[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.

Simultaneous single‐station electric field and multiple‐station TV measurements on 90 negative cloud‐to‐ground lightning flashes that occurred on 3 days in July 1979 near Tampa, Florida, have been analyzed for the following characteristics of electric field changes indicative of continuing current: frequency of occurrence, duration, duration of interstroke interval preceding, duration of interstroke interval containing, current and charge transferred, and magnitude of initiating return‐stroke electric field peak. Of the 90 flashes, 22 contained a long (greater than 40 ms) continuing current and 11 contained a short (10–40 ms) continuing current. Only one of 19 single‐stroke flashes was followed by a long continuing current, and none were followed by a short continuing current; none of the first strokes of 71 multiple‐stroke flashes were followed by either long or short continuing current. The geometric mean duration of long continuing current was 115 ms and that of short continuing current was 23 ms. Long and short continuing current average amplitudes were primarily in the range 30–200 A. There is an inverse relation between the duration of the interstroke interval just preceding the interval containing continuing current and the duration of the continuing current. Twenty‐two interstroke intervals just preceding interstroke intervals containing long continuing current have a geometric mean duration of 28 ms, and 16 intervals preceding interstroke intervals containing short continuing current have a geometric mean duration of 53 ms; however, the geometric mean duration of 161 interstroke intervals neither containing continuing current nor preceding it is 64 ms and the geometric mean duration of all 258 interstroke intervals in the 90 ground flashes is 65 ms. On average, the return strokes that precede continuing current have smaller initial peak electric fields, and hence smaller peak currents, than do other return strokes. Sixteen electric field peaks associated with return strokes preceding long continuing current have a geometric mean, normalized to 100 km, of 2.6 V/m, and 15 field peaks initiating short continuing current have a geometric mean of 2.4 V/m, whereas 199 field peaks associated with strokes not initiating continuing current have a geometric mean of 3.5 V/m.

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To clarify the &hara&te~stics of lightning on the coast of the Sea of Japan in winter season, the current w a v~~o r m and the pro~ression of lightning discharge to a high stack were observed. Observation results from 1989 to 1994 show that ; (1) There are two types of lightning ne with large currents and strong luminosity in the ~ightning path, and the other with small currents of long duration and weak luminosity of lightning path. (2) The parameters of ligh~ning currents of the two types of discharges are quite different. (3) There is a quantitative correlation between the change of luminosity in a lightning path and the~i~htning currentwaveform.

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The mechanism of the guidance effect of laser plasmas on electrical discharges has been studied. A 45 J CO2 laser pulse produces many spherical plasmas over a gap of up to 2 m, and the laser-guided discharge is formed along the plasma by the application of a lightning impulse voltage. Unusual properties of the laser guided discharge are obtained from streak photographs of the discharge development. The laser produced plasmas guide streamers and leaders from a negative electrode more effectively than from a positive electrode. The discharge development from the negative electrode plays an important role in the guidance effect.

Experiments to guide electric discharges with a chain of apparently discrete a i r -breakdown plasmas ( p l a s m a channel) produced by a l a s e r were c a r r i e d o u t . The electric d i s c h a r g e was guided u p t o 2m with a high power CO2 laser focused by a 10 -m focal l e n g t h m i r r o r . V o l t a g e w a s a p p l i e d a t s e l e c t e d delay times 5 f o l l o w i n g l a s e r r a d i a t i o n . The r el a t i o n s b e t w e e n 50% f l a s h o v e r v o l t a g e of a g a p filled with laser -produced plasmas and delay times r , between the guided length and the peak of the appiled voltage, were obtained experimentally. The e f f e c t s of t h e p o l a r i t y of a n a p p l i e d v o l t a g e a n d t h e p o s i t i o n of t h e p l a s m a c h a n n e l o n f l a s h o v e r voltage a r e described. Development characteristics of the guided discharge were a l s o investigated.