The Impact of Boreal Summer ENSO Events on Tropical Lower Stratospheric Ozone

The interannual variability of Tropical Lower Stratosphere (TLS) ozone and its connections to sea surface temperatures (SSTs) in the equatorial Pacific are examined using a combination of chemistry climate model (CCM) simulations, satellite observations, and reanalyses. The model simulations and observations show large differences in the magnitude of interannual variability in ozone between Northern and Southern tropics (NT (EQ-18^o N) and ST (EQ-18^oS) respectively) during boreal summer, but small differences in winter. The interannual variability during boreal summer is highly correlated with summer SSTs in the eastern and central Pacific Ocean and El Niño -- Southern Oscillation (ENSO) events. Larger variability in NT ozone is primarily due to meridional advection, connected to the changes in the onset date and strength of the Asian Summer Monsoon (ASM) anticyclone. The ASM anticyclone forms earlier in a season and tends to be stronger during cold (La Niña) events leading to more isentropic transport of ozone from the extratropics into the NT, with the reverse for warm (El Niño) events.