Spatiotemporal Distribution,Source Region Analysis And Assessments On Environmental Effects Of External Dust Aerosol Over Tibetan Plateau

As an important component of the Earth’s atmospheric aerosols,dust aerosol has important impacts on global climate,ecological environment and human health.At present,domestic and international research on dust aerosol in the Tibetan Plateau（TP）region has made advances in many aspects with numerical simulation,satellite remote sensing and field observation,but due to the complex sources of dust over TP,the drastic variations in meteorological conditions and the limits of research method,the relevant research results still have large uncertainties.In this paper,based on the Second Tibetan Plateau Scientific Expedition and Research program,we studied the distribution of dust aerosol,the meteorological factors in the source regions and the climatic and environmental effects caused by the dust in the TP using ground observation,satellite remote sensing,reanalysis data and assimilation datasets.By analyzing the optical parameters such as aerosol optical thickness（AOD）in the TP region and the observations of meteorological factors in the same period,we obtain the characteristics and trends of spatial and temporal distribution of dust activities in the TP;analyze the relative contribution from dust source regions by using the Dust COMM dataset;compare the differences of convection,precipitation,wind speed and other meteorological factors in the TP,East Asia,Middle East and Central Asia and North Africa;and summarize the mechanisms of dust transport in the East Asia and the Middle East and Central Asia and the characteristics of external dust sources affecting TP.Finally,we use reanalysis data and the photovoltaic energy model to quantitatively assess the climatic and environmental effects caused by dust aerosol.（1）UKMO MIDAS（UK Meteorological Office MIDAS）dataset,MIDAS（Mod Is Dust Aero Sol）data,and MERRA-2 reanalysis data are utilized in this study to quantitatively analyze the spatiotemporal characteristics of dust aerosol,including particle size,optical properties,surface mass concentration and other variables,and quantify the trend of the dust weather occurrence frequency since 1980s over the TP.According to spatial distribution of the infrared differential dust index（IDDI）and dust aerosol optical depth（DOD）,the dust activity in the TP is most active in spring.The dust aerosol concentration shows a decreasing trend from north to south,and the central part of TP is the area with low value of aerosol mass concentration,and the area of high value of that exists over the Qaidam Basin in the northeastern part of the TP.In Qiangtang Plateau,there are areas with high value of IDDI in both spring and summer,and the intensity of dust activity is much higher than other parts of TP.Based on ground meteorological observation records,the maximum of dust day during observation period is found in the Tianshan Range（the northwestern part of TP）,and the site in this region reports 143 dust days occurred in1980s.In addition to the Qaidam Basin,Qiangtang Plateau and Tianshan Mountains,it also has seasonal distribution of high value over the southern edge of TP,mainly in summer and winter time,all related to external aerosol transport activities.There are also differences in dust aerosol trends from different regions within TP:the number of dust day in the central part does not change significantly according to time;but the northern and southern parts both show a decreasing trend in the frequency and intensity of dust activity after 2000.（2）Using CALIPSO L2 VFM data,Dust COMM（Dust Constraints from joint Observational-Modelling-experi Mental analysis）dataset and ERA5 reanalysis data,etc.,we analyze relative contributions of the dust sources to dust aerosol over the TP and the meteorological factors affecting the dust transport mechanisms,and furthermore summarize the dominant influencing factor of different transport mechanisms.In the emission and long-distance transport of dust from the Middle East and Central Asia,the wind field at middle-high altitude and convection are the dominant factors,and precipitation is main negative factor;but the dust transport activity is mainly concentrated near ground and the influence of topography and near-surface wind speed is oppositely more significant over East Asia.The main sources of dust aerosols in the TP are East Asia,Middle East and Central Asia,and North Africa,accounting for about 45%-58%,32%-38%,and6%-13%,separately.From the analysis of the mass concentration and optical properties of dust aerosol,the dust contribution from East Asia is mainly found near the ground in the TP is higher than that at higher altitude in the atmosphere,and the contribution to the optical thickness DOD of dust aerosols is smaller;while dust from the Middle East and Central Asia and North Africa,the vertical distribution characteristics of dust transport over the TP are completely opposite,and also have a higher contribution to DOD.It shows that there are differences in the contributions of different dust source regions to the vertical distribution of dust aerosols over the TP:dust from East Asia has a higher contribution to the near-surface,while dust from the Middle East and Central Asia and North Africa has a greater contribution to the atmosphere above the near-surface layer.East Asia and Middle East and Central Asia have very different vertical distribution of external dust transport characteristics under the combined influence of meteorological factors such as wind speed,dust lifting height and convection which further impact on the vertical structure of dust transport in the TP region.（3）Using MERRA-2 reanalysis information,CERES-SYN radiation data and photovoltaic energy model PVLIB,we analyze the climate and environmental effects caused by dust aerosol.The photovoltaic energy loss due to dust aerosol soiling effect on the TP is the intensive in spring(38.9 W·m^-2)and less in summer(30.3 W·m^-2),while the photovoltaic energy loss on the Qiangtang Plateau and the Qaidam Basin can exceed 100.0 W·m^-2.The multi-year averaged aerosol surface shortwave radiative forcing over the TP is approximately-4.38 W·m^-2.If considering atmospheric extinction,aerosol-cloud interactions,the difference between the shortwave radiation flux at the surface and the top of the atmosphere（TOA）at the TP is greatest in summer;while the longwave radiation flux at the surface over the TP is heated.The difference between the longwave radiation flux at the surface and the TOA is about 151 W·m^-2 in summer.The impact of dust aerosol on photovoltaic energy utilization and conversion is much greater than that on solar radiation forcing:the multi-year mean of photovoltaic（PV）energy loss due to soiling effect in spring,summer,autumn and winter is 38.9,30.3,36.2 and 35.4 W·m^-2,respectively,and the value of PV energy loss due to soiling effect in the TP is greater than that of direct radiative forcing due to aerosol in the Taklamakan Desert and northern India Subcontinent with high value of aerosol mass concentration(about-30.0 W·m^-2).The areas with high value of PV energy loss are mainly located over the Qiangtang Plateau and the Qaidam Basin,where the maximum of PV energy loss due to dust aerosol could exceed 100.0 W·m^-2 caused by weaker precipitation and more active wind-driven dust activity in spring.