The phase and amplitude relationships between dynamical quantities and ozone within the Quasi-biennial Oscillation (QBO) are explored. An initial assessment of this is done by applying a Principal Oscillation Pattern analysis to observations (SWOOSH for Ozone) and reanalysis data (ERA5). This analysis highlights features of the ozone and temperature variability including two peaks in amplitude in the QBO region as well as more subtle phase differences that cannot be explained by a simple QBO theory. We also quantify the sizes of the ozone and temperature advection terms and show that the contribution of background upwelling on variations in ozone gradient is not negligible (~25%). A radiative-convective equilibrium and photochemical equilibrium model, with the imposed ERA5 QBO variation in upwelling and OSIRIS NOx variations, is used to further understand ozone and temperature changes. The results show that photochemistry and transport are important at all levels and it is misleading to divide the QBO into separate regimes. Prominent aspects of the variability can be reproduced if ERA5 upwelling is reduced by ~60% between 15 and 50 hPa where ERA5 is likely over-predicting the strength of the secondary meridional circulation. Finally, we demonstrate that non-locality in the vertical plays a major role in QBO dynamics. This arises from ozone transport, the dependence on column ozone of photochemical production and radiative transfer between layers.

Major tropical volcanic eruptions have emitted large quantities of stratospheric sulphate and are potential sources of stratospheric chlorine although this is less well constrained by observations. This study combines model and ice core analysis to investigate past changes in total column ozone. Historic eruptions are a good analogue for future eruptions as stratospheric chlorine levels have been decreasing since the year 2000. We perturb the pre-industrial atmosphere of a chemistry-climate model with high and low emissions of sulphate and chlorine. The sign of the resulting Antarctic ozone change is highly sensitive to the background stratospheric chlorine loading. In the first year, the response is dynamical, with ozone increases over Antarctica. In the high HCl (10 Tg emission) experiment, the injected chlorine is slowly transported to the polar regions with subsequent chemical ozone depletion. These model results are then compared to measurements of the stable nitrogen isotopic ratio, δ15N(NO−3), from a low snow accumulation Antarctic ice core from Dronning Maud Land (recovered in 2016-17). We expect ozone depletion to lead to increased surface ultraviolet (UV) radiation, enhanced air-snow nitrate photo-chemistry and enrichment in δ15N(NO−3) in the ice core. We focus on the possible ozone depletion event that followed the largest volcanic eruption in the past 1000 years, Samalas in 1257. The characteristic sulphate signal from this volcano is present in the ice-core but the variability in the δ15N(NO−3) dominates any signal arising from changes in UV from ozone depletion. Whether Samalas caused ozone depletion over Antarctica remains an open question.

The interannual variability in mid and lower stratospheric temperatures for the period 1984–2019 is decomposed into dynamical and radiative contributions using a radiative calculation perturbed with changes in dynamical heating, trace gases and aerosol optical depth. The temperature timeseries obtained is highly correlated with the de-seasonalised ERA5 temperature (r2>0.6 for 1995 to 2019 in the region 15 to 70 hPa). Contributions from ozone and dynamical heating are found to be of similar importance, with water vapor, stratospheric aerosols, and carbon dioxide playing smaller roles. Prominent aspects of the temperature timeseries are closely reproduced, including the 1991 Pinatubo volcanic eruption, the year-2000 water vapour drop, and the 2016 Quasi-biennial oscillation (QBO) disruption. Ozone below 20 hPa is primarily controlled by transport and is positively correlated to the upwelling. This ozone-transport feedback acts to increase the temperature response to a change in upwelling by providing an additional ozone-induced radiative temperature change. This can be quantified as an enhancement of the dynamical heating of about 20% at 70 hPa. A principle oscillation pattern (POP) analysis is used to estimate the contributionof the ozone QBO (±1 K at 70 hPa). The non-QBO ozone variability is also shown to be significant. Using the QBO leading POP timeseries as representative of the regular QBO signal, the QBO 2016 disruption is shown to have an anomalously large radiative impact on the temperature due to the ozone change (>3 K at 70 hPa).