Can Anthropogenic Aerosol Particles Influence the Asian Monsoon?

Anthropogenic emissions of precursor gases and aerosols have been high in Europe and have grown rapidly with increasing population and industrialization in Asia. Several authors have noted a shift in the monsoon regime around 1979. It has been reported that for example the monsoon - ENSO coupling weakened, the south Asian summer season lengthened and that a shift occurred of summer rainfall in China. We investigate the possible influence of anthropogenic aerosols on the dynamics of the monsoon system with climate simulations of ECHAM4 GCM of the Max Planck Institute for Meteorology in Hamburg. The possible impact of aerosols on the monsoon and the coupled effect of greenhouse gas warming and aerosol on the monsoon system will be assessed. The atmospheric component of the ECHAM4 has a fully coupled aerosol scheme with all major natural and anthropogenic species including black carbon, organic carbon, and sulfate. The ECHAM4 used for this study is run with a mixed layer ocean. The model is capable to simulate the aerosol - cloud interactions and the direct aerosol effect. The meteorology also feeds back to the aerosol burdens. Three sets of experiments are discussed: one set with a run with pre-industrial aerosol and greenhouse gas and a run with present-day greenhouse gas and aerosol concentrations, the second set with present-day greenhouse gas and pre-industrial aerosol and present day greenhouse gases and aerosol concentrations and a third set with pre-industrial and present day greenhouse gas concentrations and an aerosol climatology. All experiments are run for 170 years. The last 50 years are utilized for this study.