人为气溶胶对中国东部冬季风影响的模拟研究

A modeling study of effects of anthropogenic aerosol on East Asian winter monsoon over eastern China

摘要:

采用美国国家大气研究中心（NCAR）的公共大气模式CAM5.1研究了人为气溶胶排放增加对中国东部冬季风的影响，同时通过对比中国东部地区不同人为气溶胶排放源的敏感性试验结果，探讨了人为硫酸盐、黑碳及总人为气溶胶（硫酸盐+黑碳）增加对东亚冬季风的影响。结果表明：冬季硫酸盐气溶胶排放增加的直接和第一间接效应减少了到达地表的短波辐射通量，引起了陆地地表和对流层低层降温，海平面气压升高，增加了海陆间气压梯度，使得东亚冬季风增强。其第二间接效应导致中国南部大尺度降水率减少；黑碳气溶胶排放增加导致到达地表的短波辐射通量减少和大气中短波辐射通量增加，其半直接效应部分抵消了直接效应，故地表温度变化微小且不显著。加热的对流层低层导致中国南部对流活动和对流降水率增加；总人为气溶胶排放增加导致的大气温度变化表现为弱的降温作用，引起中国北部对流和大尺度降水率减少，而南部对流降水率增加。总人为气溶胶和黑碳气溶胶排放增加是导致中国北（南）部的东亚冬季风增强（减弱）的重要因素。

Abstract:

East Asian region is one of the largest monsoon regions in the world,and East Asian winter monsoon(EAWM) plays an important role in the regional climate.Anthropogenic sulfate and black carbon(BC) are most important radiation active aerosols in East Asia.The interaction between aerosols and East Asian monsoon climate has received more and more attention in recent years.In this study,the impact of increase in anthropogenic aerosols on EAWM over eastern China are investigated using the NCAR Community Atmospheric Model version 5.1(CAM5.1),a state-of-the-art climate model considering aerosol direct,semi-direct and indirect effects.The effects of increase in anthropogenic sulfate,BC and both of them on EAWM are decomposed from different sensitivity simulations by changing anthropogenic aerosol emission sources in eastern China,and the experiments differed only in the aerosol and precursor gas emissions.CAM5.1 can generally capture the main features of winter atmospheric circulation in East Asia.
In winter,the direct and 1st indirect effects of sulfate reduce the solar flux reaching the surface,leading to a reduction of air temperature of surface and low troposphere and an increase of sea level pressure over land.Adjustments in surface temperature and pressure fields result in a weakened wind field above 925 hPa.The gradient of pressure between land and sea is increased,which enhances EAWM.The large-scale precipitation in southern China is reduced by the 2nd indirect effects of sulfate,and the convective precipitation is reduced in northern China,which is caused by the changed circulation.In winter,the effects of BC reduce the solar flux reaching the surface,and increase the solar flux in the atmosphere by absorbing.The surface air temperature has an insignificant reduction because the semi-direct effects of BC partly offset the direct.The heating of the low troposphere leads to the enhanced convection and the increased convective precipitation in southern China.The changed circulation results in temperature increase in troposphere over China.Adjustments in surface temperature and pressure fields result in an enhanced north wind in northern China and a weakened wind field in southern China above 925 hPa.The effects of BC result to an enhanced(a weakened) EAWM in northern(southern) China.The effects of BC on cloud are different from sulfate,which come from the feedback of semi-direct effect and the changed circulation.The effects of total anthropogenic aerosols(both sulfate and BC aerosols) result in a weaker reduction of air temperature in winter,which are the common result of two kinds of aerosols.The convective and large-scale precipitations are both reduced in northern China,and the convective precipitation is increased in southern China.The changes in surface temperature and pressure fields also result in an enhanced wind field in northern China and a weakened wind field in southern China above 925 hPa.The effects of total anthropogenic aerosols also result in an enhanced(a weakened) EAWM in northern(southern) China.The effects of total anthropogenic aerosols on monsoon are not simply a linear summation between the two types of aerosols.