A Study Of The Mechanism Of The Aerosol Effect On East Asian Summer Monsoon And The Cloud Droplets Spectral Dispersion’s Influence On Aerosol Climate Effect

In this paper,we use the NCEP / NCAR(National Centers for Environmental Prediction / National Center for Atmospheric Research)2001-2010 reanalysis data to test the simulation capabilities of atmospheric module CAM 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 aerosol on the divergent wind and the rotational wind component the reason why the Asian summer monsoon weakened is explained.The results indicate that the increase of anthropogenic aerosols makes the intensity of Asian summer monsoon weaken in the southeastern China,northern part of Indochina Peninsula and Indian peninsula.The weakening of monsoon in southeastern China has led to the decrease of inland precipitation and the increase of coastal precipitation.Further analysis find that the anthropogenic aerosols increases result in changes of 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 aerosol mainly affects latent heat to change the atmospheric heat source.The changes of latent heat is chiefly changes from convection process.On the other hand,the changes of atmospheric heat source alter the thermal structure of the monsoon region to weaken atmospheric heat source in the southeastern China and the north part of the Indochina Peninsula.The weakening of atmospheric heat source reduces the generation of the total potential energy to cut transform from total potential energy into the divergent wind,which weakens.At the same time,in the southeastern China and the north part of Indochina peninsula the transform from the divergent wind into rotational wind decreases,which eventually led to the weakening of the summer monsoon.Moreover,the effect of anthropogenic aerosols on the Asian summer monsoon is mainly through the response of atmospheric heat and dynamic processes.The five methods for solving relative dispersion of the cloud droplet spectra has been evaluated in the model CAM5.The simulation ability and the aerosol effect on climate from five different parameterization schemes has been compared.The model result from old scheme shows that it reflects the distribution of some meteorological parameters well when compared with observations except some deviations in the polar area.Compared with the old scheme,the scheme with new method for solving relative dispersion of the cloud droplet spectra has improved the modeling result in precipitation amount and cloud short wave radiation forcing much and it works best among the five schemes.There is a little modeling improvement of other parameters.The total aerosol climate effects with five different schemes show good agreement with each other.The total cloud amount increases while the surface temperature,the precipitation amount and the net radiation flux at the top of atmosphere decrease.Both of the cloud long and short wave radiation forcing are enhanced.The difference of aerosol climate effect on the precipitation amount,the cloud long wave radiation forcing and the upwelling net long wave radiation flux from five schemes are large while the total cloud amount,the surface temperature,the cloud short wave radiation forcing and the downwelling net short wave radiation forcing flux have difference only in polar area.