Meteorology Ph.D. student Lee Dunnavan will discuss his research, titled "An Approach for Testing and Comparing Predicted Ice Particle Shapes with In Situ Aspect Ratio Projections."
Dunnavan's adviser is Jerry Harrington.
This paper develops an approach for transforming 3-D ice particle aspect ratio distributions into corresponding 2-D projections. This method is applied to the Ice-Spheroids Habit Model with Aspect-ratio EvoLution (ISHMAEL) WRF microphysics scheme as a way to test the nonsphericity of modeled stratiform ice particles. Such a comparison between modeled and in situ derived projections can then be used to infer how future models should parameterize adaptive habit growth. Single spheroid projection tests demonstrate how spheroid geometry and orientation can drastically alter corresponding projection measures. Joint probability distributions of projected size and shape from ISHMAEL are then compared with analogous ellipse fit measures derived from Cloud Imaging Probe (CIP) projections. Two model runs are used for comparison: One model run assumes columnar (prolate) particle growth below -22 C whereas another assumes planar (oblate) growth for this range. Projection aspect ratios of the prolate assumption are shown to span a more comparable range with observations than oblate particles. Overall, the single projection tests and bulk projection comparisons indicate that modeling aggregates as oblate spheroids with fallspeed canting cannot explain much of the observed aspect ratio distribution.