The authors thank Mr. Shoin Yagi in Meteorological Research Institute in Japan for kindly providing detailed information on the operational radiosonde observation archive at JMA. The GFD-DENNOU library was used for drawing figures. This research was supported in part by Grant-in-Aid for Scientific Research (B)(2) 12440126 of the Ministry of Education, Culture, Sports, Science and Technology in Japan, by the National Science Foundation Grant ATM-9903514, and by the National Aeronautics and Space Administration Contract NAS1-99130.
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