Changes in the Indian Summer Monsoon Synoptic Activity in a Warming Scenario

The Low Pressure Systems (LPS) that form during summer monsoon season can penetrate deep inland over India and thus play a critical role in bringing rainfall over core monsoon region. A robust technique is developed to detect and track LPS from reanalysis and climate model simulations. This technique is applied to Coupled General Circulation Model (CGCM) simulations of fifth generation Coupled Model Inter-comparison Project (CMIP5). Analysis of LPS tracks in RCP8.5 scenario simulations show that, under extreme warming projections, the spatial pattern of monsoon synoptic activity over India changes significantly. The changes in synoptic activity in warming scenario are manifested as weakening of the monsoon trough and a south-westward shift of the LPS tracks. Consistent with the changes in the spatial structure of synoptic activity, the ratio of LPS-related to LPS-unrelated rainfall also changes. The change in the pattern of synoptic activity is well explained by the largest mode of variability in surface temperature over Southeast Asia, suggesting that the changes in LPS are triggered by external radiative forcing.