ORIGIN OF LIGHTNING ELECTRIC-FIELD SIGNATURES SHOWING 2 RETURN-STROKEWAVE-FORMS SEPARATED IN TIME BY A MILLISECOND OR LESS

Based on simultaneous single-station electric field and multiple-stati on TV records of 76 negative cloud-to-ground flashes in Florida, we ha ve examined the relation between (1) the electric field waveforms char acteristic of return strokes but separated by the relatively short tim e interval of typically some tens to some hundreds of microseconds (th e extreme values were 15 mus and 3.3 ms) and (2) the number of TV-obse rved channel terminations on ground. Double field waveforms (15 total) were observed in about 20 % of all flashes analyzed. Nine of the 15 d ouble field waveforms were associated with lightning channels having d ouble terminations on ground. The remaining six double field waveforms were associated with channels showing single ground attachments. The latter observation suggests that double field waveforms can be due to two return strokes, each initiated by its own leader process, occurrin g in the same channel within a millisecond or less of each other. Such short interstroke intervals imply that the minimum time for the light ning channel to decay to the point that a new leader-return stroke seq uence can occur is significantly shorter than previously thought.