The modulation of Indian summer monsoon onset processes during ENSO through equatorward migration of the subtropical jet stream

Devanil Choudhury, Debashis Nath*, Wen Chen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

In this study, we demonstrate a new mechanism, on how the warm phase of El Niño and Southern Oscillation (ENSO) delays the Indian Summer Monsoon onset through coupled ocean-atmospheric processes. Strong basin-wide warming is prominent over North Indian Ocean (NIO) during the El Niño years. The warming is intense over the South West Indian Ocean (SWIO) due to the westward propagation of the equatorial Rossby waves from the Pacific Ocean. It increases the convective activities over the southern tropical Indian Ocean (0–10° S), adjacent to the SWIO region. The warming over the SWIO and the NIO strengthens the divergent wind from the Indian Ocean to the sub-tropics via a wind-evaporation-SST feedback mechanism, which causes more upper-level convergence within 30° N latitudes. Besides, a warmer Indian Ocean enhances the upper-level diabatic heating over the southern Arabian Peninsula and Eastern Indian landmass. These factors strengthen but shift the local Hadley circulation over the Indian Ocean more southward, with an ascending branch centered over the SWIO region. The shifting of the local Hadley circulation during the El Niño years causes the Sub Tropical Jet (STJ) to migrate more southward and centered more over the Indian subcontinent. This southward movement of the STJ over the Indian subcontinent in response to the El Niño condition inhibits the establishment and propagation of the tropical easterly jet during the monsoon season, which subsequently hinders the monsoon circulation, thus delays its onset.

Original languageEnglish (US)
Pages (from-to)141-152
Number of pages12
JournalClimate Dynamics
Volume57
Issue number1-2
DOIs
StatePublished - Jul 2021

Bibliographical note

Funding Information:
The authors highly acknowledge the scientific discussions and exchanges with scientists and teachers at the Centre for Monsoon System Research, Institute of Atmospheric Physics. The authors also would like to thank the anonymous reviewers for their valuable suggestions. This work is supported jointly by the Ministry of Science and Technology of China (2016YFA0600604), Key Research Program of Frontier Sciences, CAS (QYZDY-SSW-DQC024), National Natural Science Foundation of China (Grant No. 41750110484, 41675061).

Funding Information:
The authors highly acknowledge the scientific discussions and exchanges with scientists and teachers at the Centre for Monsoon System Research, Institute of Atmospheric Physics. The authors also would like to thank the anonymous reviewers for their valuable suggestions. This work is supported jointly by the Ministry of Science and Technology of China (2016YFA0600604), Key Research Program of Frontier Sciences, CAS (QYZDY-SSW-DQC024), National Natural Science Foundation of China (Grant No. 41750110484, 41675061).

Publisher Copyright:
© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.

Keywords

  • ENSO
  • Hadley circulation
  • Indian summer monsoon onset
  • Subtropical westerly jet
  • Tropical easterly jet

ASJC Scopus subject areas

  • Atmospheric Science

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