Trends in measured and modeled lower stratospheric Antarctic vortex ozone over the past two decades

Abstract. We analyze 2004 to 2023 winter/spring lower stratospheric Antarctic ozone data from the Aura Microwave Limb Sounder (MLS), along with similarly sampled profiles from two simulations from the Whole Atmosphere Community Climate Model (WACCM) run with specified dynamics. One of these simulations uses fixed surface organic halogens from 1998 onward. The interannual variability in MLS vortex-average ozone is well matched by WACCM, although WACCM shows a smaller seasonal decrease. Probability density functions of vortex ozone profiles reveal slow increases in the smallest values; WACCM shows good agreement with MLS distribution shifts and simple linear trends. We also use multivariate linear regression with two periodic functions and a proxy for polar stratospheric clouds to derive trends in vortex-average ozone during September and October. Calculated trends are consistent with slow Antarctic vortex ozone recovery from the impact of ozone-depleting substances, with values between ~5 and 16 ppbv yr^-1 in the 56–100 hPa layer. WACCM results agree well with those from MLS. The simulation with fixed surface organic halogens is consistent with zero trend. We also apply the Match technique, which follows MLS-observed parcels along trajectories to estimate vortex-average chemical ozone loss. Match estimates also show reductions in seasonal Antarctic ozone loss, although few of the Match results represent greater than two-sigma departures from zero. Our work confirms the emergence of ozone recovery, a key goal of the Aura mission, and underscores the importance of the 1987 Montreal Protocol and its Amendments in curtailing emissions of ozone-depleting substances.