Observations of precipitating convective systems at 92 and 183 GHz: Aircraft results

Summary High spatial resolution data from an airborne microwave imaging radiometer operating at 92 and 183 GHz (0.32 and 0.16 cm wavelengths) are compared with ground-based radar data for a series of observations of precipitating convective systems. An inverse relationship between microwave brightness temperature (T _B ) and radar-derived rain rate (RR) is observed. Differences in the empirical curves between midlatitude and tropical cloud systems are related to the differing microphysical and dynamical environments.ColdT _B features in the aircraft images are collocated with high reflectivity values in the radar data. Over a water back-ground, which has a low surface emissivity at these frequencies, small convection produces an increase inT _B at 92 GHz due to emission by liquid water in the cloud. As the convection deepens and ice forms,T _B at both frequencies decreases rapidly with increasing rain rate. The large decrease inT _B with increasing storm intensity is due to scattering of upwelling radiation by precipitation-sized ice particles within the clouds. With high rain rates, there is little difference betweenT _B observed over both land and water backgrounds.TheT _B features in the aircraft imagery are qualitatively similar to radar echoes in plan position indicator (PPI) images. Areas of extremely coldT _B (<150 K) coincide with high radar reflectivities. The highest correlations between microwave and radar features with regard to location, intensity, and shape occur more frequently with mid-to upperlevel echoes rather than low-level reflectivity features.With 12 Figures