1. Division of Earth and Planetary Sciences Kyoto University Kitashirakawaoiwake‐cho, Sakyo‐ku Kyoto 606‐8502 Japan
2. Department of Earth and Planetary Sciences Kyushu University 744 Motooka, Nishi‐ku Fukuoka 812‐0395 Japan
3. Department of Earth and Planetary Systems Science Hiroshima University 1‐3‐1 Kagamiyama Higashi‐Hiroshima 739‐8526 Japan
4. Nihon Thermal Consulting Co. 1‐5‐11 Nishi‐Shinjyuku, Shinjyuku Tokyo 160‐0023 Japan
5. National Institute of Polar Research 10‐3 Midori‐cho Tachikawa 190‐8518 Japan
6. Advanced Light Source Lawrence Berkeley National Laboratory Berkeley California 94720 USA
7. Department of Applied Physics Osaka University 2‐1 Yamadaoka, Suita Osaka 565‐0871 Japan
8. Department of Earth and Planetary Science The University of Tokyo Hongo, Bunkyo‐ku Tokyo 113‐0033 Japan