Electric field pulses, their times of occurrence in the flash, and their relationship to slower electric field variations were studied for lightning cloud flashes at a distance of about 10 km in Florida. Large pulses with a width of a few microseconds tended to occur more frequently early in the flash. If only pulses with amplitudes greater than 50% above the system noise and widths greater than 1.6 μs were counted, 58% of 332 pulses in 89 flashes occurred in the first third of the field records, while only 14% occurred in the final third. The mean total flash duration was 660 ms. The 31 largest pulse peaks (those with amplitudes more than 3 times the system noise) in six flashes that were analyzed in detail had a median 30--90% risetime of 1.0 μs. The 25 pulses in which these peaks occurred had a median half width of 2.7 μs and had mean full widths, including the positive overshoot, of 74 μs.

All these pulses were of negative polarity and were superimposed on negative-going field changes. Most occurred in the first third of the overall field change. In the latter part of these six records, microsecond-scale field variations were more than 50% above the tape noise (effectively 4 V/m) in only nine of 49 K changes. Not all pulses associated with K changes had the same polarity as the K change, and their pulse structure was relatively complex in contrast to the negative pulses that occurred early in the records. We infer that the process that produces the K change pulses is different from that which produces the large pulses that occur earlier in the discharges. ¿ American Geophysical Union 1988