Clear air turbulence over the Tibetan Plateau and its effect on ozone transport in the upper troposphere-lower stratosphere

Abstract

Serious bumps caused by clear air turbulence (CAT) pose significant safety hazards during flight. CAT is also a mechanism of the stratosphere-troposphere exchange (STE), influencing the mixing of trace gases in the upper troposphere and lower stratosphere (UTLS). The strong vertical wind shear in the upper level induced by the large topography and unique climatic conditions facilitate the formation of CAT over the Tibetan Plateau (TP). This paper utilizes ERA5 reanalysis data from 1979 to 2019 to investigate the distribution characteristics of CAT over the TP. Additionally, the effects of tropopause folds on CAT were also discussed. Finally, we compare the rate of ozone change in the UTLS between cases with folds but no CAT and those with both folds and CAT, using CAMS ozone reanalysis data from 2003 to 2019. Results indicate that the occurrence frequency of CAT over the TP is significantly higher than in surrounding areas. CAT is more frequent in winter and spring, with a significant increasing trend in winter over the past 40 years. The distribution and intensity of CAT are correlated with the subtropical westerly jet stream, occurring both above and below the jet axis, showing stronger CAT observed beneath the axis. Additionally, tropopause folds significantly enhance the frequency and intensity of CAT, especially as the depth of the fold increases. CAT intensifies STE associated with folds, leading to a reduction in stratospheric ozone and a corresponding increase in tropospheric ozone.