Forced Response in the Mean State and Interannual Variability of the Indian Summer Monsoon in Future Projections

The Indian summer monsoon (ISM) is a complex system that plays a significant role in the climate of South Asia. We used Community Earth System Model 2-Large Ensemble (CESM2-LE) simulations to explore the forced response in the mean state and interannual variability of the ISM in future projections. The model is able to reproduce the mean state and interannual variability of the ISM during historical periods. The strengthening of monsoon circulation during excess rainfall years and weakening during deficient years are also well simulated by the model. It is also noticed that though the low-level jet stream shows a weakening during deficit monsoon years, it has more eastward extension up to the western Pacific Ocean compared to excess monsoon years. In simulations for future years, the mean structure of both the low-level jet stream and the tropical easterly jet stream becomes weaker compared to historical years. However, the precipitation pattern shows an enhancement in the future periods, and also the excess rainfall years in the future can be wetter than the historical excess years. Thus, the outcomes of CESM2-LE simulations are essential for formulating better plans for handling the effects of monsoon variability and policy-making efforts aimed at mitigating the impacts in a warming world.