SEMINAR SERIES and COLLOQUIA

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 cross correlation coefficient that depend on cloud/precipitation physics. Polarimetric radar measurements provide information about hydrometeor size, shape, orientation and phase and allow retrieval of drop size distributions (DSDs). The two dimensional video disdrometer (2DVD) directly measures the shape, size and falling velocity of precipitation particles, which is essential for interpreting polarization radar data.

Observations and data analysis of several rain events collected with S-band polarimetric KOUN radar and 2DVDs in Oklahoma during the period from 2005-2009 are presented in this study. Cases studied include the following storm types: a convective, a stratiform, a convective-stratiform, a winter convection, a tropical rain, and a squalline case. Time evolution of DSD, mass, reflectivity and differential reflectivity distributions obtained with 2DVD are examined, and integral polarimetric radar variables were calculated for comparison with KOUN radar measurements. Storm structure and evolution are studied using the polarimetric radar and disdrometer observations. The PPIs of ZH, ZDR, ρhv and hydrometeor classification are shown to reveal the morphology of each storm. The radar mesured vertical structure and time evolution of ZH, ZDR and ρhv at disdrometer site are extracted and presented. Also, radar retrieved raindrop size distributions (DSDs) are compared with the disdrometer measurements. Microphysical parameters of radar retrieved DSDs, such as rainfall rate (R) and median volume diameter (D0), generally agree well with 2DVD measurements.

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