Response of Australian Summer Monsoon Precipitation to a Strengthening Antarctic Circumpolar Current

The Australian summer monsoon (AUSM) is the strongest monsoon in the Southern Hemisphere and it is greatly influenced by the climate conditions in the Indo-Pacific and adjacent regions. Inspite of the substantial studies of the monsoon, the linkage between the AUSM and the high-latitude Southern Ocean climate has not been fully understood. This study investigates how AUSM rainfall is affected by the Antarctic Circumpolar Current (ACC) by simulating scenarios with a closed and an opened Drake Passage with the Community Earth System Model. It is found that AUSM precipitation decreases as a result of reduced local humidity caused by a strengthening ACC. An opened Drake Passage leads to strengthening ACC and Atlantic Meridional Overturning Circulation, which in turn creates an El Niño-like state in the Pacific. This weakens the Walker Circulation, resulting in reduced local moisture, anomalous subsidence over the AUSM region, and a subsequent decrease in monsoon precipitation.