Processes that Contribute to Future South Asian Monsoon Differences in E3SMv2 and CESM2

• Published in: Geophysical research letters Vol. 51; no. 14
• Main Authors: Meehl, Gerald A., Shields, Christine A., Arblaster, Julie M., Fasullo, John, Rosenbloom, Nan, Hu, Aixue, Neale, Richard, Capotondi, Antonietta, Golaz, Jean‐Christophe, Roekel, Luke, Annamalai, H.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.07.2024; American Geophysical Union (AGU); Wiley
• Subjects: Amplitude; Amplitudes; CESM2; E3SMv2; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; ENVIRONMENTAL SCIENCES; future monsoon; GEOSCIENCES; global coupled earth system modeling; Indian monsoon; Monsoon precipitation; Monsoons; Precipitation; South Asian monsoon; Southern Oscillation; Walker circulation; Wind
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL109056

Two Earth system models are analyzed to gain insight into the processes that govern projected changes in the South Asian monsoon. Warmer present‐day base state tropical SSTs contribute to coupled processes that produce greater future tropical Pacific warming in CESM2 with less of an increase in season‐mean monsoon precipitation compared to E3SMv2. This is attributed to changes in the large‐scale east‐west atmospheric Walker circulation, with relatively larger increases in precipitation and upper‐level divergence over the tropical Pacific and increases in upper‐level convergence over South Asia in CESM2. The stronger El Niño‐like response in CESM2, which increases Pacific precipitation and upper‐level divergence farther to the east, and larger future ENSO amplitude in E3SMv2, produce a greater relative increase in future monsoon‐ENSO connections in E3SMv2 compared to CESM2. This analysis indicates that the key processes that affect future monsoon‐ENSO connections are ENSO amplitude and size of the future tropical Pacific El Niño‐like response. Plain Language Summary Two different Earth system models are analyzed to investigate processes that contribute to possible future changes of South Asian monsoon precipitation and connections to ENSO. The stronger increase of precipitation in CESM2 over the tropical Pacific, due in part to a larger El Niño‐like response of Pacific SSTs, produces less of an increase in future monsoon precipitation in CESM2 compared to E3SMv2. The eastward shift of precipitation in CESM2, along with the larger increase of ENSO amplitude in E3SMv2, produce a stronger future monsoon‐ENSO connection in E3SMv2 compared to CESM2. Key Points Warmer future tropical Pacific SSTs in CESM2 compared to E3SMv2 produce less of an increase in South Asian monsoon precipitation through the Walker Circulation Future monsoon‐ENSO connections are stronger in E3SMv2 compared to CESM2 due to larger increases in future ENSO amplitude and shifts in the Walker Circulation Key processes that affect future monsoon‐ENSO connections are ENSO amplitude and the size of the future tropical Pacific El Niño‐like response