Total ozone trends at three northern high-latitude stations.

After the decrease of ozone-depleting substances (ODSs) as a consequence of the Montreal Protocol, it is still challenging to detect a recovery in the total column amount of ozone (total ozone) at northern high-latitudes. To assess regional total ozone changes in the "ozone-recovery"-period (2000-2020) at northern high-latitudes, this study investigates trends from ground-based total ozone measurements at three stations in Norway (Oslo, Andøya, and Ny-Ålesund). For this purpose, we combine measurements from Brewer spectrophotometers, ground-based UV filter radiometers (GUVs), and a SAOZ instrument. The Brewer measurements have been extended to work under cloudy conditions using the global irradiance (GI) technique, which is also presented in this study. We derive trends from the combined ground-based time series with the multiple linear regression model from the Long-term Ozone Trends and Uncertainties in the Stratosphere (LOTUS) project. We evaluate various predictors in the regression model and found that tropopause pressure and lower-stratospheric temperature contribute most to ozone variability at the three stations. We report significant positive trends at Andøya (0.9% per decade) and NyÅlesund (1.5% per decade) and no annual trends at Oslo, but significant positive trends in autumn at all stations. Finally we found positive but insignificant trends of around 3% per decade in March at all three stations, which may be an indication for Arctic spring-time ozone recovery. Our results contribute to a better understanding of regional total ozone trends at northern high-latitudes, which is essential to assess how Arctic ozone responds to changes in ODSs and to climate change. [ABSTRACT FROM AUTHOR]