Burst of pulses in lightning electromagnetic radiation: observations and implications for lightning test standards

Bursts of regular microsecond-scale electric field pulses produced by three multiple-stroke cloud-to-ground discharges (a total of 2782 pulses) and by three cloud discharges (a total of 1436 pulses), all recorded within 20 km or so at the NASA Kennedy Space Center, are analyzed. The regular pulse bursts are similar in both cloud-to-ground and cloud discharges. A burst is characterized by some tens of pulses, each having a total width of a few microseconds, with an average interpulse interval of 6-7 /spl mu/m. Pulse peaks in cloud-to-ground discharges are approximately two orders of magnitude smaller than return-stroke initial field peaks in the same flash. In both cloud and ground discharges, there is a tendency for the bursts to occur in the latter stages of a discharge, and positive and negative pulse polarities are about equally probable. Many bursts were found to be associated with the latter part of K changes while one pronounced M change appeared to be initiated by a regular pulse burst. The observed regular burst exhibit some similarity to the "multiple burst" (component H) of the standard lightning environment for the design and testing of aerospace vehicles. Overall, neither the present definition of the H component given in a previously published document (see Fed. Aviation Admin., US Dept. of Trans., advisory circular no. 20-136, Mar. 5, 1990) nor its newly proposed revision appears to be based on adequate experimental data.