.; Haaland, S. E.; Coxon, J.; Pedatella, N. M.; Förster, M.; Reistad, J. P.

    2017-03-01

    The solar-wind magnetosphere interaction primarily occurs at altitudes where the dipole component of Earth's magnetic field is dominating. The disturbances that are created in this interaction propagate along magnetic field lines and interact with the ionosphere-thermosphere system. At ionospheric altitudes, the Earth's field deviates significantly from a dipole. North-South asymmetries in the magnetic field imply that the magnetosphere-ionosphere-thermosphere (M-I-T) coupling is different in the two hemispheres. In this paper we review the primary differences in the magnetic field at polar latitudes, and the consequences that these have for the M-I-T coupling. We focus on two interhemispheric differences which are thought to have the strongest effects: 1) A difference in the offset between magnetic and geographic poles in the Northern and Southern Hemispheres, and 2) differences in the magnetic field strength at magnetically conjugate regions. These asymmetries lead to differences in plasma convection, neutral winds, total electron content, ion outflow, ionospheric currents and auroral precipitation.

  12. Insights into the phylogeny of Northern Hemisphere Armillaria: Neighbor-net and Bayesian analyses of translation elongation factor 1-α gene sequences.

    Science.gov (United States)

    Klopfenstein, Ned B; Stewart, Jane E; Ota, Yuko; Hanna, John W; Richardson, Bryce A; Ross-Davis, Amy L; Elías-Román, Rubén D; Korhonen, Kari; Keča, Nenad; Iturritxa, Eugenia; Alvarado-Rosales, Dionicio; Solheim, Halvor; Brazee, Nicholas J; Łakomy, Piotr; Cleary, Michelle R; Hasegawa, Eri; Kikuchi, Taisei; Garza-Ocañas, Fortunato; Tsopelas, Panaghiotis; Rigling, Daniel; Prospero, Simone; Tsykun, Tetyana; Bérubé, Jean A; Stefani, Franck O P; Jafarpour, Saeideh; Antonín, Vladimír; Tomšovský, Michal; McDonald, Geral I; Woodward, Stephen; Kim, Mee-Sook

    2017-01-01

    Armillaria possesses several intriguing characteristics that have inspired wide interest in understanding phylogenetic relationships within and among species of this genus. Nuclear ribosomal DNA sequence-based analyses of Armillaria provide only limited information for phylogenetic studies among widely divergent taxa. More recent studies have shown that translation elongation factor 1-α (tef1) sequences are highly informative for phylogenetic analysis of Armillaria species within diverse global regions. This study used Neighbor-net and coalescence-based Bayesian analyses to examine phylogenetic relationships of newly determined and existing tef1 sequences derived from diverse Armillaria species from across the Northern Hemisphere, with Southern Hemisphere Armillaria species included for reference. Based on the Bayesian analysis of tef1 sequences, Armillaria species from the Northern Hemisphere are generally contained within the following four superclades, which are named according to the specific epithet of the most frequently cited species within the superclade: (i) Socialis/Tabescens (exannulate) superclade including Eurasian A. ectypa, North American A. socialis (A. tabescens), and Eurasian A. socialis (A. tabescens) clades; (ii) Mellea superclade including undescribed annulate North American Armillaria sp. (Mexico) and four separate clades of A. mellea (Europe and Iran, eastern Asia, and two groups from North America); (iii) Gallica superclade including Armillaria Nag E (Japan), multiple clades of A. gallica (Asia and Europe), A. calvescens (eastern North America), A. cepistipes (North America), A. altimontana (western USA), A. nabsnona (North America and Japan), and at least two A. gallica clades (North America); and (iv) Solidipes/Ostoyae superclade including two A. solidipes/ostoyae clades (North America), A. gemina (eastern USA), A. solidipes/ostoyae (Eurasia), A. cepistipes (Europe and Japan), A. sinapina (North America and Japan), and A. borealis

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

    Science.gov (United States)

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

    2017-09-13

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

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

    Science.gov (United States)

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

    2017-08-01

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

  15. Solar wind entry into the high-latitude terrestrial magnetosphere during geomagnetically quiet times.

    Science.gov (United States)

    Shi, Q Q; Zong, Q-G; Fu, S Y; Dunlop, M W; Pu, Z Y; Parks, G K; Wei, Y; Li, W H; Zhang, H; Nowada, M; Wang, Y B; Sun, W J; Xiao, T; Reme, H; Carr, C; Fazakerley, A N; Lucek, E

    2013-01-01

    An understanding of the transport of solar wind plasma into and throughout the terrestrial magnetosphere is crucial to space science and space weather. For non-active periods, there is little agreement on where and how plasma entry into the magnetosphere might occur. Moreover, behaviour in the high-latitude region behind the magnetospheric cusps, for example, the lobes, is poorly understood, partly because of lack of coverage by previous space missions. Here, using Cluster multi-spacecraft data, we report an unexpected discovery of regions of solar wind entry into the Earth's high-latitude magnetosphere tailward of the cusps. From statistical observational facts and simulation analysis we suggest that these regions are most likely produced by magnetic reconnection at the high-latitude magnetopause, although other processes, such as impulsive penetration, may not be ruled out entirely. We find that the degree of entry can be significant for solar wind transport into the magnetosphere during such quiet times.

  16. Dynamical contribution to formation of an ozone mini hole in the Northern Hemisphere in mid-winter

    OpenAIRE

    Iwao,Koki; Hirooka,Toshihiko

    2002-01-01

    Ozone mini holes are localized and transient (several days) column ozone amount depletion phenomena which often appear over northern Europe. In early February 1989, the extremely low ozone value of 172 DU was observed by Total Ozone Mapping Spectrometer observation. Quantitative analyses of this event using a forward and backward trajectory method show that the total ozone depletion is by uplift of air throughout the lower stratosphere, whereas the effect of horizontal advection of ozone-poor...

  17. Extra-long interglacial in Northern Hemisphere during MISs 15-13 arising from limited extent of Arctic ice sheets in glacial MIS 14

    Science.gov (United States)

    Hao, Qingzhen; Wang, Luo; Oldfield, Frank; Guo, Zhengtang

    2015-07-01

    Knowledge of the behavior of Northern Hemisphere (NH) ice sheets over the past million years is crucial for understanding the role of orbitally driven insolation changes on glacial/interglacial cycles. Here, based on the demonstrable link between changes in Chinese loess grain-size and NH ice-sheet extent, we use loess grain-size records to confirm that northern ice-sheets were restricted during marine oxygen isotope stage (MIS) 14. Thus, an unusually long NH interglacial climate of over 100 kyr persisted during MISs 15-13, much longer than expected from marine oxygen isotope records. Taking a global view of the paleoclimate records, MIS 14 inception seems to be a response to changes in Antarctic ice-sheets rather than to NH cooling. Orbital configuration in the two Polar regions shows that the onset of MIS 14 was forced by austral insolation changes, rather than by boreal summer insolation, as Milankovitch theory proposes. Our analysis of MIS 14 raises the possibility that southern insolation forcing may have played an important role in the inception of several other glacials. We suggest that the extra-long NH interglacial climate during MISs 15-13 provided favorable conditions for the second major dispersal episode of African hominins into Eurasia.

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

    Science.gov (United States)

    Garrido-Perez, Jose M.; Ordóñez, Carlos; García-Herrera, Ricardo

    2017-10-01

    This paper analyses the impact of high-latitude blocks and subtropical ridges on daily PM10 (particulate matter ≤ 10 μm) observations obtained from the European Environment Agency's air quality database (AirBase) for the winter period of 2000-2010. The response of the pollutant concentrations to the location of blocks and ridges with centres in two main longitudinal sectors (Atlantic, ATL, 30°-0° W; European, EUR, 0°-30° E) is examined. In particular, EUR blocking is associated with a collapse of the boundary layer as well as reduced wind speeds and precipitation occurrence, yielding large positive anomalies which average 12 μg m-3 over the whole continent. Conversely, the enhanced zonal flow around 50°-60° N and the increased occurrence of precipitation over northern-central Europe on days with ATL ridges favour the ventilation of the boundary layer and the impact of washout processes, reducing PM10 concentrations on average by around 8 μg m-3. The presence of EUR blocks is also concurrent with an increased probability of exceeding the air quality target (50 μg m-3 for 24-h averaged PM10) and the local 90th percentiles for this pollutant at many sites in central Europe, while the opposite effect is found for ridges. In addition, the effect of synoptic persistence on the PM10 concentrations is stronger for EUR blocks than for ATL ridges. This could benefit the predictability of PM10 extremes over wide areas of the region. Finally, we have found that the combined or isolated effect of both synoptic patterns can partly control the interannual variability of winter mean PM10 at many sites of north-western and central Europe, with coefficients of determination (R2) exceeding 0.80 for southern Germany. These results indicate that the response of the particulate matter (PM) concentrations to large-scale circulation patterns is stronger than previously reported for Europe and other mid-latitude regions.

  19. 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

  20. 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

  1. High latitude regulation of low latitude thermocline ventilation and planktic foraminifer populations across glacial-interglacial cycles

    Science.gov (United States)

    Sexton, Philip F.; Norris, Richard D.

    2011-11-01

    One of the earliest discoveries in palaeoceanography was the observation in 1935 that the (sub)tropical planktic foraminifer Globorotalia menardii became absent or extremely rare in the Atlantic Ocean during glacials of the late Pleistocene. Yet a mechanistic explanation for G. menardii's extraordinary biogeographic behaviour has eluded palaeoceanographers for 75 years. Here we show that modern G. menardii, along with two other species that also suffer Atlantic population collapses during glacials, track poorly ventilated waters globally in their thermocline habitats. The ventilation states of low latitude thermoclines are 'set', to a first order, by intermediate water masses originating at high latitudes. In the modern Atlantic this control on low latitude thermocline ventilation is exerted by relatively poorly ventilated, southern-sourced Antarctic Intermediate Water (AAIW) and sub-Antarctic Mode Water (SAMW). We suggest that the glacial Atlantic foraminifer population collapses were a consequence of a low latitude thermocline that was better ventilated during glacials than it is today, in line with geochemical evidence, and driven primarily by a well-ventilated, northern-sourced intermediate water mass. A ventilation mechanism driving the glacial population collapses is further supported by our new constraints on the precise timing of these species' Atlantic proliferation during the last deglaciation — occurring in parallel with a wholesale, bipolar reorganisation of the Atlantic's thermocline-to-abyssal overturning circulation. Our findings demonstrate that a bipolar seesaw in the formation of high latitude intermediate waters has played an important role in regulating the population dynamics of thermocline-dwelling plankton at lower latitudes.

  2. Baseline assessment of high-latitude coral reef fish communities in ...

    African Journals Online (AJOL)

    The Western Indian Ocean (WIO) is a region where detailed coral reef fish research has been relatively limited. This study constitutes an assessment of the fish communities of seven southern African high-latitude coral reefs. The aim was to provide ichthyological baseline data consisting of species abundance and diversity, ...

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    The geomagnetic storm of 17–18 March 2015 was caused by the impacts of a coronal mass ejection and a high-speed plasma stream from a coronal hole. The high-latitude ionosphere dynamics is studied using arrays of ground-based instruments including GPS receivers, HF radars, ionosondes, riometers...

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

    NARCIS (Netherlands)

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

    2014-01-01

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

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

    DEFF Research Database (Denmark)

    Kjellerup, Sanne

    2014-01-01

    High latitude ecosystems are shaped by seasonality in light, ranging from complete darkness in winter to midnight sun in summer, influencing both temperature and primary production. Copepods are important grazers on phytoplankton in marine systems and occupy a central role in the marine food-web...

  6. Morphology and phenomenology of the high-latitude E and F regions

    Science.gov (United States)

    Hunsucker, R. D.

    1979-01-01

    Results obtained at high latitude observatories on the behavior of E and F region ionization are presented including a bibliography. Behavior of E and F region ionization during day and night for quiet and disturbed conditions in the auroral and polar regions is described. Daily, seasonal and sunspot variations are also outlined.

  7. A climatology of PSC composition for the northern and southern hemisphere from 2002 and 2012 observed by MIPAS/Envisat

    Science.gov (United States)

    Spang, Reinhold; Hoffmann, Lars; Grooss, Jens-Uwe; Höpfner, Michael; Müller, Rolf; Griessbach, Sabine; Orr, Andrew; Riese, Martin

    2017-04-01

    The MIPAS instrument onboard the ESA Envisat satellite operated from July 2002 until April 2012. The infrared limb emission measurements represent a unique dataset of day and night observations of polar stratospheric clouds (PSCs) up to both poles. Cloud detection sensitivity is comparable to spaceborne lidars, and it is possible to classify different cloud types from the spectral measurements in different atmospheric window regions. Results of a new PSC classification scheme will be presented by combining a well-established two-colour ratio method and multiple 2D brightness temperature difference probability density functions. The method is a simple probabilistic classifier based on Bayes' theorem with a strong independence assumption. The Bayesian classifier distinguishes between solid particles of ice and nitric acid trihydrate (NAT), as well as liquid droplets of super-cooled ternary solution (STS). The spatial, intra-seasonal, and inter-annual variation in the PSC type occurrence have been analysed. The MIPAS PSC climatology can be used to validate the PSC schemes of chemical transport and chemistry climate models. Higher level data products retrieved from the climatology, like Volume and Area PSC (VPSC and APSC), frequently used as a proxy for ozone depletion, will be investigated in comparison with model results of the Chemical Lagrangian Model for the Stratosphere (CLaMS). The analysis of mountain wave (MW) induced formation of NAT clouds based on measurements of the nadir looking AIRS instrument and the MIPAS climatology will be presented focusing on both hemispheres, the complete season of PSC activity, and specific years.

  8. Effect of the tropical Pacific and Indian Ocean warming since the late 1970s on wintertime Northern Hemispheric atmospheric circulation and East Asian climate interdecadal changes

    Science.gov (United States)

    Chu, Cuijiao; Yang, Xiu-Qun; Sun, Xuguang; Yang, Dejian; Jiang, Yiquan; Feng, Tao; Liang, Jin

    2017-07-01

    Observation reveals that the tropical Pacific-Indian Ocean (TPIO) has experienced a pronounced interdecadal warming since the end of the 1970s. Meanwhile, the wintertime midlatitude Northern Hemispheric atmospheric circulation and East Asian climate have also undergone substantial interdecadal changes. The effect of the TPIO warming on these interdecadal changes are identified by a suite of AMIP-type atmospheric general circulation model experiments in which the model is integrated from September 1948 to December 1999 with prescribed historical, observed realistic sea surface temperature (SST) in a specific region and climatological SST elsewhere. Results show that the TPIO warming reproduces quite well the observed Northern Hemispheric wintertime interdecadal changes, suggesting that these interdecadal changes primarily originate from the TPIO warming. However, each sub-region of TPIO has its own distinct contribution. Comparatively, the tropical central-eastern Pacific (TCEP) and tropical western Pacific (TWP) warming makes dominant contributions to the observed positive-phase PNA-like interdecadal anomaly over the North Pacific sector, while the tropical Indian Ocean (TIO) warming tends to cancel these contributions. Meanwhile, the TIO and TWP warming makes dominant contributions to the observed positive NAO-like interdecadal anomaly over the North Atlantic sector as well as the interdecadal anomalies over the Eurasian sector, although the TWP warming's contribution is relatively small. These remote responses are directly attributed to the TPIO warming-induced tropical convection, rainfall and diabatic heating increases, in which the TIO warming has the most significant effect. Moreover, the TPIO warming excites a Gill-type pattern anomaly over the tropical western Pacific, with a low-level anticyclonic circulation anomaly over the Philippine Sea. Of three sub-regions, the TIO warming dominates such a pattern, although the TWP warming tends to cancel this effect

  9. Does the Arcto-Tertiary Biogeographic Hypothesis Explain the Disjunct Distribution of Northern Hemisphere Herbaceous Plants? The Case of Meehania (Lamiaceae)

    Science.gov (United States)

    Deng, Tao; Nie, Ze-Long; Drew, Bryan T.; Volis, Sergei; Kim, Changkyun; Xiang, Chun-Lei; Zhang, Jian-Wen; Wang, Yue-Hua; Sun, Hang

    2015-01-01

    Despite considerable progress, many details regarding the evolution of the Arcto-Tertiary flora, including the timing, direction, and relative importance of migration routes in the evolution of woody and herbaceous taxa of the Northern Hemisphere, remain poorly understood. Meehania (Lamiaceae) comprises seven species and five subspecies of annual or perennial herbs, and is one of the few Lamiaceae genera known to have an exclusively disjunct distribution between eastern Asia and eastern North America. We analyzed the phylogeny and biogeographical history of Meehania to explore how the Arcto-Tertiary biogeographic hypothesis and two possible migration routes explain the disjunct distribution of Northern Hemisphere herbaceous plants. Parsimony and Bayesian inference were used for phylogenetic analyses based on five plastid sequences (rbcL, rps16, rpl32-trnH, psbA-trnH, and trnL-F) and two nuclear (ITS and ETS) gene regions. Divergence times and biogeographic inferences were performed using Bayesian methods as implemented in BEAST and S-DIVA, respectively. Analyses including 11 of the 12 known Meehania taxa revealed incongruence between the chloroplast and nuclear trees, particularly in the positions of Glechoma and Meehania cordata, possibly indicating allopolyploidy with chloroplast capture in the late Miocene. Based on nrDNA, Meehania is monophyletic, and the North American species M. cordata is sister to a clade containing the eastern Asian species. The divergence time between the North American M. cordata and the eastern Asian species occurred about 9.81 Mya according to the Bayesian relaxed clock methods applied to the combined nuclear data. Biogeographic analyses suggest a primary role of the Arcto-Tertiary flora in the study taxa distribution, with a northeast Asian origin of Meehania. Our results suggest an Arcto-Tertiary origin of Meehania, with its present distribution most probably being a result of vicariance and southward migrations of populations during

  10. Responses and changes in the permafrost and snow water equivalent in the Northern Hemisphere under a scenario of 1.5 °C warming

    Directory of Open Access Journals (Sweden)

    Ying Kong

    2017-12-01

    Full Text Available In this study, the period that corresponds to the threshold of a 1.5 °C rise (relative to 1861–1880 in surface temperature is validated using a multi-model ensemble mean from 17 global climate models in the Coupled Model Intercomparison Project Phase 5 (CMIP5. On this basis, the changes in permafrost and snow cover in the Northern Hemisphere are investigated under a scenario in which the global surface temperature has risen by 1.5 °C, and the uncertainties of the results are further discussed. The results show that the threshold of 1.5 °C warming will be reached in 2027, 2026, and 2023 under RCP2.6, RCP4.5, RCP8.5, respectively. When the global average surface temperature rises by 1.5 °C, the southern boundary of the permafrost will move 1–3.5° northward (relative to 1986–2005, particularly in the southern Central Siberian Plateau. The permafrost area will be reduced by 3.43 × 106 km2 (21.12%, 3.91 × 106 km2 (24.1% and 4.15 × 106 km2 (25.55% relative to 1986–2005 in RCP2.6, RCP4.5 and RCP8.5, respectively. The snow water equivalent will decrease in over half of the regions in the Northern Hemisphere but increase only slightly in the Central Siberian Plateau. The snow water equivalent will decrease significantly (more than 40% relative to 1986–2005 in central North America, western Europe, and northwestern Russia. The permafrost area in the Qinghai–Tibet Plateau will decrease by 0.15 × 106 km2 (7.28%, 0.18 × 106 km2 (8.74%, and 0.17 × 106 km2 (8.25%, respectively, in RCP2.6, RCP4.5, RCP8.5. The snow water equivalent in winter (DJF and spring (MAM over the Qinghai–Tibet Plateau will decrease by 14.9% and 13.8%, respectively.

  11. Stable isotope-based Plio-Pleistocene southern hemisphere climate and vegetation reconstructions (Chiwondo Beds, Northern Malawi)

    Science.gov (United States)

    Luedecke, T.; Thiemeyer, H.; Schrenk, F.; Mulch, A.

    2013-12-01

    Oxygen and carbon isotope geochemistry of multi-proxy archives is a powerful tool to reconstruct paleoclimatic and paleoenvironmental conditions in particular when climate seasonality plays a key role in the evolution of ecosystems. Here we present the first pedogenic Plio-Pleistocene long-term East-African carbon, oxygen and clumped isotope (Δ47) records from some of the earliest hominid fossil sites in Eastern Africa. The studied 5.0 to 0.6 Ma paleosol, fluviatile, and lacustrine deposits of the Chiwondo Beds (Karonga-Chilumba area, NE shore of Lake Malawi) comprise abundant pedogenic carbonates and fossil remains of a diverse fauna which are dominated by large terrestrial mammals. The sediments are also home to two hominid fossil finds, a maxillary fragment of Paranthropus boisei and a mandible of Homo rudolfensis, both dated around 2.4 Ma. Here, we present stable carbon (δ13C) and oxygen (δ18O) isotope data from fossil enamel of different suid, bovid, and equid species as well as δ13C and δ18O values of pedogenic carbonate. We complement the latter by clumped isotope data as proxy for soil temperature. Our data represent the first southern hemisphere record in the East African Rift (EAR), a region particularly interesting for reconstructing vegetation patterns and correlating these across the ITCZ with data on the evolution and migration of early hominids. As our study site is situated between the well-known hominid-bearing sites of eastern and southern Africa it fills an important geographical gap for early hominid research. The δ13C values of enamel and pedogenic carbonate assess the evolutionary history of C3 and C4 biomass which is closely linked to climate patterns in the Malawi Rift Valley during the time of early hominid evolution. The reconstruction of the development of C4-grasslands give insights of changing atmospheric CO2-concentration, seasonality and distribution of precipitation, and the retreat of tree cover. Results of almost 500

  12. Latitudinal extent of the January 2005 solar proton event in the Northern Hemisphere from satellite observations of hydroxyl

    Directory of Open Access Journals (Sweden)

    P. T. Verronen

    2007-11-01

    Full Text Available We utilise hydroxyl observations from the MLS/Aura satellite instrument to study the latitudinal extent of particle forcing in the northern polar region during the January 2005 solar proton event. MLS is the first satellite instrument to observe HOx changes during such an event. We also predict the hydroxyl changes with respect to the magnetic latitude by the Sodankylä Ion and Neutral Chemistry model, estimating the variable magnetic cutoff energies for protons using a parameterisation based on magnetosphere modelling and the planetary magnetic index Kp. In the middle and lower mesosphere, HOx species are good indicators of the changes in the atmosphere during solar proton events, because they respond rapidly to both increases and decreases in proton forcing. Also, atmospheric transport has a negligible effect on HOx because of its short chemical lifetime. The observations indicate the boundary of the proton forcing and a transition region, from none to the "full" effect, which ranges from about 57 to 64 degrees of magnetic latitude. When saturating the rigidity cutoff Kp at 6 in the model, as suggested by earlier studies using observations of cosmic radio noise absorption, the equatorward boundary of the transition region is offset by ≈2 degrees polewards compared with the data, thus the latitudinal extent of the proton forcing in the atmosphere is underestimated. However, the model predictions are in reasonable agreement with the MLS measurements when the Kp index is allowed to vary within its nominal range, i.e., from 1 to 9 in the cutoff calculation.

  13. Sulphur hexafluoride (SF6): comparison of FTIR-measurements at three sites and determination of its trend in the northern hemisphere

    Science.gov (United States)

    Krieg, J.; Nothholt, J.; Mahieu, E.; Rinsland, C. P.; Zander, R.

    2005-05-01

    Fourier transform infrared spectrometry has been used to retrieve the total column abundances of SF6 at three locations in the northern hemisphere, i.e., the Ny Ålesund site in Spitsbergen/Norway at 79N, the Jungfraujoch observatory in Switzerland at 47N and the Kitt Peak observatory in Arizona, USA, at 32N. The total column results have been converted to average tropospheric mixing ratios. The mean increases in these mixing ratios have been found to be equal to 0.31±0.08pptvyr at Ny Ålesund, 0.24±0.01pptvyr at the Jungfraujoch and 0.28±0.09pptvyr at Kitt Peak for the common period March 1993 to March 2002, in agreement with corresponding CMDL data (0.21±0.0002pptvyr) at the surface. The limited accuracy of the Ny Ålesund and Kitt Peak data results from strong tropospheric water vapour interferences at these lower altitude sites. Observations at all three locations show that SF6 is still accumulating in the atmosphere. Extrapolations of linear and second-order fits to the Jungfraujoch data predict tropospheric mixing ratios of SF6, respectively equal to 16.4±0.5 and 14.7±0.6 in 2050, and 28.2±0.9 and 22.2±0.8pptv in 2100, significantly lower than those reported in the literature so far.

  14. H3N2 Mismatch of 2014-15 Northern Hemisphere Influenza Vaccines and Head-to-head Comparison between Human and Ferret Antisera derived Antigenic Maps

    Science.gov (United States)

    Xie, Hang; Wan, Xiu-Feng; Ye, Zhiping; Plant, Ewan P.; Zhao, Yangqing; Xu, Yifei; Li, Xing; Finch, Courtney; Zhao, Nan; Kawano, Toshiaki; Zoueva, Olga; Chiang, Meng-Jung; Jing, Xianghong; Lin, Zhengshi; Zhang, Anding; Zhu, Yanhong

    2015-10-01

    The poor performance of 2014-15 Northern Hemisphere (NH) influenza vaccines was attributed to mismatched H3N2 component with circulating epidemic strains. Using human serum samples collected from 2009-10, 2010-11 and 2014-15 NH influenza vaccine trials, we assessed their cross-reactive hemagglutination inhibition (HAI) antibody responses against recent H3 epidemic isolates. All three populations (children, adults, and older adults) vaccinated with the 2014-15 NH egg- or cell-based vaccine, showed >50% reduction in HAI post-vaccination geometric mean titers against epidemic H3 isolates from those against egg-grown H3 vaccine strain A/Texas/50/2012 (TX/12e). The 2014-15 NH vaccines, regardless of production type, failed to further extend HAI cross-reactivity against H3 epidemic strains from previous seasonal vaccines. Head-to-head comparison between ferret and human antisera derived antigenic maps revealed different antigenic patterns among representative egg- and cell-grown H3 viruses characterized. Molecular modeling indicated that the mutations of epidemic H3 strains were mainly located in antibody-binding sites A and B as compared with TX/12e. To improve vaccine strain selection, human serologic testing on vaccination-induced cross-reactivity need be emphasized along with virus antigenic characterization by ferret model.

  15. The Mass Balance of Glacier No. 1 at the Headwaters of the Urumqi River in Relation to Northern Hemisphere Teleconnection Patterns

    Directory of Open Access Journals (Sweden)

    Feifei Yuan

    2016-03-01

    Full Text Available Most small glaciers in the world have significantly decreased their volume during the last century, which has caused water shortage problems. Glacier No. 1, at the headwaters of the Urumqi River, Tianshan, China, has been monitored since 1959 and similarly has experienced significant mass and volume losses over the last few decades. Thus, we examined the trend and potential abrupt changes of the mass balance of Glacier No. 1. Principal component analysis and singular value decomposition were used to find significant relations between the mass balance of Glacier No. 1 and Northern Hemisphere teleconnection patterns using climate indices. It was found that the mass balance of Glacier No. 1 had a significantly decreasing trend corresponding to −14.5 mm/year from 1959 to 2010. A change point was detected in 1997 with 99% confidence level. Two time periods with different mass balances were identified as 1959–1996 and 1997–2010. The mass balance for the first period was −136.4 mm/year and up to −663.9 mm/year for the second period. The mass balance of Glacier No. 1 is positively related to the Scandinavian Pattern (SCA, and negatively related to the East Atlantic Pattern (EA. These relationships are useful in better understanding the interaction between glacier mass balance and climate variability.

  16. The Mass Balance of Glacier No. 1 at the Headwaters of the Urumqi River in Relation to Northern Hemisphere Teleconnection Patterns

    Science.gov (United States)

    Yuan, Feifei; Hao, Zhenchun

    2017-04-01

    Most small glaciers in the world have significantly decreased their volume during the last century, which has caused water shortage problems. Glacier No. 1, at the headwaters of the Urumqi River, Tianshan, China, has been monitored since 1959 and similarly has experienced significant mass and volume losses over the last few decades. Thus, we examined the trend and potential abrupt changes of the mass balance of Glacier No. 1. Principal component analysis and singular value decomposition were used to find significant relations between the mass balance of Glacier No. 1 and Northern Hemisphere teleconnection patterns using climate indices. It was found that the mass balance of Glacier No. 1 had a significantly decreasing trend corresponding to -14.5 mm/year from 1959 to 2010. A change point was detected in 1997 with 99% confidence level. Two time periods with different mass balances were identified as 1959-1996 and 1997-2010. The mass balance for the first period was -136.4 mm/year and up to -663.9 mm/year for the second period. The mass balance of Glacier No. 1 is positively related to the Scandinavian Pattern (SCA), and negatively related to the East Atlantic Pattern (EA). These relationships are useful in better understanding the interaction between glacier mass balance and climate variability.

  17. Martian ionospheric plasma densities: First results from MAVEN/LPW of the near-terminator ionosphere in the Northern hemisphere of Mars

    Science.gov (United States)

    Andrews, David; McEnulty, Tess; Andersson, Laila; Ergun, Robert; Delory, Gregory; Morooka, Michiko; Fowler, Christopher; Weber, Tristan; Eriksson, Anders; Eparvier, Frank

    2015-04-01

    MAVEN began its science mission at Mars in November 2014. Since then, it has been making measurements with a suite of plasma instrumentation, among which is the Langmuir Probe and Waves (LPW) instrument package. LPW consists of two probes mounted on 7m booms which can be operated as independent Langmuir probes, or jointly as an electric field sensor. LPW can accurately measure the thermal electron plasma density and temperature encountered by the spacecraft during periapsis by performing current-voltage sweeps. Alternatively, the instrument can be operated in 'waves' mode, yielding electric field spectra spanning frequencies in the Hz - MHz range. Additionally, an active sounding mode is available, whereby a low power white-noise signal is fed to the plasma to stimulate the generation of waves at the local plasma frequency. Through these measurement techniques, electron densities accurate to within ~5% can be derived, along with the electron temperature. The instrument cadence and typical spacecraft velocities translate to measurements of the plasma on length scales concentrating in particular on plasma density structures observed in the near-terminator ionosphere in the northern hemisphere of Mars.

  18. Causality of global warming seen from observations: a scale analysis of driving force of the surface air temperature time series in the Northern Hemisphere

    Science.gov (United States)

    Yang, Peicai; Wang, Geli; Zhang, Feng; Zhou, Xiuji

    2016-05-01

    By using the slow feature analysis, we reconstructed the driving force for an observed monthly surface air temperature anomaly time series in the northern hemisphere. Wavelet transformation technique was then used to analyze the scale structure of the derived driving force and its causal relationship with global warming. Results showed that the driving force for the analyzed temperature climate system included two independent degrees of freedom which respectively represented the effects of 22-year solar cycle and Atlantic Multidecadal Oscillation on the climate. More importantly, the driving force is modulated in amplitude by signals with much longer time periods. The modulation controls the energy input to the climate system and its effect on the global warming is decisive. In addition, through analyzing phase transitions from zero to extremes of the modulating signals, we provide a projection for the future trend of the surface air temperature. In specific, in the next 45-65 years, the driving force will continue to rise which will drive the air temperature even warmer. This is a long term natural trend determined by the modulating amplitude signals, but not directly related to human activity.

  19. Landscape: A Southern Hemisphere perspective

    Science.gov (United States)

    Squires, V. R.

    1988-12-01

    Well into the Mesozoic Era, Africa, South America, India and Australia were joined to Antarctica in one supercontinent—Gondwanaland. The northern continents were also joined to form the supercontinent Laurasia. Southern Hemisphere land masses, especially Australia, have been characterised by a long period of relative geological stability and a short period of glaciation during the Quaternary. These circumstances have led to the development of quite old landscapes, developed on surfaces subjected to the processes of weathering for millions of years. Unlike the Gondwanaland continents, much of the Northern Hemisphere has been tectonically active with orogenic processes producing young uplifted surfaces subjected to active erosion. The Northern Hemisphere has experienced four extensive and intense Pleistocene glaciations. The consequence of these periods of glaciation is that present-day landscapes are substantially the product of climate over the past 10,000 years and commonly have not undergone extensive weathering. The applicability therefore of Northern Hemisphere-derived models to explain things as diverse as landforms, stream patterns and processes, soil genesis and ecological theory in the Southern Hemisphere has increasingly come into question. Because southern landscapes have a physiography and palaeohistory quite different from that of the Northern Hemisphere, it provides an unparalleled opportunity to develop new concepts and theories which may have implications for the whole globe.

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

    Directory of Open Access Journals (Sweden)

    G. I. Mingaleva

    1997-10-01

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

  1. 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.

  2. S-N secular ocean tide: explanation of observably coastal velocities of increase of a global mean sea level and mean sea levels in northern and southern hemispheres and prediction of erroneous altimetry velocities

    Science.gov (United States)

    Barkin, Yury

    2010-05-01

    The phenomenon of contrast secular changes of sea levels in the southern and northern hemispheres, predicted on the basis of geodynamic model about the forced relative oscillations and displacements of the Earth shells, has obtained a theoretical explanation. In northern hemisphere the mean sea level of ocean increases with velocity about 2.45±0.32 mm/yr, and in a southern hemisphere the mean sea level increases with velocity about 0.67±0.30 mm/yr. Theoretical values of velocity of increase of global mean sea level of ocean has been estimated in 1.61±0.36 mm/yr. 1 Introduction. The secular drift of the centre of mass of the Earth in the direction of North Pole with velocity about 12-20 mm/yr has been predicted by author in 1995 [1], [2], and now has confirmed with methods of space geodesy. For example the DORIS data in period 1999-2008 let us to estimate velocity of polar drift in 5.24±0.29 mm/yr [3]. To explain this fundamental planetary phenomenon it is possible only, having admitted, that similar northern drift tests the centre of mass of the liquid core relatively to the centre of mass of viscous-elastic and thermodynamically changeable mantle with velocity about 2-3 cm/yr in present [4]. The polar drift of the Earth core with huge superfluous mass results in slow increase of a gravity in northern hemisphere with a mean velocity about 1.4 ?Gal and to its decrease approximately with the same mean velocity in southern hemisphere [5]. This conclusion-prediction has obtained already a number of confirmations in precision gravimetric observations fulfilled in last decade around the world [6]. Naturally, a drift of the core is accompanied by the global changes (deformations) of all layers of the mantle and the core, by inversion changes of their tension states when in one hemisphere the tension increases and opposite on the contrary - decreases. Also it is possible that thermodynamical mechanism actively works with inversion properties of molting and

  3. Estimation of surface albedo from NOAA AVHRR data in high latitudes

    OpenAIRE

    Laine, Vesa; Heikinheimo, Martti

    2011-01-01

    A method for determining the surface albedo from routine daily NOAA AVHRR data is described and tested for applicability under high latitude conditions in a boreal-sub-arctic region. The test period included all received satellite data from April to October 1994, giving a good coverage of various and changing surface conditions. Albedo values obtained initially for each cloud-free pixel and satellite over-pass were averaged over nine-day periods to include a full cycle of measuring geometries...

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

    OpenAIRE

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

    1990-01-01

    Recent observations of ionospheric flows by ground-based radars, in particular by the European Incoherent Scatter (EISCAT) facility using the “Polar” experiment, together with previous analyses of the response of geomagnetic disturbance to variations of the interplanetary magnetic field (IMF), suggest that convection in the high-latitude ionosphere should be considered to be the sum of two intrinsically time-dependent patterns, one driven by solar wind-magnetosphere coupling at the dayside ma...

  5. Engineering challenges of operating year-round portable seismic stations at high-latitude

    Science.gov (United States)

    Beaudoin, Bruce; Carpenter, Paul; Hebert, Jason; Childs, Dean; Anderson, Kent

    2017-04-01

    Remote portable seismic stations are, in most cases, constrained by logistics and cost. High latitude operations introduce environmental, technical and logistical challenges that require substantially more engineering work to ensure robust, high quality data return. Since 2006, IRIS PASSCAL has been funded by NSF to develop, deploy, and maintain a pool of polar specific seismic stations. Here, we describe our latest advancements to mitigate the challenges of high-latitude, year-round station operation. The IRIS PASSCAL program has supported high-latitude deployments since the late 1980s. These early deployments were largely controlled source, summer only experiments. In early 2000 PASSCAL users began proposing year-round deployments of broadband stations in some of the harshest environments on the planet. These early year-round deployments were stand-alone (no telemetry) stations largely designed to operate during summer months and then run as long as possible during the winter with hopes the stations would revive come following summer. In 2006 and in collaboration with UNAVCO, we began developing communications, power systems, and enclosures to extend recording to year-round. Since this initial effort, PASSCAL continued refinement to power systems, enclosure design and manufacturability, and real-time data communications. Several sensor and data logger manufacturers have made advances in cold weather performance and delivered newly designed instruments that have furthered our ability to successfully run portable stations at high-latitude with minimal logistics - reducing size and weight of instruments and infrastructure. All PASSCAL polar engineering work is openly shared through our website: www.passcal.nmt.edu/content/polar

  6. [A stereological analysis of the myocardium in rats adapting to the conditions at high latitudes].

    Science.gov (United States)

    Nepomniashchikh, L M; Lushnikova, E L; Nepomniashchikh, G I

    1993-10-01

    Qualitative and quantitative morphologic analysis of myocardium of Wistar rats were carried out when they have been transferred to high latitudes (being in latitude 69 degrees north during 37 days). It was shown, that already in a day after transferring to high latitudes pronounced disorders of lymph and blood circulations developed and heterogeneity of cardiomyocyte lesions was noted. By the end of the experiment atrophic and necrobiotic cardiomyocytes resorbed by macrophages were registered. In the group of animals, whose were transported in middle latitudes morphologic changes in myocardium gradually increased by the end of the experiment. Stereologic analysis revealed stereotype dynamics of tissue reorganization of myocardium in both animal groups. A key event in tissue reorganization of myocardium was the significant decrease of volume and surface densities of capillaries at 12th day of experiment and as consequence of these changes the volume and surface-to-volume ratios of capillaries to cardiomyocytes were decreased. The decrease of these parameters was more pronounced in animals whose were transported to high latitudes.

  7. Effects of climate warming, North Atlantic Oscillation, and El Niño-Southern Oscillation on thermal conditions and plankton dynamics in northern hemispheric lakes.

    Science.gov (United States)

    Gerten, Dieter; Adrian, Rita

    2002-03-08

    Impacts of climate warming on freshwater ecosystems have been documented recently for a variety of sites around the globe. Here we provide a review of studies that report long-term (multidecadal) effects of warming trends on thermal properties and plankton dynamics in northern hemispheric lakes. We show that higher lake temperatures, shorter periods with ice cover, and shorter stagnation periods were common trends for lakes across the hemisphere in response to the warmer conditions. Only for shallow dimictic lakes was it observed that deep-water temperatures decreased. Moreover, it became evident that phytoplankton dynamics and primary productivity altered in conjunction with changes in lake physics. Algal spring blooms developed early and were more pronounced in several European lakes after mild winters with short ice cover periods, and primary productivity increased in North American lakes. Effects of elevated temperatures on zooplankton communities were seen in an early development of various species and groups, as is documented for cladocerans, copepods, and rotifers in European lakes. Furthermore, thermophile species reached higher abundance in warmer years. Obviously, the nature of responses is species specific, and depends on the detailed seasonal patterning of warming. Complex responses such as effects propagating across trophic levels are likely, indicating that observed climate-ecosystem relationships are not generally applicable. Nonetheless, the picture emerges that climate-driven changes in freshwater ecosystems may be synchronised to a certain extent among lakes even over great distances if climatic influences are not masked by anthropogenic impacts or differences in lake morphology. Macro-scale climatic fluctuations--such as the North Atlantic Oscillation or the El Niño-Southern Oscillation--were identified as the most important candidates responsible for such coherence, with the former predominating in Europe and the latter in North America. We

  8. Strong asymmetry of hemispheric climates during MIS-13 inferred from correlating China loess and Antarctica ice records

    Directory of Open Access Journals (Sweden)

    Z. T. Guo

    2009-02-01

    Full Text Available We correlate the China loess and Antarctica ice records to address the inter-hemispheric climate link over the past 800 ka. The results show a broad coupling between Asian and Antarctic climates at the glacial-interglacial scale. However, a number of decoupled aspects are revealed, among which marine isotope stage (MIS 13 exhibits a strong anomaly compared with the other interglacials. It is characterized by unusually positive benthic oxygen (δ18O and carbon isotope (δ13C values in the world oceans, cooler Antarctic temperature, lower summer sea surface temperature in the South Atlantic, lower CO2 and CH4 concentrations, but by extremely strong Asian, Indian and African summer monsoons, weakest Asian winter monsoon, and lowest Asian dust and iron fluxes. Pervasive warm conditions were also evidenced by the records from northern high-latitude regions. These consistently indicate a warmer Northern Hemisphere and a cooler Southern Hemisphere, and hence a strong asymmetry of hemispheric climates during MIS-13. Similar anomalies of lesser extents also occurred during MIS-11 and MIS-5e. Thus, MIS-13 provides a case that the Northern Hemisphere experienced a substantial warming under relatively low concentrations of greenhouse gases. It suggests that the global climate system possesses a natural variability that is not predictable from the simple response of northern summer insolation and atmospheric CO2 changes. During MIS-13, both hemispheres responded in different ways leading to anomalous continental, marine and atmospheric conditions at the global scale. The correlations also suggest that the marine δ18O record is not always a reliable indicator of the northern ice-volume changes, and that the asymmetry of hemispheric climates is one of the prominent factors controlling the strength of Asian, Indian and African monsoon circulations, most likely through modulating the position of

  9. 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.

  10. 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

    their foraging behavior and ecology. Here we use acoustic recording tags to study the diving and acoustic behavior of male sperm whales foraging off northern Norway. Sixty-five hours of tag data provide detailed information about the movements and sound repertoire of four male sperm whales performing 83 dives......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...... and 218 m and the last usual click at depths ranging between 1 and 1114 m. Echolocation buzzes, which are used as an indication of prey capture attempts, were emitted at depths between 17 and 1860 m, during both the descent and ascent phase of deep dives. The foraging behavior varied markedly with depth...

  11. 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.

  12. OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. V. TNG, KPNO, AND OAN OBSERVATIONS OF BLAZAR CANDIDATES OF UNCERTAIN TYPE IN THE NORTHERN HEMISPHERE

    Energy Technology Data Exchange (ETDEWEB)

    Álvarez Crespo, N.; Massaro, F. [Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, I-10125 Torino (Italy); Masetti, N. [INAF—Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, I-40129, Bologna (Italy); Ricci, F.; La Franca, F. [Dipartimento di Matematica e Fisica, Università Roma Tre, via della Vasca Navale 84, I-00146, Roma (Italy); Landoni, M. [INAF-Osservatorio Astronomico di Brera, Via Emilio Bianchi 46, I-23807 Merate (Italy); Patiño-Álvarez, V.; Chavushyan, V.; Torrealba, J. [Instituto Nacional de Astrofisica, Óptica y Electrónica, Apartado Postal 51-216, 72000 Puebla, México (Mexico); D’Abrusco, R.; Paggi, A.; Smith, Howard A. [Harvard—Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Jiménez-Bailón, E. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, Ensenada, 22800 Baja California, México (Mexico); Latronico, L. [Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino (Italy); Tosti, G. [Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia (Italy)

    2016-02-15

    The extragalactic γ-ray sky is dominated by emission from blazars, a peculiar class of active galactic nuclei. Many of the γ-ray sources included in the Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar candidates of uncertain type (BCUs) because there are no optical spectra available in the literature to confirm their nature. In 2013, we started a spectroscopic campaign to look for the optical counterparts of the BCUs and of the unidentified γ-ray sources to confirm their blazar nature. Whenever possible we also determine their redshifts. Here, we present the results of the observations carried out in the northern hemisphere in 2013 and 2014 at the Telescopio Nazionale Galileo, Kitt Peak National Observatory, and Observatorio Astronómico Nacional in San Pedro Mártir. In this paper, we describe the optical spectra of 25 sources. We confirmed that all of the 15 BCUs observed in our campaign and included in our sample are blazars and we estimated the redshifts for three of them. In addition, we present the spectra for three sources classified as BL Lacs in the literature but with no optical spectra available to date. We found that one of them is a quasar (QSO) at a redshift of z = 0.208 and the other two are BL Lacs. Moreover, we also present seven new spectra for known blazars listed in the Roma-BZCAT that have an uncertain redshift or are classified as BL Lac candidates. We found that one of them, 5BZB J0724+2621, is a “changing look” blazar. According to the spectrum available in the literature, it was classified as a BL Lac, but in our observation we clearly detected a broad emission line that led us to classify this source as a QSO at z = 1.17.

  13. A meta-analysis of cambium phenology and growth: linear and non-linear patterns in conifers of the northern hemisphere

    Science.gov (United States)

    Rossi, Sergio; Anfodillo, Tommaso; Čufar, Katarina; Cuny, Henri E.; Deslauriers, Annie; Fonti, Patrick; Frank, David; Gričar, Jožica; Gruber, Andreas; King, Gregory M.; Krause, Cornelia; Morin, Hubert; Oberhuber, Walter; Prislan, Peter; Rathgeber, Cyrille B. K.

    2013-01-01

    Background and Aims Ongoing global warming has been implicated in shifting phenological patterns such as the timing and duration of the growing season across a wide variety of ecosystems. Linear models are routinely used to extrapolate these observed shifts in phenology into the future and to estimate changes in associated ecosystem properties such as net primary productivity. Yet, in nature, linear relationships may be special cases. Biological processes frequently follow more complex, non-linear patterns according to limiting factors that generate shifts and discontinuities, or contain thresholds beyond which responses change abruptly. This study investigates to what extent cambium phenology is associated with xylem growth and differentiation across conifer species of the northern hemisphere. Methods Xylem cell production is compared with the periods of cambial activity and cell differentiation assessed on a weekly time scale on histological sections of cambium and wood tissue collected from the stems of nine species in Canada and Europe over 1–9 years per site from 1998 to 2011. Key Results The dynamics of xylogenesis were surprisingly homogeneous among conifer species, although dispersions from the average were obviously observed. Within the range analysed, the relationships between the phenological timings were linear, with several slopes showing values close to or not statistically different from 1. The relationships between the phenological timings and cell production were distinctly non-linear, and involved an exponential pattern Conclusions The trees adjust their phenological timings according to linear patterns. Thus, shifts of one phenological phase are associated with synchronous and comparable shifts of the successive phases. However, small increases in the duration of xylogenesis could correspond to a substantial increase in cell production. The findings suggest that the length of the growing season and the resulting amount of growth could respond

  14. Influence of high-latitude geomagnetic pulsations on recordings of broadband force-balanced seismic sensors

    Directory of Open Access Journals (Sweden)

    E. Kozlovskaya

    2012-08-01

    Full Text Available Seismic broadband sensors with electromagnetic feedback are sensitive to variations of surrounding magnetic field, including variations of geomagnetic field. Usually, the influence of the geomagnetic field on recordings of such seismometers is ignored. It might be justified for seismic observations at middle and low latitudes. The problem is of high importance, however, for observations in Polar Regions (above 60° geomagnetic latitude, where magnitudes of natural magnetic disturbances may be two or even three orders larger. In our study we investigate the effect of ultra-low frequency (ULF magnetic disturbances, known as geomagnetic pulsations, on the STS-2 seismic broadband sensors. The pulsations have their sources and, respectively, maximal amplitudes in the region of the auroral ovals, which surround the magnetic poles in both hemispheres at geomagnetic latitude (GMLAT between 60° and 80°. To investigate sensitivity of the STS-2 seismometer to geomagnetic pulsations, we compared the recordings of permanent seismic stations in northern Finland to the data of the magnetometers of the IMAGE network located in the same area. Our results show that temporary variations of magnetic field with periods of 40–150 s corresponding to regular Pc4 and irregular Pi2 pulsations are seen very well in recordings of the STS-2 seismometers. Therefore, these pulsations may create a serious problem for interpretation of seismic observations in the vicinity of the auroral oval. Moreover, the shape of Pi2 magnetic disturbances and their periods resemble the waveforms of glacial seismic events reported originally by Ekström (2003. The problem may be treated, however, if combined analysis of recordings of co-located seismic and magnetic instruments is used.

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

    Science.gov (United States)

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

    2014-05-06

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

  16. Nonlinear Evolution of the Kelvin-Helmholtz Instability in the High Latitude Ionosphere.

    Science.gov (United States)

    1987-12-21

    Report 6043 AD-A 188 875 Nonlinear Evolution of the Kelvin-Helmholtz Instability in the High Latitude Ionosphere M.J. KESKINEN, H.G. MITCHELL,* J.A...Nonlinezir Evolut ion of the Ke lvi n-HIlmhoIt z Inst ah i its’ in) tHe High l.a t itlude’ 1011IF~sh~re a 12 PERSONAL AUTHOR(S) (c aei)O 13a TYPE OF...be described as "brcaknoiws . and 141 Lcencrate. in tile nosni near ret! it I. ,mlil seci c t urbu lenrce by mecans of’ sectsnla r\\ instabilities

  17. 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.

  18. Initial studies of high latitude magnetic field data during different magnetospheric conditions

    Science.gov (United States)

    Cersosimo, D. O.; Wanliss, J. A.

    2007-01-01

    We investigate the statistical properties of high-latitude magnetometer data for differing geomagnetic activity. This is achieved by characterizing changes in the nonlinear statistics of the geomagnetic field, by means of the Hurst exponent, measured from a single ground-based magnetometer station. The long-range statistical nature of the geomagnetic field at a local observation site can be described as a multifractional Brownian motion, thus suggesting the statistical structure required of mathematical models of magnetospheric activity. We also find that, in general, the average Hurst exponent for quiet magnetospheric intervals is smaller than that for more active intervals.

  19. Northern Hemisphere Synoptic Weather Maps

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Daily Series of Synoptic Weather Maps. Part I consists of plotted and analyzed daily maps of sea-level and 500-mb maps for 0300, 0400, 1200, 1230, 1300, and 1500...

  20. GPS TEC, scintillation and cycle slips observed at high latitudes during solar minimum

    Directory of Open Access Journals (Sweden)

    P. Prikryl

    2010-06-01

    Full Text Available High-latitude irregularities can impair the operation of GPS-based devices by causing fluctuations of GPS signal amplitude and phase, also known as scintillation. Severe scintillation events lead to losses of phase lock, which result in cycle slips. We have used data from the Canadian High Arctic Ionospheric Network (CHAIN to measure amplitude and phase scintillation from L1 GPS signals and total electron content (TEC from L1 and L2 GPS signals to study the relative role that various high-latitude irregularity generation mechanisms have in producing scintillation. In the first year of operation during the current solar minimum the amplitude scintillation has remained very low but events of strong phase scintillation have been observed. We have found, as expected, that auroral arc and substorm intensifications as well as cusp region dynamics are strong sources of phase scintillation and potential cycle slips. In addition, we have found clear seasonal and universal time dependencies of TEC and phase scintillation over the polar cap region. A comparison with radio instruments from the Canadian GeoSpace Monitoring (CGSM network strongly suggests that the polar cap scintillation and TEC variations are associated with polar cap patches which we therefore infer to be main contributors to scintillation-causing irregularities in the polar cap.

  1. 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

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

    Science.gov (United States)

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

    2015-05-01

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

  3. Tropical seaways played a more important role than high latitude seaways in Cenozoic cooling

    Directory of Open Access Journals (Sweden)

    Z. Zhang

    2011-07-01

    Full Text Available Following the Early Eocene climatic optimum (EECO, ~55–50 Ma, climate deteriorated and gradually changed the earth from a greenhouse into an icehouse, with major cooling events at the Eocene-Oligocene boundary (∼34 Ma and the Middle Miocene (∼15 Ma. It is believed that the opening of the Drake Passage had a marked impact on the cooling at the Eocene-Oligocene boundary. Based on an Early Eocene simulation, we study the sensitivity of climate and ocean circulation to tectonic events such as the closing of the West Siberian Seaway, the deepening of the Arctic-Atlantic Seaway, the opening of the Drake Passage, and the constriction of the Tethys and Central American seaways. The opening of the Drake Passage, together with the closing of the West Siberian Seaway and the deepening of the Arctic-Atlantic Seaway, weakened the Southern Ocean Deep Water (SODW dominated ocean circulation and led to a weak cooling at high latitudes, thus contributing to the observed Early Cenozoic cooling. However, the later constriction of the Tethys and Central American Seaways is shown to give a strong cooling at southern high latitudes. This cooling was related to the transition of ocean circulation from a SODW-dominated mode to the modern-like ocean circulation dominated by North Atlantic Deep Water (NADW.

  4. Mudstone sedimentation at high latitudes: Ice as a transport medium for mud and supplier of nutrients

    Science.gov (United States)

    Macquaker, J.H.S.; Keller, M.A.

    2005-01-01

    Controls on mudstone deposition at high latitudes are poorly known relative to low latitudes. In recent sediments deposited in these environments, ice significantly influences sediment transport and primary productivity. The products of ice transport are relatively well known in glacimarine settings, but are less well known from below melting sea ice. This latter setting is significant as today it is associated with high primary organic productivity. The aim of this study is to assess how sea ice might have controlled lithofacies variability and organic-matter distribution and preservation in an ancient marine, siliciclastic mudstone-dominated succession deposited at high latitudes. Combined sedimentary logging, optical and electron optical (back-scatte red electron imagery), geochemical, and isotopic methods were used to determine sample variability in forty-five samples collected from the Lower Cretaceous succession in the Mikkelsen Bay State #1 borehole (North Slope, Alaska). The succession overall fines upward and contains muddy sandstones and sand- and silt-bearing, clay-rich mudstones towards its base in contrast to clay-rich and clay-dominated mudstones towards its top. Some of the mudstone units exhibit thin (Copyright ?? 2005, SEPM (Society for Sedimentary Geology).

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

    Directory of Open Access Journals (Sweden)

    J.-P. St.-Maurice

    2000-05-01

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

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

    Science.gov (United States)

    Honary, Farideh

    2014-05-01

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

  7. The distribution and biogeochemical importance of high-latitude dust in the Arctic and Southern Ocean-Antarctic regions

    Science.gov (United States)

    Bullard, Joanna E.

    2017-03-01

    Recent studies suggest that around 5% of global dust emissions come from sources in the high latitudes (≥50°N and ≥40°S). A substantial proportion of this dust remains within the high latitudes and is deposited in marine and terrestrial environments. Stable air masses and limited atmospheric convection associated with cold climates reduce vertical mixing of dust plumes and can restrict the altitudes at which the deposition of dust originating from high latitudes can take place. Within local high-latitude systems, dust transport pathways facilitate links between different landscape components contributing nutrients and sediments. Dust deposition to the polar areas may also be a critical source of sediments and nutrients that trigger and maintain phytoplankton blooms.

  8. The First in situ Observation of Kelvin-Helmholtz Waves at High-Latitude Magnetopause during Strongly Dawnward Interplanetary Magnetic Field Conditions

    Science.gov (United States)

    Hwang, K.-J.; Goldstein, M. L.; Kuznetsova, M. M.; Wang, Y.; Vinas, A. F.; Sibeck, D. G.

    2012-01-01

    We report the first in situ observation of high-latitude magnetopause (near the northern duskward cusp) Kelvin-Helmholtz waves (KHW) by Cluster on January 12, 2003, under strongly dawnward interplanetary magnetic field (IMF) conditions. The fluctuations unstable to Kelvin-Helmholtz instability (KHI) are found to propagate mostly tailward, i.e., along the direction almost 90 deg. to both the magnetosheath and geomagnetic fields, which lowers the threshold of the KHI. The magnetic configuration across the boundary layer near the northern duskward cusp region during dawnward IMF is similar to that in the low-latitude boundary layer under northward IMF, in that (1) both magnetosheath and magnetospheric fields across the local boundary layer constitute the lowest magnetic shear and (2) the tailward propagation of the KHW is perpendicular to both fields. Approximately 3-hour-long periods of the KHW during dawnward IMF are followed by the rapid expansion of the dayside magnetosphere associated with the passage of an IMF discontinuity that characterizes an abrupt change in IMF cone angle, Phi = acos (B(sub x) / absolute value of Beta), from approx. 90 to approx. 10. Cluster, which was on its outbound trajectory, continued observing the boundary waves at the northern evening-side magnetopause during sunward IMF conditions following the passage of the IMF discontinuity. By comparing the signatures of boundary fluctuations before and after the IMF discontinuity, we report that the frequencies of the most unstable KH modes increased after the discontinuity passed. This result demonstrates that differences in IMF orientations (especially in f) are associated with the properties of KHW at the high-latitude magnetopause due to variations in thickness of the boundary layer, and/or width of the KH-unstable band on the surface of the dayside magnetopause.

  9. Polar stratospheric cloud observations by MIPAS on ENVISAT: detection method, validation and analysis of the northern hemisphere winter 2002/2003

    Directory of Open Access Journals (Sweden)

    R. Spang

    2005-01-01

    Full Text Available The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS on ENVISAT has made extensive measurements of polar stratospheric clouds (PSCs in the northern hemisphere winter 2002/2003. A PSC detection method based on a ratio of radiances (the cloud index has been implemented for MIPAS and is validated in this study with respect to ground-based lidar and space borne occultation measurements. A very good correspondence in PSC sighting and cloud altitude between MIPAS detections and those of other instruments is found for cloud index values of less than four. Comparisons with data from the Stratospheric Aerosol and Gas Experiment (SAGE III are used to further show that the sensitivity of the MIPAS detection method for this threshold value of cloud index is approximately equivalent to an extinction limit of 10-3km-1 at 1022nm, a wavelength used by solar occultation experiments. The MIPAS cloud index data are subsequently used to examine, for the first time with any technique, the evolution of PSCs throughout the Arctic polar vortex up to a latitude close to 90° north on a near-daily basis. We find that the winter of 2002/2003 is characterised by three phases of very different PSC activity. First, an unusual, extremely cold phase in the first three weeks of December resulted in high PSC occurrence rates. This was followed by a second phase of only moderate PSC activity from 5-13 January, separated from the first phase by a minor warming event. Finally there was a third phase from February to the end of March where only sporadic and mostly weak PSC events took place. The composition of PSCs during the winter period has also been examined, exploiting in particular an infra-red spectral signature which is probably characteristic of NAT. The MIPAS observations show the presence of these particles on a number of occasions in December but very rarely in January. The PSC type differentiation from MIPAS indicates that future comparisons of PSC

  10. Epidemiology of Hospital Admissions with Influenza during the 2013/2014 Northern Hemisphere Influenza Season: Results from the Global Influenza Hospital Surveillance Network

    Science.gov (United States)

    Puig-Barberà, Joan; Natividad-Sancho, Angels; Trushakova, Svetlana; Sominina, Anna; Pisareva, Maria; Ciblak, Meral A.; Badur, Selim; Yu, Hongjie; Cowling, Benjamin J.; El Guerche-Séblain, Clotilde; Mira-Iglesias, Ainara; Kisteneva, Lidiya; Stolyarov, Kirill; Yurtcu, Kubra; Feng, Luzhao; López-Labrador, Xavier; Burtseva, Elena

    2016-01-01

    Background The Global Influenza Hospital Surveillance Network was established in 2012 to obtain valid epidemiologic data on hospital admissions with influenza-like illness. Here we describe the epidemiology of admissions with influenza within the Northern Hemisphere sites during the 2013/2014 influenza season, identify risk factors for severe outcomes and complications, and assess the impact of different influenza viruses on clinically relevant outcomes in at-risk populations. Methods Eligible consecutive admissions were screened for inclusion at 19 hospitals in Russia, Turkey, China, and Spain using a prospective, active surveillance approach. Patients that fulfilled a common case definition were enrolled and epidemiological data were collected. Risk factors for hospitalization with laboratory-confirmed influenza were identified by multivariable logistic regression. Findings 5303 of 9507 consecutive admissions were included in the analysis. Of these, 1086 were influenza positive (534 A(H3N2), 362 A(H1N1), 130 B/Yamagata lineage, 3 B/Victoria lineage, 40 untyped A, and 18 untyped B). The risk of hospitalization with influenza (adjusted odds ratio [95% confidence interval]) was elevated for patients with cardiovascular disease (1.63 [1.33–2.02]), asthma (2.25 [1.67–3.03]), immunosuppression (2.25 [1.23–4.11]), renal disease (2.11 [1.48–3.01]), liver disease (1.94 [1.18–3.19], autoimmune disease (2.97 [1.58–5.59]), and pregnancy (3.84 [2.48–5.94]). Patients without comorbidities accounted for 60% of admissions with influenza. The need for intensive care or in-hospital death was not significantly different between patients with or without influenza. Influenza vaccination was associated with a lower risk of confirmed influenza (adjusted odds ratio = 0.61 [0.48–0.77]). Conclusions Influenza infection was detected among hospital admissions with and without known risk factors. Pregnancy and underlying comorbidity increased the risk of detecting influenza

  11. Recurrent partial mortality events in winter shape the dynamics of the zooxanthellate coral Oculina patagonica at high latitude in the Mediterranean

    Science.gov (United States)

    Serrano, Eduard; Ribes, Marta; Coma, Rafel

    2017-03-01

    Global warming has many biological effects on corals and plays a central role in the regression of tropical coral reefs; therefore, there is an urgent need to understand how some coral species have adapted to environmental conditions at higher latitudes. We examined the effects of temperature and light on the growth of the zooxanthellate coral Oculina patagonica (Scleractinia, Oculinidae) at the northern limit of its distribution in the eastern Iberian Peninsula (western Mediterranean) by transplanting colonies onto plates and excluding them from space competition over a 4-yr period. Each year, most of the colonies ( 70%) exhibited denuded skeletons with isolated polyps persisting on approximately half of the coral surface area. These recurrent episodes of partial coral mortality occurred in winter, and their severity appeared to be related to colony exposure to cold but not to light. Although O. patagonica exhibited high resistance to stress, coral linear extension did not resume until the coenosarc regenerated. The resumption of linear extension was related to the dissociation of the polyps from the coenosarc and the outstanding regenerative capacity of this species (10.3 mm2 d-1). These biological characteristics allow the species to survive at high latitudes. However, the recurrent and severe pattern of denuded skeletons greatly affects the dynamics of the species and may constrain population growth at high latitudes in the Mediterranean.

  12. 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.

  13. Beringia: Intercontinental exchange and diversification of high latitude mammals and their parasites during the Pliocene and Quaternary

    Science.gov (United States)

    Cook, Joseph A.; Hoberg, Eric P.; Koehler, Anson V.; Henttonen, Heikki; Wickström, Lotta; Haukisalmi, Voitto; Galbreath, Kurt E.; Chernyavski, Felix; Dokuchaev, Nikolai; Lahzuhtkin, Anatoli; MacDonald, Stephen O.; Hope, Andrew G.; Waltari, Eric; Runck, Amy; Veitch, Alasdair; Jenkins, Emily; Kutz, Susan; Eckerlin, Ralph P.

    2005-01-01

    Beringia is the region spanning eastern Asia and northwestern North America that remained ice-free during the full glacial events of the Pleistocene. Numerous questions persist regarding the importance of this region in the evolution of northern faunas. Beringia has been implicated as both a high latitude refugium and as the crossroads (Bering Land Bridge) of the northern continents for boreal mammals. The Beringian Coevolution Project (BCP) is an international collaboration that has provided material to assess the pattern and timing of faunal exchange across the crossroads of the northern continents and the potential impact of past climatic events on differentiation. Mammals and associated parasite specimens have been collected and preserved from more than 200 field sites in eastern Russia, Alaska and northwestern Canada since 1999. Previously, fossils and taxonomic comparisons between Asia and North America mammals have shed light on these events. Molecular phylogenetics based on BCP specimens is now being used to trace the history of faunal exchange and diversification. We have found substantial phylogeographic structure in the Arctic and in Beringia in mustelid carnivores, arvicoline rodents, arctic hares and soricine shrews, including spatially concordant clades and contact zones across taxa that correspond to the edges of Beringia. Among the tapeworms of these mammalian hosts, new perspectives on diversity have also been developed. Arostrilepis horrida (Hymenolepididae) was considered to represent a single widespread and morphologically variable species occurring in a diversity of voles and lemmings in eastern and western Beringia and more broadly across the Holarctic region. The BCP has demonstrated a complex of at least 10 species that are poorly differentiated morphologically. The diversity of Paranoplocephala spp. and Anolocephaloides spp. (Anoplocephalidae) in Beringia included relatively few widespread and morphologically variable species in arvicolines

  14. LARGE CHANGES IN LOESS GEOCHEMISTRY AND HIGH LATITUDE WIND REGIMES DURING THE LAST TWO MILLION YEARS, CENTRAL ALASKA

    Science.gov (United States)

    Keskinen, M. J.; Beget, J. E.

    2009-12-01

    Ice wedge casts and thermokarst deposits near the base of 80-m-high loess cliffs at Gold Hill record a cycle of transient climate cooling and permafrost formation followed by an interval of climate warming and permafrost degradation about two million years ago (Beget et al., 2008). Ice wedge casts and thermokarst features occur below the PA tephra (ca. 2.02 myr) but formed after the Reunion paleomagnetic excursion (ca. 2.14 myr), suggesting the Alaskan cold interval was correlative with marine isotope stage 77, a time of significant global glaciation and cooling. The subsequent period of ice wedge thawing records warmer conditions, probably during marine isotope stage 76. Magnetic susceptibility profiling of the 2 MA Alaskan loess reveals glacial-interglacial cycles similar to those seen in late Pleistocene loess. However, new geochemical data from the 2 MA loess shows that it was significantly more calcareous then late Pleistocene loess and contains numerous calcareous concretions, some weighing as much as several kg. For most of the past two million years the loess geochemistry indicates winds came dominantly from the south and southwest carrying non-calcarous silts derived from glaciation of the Alaska Range, with only a minor eolian contribution from the calcareous-rich silts of the Yukon River. The calcareous loess deposits that formed 2.1 MA record eolian silt transport from the Yukon River and the calcareous Brooks Range to the north. The loess record shows that an interval characterized by a major shift in the atmospheric circulation regime from one dominated by southerly winds from the northern Pacific Ocean and Gulf of Alaska to one dominated by northerly winds from the Chuckchi Sea and western Arctic Ocean areas occurred ca. 2.1 MA. At least one additional interval of calcareous loess deposition also occurs in mid-Pleistocene time, and records another large but transient change in high latitude atmospheric circulation at ca. 0.4-0.5 MA.

  15. Design for low angle sunlight in high latitudes techniques to analyse and improve visual comfort

    Energy Technology Data Exchange (ETDEWEB)

    Evans, J.M.; Schiller, S. de [Research Centre Habitat and Energy Faculty of Architecture, Design and Urbanism, University of Buneos Aires, Capital Federal (Argentina)

    1997-12-31

    This presentation analyses the incidence of low angle sun in high latitudes of Argentina from 45 deg to 55 deg S. taking into account the solar geometry and the relative cloud cover. This low angle sun, desirable for heat gain in cold climates, can cause visual discomfort, especially in buildings such as schools, hospitals, offices with VDU screens and other situations where users have fixed working positions. Three different techniques for evaluating situations of thermal discomfort are compared: physical models with direct observation or video recordings, computer animations, and graphic techniques, taking into account the time, accuracy, and ease of comprehension of the results. The use of these methods for teaching is also considered. (orig.) 5 refs.

  16. Model of Semidiurnal Pseudo Tide in the High-Latitude Upper Mesosphere

    Science.gov (United States)

    Talaat, E. R.; Mayr, H. G.

    2011-01-01

    We present numerical results for the m = 1 meridional winds of semi diurnal oscillations in the high-latitude upper mesosphere, which are generated in the Numerical Spectral Model (NSM) without solar excitations of the tides. Identified with heuristic computer runs, the pseudo tides attain amplitudes that are, at times, as large as the non-migrating tides produced with standard solar forcing. Under the influence of parameterized gravity waves, the nonlinear NSM generates internal oscillations like the quasi-biennial oscillation, that are produced with periods favored by the dynamical properties of the system. The Coriolis force would favor at polar latitudes the excitation of the 12-hour periodicity. This oscillation may help explain the large non-migrating semidiurnal tides that are observed in the region with ground-based and satellite measurements.

  17. Analytic radiative-advective equilibrium as a model for high-latitude climate

    Science.gov (United States)

    Cronin, Timothy W.; Jansen, Malte F.

    2016-01-01

    We propose radiative-advective equilibrium as a basic-state model for the high-latitude atmosphere. Temperature profiles are determined by a competition between stabilization by atmospheric shortwave absorption and advective heat flux convergence, and destabilization by surface shortwave absorption. We derive analytic expressions for temperature profiles, assuming power law atmospheric heating profiles as a function of pressure and two-stream windowed-gray longwave radiative transfer. We discuss example profiles with and without an atmospheric window and show that the sensitivity of surface temperature to forcing depends on the nature of the forcing, with greatest sensitivity to radiative forcing by increased optical thickness and least sensitivity to increased atmospheric heat transport. These differences in sensitivity of surface temperature to forcing can be explained in terms of a forcing-dependent lapse-rate feedback.

  18. 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

    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....... 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 ... conditions. It is found that the location of the convection cell focus in this event is at least two hours earlier than those previously observed and about 5 hours earlier than that predicted by the MHD model. The observations may have some significant implications on the antiparallel merging theory....

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

    Science.gov (United States)

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

    1987-01-01

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

  20. Reconstructing atmospheric circulation over southern New Zealand: Establishment of modern westerly airflow 5500 years ago and implications for Southern Hemisphere Holocene climate change

    Science.gov (United States)

    Turney, C. S. M.; Wilmshurst, J. M.; Jones, R. T.; Wood, J. R.; Palmer, J. G.; Hogg, A. G.; Fenwick, P.; Crowley, S. F.; Privat, K.; Thomas, Z.

    2017-03-01

    Late-twentieth century changes in the intensity and migration of Southern Hemisphere westerly winds have been implicated in spatially complex variability in atmospheric and ocean circulation, and ice-sheet dynamics, across the mid- to high-latitudes. A major uncertainty, however, is whether present day hemispheric-wide symmetrical airflow is representative of past behaviour. Here we report a multi-proxy study from Stewart Island and southern Fiordland, New Zealand (46-47°S) reconstructing Holocene changes at the northern limit of westerly airflow. Increased minerogenic input and a pronounced shift in cool-loving vegetation around 5500 years ago is consistent with the establishment of westerly airflow at this latitude in the southwest Pacific. In marked contrast, stronger winds are reported further south over the subantarctic Auckland (50°S) and Campbell (52°S) Islands from 8000 years ago. Intriguingly, reconstructions from the east Pacific suggest a weakening of core westerly airflow after 8500 years ago, but an expansion along the northern limits sometime after 5500 years ago. Our results suggest similar atmospheric circulation changes have been experienced in the Pacific since 5500 years ago, but indicate an expanded network of sites is needed to comprehensively test the driver(s) and impact(s) of Holocene mid-latitude westerly winds across the Southern Hemisphere.

  1. 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

  2. Localized structure in the cusp and high-latitude ionosphere: a modelling study

    Directory of Open Access Journals (Sweden)

    H. F. Balmforth

    1999-04-01

    Full Text Available The ionospheric signature of a flux transfer event (FTE seen in EISCAT radar data has been used as the basis for a modelling study using a new numerical model of the high-latitude ionosphere developed at the University of Sheffield, UK. The evolution of structure in the high-latitude ionosphere is investigated and examined with respect to the current views of polar patch formation and development. A localized velocity enhancement, of the type associated with FTEs, is added to the plasma as it passes through the cusp. This is found to produce a region of greatly enhanced ion temperature. The new model can provide greater detail during this event as it includes anisotropic temperature calculations for the O+ ions. This illustrates the uneven partitioning of the energy during an event of this type. O+ ion temperatures are found to become increasingly anisotropic, with the perpendicular temperature being substantially larger than the parallel component during the velocity enhancement. The enhanced temperatures lead to an increase in the recombination rate, which results in an alteration of the ion concentrations. A region of decreased O+ and increased molecular ion concentration develops in the cusp. The electron temperature is less enhanced than the ions. As the new model has an upper boundary of 10 000 km the topside can also be studied in great detail. Large upward fluxes are seen to transport plasma to higher altitudes, contributing to the alteration of the ion densities. Plasma is stored in the topside ionosphere and released several hours after the FTE has finished as the flux tube convects across the polar cap. This mechanism illustrates how concentration patches can be created on the dayside and be maintained into the nightside polar cap.Key words. Ionosphere (ionosphere-magnetosphere interactions; polar ionosphere. Magnetospheric physics (magnetopause · cusp and boundary layers

  3. Inverse procedure for high-latitude ionospheric electrodynamics: Analysis of satellite-borne magnetometer data

    Science.gov (United States)

    Matsuo, Tomoko; Knipp, Delores J.; Richmond, Arthur D.; Kilcommons, Liam; Anderson, Brian J.

    2015-06-01

    This paper presents an analysis of data from the magnetometers on board the Defense Meteorological Satellite Program (DMSP) F-15, F-16, F-17, and F-18 satellites and the Iridium satellite constellation, using an inverse procedure for high-latitude ionospheric electrodynamics, during the period of 29-30 May 2010. The Iridium magnetometer data are made available through the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) program. The method presented here is built upon the assimilative mapping of ionospheric electrodynamics procedure but with a more complete treatment of the prior model uncertainty to facilitate an optimal inference of complete polar maps of electrodynamic variables from irregularly distributed observational data. The procedure can provide an objective measure of uncertainty associated with the analysis. The cross-validation analysis, in which the DMSP data are used as independent validation data sets, suggests that the procedure yields the spatial prediction of DMSP perturbation magnetic fields from AMPERE data alone with a median discrepancy of 30-50 nT. Discrepancies larger than 100 nT are seen in about 20% of total samples, whose location and magnitude are generally consistent with the previously identified discrepancy between DMSP and AMPERE data sets. Resulting field-aligned current (FAC) patterns exhibit more distinct spatial patterns without spurious high-frequency oscillatory features in comparison to the FAC products provided by AMPERE. Maps of the toroidal magnetic potential and FAC estimated from both AMPERE and DMSP data under four distinctive interplanetary magnetic field (IMF) conditions during a magnetic cloud event demonstrate the IMF control of high-latitude electrodynamics and the opportunity for future scientific investigation.

  4. High-Latitude Thermosphere Neutral Density Response to Solar Wind Dynamic Pressure Enhancement

    Science.gov (United States)

    Shi, Y.; Zesta, E.; Connor, H. K.; Su, Y.-J.; Sutton, E. K.; Huang, C. Y.; Ober, D. M.; Christodoulou, C.; Delay, S.; Oliveira, D. M.

    2017-11-01

    We examine the response of the thermosphere to the impact of solar wind dynamic pressure enhancements using observations and global magneto-hydrodynamics (MHD) simulations by the OpenGGCM model. Combining neutral density observations from the Challenging Minisatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE) satellites with simultaneous Poynting flux measurements from the Defense Meteorological Satellite Program (DMSP) F16, we find that thermospheric density as well as downward Poynting flux intensified shortly after a sudden enhancement of the solar wind dynamic pressure. The intensification manifested mostly on the dayside high-latitude region with peak intensity in the vicinity of the noon and prenoon cusp. OpenGGCM modeling results show that the ionospheric Joule heating increased abruptly in response to the sudden enhancement of the dynamic pressure in the same region as the observed Poynting flux and neutral density enhancements. The modeling results show that the enhanced Joule heating coincides, both in time and location, with the appearance of a pair of high-latitude localized field-aligned currents (FACs) in the cusp region. The FACs intensified and extended azimuthally. Coincidental with the solar wind dynamic pressure enhancement, the y component of the interplanetary magnetic field (IMF) By became strongly positive and, in addition, had some large fluctuations. We explore the separate and combined effects of the dynamic pressure and IMF By perturbations, with specifically designed simulation experiments that isolate the effect of each solar wind parameter. We find that the dynamic pressure enhancement is the primary source for the Joule heating and neutral density enhancements, but the IMF By modulates the level of enhancement.

  5. A high-latitude coral community with an uncertain future: Stetson Bank, northwestern Gulf of Mexico

    Science.gov (United States)

    DeBose, J. L.; Nuttall, M. F.; Hickerson, E. L.; Schmahl, G. P.

    2013-03-01

    Limited data exist that detail trends in benthic community composition of high-latitude coral communities. As anthropogenic stressors are projected to increase in number and intensity, long-term monitoring datasets are essential to understanding community stability and ecosystem resilience. In 1993, a long-term monitoring program was initiated at Stetson Bank, in the Gulf of Mexico. Over the course of this monitoring, a major shift in community structure occurred, in which the coral-sponge community was replaced by an algal-dominated community. During the initial years of this study, the coral community at Stetson Bank was relatively stable. Beginning in the late 1990s, sponge cover began a steady decline from over 30 % to less than 25 %. Then, in 2005, the benthic community underwent a further significant change when living coral cover declined from 30 % to less than 8 % and sponges declined to less than 20 % benthic cover. This abrupt shift corresponded with a Caribbean-wide bleaching event in 2005 that caused major mortality of Stetson Bank corals. Previous bleaching events at Stetson Bank did not result in wide-scale coral mortality. Several environmental parameters may have contributed to the rapid decline in this benthic community. We suggest that the combined effects of coastal runoff and elevated temperatures contributed to the observed shift. We present an analysis of 15 years of monitoring data spanning from 1993 to 2008; this dataset provides both a biological baseline and a multiyear trend analysis of the community structure for a high-latitude coral-sponge community in the face of changing climatic conditions.

  6. 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

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

    Directory of Open Access Journals (Sweden)

    A. Eisenhauer

    2009-01-01

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

  8. Asynchronous marine-terrestrial signals of the last deglacial warming in East Asia associated with low- and high-latitude climate changes.

    Science.gov (United States)

    Xu, Deke; Lu, Houyuan; Wu, Naiqin; Liu, Zhenxia; Li, Tiegang; Shen, Caiming; Wang, Luo

    2013-06-11

    A high-resolution multiproxy record, including pollen, foraminifera, and alkenone paleothermometry, obtained from a single core (DG9603) from the Okinawa Trough, East China Sea (ECS), provided unambiguous evidence for asynchronous climate change between the land and ocean over the past 40 ka. On land, the deglacial stage was characterized by rapid warming, as reflected by paleovegetation, and it began ca. 15 kaBP, consistent with the timing of the last deglacial warming in Greenland. However, sea surface temperature estimates from foraminifera and alkenone paleothermometry increased around 20-19 kaBP, as in the Western Pacific Warm Pool (WPWP). Sea surface temperatures in the Okinawa Trough were influenced mainly by heat transport from the tropical western Pacific Ocean by the Kuroshio Current, but the epicontinental vegetation of the ECS was influenced by atmospheric circulation linked to the northern high-latitude climate. Asynchronous terrestrial and marine signals of the last deglacial warming in East Asia were thus clearly related to ocean currents and atmospheric circulation. We argue that (i) early warming seawater of the WPWP, driven by low-latitude insolation and trade winds, moved northward via the Kuroshio Current and triggered marine warming along the ECS around 20-19 kaBP similar to that in the WPWP, and (ii) an almost complete shutdown of the Atlantic Meridional Overturning Circulation ca. 18-15 kaBP was associated with cold Heinrich stadial-1 and delayed terrestrial warming during the last deglacial warming until ca. 15 kaBP at northern high latitudes, and hence in East Asia. Terrestrial deglacial warming therefore lagged behind marine changes by ca. 3-4 ka.

  9. Observations and modeling of air quality trends over 1990-2010 across the Northern Hemisphere: China, the United States and Europe

    Science.gov (United States)

    Xing, J.; Mathur, R.; Pleim, J.; Hogrefe, C.; Gan, C.-M.; Wong, D. C.; Wei, C.; Gilliam, R.; Pouliot, G.

    2015-03-01

    Trends in air quality across the Northern Hemisphere over a 21-year period (1990-2010) were simulated using the Community Multiscale Air Quality (CMAQ) multiscale chemical transport model driven by meteorology from Weather Research and Forecasting (WRF) simulations and internally consistent historical emission inventories obtained from EDGAR. Thorough comparison with several ground observation networks mostly over Europe and North America was conducted to evaluate the model performance as well as the ability of CMAQ to reproduce the observed trends in air quality over the past 2 decades in three regions: eastern China, the continental United States and Europe. The model successfully reproduced the observed decreasing trends in SO2, NO2, 8 h O3 maxima, SO42- and elemental carbon (EC) in the US and Europe. However, the model fails to reproduce the decreasing trends in NO3- in the US, potentially pointing to uncertainties of NH3 emissions. The model failed to capture the 6-year trends of SO2 and NO2 in CN-API (China - Air Pollution Index) from 2005 to 2010, but reproduced the observed pattern of O3 trends shown in three World Data Centre for Greenhouse Gases (WDCGG) sites over eastern Asia. Due to the coarse spatial resolution employed in these calculations, predicted SO2 and NO2 concentrations are underestimated relative to all urban networks, i.e., US-AQS (US - Air Quality System; normalized mean bias (NMB) = -38% and -48%), EU-AIRBASE (European Air quality data Base; NMB = -18 and -54%) and CN-API (NMB = -36 and -68%). Conversely, at the rural network EU-EMEP (European Monitoring and Evaluation Programme), SO2 is overestimated (NMB from 4 to 150%) while NO2 is simulated well (NMB within ±15%) in all seasons. Correlations between simulated and observed O3 wintertime daily 8 h maxima (DM8) are poor compared to other seasons for all networks. Better correlation between simulated and observed SO42- was found compared to that for SO2. Underestimation of summer SO42- in

  10. 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

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

    Directory of Open Access Journals (Sweden)

    C. L. Waters

    2004-09-01

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

  12. Coverage, diversity, and functionality of a high-latitude coral community (Tatsukushi, Shikoku Island, Japan.

    Directory of Open Access Journals (Sweden)

    Vianney Denis

    Full Text Available BACKGROUND: Seawater temperature is the main factor restricting shallow-water zooxanthellate coral reefs to low latitudes. As temperatures increase, coral species and perhaps reefs may move into higher-latitude waters, increasing the chances of coral reef ecosystems surviving despite global warming. However, there is a growing need to understand the structure of these high-latitude coral communities in order to analyze their future dynamics and to detect any potential changes. METHODOLOGY/PRINCIPAL FINDINGS: The high-latitude (32.75°N community surveyed was located at Tatsukushi, Shikoku Island, Japan. Coral cover was 60±2% and was composed of 73 scleractinian species partitioned into 7 functional groups. Although only 6% of species belonged to the 'plate-like' functional group, it was the major contributor to species coverage. This was explained by the dominance of plate-like species such as Acropora hyacinthus and A. solitaryensis. Comparison with historical data suggests a relatively recent colonization/development of A. hyacinthus in this region and a potential increase in coral diversity over the last century. Low coverage of macroalgae (2% of the benthic cover contrasted with the low abundance of herbivorous fishes, but may be reasonably explained by the high density of sea urchins (12.9±3.3 individuals m⁻². CONCLUSIONS/SIGNIFICANCE: The structure and composition of this benthic community are relatively remarkable for a site where winter temperature can durably fall below the accepted limit for coral reef development. Despite limited functionalities and functional redundancy, the current benthic structure might provide a base upon which a reef could eventually develop, as characterized by opportunistic and pioneer frame-building species. In addition to increasing seawater temperatures, on-going management actions and sea urchin density might also explain the observed state of this community. A focus on such 'marginal' communities

  13. Ellesmere Island (Canada) and Northern Greenland

    Science.gov (United States)

    2002-01-01

    In late July, our planet.s northernmost land masses appear to finally be responding to the warmth of Northern Hemisphere summer. Ellesmere Island, Canada, (top left) and northern Greenland (right) have decided kick off their snowy winter garments in this true-color Moderate Resolution Imaging Spectroradiometer (MODIS) image from July 3, 200. Bare brown soils are exposed along the coasts of the still frozen (but thawing!) Arctic waters. Several large, permanent ice caps and glaciers will remain on Ellesmere Island year-round, and Greenland does little more than remove her mittens, but thinning, blue ice is showing up in the many fjords and inlets in the rocky coastlines, showing that temperatures are on the rise. The Nares Strait, which separates the two land masses, still has a way to go before a passage opens up between Baffin Bay to the south and the Artic Ocean to the north. Although Ellesmere Island appears to be 'higher' or farther north than Greenland, that is simply a result of the way the high-latitude scene was projected into an image. To better picture the terrain, imagine that you took a printed copy of the rectangular image and rolled it into a cylinder along its northeast-southwest axis. If you held that cylinder straight up in front of you, you would find that Peary Land, Greenland (right of center), is actually the more northern terrain. In fact Peary Land is the northernmost point on land on the Earth.

  14. 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.

  15. 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.

  16. Ulysses reaches maximum latitude over the Sun's northern pole

    Science.gov (United States)

    1995-08-01

    All operations and science experiments continue to go well and NASA's tracking facilities near Madrid and Goldstone, California, are monitoring the spacecraft 24 hours a day as manoeuvres are performed to keep Ulysses' radio antenna pointing toward the Earth. Launched in October 1990 aboard the space shuttle Discovery, the 370-kilogram spacecraft was designed to study the heliosphere - that region of space dominated by the solar wind -at all latitudes above and below the Sun's equatorial plane. These high latitude regions have never been explored before. Named after the legendary adventurer who journeyed to the "hidden" side of the Sun, Ulysses carries nine scientific instruments provided by research institutes in Europe and the United States to make detailed studies of solar wind, magnetic fields, energetic solar and cosmic ray particles, natural radio waves, and interplanetary dust and gas. In addition, a gamma- ray burst detector helps determine the source of the brightest cosmic gamma-ray bursts. In a permanent 6-year orbit about the Sun, the spacecraft is currently travelling at about 90,000 kilometers per hour with respect to the Sun. Having made its greatest northern excursion, Ulysses is now gradually descending in latitude. On 29 September 1995, the spacecraft will complete the northern polar pass and begin to travel back out to the orbit of Jupiter, reaching Jupiter's distance of about 800 million kilometers in April, 1998. Ulysses will then head back on its high latitude trajectory toward the Sun, returning first to the south polar regions in the year 2000, followed by a second flight over the north pole in 2001. Initial results from the climb to high northern latitudes have already confirmed a number of the findings from Ulysses' southern polar pass that took place last year. As expected, once the spacecraft moved away from the equatorial regions heading north, it became permanently immersed in fast solar wind from the northern polar cap. Another

  17. Influence of the solar flares in March 2012 on the conductivity profile of the high-latitude lower ionosphere

    Directory of Open Access Journals (Sweden)

    Lebed O. M.

    2016-03-01

    Full Text Available The ionospheric D-layer affects the electromagnetic waves propagated in the Earth – ionosphere waveguide. It is known that the propagation velocity of atmospherics – electromagnetic pulses from lightning discharge depends on the conductivity profile of the lower ionosphere. In this paper the authors have considered the influence of solar flares in March 2012 on the propagation velocity of atmospherics and thus the state of the high-latitude lower ionosphere. The possibility to estimate the conductivity profiles of the daytime ionosphere under disturbed and undisturbed geomagnetic conditions using the measurements of the propagation velocity of atmospherics along the high-latitude path has been demonstrated

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

    Science.gov (United States)

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

    2017-01-01

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

  19. Structure of high latitude currents in global magnetospheric-ionospheric models

    Science.gov (United States)

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

    2016-01-01

    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.

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

    Directory of Open Access Journals (Sweden)

    B. M. Rogers

    2013-02-01

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

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

    DEFF Research Database (Denmark)

    W. Livermore, Philip; Hollerbach, Rainer; Finlay, Chris

    2016-01-01

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

  2. Genome wide transcriptional profiling of acclimation to photoperiod in high-latitude accessions of Arabidopsis thaliana.

    Science.gov (United States)

    Lewandowska-Sabat, Anna Monika; Winge, Per; Fjellheim, Siri; Dørum, Guro; Bones, Atle Magnar; Rognli, Odd Arne

    2012-04-01

    Three Arabidopsis thaliana accessions originating from the northernmost boundary of the species distribution in Norway (59-68°N) were used to study global wide transcriptional responses to 16 and 24 h photoperiods during flower initiation. Significant analysis of microarrays (SAM), analyses of statistically overrepresented gene ontologies (GOstat) and gene set enrichment analyses (GSEA) were used to identify candidate genes and genetic pathways underlying phenotypic adaptations of accessions to different photoperiods. Statistical analyses identified 732 and 258 differentially expressed genes between accessions in 16 and 24 h photoperiod, respectively. Among significantly expressed genes, ethylene mediated signaling pathway was significantly overrepresented in 16 h photoperiod, while genes involved in response to auxin stimulus were found to be significantly overrepresented in 24 h photoperiod. Several gene sets were found to be differentially expressed among accessions, e.g. cold acclimation, dehydration response, phytochrome signaling, vernalization response and circadian clock regulated flowering time genes. These results revealed several candidate genes and pathways likely involved in transcriptional control of photoperiodic response. In particular, ethylene and auxin signaling pathway may represent candidate genes contributing to local adaptation of high-latitude accessions of A. thaliana. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

  3. The energy impacts of a new glazing technology at high latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Aschehoug, O. (Norwegian Inst. of Technology, Trondheim (NO)); Nielsen, A.F. (Norwegian Building Research Inst., Trondheim (NO))

    1991-03-01

    New developments within optical materials now offer promising window options for high latitude buildings. Superinsulated windows can be achieved with multiple glazings with low-emissivity coatings and krypton gas cavity filling; vacuum glazing; and transparent ''invisible'' aerogel cavity insulation. These technologies will potentially give U-values in the range 0.3-0.7 W/m{sup 2}K, while maintaining solar energy and daylight transmissivity comparable to conventional glazing. Also, glazings with variable properties are being developed in laboratories around the world. A research project was started in 1988 to study the energy-saving and economic potential offered by these new glazing technologies when used in Norwegian climates. In the first phase, recently finished and described here, these new types of glazing were studied as substitutes for conventional glazing in four typical situations: a single family one-storey house; an apartment in a multistorey block; a school classroom and an office module. (author).

  4. Epithermal Neutron Evidence for a Diurnal Surface Hydration Process in the Moon's High Latitudes

    Science.gov (United States)

    McClanahan, T. P.; Mitrofanov, I. G.; Boynton, W. V.; Chin, G.; Parsons, A.; Starr, R. D.; Evans, L. G.; Sanin, A.; Litvak, M.; Livengood, T.

    2015-01-01

    We report evidence from epithermal neutron flux observations that show that the Moon's high latitude surfaces are being actively hydrated, dehydrated and rehydrated in a diurnal cycle. The near-surface hydration is indicated by an enhanced suppression of the lunar epithermal neutron leakage flux on the dayside of the dawn terminator on poleward-facing slopes (PFS). At 0600 to 0800 local-time, hydrogen concentrations within the upper 1 meter of PFS are observed to be maximized relative to equivalent equator-facing slopes (EFS). During the lunar day surface hydrogen concentrations diminish towards dusk and then rebuild overnight. Surface hydration is determined by differential comparison of the averaged EFS to PFS epithermal neutron count rates above +/- 75 deg latitude. At dawn the contrast bias towards PFS is consistent with at least 15 to 25 parts-per-million (ppm) hydrogen that dissipates by dusk. We review several lines of evidence derived from temperature and epithermal neutron data by a correlated analysis of observations from the Lunar Reconnaissance Orbiter's (LRO) Lunar Exploration Neutron Detector (LEND) that were mapped as a function of lunar local-time, Lunar Observing Laser Altimeter (LOLA) topography and Diviner (DLRE) surface temperature.

  5. 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 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.

  6. 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.

  7. 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.

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

    Science.gov (United States)

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

    2016-12-01

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

  9. 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.

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

    Directory of Open Access Journals (Sweden)

    A. W. Wernik

    1996-01-01

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

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

    Directory of Open Access Journals (Sweden)

    D. W. Idenden

    1998-08-01

    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

  12. Synergies between climate and management for Atlantic cod fisheries at high latitudes.

    Science.gov (United States)

    Kjesbu, Olav Sigurd; Bogstad, Bjarte; Devine, Jennifer A; Gjøsæter, Harald; Howell, Daniel; Ingvaldsen, Randi B; Nash, Richard D M; Skjæraasen, Jon Egil

    2014-03-04

    The widespread depletion of commercially exploited marine living resources is often seen as a general failure of management and results in criticism of contemporary management procedures. When populations show dramatic and positive changes in population size, this invariably leads to questions about whether favorable climatic conditions or good management (or both) were responsible. The Barents Sea cod (Gadus morhua) stock has recently increased markedly and the spawning stock biomass is now at an unprecedented high. We identify the crucial social and environmental factors that made this unique growth possible. The relationship between vital rates of Barents Sea cod stock productivity (recruitment, growth, and mortality) and environment is investigated, followed by simulations of population size under different management scenarios. We show that the recent sustained reduction in fishing mortality, facilitated by the implementation of a "harvest control rule," was essential to the increase in population size. Simulations show that a drastic reduction in fishing mortality has resulted in a doubling of the total population biomass compared with that expected under the former management regime. However, management alone was not solely responsible. We document that prevailing climate, operating through several mechanistic links, positively reinforced management actions. Heightened temperature resulted in an increase in the extent of the suitable feeding area for Barents Sea cod, likely offering a release from density-dependent effects (for example, food competition and cannibalism) through prolonged overlap with prey and improved adult stock productivity. Management and climate may thus interact to give a positive outlook for exploited high-latitude marine resources.

  13. 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.)

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

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    1999-07-01

    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

  15. 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.

  16. Saturn's UV aurora: the (high latitude) point of view of Cassini (Invited)

    Science.gov (United States)

    Grodent, D. C.; Bonfond, B.; Gustin, J.; Radioti, A.; Gerard, J. M.; Pryor, W. R.

    2013-12-01

    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 far with the UVIS camera on board Cassini. In particular we will link the morphology of the aurora with specific magnetospheric processes, such as dayside reconnection and auroral bifurcations, nightside reconnection, hot plasma injections. We will also take advantage of the view from nearly above the poles to describe the overall shape and size of the aurora, which are expected to respond to the solar wind conditions. Moreover, this presentation will focus on small-scale features, which can only be observed by an instrument close enough to the planet. We will also present movies of these observations, allowing us to explore the auroral dynamics at various timescales. This information will be used to identify the various mechanisms at play in Saturn's magnetosphere.

  17. 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

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

    Science.gov (United States)

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

    2017-10-01

    Pesticide loadings to watersheds increase during agricultural development and may vary in accordance with different crop types and seasons. High pesticide loadings can potentially result in polluted stream water. The objective of this study was to determine the pesticide loadings and concentrations of three typical pesticides (atrazine, oxadiazon, and isoprothiolane) in river water from a middle-high latitude agricultural watershed in northern China. During this study, we evaluated the watershed pesticide loss patterns for two crop types over three decades. For this purpose, we integrated data from field investigations, laboratory experiments, and modeling simulations involving a distributed hydrological solute transport model (Soil and Water Assessment Tool, SWAT). SWAT was employed to compare the temporal-spatial fate and behaviors of atrazine, oxadiazon, and isoprothiolane from 1990 to 2014 in a watershed area amounting to 141.5 km2. The results showed that the three pesticides could be detected at different locations throughout the watershed, and isoprothiolane was detected at the maximum value of 1.082 μg/L in surface runoff of paddy land. The temporal trend for the yearly loading of atrazine decreased slightly over time, but the trends for oxadiazon and isoprothiolane increased markedly over an 18-year analysis period. In regard to the pesticide concentrations in water, atrazine was associated with the largest value of nearly 1.4 μg/L. July and August were the found to be prime periods for pesticide loss from paddy land, and the biggest monthly loss of atrazine from dryland appeared in June. Under similar usage conditions, isoprothiolane loading from paddy fields ranked as the largest one among the three types of pesticides and reached up to 17 g/ha. Limited monitoring data were useful for validating the model, which yielded valuable temporal-spatial data on the fate of pesticides in this watershed. With the expansion of paddy rice cultivation, risks

  19. Annotated bibliography on soil erosion and erosion control in subarctic and high-latitude regions of North America.

    Science.gov (United States)

    C.W. Slaughter; J.W. Aldrich

    1989-01-01

    This annotated bibliography emphasizes the physical processes of upland soil erosion, prediction of soil erosion and sediment yield, and erosion control. The bibliography is divided into two sections: (1) references specific to Alaska, the Arctic and subarctic, and similar high-latitude settings; and (2) references relevant to understanding erosion, sediment production...

  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 di...

  1. Landscape influences on climate-related lake shrinkage at high latitudes

    Science.gov (United States)

    Roach, Jennifer K.; Griffith, Brad; Verbyla, David

    2013-01-01

    Climate-related declines in lake area have been identified across circumpolar regions and have been characterized by substantial spatial heterogeneity. An improved understanding of the mechanisms underlying lake area trends is necessary to predict where change is most likely to occur and to identify implications for high latitude reservoirs of carbon. Here, using a population of ca. 2300 lakes with statistically significant increasing and decreasing lake area trends spanning longitudinal and latitudinal gradients of ca. 1000 km in Alaska, we present evidence for a mechanism of lake area decline that involves the loss of surface water to groundwater systems. We show that lakes with significant declines in lake area were more likely to be located: (1) in burned areas; (2) on coarser, well-drained soils; and (3) farther from rivers compared to lakes that were increasing. These results indicate that postfire processes such as permafrost degradation, which also results from a warming climate, may promote lake drainage, particularly in coarse-textured soils and farther from rivers where overland flooding is less likely and downslope flow paths and negative hydraulic gradients between surface water and groundwater systems are more common. Movement of surface water to groundwater systems may lead to a deepening of subsurface flow paths and longer hydraulic residence time which has been linked to increased soil respiration and CO2 release to the atmosphere. By quantifying relationships between statewide coarse resolution maps of landscape characteristics and spatially heterogeneous responses of lakes to environmental change, we provide a means to identify at-risk lakes and landscapes and plan for a changing climate.

  2. Probe experiment characterizing 30-MHz radio wave scatter in the high-latitude ionosphere

    Science.gov (United States)

    Nishino, M.; Gorokhov, N.; Tanaka, Y.; Yamagishi, H.; Hansen, T.

    1999-07-01

    A probe experiment, consisting of radio links between a common 30-MHz transmitter located at Murmansk, Russia, and two receivers used as the imaging riometer (two-dimensional 64 multiple-beam antenna) located at Ny Ålesund, Svalbard, and Tjornes, Iceland, was carried out to characterize wave scatter in the high-latitude ionosphere. They are nearly aligned with and perpendicular to the geomagnetic meridian, respectively. In experiments conducted in March-April 1994, the 30-MHz probe signals were identified at nighttime more frequently than during the day at both receiver stations during periods of increased geomagnetic activity near the path midpoints, indicating that a relationship between the propagation path and the location of the auroral oval controls signal identification. For the nighttime propagation paths within or crossing through the auroral oval, duty cycles of the probe signals were roughly correlated with increases in geomagnetic activity. Their arrival directions showed a spread with a dominant power on the low elevation and a normal distribution in azimuth. These results indicate that the probe signals are characterized as nonmeteoric "auroral E" scatter caused by irregular, large-scale profiles of electron density enhancements at the lower edge of the ionosphere. However, on 2 days of weak geomagnetic activity, strong probe signals with bursty behavior were identified by an extremely high duty cycle (˜98%) for the nighttime meridian path only, and their arrival directions showed an isotropic spread in azimuth. Such nonmeteoric probe signals are characterized as "coherent" scatter caused by small-scale (˜5 m) field-aligned irregularities in electron density in the E region ionosphere, related to "sporadic E" occurrence.

  3. 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.

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

    Science.gov (United States)

    Derryberry, Elizabeth P

    2017-10-01

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

  5. O+ and H+ ion heat fluxes at high altitudes and high latitudes

    Directory of Open Access Journals (Sweden)

    I. A. Barghouthi

    2014-08-01

    Full Text Available Higher order moments, e.g., perpendicular and parallel heat fluxes, are related to non-Maxwellian plasma distributions. Such distributions are common when the plasma environment is not collision dominated. In the polar wind and auroral regions, the ion outflow is collisionless at altitudes above about 1.2 RE geocentric. In these regions wave–particle interaction is the primary acceleration mechanism of outflowing ionospheric origin ions. We present the altitude profiles of actual and "thermalized" heat fluxes for major ion species in the collisionless region by using the Barghouthi model. By comparing the actual and "thermalized" heat fluxes, we can see whether the heat flux corresponds to a small perturbation of an approximately bi-Maxwellian distribution (actual heat flux is small compared to "thermalized" heat flux, or whether it represents a significant deviation (actual heat flux equal or larger than "thermalized" heat flux. The model takes into account ion heating due to wave–particle interactions as well as the effects of gravity, ambipolar electric field, and divergence of geomagnetic field lines. In the discussion of the ion heat fluxes, we find that (1 the role of the ions located in the energetic tail of the ion velocity distribution function is very significant and has to be taken into consideration when modeling the ion heat flux at high altitudes and high latitudes; (2 at times the parallel and perpendicular heat fluxes have different signs at the same altitude. This indicates that the parallel and perpendicular parts of the ion energy are being transported in opposite directions. This behavior is the result of many competing processes; (3 we identify altitude regions where the actual heat flux is small as compared to the "thermalized" heat flux. In such regions we expect transport equation solutions based on perturbations of bi-Maxwellian distributions to be applicable. This is true for large altitude intervals for protons

  6. High Latitude Epipelagic and Mesopelagic Scattering Layers—A Reference for Future Arctic Ecosystem Change

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    Tor Knutsen

    2017-11-01

    Full Text Available Scattering structures, including deep (>200 m scattering layers are common in most oceans, but have not previously been properly documented in the Arctic Ocean. In this work, we combine acoustic data for distribution and abundance estimation of zooplankton and fish with biological sampling from the region west and north of Svalbard, to examine high latitude meso- and epipelagic scattering layers and their biological constituents. Our results show that typically, there was strong patchy scattering in the upper part of the epipelagic zone (<50 m throughout the area. It was mainly dominated by copepods, krill, and amphipods in addition to 0-group fish that were particularly abundant west of the Spitsbergen Archipelago. Off-shelf there was a distinct deep scattering layer (DSL between 250 and 600 m containing a range of larger longer lived organisms (mesopelagic fish and macrozooplankton. In eastern Fram Strait, the DSL also included and was in fact dominated by larger fish close to the shelf/slope break that were associated with Warm Atlantic Water moving north toward the Arctic Ocean, but switched to dominance by species having weaker scattering signatures further offshore. The Weighted Mean Depths of the DSL were deeper (WMD > 440 m in the Arctic habitat north of Svalbard compared to those south in the Fram Strait west of Svalbard (WMD ~400 m. The surface integrated backscatter [Nautical Area-Scattering Coefficient, NASC, sA (m2 nmi−2] was considerably lower in the waters around Svalbard compared to the more southern regions (62–69°N. Also, the integrated DSL nautical area scattering coefficient was a factor of ~6–10 lower around Svalbard compared to the areas in the south-eastern part of the Norwegian Sea ~62°30′N. The documented patterns and structures, particularly the DSL and its constituents, will be key reference points for understanding and quantifying future changes in the pelagic ecosystem at the entrance to the Arctic Ocean.

  7. 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.

  8. 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

  9. Complexity in the high latitude HF radar spectral width boundary region

    Directory of Open Access Journals (Sweden)

    M. L. Parkinson

    20