Application of Raindrop Spectrum and Dual Polarization Radar Data to a Heavy Rain Process
From 20:00 BT 9 to 20:00 BT 13 August 2020, due to the combined effects of the westerly trough and the Typhoon Lichma, largescale severe precipitation occurred in Shandong Province. The center of the severe precipitation was at Zhangqiu Station. In order to use multisource data to study the microphysical structure characteristics of heavy rainfalls in the typhoon rain belt, this paper analyzes the data of minutely precipitation, raindrop spectrum, dual polarization Doppler radar, wind profiler radar, etc. during the severe rainfall process at Zhangqiu Station. The results show that there was an obvious cold cloud precipitation mechanism at the beginning of this precipitation process. During the precipitation, the scale spectrum of raindrops changed significantly with time. During the period of severe precipitation, the spectrum of raindrops was broad, showing an obvious bimodal structure. The correlation coefficient between the sequence of raindrop numbers with a diameter greater than 1 mm and the sequence of minutely precipitation reached 0.956 〖KG-*5〗8. However, during periods of weakening precipitation, the spectrum of raindrops gradually narrowed, showing a singlepeak structure clearly, and the number of raindrops with a diameter greater than 1 mm decreased. When the radar echo height was high, the proportion of raindrops with a diameter greater than 1 mm increased, the raindrop spectrum was wider, and the multimodal distribution appeared. Strong wet turbulence clusters formed a large value area of the differential reflectance factor (ZDR), which neither corresponded to severe convection nor to surface heavy raindrops. This was caused jointly by the deformation of the wet turbulence resulting from updraft, downdraft and other reasons. During heavier precipitation, a thin layer structure with abrupt changes in wind direction and wind speed appeared in the time crosssection of wind profile in the 0.9-1.4 km height. Corresponding to the thin layer, the minutely rainfall was the heaviest, and the proportion of raindrops with a diameter greater than 1 mm was obviously biased. The phenomenon revealed by the analysis results could provide a reference for understanding the droplet spectrum characteristics and microphysical structure of typhoon heavy rainfall.