六盘山区一次降水天气过程分析

Analysis on the Weather Background and the Macroscopic Characteristics of Cloud Radar During the Primary Precipitation in Liupan Mountain Area

基于六盘山区区域自动站和探空资料、ERA-Interim高时空分辨率的再分析资料以及Ka波段毫米波云雷达资料,采用天气特征分析、物理量诊断以及多资料融合分析方法,对六盘山区一次降水天气过程进行诊断分析。结果表明:该次降水过程是受“两槽一脊”的环流背景以及500 hPa短波槽和700 hPa切变的共同影响形成的稳定性层状云降水;六盘山区降水强盛阶段,水汽通量散度在六盘山系东坡存在低层辐合或弱辐散、高层辐散的动力场,区域平均水汽通量为2.50 g/(s·hPa·cm),水汽来源为孟加拉湾、南海;此次降水前后云层数呈双峰型,降水发生时,云系从多层云变为深厚的单层云,且在小时雨量最大值出现的前1 h,达最大云厚,降水过程结束前1 h,云系由单层云变为双层云,随着降水过程的结束,云系波动性消散;低云云厚的发展有利于促进降水过程的形成。

Based on the regional automatic station and sounding data of Liupan mountain area and the re-analysis data of era-interim with high spatial and temporal resolution,combined with the ka-band millimeter-wave cloud radar,the weather feature analysis,physical quantity diagnosis and multi-data fusion analysis method are used to diagnose and analyze a precipitation weather process in Liupan mountain area.The results show that:(1)The precipitation process is a stable stratiform cloud precipitation formed by the circulation background of two trough and one ridge and the main influencing systems are 500 hPa short-wave trough and 700 hPa shear.(2)In the strong precipitation stage of Liupan mountains,the water vapor flux divergence in the eastern slope of the Liupan mountains system has the dynamic field of low-level auxiliary dispersion or weakly auxiliary dispersion of high-level auxiliary dispersion.The regional average water vapor flux is 2.50 g/(s·hPa·cm)and the source of water vapor is the bay of Bengal and south China sea.(3)The number of clouds before and after the precipitation shows a bimodal pattern.The cloud system changes from multi-layer clouds to thick monolayer clouds at the beginning of precipitation,reaching the maximum cloud thickness 1h before the maximum hourly rainfall.The cloud system changes from single-layer cloud to double-layer cloud.1h before the end of the precipitation process,with the end of the precipitation process,the fluctuation of the cloud system dissipates.(4)The development of low cloud thickness is conducive to the formation of precipitation process.