1. Laboratoire des Sciences du Climat et de l'Environnement; CEA-CNRS-UVSQ; Gif-sur-Yvette France
2. Now at Department of Environmental Sciences; University of Virginia; Charlottesville Virginia USA
3. Now at Climate Research Division; Environment Canada; Toronto Ontario Canada
4. Now at Institut für Umweltphysik; University of Heidelberg; Heidelberg Germany
5. Laboratoire de Météorologie Dynamique; CNRS-Ecole Polytechnique; Palaiseau France