The use of polarimetric radar data to characterize drop size distribution regimes in moderate to heavy convective rain

Joint considerations of several of the quantities measured by dual-polarization radars have been used to infer various characteristics of raindrop populations. In an effort to extract information on raindrop aspect ratios, Gorgucci et. al (JAS 2006, p 3033-3044) used a two dimensional parameter space with axes of (Kdp/Z) and Zdr. In addition to revealing drop shape information, they also determined that variations in raindrop size distribution (RSD) parameters caused displacements in this parameter space. The advantage of this method is that, by making a ratio of Kdp to Z, the concentration term is cancelled out and the resulting ratio is only a function of RSD median diameter (D0) and shape factor (µ). Similarly, Zdr is also a strong function of the drop median diameter. To explore this response to RSD variations, plots of (Kdp/Z) vs. Zdr are being generated from data collected by the CSU-CHILL and NCAR S-Pol radars in various climatological settings. Preliminary results indicate that the scatterplots from convective rain in low latitude, maritime areas are appreciably different from those derived from thunderstorms in the high plains of Colorado. Outputs from an electromagnetic scattering model are used to associate various RSD parameters, particularly median drop diameter categories, with regions in the (Kdp/Z) vs. Zdr domain. This characterization technique presents great potential for using polarimetric radar observations to make rain regime classifications via inferred RSD properties.