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|Title:||Growth of faceted crystals in a snow cover|
|Authors:||Colbeck, Samuel C.|
|Publisher:||Cold Regions Research and Engineering Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||CRREL report ; 82-29.|
Abstract: Ice grains in a snow cover with a low temperature gradient assume a well-rounded equilibrium form. However, at temperature gradients of 0.1 to 0.2°C/cm (depending somewhat on temperature and snow density), the rounded grains recrystallize into a faceted kinetic growth form. The large temperature gradient must play a decisive role in moving the vapor fast enough to sustain the rapid growth rate associated with the kinetic growth form. Once the large temperature gradient is removed, the grains recrystallize back to the equilibrium form, The recrystallization occurs in either direction without a change in bulk density. The growth of faceted crystals begins at the warmer base of the snow cover where the excess vapor pressure is largest. A transition between the overlying rounded grains moves upward in time. Faceted crystals also grow just below crusts of reduced permeability, where the increased vapor accumulation can sustain the excess vapor pressure needed for kinetic growth. The heat and vapor flows are described using a model based on thermodynamic equilibrium. The temperature distribution is shown to be quasi-linear at steady state in homogeneous snow. The recrystallization of the snow is modeled using the rounded grains as sources and the faceted grains as sinks. In the fuwre this model should be extended to account for different temperatures among the sources and sinks.
|Appears in Collections:||CRREL Report|