Continuing current in negative cloud‐to‐ground lightning

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Abstract
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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