1. Department of the Geophysical Sciences; University of Chicago; Chicago Illinois USA
2. Max Planck Institute for Meteorology; Hamburg Germany
3. Institut de Physique du Globe de Paris; Université Paris 7-Denis Diderot; Paris France
4. Department of Atmospheric Science; Colorado State University; Fort Collins Colorado USA
5. Earth and Environmental Systems Institute, College of Earth and Mineral Sciences; Pennsylvania State University; University Park Pennsylvania USA