冬奥会张家口赛区一次降水相态特征分析

利用冬奥会气象观测站网资料、ERA5的0.25°×0.25°高分辨率再分析资料、常规探空资料以及激光雷达和风廓线雷达资料，从环流形势、温湿度和微物理特征以及雷达特征等方面对2020年11月17-19日冬奥会张家口赛区一次明显的雨转雪天气过程进行分析。结果表明：低层前期的暖湿西南气流，为降水提供好的水汽和能量条件，后期强的干冷平流为相态转换提供有利条件。赛区出现雨转雪时，700 hPa温度低于-2℃，同时850 hPa温度低于2℃。零度层高度的快速下降是相态转换的重要温度判据，0℃线降到距地面400 m左右赛区降水相态已经转变为纯雪，低层风向的转向对赛场的雨雪相态转换有一定的指示意义。随着高空云冰和雪水含量逐渐增加，其出现最大值后，雨雪相态开始转换。降雪时激光雷达最大探测高度比降雨时有明显的降低，风廓线雷达低层风场的变化和雨雪相态关系密切，风廓线雷达探测的垂直速度变化也能反映雨雪相态的转换。

Analysis of phase characteristics of a precipitation process in Zhangjiakou area of Winter Olympic Games

Based on the meteorological observation network data of the Winter Olympics Games,the high-resolution reanalysis data of ERA5(ECMWF Reanalysis v5)(0.25°×0.25°),the conventional sounding data,and the laser radar and wind profile radar data,a rain-to-snow weather process in Zhangjiakou area of the Winter Olympics Games from November 17-19,2020 was analyzed.The variables analyzed include the circulation situation,temperature and relative humidity,microphysical and radar characteristics,and other new data.The results show that the warm and wet southwest airflow in the early stage of the low layer provides water vapor and energy conditions for precipitation,and the strong dry and cold advection in the later stage provides favorable conditions for phase transition.When rain turns to snow in the competition area,the temperature at 700 hPa is below-2℃,while the temperature at 850 hPa is below 2℃.The rapid decline of the height of zero-temperature level is an important temperature criterion for phase transition.When the 0℃line drops to about 400 m above the ground,the phase of precipitation in the competition area has turned into pure snow,and the shift of the wind direction at a low level has certain indicative significance for the phase transition of rain and snow in the competition area.As the content of cloud ice and snow water increases gradually,the phase of rain and snow begins to change after the cloud ice and snow water reach the maximum.The maximum detection height of lidar during snowfall is significantly lower than that during rainfall.The change of low-level wind field of wind profiler radar is closely related to the phase state of rain and snow,and the change of vertical velocity detected by wind profiler radar can also reflect the transformation of rain and snow phase state.