青海高原短时强降水时空分布及天气学概念模型

Temporal-Spatial Distribution Characteristics and Synoptic Conceptual Models of Short-Time Heavy Rainfall over the Qinghai Plateau

利用青海52个地面气象站小时降水并结合常规观测资料和NCEP FNL再分析资料,使用K-means聚类法和合成分析方法,将青海的短时强降水天气环流形势配置划分为西风气流型、副热带高压型和高原低涡切变型。结果表明:(1)青海短时强降水发生在95°E以东地区,中心在东南部;主要出现在5-9月,8月最多,7月次之;每日17:00-2:00(北京时)出现站次多。(2)西风气流型的影响系统是高空槽和平直西风短波槽,高低空风垂直切变引起的动力不稳定导致短时强降水发生;副热带高压型是以低层偏南或偏东暖湿气流引起的热力不稳定造成短时强降水;高原低涡切变型是高原加热及弱冷空气活动使得低层锋区加强触发短时强降水。(3)合成分析表明:对流层高层的南亚高压和副热带西风急流,对流层中低层的短波槽、冷式和暖式辐合切变线,偏南暖湿气流,高原加热场等是短时强降水发生的主要影响系统。(4)来自印度季风低压偏南方向的水汽、西太平洋副热带高压东南方向的水汽、西风带高空槽西北方向的水汽在青海东部形成水汽辐合区,有利于短时强降水发生。

Based on the hourly rainfall data and other conventional data from 52 surface weather stations,and the National Centers for Environmental Prediction(NCEP)Final Analysis(FNL)data,the synoptic circulation patterns for the short-time heavy rainfall over the Qinghai Plateau are classified into three categories,namely the westerly airflow pattern,the subtropical high pattern,and the plateau low vortex-shear line pattern. Results show that the short-time heavy rainfall over the Qinghai Plateau occurs in the area east of 95°E,with the center in the southeast of the plateau. It mainly occurs from May to September,with the maximum in August,followed by July. For the diurnal variation,the short-time heavy rainfall occurs most from 17: 00 to 22: 00(Beijing Time),i. e.,the nightfall to midnight. The influence systems of the westerly airflow pattern are the high-level trough and the straight westerly short-wave trough. The dynamical instability caused by the vertical wind shear induces the short-time heavy rainfall. For the subtropical high pattern,the thermal instability caused by the low-level southerly or easterly warm-humid airflows results in the short-time heavy rainfall. For the plateau low vortexshear line pattern,the plateau heating,and the weak cold airflow strenthen the low-level frontal area and trigger the short-time heavy rainfall. The composite analysis shows that the South Asian high,the subtropical westerly jet in the upper troposphere,the short-wave trough in the middle-lower troposphere,the shear line,the southerly warm-humid airflow,and the plateau heating field are the main influence systems for the short-time heavy rainfall. The convergence of water vapor from the Indian monsoon,the southeast of the western Pacific subtropical high and the northwest of the westerly trough is conducive to the short-time heavy rainfall in eastern Qinghai.