Source,Vertical Transport And Radiation Effects Of Dust Aerosol In The Tibetan Plateau

The Tibetan Plateau,with its unique topography,plays an important role in global climate change.Aerosol over the plateau,as an important influencing factor,has been widely concerned by the academic community.Different regions of the Tibetan Plateau have different climates,sparsely inhabited populations,low anthropogenic aerosol emissions and dry and clean atmosphere.Dust aerosol,as an important component of atmospheric aerosol over the Tibetan Plateau,not only directly causes air pollution,but also affects the atmospheric radiation budget,cloud and precipitation processes,and then affects the change of snow（ice）and snow line.Under the action of the plateau’s thermodynamic dynamics,dust from different sources of the world can uplift and accumulate over the plateau and transport to the outside of the plateau,thus affecting the surrounding region and the global environment and weather climate.There are many well-known dust sources distributed around the Tibetan Plateau,but the Tibetan Plateau is also an important source of dust aerosol,desertification is serious in various regions of the plateau,and there are many dunes on plateau,which make local materials available for dust events.However,most studies in this field have focused on the sources,transport and climatic environment of exotic dust aerosols over the Tibetan Plateau,while there are few studies on the sources,distribution and transport characteristics of dust aerosols in the Tibetan Plateau,as well as the climate effects caused by them.The main reason is the lack of local measured data and limited model parameterization.Based on the field observation data of the second Tibetan Plateau scientific survey project and satellite remote sensing data,the plateau research area is divided into three regions,namely the west,south and north,according to the characteristics of surface vegetation and climate,and the Weather Research and Forecasting model with Chemistry（WRF-Chem）is adopted to improve the sediment lifting scheme.The high resolution numerical simulation from 2004 to 2006 was carried out to quantitatively study the temporal and spatial distribution of dust sources,diffusion transport and dust aerosols in the Tibetan Plateau and their climatic effects.The quantitative characteristics of the release,diffusion and vertical transport of dust aerosols in the Tibetan Plateau were initially revealed,which provided important data and model reference for further research.The main conclusions are as follows:1.Quantitative analysis of the amount of sediment deposition within the Tibetan Plateau was conducted to determine the spatial distribution and amount of sediment deposition within the plateau.The annual total amount of sediment deposition can reach343 Tg,which is one of the main sources of dust aerosol over the plateau.The dust sources within the plateau are mainly distributed in the northern Qiangtang Plateau,Yarlung Zangbo River basin,Namtso,Lhasa area,Qaidam Basin,the source region of the Yellow River and the Yangtze River,Qinghai Lake and surrounding areas.The annual dust emissions in the plateau is the highest in the west,the second in the north and the lowest in the south,the plateau of dust emissions peak appeared in January,respectively,11.00×10⁷（west）,3.30×10⁷（south）,and 4.50×10⁷（north）μg·m^-2,It is related to the influence of high wind and dry soil in winter.However,from May to October,the dust emissions remained at a low value,with the lowest values of 0.82×10⁷（west）,0.27×10⁷（south）and 0.85×10⁷（north）μg·m^-2,respectively.2.Through the simulation calculation of the dust column concentration over the Tibetan Plateau,the contribution of the inner dust source to the concentration of the high altitude dust aerosol and the vertical transport characteristics of the dust were clarified.In terms of the average dust column concentration in the western,southern and northern regions of the Tibetan Plateau,the dust transported to the altitude above8 km in summer accounts for more than 12%of the total dust in the whole column,while in winter the proportion is less,about 2.2%or less,and in other seasons it is in between.On average,dust in the Tibetan Plateau area above 8 km above sea level accounts for about 10%of the total dust in the whole air column,that is,about 10%of the surface dust can be lifted to the upper air and transported to the downstream.The ratio of the amount of dust transported to the upper air from the inner dust lifting in the plateau to the input from external sources was 82%,and the ratio of the amount of dust transported to the upper air from the inner dust lifting in the plateau to the total dust aerosol over the plateau was 45%.3.It is illustrated that the variation of dust emissions,deposition and transport quantity in the Tibetan Plateau is greatly affected by local soil moisture,surface temperature and wind speed,which shows that the corresponding relationship between local dust emissions and dust loading is different.In the western region,the annual variation trends of the high value of dust emissions and the high value of dust loading are consistent,while the annual variation trends of the above two variables in the northern and southern regions are significantly different in spatial distribution.In the western and southern regions,the dust loading is lower than the amount of dust emissions,while in the northern region,the dust loading is higher than the amount of dust emissions.This difference is related to the influence of ground temperature,wind speed and soil moisture.The higher the temperature of soil moisture and 2 m on the ground,the more dust stays in the air,while the high wind speed at 10 m on the ground is not conducive to the dust staying in the local air.4.Dust aerosol generally heats the atmosphere over the Tibetan Plateau.The maximum net radiative forcing of dust aerosol on the whole atmosphere in the western,southern and northern regions is 28.99,29.56 and 154.92 W·m^-2,respectively,but the radiation effect on the top of the atmosphere and the ground in the three regions is not consistent.The dust in the northern region can reduce the short-wave radiation reaching the ground through absorption and scattering,so that the whole atmosphere presents a positive forcing of short-wave radiation,and the maximum value is 595.09 W·m^-2 in May.After absorbing energy,the dust layer will heat the atmosphere to make it warmer,which leads to the increase of long-wave radiation emitted by the atmosphere.As a result,the negative forcing of long-wave radiation appears in the whole atmosphere,and the maximum value is-443.17 W·m^-2 in May.However,the short-wave radiative forcing and long-wave radiative forcing generated by dust in the two regions on the whole atmosphere are opposite to those in the northern region,which may be caused by the low dust concentration in the atmosphere in the western and southern regions.