Interannual variations of the rainy season withdrawal of the monsoon transitional zone in China
The monsoon transitional zone (MTZ) is the interactional belt between humid and arid regions. This study examines the interannual variation of the MTZ rainy season withdrawal over China. A withdrawal index is firstly defined according to pentad mean precipitation data. The index shows pronounced interannual variations, with a significant dominant period around 2–4 years. When the withdrawal of the MTZ rainy season is later than normal, pronounced precipitation increase appears over the MTZ in August. Meanwhile, a significant anticyclonic anomaly appears over the tropical western North Pacific (WNP) and a marked atmospheric wave train is seen originating from the North Atlantic and flowing across Eurasia to East Asia. Both the anomalous anticyclone over the WNP and the negative geopotential height anomalies related to the Eurasian wave train around the MTZ contribute to the precipitation increase over the MTZ in August, and lead to the late withdrawal of the MTZ rainy season in China. It is showed that preceding winter El Niño-like events have a contribution to the generation of anticyclonic anomalies over the WNP. In addition, the northern tropical Atlantic (NTA) sea surface temperature (SST) warming, which is independent of the preceding winter El Niño, is found to play a crucial role in the formation of the WNP anticyclone and the Eurasian atmospheric wave train. The importance of the NTA SST anomalies on the MTZ rainy season withdrawal is also confirmed by a set of atmospheric general circulation model experiments.
KeywordsMonsoon transitional zone Withdrawal of rainy season Northern tropical Atlantic SST WNP anticyclone Eurasian atmospheric teleconnection
We thank two anonymous reviewers for their constructive suggestions, which helped to improve the paper. This study is jointly supported by the National Key Research and Development Program of China (Grant no. 2016YFA0600604), the National Natural Science Foundation of China (Grant nos. 41461144001, 41605050, and 41721004), the Chinese Academy of Sciences “Belt and Road Initiatives” Program on International Cooperation: Climate Change Research and Observation Project (134111KYSB20160010), and the Young Elite Scientists Sponsorship Program by the China Association for Science and Technology (2016QNRC001).
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Conflict of interest
The authors declare that they have no conflict of interest.
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