Poster Session P1.55 The parameterization of primary ice habit for bulk models: Influences on mixed-phase cloud glaciation

Monday, 28 June 2010
Exhibit Hall (DoubleTree by Hilton Portland)
Kara Sulia, NOAA/GFDL, Princeton, NJ; and J. Y. Harrington and H. Morrison

Handout (2.9 MB)

The importance of primary ice habit prediction and its effects on the lifetime of mixed-phase clouds is explored. Current methods for computing ice vapor growth rely on crude estimations of ice shape, which produce large uncertainties in the prediction of glaciation and dissipation times of mixed-phase clouds. We present a simplified method for evolving the primary habits of ice crystals that compares well with detailed model calculations. The method is used to explore the impact of evolving ice habits on the lifecycle of mixed-phase cloud structure. A Lagrangian-bin parcel model is used for this purpose and we explore the dependencies of primary habit parameterization. While it is well known that temperature plays a direct role in primary habit evolution, we show that initial particle size and concentration also play a direct role. Initially smaller particles grow much more rapidly than initially larger particles. Because of the non-linear dependence of vapor growth on shape, the initially smaller particles are more likely to evolve into extreme habits. This is particularly true at temperatures where extreme habits are expected. Moreover, for a given environment, more extreme habits are produced for lower, rather than higher, ice concentrations. As a consequence, where low ice concentrations occur extreme habits can be produced, vapor growth rates are enhanced and glaciation occurs rapidly. In addition, work is currently being done to implement a version of our parameterization into Eulerian-Bulk microphysical model. This is accomplished by predicting only one semi-major axis length, particle concentration, and total ice water mass. Our initial results show that this method is accurate in comparison to our more detailed calculations.
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