Interdecadal Increase in Summertime Extreme Precipitation over East China in the Late 1990’s
Interdecadal Increase in Summertime Extreme Precipitation over East China in the Late 1990’s
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DOI：
10.3389/feart.2022.969853
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发表时间：
2022-08
期刊：
影响因子：
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通讯作者：
Z. Zang;Junyao Luo;Y. Ha
中科院分区：
文献类型：
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作者：
Z. Zang;Junyao Luo;Y. Ha
本文主要研究了20世纪90年代后期中国东部夏季极端降水的年代际变化及其物理机制。结果表明，1979-2020年中国东部夏季极端降水呈上升趋势，1997/1998年前后出现显著的年代际增加。1997年以来，我国东部地区极端降水异常由偏少转为偏多，对应于对流层低层的强烈上升运动。华南低层出现一个由强东南风控制的气旋式正涡度环流。从南亚副热带高压异常偏强和热带海洋纬向海温梯度引起的大气环流异常的角度分析了中国东部夏季极端降水年代际增多的原因。1997年以后，青藏高原春季出现感热正异常，是维持南亚高压强度的主要因素。此外，热带海洋海温呈明显的“高-低-高”纬向梯度分布，印度洋和西太平洋海温距平为正，海洋大陆海温距平为负。纬向SST梯度导致海洋大陆上空异常下沉气流和边界层辐散。热带纬向海温梯度触发了一个局地Hadley环流，其上升分支位于华东地区。这是一个有利于极端降水发展的环流条件。另外，自90年代后期以来，华南地区对流层上层的南亚高压有加强的趋势。高层的异常辐散有效地维持了高空的上升运动，反过来又促进了极端降水的发生。结果表明，青藏高原春季感热变化和热带海温纬向梯度共同影响了中国东部夏季极端降水，导致了20世纪90年代后期极端降水的年代际增长。
This study focuses on the interdecadal increase of summertime extreme precipitation over East China in the late 1990s and physical mechanisms behind. The results show that summer extreme precipitation over East China during 1979–2020 demonstrates an upward trend and a significant interdecadal increase occurs around 1997/1998. Since 1997, extreme precipitation anomalies turn from less than normal to more than normal, corresponding to a strong upward movement in the lower troposphere over East China. A cyclonic circulation with positive vorticity controlled by a strong southeasterly flow appears in the lower level over South China. The reasons for the interdecadal increase of summer extreme precipitation over East China are analyzed from the perspective of the abnormally strong South Asian subtropical high (SAH) and the atmospheric circulation anomalies caused by zonal sea surface temperature (SST) gradient in the tropical oceans. After 1997, positive sensible heat anomalies appear over the Tibetan Plateau in spring, which is the major factor that maintains the intensity of the SAH. Besides, the SST of the tropical oceans presents an obvious “high-low-high” zonal gradient distribution with positive sea surface temperature anomaly (SSTA) in the Indian Ocean and western Pacific, and negative SSTA over the Maritime Continent. The zonal SST gradient results in an anomalous downdraft and boundary layer divergence over the Maritime Continent. The tropical zonal SST gradient triggers a local Hadley circulation, and its ascending branch is located in East China. This is a circulation condition favorable for the development of extreme precipitation. In addition, since the late 1990s, the SAH has strengthened in the upper troposphere above the southeastern China. The anomalous divergence at the upper level effectively maintains the upward movement, which in turn facilitates the occurrence of extreme precipitation. As a result, the sensible heat changes in the Tibetan Plateau in spring and the tropical SST zonal gradient jointly affect summer extreme precipitation over East China, leading to the interdecadal increase of extreme precipitation in the late 1990s.