The lightning data were obtained from Global Atmospherics, Inc., Tucson, Arizona. The interest, assistance, and cooperation of Ken Cummins and Pat Zumbusch in this project are greatly appreciated. We could not have completed this research without their support. The detailed comments of Ken Cummins, Martin Murphy, and two anonymous reviewers significantly improved an early version of this paper and we appreciate their efforts. We thank Barbara Orville for her editorial assistance. Data handling at Texas A&M University is under the direction of Jerry Guynes and we are pleased to acknowledge his assistance. This research is part of a lightning program supported by the National Science Foundation (ATM-9806189) and the National Oceanic and Atmospheric Administration (Cooperative Agreement NA87WA0063).
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