Abstract/Summary

Stratospheric ozone has been shown to impact stratospheric variability and subseasonal-to-seasonal (S2S) prediction via its strong radiative properties. Previous research investigating the impact of interactive ozone in atmospheric models, compared with the use of a prescribed climatology, has focused largely on the zonal-mean impacts. Here, we employ a process-based diagnostic to quantify the impact of interactive ozone on high-latitude stratospheric variability in the Southern Hemisphere during the vortex breakdown period using two seasonal hindcast ensembles (one with and one without interactive ozone) initialised on October 1st over a period of 29 years. We focus on the amplitudes of waves (i.e., the longitudinal deviations from the zonal mean) and of zonal-mean deviations from the ensemble mean, for both temperatures and zonal winds. The effect is quantified as a function of day of year, considering the strong non-stationarity during this season, and we focus on the lower stratosphere, a region crucial for stratosphere-troposphere coupling. For both the waves and the zonal mean, we show that interactive ozone provides a positive radiative feedback on the variability. This increases the variances of both the waves and the zonal-mean deviations. Also, the ozone-temperature correlations are strengthened. The feedback acts most strongly on zonal wavenumbers 1 and 2. Interactive ozone is found to increase the predictable signal of the final warming date, bringing it closer to reanalysis, even though the anomaly correlation coefficient is reduced. This reflects the limitations of the anomaly correlation coefficient as a metric of skill in the presence of a signal deficit.