We thank two anonymous referees for their useful comments. Numerical experiments were performed with HPC2500 at the Academic Center for Computing and Media Studies, Kyoto University; at the Information Technology Center, Nagoya University; and the KDK system of Research Institute for Sustainable Humanosphere (RISH) at Kyoto University as a collaborative research project. GFD-DENNOU Library was used for drawing the figures. ISPACK-0.71 was used for numerical experiments and analyses. N. Sugimoto is supported by Grant-in-Aids for the 21st Century COE programs “Elucidation of the Active Geosphere” and “Frontiers of Computational Science.” This work was also supported by a Grant-in-Aid for Young Scientists (B) (19740290) from the Ministry of Education Culture, Sport, Science and Technology in Japan.
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