青藏高原东北部一次强暴雨过程环流特征分析

Analysis on Circluation Character of a Severe Rainstorm Process in Northeastern Tibetan Plateau

利用NCEP再分析资料,对2007年8月25日青藏高原(下称高原)东北部的强暴雨天气过程的影响系统、垂直环流特征、不稳定条件和水汽输送进行了分析和研究。结果表明:(1)强暴雨天气过程发生的主要影响系统是西伸到高原东部的副热带高压、生成于高原中部的热低压及自高原北侧移入的冷温槽。(2)高原东北侧的冷空气移上高原后,呈楔形插入高原南侧西南暖湿气流的下部,高低层之间产生的强风切变和暴雨区上空形成强盛上升气流是暴雨发生的有利环流条件。(3)热低压中的上升气流与冷锋后的下沉气流构成纬向(纬圈方向)闭合环流,经向(经圈方向)闭合环流是由高原热低压中的上升气流与副热带高压中的下沉气流构成的,垂直闭合环流的形成提供了稳定的上升气流和源源不断的暖湿气流,持续的降水造成了暴雨天气。(4)θse线的锋区进入暴雨区,配合强上升运动和高原中部热低压暖中心的加强伸展到高原东部,在暴雨中心区(36°N、102°E)附近上空的中低层之间产生了强的大气层结对流不稳定,是暴雨发生的稳定度条件。(5)由于高原中部热低压逐渐东移,在热低压东部和西伸副热带高压西部之间形成强暖湿气流带,将水汽源源不断地输送到高原东北部,同时冷空气通过祁连山进入高原东北部,在暴雨区上空形成偏南和偏西的强水汽辐合带,暖湿气流交汇造成强暴雨的发生。

Based on the NCEP data,the severe rainstorm process of northeastern Tibetan Plateau on August 25,2007 is analyzed including its influencing system,feature of vertical circulation,instability condition and water vapor condition.The results show that：（1） The predominate influencing systems of this process are the subtropical high which extends westward to the south of Tibetan Plateau,the tropic low pressure generating from the central Plateau and the cold-temperature trough coming from the northern Plateau.（2） The cold air moving from the northeast of Plateau inserts into the warm-wet air′s bottom which warm-wet air comes from the southern of Plateau.Not only the strong wind shear in the layer but also the forceful low-high lower-upper updraft generating from the upper layer are advantageous to the occurrence of rainstorm.（3） The zonal closed circulation is constituted by the air flow from the hot low on the Plateau and the downdraft in the subtropical high.The latitudinal closed circulation is constituted by the air flow in the hot low and the downdraft after the cold front.（4） With the front zone of θ se moving into the storm area,the strong upward motion and the warm-center thermal low pressure in the central Plateau strengthening and extending to the eastern Plateau,a strong convective instability is generated in the middle-lower layer of the rainstorm center near 36°N,102°E which has a condition of stability.（5） A cold air moves into the northeast Plateau through Qilian Mountain and then arrives at near region rainstorm.An intense warm-wet flow is transported to the northeast Plateau which is generated between the northern thermal low and the western subtropical high.Finally,a severe rainstorm is caused by the encounter of the intense warm-wet flow and the water vapour convergence area.