Contrasting impacts of Asian sulfate aerosols on regional summer extreme precipitation under different climate backgrounds

Abstract. This study investigates the impact of Asian sulfate aerosols on regional summer extreme precipitation under both pre-industrial and pre-industrial +1 K climate states, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 (FORTE2) with Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce extreme precipitation, characterized by lower frequency and weaker intensity over East and South Asia in both climates, but the suppression is more pronounced over northern India in the +1 K climate. Atmospheric energy budget analysis reveals this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate state, an increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, reducing the meridional temperature gradient and thus diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses between the two climates results from the nonlinear effect between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that continued global warming alone will exacerbate Asian sulfate aerosols’ weakening of precipitation, including extremes, over northern India. This implies that future reductions in aerosol emissions may unmask or amplify extreme precipitation increases in this region.