Model simulation of the influence of anthropogenic aerosols on the Asian monsoon

Aerosols, in particular those related to anthropogenic activities, including black carbon, organic carbon, and sulfate aerosols, have been found to affect the Asian monsoon through direct and indirect aerosol radiative forcing. In this work, we use the coupled regional Weather Research and Forecasting model with Chemistry (WRF-Chem) to understand how aerosol changes caused by human activities could modulate the Asian monsoon system (i.e., monsoon development and evolution) through aerosol direct and indirect radiative effects. Our modeling results with the consideration of the local emissions show an improvement in simulated monsoon precipitation, when compared to reanalysis data and satellite observations. Aerosols generally induce a reduction in pre-monsoon and monsoon precipitation in East Asia. Over the Indian region, local anthropogenic emissions tend to reduce precipitation in the source regions while slightly increasing precipitation outside of the emission source regions. Analysis of vertical cloud properties suggests that the increased cloud droplet number and prolonged cloud lifetime due to the local anthropogenic emissions are responsible for the reduced precipitation over East Asia. The increase in precipitation in the Indian region is corresponding to the decrease in the cloud base level. Anthropogenic aerosols from local emissions also play a very important role in the simulated surface temperature, radiation, and monsoon circulations.