A self-consistent method for the analysis of lightning stroke data sets containing misclassified stroke: the variation of lightning over southern Africa

摘要

Historically the low peak current portion of the positive cloud-to-ground lightningudstroke data set is discarded since it is dominated by misclassified strokes. This thesisudpresents a self-consistent resolution to the problem of analysing lightning stroke dataudsets where misclassified strokes are present, without discarding sections of the dataudset. It is shown in this thesis that the misclassification problem is present in all theuddata sets, but is most prominent in the positive cloud-to-ground data set. The effectudof truncating the positive cloud-to-ground lightning stroke data set from the SouthudAfrican Lightning Detection Network is that 43� is discarded by truncating theuddata set below 10 kA, and 53� is discarded if the data set is truncated below 15 kA.udThe statistical distribution of lightning stroke peak current over southern Africa isudcomputed with the self-consistent method. A new measure of lightning activity isudestablished that, in addition to activity, describes the energy of strokes. A previouslyudundocumented inverse relationship between lightning stroke activity and peak currentudis presented in this thesis. The self-consistent method is extended to describeudthe diurnal variation of intracloud and cloud-to-ground parameters. The presenceudof positive cloud-to-ground lightning at the beginning and end of storms is verifiedudfrom lightning detection network measurements. The new measure is applied to singleudstorm days and single storms, and from this measure the charge distribution ofudthe lightning producing clouds is inferred. To complement the diurnal and temporaludvariations, the unique orographic sensitivity of the various lightning polarity typeudcombinations is presented over the extensive altitude of the Drakensberg mountainudrange. The self-consistent method presented in this thesis has direct application inudmeteorology; transmission line design and fault investigations; as well as improvingudrisk analyses by providing the true distribution of lightning stroke peak currents.