Upper tropospheric ozone transport from the sub-tropics to tropics over the Indian region during Asian summer monsoon

Abstract

In this study, we investigate the role of the Asian summer monsoon (ASM) anticyclone in the distribution of ozone over the southern India and tropical Indian Ocean. We present the horizontal and vertical structure of ozone in the upper troposphere and lower stratosphere (UTLS) region. The analysis shows that the region within the ASM anticyclone has low ozone, and high tropopause altitude, as compared to the region outside the anticyclone during boreal summer. The southern edge of the ASM anticyclone, i.e. the southern India and tropical Indian Ocean show a remarkably high ozone concentration in the UTLS region during summer. Analysis of daily fields shows that ozone concentration in the upper troposphere over the southern India and tropical Indian Ocean increases with the strength of the tropical easterly jet, which is an outcome of ASM circulation. Different mechanisms responsible for the ozone enhancement in the UTLS region over the tropical Indian region have been discussed in this paper. The in situ ozonesonde observations from six Indian stations also support the space-based Aura-MLS observations, concluding that ASM anticyclone effectively transports ozone from the mid-latitude stratosphere to deep tropics. Shear generated turbulence and mixing in the vicinity of easterly jet also likely to play a minor role in the local ozone distribution.