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Title: Thermodynamic studies of a snow cover in northern Michigan : analysis of micrometeorological and related snow and soil data from the Keweenaw Field Station
Authors: Portman, Donald J., 1922-
Ryznar, Edward
Keywords: Snow
Snow physics
Snow mechanics
Heat transfer
Heat transmission
Air temperature
Radiation absorption
Solar radiation
Snow cover
Snow metamorphism
Publisher: U.S. Army Snow, Ice, and Permafrost Research Establishment.
Engineer Research and Development Center (U.S.)
Series/Report no.: Research report (U.S. Army Snow
Description: Research Report
Summary: The heat exchange of a snow cover was studied with respect to the effects of heat transfer processes on metamorphic action within the snow cover and the prediction of heat fluxes and the resulting changes in snow cover characteristics from standard meteorological information. Data collected at the USA SIPRE Keweenaw Field Station, Houghton, Michigan, were used to determine heat transfer by thermal radiation, convection, and conduction. The percent of daily incident solar radiation at the outer limits of the earth's atmosphere which reaches the snow surface ranged from 94 with clear skies to less than 20 with an overcast less than 1000 ft high and precipitation. Average diurnal patterns of total solar radiation may be estimated for various cloudiness. Total solar radiation with overcast clouds less than 5000 ft high averaged about 70% of the clear-sky radiation. Atmospheric radiation related to temperatures during clear nights gave a curve paralleling the black body radiation curve, although about 7 ly/hr lower in absolute values. Atmospheric radiation during clear skies was about 9 ly/hr less than that with low overcast conditions with no snow falling. In the presence of falling snow, total hemispherical radiation was about 5 ly/hr greater than with no snow falling but with' similar low overcast cloudiness. With low overcast cloudiness, the net long-wave exchange averaged about -17 ly/day in January and -8 ly/day in February. With clear skies the net long-wave exchange averaged about -128 ly/day in January and -120 ly/day in February. The net radiation exchange with clear skies during midday remained slightly negative in January and became increasingly positive through February. The highest positive values of net radiation occurred during the day with low overcast or broken cloudiness and precipitation. The largest net radiational loss of 9 ly/hr occurred at night with clear skies and nearly calm winds. The average magnitude of surface temperature inversions over snow was related to observations of cloudiness and wind speeds for both day and night. With winds of 12 knots or greater, the temperature difference in the first 10m was usually near adiabatic even with clear skies at night. During the day inversions seldom exceeded 1-2°C, and a slight lapse commonly occurred during low overcast conditions and moderate winds. The Liljequist method for computing turbulent heat transfer and conductive heat transfer in snow was used. Average air temperature is shown to exert a pronounced effect upon snow heat conduction, cold content and temperature profile. Average temperature differences through the snow, responsible for metamorphic action leading to the formation of depth hoar, can be estimated by a knowledge of the previous 20-hr average temperature. Snow hardness distributions, indicators of supporting capacity of snow, can be estimated graphically from snow density and depth observations.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Research Report

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