浙北梅雨季低空急流特征及其与暴雨的关系

Characteristics of Low-Level Jets over Northern Zhejiang in Meiyu Season and Their Relationship with Heavy Rain Events

应用2004—2011年常规探空资料、浙江北部雨量资料和2011年NCEP/NCAR再分析资料,对梅雨季影响浙北的西南低空急流进行统计,并在此基础上对急流活动与浙北暴雨的关系进行了分析,为浙江北部梅雨期暴雨的预报提供实际参考价值。结果表明:西南风低空急流在700hPa层上出现次数最多,自上而下减少,其活动有明显的日变化特征,早晨增强,傍晚减弱;在不同类型的低空急流中,以SJ型、DJU型和TJ型居多,而DJL型急流偏少。浙北梅雨季暴雨发生前近90%伴有急流活动,其中DJU型急流较多;夜间暴雨比白天暴雨更依赖于低空急流,夜间暴雨发生前12h即有低空急流建立。2011年6月中旬的暴雨集中期对应着两次西南风低空急流的增强过程,低空急流最大风速出现在600hPa附近并向低层伸展。

Based on the conventional radiosonde rainfall data from 2004 to 2011 of the northern Zhejiang and 2011 NCEP/NCAR reanalysis data,analyzed are the statistic Characteristics of low-level jets and their relationship with heavy rain events.The results show that the south-west low-level jet at 700 hPa appeared most frequently;the frequency decreased with altitude,and there was significant diurnal variation,strengthening in the morning and weakening in the evening;in different types of low-level jets,SJ DJU,and TJ occurred relatively frequently.There were nearly 90% rainstorms over the northern Zhejiang in Meiyu season accompanied with low level jets,most of which were the DJU type.The night rainstorms were more closely related to low level jets,compared with daytime rainstorms,and low level jets occur usually 12 h before the happening of the night storms.The heavy rain process in mid-June 2011 corresponded to two enhancing processes of the south-west low-level jet,with the maximum wind speed at 600 hPa and stretching down to the lower levels.