Modulation of Indian Summer Monsoon Rainfall response to ENSO in the recent decades and its large-scale dynamics

Author:

Sharma Tanu1,Ratna Satyaban B.1,Pai D. S.2

Affiliation:

1. India Meteorological Department

2. The Institute for Climate Change Studies (ICCS)

Abstract

Abstract The El Niño-Southern Oscillation (ENSO) is one of the major drivers of prominent ocean-atmosphere coupled phenomenon over the equatorial Pacific Ocean that strongly modulates the interannual variability of Indian summer monsoon rainfall (ISMR). However, the relationship between ENSO-ISMR has gone through secular variation during different decades. This study comprises a detailed analysis of the changing relationship between the ENSO and ISMR during two recent independent 30-year periods; (i) 1961–1990 and (ii) 1991–2020, using Sea Surface Temperature (SST), rainfall and various atmospheric variables. It was observed that the negative correlation of ENSO with ISMR has significantly weakened during 1991–2020 compared to 1961–1990. It was found that the La Niña associated positive rainfall intensity over central India was reduced during 1991–2020 due to weakening of vertical wind shear as compared to 1961–1990. Similarly, the El Niño associated negative rainfall intensity was reduced over large parts of north and central India during 1991–2020 due to weaker subsidence anomaly compared to 1961–1990. However, the weakened ENSO-ISMR relation in the recent period (1991–2020) mostly contributed from the disconnection of La Niña-ISMR relationship compared to El Niño-ISMR, as seen from the large-scale dynamics including the changes in the vertical wind shear and the shift in the Walker circulation. This study highlights how the changes in the patterns and the intensity of the atmospheric as well as oceanic fields within the tropical Indo-Pacific Ocean contributed to the weakening of ENSO-ISMR relation in the recent decades.

Publisher

Research Square Platform LLC

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