Trace gases distribution in the Upper Troposphere and Lower Stratosphere (UTLS) over different Asian Summer Monsoon Anticyclone (ASMA) regions obtained using satellite measurements

Abstract

The Asian summer monsoon anticyclone (ASMA) is an important large-scale dynamical circulation system in the upper troposphere and lower stratosphere (UTLS) region in the Northern hemisphere during the boreal summer. Using NCEP-NCAR reanalysis data set, our analysis revealed the spatial asymmetry in the ASMA. Based on this, the entire ASMA region has been divided into four regions namely North-West (NW: 32.5°-37.5° N, 40°-70°E), North-East (NE: 32.5°-37.5° N, 70°-100°E), South-West (SW: 27.5°-32.5° N, 40°-70°E) and South-East (SE: 27.5°-32.5° N, 70°-100°E). By making use of MLS satellite observations (for chemical constituents) and re-analysis datasets (for dynamical parameters), this work mainly focus in investigating the effect of the background dynamical conditions on the vertical distribution of carbon-monoxide (CO), water vapor (WV) and ozone (O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> ) in the UTLS region over these different ASMA regions. Similar to Tibetan Plateau (TP) mode, the MLS satellite observations for the period 2004–2020 showed enhancement in the tropospheric tracers (CO and WV) throughout the upper troposphere over eastern region (SE and NE) of the ASMA indicating the transport of boundary layer air to the UTLS region across these regions. This type of enhancement is seen only near tropopause over SW throughout the season and NW region of ASMA during the peak monsoon months. Our study also revealed the vertical transport of the tropospheric tracers to the higher altitudes over SE region is due to the strong updrafts associated with the deep convection over this region coupled with weakening of the zonal wind in the mid and upper troposphere. The enhancement of the tropospheric species over NW and SW only near troposphere is mainly due to the convective uplifting over the eastern region (particularly SE) and strong horizontal advection towards these regions. The increase in O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> concentration near tropopause over the NE and NW is found mainly due to the frequent stratospheric intrusions which occur over these regions during this season. This information is very useful in interpreting the different sources of chemical constituents in the ASMA.