A self-consistent method for the analysis of lightning stroke data sets containing misclassified stroke: the variation of lightning over southern Africa
Grant, Michael David
Historically the low peak current portion of the positive cloud-to-ground lightning stroke data set is discarded since it is dominated by misclassified strokes. This thesis presents a self-consistent resolution to the problem of analysing lightning stroke data sets where misclassified strokes are present, without discarding sections of the data set. It is shown in this thesis that the misclassification problem is present in all the data sets, but is most prominent in the positive cloud-to-ground data set. The effect of truncating the positive cloud-to-ground lightning stroke data set from the South African Lightning Detection Network is that 43� is discarded by truncating the data set below 10 kA, and 53� is discarded if the data set is truncated below 15 kA. The statistical distribution of lightning stroke peak current over southern Africa is computed with the self-consistent method. A new measure of lightning activity is established that, in addition to activity, describes the energy of strokes. A previously undocumented inverse relationship between lightning stroke activity and peak current is presented in this thesis. The self-consistent method is extended to describe the diurnal variation of intracloud and cloud-to-ground parameters. The presence of positive cloud-to-ground lightning at the beginning and end of storms is verified from lightning detection network measurements. The new measure is applied to single storm days and single storms, and from this measure the charge distribution of the lightning producing clouds is inferred. To complement the diurnal and temporal variations, the unique orographic sensitivity of the various lightning polarity type combinations is presented over the extensive altitude of the Drakensberg mountain range. The self-consistent method presented in this thesis has direct application in meteorology; transmission line design and fault investigations; as well as improving risk analyses by providing the true distribution of lightning stroke peak currents.