Publication Date:
2013-02-24
Description:
[1] Abstract Time correlated high-speed video and electromagnetic data for 15 cloud-to-ground and intracloud lightning flashes reveal bursts of light, bright enough to be seen through intervening cloud, during the initial breakdown (IB) stage and within the first 3 ms after flash initiation. Each sudden increase in luminosity is coincident with a CG-type (12 cases) or IC-type(3 cases) IB pulse in fast electric field change records. The E-change data for 217 flashes indicate that all CG and IC flashes have IB pulses. The luminosity bursts of 14 negative CG flashes occur 11-340 ms before the first return stroke, at altitudes of 4-8 km, and at 4-41 km range from the camera.In seven cases, linear segments visibly advance away from the first light burst for 55-200 µs, then the entire length dims, then the luminosity sequence repeats along the same path. These visible initial leaders or streamers lengthen intermittently to about 300-1500 m. Their estimated 2-D speeds are 4 to 18 x 10 5 m s -1 over the first few hundred microseconds and decrease by about 50% over the first 2 ms.In other cases, only a bright spot or a broad area of diffuse light, presumably scattered by intervening cloud, is visible. The bright area grows larger over 20-60 µs before the luminosity fadesin about 100 µs, then this sequence may repeat several times. In several flashes a 1-2 ms period of little or no luminosity and small E-change is observed following the IB stage prior to stepped leader development.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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