Influences of North Pacific anomalies on Indian summer monsoon onset

Devanil Choudhury*, Yurun Tian, Wen Chen, Yongqi Gao

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

This study finds a significantly decreasing (increasing) trend (1979–2018) of sea level pressure (SLP) over coastal East Asia (far North Pacific) during May and June, which resembles the negative (positive) Pacific Decadal Oscillation (PDO) (North Pacific Oscillation, NPO)-like pattern. Thus, we examine May composite differences between early and late Indian summer monsoon (ISM) onset years. Sea surface temperature (SST) differences show that early (late) ISM onset is accompanied by a negative (positive) PDO-like state. Whereas, in SLP, an intense low pressure over northwestern India, the Arabian Sea to Southeast Asia (far North Pacific, East Asia) is associated with the early (late) onset. During the early onset, warm surface air temperature (SAT) anomalies over southeast Russia propagate towards Central Asia to the Middle East and the northwest Indian subcontinent, strengthening the land-sea thermal contrast, which subsequently strengthens the monsoon low. We thus show how the positive NPO, negative PDO, and high spring Bering Sea ice link with the SAT anomalies. In the early onset, more wave packets generated in response to these North Pacific anomalies propagate towards the Atlantic and European region, reaching and converging over the northwest Indian subcontinent. The warm surface anomalies possibly draw eastward-propagating waves towards northwest India, thus intensifying the monsoon low there. Meanwhile, in the CAM5 PDO simulation, we observe a similar pattern of atmospheric responses, where warm SAT anomalies associated with stationary Rossby wave trains propagate from the North Pacific towards the North Atlantic to Central Asia and the northwest Indian subcontinent, strengthening the monsoon low. Terefore, our study highlights the crucial role of the North Pacific anomalies in modulating the ISM onset processes via atmospheric pathways.

Original languageEnglish (US)
Pages (from-to)3111-3123
Number of pages13
JournalQuarterly Journal of the Royal Meteorological Society
Volume147
Issue number739
DOIs
StatePublished - Jul 1 2021

Keywords

  • Bering Sea ice
  • CAM5
  • ISM onset
  • North Pacific Ocean
  • PDO
  • WAF

ASJC Scopus subject areas

  • Atmospheric Science

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