| The distribution and transportation characteristics of dust aerosol over the Tibetan Plateau(TP)and Taklimakan Desert(TD)are analyzed during 1980-2017 using MERRA-2(second Modern-Era Retrospective analysis for Research and Applications)and CALIPSO(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)products.The aerosol optical depths(AOD)of MERRA-2 are compared with those of AERONET(Aerosol Robotic Network)in six sites and the corresponding MISR(Multi-angle Imaging Spectro Radiometer)data.The range and value of correlation coefficients are 0.73-0.88 and 0.78,respectively.The spatial distribution of AOD of MERRA-2 and MISR is similar,and the spatial correlation coefficient is 0.94.The variations of seasonal AOD over the TD and the TP are similar,showing the values decreasing from north to south and the peak values appearing in spring,followed by summer and the lowest in winter.The AOD value of the TP is less than 0.30 during the whole year,with the highest value(? 0.25)appearing in April and the lowest value(? 0.10)appearing in December.The zonal variations of AOD are obvious over the TP.The zonal mean AOD in the north and south of 34°N has different monthly changes.The peak of monthly zonal mean AOD in the north appears in April to June,and in the south appears in June to August.From 1980 to 2017,the monthly zonal mean peak of AOD over the TD and the TP is increasing,and its impact on the TP is expanding.The aerosol types over the TP are mainly dust,accounting for about 50%.Sulfate aerosols accounted for about 35%.Carbonaceous aerosols accounted for about 15%,among which organic carbon is the main component.The variations of seasonal AOD and dust AOD(DAOD)over the research region are similar,showing the values from high to low are in the order of spring,summer,autumn and winter,respectively.The highest value of DAOD over the TD and the TP both appears in May.The DAOD of the northern TP is 0.06-0.10 higher than the southern TP,and the difference of DAOD value between northern TP and southern TP is the highest in May.Since 2000,the strength and area of the high DAOD region over the TD and the Indo-Gangetic Plain(IGP)have increased,and the transportation of dust from these two dust source to the TP has been enhanced.In the past 38 years,the annual change of DAOD in the whole research area presents an upward trend,and all of them passed the significance test with a confidence degree of 0.05.The climbing rate of DAOD over the TD is the highest,reaching 0.004.The TP has the lowest ascending rate,which is lower than 0.001.From 2000 to 2017,DAOD over the TP is significantly higher than that of 1980 s and 1990 s.Observations of CALIPSO suggest that the dust over the TP comes mainly from the TD,with the largest dust transport volume in spring and the smallest in autumn and winter,and partly from the IGP,with the transmission occurring mainly in the summer and autumn.The dust moves from the TD to the TP is mainly through the Qaidam Basin in the layer of 4-8km aloft and could transport as far as 30°N.The dust over the TP in winter mainly comes from frequent sandstorms occurred in the Qaidam Basin.The largest profile of dust extinction coefficient over the TD and the TP appears in spring and summer,respectively.The average dust thickness in the TD and TP are 1.00 km and 0.82 km respectively.The thickness of the dust layer over the TP is the thickest in spring,followed by the thickest in winter and the thinnest in summer.From 2007 to 2017,the dust layer thickness of the TD decreases significantly,with an annual decline rate of 0.018 km.The annual change trend of dust layer thickness over the TP is not significant. |
PDF Full Text Request