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United States Department of Agriculture

Agricultural Research Service

Title: A sensitivity study of daytime net radiation during snowmelt to forest canopy and atmospheric conditions

Authors
item Sicart, Jean - UNIV OF WALES
item Pomeroy, John - UNIV OF SASKATCHEWAN
item Essery, Richard - UNIV OF WALES
item Hardy, Janet - US ARMY ERDC
item Link, Timothy - UNIV OF IDAHO
item Marks, Daniel

Submitted to: Journal of Hydrometeorology
Publication Type: Abstract Only
Publication Acceptance Date: July 20, 2004
Publication Date: July 20, 2004
Citation: Sicart, J.E., Pomeroy, J.W., Essery, Richard, Hardy, J., Link, T., and Marks, Danny. Journal of Hydrometeorology - Special Section 2004, A sensitivity study of daytime net radiation during snowmelt to forest canopy and atmospheric conditions, abstract: vol 5, pp 774-784.

Technical Abstract: This study investigates the dependence of net radiation at snow surfaces under forest canopies on the overlying canopy density. The daily sum of positive values of net radiation is used as an index of the snowmelt rate. Canopy cover is represented in terms of short-wave transmissivity and sky view factor. The cases studied are a spruce forest in the Wolf Creek basin, Yukon Territory, Canada, and a pine forest near Fraser, Colorado, USA. Of particular interest are the atmospheric conditions that favor an offset between short-wave energy attenuation and long-wave irradiance enhancement by the canopy, such that net radiation does not decrease with increasing forest density. Such an offset is favored in dry climates and at high altitudes, where atmospheric emissivities are low, and in early spring when snow albedos are high and solar elevations are low. For low snow albedos, a steady decrease in snowmelt energy with increasing canopy cover is found, up to a forest density close to the actual densities of mature spruce forests. Snowmelt rates for high albedos are either insensitive or increase with increasing canopy cover. At both sites, foliage area indices close to 2 are associated with a minimum in net radiation, independent of snow albedo or cloud cover. However, these results are more uncertain for open forests because solar heating of trees may invalidate the long-wave assumptions, increasing the long-wave irradiance.

Last Modified: 10/26/2014
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