Impact of the Indian Ocean SST on Wintertime Total Column Ozone Over the Tibetan Plateau

Abstract

Using various observations and a chemistry‐climate model, this study investigates the impact of the Indian Ocean sea surface temperature (SST) on the wintertime total column ozone (TCO) over the Tibetan Plateau (TP). Our analysis reveals that increases in TCO over the TP are accompanied by anomalously high Indian Ocean SSTs, and vice versa. Further analysis reveals that high Indian Ocean SSTs are accompanied by a narrowing of the northern branch of the Hadley cell, and consequently, the subtropical westerly jet in the Northern Hemisphere (NH) tends to shift southward. The southward shift of subtropical westerly jet can lead to a descent of tropopause and higher lower‐stratospheric temperatures over the TP. The latter causes a descent of isentropic surfaces in the upper troposphere and lower stratosphere. Rossby waves triggered by diabatic heating in the upper troposphere over the Indian Ocean can also lead to a descent of isentropic surfaces over the TP. On the other hand, local descending motions over the TP caused by the Gill Pattern circulation and enhanced Brewer‐Dobson circulation bring ozone‐rich air in the lower stratosphere downward. The descent of tropopause and isentropic surfaces and the downward transport of ozone lead to a downward shift of ozone profiles, and consequently, TCO increases over the TP. Based on multiple linear regression analysis, during 1996–2020 the Indian Ocean SST increase and the equivalent effective stratospheric chlorine decline dominate the wintertime TCO increase over the TP, which is partly offset by the TCO decline due to the TP warming.