Polarimetric radar observations and microphysical model simulations of melting hail

A one-dimensional bin microphysical model of melting hail has been developed. The model includes explicit treatment of melting of hailstones of arbitrary density, shedding of excess melt water, and breakup of giant raindrops. The model also has an electromagnetic scattering component that allows for computation of the polarimetric radar variables at any wavelength. The sensitivity of the computed vertical profiles of the polarimetric variables to the temperature lapse rate, humidity, size distributions of graupel / hail aloft (e.g., maximum hail size) and hailstone density is examined. The impact of vertical air velocities associated with downdrafts or microbursts is also investigated. Results of theoretical simulations are compared to and substantiated by the data simultaneously collected with nearly collocated S- and C-band polarimetric radars in central Oklahoma and are consistent with reported measurements at S and C bands in various parts of the world.

The melting hail model is the basis for a hail size discrimination algorithm (HSDA) under development at the National Severe Storms Laboratory, which classifies hail into three categories: small (diameter < 2.5 cm), large (diameter >= 2.5 cm and < 5 cm), and giant (diameter >= 5 cm). Initial validation of the HSDA using observed data from the Severe Hazards Analysis and Verification Experiment (SHAVE; Ortega et al. 2009) collected from across the United States will be presented.