| Summary: | Long-term changes in the vertical ozone distribution over Switzerland are examined for the period 1967–2000. A statistical trend analysis is performed accounting for chemical and dynamical variability. The tropopause pressure, the North Atlantic oscillation (NAO), the Arctic oscillation (AO), and the quasi-biennial oscillation (QBO) are used as dynamical quantities. In addition, the solar effect and an ozone depletion factor (ODF), which describes the joint effect of stratospheric chlorine and aerosol loading, are included. A term is allowed for an unexplained linear trend. The various influences on ozone are estimated employing stepwise regression. Tropopause pressure and lower stratospheric ozone (10–19 km) variability are found to be strongly linked throughout the year. The NAO-AO indices show a negative correlation with lower stratospheric ozone in winter-spring. A positive correlation of NAO-AO and ozone is found in the middle stratosphere (23–30 km) during late summer to early winter. There is a solar signal in the middle stratosphere which becomes strongly significant in summer. The QBO signal is prominent at the height of the ozone maximum in winter-spring. The unexplained trends are much larger than the contributions of the ODF, suggesting that mechanisms other than midlatitude in situ chemistry are mostly responsible for the observed ozone loss. In the lowermost stratosphere (10–15 km), the observed ozone trends are found to be caused by dynamics. Above, the residual ozone trend (in percent) is independent of height and in the range of −2% to −5% per decade up to 30 km.
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