Abstract

Cloud-to-ground lightning flash characteristics of a series of four mesoscale convective systems (MCS) that occurred in Oklahoma and Kansas on 3–4 June 1985 during the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central project are described. A total of 23 490 flashes were detected by the network from all four MCSs; 96% of them lowered negative charge to ground. Because the second MCS (MCS II) spent nearly all of its lifetime within the optimal region of coverage of the lightning and radar networks, trends in ground-flash characteristics could be documented throughout the system's life cycle. Lightning trends were analyzed relative to rainfall parameters based on radar network data and were stratified by the flashes’ polarity and locations according to their association with convective and stratiform radar echoes.

Most flashes in the second MCS were negative ground strikes within convective radar echoes. In convective regions the flashes were primarily negative; in stratiform regions the negatives were somewhat more than half the flashes. Positive flashes were much less frequent than negative ground strikes for the entire storm. Positive strikes in stratiform echoes during the last half of the storm exceeded the number of negative flashes, but positive ground strikes were always scarce in convective regions. For the second MCS, time series of flashes were developed for flash density, flash rate per rain volume, and number according to radar echo type. Severe weather tended to occur during the growth and mature stages of the storm and was located on the southern and western sides of the MCS's lightning activity. During the growth stage, smaller elements within the new storm had a somewhat linear organization of frequent negative flashes in convective echoes. During the mature stage, negative flashes were in a large cluster, their rates peaked, and then began to decrease. During the decay stage, negative flash rates rapidly decreased but continued to cluster in convective regions. At most, a few percent of the flashes in convective regions lowered positive charge to ground, and positive flash rates in convective regions followed trends very similar to those of negative flash rates. Positive flash rates in the stratiform region, however, tended to increase until early in the decay stage. In the stratiform region during the decay stage, positive flashes were spread over a much larger area than negative flashes.

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