1. British Antarctic Survey; Cambridge UK
2. Department of Physics; Norwegian University of Science and Technology; Trondheim Norway
3. Also at Birkeland Centre for Space Science; Bergen Norway
4. Department of Physics; University of Otago; Dunedin New Zealand
5. Also at Earth Observation; Finnish Meteorological Institute; Helsinki Finland
6. Max Planck Institute für Solar System Research; Katlenburg-Lindau Germany
7. Now at Swiss Federal Office for Statistics; Neuchâtel Switzerland
8. Norwegian Polar Institute; Tromsø Norway