2003年长江流域梅雨过程强降水条件分析

利用2003年6月21～29日NCEP/NCAR再分析资料,计算了这一时间段内各层的大尺度大气环流特征以及水汽通量、水汽通量散度等与降水有关的物理量,并对这些物理量对此次降水过程的不同作用进行了分析,探讨此次梅雨异常偏强的原因。结果表明,在2003年梅雨期间,在对流层中低层,长江流域以南地区有一很强的低空西南风急流,低空急流造成的低层辐合上升气流中将有对流发展,导致水汽大量凝结产生暴雨,凝结潜热的释放又使低层气压降低,南高北低的气压梯度更大,偏南气流加速更快,导致低空急流的维持,也使得暴雨长时间维持;在500 hPa气压面图上,中高纬地区呈现出典型的双阻型环流形势,即乌拉尔山地区和鄂霍茨克附近均被强大的阻塞高压所控制,2个阻高之间是一宽广的西风槽;200 hPa,南压高压作为大气对流层高层最重要的系统在这段时期内基本保持稳定,且高压中心基本与暖中心对应;南压高压的位置使得对流层高层的整个长江流域特别是中游和下游地区有明显的辐散气流。对水汽输送和水汽的辐合辐散的状况分析表明,长江流域是该时期全球范围内水汽汇的一个高值中心,且水汽通量大值区和水汽辐合区与降水大值区基本一致;夏季印度风环流和东亚夏季风是向江淮流域输送水汽的主要通道。

Analysis of Heavy Precipitation Conditions during Meiyu Process in Yangze River Basin in 2003

Based on June 21-29,2003 NCEP/NCAR reanalysis data,each layer large-scale atmospheric circulation characteristics and the vapor flux,vapor flux dispersion degree were calculated,and different functions of these physical quantities on the precipitation process were analyzed,causes for the abnormal strong precipitation were discussed.As indicated by the results,during the period of Meiyu in 2003,in middle and lower level of troposphere,low layer convergence upgrade airflow caused by a strong low level southwest wind jet current in the south region of Yangze River Basin result in convection and a great amount of vapor congealed to produce rainstorm;the release of latent heat decreased low level pressure,the pressure gradient became larger,which caused low level jet current maintaining and long-term continuous of rainstorm.In 500 hPa,the typical double block circulation situation occurred in middle and high latitude region,namely Mount Ural and Okhotsk both were controlled by stronger blocked high pressure with a wide westerly trough between them.In 200 hPa,as the most important system of atmospheric upper troposphere,South Asian High basically maintained stable during the period,and high pressure center was corresponding with thermal center;the location of South Asian High caused obvious divergent flow of whole Yangze River Basin especially for the middle and lower reaches.Analysis of the water vapor transport and moisture convergence and divergence conditions showed that this area is a high value center of the worldwide during the moisture sinks.Water vapor transport high value and water vapor convergence area are corresponding to the precipitation areas.India summer monsoon circulation and East Asian summer monsoon are the main channels of transmission of water vapor to the Yangtze River Basin.