Identification of an El Niño‐Southern Oscillation signal in a multiyear global simulation of tropospheric ozone

We present the first study of the El Niño-Southern Oscillation (ENSO) interannual variability in tropical tropospheric ozone in a multiyear simulation with a global three-dimensional chemistry-transport model. A 15-year period (1979-1993) was simulated using European Centre for Medium-Range Weather Forecasts meteorological reanalysis data and a time-varying emission data set. A comparison of model calculations with observations shows good agreement for surface ozone, seasonal cycles, and ozone concentrations at remote stations, but reveals an underestimate of ozone in the free troposphere, which is most pronounced during biomass burning seasons. The ENSO signal is the most important component of interannual variability in tropical tropospheric ozone columns (TTOC), being responsible for nearly 25% of the total interannual variability of ozone in the tropics. The amplitude of the modeled ENSO signal in TTOC is 3 Dobson units, in close agreement with satellite observations. This signal is evenly distributed with height, indicating that rapid vertical transport plays an important role. The ENSO signal is also detectable at the surface, for example at the Pacific island Samoa, for which model-calculated and measured ozone agree well.