2002 Annual

Thursday, 17 January 2002: 11:45 AM
The value of cloud lightning in probabilistic thunderstorm warning
Martin J. Murphy, Global Atmospherics, Inc., Tucson, AZ; and N. W. S. Demetriades and K. L. Cummins
In this study, lightning location information is used to anticipate the onset of lightning in a small area of interest. The present analysis addresses the question of whether detecting cloud lightning, in addition to cloud-to-ground (CG) flashes, improves the probability of warning or the false alarm rate. Developing thunderstorms typically produce cloud lightning flashes prior to the first CG flash for a time on the order of five to ten minutes. However, in many localities, storms rarely develop overhead but rather move in from elsewhere and are already producing CG lightning. While the former tendency suggests that there is some usefulness for cloud lightning information, the latter suggests that there should be a limit to that usefulness. That limit is determined in part by the distribution of the time from first cloud flash to first CG flash in a developing storm and in part by the fraction of storms that develop overhead. This upper limit on the usefulness of cloud lightning detection can, of course, only be achieved by detecting all cloud flashes. To explore this limit, we employ data from a VHF lightning detection system that is capable of detecting at least some portion of all flashes. We then examine cloud lightning information from detection systems having probabilities of detection for cloud flashes ranging between 10% and 1% in order to see whether the reduced cloud lightning data sets produce a noticeable change in the probability of warning and false alarm rate. Preliminary results from different climate regimes are discussed.

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