Impacts of Oceanic Mesoscale Structures on Sea Surface Temperature in the Arabian Sea and Indian Summer Monsoon Revealed by Climate Model Simulations

Climate models typically have a cold sea surface temperature (SST) bias for the Arabian Sea, which regu-lates the Indian monsoon system as a water vapor source. Since the SST for the Arabian Sea is critical for the Indian mon-soon, a better understanding of the processes that affect the SST is required. In this study, the effects of mesoscale oceanic variability on simulations of the Arabian Sea SST and Indian summer monsoon precipitation were investigated based on a comparison of climate model experiments in which non-eddying and eddy-permitting ocean components are coupled. In the eddy-permitting model, warm water advection driven by mesoscale variability near the Gulf of Aden and the Gulf of Oman increases the SST in the western Arabian Sea. Lateral eddy heat transport enhances warm water outflows to the Arabian Sea and suppresses surface water cooling by coastal upwelling during the southwestern monsoon season. Further-more, a sensitivity experiment shows the primary importance of resolving oceanic mesoscale eddies and the secondary im-portance of resolving the Persian Gulf and Red Sea for the Arabian Sea SST. Also, the summer monsoonal precipitation decreases (increases) over the southeastern Arabian Sea (western and northern India) in the eddy-permitting model due to enhancement of wind convergence in the lower troposphere. Atmospheric general circulation model experiments indi-cate that the precipitation difference is partly caused by SST changes over the western Arabian Sea. The findings imply that the ocean resolution of climate models is a key factor in efficiently simulating the Indian monsoon.