Air-Sea Transition Zone Evolution over the Arabian Sea Region during the Summer Monsoon Onset: Case Study Using a Data Assimilative Regional SKRIPS Coupled Model

Prior to the South Asian monsoon onset, the Arabian Sea experiences a warming phase from January to April. The Arabian Sea mini warm pool (ASMWP) becomes one of the world’s warmest oceanic regions during this period characterized by high sea surface temperatures exceeding 30°C (> 30°C). Given the pronounced warming trend witnessed over the past century in the ASMWP region and the broader tropical Indian Ocean, understanding the mechanisms governing this anomalous warming and its role in the changes to the monsoon onset is crucial. In our study, we employed a data assimilative regional coupled ocean–atmosphere model tailored for the Arabian Sea region to analyze how the ASMWP impacts key monsoon characteristics, such as rainfall and wind. Our findings show that inhibiting oceanic upwelling in the coupled model causes the western Arabian Sea to be anomalously warm, which in turn leads to increased evaporation in the region. This leads to greater water vapor transport to the eastern Arabian Sea, resulting in increased monsoon convection and precipitation. We will also present results from an atmosphere-ocean coupled energy budget analysis of tropical convective discharge-recharge cycles during monsoon onset. Sensitivity analyses using stand-alone WRF and MITgcm models are also performed to investigate the processes in the Arabian Sea transition layer.