1. Institute of Marine and Atmospheric Research Utrecht; Utrecht University; Utrecht The Netherlands
2. SRON Netherlands Institute for Space Research; Utrecht The Netherlands
3. IMK-ASF; Karlsruhe Institute of Technology; Eggenstein-Leopoldshafen Germany
4. Now at Laboratoire de Météorologie Dynamique; Institut Pierre-Simon Laplace; Paris France
5. Jet Propulsion Laboratory; California Institute of Technology; Pasadena USA