2018年南京梅雨异常特征及环流分析

Characteristics and associated circulation analysis of Meiyu anomalies in 2018 in Nanjing

利用自动站降水数据和NCEP/NCAR再分析资料,结合江苏入、出梅指标对2018年南京梅雨进行讨论,分析导致当年南京梅雨异常的环流因子特征。结果表明:1)当年入梅偏晚、出梅正常,梅雨分布不均匀,总量偏少,其中南部异常偏少8成;2)前期南支槽活动频繁,副热带高压相比同期偏南,季节北跳偏迟,且南亚高压主体偏强,位置偏东偏北,导致入梅偏迟;3)入梅后,副热带高压大幅度北抬,南亚高压东伸明显,加之东北冷涡活动弱,使得冷暖气流交汇偏北,因此江苏沿江地区梅雨量偏少;4)南京地区的梅雨量与6—7月副热带高压的南北跨度具有显著的负相关;5)东亚夏季风偏强时,南京中北部地区的梅雨量很可能偏少。

This paper,based on the index of Jiangsu Meiyu,analyzes the characteristics of Meiyu precipitation in Nanjing in 2018,and the associated circulation causing the anomaly Meiyu,by using the daily precipitation data of Nanjing and daily NCEP/NCAR reanalysis data.The results show the following:1) The Meiyu in Nanjing in 2018 was characterized by the later beginning date,nonuniform distribution of Meiyu precipitation in space,and a significantly lesser amount of Meiyu precipitation (80% less than the climatic mean in the southern Nanjing).2) The previous trough in westerlies was active,and this caused the Northwest Pacific Subtropical High (NPSH) to occur more southerly than normal.In such a case,the seasonal northward of NPSH occurred late,which in turn resulted in a late beginning date of Meiyu.Meanwhile,the South Asia High (SAH) in 2018,which was stronger and more northeastward than the climatic mean,was conducive to a late beginning of Meiyu.3) During the Meiyu period,the ridge of NPSH jumped to north sharply and the SAH was stronger and more northeastward than the climatic mean.These circulations,together with the weak activities of the Northeast China cold vortex,led to a northward conglomeration between cold air and warm air,as well as significantly less rainfall during the Meiyu period in the region along the Yangtze River.4) The amount of Meiyu precipitation in Nanjing shows a negative correlation with the north-south span of the NPSH from June to July.5) In the years of strong East Asia summer monsoon,the Meiyu precipitation in the central and northern parts of Nanjing was less than the climatic mean.These insights will be useful in the forecast of Nanjing Meiyu.