13 Feb 2023
 | 13 Feb 2023
Status: this preprint is currently under review for the journal ACP.

Interannual polar vortex-ozone co-variability

Frederik Harzer, Hella Garny, Felix Ploeger, Harald Bönisch, Peter Hoor, and Thomas Birner

Abstract. Stratospheric ozone is important for both stratospheric and surface climate. In the lower stratosphere during winter its variability is governed primarily by transport dynamics induced by wave-mean flow interactions. Here, we focus on interannual co-variations between the zonal mean ozone distribution and the strength of the polar vortex during northern hemispheric winter. Specifically, we study co-variability between the seasonal means of the ozone field from modern reanalyses and polar cap-averaged temperature at 100 hPa, which represents a robust and well-defined index for polar vortex strength. We consider variability in both pressure and isentropic coordinates. In the former case, we find that anomalously weak polar vortex years are associated with increased polar ozone amounts, showing two pronounced local maxima: one in the lower to mid-stratosphere and one just above the polar tropopause. In contrast, in isentropic coordinates, only the mid- to lower stratosphere shows increased ozone, while a small negative ozone anomaly appears in the lowermost stratosphere. These differences are related to contributions due to anomalous adiabatic vertical motion, which are implicit in potential temperature coordinates. In general, our analyses of the ozone budget in the extratropical middle stratosphere show that interannual polar ozone variability can be explained by a combination of anomalous diabatic downwelling and quasi-isentropic eddy mixing that are associated with consecutive, counteracting anomalous ozone tendencies on daily time scales. We find that approx. 71 % of the total variability of polar column ozone in the stratosphere is associated with year-by-year variations in polar vortex strength based on ERA5 reanalyses for the winter seasons 1980–2022. MLS observations for 2005–2020 show that around 86 % can be explained by polar vortex co-variability.

Frederik Harzer et al.

Status: open (until 27 Mar 2023)

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Frederik Harzer et al.

Frederik Harzer et al.


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Short summary
Stratospheric ozone is important for both stratospheric and surface climate. Here, we study the statistical relation between year-by-year fluctuations in winter-mean lower stratospheric ozone and the strength of the stratospheric polar vortex. These fluctuations are found to be primarily associated with variations in transport, with non-trivial combinations of polar-cap downwelling due to radiative cooling and quasi-horizontal mixing due to dissipating planetary waves.