Microwave Radiative Transfer Studies Using Combined Multiparameter Radar and Radiometer Measurements during COHMEX

Abstract

Theoretical calculations of the upwelling microwave radiances from clouds containing layers of rain, ice, and a melting region were performed at frequencies of 18, 37, and 92 GHz. These frequencies coincide with high-resolution microwave radiometer measurements taken aboard the NASA ER-2 high-altitude aircraft during the summer 1936 COHMEX (Cooperative Huntsville Meteorological Experiment) in Alabama. For purposes of brightness temperature computations, the storms were modeled with rain, melting phase, and ice layers. The melting phase region was composed of water-coated ice spheres defined by a ?melt index? in terms of the volume fraction of water. Single scatter albedo, scattering, and extinction coefficients were computed at the above frequencies as a function of the rain rate and melt index. In addition, multiparameter radar observations of the storm were mapped into a cartesian space and averaged over regions comparable to the radiometer footprint. Vertical profiles of these data under the ER-2 flight path were constructed to reveal quantitative estimates of regions of rain, melting, and ice phases, and also to retrieve a two-parameter exponential size distribution. This information was used to compute extinction coefficients and Mie phase matrices for each layer of specified microphysical characteristics. Upwelling multifrequency brightness temperatures were computed using plane-parallel radiative transfer modeling, and compared with those observed by the ER-2 airborne radiometers.