1. Department of Meteorology, University of Maryland, College Park, MD 20742, USA.
2. Department of Environmental Sciences, Rutgers—The State University of New Jersey, 14 College Farm Road, New Brunswick, NJ 08901–8551, USA.
3. Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration (NOAA), Post Office Box 308, Princeton, NJ 08542, USA.
4. Department of Atmospheric Sciences, University of Illinois, 105 South Gregory Street, Urbana, IL 61801, USA.
5. Code 971, Oceans and Ice Branch, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
6. Hadley Centre for Climate Prediction and Research, Meteorological Office, Bracknell, RG12 2SZ, UK.
7. Climate Prediction Center, National Weather Service, National Centers for Environmental Prediction, NOAA, 5200 Auth Road, Room 800, Camp Springs, MD 20746, USA.
8. Arctic and Antarctic Research Institute, 38 Bering Street, St. Petersburg 199397, Russia.