Sensitivity of the 2023 Asian Summer Monsoon Water Vapor Transport to Arabian Sea Surface Temperature Anomalies

Abstract Prior to the onset of the South Asian monsoon, the Arabian Sea experiences a warming phase during which the Arabian Sea mini warm pool (ASMWP) becomes one of the world's warmest oceanic regions, characterized by sea surface temperatures (SSTs) exceeding 30C. To understand the role of this warming in monsoon evolution, we performed an SST sensitivity experiment using the Weather Research and Forecasting (WRF) atmospheric model. Our case study focuses on the 2023 monsoon, which was characterized by high initial SST that declined faster than in normal years. We found that if the SST declines more slowly than normal, the off‐shore precipitation increases by more than 100% around the ASMWP, but decreases in the northern Arabian Sea and the western coast of India. To understand the precipitation differences, we separated the components of the integrated vapor transport (IVT) and found that the changes in both water vapor and wind affect precipitation. The analysis revealed that the changes in water vapor are due to (a) stronger evaporation and precipitation in the ASMWP, and (b) moisture advection outside the ASMWP. It is also shown that the pressure adjustment mechanism can explain the changes in wind speed. With warmer SST conditions, the atmosphere pressure drops and causes wind convergence, thereby creating a weak cyclonic wind anomaly that redistributes the water vapor. Finally, we examined the vertically integrated buoyancy in the context of an idealized plume model. In the ASMWP, temperature changes contribute to increases in buoyancy below 850 hPa, but humidity changes contribute to far more increases in buoyancy between 800 and 600 hPa, which enhance the convection and lead to more precipitation.