Sensitivity of the Asian Summer Monsoon water vapor transport to Arabian Sea SST anomalies: A case study from 2023

Prior to the South Asian monsoon onset, the Arabian Sea experiences a warming phase and the Arabian Sea mini warm pool (ASMWP) becomes one of the world’s warmest oceanic regions during this period, characterized by sea surface temperatures exceeding 30 Celsius degrees. To understand the role of this anomalous warming, we performed an SST sensitivity experiment using the Weather Research and Forecasting (WRF) atmosphere model for the 2023 monsoon when the initial SST is high but declines faster than in normal years. We found that if the SST declines slower than normal, the off-shore precipitation significantly increases in most of the warm pool region, but decreases in the north Arabian Sea and Western Ghats. To understand the precipitation differences, we separate the integrated vapor transport (IVT) components and find that the water vapor and wind changes affect precipitation. From the water vapor budget analysis, the changes in water vapor are due to (1) stronger evaporation and precipitation in the warm pool region and (2) moisture advection outside the warm pool region. The changes in the wind speed can be explained by the pressure adjustment mechanism. When the warm pool SST declines slower, pressure gradients are generated and cause wind divergence, then the weak cyclonic anomaly of the wind redistributes the water vapor. Finally, we examined the vertically integrated buoyancy using an idealized plume model. We find that the atmosphere is less stable and the deep convective discharge–recharge cycles are stronger under warmer SST conditions .