Occurrence of new upward positive leaders triggered by negative downward CG lightning

Abstract

Characterizing upward leaders is not obvious because their maximum flash intensity (some kA) is small if compared to similar LPS installed at low altitude, so the discrimination between leaders involved in lightning attachment process and those non-connecting ones is not straightforward. A simplified model of the field produced by a negative CG flash has been tested in order to predict most of the vulnerable points of neighboring structures from where upward leaders might occur. As shown earlier, a positive upward leader needs for reaching a substantial enough development to satisfy physical criteria such like a threshold field for leader inception and a threshold field for its self-sustained propagation. Analytical relationships allow to estimate the region inside which an upward leader may occur and eventually only lead to a non-connecting form. Experimental evidences will be looked for using data of Météorage, the French lightning detection network. During previous lightning season, several events inside a period of one year have been recorded, some of them being non-connecting upward leaders created at the lightning rod tip.