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  • 1
    Electronic Resource
    Electronic Resource
    Meltwater production in Antarctic blue-ice areas: sensitivity to changes in atmospheric forcing (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Polar research 18 (1999), S. 0 
    Details
    ISSN: 1751-8369
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Geosciences
    Notes: In the near coastal regions of Dronning Maud Land, Antarctica, below-surface ice-melt in blue-ice areas has been observed. The low scattering coefficients of the large-grained blue-ice allow penetration of solar radiation, thus providing an energy source below the ice surface. The sub-surface meltwater is significant enough to show up on remote-sensing imagery in the form of ice-covered lakes. Adjacent snow-accumulation areas have much higher scattering coefficients and consequently limit solar radiation penetration in these regions. These snow and ice surfaces are generally below freezing, and little surface melting occurs. To assess the response of these melt features to changes in atmospheric forcings such as cloudiness, air temperature, and snow accumulation, a physically-based model of the coupled atmosphere, radiation, snow, and blue-ice system has been developed. The model consists of a heat transfer equation with a spectrally-dependent solar-radiation source term. The penetration of radiation into the snow and blue-ice depends on the surface albedo, and the snow and blue-ice grain size and density. Model simulations show that ice melt occurring in this area is sensitive to potential variations in atmospheric forcing. Under certain conditions more traditional surface melting occurs and, under other conditions, the existing melt processes can be shut down completely. In light of the sensitivity of this system to variations in atmospheric forcing, and the ability to view melt-related features using remote sensing, a tool exists to efficiently monitor variations in Antarctic coastal climate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1751-8369.1999.tb00305.x
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  • 2
    Electronic Resource
    Electronic Resource
    Modelled changes in arctic tundra snow, energy and moisture fluxes due to increased shrubs (2002)
    Oxford, UK : Blackwell Science, Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: In arctic tundra, shrubs can significantly modify the distribution and physical characteristics of snow, influencing the exchanges of energy and moisture between terrestrial ecosystems and the atmosphere from winter into the growing season. These interactions were studied using a spatially distributed, physically based modelling system that represents key components of the land–atmosphere system. Simulations were run for 4 years, over a 4-km2 tundra domain located in arctic Alaska. A shrub increase was simulated by replacing the observed moist-tundra and wet-tundra vegetation classes with shrub-tundra; a procedure that modified 77% of the simulation domain. The remaining 23% of the domain, primarily ridge tops, was left as the observed dry-tundra vegetation class. The shrub enhancement increased the averaged snow depth of the domain by 14%, decreased blowing-snow sublimation fluxes by 68%, and increased the snowcover's thermal resistance by 15%. The shrub increase also caused significant changes in snow-depth distribution patterns; the shrub-enhanced areas had deeper snow, and the non-modified areas had less snow. This snow-distribution change influenced the timing and magnitude of all surface energy-balance components during snowmelt. The modified snow distributions also affected meltwater fluxes, leading to greater meltwater production late in the melt season. For a region with an annual snow-free period of approximately 90 days, the snow-covered period decreased by 11 days on the ridges and increased by 5 days in the shrub-enhanced areas. Arctic shrub increases impact the spatial coupling of climatically important snow, energy and moisture interactions by producing changes in both shrub-enhanced and non-modified areas. In addition, the temporal coupling of the climate system was modified when additional moisture held within the snowcover, because of less winter sublimation, was released as snowmelt in the spring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1354-1013.2001.00416.x
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  • 3
    Electronic Resource
    Electronic Resource
    Land–atmosphere energy exchange in Arctic tundra and boreal forest: available data and feedbacks to climate (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Global change biology 6 (2000), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This paper summarizes and analyses available data on the surface energy balance of Arctic tundra and boreal forest. The complex interactions between ecosystems and their surface energy balance are also examined, including climatically induced shifts in ecosystem type that might amplify or reduce the effects of potential climatic change.High latitudes are characterized by large annual changes in solar input. Albedo decreases strongly from winter, when the surface is snow-covered, to summer, especially in nonforested regions such as Arctic tundra and boreal wetlands. Evapotranspiration (QE) of high-latitude ecosystems is less than from a freely evaporating surface and decreases late in the season, when soil moisture declines, indicating stomatal control over QE, particularly in evergreen forests. Evergreen conifer forests have a canopy conductance half that of deciduous forests and consequently lower QE and higher sensible heat flux (QH). There is a broad overlap in energy partitioning between Arctic and boreal ecosystems, although Arctic ecosystems and light taiga generally have higher ground heat flux because there is less leaf and stem area to shade the ground surface, and the thermal gradient from the surface to permafrost is steeper.Permafrost creates a strong heat sink in summer that reduces surface temperature and therefore heat flux to the atmosphere. Loss of permafrost would therefore amplify climatic warming. If warming caused an increase in productivity and leaf area, or fire caused a shift from evergreen to deciduous forest, this would increase QE and reduce QH. Potential future shifts in vegetation would have varying climate feedbacks, with largest effects caused by shifts from boreal conifer to shrubland or deciduous forest (or vice versa) and from Arctic coastal to wet tundra. An increase of logging activity in the boreal forests appears to reduce QE by roughly 50% with little change in QH, while the ground heat flux is strongly enhanced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.06015.x
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    Paper (German National Licenses)
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