2013年7月四川盆地一次特大暴雨的中尺度系统演变特征

Mesoscale System Study of Extreme Rainfall over Sichuan Basin in July 2013

利用常规观测资料、地面加密资料、卫星观测资料和NCEP再分析资料等,对2013年7月8日四川盆地西部大暴雨过程的天气背景、水汽来源、地面环境场特征、中尺度云团活动等进行了分析并开展了数值模拟研究。这次过程发生在中纬度"东高西低"的环流背景下,西风槽与西太平洋副热带高压稳定的同时有高原东部小槽东移,孟加拉湾低槽槽前西南暖湿气流在盆地转为偏东风,输送充沛水汽。地面偏东风与偏北风形成的中尺度辐合线上有对流云团发展加强,为此次大暴雨的发生提供了有利的中尺度辐合条件。模拟结果表明,在川西高原地形阻挡影响下,偏东气流被迫抬升,配合中低层低涡发展形成的辐合上升,形成有利于对流系统发生和维持的环境条件。近地层辐合线北侧偏北冷空气的侵入促使对流不稳定能量释放,对对流的触发和维持有一定作用。

The atmospheric circulation,sources of water vapor,mesoscale systems related to extremely heavy rainfall over the Sichuan Basin on 8 July 2013 are analyzed by using the conventional data,surface dense observation,satellite data and NECP reanalysis data.This process occurs in the background with 'high pressure to the east and low pressure to the west'.A small trough moves eastward over the eastern part of plateau under the stable weather pattern of westerly trough and subtropical high over Sichuan Basin.The southwest flow from the Bay of Bengal veers to easterly in Sichuan Basin transporting the moisture to western Sichuan Basin.The surface mesoscale convergence line which developed from surface easterly and northerly winds is the favorite condition for the development and strengths of convective cloud cluster.The simulated results from WRF model show that the effect of steep terrain in western Sichuan Basin and the development of low vortex provides favorite conditions for development of the convective system.The north wind invading to the north of the surface convergence line induces to the realease of convective energy,which is also favorite for the outbreak and maintainence of convective systems.