1. Department of Mathematics and Statistics; Memorial University of Newfoundland, St. John's, Newfoundland; Canada
2. British Antarctic Survey; Natural Environment Research Council; Cambridge UK
3. Department of Atmospheric and Oceanic Sciences; University of California; Los Angeles California USA
4. Institute of Geophysics and Planetary Physics and Department of Earth and Space Sciences; University of California; Los Angeles California USA
5. Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA