The thermoinsulation effect of snow cover within a climate model |
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| Authors: | Benjamin I Cook Gordon B Bonan Samuel Levis Howard E Epstein |
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| Institution: | (1) Lamont Doherty Earth Observatory, Ocean and Climate Physics, 61 Route 9W, PO Box 1000, Palisades, NY 10964-8000, USA;(2) NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA;(3) National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80307-3000, USA;(4) National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80307-3000, USA;(5) Department of Environmental Sciences, University of Virginia, 291 McCormick Road, Charlottesville, VA 22903, USA |
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| Abstract: | We use a state of the art climate model (CAM3–CLM3) to investigate the sensitivity of surface climate and land surface processes
to treatments of snow thermal conductivity. In the first set of experiments, the thermal conductivity of snow at each grid
cell is set to that of the underlying soil (SC-SOIL), effectively eliminating any insulation effect. This scenario is compared
against a control run (CTRL), where snow thermal conductivity is determined as a prognostic function of snow density. In the
second set of experiments, high (SC-HI) and low (SC-LO) thermal conductivity values for snow are prescribed, based on upper
and lower observed limits. These two scenarios are used to envelop model sensitivity to the range of realistic observed thermal
conductivities. In both sets of experiments, the high conductivity/low insulation cases show increased heat exchange, with
anomalous heat fluxes from the soil to the atmosphere during the winter and from the atmosphere to the soil during the summer. The increase in surface heat exchange leads to soil cooling of up to 20 K in the winter, anomalies that
persist (though damped) into the summer season. The heat exchange also drives an asymmetric seasonal response in near-surface
air temperatures, with boreal winter anomalies of +6 K and boreal summer anomalies of −2 K. On an annual basis there is a
net loss of heat from the soil and increases in ground ice, leading to reductions in infiltration, evapotranspiration, and
photosynthesis. Our results show land surface processes and the surface climate within CAM3–CLM3 are sensitive to the treatment
of snow thermal conductivity. |
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| Keywords: | Snow cover Snow thermal conductivity Climate model sensitivity Soil/atmosphere exchange Permafrost |
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