The authors would like to thank Prof. Kunio Shimizu of Tokyo Science University, who gave helpful comments regarding the threshold method. The comments of three anonymous reviewers were very helpful to improve the original version. We also thank Dr. Y. Makihara and Dr. T. Nakazawa (Meteorological Research Institute) for providing the radar–AMeDAS data, and Dr. Utashima (National Space Development Agency of Japan) for his program to compute the TRMM orbits. R. O. wishes to thank Dr. W. K.-M. Lau and Mr. O. W. Thiele of NASA/GSFC for sponsoring her visit to GSFC.
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