Multiparameter Radar and Aircraft Study of Raindrop Spectral Evolution in Warm-based Clouds

Abstract

Radar measurements of reflectivity differential reflectivity, and X-band (3-cm wavelength) specific attenuation are used to inter some microphysical characteristics of warm-based convective clouds with emphasis on raindrop spectral evolution. The case study of 22 July 1986, during the Cooperative Huntsville Meteorological Experiment, was chosen for analysis. This day was characterized by multicellular storm types; one such multicell configuration was repeatedly penetrated by the University of North Dakota Citation aircraft equipped with cloud physics instrumentation. Radar data acquisition was coordinated with aircraft penetrations made at a constant pressure altitude of 2.7 km enabling a detailed interpretation of differential reflectivity in terms of mean raindrop size. The evolution of several radar reflectivity cells was studied and certain key microphysical features were identified, notably the evolution of raindrop spectra from a ?growth? type to an equilibrium type. Further evidence that positive differential reflectivity columns are centered on regions of updraft is provided. A small hail melting model is used to show that the large observed differential reflectivities near cloud base may be due to substantial raindrop growth occurring during continuous collection of cloud water as the particle melts and descends in moderate updrafts.