The authors wish to thank Drs. Y. Hayashi and A. Numaguti for their helpful discussions and comments on this work. GFD-DENNOU Library was used for drawing figures and the model used in this study is based on a GCM (AGCM5) in this library. Numerical calculation was done on the SX3 at Computation Center, Osaka University, and on the KDK system at Radio Atmospheric Science Center, Kyoto University. This work was supported in part by the Grant-in-Aid for Scientific Research of the Ministry of Education, Science, Sports and Culture of Japan; and by the Grant-in-Aid for the Cooperative Research with Center for Climate System Research, University of Tokyo.
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