Effect of spring Bering Sea ice on the Indian summer monsoon onset process.

We examine the relationship between spring Bering Sea ice concentration (SIC) and the background of the Indian summer monsoon (ISM) onset processes using observational datasets. We select five high and eight low spring Bering SIC years based on the time series analysis from 1980 to 2019. We find that during the high SIC years, upper-level warm temperature anomalies over East Asia are associated with eastward propagating wave-train from the Northeast Pacific Ocean and the North Atlantic Ocean. In addition, the strengthening of the South Asian High (SAH) and weakening of the subtropical jet facilitates the establishment of the tropical easterly jet (TEJ) and favors an early ISM onset in the high SIC years. Also, we find that the SST pattern during the high SIC years coincides with the negative Pacific Decadal Oscillation (PDO-) like SST state over the North Pacific Ocean, which is accompanied by warmer SST over the Southeast Indian Ocean. This SST pattern strengthens the trade wind over the tropical Western Pacific Ocean and develops convergence over Southeast Asia and the Indian Ocean region bringing abundant moisture supply and triggering deep convection. Therefore, high Bering SIC in association with the PDO- like SST pattern and the warm Southeast Indian Ocean strengthens the SAH and TEJ, which subsequently helps to establish a stronger ISM circulation, while vice versa during the low Bering SIC years. [ABSTRACT FROM AUTHOR]