Extended Abstract (228K)11A.6
Lightning Meteorology II: An advanced course on forecasting with lightning data
Bard A. Zajac, CIRA/Colorado State Univ., Fort Collins, CO; and J. F. Weaver, D. E. Bikos, and D. T. Lindsey
The National Weather Service / Virtual Institute for Satellite Integration Training has developed a two-part teletraining course on forecasting with cloud-to-ground (CG) lightning data using the Advanced Weather Interactive Processing System (AWIPS). The first course, Lightning Meteorology I, examines CG lightning activity in typical warm season storms. The second course, Lightning Meteorology II, examines CG lightning activity in severe warm season storms and cold season storms. This paper provides an overview of the second course.
Lightning Meteorology II is organized into five sections. Lightning Meteorology I is reviewed in Section 1. Section 2 describes the two main lightning parameters in AWIPS, CG flash rate and the percentage of +CGs, and factors that control these parameters. In Section 3, lightning climatologies reveal that most warm season storms are negative strike dominated (NSD) and characterized by less than 15% +CGs. In contrast, cold season storms are characterized by greater than 15% +CGs. Several AWIPS cases illustrate the higher percentage of +CGs during the cold season. This behavior is explained by lower cloud tops, greater vertical wind shear, and less cloud liquid water during the cold season. These seasonal differences modify or invert the normal dipole charge distribution (positive charge above negative charge) and increase the likelihood of +CGs.
In Section 4, severe warm season NSD storms are contrasted with typical warm season NSD storms. Unlike typical NSD storms, severe NSD storms can exhibit dramatic fluctuations in CG flash rate with periods of roughly 30 minutes. In addition, severe NSD storms can exhibit percent +CGs well above the typical 15%. Fluctuations in CG flash rate are attributed to pulsing in updraft intensity and its effect on the vertical distribution of charged hydrometeors. The higher percentage of +CGs is attributed to tilting of the updraft, which exposes upper-level positive charge to the earth's surface.
In Section 5, lightning climatologies are reexamined and reveal that the percentage of +CGs is significantly greater than 15% over parts of the central U.S. during the warm season. Severe storm climatologies indicate that this signal is associated with severe positive strike dominated (PSD) storms. Two outbreaks of severe PSD storms over the central U.S. are presented and three anomalies are identified: clusters of +CGs in the storm core and -CGs from the anvil, reversals in dominant CG lightning polarity, and extended periods of low CG flash rate. Anomalous CG strike locations are consistent with an inverted dipole. Polarity reversals appear to be linked to the amount of low- and mid-level moisture encountered by storms. Low CG flash rate may be explained by intense updrafts, which elevate charged hydrometeors away from the earth's surface.
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Session 11A, Lightning Studies
Wednesday, 14 August 2002, 4:30 PM-6:00 PM
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