1. Institute for Space‐Earth Environmental Research Nagoya University Nagoya Japan
2. Now at Nippon Steel Corporation Nagoya Works Tokai‐shi Japan
3. National Institute of Polar Research Tokyo Japan
4. Sodankylä Geophysical Observatory University of Oulu Oulu Finland
5. Center for Space Science and Radio Engineering University of Electro‐Communications Chōfu Japan
6. Research Institute for Sustainable Humanosphere Kyoto University Kyoto Japan