Transport And Spatial Variations Of Aerosols In The Upper Troposphere And The Lower Stratosphere Over The Tibetan Plateau

Using the mesoscale model WRF coupled with a dust module together with the CAPLIPSO and TOMS satellite observations and NCEP reanalysis data, the transport characteristics and mechanisms of aerosol over the Tibetan Plateau from the troposphere to the stratosphere are investigated and the temporal and spatial variations of aerosols in the upper troposphere and the lower stratosphere (UTLS) region are analyzed. The main conclusions are as follows:1. Using a mesoscale model (WRF) coupled with a dust module, the characteristics and mechanism of the vertical transport of dust aerosols from the near surface to the upper troposphere and the lower stratosphere are investigated through a case study and the effect of the Tibetan Plateau on the stratosphere and troposphere mass exchanges is also discussed. The analysis reveals that deep convection can inject dust aerosols into the stratosphere. However, the aerosol concentrations in the lower stratosphere are largely affected by locations of dust sources and convection intensity as well as the precipitation. When there is no overshooting convection, vertical motions can not transport aerosols directly into the lower stratosphere. However, small scale diffusion and mixing processes can slowly transport aerosols in the upper troposphere into the lower stratosphere using a few hours of time. Under conditions of no system precipitation, the strong convective activities in summer over the Tibetan Plateau make it a favorable location for aerosols in the troposphere entering into the lower stratosphere. The stratospheric air intrusion has a large impact on time variation and spatial distribution of aerosol concentration in the upper troposphere when there are no strong dust emissions near the surface.2. Using CALOPSO satellite observations of aerosols in2008and NCEP reanalysis data, spatial and temperal variations of aerosol in the upper troposphere and lower stratosphere (UTLS) over the Tobetan Plateau (TP) in summer time (June, July, August) are analyzed. The analysis reveals that there is an aerosols layer at the altitude range of4-18km over TP with different horizontal distributions at different altitudes. At14km level, the backscatter coefficients are rather small and evenly distributed over northern plateau and the area to the north of plateau, indicating that aerosol particles at14km level over these regions are rare. However, there exist some aerosols in the southern and southeastern plateau at14km level. At12km altitude, aerosols can be noted over the northeast of plateau and high cloud signals appear to the east of plateau. There are clearly more aerosols at12km level than at14km level and there are more aerosola over the south of TP than that over the north of the TP. At10km altitude, the cloud covers most of area of the north plateau (40°-55°N,80°-120°E) while a large amount of aerosol particles and cloud appear over the middle of plateau (around85°E and95°E) and the east of plateau (around28°-36°N,110°-120°E). As this area covers the most important aerosol emision sources in eastern Asia, including the deserts and gobi on the northwest China and Mongolia, it is understandable that aerosols can be noted in the upper stratosphere over this area.At the altitude of8km, the backscattering coefficient over the whole plateau area lies between0.0045-1.12km-1sr-1indicating that the plateau is covered mostly by clouds. However, the backscattering coefficient over most of the area of the north and east of plateau is between0.001-0.003km-1sr-1. The results suggest that the atmosphere in altitude8km over the TP is rich in both aerosols and cloud particles. The spatial distributions of aerosols over the TP are not only affected by aerosols emission sources over the deserts and gobi in northwest China and Mongolia, but also related the high orography of the TP as the average altitude of the plateau is beyond4km and large amount of aerosols in the boundary layer can be transported to the upper troposphere.An analysis of the vertical profiles of aerosol backscattering coefficients in several weather cases occurred over the plateau region and its surroundings in summer reveals that the aerosols backscattering coefficient is large in the altitude8-18km and reaches a maximum of15×10-4km-1sr-1at altitude11km suggesting that there are more dust aerosols exist in this altitude. Above20km, the aerosol backward scattering coefficient is very small implying that aerosols are not transported to altitudes above20km in these selected weather cases.3. Using monthly mean aerosol data in2008measured by CALIPSO satellite and TOMS total column ozone data, the horizontal distribution and seasonal variations of aerosol optical depth (AOD) and total column ozone (TCO) over the Tibet Plateau and its surroundings are analyzed and the correlations between the the TCO deviations from the corresponding zonal mean and AOD as well as relative humidity are discussed. The analysis indicates that the total column ozone low over the TP in summer is accompanied by the higher AOD values over the TP. The area-aveaged TCO deviations from the zonal mean and AOD over the TP (27.5°-37.5°N,75°-105°E average) shows a good anticorrelation in different seasons. The further analysis reveals that the correlations between the TCO deviations from the zonal mean and aerosol backscattering coefficient of532nm channel over the Tibetan Plateau is high at2km altitude, while the correlations between the TCO deviations from the zonal mean and relative humidity over the Tibetan Plateau are high at8km and10km altitude. The good correlations between the TCO deviations, aerosol optical depth and relative humidity are arising from the facts that the concentrations of these three species are all affected by atmospheric transport processes on one hand and they are also involved in complex physical and chemical processes on the other hand. The detailed characteristics of the aerosol layer in the upper troposphere and lower stratosphere over the TP and its effects on the ozone layer over the TP need further analysis and verification using extensive measurements of atmospheric constitutes over this area together with atmospheric chemistry models.