The first author was sponsored by the FINNIDA/WMO/SADC Meteorology Project. Part of this research was also supported by National Science Foundation Grant ATM-9415407 and Air Force Grant AFOSR F49620-96-1-0172. We acknowledge gratefully the Mesoscale and Microscale Meteorology Division of the National Center for Atmospheric Research and the Cooperative Institute for Research in the Environmental Sciences, Boulder, Colorado, where a significant part of this work was carried out. We are also grateful to Drs. Mark Borges, Roberto Buizza, Jorgen Frederiksen, Melvin Shapiro, and Jeffrey Whitaker and two anonymous reviewers for their valuable comments.
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