Causal Impact of ENSO on Future Ozone Concentrations and Transport in the Tropical Tropopause Layer

Abstract Alterations in the tropopause are recognized as key signals of anthropogenic climate change and further understanding of the major drivers of future changes in the tropical tropopause layer (TTL) is crucial. Nevertheless, the causal effects of the El Niño‐Southern Oscillation (ENSO) on TTL remain elusive, particularly in a future warming climate. Here, we investigated the response of ozone concentrations in the TTL to ENSO over the period from 2015 to 2100, utilizing data from the Coupled Modeling Intercomparison Project Phase 6 (CMIP6) models. The results demonstrate a robust causal impact of ENSO on future TTL ozone across much of the tropics, particularly at the upper TTL at 70 hPa pressure level. ENSO‐induced changes in TTL zonal winds and vertical convection play a key role in the redistribution of TTL ozone. As air enters the TTL, it is influenced by zonal transport, resulting in a significant response of ozone concentration to ENSO throughout the tropics. Slightly weaker responses of ozone concentration at the 100 hPa and 150 hPa levels over several regions are linked to decreased ENSO‐induced zonal winds. The models exhibit consistent patterns in modeling the causal effects of ENSO on future TTL ozone.