1. NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
2. Center for Ocean-Land-Atmosphere Studies, Calverton, MD 20705, USA.
3. National Center for Atmospheric Research, Boulder, CO 80307, USA.
4. Meteorological Service of Canada, Toronto, Ontario M34 5T4, Canada.
5. Hadley Centre for Climate Prediction and Research, Exeter EX1 3PB, UK.