The Response to Spatial and Temporal Phase Differences of Aerosol Radiative Forcing During the South Asian Summer Monsoon

Although modeling studies agree that anthropogenic aerosols can alter monsoon climate, there is still no consensus on the dominant mechanism through which these aerosols act and even the specific climate response. We evaluate the possible mechanisms through which the radiative effect of absorbing aerosols impact the South Asian summer monsoon, using a series of atmosphere-ocean general circulation model runs where aerosol radiative forcing was prescribed with different spatial distributions or at different temporal phases. Monthly climatological forcing values were prescribed over South Asia every year to the Community Earth System Model (CESM 1.0.4) with all model components from atmosphere, ocean, land, to sea and land ice active, and integrated over at least 200 years under year 2000 conditions. Runs prescribed with forcing representing a large uniform aerosol cloud is compared with those with forcing representing a strong inland aerosol concentration. Runs with forcing prescribed only during the pre-monsoonal phase (April-May) are compared to runs with only during the monsoon phase (June-September). These runs are used to understand the mechanisms that operate under realistic forcing throughout the entire season (April-September).