Dust Aerosol Properties Over East Asia Derived From Satellite-based Lidar

East Asia has the two major dust deserts,Taklimakan Desert(TD)and Gobi Desert(TD),which are also the major dust source area over the world.Trans-Pacific transportation of East Asian dust aerosols is the largest scale of the dust transmission process on Earth.It has very important effect on global environment,ecosystem,weather systems,and climate.Therefore,it is of great scientific significance to understand the temporal and spatial distribution and optical properties of dust over East Asia.Based on CALIPSO Level 2 VFM,5 km Aerosol Profile,5 km Cloud Layer and MISR products from 2007 to 2012,we revealed the spatial and temporal distribution of dust aerosol in different height layers over East Asia,analyzed the differences of dust properties between sandy land and long-distance transmission area,and then the optical properties and mixing ratio in the atmospheric column of the dust aerosol were retrieved.The main conclusions are as follows:(1)The distribution of dust has significant seasonal difference.Dust occurrence frequency decreases with the seasons,the highest in spring,summer and autumn are similar,and the lowest in winter.For the main sandy land of the TD and GD,the frequency of the former is significantly higher than the latter in any season.The dust activity in the two East Asian dust sources have occurred throughout the year,reaching the maximum in spring and the minimum in winter,but which of TD is the most typical.The dust long-distance transmission area is mainly concentrated in spring and winter,and the summer and autumn seasons are small,which is obviously related to the clear wet removal process in the summer and autumn seasons.The frequency of dust in the TD is greater than that in the GD,and the maximum height of the dust aerosol in the TD is larger than that in the GD in both conditions.(2)There are obvious differences in the characteristics of dust particles between sandy land and long-distance transmission area over East Asia.The dust particulate depolarization ratios(PDR)decrease with height in the TD and GD areas,on the contrary,increase with height in the long-distance transmission zone.The PDR values in the two dust source areas are larger than those in the long-distance transmission area,indicating that the dust particles of the non-spherical reduced due to its own gravity subsidence and other types Aerosol pollution when the dust aerosol is transported from the source area to east.All properties such as volume depolarization ratio(VDR),PDR,total color ratio(TCR)and particulate color ratio(PCR)showed a gradual decrease from the west to the east along the dust transmission path.The average of the dust PDR in TD,GD and the long-distance transmission area is mainly in the range of 0.25-0.35.(3)According to the threshold of PDR,the backscattering coefficient of dust aerosol can be separated accurately from the total backscatter coefficient,and then the degree of mixing of dust aerosols and the dust optical characteristics in both clear-sky and above-cloud conditions can be eastimated.The statistical study found that the dust mixing ratio in the entire column of the Taklimakan Desert was more than 60% in four seasons,indicating that dust is the dominant aerosol in the area,and the total optical thickness of the monthly mean and the total optical thickness of the MISR comes a high consistency;The mean values of dust mixing ratio in the Gobi Desert area were 57%,43%,45% and 48%,respectively;Due to the wet and dry deposition effect,the dust mixing ratio of the air column is obviously smaller than that of the sandy land area,as a result the average dust mixed ratio in the long-distance transmission is about 40% in winter and spring,and only 30% in summer and autumn.The average extinction coefficient of spring in the two sandstorms is obviously larger than that in the summer,and which of TD is larger than GD,which shows good consistency with dust occurrence;and the difference in extinction coefficient in the same area between clear-sky and above-cloud conditions is not obvious.The assumption of dust lidar ratio may introduce a certain error in the inversion process of dust thickness.