An Investigation of the Characteristics of Indian Summer Monsoon Low‐Pressure Systems Under Stratospheric Aerosol Geoengineering

Abstract

Monsoon Low‐Pressure Systems (LPSs) that govern the rainfall of the Indian Summer Monsoon (ISM) contribute more than half of its rainfall and extreme rainfall events. In this study, we explore how LPS activity changes under greenhouse warming and Stratospheric Aerosol Intervention (SAI) using simulations from the fully coupled CESM2.1.3 climate model. We simulate three different climate scenarios: CTRL (control climate), 2XCO2 (doubling of ), and UNIFORM (a globally uniform stratospheric sulfate aerosol forcing superimposed on the 2XCO2 climate). In the 2XCO2 simulation, the global mean surface temperature increases by 3.22 K, accompanied by a weakened ISM circulation, reflected in a weaker Walker circulation, reduced vertical zonal wind shear, and weaker low‐level Barotropic Shear (BS). However, despite 6% increase in the All‐India rainfall (AIR) due to increased atmospheric water vapor, the total count of LPSs and LPS days decreases by approximately 9%–14%, but the systems on average produce stronger rainfall and extreme rainfall events in central and northern India. The UNIFORM scenario restores global mean surface temperature within 0.03 K of CTRL and partially revives monsoon circulation, BS, and recovers LPS frequency and spatial distribution toward CTRL levels. However, this aerosol experiment forcing suppresses the hydrological cycle, decreasing atmospheric moisture and AIR by 3.82% compared to CTRL (9.28% relative to 2XCO2), along with weakened LPS rainfall and extreme rainfall events. In summary, while uniform SAI can partially revive monsoon circulation and LPS activity, it simultaneously suppresses the thermodynamically driven increase in rainfall and extreme rainfall events associated with greenhouse warming.