South Asian Summer Monsoon Precipitation Is Sensitive to Southern Hemisphere Subtropical Radiation Changes

• Published in: Geophysical research letters Vol. 51; no. 11
• Main Authors: Hingmire, Dipti, Hirasawa, Haruki, Singh, Hansi, Rasch, Philip J., Kim, Sookyung, Hazarika, Subhashis, Mitra, Peetak, Ramea, Kalai
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.06.2024; Wiley
• Subjects: Bias; Climate; Climate models; Climatological means; Equator; Global climate; ITCZ; Livelihoods; Meridional circulation; monsoon; Monsoon precipitation; Monsoons; Ocean basins; Oceans; Precipitation; precipitation bias; Radiation; Rainfall; Sensitivity; Solar radiation; Southern Hemisphere; Subtropical climates; Summer; Summer monsoon; Wind; Zonal flow; Zonal flow (meteorology); Southern Hemisphere
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108499

We study the sensitivity of South Asian Summer Monsoon (SASM) precipitation to Southern Hemisphere (SH) subtropical Absorbed Solar Radiation (ASR) changes using Community Earth System Model 2 simulations. Reducing positive ASR biases over the SH subtropics impacts SASM, and is sensitive to the ocean basin where changes are imposed. Radiation changes over the SH subtropical Indian Ocean (IO) shifts rainfall over the equatorial IO northward causing 1–2 mm/day drying south of equator, changes over the SH subtropical Pacific increases precipitation over northern continental regions by 1–2 mm/day, and changes over the SH subtropical Atlantic have little effect on SASM precipitation. Radiation changes over the subtropical Pacific impacts the SASM through zonal circulation changes, while changes over the IO modify meridional circulation to bring about changes in precipitation over northern IO. Our findings suggest that reducing SH subtropical radiation biases in climate models may also reduce SASM precipitation biases. Plain Language Summary Precipitation from South Asian Summer Monsoon (SASM) is of high significance to the livelihoods of over a billion people. As the global climate continues to evolve, it is essential to have a clear understanding of the possible future changes to the SASM. However, current state‐of‐the‐art climate models have difficulties in simulating climatological mean SASM precipitations. Here we study sensitivity of SASM precipitation to subtropical southern ocean radiation as one of the possible causes of SASM precipitation bias. Our experiments indicate that SASM precipitation is sensitive to southern hemisphere (SH) subtropical radiation changes particularly to those in subtropical Pacific. These findings imply that improving SH subtropical radiation biases might improve SASM precipitation simulations in climate models. Key Points We test if biases in southern hemisphere shortwave radiation contributes to biases in South Asian summer monsoon precipitation in the CESM2 Reducing incoming shortwave radiation in the subtropical southern hemisphere reduces dry biases over continental South Asia This effect is mostly due to forcing in the South Pacific, with less impact from the Atlantic or Indian Ocean