We thank two anonymous reviewers for their constructive comments on the manuscript. We also acknowledge stimulating discussions with Kunihiko Kodera, Yuhji Kuroda, Koji Yamazaki, Saburo Miyahara, Hisanori Itoh, Tomoko Ichimaru, and all the members in the Climate Prediction Division in JMA. The extended refractive index for stationary waves was calculated using routines originally developed by Hisashi Nakamura. This work was partly supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.
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