Precipitation Observed in Oklahoma Mesoscale Convective Systems with a Polarimetric Radar

A. V. Ryzhkov NOAA/ERL, National Severe Storms Laboratory, Norman, Oklahoma

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D. S. Zrnić NOAA/ERL, National Severe Storms Laboratory, Norman, Oklahoma

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Abstract

In this paper, the fields of three radar polarimetric variables-differential reflectivity ZDR, specific differential phase KDP, and correlation coefficient between horizontally (H) and vertically (V) polarized echoes ρhv-along with radar reflectivity Zh, are examined within two Oklahoma mesoscale convective systems (MCSs). The analysis of the whole set of polarimetric variables reveals at least three types of hydrometeor populations in the precipitation within thew MCSs. It seems to be possible to discriminate between pure liquid raindrops, drops with ice cores inside them, and mixed-phase precipitation containing rain and hail using joint analysis of all the polarimetric measurands available. Hail-bearing zones are characterized by significant reduction of ZDR and ρhv, as well as large values of Zh. Specific differential phase KDP is usually high in these zones, and sometimes a pronounced differential phase shift upon scattering is evident.

Experimental data show that the differential phase ΦDP and its derivative KDP are reliable indicators of liquid water in heavy precipitation. A negative bias of ZDR due to differential attenuation in precipitation could be significant in this type of storm. The validity of the correction scheme for ZDR estimates based on the ΦDP evaluation proposed in earlier theoretical papers was examined. It was found that differential attenuation was underestimated at least twofold in the previous theoretical predictions.

Abstract

In this paper, the fields of three radar polarimetric variables-differential reflectivity ZDR, specific differential phase KDP, and correlation coefficient between horizontally (H) and vertically (V) polarized echoes ρhv-along with radar reflectivity Zh, are examined within two Oklahoma mesoscale convective systems (MCSs). The analysis of the whole set of polarimetric variables reveals at least three types of hydrometeor populations in the precipitation within thew MCSs. It seems to be possible to discriminate between pure liquid raindrops, drops with ice cores inside them, and mixed-phase precipitation containing rain and hail using joint analysis of all the polarimetric measurands available. Hail-bearing zones are characterized by significant reduction of ZDR and ρhv, as well as large values of Zh. Specific differential phase KDP is usually high in these zones, and sometimes a pronounced differential phase shift upon scattering is evident.

Experimental data show that the differential phase ΦDP and its derivative KDP are reliable indicators of liquid water in heavy precipitation. A negative bias of ZDR due to differential attenuation in precipitation could be significant in this type of storm. The validity of the correction scheme for ZDR estimates based on the ΦDP evaluation proposed in earlier theoretical papers was examined. It was found that differential attenuation was underestimated at least twofold in the previous theoretical predictions.

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