The authors thank Dr. J. D. McCalpin, who provided a quasigeostrophic model code written in FORTRAN 90. The authors also thank two anonymous reviewers for valuable comments. This research was supported by the Japanese Ministry of Education, Sports, Culture, Science and Technology through Grant 20540431 and by the National Research Institute for Erath Science and Disaster Prevention through a research project on long-term prediction of typhoons and their disaster.
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