Spatial structure and time evolution of rain drop size distributions revealed from disdrometer and polarimetric radar observations

A better understanding of rain microphysical properties is needed for accurate rain estimation and model parameterization. Polarimetric radars measure reflectivity at horizontal and vertical polarization, differential reflectivity, specific differential phase, and copolar cross correlation coefficient. The polarimetric radar measurements provide information about hydrometeor size, shape, orientation and phase and allow the retrieval of drop size distributions (DSDs). The 2D video disdrometer (2DVD) directly measures the shape, size and falling velocity of precipitation particles, which is essential for interpreting polarization radar data.

In this paper, we present observations and data analysis of several rain events collected with S-band polarimetric KOUN radar and a 2DVD in Oklahoma during the period from 2005 to 2009. Cases studied include the following storm types: convective, stratiform, mixed convective-stratiform, winter convection, tropical rain, supercell, and squalline case. Storm structure and evolution are studied through the polarimetric radar and disdrometer observations and comparisons. Time evolution of DSD, mass, and reflectivity distributions were obtained with 2DVD. The radar measured vertical structure and time evolution of Z, ZDR and ρhv at disdrometer site are extracted and shown. For each storm-case hydrometeor classification has been made, and then, raindrop size distributions (DSDs) are retrieved from the polarimetric radar measurements. Disdrometer is used to validate the DSD retrieval, deduce the microphysical properties, and relate these to storm features.