The Relationship Between The Intraseasonal Variation Of The Asian Tropopause Aerosol Layer And The South Asia High

The Asian Tropopause Aerosol Layer refers to the planetary-scale aerosol layer that occurs within 13-18 km during the Asian summer monsoon season and covers the Middle East,South Asia and East Asia.The various pollutants can directly affect the radiative forcing of the upper troposphere and lower stratospheres in the region,or influence the radiation balance of the earth-atmosphere system and then have an important impact on the global climate after entering the lower stratosphere.Therefore,studying the change characteristics of pollutants in ATAL is of great significance for understanding and predicting future climate changes.Since ATAL was discovered,it has aroused extensive research.In recent years,it has been found that the ATAL is closely related to the variation of the South Asia High on both the interannual and subseasonal scales,and the intraseasonal oscillation of the South Asia High has an important effect on the horizontal distribution of Carbon Monoxide(CO)in ATAL.However,there is still a lack of analysis of its effect on vertical transport,and the influence of the South Asia High intraseasonal oscillation on other pollutants in the atmosphere such as aerosols is unclear.Therefore,this paper mainly uses the MERRA-2(Modern Era RET-rospective analysis for Research and Application,Version 2)and NCEP-DOE 2(National Centers for Environmental Prediction(NCEP)/Department of Energy(DOE)Reanalysis2)reanalysis data from2007 to 2018 to describe the east-west oscillation phenomenon of the South Asia High from the subseasonal scale by the South Asia High index,and focuses on the impact of the east-west oscillation of the South Asia High on the horizontal and vertical distribution of pollutants(CO,carbon aerosols and dust aerosols are representative)in ATAL.The main research results are as follows:(1)From the twelve-year average distribution characteristics,the distribution range of pollutants in ATAL is basically the same as the location of the South Asia High,and the vertical transport of CO and carbon aerosols to ATAL near the Tibetan Plateau is obvious,while dust aerosol is not obvious.Moreover,the east-west oscillation phenomenon of the South Asia High is obvious,and the movement of its center position will have an impact on the thermal structure and vertical movement of the atmosphere.When the center of the South Asia High is located over the Tibetan Plateau,a positive temperature anomaly appears here,the upward movement and anticyclonic circulation increase.There is a negative temperature anomaly over the Iranian Plateau and the subsidence movement near the surface is weakened.(2)The east-west oscillation of South Asia High has an important effect on the horizontal and vertical distribution of pollutants.When the South Asia High is in the mode of the Tibetan Plateau,the positive and negative anomaly centers of pollutants appear in the Tibetan Plateau and the Iranian Plateau respectively,and the positive and negative anomaly centers of pollutants correspond to the anticyclonic and cyclonic circulation anomalies respectively.The increase of CO and carbon aerosol concentration from the surface to ATAL can be observed in the Tibetan Plateau region,which corresponds to the increasing trend of upward movement,while the dust is not obvious.(3)The distribution of CO and carbon aerosols can be changed by adjusting the upper air circulation field and influencing the position and intensity of vertical transport during the quasi-biweekly oscillation of South Asia High.During the movement of the center of the South Asia High from the Iranian Plateau to the Tibetan Plateau,the pair of anticyclonic-cyclonic anomalies located on the Iranian and Tibetan Plateau at ATAL altitude will eventually be replaced by cyclonic-anticyclonic anomalies.The change of circulation field changes the anomalous center of CO and carbon aerosol concentration from negative to positive over the Tibetan Plateau.In the vertical direction,the concentration of CO and carbon aerosols increases from the ground to the ATAL area in the Tibetan Plateau and the Sichuan Basin of China.In the process of South Asia High returning from the Tibetan Plateau to the Iranian Plateau,the adjustment of circulation field and the change of pollutant concentration are just opposite to the above process.(4)During the quasi-biweekly oscillation of South Asia High,the South Asia High index is obviously related to the daily variation of CO and carbon aerosols.The CO and carbon aerosols in the upper troposphere and the South Asia High index are in the same phase over the Tibetan Plateau,but just the opposite over the Iranian Plateau.The changes of CO,carbon aerosols and South Asia High index in the middle troposphere are consistent over the Tibetan Plateau and the Iranian Plateau,that is,when the center of South Asia High moves towards the Tibetan Plateau,the CO and carbon aerosols in the middle troposphere are consistent over the Tibetan Plateau and the Iranian Plateau,that is,when the center of South Asia High moves towards the Tibetan Plateau,the CO and carbon aerosols in the middle troposphere also increase over the Tibetan Plateau and the Iranian Plateau.