1. Department of Geosciences, Penn State University, University Park, PA 16802, USA
2. School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
3. National Center for Atmospheric Research, Boulder, CO 80301, USA
4. Center for Climate Systems Research, Columbia University, New York, NY 10025, USA
5. NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA