Axis Ratios and Flutter Angles of Cloud Ice Particles: Retrievals from Radar Data

Valery Melnikov Cooperative Institute for Mesoscale Meteorology, University of Oklahoma, and National Severe Storms Laboratory, Norman, Oklahoma

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Jerry M. Straka School of Meteorology, University of Oklahoma, Norman, Oklahoma

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Abstract

A novel method of retrieving the mean axis ratio (width/length) and standard deviation of orientation angles (σθ, which is called herein the intensity of fluttering) of ice cloud particles from polarimetric radar data is described. The method is based on measurements of differential reflectivity ZDR and the copolar correlation coefficient in cloud areas with ZDR > 4 dB. In three analyzed cases, the values of the retrieved axis ratio were in an interval from 0.15 to 0.4 and σθ found in an interval from 2° to 20°. The latter values indicate that the particles experienced light to moderate fluttering. Ambiguities in the retrievals because of uncertainties in the bulk ice density of the particles and possible presence of columnar crystals are considered. The retrieval method is applicable for centimeter-wavelength radars; the analyzed data were collected with the dual-polarization S-band Weather Surveillance Radar-1988 Doppler (WSR-88D).

Corresponding author address: Valery Melnikov, Cooperative Institute for Mesoscale Meteorology, University of Oklahoma, Norman, OK 73072. E-mail: valery.melnikov@noaa.gov

Abstract

A novel method of retrieving the mean axis ratio (width/length) and standard deviation of orientation angles (σθ, which is called herein the intensity of fluttering) of ice cloud particles from polarimetric radar data is described. The method is based on measurements of differential reflectivity ZDR and the copolar correlation coefficient in cloud areas with ZDR > 4 dB. In three analyzed cases, the values of the retrieved axis ratio were in an interval from 0.15 to 0.4 and σθ found in an interval from 2° to 20°. The latter values indicate that the particles experienced light to moderate fluttering. Ambiguities in the retrievals because of uncertainties in the bulk ice density of the particles and possible presence of columnar crystals are considered. The retrieval method is applicable for centimeter-wavelength radars; the analyzed data were collected with the dual-polarization S-band Weather Surveillance Radar-1988 Doppler (WSR-88D).

Corresponding author address: Valery Melnikov, Cooperative Institute for Mesoscale Meteorology, University of Oklahoma, Norman, OK 73072. E-mail: valery.melnikov@noaa.gov
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