双偏振雷达对一次水凝物相态演变过程的分析

基于常规气象观测资料、NCEP再分析资料以及长沙双偏振雷达、风廓线雷达资料，对湖南2021年12月下旬一次雨雪天气过程降水相态转变的大气环境条件和雷达双偏振特征进行分析，得到以下结论：(1) 降雪前干层消失，湿层增厚，整层湿球温度低于0 ℃，逆温层下冷垫的饱和层结对雪花丛集增长有利，有利于降雪增强。(2) 湘中及以北地区位于700 hPa西南急流出口区，600—800 hPa强烈水汽辐合和中低层强上升气流为暴雪过程提供充足水汽。(3) 25日夜间长沙出现间歇性小雨(雪)和多次短波槽过境密切相关；26日上午西南风转为偏西风导致长沙降雪出现短时减弱；冷垫上西南暖湿气流增强时段、冷垫内东南风转为东北风时段，分别对应26日长沙降雪两个峰值。(4) 不同相态降水时段相关系数(CC)、差分反射率(Z_dr)、水平反射率因子(Z_h)有一定差异，双偏振产品对本次雨雪天气过程中降水相态转变的识别有一定指示作用。(5) 低层“零速度线”成直线且有风速辐合特征，西南急流核增强、向下扩展等特征预示暖湿气流在冷垫之上的动力爬升增强，降雪得以长时间维持、且强度增强；而随着径向速度风场辐散特征出现，降雪逐渐减弱。

A process of hydrometeor phase change with dual-polarimetric radar

Based on the conventional meteorological observation data, the NCEP reanalysis data, the dual-polarization radar data, wind pro? filer radar data, and other datasets, the environmental conditions and dual-polarization radar characteristics of the phase transformation of precipitation in a rain and snow event in Hunan in late December 2021 is studied. The results are as follows: (1) The disappearing of dry lay? er, the thickening of wet layer, the whole-layer wet bulb temperature below 0 ℃, and the saturated stratification in the cold pad under the in? version layer before the snowfall favored the further cluster growth of falling snowflakes, resulting in the further enhancement of snowfall. (2) That the southwest jet exits at 700hPa and the strong water vapor convergences at 600-800 hPa, combined with the significant vertical up? draft at the middle and lower layers, provided sufficient moisture for the snowstorm. (3) The intermittent light rain (snow) in the evening of the 25th is closely related to the transit of short-wave trough frequently. In the morning of the 26th, the southwesterly wind turned to the westerly wind, which led to a short-term weakening of snowfall in Changsha. Furthermore, the warm-humid southwesterly flow strengthened over the cold pad, and the southeast wind in the cold pad turned to the northeast wind, which corresponded to the two peaks of snowfall in Changsha on the 26th. (4) There are certain differences in the correlation coefficient (CC), differential reflectance (Z_dr), and horizontal reflectance factor (Z_h) of different phases of precipitation. The dual-polarization products have a certain indication effect on the identification of rain and snow phases of this case. (5) The low-level