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 ZH, the reflectivity factor for horizontal polarization, ZDR, the differential reflectivity, and KDP, 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 ZH, ZDR, and KDP. It is shown that it is possible to distinguish the mixed-phase precipitation from either rain or hail by using ZH, KDP pair and also to infer the thermodynamic phase and orientation from ZH, ZDR pair. On the basis of physical principles, it is shown that KDP senses primarily liquid water in the form of raindrops even when these are mixed with hailstones. The self-consistency Of ZH, ZDR, and KDP 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.