一次台风远距离作用下的西南低涡大暴雨个例分析

Case Analysis on Heavy Rainstorm Caused Southwest Vortex under the Influence of Long-Distance Typhoon

利用2009年8月2—5日发生在川渝地区一次远距离台风暴雨的实况降水资料和NCEP/NCAR再分析资料,研究了远距离台风作用下的水汽和温湿能输送特征;利用25点平滑算子方法研究了台风"天鹅"对此次暴雨影响系统——西南低涡作用下的中尺度特征。结果表明,此次大暴雨过程是在有利的环流背景下发生的,东移的高空槽耦合了西南低涡,远距离的台风"天鹅"使得西南低涡在川渝地区长时间维持,台风"天鹅"倒槽对低涡系统暖湿结构具有重要作用;在台风倒槽偏东气流驱动下,其携带的水汽和能量与西南低空急流输送的暖湿水汽汇合,构建了输送到低值系统附近的水汽和能量通道,增强了强降水区水汽和能量积聚效应,这种积聚效应促使低涡系统物理结构的维持;在台风倒槽顶部偏东气流动力作用下,促使低涡系统中低层正涡度增强,进一步促使垂直涡度增长,对低涡系统动力结构维持起到积极作用,进而促使低涡系统长时间维持,最终导致长时间强降水的发生。

The features of water vapor transport and enthalpy with the influence of the long-distance ty- phoon were studied based on the observation station data and NCEP/NCAR reanalysis data in Sichuan and Chongqing from 2 to 5 August 2009. The mesoscale characteristics of rainstorm system-southwest vortex affected by typhoon ＇Swan were investigated with 25 points smoothing operator. The results show that the heavy rainstorm is due to favorable atmospheric circulation background. The upper trough moving eastward couples the maintaining southeast vortex system with the influence of typhoon ＂Swan＇ . The long distance in typhoon ＇Swan＇ makes southwest vortex maintaining in Sichuan and Chongqing. The in- verted trough of typhoon ＇Swan＇ is significant for warm and humid structures of vortex system. The mois- ture and energy driven by the typhoon trough easterly flow converge with the warm water vapor transpor- ted moisture and energy by southeast warm airflow, which built the moisture and energy channel that transported moisture and energy to low system neighborhood and enhanced accumulation effect in heavy rainstorm area. The accumulated effect contribute to the maintenance of low vortex system physical struc- ture. The easterly airflow at the top of the inverted trough plays a positive role in promoting maintaining of the low vortex system dynamic structure, which enhanced positive vorticity at the middle and low level of vortex system and further promoted the vertical vorticity increasing. The maintained low vortex system leads to the occurrence of prolonged heavy precipitation ultimately.