2016年我国梅雨异常特征及成因分析

Characteristics and Causes Analysis of Abnormal Meiyu in China in 2016

利用国家气候中心梅雨监测资料和NCEP再分析资料,对2016年我国梅雨异常特征及其大尺度环流成因进行了分析。结果表明:(1)2016年我国梅雨有明显的区域特征,其中江南区入梅偏早14天,与1995年并列成为1951年以来入梅最早的年份,出梅偏晚11天,梅雨期(量)偏长(多),但梅雨期日平均降水量偏少;长江区入梅和出梅均偏晚,梅雨期接近常年,但梅雨量偏多一倍以上,梅雨量和梅雨期日平均降水量分别为1951年以来历史同期第三和第二高值;江淮区入梅、出梅及梅雨期接近常年,但梅雨量偏多。(2)对流层高、中、低层环流系统冬夏季节性调整和转变显著提前的共同作用,导致了2016年江南区入梅显著偏早;东亚副热带西风急流、西太平洋副热带高压(副高)和东亚夏季风涌在7月中旬阶段性地南落导致了江南区和长江区出梅偏晚。(3)受到前冬超强厄尔尼诺衰减和春、夏季热带印度洋全区一致海温模态偏暖的影响,梅雨期副高异常偏强,副高西南侧转向的水汽输送异常偏强,并在长江区和江淮区与北方弱冷空气辐合,造成梅雨量异常偏多。

Based on the National Climate Center Meiyu monitoring data and NCEP reanalysis dataset, the characteristics of abnormal Meiyu and associated large scale circulation during the Meiyu period of 2016 in China are analyzed. The results are as follows：（1） There were obvious regional characteristics of Meiyu in 2016 in China. The Meiyu onset date over regions to the south of the Yangtze River was 14 days earlier than normal and was the earliest as that in 1995 since 1951. The Meiyu outset date in 2016 was 11 days later than normal with a longer duration and more Meiyu precipitation, whereas daily average precipitation was weaker. The Meiyu onset（outset） date over the Yangtze River valley was later than normal, while the Meiyu duration was close to normal with more than double of normal Meiyu precipitation. The amount of total Meiyu precipitation and average daily precipitation are ranked as the third and the second highest values since 1951, respectively. The Meiyu onset, outset, and duration over the Yangtze–Huaihe valley were close to normal, but the amount of total Meiyu precipitation was more than normal.（2） The significantly early Meiyu onset over regions to the south of the Yangtze River was induced by abnormally early transition of East Asian circulation from winter pattern to summer pattern. The southward shift of East Asian subtropical upper-level westerly jet and the western Pacific subtropical high（WPSH） were combined with the southward displacement of the East Asian summer monsoon surge in middle July, leading to late than normal Meiyu outset.（3） The decay of the extremely strong El Ni？o event in the previous winter and the persistent warming of the Indian Ocean Basin-Wide mode（IOBW） in spring and summer were the main reasons that caused the WPSH to be extremely strong during the Meiyu period in 2016. The abnormally strong moisture flux from the southwest of the WPSH and weak cold air from the north converged over the Yangtze-Huaihe valley, resulting in higher than normal Meiyu precipitation over this region.