Analysis of Precipitation Phase Characteristics of One Rain-snow Process in Huaihua,Hunan Province,Based on Multi-source Observation Data
In order to explore the application of multi-source data in the phase prediction of rain-snow,based on the ERA5 reanalysis data,microwave radiometer and SA dual-polarization Doppler radar observation data,we analyze the precipitation phase characteristics of a rain-snow weather process in Huaihua region of Hunan Province in December 27-28,2022,by using the methods of conventional statistics,circulation background analysis,correlation analysis,etc..The results show that:(1)The cold air moved southward under the guidance of the mid-level trough in the mid-high latitudes,and the southwest airflow moved eastward with the south branch trough in the mid-low latitudes.This led to in the intersection of the cold air and the warm and humid air,changing the precipitation phase.Before the rain-snow process,the low-level shear line moved southward and the low-level southwest jet developed.The low-level system was in the warm advection,and the surface temperature was high,thus the precipitation phase was rain.After 20∶00 on the 28th,the cold advection developed rapidly,cooling the ground rapidly,and a"cold pad"was formed,causing the precipitation phase to turn into sleet.Later,due to the influence of strong cold air from the south,the precipitation phase changed to snow.(2)Through the dynamic diagnosis of divergence and vertical velocity,it is found that the dynamic forcing during the rainfall period was mainly located in the upper layer,while during the snowfall period it was mainly located in the lower layer.(3)The polarization analysis results of the SA dual-polarization Doppler radar show that the differential reflectivity in the larger horizontal reflectivity zone of 20~35 dBz is smaller,being about 0.8~1.6 dBz,and the differential displacement rate is also relatively small,ranging from-1.2 to 0.6,and the correlation coefficient exceeds 0.88.The 0℃line retrieved by microwave radiometer can be used as an important criterion for snowfall.The liquid water content is high during rainfall,and the water vapor concentration decreases significantly during snowfall,by which we can accurately determine the specific time of snowfall.Therefore,the combined application of microwave radiometer and dual-polarization radar can be used as an important ground-based observation equipment for the critical prediction of precipitation phase transition in Huaihua region.