2020年江苏省梅雨异常及暴雨日气候特征分析

利用ERA5再分析资料和江苏省自动站降水数据等,结合江苏地区入、出梅标准,分析了2020年江苏省梅雨的时空分布异常特征,从梅雨特征量和大尺度环流因子等特征,揭示了梅雨异常的关键因子,并对暴雨日的大尺度环流特征进行合成分析,得到影响梅汛期暴雨的关键环流因子。结果表明:(1)2020年江苏省梅雨时空分布显著异常,入梅早、出梅晚,梅期达51 d,比常年平均多出一倍;沿江以南和沿淮东部地区梅雨总量为常年平均的2.5倍;梅汛期共15个暴雨日,强降水持续时间长,区域范围大,整体雨强大。(2)梅雨特征量较好的反映了江苏省梅雨的入出梅时间,当特征量显著增强北抬对梅雨期的开始有较好指示意义,当特征量再次北抬,则梅雨季结束,各特征量均呈现一致的时间变化特征。特征量在梅雨期间的异常波动均与暴雨过程相对应,2020年梅雨特征量的多个异常高值中心反映了梅雨期暴雨过程频繁、降水极端性强的特征。(3)梅雨期间大尺度环流形势异常,西太平洋副热带高压呈显著正异常,强度偏强,脊点偏西,引导其西北侧的西南暖湿气流向江淮地区输送,同时北方位势高度偏低,东北冷涡强度略偏强,浅槽活动频繁,携弱冷空气南下与暖湿气流交汇,形成稳定维持的梅雨锋,是超强梅雨形成的主要环流因子(4)印度洋和孟加拉湾、西北太平洋是江苏省梅汛期暴雨的重要水汽源地,通过强烈的西南风,将暖湿气流向长江下游地区输送,配合上空的强烈辐合抬升运动,导致该地区水汽积聚并稳定维持,有利于出现梅汛期暴雨天气。

Anomalous climatic characteristics during Meiyu period of 2020 and rainstorm days in recent ten years over Jiangsu Province

By using the data from ERA5 dataset and daily precipitation data collected at weather stations in China, anomalous characteristics during Meiyu period of 2020 over Jiangsu Province were analyzed, revealing the possible factors for the ultra-strong Meiyu, and the largescale circulation characteristics of rainstorm days were analyzed to reveal the key circulation factors affecting the rainstorm in Meiyu season. Results indicate that: (1) the Meiyu period of 2020 lasts for 51 days. The amount of precipitation during Meiyu period is 2.5 times than the normal year, which is the first multiple value on record. There are 15 rainstorm days in the Meiyu period of 2020, and the average day of heavy precipitation is 3.3 days. (2) The characteristic quantity of meiyu better reflects the time of entering and exiting the meiyu in Jiangsu Province. When the characteristic quantity significantly increases to the north, it has a good indication for the beginning of Meiyu. When the characteristic quantity again rises to the north, the Meiyu season ends. Each characteristic quantity presents variations of consistent characteristics. The anomalous fluctuations of the characteristic quantities during the Meiyu are corresponding to the rainstorm process. The multiple anomalously high value centers of Meiyu characteristic quantities in 2020 reflect the characteristics of frequent rainstorm processes and extremes during the Meiyu period.(3) In 2020, West Pacific subtropical high is stronger than normal and westward, then the southwest warm and wet air flows along the northwest boundary of the subtropical high transport to the middle and lower reaches of the Yangtze River. At the same time, the northern geopotential height is relatively lower, the northeast cold vortex is slightly stronger, and shallow troughs are active frequently. The weak cold air is carried to the south and converged with warm and humid air. Then a stable and maintained Meiyu front is formed, which is the main circulation factor for the formation of ultra-strong Meiyu.(4) The Indian Ocean-the Bay of Bengal and the Northwest Pacific are important sources of water vapor for rainstorms during the Meiyu season in Jiangsu Province. The warm and humid air is transported to the lower reaches of the Yangtze River via the strong southwest wind, combined with the strong convergence and lifting movement. The water vapor is accumulated in this area and maintain stably, which is conducive to the occurrence of rainstorm in meiyu season.