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Strengthened Regulation of the Onset of the South China Sea Summer Monsoon by the Northwest Indian Ocean Warming in the Past Decade

Abstract

Traditionally, a delayed (early) onset of the South China Sea summer monsoon (SCSSM) has been observed to follow a warm (cold) El Niño-Southern Oscillation (ENSO) event in winter, supporting high seasonal predictability of SCSSM onset. However, the empirical seasonal forecasting skill of the SCSSM onset, solely based on ENSO, has deteriorated since 2010. Meanwhile, unexpected delayed onsets of the SCSSM have also occurred in the past decade. We attribute these changes to the Northwest Indian Ocean (NWIO) warming of the sea surface. The NWIO warming has teleconnections related to (1) suppressing the seasonal convection over the South China Sea, which weakens the impacts of ENSO on SCSSM onset and delays the start of SCSSM, and (2) favoring more high-frequency, propagating moist convective activities, which enhances the uncertainty of the seasonal prediction of SCSSM onset date. Our results yield insight into the predictability of the SCSSM onset under the context of uneven ocean warming operating within the larger-scale background state of global climate change.

摘 要

通常,冬季发生厄尔尼诺(拉尼娜)时,次年的南海夏季风爆发会偏晚(偏早)。这种对应关系意味着南海夏季风爆发具有很高的季节可预测性。然而,从2010年以后,仅根据上述的对应关系,很难成功预测南海夏季风爆发的早晚。与此同时,南海夏季风爆发在年代际尺度上也表现出异常偏晚。研究发现,这些异常的表现跟西北印度洋的海温增暖有关:一方面,西北印度洋海温增暖能够在季节尺度上抑制南海地区的对流,削弱了ENSO对南海夏季风爆发的调控作用,推迟南海夏季风的爆发时间;另一方面,增暖的印度洋海温有利于触发更多的次季节及天气尺度的对流活动,进而影响南海夏季风的爆发,增大南海夏季风爆发季节预测的不确定性。本文揭示了全球变暖背景下,海洋的不均匀增温对南海夏季风爆发可预测性的影响。

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Acknowledgements

This study was jointly supported by the National Natural Science Foundation of China (Grant Nos. 42005011, 41830969), the Scientific Development Foundation of the Chinese Academy of Meteorological Sciences (CAMS) (Grant No. 2020KJ012 and 2020KJ009), the Basic Scientific Research and Operation Foundation of CAMS (Grant Nos. 2021Z004). This study was also supported by the Jiangsu Collaborative Innovation Center for Climate Change.

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Correspondence to Ning Jiang.

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Article Highlights

• The seasonal forecast of SCSSM onset based on ENSO has frequently failed, and the onset time has been delayed since 2010.

• The NWIO warming has delayed the SCSSM onset by enhancing the western Pacific subtropical high pressure system in May.

• The NWIO warming induces more convective activities and reduces the seasonal predictability of SCSSM onset.

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Strengthened Regulation of the Onset of the South China Sea Summer Monsoon by the Northwest Indian Ocean Warming in the Past Decade

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Ai, Y., Jiang, N., Qian, W. et al. Strengthened Regulation of the Onset of the South China Sea Summer Monsoon by the Northwest Indian Ocean Warming in the Past Decade. Adv. Atmos. Sci. 39, 943–952 (2022). https://doi.org/10.1007/s00376-021-1364-8

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  • DOI: https://doi.org/10.1007/s00376-021-1364-8

Key words

  • Indian Ocean
  • South China Sea summer monsoon
  • monsoon onset
  • ENSO

关键词

  • 印度洋
  • 南海夏季风
  • 季风爆发
  • ENSO