乌鲁木齐机场一次寒潮多相态降水过程分析

Process Analysis of Multi-phase Precipitation During Cold Wave at Urumqi International Airport

利用常规观测资料及新疆区域自动站、乌鲁木齐风廓线雷达、多普勒雷达资料,针对2015年2月13日发生在乌鲁木齐地区的一次雨雪天气过程,从大气背景环境、风温垂直结构、冷暖平流及雨、雪相态转换成因等方面进行分析。结果表明:此次寒潮降水天气的大尺度环流背景是中亚地区高空脊向极区发展,脊顶北风引导极地冷空气南下,在西西伯利亚地区发展成大槽。大槽东移进入新疆地区后,槽后冷空气与北上的西南暖湿气流在天山山区汇合造成此次寒潮降水天气。乌鲁木齐机场出现雪转雨再转雪等相态转换,是由于先受冷平流控制,随着地面冷锋前部暖平流临近,低空暖层厚度加大,降雪粒子在降落过程中融化为雨滴,地面降水相态转为雨夹雪和雨,冷锋系统进入后,再次处于冷平流控制下,降水相态再由雨转为雪。风廓线雷达风场资料的分析结果表明,空中冷暖平流的性质和转换与降水相态变化有较好的对应关系;风廓线垂直速度显示,降雪粒子与雨滴粒子相比,垂直速度较小且雨滴粒子主要集中在1000 m以下。利用多普勒雷达产品分析地面冷锋的移动、空中冷暖平流的变化,有助于对降水相态变化的预报。

Using conventional observation data and data from Xinjiang area automatic weather stations, wind profile radar, Doppler radar are used to analyze the background environment, vertical structure of wind and temperature, cold and warm advection and the cause of rain and snow conversion of a multi phase precipitation on February 13, 2015 in Urumqi. The results show that： this cold wave precipitation happened in the background of middle Asia high ridge roof developing northward, leading the polar region cold air southward, and developing into trough at west Siberia area. When the trough moved eastward to Xinjiang area, the cold air behind it and southwest warm air moving northward converged at the Tianshan mountain and caused the cold wave precipitation weather. The reason of multi phase conversion between “snow rain snow” at Urumqi airport was that the area was controlled by cold advection at the beginning, when the warm advection ahead of cold front moved closer, the lower warm layer became thicker, the snow particle melted to rain particle while falling, so the phase of precipitation became to sleet and rain. When the cold front moved across, the area was controlled by cold advection again, and precipitation phase changed from rain to snow again. Analysis results of wind profile radar data show the characteristic and transformation of cold and warm advection in upper air are corresponding to the conversion of precipitation phase quite well. Wind profile vertical velocity indicates snow particle is slower than rain particle and rain particle is mostly distributed below 1000 m. Using Doppler radar to analyze the movement of surface cold front, the transformation of cold and warm advection in the air is conductive to the forecast of precipitation phase conversion.