Climatological analysis of DSDs in Oklahoma as revealed by 2D-video disdrometer and polarimetric WSR-88D radar

Since the Spring of 1998, over 47,000 one-minute drop size distribution (DSD) measurements have been made by the National Severe Storms Laboratory 2D-video disdrometer in Norman, OK. Collected over many seasons and precipitation regimes, these DSDs reveal much information about natural DSD variability over the southern Great Plains. In this study, we use this large dataset to examine DSD differences between a variety of storm and precipitation system types, continental and tropical precipitation, warm and cold season precipitation, and the height of the bright band in stratiform precipitation. A variety of environmental factors are also considered. Measured DSDs are used to compute average dependencies of differential reflectivity (ZDR) and specific differential phase (KDP) on radar reflectivity (Z) for different storm types. These dependencies are then compared with the corresponding ones obtained from the polarimetric KOUN WSR-88D data for similar types of rain. Within-storm variations of DSDs are illustrated with the fields of DSD parameters retrieved from polarimetric data. Special consideration is given to the relative frequency and importance of DSDs dominated by big drops, characterized by an unusually large median volume diameter (D0), and their impact on polarimetric rainfall estimation.