Microphysical Characteristics of Ice Crystals and Snowflakes as Revealed by Polarimetric Radar Measurements

摘要

This research encompassed both observational and theoretical aspects of Co-polar and differential reflectivity in the less explored, yet important, winter season precipitation. The observational portion was conducted with the multiparameter, CSU-CHILL radar and supplemented by observers at the Fort Collins Weather Station on the Campus of Colorado State University (FCL) who recorded microphysical features of the snowfall such as snow type, composition, size, and degree of riming. Additionally, a 2-D video disdrometer, located at FCL, made particle size distribution measurements. In order to compare the appropriate radar data with the ground observations, the approximate trajectory of the snow was computed from the height it was interrogated by the radar to the surface. The trajectory, applied in reverse from FCL, identified the source region of the observed snow in the 0.5 deg and 1 deg elevation scans of the radar. The results of the observational analyses suggest that nearly homogeneous populations of aggregates can be distinguished from platelike crystals (i.e., dendrites, stellar crystals, and plates) using a combination of co-polar and differential reflectivity (Z and Z(DR)) radar observations. Furthermore, it appears possible to discern whether or not the platelike crystals are intensely rimed. Additionally, the results challenge the validity of the common assumption that aggregates always produce a Z(DR) value of 0 dB.