Metamorphism of dry snow as a result of temperature gradient and excess vapor density

Abstract

A heat conduction equation to determine the temperature profile in a snowpack is developed. The magnitude of temperature gradient tends to increase as the snow surface is approached, with local minimums through high snow density layers and local maximums above and below these layers. Calculations are made which determine the excess vapor density over the ice grain surfaces which border the pore space. In the presence of a temperature gradient faceted crystals will develop near the top of the pore, as ice is sublimated off of the surfaces in the lower region. Necks will deteriorate most readily, causing an overall weakening of the snowpack. There will be a reduction in the percentage of rounded grains as the faceted form develops. The process is enhanced at warmer temperature and larger temperature gradients. Temperature and excess vapor density are known to determine the habit of ice crystals grown in air. The model predicts excess vapor densities in the snowpack which are similar to those which exist in the atmosphere. Comparison of crystal habits predicted by the model are in good agreement with experimental evidence, when the pore geometry and temperature conditions are specified.