a Theoretical Study of Ice Crystal Growth in the Atmosphere.
Abstract
Starting from the assumptions of the terrace, ledge, kink model and steady state conditions, we derive 3 models for analyzing ice crystal growth in the atmosphere in terms of elementary processes. These models are all based on the assumption that the flux of vapor to the crystal surface is uniform and thereby all differ fundamentally from the standard models used heretofore by the atmospheric sciences community, in which the vapor density is assumed uniform at the surface. In the new models the surface impedance to growth is calculated self-consistently in terms of local environmental conditions, again differing sharply from the standard models in which this impedance is either ignored or assigned a uniform, externally prescribed value. Beginning with a model for uncoupled surface and vapor diffusion to a growing spherically shaped ice crystal, we build a model which applies to cylindrically shaped ice crystals with coupled surface and vapor diffusion in the presence of gaseous impurities. This model is expected to apply to a wide range of environmental conditions and surface parameters provided only that there exist many ledges on each crystal face. When there is only a single ledge on the face, the growth rate will depend on whether the ledge is part of a continuous spiral, or a circular island. A model for each ledge shape is described, and the predictions from the spiral case are shown to be consistent with the (limited) experimental data. Some of the predictions from our analysis of the stability of uniform growth (hollowing conditions), and the formation of non-isometric crystal shapes are shown to be consistent with the observed data, but again, the available evidence is very limited.
- Publication:
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Ph.D. Thesis
- Pub Date:
- January 1994
- Bibcode:
- 1994PhDT........32N
- Keywords:
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- Physics: Atmospheric Science