Sensitivity of Microwave Properties to Melting Ice-Phase Precipitation

Microwave remote sensing is ideally suited for detecting and estimating precipitation due the fact that microwave radiation strongly interacts with precipitation hydrometeors, while remaining relatively insensitive to clouds and atmospheric gases. For rain, the relationships between observed microwave quantities (whether passive or active) are fairly well established. For ice-phase precipitation, such as snow, graupel, frozen rain, etc., the relationship between what is observed and the physical properties of the precipitation is much more uncertain. The shape of ice-phase hydrometeors can be highly variable, even when the total particle mass is the same. Because microwave remote sensing of ice-phase precipitation often exploits the fact that ice is a strong scatterer of microwave radiation, the shape of the particles within the field of view have a non-trivial impact on the scattered field of radiation. This becomes further complicated when these particles begin to melt, due to the presence and distribution of liquid water. The present study examines the role of particle shape and melting in simulating observable quantities for both passive and active microwave applications. We specifically focus on the Global Precipitation Measurement Mission and the CloudSat mission for the selection of microwave frequencies examined; ranging from 10.65 GHz to 183.31 GHz for the passive, and 13.4, 35.6, and 94.0 GHz for radar remote sensing.