The Local Surface Energy Balance and Subsurface Temperature Regime in Antarctica

Thomas W. Schlatter Notional Center for Atmospheric Research, Boulder, Colo., and St. Louis University, St. Louis, Mo.

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Abstract

The physical processes occurring within a perennial snow cover and at its surface are discussed with particular emphasis on monthly variations in Antarctic snow. Results of a one-year simulation of physical processes In snow are compared with 1958 data at Mirny and Pionerskaya, Antarctica. The simulation demonstrates the following: first, solar radiation is effective to a depth of 50 cm or so, but longwave radiation cools the surface alone, causing the “greenhouse” effect first observed in snow at least four decades ago. Highest summertime temperature and initial snowmelt thus occur not at the surface but roughly 10 cm below It. Second, the percolation of meltwater with eventual refreezing during the subsequent winter is the most efficient mechanism for modifying the temperature profile at depths of several meters of more. Third, concerning the surface energy budget, at temperatures below −20C, atmospheric sensible heat flux approximately compensates net radiation throughout the year. When the temperature nears 0C (only in summer), the surplus of net radiation Is used primarily for changes of phase—sublimation and possibly melting; little energy is used to heat the snow. Then latent beat flux approximately compensates net radiation.

Abstract

The physical processes occurring within a perennial snow cover and at its surface are discussed with particular emphasis on monthly variations in Antarctic snow. Results of a one-year simulation of physical processes In snow are compared with 1958 data at Mirny and Pionerskaya, Antarctica. The simulation demonstrates the following: first, solar radiation is effective to a depth of 50 cm or so, but longwave radiation cools the surface alone, causing the “greenhouse” effect first observed in snow at least four decades ago. Highest summertime temperature and initial snowmelt thus occur not at the surface but roughly 10 cm below It. Second, the percolation of meltwater with eventual refreezing during the subsequent winter is the most efficient mechanism for modifying the temperature profile at depths of several meters of more. Third, concerning the surface energy budget, at temperatures below −20C, atmospheric sensible heat flux approximately compensates net radiation throughout the year. When the temperature nears 0C (only in summer), the surplus of net radiation Is used primarily for changes of phase—sublimation and possibly melting; little energy is used to heat the snow. Then latent beat flux approximately compensates net radiation.

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