江淮梅雨与东亚副热带夏季风进程变异的关系

根据中国气象局《梅雨监测业务规定》中的入、出梅标准,结合1960—2016年全国661个常规气象站逐日气象资料,以及NCEP/NCAR月平均再分析资料,分析了江淮梅雨和东亚副热带夏季风进程变异的时空特征,提取季风关键区(32°~34°N,112°~120°E,包含17个站点),并分析了江淮梅雨和季风关键区的联系与成因。结果表明:1960—2016年平均梅雨期为6月8日—7月15日,平均梅雨量为303 mm。比东亚平均梅雨季的开始时间早9 d,比其结束时间晚7 d。梅雨量在近57 a中也呈波动式变化,但整体为上升趋势。入梅越早,出梅越晚,则梅雨期越长,梅雨量越多。副热带夏季风推进到关键区的平均时间为5月19日,其在1970s末和1990s末分别发生了由偏晚向偏早和由偏早向偏晚的突变。夏季风到达关键区偏早时,出梅日偏晚,梅雨量偏多,季风到达偏晚时,出梅日偏早,梅雨量偏少。副热带夏季风推进时间和江淮梅雨量呈全区一致的负相关,负相关区位于湖南、湖北及江西三省临近的两湖地区。东亚副热带夏季风到达关键区时间偏早(晚)年,500 hPa高度场上乌拉尔山—鄂霍茨克海为正(负)距平,阻塞高压增强(减弱);日本海附近为负(正)距平,东亚大槽加深(西退北缩),加强(削弱)了槽后冷空气向南输送且不(有)利于中低纬度副热带高压的北跳,西太平洋副热带高压中心强度增强(减弱),位置偏西(东),其西北侧的西南暖湿气流输送加强(减弱),江淮地区有水汽的辐合(辐散),有(不)利于梅雨量偏多。

The relationship between the Meiyu in the Yangtze-Huaihe Region and the variation of the East Asian subtropical summer monsoon process

Based on the Meiyu criterion provided by China Meteorological Administration,the daily meteorological data of Meiyu from 661 conventional stations in China during the period of 1960—2016,and the monthly mean reanalysis data of NCEP/NCAR,the spatial and temporal characteristics of Meiyu and the variation of the East Asian subtropical summer monsoon process were analyzed;the key monsoon areas(32°—34°N,112°—120°E,including 17 stations)are extracted,and the relationship between key monsoon areas and Meiyu and their causes of formation are analyzed.The results show that the average Meiyu period during the period of 1960—2016 lasted from June 8 to July 15,and the average precipitation is 303 mm.The average onset time of the Meiyu period is nine days earlier than that in the East Asia,and the end time of the Meiyu period is seven days later than that in the East Asia.The precipitation in the Meiyu period has fluctuated in the past 57 years,but shows a rising trend on the whole.An earlier start of Meiyu season is always followed by a later end,and a longer Meiyu period means more precipitation.The average time for the subtropical summer monsoon to advance to the key area is May 19.The subtropical summer monsoon suddenly changed from early arrival to late arrival,and from late arrival to early arrival in the late 1970s and late 1990s,respectively.When the summer monsoon arrives at the key area early,the Meiyu period will end late,accompanied with a large amount of precipitation.When the summer monsoon arrives at the key area late,the Meiyu period will end early,accompanied with less precipitation.The subtropical summer monsoon and the Meiyu precipitation are consistently negatively correlated with the whole region,and the negative correlation center is at the junction of Hunan,Hubei and Jiangxi.The East Asian subtropical summer monsoon arrives at the key area early(late),the Ural Mountains-Okhotsk Sea is positive(negative)anomalies at the level of 500 hPa,and the blocking high pressure is enhanced(weakened).The pressure anomaly near the Sea of Japan is negative(positive),the East Asian deep trough is strengthened(weakened),which strengthens(weakens)the cold air that is transported southward after the trough and is(not)beneficial to the northward jump of the mid-low latitude subtropical high.The West Pacific subtropical high-pressure center is strengthened(weakened),and moves westward(eastward).The southwestern warm and humid airflow at the northwestern side is strengthened(weakened),and water vapor converges(diverges)at the Yangtze-Huaihe Region,which is(not)conducive to the increase of precipitation.