We have analyzed stratospheric ozone changes using both, ground-based measurements such as the total ozone series of Arosa as well as satellite measurements. Ground based measurements started earlier but they don’t provide global coverage of the ozone shield. By data assimilation using meteorological data the ozone series CATO (Candidoz Assimilated Three-dimensional Ozone) was constructed, which provides global coverage and ozone profile information (the data can be down loaded from the web-page http://iac.ethz.ethz.ch/cato/). Since long-term ozone trends are relatively small the reliability of long-term ozone measurements has high priority. For that purpose we study simultaneous ground based ozone measurements by different instrument types, available at Arosa since the early 1990s (see Swiss long-term ozone series).

Current research topics include:

• Careful evaluation of ground-based total ozone measurements obtained by Dobson and Brewer instruments operated at Arosa operated by MeteoSwiss.
• Statistical modeling of the evolution of the stratospheric ozone shield, in particular to study the effect of the Montreal protocol and the effect of climate variability using multiple regression models in order to account for atmospheric processes based on both, ground-based and satellite measurements.

b) Chemical stratospheric ozone depletion caused by the release of anthropogenic ozone depleting substances.

c) Total ozone series of Arosa (Switzerland) (for more details see Swiss long-term ozone measurements)