Can El Nino Induce Stratosphere - Troposphere Exchange of Ozone?

The possibility of stratosphere-troposphere exchange (STE) of ozone induced by El Nino has been studied over the Indian region for two events spanning the periods April 1997-May 1998 and August 2006-February 2007 using in situ and satellite-based measurements. The response of STE to El Nino was observed to be opposite in the tropics and extra tropics. In the tropics, lifting of polluted, ozone-rich surface air led to reduced lower tropospheric and enhanced upper tropospheric and lower stratospheric ozone during the El Nino period, indicating transport from the troposphere into the stratosphere. Conversely, in the extra tropics, sinking motion from the stratosphere into the troposphere resulted in higher upper tropospheric ozone concentration during the El Nino period. An increase in the middle and lower tropospheric ozone during the La Nina period immediately following the El Nino period suggests that the response of STE to El Nino did not manifest concurrently with the period of El Nino, but lagged by several months. El Nino southern oscillation (ENSO)-induced changes in total ozone are more prominent in the extra tropics of the northeast, compared to northwest India. However, as vertical ozone profiles are available for only two El Nino events, and the ozone variability between El Nino and La Niña events are relatively small, more detailed studies are needed to understand the dynamic influence of ENSO in producing ozone variability in India.