Interdecadal enhancement in the interannual variability of the summer monsoon meridional circulation over the South Chin
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Interdecadal enhancement in the interannual variability of the summer monsoon meridional circulation over the South China Sea around the early 1990s Zhewen Wang1 · Zhiping Wen2,3,6 · Ruidan Chen1,4,5,6 · Xiuzhen Li1,4,5,6 · Sihua Huang1 Received: 7 February 2020 / Accepted: 10 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The interdecadal enhancement in the interannual variability of summer monsoon meridional circulation (SMMC) over the South China Sea around the early 1990s is investigated. Results show the change in the SMMC variability may arise from the interdecadal shift in the leading modes of low-level geopotential height over East Asia–Australia and Indo–Pacific sea surface temperature anomalies (SSTAs) in boreal summer. Before the early 1990s, the leading mode of Indo–Pacific SSTAs shows a zonal tripole pattern, with abnormally warm eastern Pacific and northern Indian Ocean and cold western Pacific. At the lower level, the western North Pacific cooling and northern Indian Ocean warming generate an anticyclonic anomaly over western North Pacific, while the cooling over the Maritime Continent and east of Australia favors an abnormal anticyclone over Australia. Hence region-wide positive geopotential height anomalies cover East Asia–Australia, which resemble the major mode of geopotential height and generate weak south–north pressure gradient and SMMC variability. After the early 1990s, the leading SSTAs mode shifts to a zonal dipole with abnormally cold western Pacific and warm equatorial central–eastern Pacific. The central Pacific warming induces an anomalous low-level cyclone over Philippines and it is further maintained by the Maritime Continent cooling. Meanwhile, the cooling over the east of Australia and Maritime Continent favors an abnormal Australian anticyclone. The low-level geopotential height thus shows south–north dipole anomalies over East Asia–Australia, resembling its major mode and generating obvious meridional pressure gradient and SMMC variability. The atmospheric responses to different SSTAs modes are confirmed by CAM4 experiments. Keywords Summer monsoon meridional circulation · Interannual variability · Indo–Pacific SST anomalies · Subtropical high · Australian high
* Zhiping Wen [email protected] 1
Center for Monsoon and Environment Research, School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, China
2
Department of Atmospheric and Oceanic Sciences, Institute of Atmospheric Sciences, Fudan University, Shanghai 200433, China
3
Innovation Center of Ocean and Atmosphere System, Zhuhai Fudan Innovation Research Institute, Zhuhai 518057, China
4
Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou, China
5
Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
6
Jiangsu Collaborative Innovation Center for Climate Change, Nanjing, China
1 Introduction The Hadley cell is a thermal-driven circulation in both hemispheres, ch
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