1. Center for Atmospheric and Oceanic Studies, Tohoku University, Sendai 980-8578, Japan;
2. National Institute for Environmental Studies, Tsukuba 305-8506, Japan;
3. Faculty of Education, Miyagi University of Education, Sendai 980-0845, Japan;
4. National Institute of Polar Research, Tokyo 173-8515, Japan;
5. The Institute of Space and Astronautical Science, Sagamihara 229-8510, Japan