1. Center for Atmospheric and Oceanic Studies, Faculty of Science, Tohoku University, Sendai 980, Japan
2. National Institute for Resources and Environment, 16-3 Onogawa, Tsukuba 305, Japan.
3. Graduate School of Environmental Earth Science, Hokkaido University, Kita 10-Nishi 5, Kita, Sapporo 060, Japan
4. Meteorological Research Institute, 1-1 Nagamine, Tsukuba 305, Japan
5. National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo 173, Japan
6. National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305, Japan
7. Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa, Nagoya 464-01, Japan