Los Alamos National Laboratory

Leader Studies with the Los Alamos Sferic Array


M J Heavner, D A Smith, and A R Jacobson


LAUR-01-4198

Leader Observations


A negative cloud to ground (-CG) lightning flash often has multiple strokes. The figure below (based on Uman, 1987) illustrates the typical timing of the processes of a multi-stroke -CG.
Typical Leader Processes

A typical stepped leader has velocity ~105 m/s) while dart leaders have velocity ~106 m/s). Predominantly, LASA (see Smith et al, 2000, or the Sferic Array web page) collected 8~ms of threshold triggered data, so the stepped leader ~20~ms before the return stroke is not observed. A longer (>250~ms) LASA record, presented in below, has good agreement with the time line presented in Panel A. The diamonds plotted are National Lightning Detection Network reported return strokes. There are four zoomed-in views of the initial leader activity (approximately 15 seconds before the initial return stroke), the leader with the initial return stroke, just the initial return stroke in the 8 ms window (representative of a typical sferic array 8 ms record), and a view of a subsequent return stroke.
Long Sferic Array Record
Initial Leader Activity Leader w/ Initial Return Stroke 8 ms record of initial Return Stroke Subsequent Return Stroke


The figure below presents a 8~ms LASA record with leader (which is extra-ordinary because of the fast/intense stepped leader).
Fast Leader with Return Stroke


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