A numerical study of the mechanism of aerosols' effect on Asian summer monsoon

In this paper, we use the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) 2001-2010 reanalysis data to evaluate the simulation capability of atmospheric module CAM (Community Atmosphere Model) in the global climate system model CESM for Asian summer monsoon and atmospheric heat sources. The results show that the model can reproduce the main features of the Asian summer monsoon and atmospheric heat sources. The mechanism of aerosol climate effects on the Asian summer monsoon is investigated by sensitive experiments. By analyzing the influence of the inhomogeneous heating changes induced by aerosols on the divergent wind and rotational wind components, the reason for the Asian summer monsoon weakening is explained. The results indicate that the increase in anthropogenic aerosols weakens the Asian summer monsoon in southeastern China, northern Indochina Peninsula and Indian peninsula. The weakened monsoon in southeastern China has led to decrease in inland precipitation and increase in coastal precipitation. Further analysis finds that the anthropogenic aerosols increases result in changes in atmospheric heat sources, which enhance in the Arabian Sea, the Bay of Bengal and the South China Sea and weaken in the eastern China and Indochina peninsula. The aerosols mainly change the atmospheric heat source by affecting latent heat. The changes in latent heat are largely affected by convection process. On the other hand, the changes in atmospheric heat sources alter the thermal structure over the monsoon region and weaken atmospheric heat sources in southeastern China and northern Indochina Peninsula. The weakened atmospheric heat sources reduce the generation of the total potential energy and subsequent transform from total potential energy to divergent winds, resulting in weakened divergent winds. At the same time, the transform from divergent winds to rotational winds decreases in southeastern China and northern Indochina peninsula, which eventually leads to the weakening of the summer monsoon. Moreover, anthropogenic aerosols affect the Asian summer monsoon mainly through affecting atmospheric heat sources and dynamic processes.