Predicting deposition coefficients in a bulk adaptive habit microphysical model and comparison to in situ measurements

Poster PDF

Description

A multi-moment bulk microphysical model that evolves particle shape and density during vapor growth, riming, melting, and aggregation has been developed. The evolution of particle shape during vapor growth depends on ratios of the deposition coefficients (or growth efficiency) for each growth axis. Habit-evolving models typically assume that this ratio depends only on temperature, and this appears to be true at liquid saturation. At low saturation, however, the deposition coefficients can become very low, thus impeding vapor growth and altering the deposition coefficient ratio. We have developed a bulk parameterization that estimates the deposition coefficients based on crystal growth theories. The model is tested against bin microphysical models, and results from cirrus simulations will be shown at the meeting. The bulk model has also been used to simulate a squall line that was observed during MC3E. Comparisons of the projected aspect ratios predicted by the model to values derived from in situ measurements suggest that the model produces too narrow a range of aspect ratios with values closer to unity than the observations suggest.