| The Tibetan Plateau influences regional and global climate through dynamic and thermal forcing.Radiative forcing of aerosols can alter the radiation budget and then may affect these processes.In this thesis,the atmospheric chemical-climate model EMAC,which combines the 5th generation European Centre-Hamburg general circulation model（ECHAM5）with the Modular Earth Submodel System（MESSy）Atmospheric Chemistry system,is used to simulate the optical properties and radiation effects of aerosols,and then their spatial and temporal distribution characteristics are analyzed.By comparison with satellites data,it is verified that EMAC can well simulate the total aerosol optical thickness over the Tibetan Plateau.The model simulation shows that dust,water-soluble aerosols and liquid water in their intermixing state are the main aerosol extinction components in this region.Black carbon,organic carbon and sea salt aerosol are the minor aerosol extinction components.In the vertical direction,the maximum aerosol extinction coefficient appears at high altitudes of the Tibetan Plateau.Especially after the eruption of the Nabro Volcano,the extinction coefficient near the altitude of 18km could reach 2.5×10-3 km-1,which is mainly caused by water-soluble aerosols and their liquid water,while dust extinction is small at this high altitude.Seasonal variation of the aerosol direct radiation forcing at top is spring(-1.49W?m-2)>autumn(-1.22W?m-2)>summer(-0.79W?m-2)>autumn(-0.54W?m-2).At the earth surface,the seasonal variation of aerosol direct radiation forcing is spring(-5.77W?m-2)>summer(-4.54W?m-2)>autumn(-3.09W?m-2)>winter(-2.15W?m-2).In the northern region of the Tibetan Plateau,the dust aerosol produces a large positive radiation forcing at the atmospheric top and within the atmosphere and plays a role of heating.In addition,the negative radiative forcing of stratospheric aerosols at the top increased significantly in the second half of 2011,by 55%and 52%compared with the fall and winter of the other two years.The earth’s surface provides energy to the atmosphere by radiative forcing,sensible heat and latent heat.In order to better understand the thermal process of the Tibetan Plateau,this thesis analyzes the sensible heat flux and latent heat flux at the surface.The sensible heat flux is dominant in spring,the latent heat flux is dominant in summer,and the two are similar in autumn and winter.Finally,through model sensitivity experiment,it is found that the variation of regional average optical thickness is-0.020 after the aerosol emission source was closed in South Asia.The optical thickness of aerosol increases in the north of the Plateau,which is mainly caused by dust.Aerosol of South Asia has the most obvious effect on aerosol extinction at 12-18km over the Plateau.The changes of atmospheric top and atmospheric radiative forcing over the Tibetan Plateau are positive,and they are most obvious in the northern part of the Plateau. |
