Masaki Ishiwatari Graduate School of Environmental Earth Science, Hokkaido University Kita-10 Nishi-5, Kita-ku, Sapporo, 060, Japan e-mail: momoko@ees.hokudai.ac.jp
Kensuke Nakajima Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University 6-10-1 Hakozaki, Hukuoka, 812, Japan e-mail: ken-suke@deepconv.geo.kyushu-u.ac.jp
Shin-ichi Takehiro Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University 6-10-1 Hakozaki, Hukuoka, 812, Japan e-mail: takepiro@geo.kyushu-u.ac.jp
Yoshi-Yuki Hayahi Graduate School of Mathematical Sciences, University of Tokyo 3-8-1 Komaba Meguro-ku, Tokyo, 153, Japan e-mail: shosuke@ms.u-tokyo.ac.jp