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  • 1
    Electronic Resource
    Electronic Resource
    Application of theE-ε turbulence closure model to separated atmospheric surface-layer flows (1993)
    Springer
    Boundary layer meteorology 66 (1993), S. 281-301 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Neutrally buoyant atmospheric surface-layer flow over a thin vertical wall has been studied using a turbulence closure scheme designed specifically to address flow problems containing high shears. The turbulent flow model consists of a general solution of the time averaged, steady state, twodimensional Navier-Stokes equations, where theE-ε turbulence model has been used to close the system of equations. Model output compares favorably with measurements made in both a full-scale field study and in an atmospheric wind tunnel. In the simulation of flow over a solid wall, two recirculation eddies are produced. The smallest eddy is located windward of the wall with a separation point located atx/h=−0.8, and the largest is located in the lee of the wall atx/h=5.8. Immediately downwind of the wall top, the turbulent kinetic energy, the energy dissipation rate, and the momentum flux all reach a local maximum. These peak values generally maintain their height positionz/h=1.0, but decrease progressively downwind. The turbulent viscosity is strongly modified under the influence of the wall, with a local maximum forming in the lee of the wall top, and a local minimum forming at a heightz/h=2.0 above the lee recirculation eddy. The surface momentum flux reduction due to the presence of the wall begins atx/h=−10.0. Minimum zero fluxes occur at the surface separation points, and a local peak in momentum flux is produced at the centers of each recirculation eddy. Downwind of the wall, the modeled surface flux reaches an equilibrium at roughlyx/h=30.0.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705479
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  • 2
    Electronic Resource
    Electronic Resource
    A Climate Version of the Regional Atmospheric Modeling System (2000)
    Springer
    Theoretical and applied climatology 66 (2000), S. 29-47 
    Details
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary The Regional Atmospheric Modeling System (RAMS) has been widely used to simulate relatively short-term atmospheric processes. To perform full-year to multi-year model integrations, a climate version of RAMS (ClimRAMS) has been developed, and is used to simulate diurnal, seasonal, and annual cycles of atmospheric and hydrologic variables and interactions within the central United States during 1989. The model simulation uses a 200-km grid covering the conterminous United States, and a nested, 50-km grid covering the Great Plains and Rocky Mountain states of Kansas, Nebraska, South Dakota, Wyoming, and Colorado. The model’s lateral boundary conditions are forced by six-hourly NCEP reanalysis products. ClimRAMS includes simplified precipitation and radiation sub-models, and representations that describe the seasonal evolution of vegetation-related parameters. In addition, ClimRAMS can use all of the general RAMS capabilities, like its more complex radiation sub-models, and explicit cloud and precipitation microphysics schemes. Thus, together with its nonhydrostatic and fully-interactive telescoping-grid capabilities, ClimRAMS can be applied to a wide variety of problems. Because of non-linear interactions between the land surface and atmosphere, simulating the observed climate requires simulating the observed diurnal, synoptic, and seasonal cycles. While previous regional climate modeling studies have demonstrated their ability to simulate the seasonal cycles through comparison with observed monthly-mean temperature and precipitation data sets, this study demonstrates that a regional climate model can also capture observed diurnal and synoptic variability. Observed values of daily precipitation and maximum and minimum screen-height air temperature are used to demonstrate this ability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007040070031
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  • 3
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    Climate-driven fluctuations in freshwater flux to Sermilik Fjord, East Greenland, during the last 4000 years (2012)
    Sage
    In: Holocene
    Details
    Publication Date: 2012-01-04
    Description: The freshwater runoff from the glaciated and snow-covered Sermilik Fjord catchment, SE Greenland, was estimated at annual resolution for the period 1900–2008 and at decadal resolution for the past four millennia. Our simulations were forced with available meteorological station data (1900–2008) and Greenland ice core estimated temperature data (1899 bc – ad 1980) from Dye3 and GISP2. Time series of estimated ice discharge (2000–2009) for the three major outlet glaciers Helheim, Fenris, and Midgård indicate that 53–74% of the ice discharge variations could be explained by variations in areally averaged glacier terminus surface (supraglacial) runoff. Based on these data and together with calculated subglacial geothermal and frictional melting as well as net precipitation for the fjord area, the Sermilik Fjord freshwater flux was deduced for the period 1900–2008. Our simulations indicated that during the last century surface freshwater runoff has equaled 13% of the Sermilik Fjord average freshwater flux of 33.0±5.7 x 10 9 m 3 /yr, covering a periodic runoff variation of 20 years. Ice discharge has accounted for 81%, with 63% of the freshwater flux originated from the Helheim glacier. This indicates that the Helheim outlet glacier plays a dominant role as a freshwater source to both Sermilik Fjord and ultimately the Irminger Sea. For the palaeorecords of the last 4000 years, simulated surface runoff has averaged 4.4±0.2 x 10 9 m 3 /yr. A very weak decreasing trend in runoff over the last 4 k years (1899 bc – ad 1980) is presumably associated with the general insolation-generated Northern Hemisphere cooling since the Holocene Thermal Maximum. Our simulations furthermore indicated centennial- to submillennial-scale variations in surface runoff concurrent with the well-known climate episodes such as the ‘Roman Warm Period’, the ‘Dark Ages Cold Period’, the ‘Medieval Climate Anomaly’, and the ‘Little Ice Age’. During the ‘Little Ice Age’, e.g., the average surface runoff was about 0.7 x 10 9 m 3 /yr lower than today, while the increase in runoff for the Modern Warming, since the late 1800s, was the second strongest and fastest for the last 4 k years.
    Print ISSN: 0959-6836
    Electronic ISSN: 1477-0911
    Topics: Geography , Geosciences
    Published by Sage
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  • 4
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    Spatial-Temporal Variability in Turbulent Fluxes during Spring Snowmelt (2006)
    Taylor & Francis
    Details
    Publication Date: 2006-02-01
    Print ISSN: 1523-0430
    Electronic ISSN: 1938-4246
    Topics: Geography , Geosciences
    Published by Taylor & Francis
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  • 5
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    Application of theE-? turbulence closure model to separated atmospheric surface-layer flows (1993)
    Springer
    Details
    Publication Date: 1993-11-01
    Print ISSN: 0006-8314
    Electronic ISSN: 1573-1472
    Topics: Geosciences , Physics
    Published by Springer
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  • 6
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    RAMS 2001: Current status and future directions (2003)
    Springer
    Details
    Publication Date: 2003-01-01
    Print ISSN: 0177-7971
    Electronic ISSN: 1436-5065
    Topics: Geography , Physics
    Published by Springer
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  • 7
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    Representing Variability in Subgrid Snow Cover and Snow Depth in a Global Land Model: Offline Validation (2014)
    American Meteorological Society
    Details
    Publication Date: 2014-04-23
    Description: Subgrid snow cover is one of the key parameters in global land models since snow cover has large impacts on the surface energy and moisture budgets, and hence the surface temperature. In this study, the Subgrid Snow Distribution (SSNOWD) snow cover parameterization was incorporated into the Minimal Advanced Treatments of Surface Interaction and Runoff (MATSIRO) land surface model. SSNOWD assumes that the subgrid snow water equivalent (SWE) distribution follows a lognormal distribution function, and its parameters are physically derived from geoclimatic information. Two 29-yr global offline simulations, with and without SSNOWD, were performed while forced with the Japanese 25-yr Reanalysis (JRA-25) dataset combined with an observed precipitation dataset. The simulated spatial patterns of mean monthly snow cover fraction were compared with satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) observations. The snow cover fraction was improved by the inclusion of SSNOWD, particularly for the accumulation season and/or regions with relatively small amounts of snowfall; snow cover fraction was typically underestimated in the simulation without SSNOWD. In the Northern Hemisphere, the daily snow-covered area was validated using Interactive Multisensor Snow and Ice Mapping System (IMS) snow analysis datasets. In the simulation with SSNOWD, snow-covered area largely agreed with the IMS snow analysis and the seasonal cycle in the Northern Hemisphere was improved. This was because SSNOWD formulates the snow cover fraction differently for the accumulation season and ablation season, and represents the hysteresis of the snow cover fraction between different seasons. The effects of including SSNOWD on hydrological properties and snow mass were also examined.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 8
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    Future permafrost conditions along environmental gradients in Zackenberg, Greenland (2014)
    Copernicus
    Details
    Publication Date: 2014-07-16
    Description: The future development of ground temperatures in permafrost areas is determined by a number of factors varying on different spatial and temporal scales. For sound projections of impacts of permafrost thaw, scaling procedures are of paramount importance. We present numerical simulations of present and future ground temperatures at 10 m resolution for a 4 km long transect across the lower Zackenberg valley in NE Greenland. The results are based on stepwise downscaling of General Circulation Model-derived future projections using observational data, snow redistribution modeling, remote sensing data and a ground thermal model. Comparison to in-situ measurements of thaw depths at two CALM sites and 10 m ground temperatures in two boreholes suggest agreement within 0.10 m for the maximum thaw depth and 1°C for annual average ground temperature. Until 2100, modeled ground temperatures at 10 m depth warm by about 5° and the active layer thickness increases by about 30%, in conjunction with a warming of average near-surface summer soil temperatures by 2°. While permafrost remains thermally stable until 2100 in most model grid cells, the thaw threshold is exceeded for a few model years and grid cells at the end of this century. The ensemble of all 10 m model grid cells highlights the significant spatial variability of the ground thermal regime which is not accessible in traditional coarse-scale modeling approaches.
    Print ISSN: 1994-0432
    Electronic ISSN: 1994-0440
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 9
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    High resolution modelling of snow transport in complex terrain using simulated wind fields (2008)
    Copernicus
    Details
    Publication Date: 2008-07-11
    Description: Snow transport is one of the most dominant processes influencing the snow cover accumulation and ablation in high alpine mountain environments. Hence, the spatial and temporal variability of the snow cover is significantly modified with respective consequences on the total amount of water in the snow pack, on the temporal dynamics of the runoff and on the energy balance of the surface. For the presented study we used the snow transport model SnowTran-3D in combination with MM5 (Penn State University – National Center for Atmospheric Research MM5 model) generated wind fields. In a first step the MM5 wind fields were downscaled by using a semi-empirical approach which accounts for the elevation difference of model and real topography, as well as aspect, inclination and vegetation. The target resolution of 30 m corresponds to the resolution of the best available DEM and land cover map. For the numerical modelling, data of six automatic meteorological stations were used, comprising the winter season (September–August) of 2003/04 and 2004/05. In addition we had automatic snow depth measurements and periodic manual measurements of snow courses available for the validation of the results. In this paper we describe the downscaling of the wind fields and discuss the results of the snow transport simulations with respect to the measurements and remotely sensed data.
    Print ISSN: 1994-0432
    Electronic ISSN: 1994-0440
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 10
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    High resolution modelling of snow transport in complex terrain using downscaled MM5 wind fields (2010)
    Copernicus
    Details
    Publication Date: 2010-02-05
    Description: Snow transport is one of the most dominant processes influencing the snow cover accumulation and ablation in high mountain environments. Hence, the spatial and temporal variability of the snow cover is significantly modified with respective consequences on the total amount of water in the snow pack, on the temporal dynamics of the runoff and on the energy balance of the surface. For the present study we used the snow transport model SnowModel in combination with MM5 (Penn State University – National Center for Atmospheric Research MM5 model) generated wind fields. In a first step the MM5 wind fields were downscaled by using a semi-empirical approach which accounts for the elevation difference of model and real topography, and vegetation. The target resolution of 30 m corresponds to the resolution of the best available DEM and land cover map of the test site Berchtesgaden National Park. For the numerical modelling, data of six automatic meteorological stations were used, comprising the winter season (September–August) of 2003/04 and 2004/05. In addition we had automatic snow depth measurements and periodic manual measurements of snow courses available for the validation of the results. It could be shown that the model performance of SnowModel could be improved by using downscaled MM5 wind fields for the test site. Furthermore, it was shown that an estimation of snow transport from surrounding areas to glaciers becomes possible by using downscaled MM5 wind fields.
    Print ISSN: 1994-0416
    Electronic ISSN: 1994-0424
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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