江淮地区夏季持续性降水特征及其与东亚高空急流的联系

围绕1960—2011年江淮地区夏季持续性降水展开对单站和区域性持续4 d及以上降水的分析，并探讨其与东亚高空急流的联系。研究发现，近年来持续4 d及以上降水的频数有增多趋势，且在江淮地区其影响范围有逐渐扩大的趋势。持续4 d及以上单站降水频数EOF分析的前两个模态均与极锋急流和陆上副热带急流的协同作用有关。当极锋急流北移和陆上副热带急流南移时，冷暖空气易在江淮地区的西北部相遇，利于较长持续时间的单站降水在该地区发生，易于导致第一模态的全场一致变化。与第二模态相关的高空急流配置表现为陆上副热带急流的减弱和极锋急流的增强，两支急流的强弱配置通过影响水汽输送和上升运动导致江淮地区形成南湿北干的异常型。进一步研究了江淮地区持续4 d及以上区域性降水与急流协同作用的关系发现，在事件发生之前极锋急流显著增强，副热带急流略有增强。伴随着两支急流的变化，西北太平洋副热带高压和北风产生持续性异常，利于冷暖空气活动，导致持续时间较长的区域性降水发生 

THE CHARACTERISTICS OF SUMMER PERSISTENT RAINFALL OVER YANGTZE-HUAIHE RIVER VALLEY AND ITS RELATIONSHIP WITH THE EAST ASIAN JET STREAMS

Based on the summer persistent rainfall over the Yangtze-Huaihe River Basin (YHRB) during 1960—2011, the characteristics of both the individual-station-based and regional persistent rainfall and the relationship between the East Asian jet streams are investigated in this study. With focus on the long-duration precipitation (4d and above), the results indicate that the frequency has increased and the impact stations have expanded in recent years. Both the concurrent variation of the EASJ and the East Asian Polar Front jet stream (EAPJ) have contributed to the first two modes of EOF. Associated with the polar-ward (equator-ward) shift of the EAPJ (EASJ), the cold-dry air and warm-humid air may converge over YHRB and easily trigger the long-persistent precipitation. For the EOF2, the strengthened EAPJ and weakened EASJ may result in the southern-flood-northern-drought precipitation anomaly, via the water vapor and ascending motion. We further investigate the longer regional persistent precipitation. Nearly 7 days precedent of the precipitation onset, the EAPJ and EASJ significantly enhance, particularly for the EAPJ. Consequently, the persistent western Pacific subtropical high and north wind anomalies may benefit the warm-humid and cold-dry air activities, and therefore sustain the precipitation