Examination and Application of Doppler Spectral Density Data in Drop Size Distribution Retrieval in Weak Precipitation by Cloud Radar

The effects of Mie Scattering, air turbulence, and air vertical speed on drop size distribution(DSD) retrieval from Doppler spectral density data observed by cloud radar are discussed in this study. The processing algorithm for the Doppler spectral density data and retrieval algorithm for DSD, liquid water content(LWC), rain rate, and air vertical speed with Doppler spectral density data are presented. The two weak precipitation cases observed by vertical-pointing Ka-band cloud radar, Ku-band micro-rain radar, and disdrometer in July 2012 at Tengchong, Yunnan Province, are used to examine the cloud radar data quality and retrieval algorithm. The vertical profiles of reflectivity and velocity observed by cloud radar and micro-rain radar are compared. The Doppler spectral density data at an altitude of 780 m observed by cloud radar, micro-rain radar, and disdrometer calculation are compared. In addition, the DSD and rain rate are retrieved by Doppler spectral density data and compared with disdrometer data. The effect of water over the cloud radar antenna on reflectivity measurement is also discussed. The results indicate that although the effects of air turbulence on precipitation microphysical parameters are negligible, those of air vertical speed and Mie scattering are obvious. The velocity, Doppler spectral density data, and variational pattern of reflectivity with altitude observed by cloud radar and micro-rain radar show good agreement; however, the reflectivity measured by the cloud radar was weaker than that observed by the other methods. The water over the cloud radar antenna significantly reduced the reflectivity. The Doppler spectral density data and DSD observed by the cloud radar were similar with that observed by disdrometer. Therefore, this study has verified the effectiveness of Doppler spectral density data measurement by cloud radar and retrieval parameters.