Vertical Air Motion and Raindrop Size Distribution Retrieval Using a Ka/Ku Dual-Wavelength Cloud Radar and Its Preliminary Application

A new Ka/Ku dual-wavelength (Ka- and Ku-band wavelengths are 8.9 mm and 2.2 cm, respectively) cloud radar (DWCR), an upgraded from the Ka-band CR (cloud radar), was used to observe the vertical structures of cloud and precipitation in South China to improve the observational ability of vertical velocity for air motion (V_air) and microphysical parameters. Based on the study of the dynamic and microphysical parameters of precipitation in South China using the DWCR, this paper presents a retrieval algorithm (DWSZ) for the V_air, raindrop size distribution (DSD), liquid water content (LWC), rain rate (R), and radar wave attenuation correction in rain areas with the reflectivity spectral density (S_Z) data of the DWCR. The V_air was studied using the DWSZ and single Ka- and Ku-band CR in a precipitation case in Longmen, Guangdong Province. The V_air and microphysical parameters retrieved by the DWSZ were examined using the DSD data from a disdrometer. The results revealed that the DWSZ provided acceptable V_air, microphysical parameters, and vertical distributions. The attenuation correction for the Ka- and Ku-band reflectivity data minimized the bias between the two reflectivity bands. The DWCR can detect cloud and precipitation with a reflectivity of 0–30 dBZ. In the mixed cloud detected by the DWCR, the updraft and downdraft were found in front of and behind the convective cells. According to the averaged profiles, the V_air and mass-weighted mean diameter (D_m) reached their maximum at 2 km, and the drop number concentration (N_w), LWC, and R increased below this level. Water vapor condensation, raindrop collection of cloud drops are possibly the main processes. This work revealed the relationships between the microphysical and dynamic processes in this precipitation case, verified the DWCR observational ability, and provided the basis for the development of Ka/Ku-band DWCR, future improvement of single-wavelength CR observation ability, and observation of finer and more accurate structures of the microphysical and dynamic parameters.