A Study On Aerosol Vertical Structures Based On Space-Borne Lidar And Data Asssimilation

Aerosols have significant impacts on air quality,radiation balance,hydrological cycle,and climate change.Knowledge of aerosol optical properties,such as aerosol optical thickness(AOT)and their vertical distributions is critical for revealing the effects of atmospheric aerosol on climate and environment.However,investigation of aerosol particle properties and their temporal-spatial variations,especially their vertical structure,is still poor.First,the seasonal variations and diurnal variations of the aerosol vertical structures over East Asia and three selected regions(North China and Northeast China,Tibetan Plateau,and Tarim Basiin)during 2015 to 2017 are revealed by the aerosol vertical profile dataset observed from Cloud-Aerosol Transport System(CATS),which launched to the International Space Station in January 2015.The aerosol vertical structures in different regions over East Asia have significantly different seasonal and diurnal variations.As the important source region of anthropogenic aerosols,the dominant aerosol type of column integrated aerosols in North China and Northeast China is pure dust in all seasons.The primary transport path of smoke aerosols in this regions is obviously higher than that of dust aerosols.The aerosol extinction and depolarization ratio in Tibetan Plateau have significantly seasonal variations.The vertical diffusions of aerosols in summer are stronger than in other seasons,therefore,the aerosol extinctions greater than 0.05km^-1 are as high as 8 km,which is caused by smoke aerosols through thermal dynamic processes.The aerosol extinctions in Tarim Basin have obviously seasonal variations,a significant amount of relatively larger dust aerosols is lifted into the free troposphere and suspended for a longer time in summer.The aerosols within boundary layer have weaker intraseasonal variabilities in winter,and the height of boundary layer is an important factor determining the vertical distributions of aerosols from local emissions in the Tarim Basin.According to the analysis of CATS observations,the aerosol vertical structures have significantly spatio-temporal variations.Although space-borne lidar can provide aerosol vertical observations in large-scale,it still have some limitations.Model is an important tool for investigating the aerosol vertical structures and the aerosol spatio-temporal distributions.However,due to the large uncertainties in the model input and the simplified parameterizations of the various aerosol processes such as emission,transport,and deposition,it is still a challenge for model itself to accurately reproduce the aerosol vertical structures.Aerosol vertical data assimilation,which makes optimal use of both aerosol vertical observations and numerical simulations to obtain the best possible estimates of aerosol behaviors,is an emerging way for improving the investigations of aerosol vertical structures and its influences on climate and environment.Therefore,based on the Non-hydrostatic ICosahedral Atmospheric Model(NICAM)online coupled with the Spectral Radiation Transport Model for Aerosol Species(SPRINTARS),this study further developed the quality control and aggregation method for the observations of space-borne lidar,constructed the appropriate observational operator and the aerosol vertical data assimilation system.This study also revealed the influences of different assimilation parameters(i.e.,horizontal localization length,vertical localization length,and emission perturbation factor)on the aerosol vertical data assimilation.The hourly CALIOP(Cloud-Aerosol Lidar with Orthogonal Polarization)aerosol extinction coefficients in November 2016 are successfully assimilated using the four-dimensional Local Ensemble Transform Kalman Filter(4D-LETKF).Through assimilating CALIOP aerosol extinctions,MODIS(Moderate-Resolution Imaging Spectroradiometer)aerosol optical thicknesses,or simultaneously assimilating the CALIOP and MODIS observations,this study investigated the improvements of aerosol vertical data assimilation on the simulated aerosol vertical features.Results shows that CALIOP assimilation significantly reduced the underestimations of aerosol column informations over the source regions of biomass burning smoke,dust,industrial pollution,and the outflow maritime regions downwind of major dust and industrial pollution sources in control experiment,which indicates the new assimilation system can effectively improve the aerosol simulations through assimilating the aerosol vertical observations.It is found that both the CALIOP and MODIS assimilation can improve the magnitude of the simulated aerosol extinctions,however the CALIOP assimilation is superior to the MODIS assimilation in terms of modifying the incorrect aerosol vertical distributions and reproducing the magnitudes and variations.The simultaneous CALIOP and MODIS assimilation experiment has the best performance.This is probably due to the aerosol vertical distributions,which are unable to be optimized by assimilating the sparse CALIOP observations,are further optimized by the MODIS observations.