The return stroke initial electric field peak normalized to 100 km, the probability of creating a new termination on ground, and the probability of occurrence of a dart-stepped leader after an interstroke interval of 100 ms or less have been determined as a function of stroke order from simultaneous electric field and TV records of 76 negative cloud-to-ground flashes near Tampa, Florida. Fifty percent of the flashes showed multiple terminations on the ground as inferred from TV records (from 29 to 69 percent for separate thunderstorm days). For all flashes, the minimum initial electric field peak normalized to 100 km for first strokes was found to be 2.2 V/m and for subsequent strokes 0.25 V/m. The geometric mean initial electric field peak for 155 second, third and fourth strokes taken together was found to be 1.4 times larger than for 115 strokes of order 5 through 18, with the difference being statistically significant at the 0.005 significance level. The geometric mean initial electric field peak for 63 first strokes in multiple-stroke flashes was found to be 1.3 times larger than for 13 strokes in single-stroke flahses. The charge lowered by strokes in New Mexico was observed to exhibit behavior similar to that of the initial electric field peak in Florida described above. Subsequent strokes creating a new termination on ground showed a higher initial electric field peak than strokes following the same channel as the preceding stroke, but lower than for first strokes in a flash.

Second strokes showed the maximum probability of both creating a new termination on ground (0.37) and producing a dart-stepped leader along the channel of the previous stroke after an interstroke interval of 100 ms or less (0.36). None of the 115 strokes of order 5 and higher created a new termination on ground in spite of the fact that previous interstroke intervals for 22 of them were from 101 to 253 ms and did not contain long continuing current. The results presented and other relevant data available in the literature are consistent with the proposed hypothesis that successive strokes provide cumulative conditioning of the lightning channel. ¿ American Geophysical Union 1990