Three-dimensional Characteristics of Polarimetric Radar Variables

Understanding the characteristics of cloud microphysics in precipitation is important to enable accurate rainfall estimation through space-borne radar and microwave radiometers on satellites (e.g., TRMM, GPM, and AMSR-E) (e.g., Masunaga et al. 2002). One basic need is clarification of the differences in cloud microphysical characteristics, such as the drop size distribution (DSD), in convective precipitation and stratiform precipitation. Hydrometeor identification above an altitude of 0oC also provides indispensable information for rain retrieval algorithms. Some previous studies have revealed the vertical profiles of DSD and hydrometeor classification using wind profiler and polarimetric radar data (Kobayashi and Adachi 2005; May and Keenan, 2005). However, few studies have described and compared the three-dimensional characteristics of cloud microphysics in various types of precipitation on the basis of observational data. In the context of rainfall estimation through space-borne microwave radiometers, characterizing and classifying the precipitation type within an area that depends on the radiometers horizontal footprint size is also important. In the present study, we have studied polarimetric radar variables in three small areas (150 km) including different types of precipitation. In this study, we used observational data from COBRA (CRL Okinawa Bistatic Polarimetric Radar, C-band) which is operated on Okinawa Island (26.5N 128E), Japan (Nakagawa et al. 2003). We investigated the radar reflectivity factor (Zhh), differential reflectivity (ZDR), correlation coefficient (ρhv(0)), and the relationships between them to characterize each precipitation type rather than to reveal the detailed structure of precipitation. The horizontal variability and vertical distribution of these values in selected areas are provided as three-dimensional characteristics of the polarimetric radar variables in this study.