Study On Influences Of Aerosols On Lower Warm Cloud And Aerosol-cloud Radiative Effect In Shanghai

The mechanism of aerosol-cloud-radiation is one of the most important scientific problems to be solved.By using multiple satellites,such as Terra,Aqua and CALIPSO,together with ground micro pulse lidar,the spatial especially vertical distribution of aerosols were analyzed in Shanghai.With the data of MODIS carried on both Terra and Aqua,aerosol-cloud database of Shanghai was established,which would be helpful in understanding the three dimensional space distribution characteristics of aerosols in the Shanghai better,and in studying the infulences of aerosols on lower warm cloud.Finally,the radiation forcing of aerosols was calculated by the latest Accu RT radiative transfer model system.The main conclusions were as follows:(1)The average AOD(2006-2015)in urban and suburban areas of were both from 0.9 to 1.0 using MODIS data.The central urban areas were mainly polluted by fine particles,while the suburbs were dominated by coarse particles.The AOD showed a pronounced annual cycle with highest values in summer and lowest values in autumn.In spring,there were more dust aerosols appearing both near the ground and above 3 km due to the dust weather in the north.The contribution of fine particles in summer was much more than that in other seasons,which was closely related to the increase of secondary organic aerosols.Polluted dust,polluted continental(urban or industrial)and biomass burning aerosols from local and surrounding emissions were also the main aerosol type.In autumn,local pollution was the most important factor affecting air quality.The main aerosols were polluted dust,polluted continental(urban or industrial)and biomass burning aerosols.In winter,there was a certain amount of biomass burning aerosols at higher altitude,which was related to the sudden haze pollution incident in the north.In addition,the polluted dust and continental aerosols were also the main type of aerosols.(2)The study of haze and floating dust event showed the differences of aerosols between them.Haze aerosols were generated from the surface and then lifted up,but floating dust aerosols were transported vertically from higher altitude to the surface.The AOD of aerosol is slightly higher than that of haze.However,the extinction coefficient of aerosol is lower than that of floating dust aerosol.In addition,the haze weather boundary layer height and pollution conditions affect each other,while the dust weather pollution is affected by the atmospheric boundary layer.(3)The aerosol optical thickness(AOD),cloud fraction(CF),the total water vapor(WV)and K index showed a similar annual variation.The maximum value of them all appeared in summer,but the maximum peak time of CF was slightly behind the AOD.The influences of WV and atmospheric stability on the cloud development were greater than aerosols on it.The more water vapor content and the more unstable atmosphere were more conducive to the development of clouds.With the weakening of atmospheric stability,the influence of aerosol on CF was weakened rapidly.However,the effect of aerosol on the cloud top pressure(CTP)was increasing.Excluding the influences of meteorological conditions,the increase of aerosol in Shanghai would lead to the decrease of CF,the decrease of CTP.As a result,the more aerosols was favorable to the vertical development of clouds,not to the horizontal development of clouds.(4)The influence of AOD on the cloud droplet effective radius(CER)was closely related to the liquid water path(LWP),the total water vapor(WV)and the vertical distance(? H)between the height of aerosol layer and cloud bottom.The results showed that the effect of aerosols on CER in Shanghai followed not only the "Twomey" effect,but also the anti "Twomey" effect,which is mainly due to the different LWP.When LWP was less than 50 g m-2,the cloud particles increased rapidly with the increase of LWP,known as the anti-"Twomey" effect.When LWP was in the range of 50 g m-2 and 150 g m-2,CER decreased with the increase of aerosols,which followed the "Twomey" effect.The effect of aerosol on CER became larger with the decrease of WV and ? H.It was noteworthy that there was almost no correlation between aerosol and cloud when ? H was great than 150 m.(5)The short-wave radiation effect of aerosols in Shanghai was cooling whether at the top of atmosphere,at lower levels or at the surface.The absolute value of the radiative forcing increased gradually with the decrease of the height,and reached the maximum at the surface.At the top of atmosphere,the shortwave radiation of clouds reduced by the influence of aerosols,however,aerosols at the surface enhanced the short-wave radiation cooling effect of clouds.Aerosols and clouds could enhance the atmospheric absorption rate and reduce the solar radiation,In addition,the emergence of the clouds could effect the upper and lower atmospheric absorption rate,and the influence on upper atmospheric absorption rate was greater than that on lower atmospheric absorption rate.