The impact of precipitation physical processes on the polarimetric radar variables

Abstract

The ongoing upgrade of the National Weather Service WSR-88D radar network to polarimetric capabilities, as well as similar upgrades worldwide, will soon provide a wealth of data and information regarding storm precipitation physics. Fully understanding how a variety of microphysical processes are revealed in polarimetric data is necessary for the best use of these new data by operational and research meteorologists. The focus of this study is to quantify a number of these precipitation physics "fingerprints" in the polarimetric radar variables by using a synthesis of explicit microphysical modeling, electromagnetic scattering calculations, thought experiments, and polarimetric radar observations.

The complete set of polarimetric variables available from linearly-orthogonal dual-polarization radars are derived from basic electromagnetic scattering principles. A detailed physical description of these variables is then provided for applications in precipitation and other atmospheric scatterers, as is a summary of common data artifacts. The impact of various precipitation physical processes on these radar variables is then quantified. Using explicit microphysical models, scattering calculations, observations, and thought experiments, the microphysical fingerprints are determined and quantified for raindrop thermal conduction, raindrop size sorting by sedimentation, updrafts, and vertical wind shear, evaporation of raindrops, coalescence of raindrops, and freezing of raindrops in deep convective storm updrafts. A catalogue of the qualitative fingerprints of a number of precipitation processes is summarized.