基于卫星资料的西北地区高原涡强降水分析

Analysis of the Heavy Precipitation Caused by Plateau Vortex in Northwest China Based on Satellite Data

GPM(Global Precipitation Measurement)卫星目前被广泛应用于对流系统的研究中,但受限于卫星轨道扫描方式,在中纬度青藏高原东部区域,GPM轨道观测数据捕获完整的强对流系统较为困难。本文利用全球降雨观测GPM卫星资料、FY-4A卫星资料、NCEP-FNL和ERA-Interim再分析资料,结合地面观测资料,研究了2018年7月1日发生在高原东坡的一次暴雨强降水系统结构。结果表明:层云降水和对流性降水组成的混合性降水云团中,对流云样本数只有层云的1/5,但平均降水率是层云的14倍,对总降水的贡献达到75%,对流性降水贡献远高于南方强降水系统;强降水质心离地高度约2 km,具有比我国南方同类强对流系统更明显的低质心特征;对流云内云滴谱较宽,云粒子半径差异较大,2~5 km高度出现明显的粒子累积带,与层云系统具有显著差异。在副高外围西南气流的引导下,来自孟加拉湾的水汽通道打通,甘肃省南部700 hPa比湿可达16 g·kg^(-1),大气可降水量普遍达到40 kg·m^(-2)以上,加之大气不稳定能量较高,高原涡和700 hPa切变线合并触发了此次对流性强降水。受云团前侧高压脊阻挡,暴雨云团从高原东部初生至发展旺盛阶段用时接近4 h,自西向东移动约3个经度,属于准静止型暴雨云团,暴雨云团移速缓慢是导致此次局地极端强降水的重要原因。

Global Precipitation Measurement(GPM)satellites has been currently widely used in the study of convective systems at present.Limited by the orbital scanning mode of GPM satellite,it was difficult to capture complete severe convective systems with GPM orbital observation data in the eastern region of the Tibetan Plateau.In this study,the structure of a heavy rainfall system occurred over this region on 21 July 2018 has been researched by using GPM and FY-4A satellite data,ERA-Interim and NCEP-FNL reanalysis data in combination with ground observation data.The result indicates that although the number of convective cloud samples was 1/5 of the stratiform cloud samples,but averaged convective rainfall rate was 14 times larger than the stratiform rainfall rate and the contribution of convective rainfall to the total precipitation reached 75%.The contribution of convective rainfall is much higher than that of southern China heavy rainfall system.The top of the heavy rainfall system reached up to 15 km with a low core structure about 2 km above the ground,which was more obvious than that of similar strong convective systems in southern China.The convective cloud droplet spectrum and cloud particle radius differ widely.There was an obvious particle accumulation zone in convective cloud at the height of 2~5 km,which was significantly different from the stratiform cloud.In the early stage of heavy rainfall,precipitable water reached to 40 kg·m^(-2) with relative humidity to 16 g·kg^(-1).The heavy rainfall system triggered by plateau vortex and shear line at 700 hPa,consisted of a main stratiform precipitation cloud cluster and several scattered convective precipitation cloud clusters characterized by high precipitation intensity.Blocked by the high-pressure ridge,the quasi-stationary rainstorm cloud cluster took nearly 4 h from the initial stage to the strongest stage within 3 longitudes.The slow movement of heavy rain clouds led to local heavy rainfall in southeast Gansu.