Non-local Impact of South and East Asian Aerosols on Monsoon Onset and Withdrawal

Abstract:

The powerful Asian monsoon is of vital importance to the billions of people who are reliant on its rainfall, especially considering that society within its domain is largely agrarian. This monsoon system comprises smaller regional components, including the Indian monsoon and East Asian monsoon. These components are linked to one another through large scale circulation. The impacts of rapidly increasing anthropogenic aerosols over Asia on the monsoon have been widely studied. However, most studies consider only regional impacts, and not the subsequent effects on other geographical components of the system. We use observational and modelling methods to investigate the links between the regional components of the Asian monsoon and how they are affected by aerosols. Satellite observations of aerosol optical depth are used in conjunction with precipitation and atmospheric reanalysis data to investigate the problem at interannual timescales. Modelling experiments using HadGEM2-ES and GFDL CM3 are used to look at longer timescales and the potential influence of long term feedbacks. The HadGEM2 experiments use three time-evolving future anthropogenic aerosol emissions scenarios with the same time-evolving greenhouse gases. The GFDL CM3 experiments are forced by historical regional anthropogenic aerosol emissions. Using these methods, we look at the separate impact that South and East Asian aerosols have on monsoon onset and withdrawal. We focus on impacts in regions non-local to the aerosol source. We will also present proposed mechanisms for the apparent effects based on analysis of large scale circulation and atmospheric heating.