| There are a large number of aerosol particles in Eastern China including high level of anthropogenic emissions produced by human activity,black carbon and other carbonaceous produced by biomass burning and dust aerosols produced by sandstorm.Aerosol influences the local climate such as monsoon intensity and precipitation distribution,conversely,monsoon in eastern China also plays an important role in the wet deposition and transmission process of aerosol.Meanwhile,the distribution of aerosol can affect the cloud macrophysical and microphysical characteristics in eastern China.Therefore,it is of great importance to investigate the aerosol-cloud interaction(ACI)in eastern China.The objective of this study is to utilize multi-sensor satellite observations and ERA Interim Reanalysis data to explore the impacts of aerosol types,meteorological conditions and cloud process on the interaction between aerosol and cloud,and to discriminate the differences of cloud macrophysical and microphysical properties between land and ocean over eastern China,and try to explain the underlying causes for the observed differences.This study will greatly help us to understand the mechanisms of ACI and ultimately of aerosol indirect effects over eastern China.By taking the vertical locations of aerosol and cloud layers into account,we use simultaneously observed aerosol and cloud data to investigate relationships between cloud properties and the amount of aerosol particles(using aerosol optical depth,AOD,as a proxy).This study shows that the COT(cloud optical thickness)-CDR(cloud droplet effective radius)and CWP(cloud liquid water path)-CDR relationships are not unique,but affected by atmospheric aerosol loading.For well-mixed clouds in the YRD(Yangtze River Delta),the CDR shows a decrease with an increasing AOD under moderately-polluted conditions,followed by an increase under polluted and heavily-polluted conditions due to the intense water vapour competition.The cloud cover behaves qualitatively similar to CDR in response to changing values of AOD.Meanwhile,COT becomes smaller and cloud top pressure(CTP)becomes larger with increasing AOD over the whole range of AOD values.Furthermore,separation of cases with either polluted dust or smoke aerosol shows that ACI is stronger for clouds mixed with smoke aerosol than for clouds mixed with dust.The variation of cloud properties with AOD is analysed for various relative humidity and boundary layer thermodynamic and dynamic conditions,showing that high relative humidity favours the formation of larger cloud droplet particles and increases cloud formation,irrespective of vertical or horizontal level.Stable atmospheric conditions enhance cloud cover horizontally.However,unstable atmospheric conditions favour the formation of thicker and higher clouds.Dynamically,upward motion of air parcels can also facilitate the formation of thicker and higher clouds."Snapshot" studies,where the aerosol and cloud properties are retrieved at the same time(for example,Aqua 13:00 LT),have the advantage that it neglects the effect of meteorological history on the interaction between aerosol and cloud.Retrievals of aerosol loadings and cloud properties by the MODIS sensor are used to explore morning-to-afternoon variation of cloud properties under low aerosol and high aerosol conditions over land and ocean,separately.The ACI is examined using four years statistics of remotely sensed data from MODIS/Terra and MODIS/Aqua satellites.d(Cloud_X)is defined as the difference in mean change in cloud properties of the high and low aerosol populations over the timestep(3 hours).It shows that the variation in d(Cloud_X)is different for land and ocean clouds.This applies to CDR and cloud fraction(CF),but not to COT,CWP and CTP.The effects of initial meteorological conditions and cloud fraction on d(CF)are also explored,showing that impact of pressure vertical velocity on the d(CF)is weak.When relative humidity is lower than 70%,the d(CF)decreases with the increasing of relative humidity.When LTS(lower troposphere stability)is lower than 25,the d(CF)increases with the increasing of LTS.There is positive but weak correlation between d(CF)and initial cloud fraction when initial cloud fraction is lower than 0.8.In order to examine the differences of warm cloud properties among different cloud processes,this study analyzes the microphysical characteristics and transitional processes of single layer water clouds over the YRD and the Eastern China Sea(ECS)using the products of standard CloudSat on summertime.Compared to the warm clouds over the ECS,the mean COT and Nc(cloud droplet number concentration)are larger for clouds over the YRD,and the mean CDR and CWP are smaller for clouds over the YRD.This is consistent with the Twomey effect.The coordinated variations of cloud parameters are similar for clouds over the YRD and ECS.With the increasing of CWP,the CDR increases.Meanwhile,with the decreasing of CDR,the COT increases.The correlation between CDR and Nc is negative.The general macrophysical and microphysical characteristics of single-layer warm clouds over eastern China are further examined using standard CloudSat/CALIPSO products,with a focus on comparisons between North China and Jianghuai area.It reveals that cloud geometrical thickness become larger with the evolution of cloud regime and the geometrical thickness is larger in Jianghuai area compared to North China.The maximum values of LWC(liquid water content)over North China are similar to those over Jianghuai area except that the LWC distribution over North China tends to be bimodal structure,indicating that there exist low-and medium clouds over North China.The reflectivity tendency over Jianghuai area shows a frequency shift to lower reflectivity compared with that over North China with the same LWP.In addition,particle radius become somewhat smaller and occurring locations are higher below 3 km over Jianghuai area compared to those over North China,which suggests that high aerosol abundance may suppress drizzle formation and delay precipitation process over Jianghuai area. |
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