Weakening of Indian Summer Monsoon Synoptic Activity in Response to Polar Sea Ice Melt Induced by Albedo Reduction in a Climate Model.

The effect of polar sea ice melt on low latitude climate is little known. To understand the response of the Indian summer monsoon (ISM) synoptic activity to the sea ice melt, we have run a suite of coupled and uncoupled climate model simulations. In one set of simulations, the albedo of sea ice is reduced so that it would melt due to increased absorption of solar radiation. The coupled model simulation with a reduced sea ice albedo resulted in an almost complete melting of the sea ice in summer in both hemispheres. A high‐resolution (50 km) atmospheric general circulation model (AGCM) is forced with the climatological annual cycles of sea surface temperature (SST) and sea ice concentrations (SIC) from the coupled model outputs to better resolve synoptic scale variability. In the high‐resolution AGCM simulations forced with SST and SIC from the sea ice melt experiments, the ISM circulation weakened substantially, and the monsoon low‐pressure systems (LPS) activity experienced an overall decline of 23%, with a widespread weakening in the south and a moderate strengthening over the north, in response to a decline of 78% (24%) in SIC over the Arctic (Antarctic) in the June–September season. The changes in the LPS activity in response to polar sea ice melt are found to be mostly driven by the changes in low‐level absolute vorticity and vertical shear over the Bay of Bengal. Plain Language Summary: The sea ice is melting rapidly in a warming climate, which can have feedback effects on the climate system. However, the impact of sea ice melt on low latitude climate is not adequately understood. The Indian summer monsoon (ISM), known as the lifeline of South Asia, is essential to the water security of more than 1.5 billion people. We examined the response of the ISM to the polar sea ice melt using a suite of global climate model experiments. Our simulations show that the monsoon circulation and rainfall weaken substantially due to the sea ice melt. Further, the number of propagating precipitating vortices embedded in the monsoon circulation declined by about 22% in the sea ice melt experiments. Our results suggest that the Arctic and Antarctic sea ice melt could have severe implications for the water security of South Asia. Key Points: Mean monsoon and low‐pressure systems (LPS) weaken in response to the Arctic and Antarctic sea ice melt in climate model simulationsThe LPS genesis declines by 22% in response to a decline of 78% (24%) in sea ice concentrations over the Arctic (Antarctic) in the June–September seasonThe decline in LPS genesis is linked to changes in low‐level vorticity and vertical shear [ABSTRACT FROM AUTHOR]