accepted on the recommendation of

There are a lot of people whom I would like to thank for making this project possible. Firstly Thomas Peter, Eugene Rozanov and Johannes Stähelin, for writing the project proposal in the first place, and then for the many hours of discussions over the three years that followed. Thanks especially to Eugene for your patience in explaining the workings of the model (often more than once)! Also to Johannes for your very helpful suggestions with regard to the work in Chapters 4-6, and your thorough reviews of the thesis while I was writing up. I’d also like to thank Tom for providing encouragement, motivation and good ideas when I thought everything was turning to custard. Thanks to Bram Bregman for your insightful comments on the thesis, and for coming all the way to Zürich for my exam. Werner Schmutz allowed me to carry out this work at the PMOD/WRC in Davos, and was always ready with advice when it was needed. Tatiana Egorova was a great help when I got stuck with the model and Christof Appenzeller helped arrange access to the ERA-40 data, without which this would have been a really short thesis. With regard to helping me find my way around the ERA-40 archive and extracting the data I needed,