Polarimetric signatures of melting hail at S and C bands. Detection and short-term forecast

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Wednesday, 20 January 2010: 2:15 PM
B218 (GWCC)
Joseph C. Picca, CIMMS/Univ. of Oklahoma, Norman, OK; and A. V. Ryzhkov

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The development and subsequent melting of hailstones within thunderstorms are studied using polarimetric radar data at both 10 cm wavelength S band and 5 cm wavelength C band. Five convective events in Oklahoma and southern Canada are analyzed, of which two are at S band, two are at C band, and one is at both, which provides a particularly unique case where dual-polarized data from two wavelengths can be directly compared. The updraft and hail core regions of the storms are primarily investigated both to improve short-term prediction of large hail development and to observe the size of melting hail prior to reaching the surface. Within the updraft, polarimetric variables such as differential reflectivity (ZDR) and cross-correlation coefficient (ρhv) identify regions of great liquid water content necessary for hail, as well as rapid hail growth occurring within the mixed phase region above the freezing level. An increase in ZDR and decrease in ρhv within the updraft generally appear to precede noticeable increases in 0.5˚ base reflectivity, and presumably an increase in hail, by as much as 30 minutes. Furthermore, within the hail core itself these variables are analyzed below the environmental freezing level to ascertain the ability of the hailstones to reach the surface. This analysis is greatly supported by the one case which provides data from both S and C bands, where we observe much greater differential attenuation with C band data, leading to greatly decreased ZDR and ρhv values on the back side of the core relative to the radar.