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

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.

Assessing the Relationship between October-November-December Rainfall and Indian Ocean Dipole in Recent Decades over Tanzania Following the 2011 Abrupt Change

“…Past studies have documented that Hadley circulation over the Indian landmass is recognized as a meridional overturning circulation in which hot air rises at the equatorial region and moves poleward, where it cools, sinks and moves back to the equator (Sharma et al, 2023). This coupled air-sea feedback over the Indian Ocean is said to modify the meridional overturing during ENSO and IOD phases hence affect the global rainfall distribution, including Indian monsoon summer rainfall (Wu & Kirtman, 2004).…”

Distinct impacts of pure El Niño events on spring rainfall of Sri Lanka

“…During a pure CP El Niño, water availability in Sri Lanka is expected to increase, whereas, during a pure EP El Niño, water availability is expected to decrease, which may affect important sectors such as hydropower, irrigation, and ecosystem functions(Chowdary et al 2014; Karunapala and Yoo 2020; Jayawardena et al 2023). However, it is important to be aware of the potential impacts of increased (decreased) water availability, including the formation of oods (droughts), which can be a severe ecological and economic challenge in Sri Lanka, especially over the wet zone of Sri Lanka(Kajakokulan 2023b, Dilini et al 2014Sharma 2023). Thus, Sri Lanka's spring rainfall responses to different El Niño events provide critical insights into regional impacts and aid ecological and economic management.5 ConclusionTo investigate the impact of pure El Niño events on spring rainfall in SL, we conducted an analysis using 43 years of observational and reanalysis data from 1981 to 2023.…”