Estimation of rain and hail rates in mixed-phase precipitation

Abstract

Precipitation comprising rain and hail is studied. Specifically, techniques to identify and quantify such precipitation in terms of rain and hail fall rates using dual polarized radar data, are presented. Included for consideration are Z_H, the reflectivity factor for horizontal polarization, Z_DR, the differential reflectivity, and K_DP, the differential propagation constant. A variety of simple models of mixed-phase precipitation are first examined. Electromagnetic scattering computations are performed to simulate and study the behavior of Z_H, Z_DR, and K_DP. It is shown that it is possible to distinguish the mixed-phase precipitation from either rain or hail by using Z_H, K_DP pair and also to infer the thermodynamic phase and orientation from Z_H, Z_DR pair. On the basis of physical principles, it is shown that K_DP senses primarily liquid water in the form of raindrops even when these are mixed with hailstones. The self-consistency Of Z_H, Z_DR, and K_DP is then exploited to estimate both the rain and hail fall rates. The ability of the methods to estimate rain and hail fall rates is demonstrated with actual radar data from two Oklahoma storms.