[1] We examine the characteristics of the initial stage (IS) in object-initiated lightning derived from current measurements on the Gaisberg tower (100 m, Austria), the Peissenberg tower (160 m, Germany), and the Fukui chimney (200 m, Japan) and their counterparts in rocket-triggered lightning in Florida. All lightning events analyzed here effectively transported negative charge to ground. For rocket-triggered lightning the geometric mean (GM) values of the three overall characteristics of the initial stage, duration, charge transfer, and average current, are similar to their counterparts for the Gaisberg tower flashes and the Peissenberg tower flashes, while the Fukui chimney flashes are characterized by a shorter GM IS duration and a larger average current. The GM IS charge transfer for the Fukui chimney flashes is similar to that in the other three data sets.The GM values of the action integral differ considerably among the four data sets, with the Fukui action integral being the largest. The observed differences in the IS duration between the Fukui data set and all other data considered here are probably related to the differences in the lower current limits, while the differences in the action integral cannot be explained by the instrumental effects only. There appear to be two types of initial stage in upward lightning. The first type exhibits pulsations (ringing) during the initial portion of the IS, and the second type does not. The occurrence of these types of IS appears to depend on geographical location. The characteristics of pulses superimposed on the initial continuous current (ICC pulses) in object-initiated (Gaisberg, Peissenberg, and Fukui) lightning are similar within a factor of 2 but differ more significantly from their counterparts in rocket-triggered lightning. Specifically, the ICC pulses in object-initiated lightning exhibit larger peaks, shorter risetimes, and shorter half-peak widths than do the ICC pulses in rocket-triggered lightning.

[1] We analyzed high-speed video images and corresponding current records for eight upward lightning flashes initiated by the Peissenberg tower (160 m) in Germany. These flashes contained a total of 33 measurable initial stage (IS) current pulses, which are superimposed on steady IS currents. Seven IS pulses had relatively short (<8 ms) 10-to-90% risetimes and 26 IS pulses had relatively long (>8 ms) risetimes. Six (86%) of seven IS current pulses with shorter risetimes each developed in a newly-illuminated branch, and 25 (96%) of 26 IS pulses with longer risetimes occurred in already luminous (current-carrying) channels. These results support the hypothesis that longer risetimes are indicative of the M-component mode of charge transfer to ground, while shorter risetimes are associated with the leader/return stroke mode. Similar results were obtained for M-component pulses that are superimposed on continuing currents following returnstroke pulses.

A program with the ultimate aim of quantifying the fidelity of laboratory test techniques used to simulate the penetration of metallic surfaces by lightning continuing currents has been undertaken. Descriptions of the program methodology, dominant factors found to influence test results, and data obtained so far are given. Based on considerations of fundamental arc phenomenology and on the acquired experimental data, a standard test configuratidh has been established, which has been demonstrated at two independent laboratories to produce consistent results that are generally corroborative of techniques suggested elsewhere in the lightning literature.

SUMMARYThis paper presents an experimental investigation of the rear-face temperature rise of different metals struck by lightning long-duration currents on the front face. The experimental investigation simulates the heating effect of one current component of the natural lightning flashes that may strike in-flight or landed aircraft and rockets; munitions and nuclear weapons; and storage/collection tanks and pipelines of the petroleum/gas industries. In the case of a lightning strike the rear-face temperature rise must be less than certain limits to avoid catastrophic damage/accidents. A sophisticated high-speed infrared camera, having an image frequency of 50 Hz and a temperature range up to 1200 C, is used to measure the rear-face temperature profiles as a function of the coordinates and time. The results are interpreted in light of the optical observation of the arc motion, physical measurement of the spot diameter, and study of the energy balance at the cathode and anode spots. The results reveal that for constant charge transfer, lightning long-duration currents having higher amplitudes give a higher rear-face temperature rise and hence a higher risk of accidents. Both the maximum rear-face core temperature and the front-face spot diameter exponentially increase with the mean current amplitude. Moreover, the maximum rear-face core temperature varies exponentially with the charge and linearly with the action integral. Current injection with positive polarity of the test electrode gives a lower rear-face temperature for all metals used except for aluminium where the trend is reversed.

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