Impact of North Atlantic SST and Tibetan Plateau forcing on seasonal transition of springtime South Asian monsoon circul
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Impact of North Atlantic SST and Tibetan Plateau forcing on seasonal transition of springtime South Asian monsoon circulation Wei Yu1,2 · Yimin Liu2,3,4 · Xiu‑Qun Yang1 · Guoxiong Wu2,3 · Bian He2,3 · Jinxiao Li2,3 · Qing Bao2,3 Received: 3 March 2020 / Accepted: 6 October 2020 © The Author(s) 2020
Abstract The South Asian circulation and precipitation in spring shows a clear seasonal transition and interannual variation. We investigate how the North Atlantic sea surface temperature (SST) and Tibetan Plateau (TP) forcing affect this seasonal transition over South Asia on interannual timescale. Our results suggest that North Atlantic SST can affect the seasonal transition of South Asian monsoon via TP forcing in spring. The positive tripole pattern of North Atlantic SST anomaly during winter–spring can trigger a steady downstream Rossby wave train with cyclonic circulation over the southwestern TP. This forms a spring dipole mode of surface sensible heating and 10 m winds over the plateau, with a westerly (easterly) flow and positive (negative) surface sensible heating over its southern (northern) regions. A distinct land–air coupling configuration in May is then generated on the southwestern TP via such a positive TP dipole mode, which consists of anomalous positive precipitation, negative surface sensible heating and a baroclinic circulation structure with cyclonic circulation in the mid- to upper troposphere and a shallow anticyclonic circulation in the lower layer. The anticyclonic circulation is opposite to the summertime monsoon circulation. It weakens the cross-equatorial flow and water vapor transport to the South Arabian Sea and Bay of Bengal, resulting in in-situ precipitation reduction. Consequently, the seasonal transition in circulation over South Asia from winter to summer is delayed. Keywords Interannual variability · North Atlantic SST · Tibetan Plateau dipole mode · Land–air coupling mode · Seasonal transition over South Asia
1 Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05491-0) contains supplementary material, which is available to authorized users. * Yimin Liu [email protected] 1
China Meteorological Administration–Nanjing University Joint Laboratory for Climate Prediction Studies, School of Atmospheric Sciences, Nanjing University, Nanjing 210023, Jiangsu, China
2
State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
3
University of Chinese Academy of Sciences, Beijing 100049, China
4
Chinese Academy of Sciences Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China
In South Asia, the seasonal transition features as the onset of the monsoon associated with strong rainfall, which is usually considered to be a consequence of the atmospheric circulation response to the seasonal transition of the land–sea thermal contrast induced by the annual cyc
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