HR: 08:44h
AN: AE41A-04    [Abstracts]
TI: The dE/dt and E Waveforms Radiated by Leader Steps Just Before the First Return Stroke in Cloud-to-Ocean Lightning
AU: * Krider, E P
EM: krider@atmo.arizona.edu
AF: Institute of Atmospheric Physics, The University of Arizona PO Box 210081, Tucson, AZ 85721 United States
AU: Baffou, G
EM: Guillaume.Baffou@crans.org
AF: Department of Physics, Ecole Normale Superieure de Cachan, Cachan, 94230 France
AU: Murray, N D
EM: murray@atmo.arizona.edu
AF: Institute of Atmospheric Physics, The University of Arizona PO Box 210081, Tucson, AZ 85721 United States
AU: Willett, J C
EM: willettj@compuserve.com
AF: Independent Scholar, PO Box 41, Garrett Park, MD 20896 United States
AB: We have analyzed the shapes and other characteristics of the electric field, E, and dE/dt waveforms that were radiated by leader steps just before the first return stroke in cloud-to-ocean lightning. dE/dt waveforms were recorded using an 8-bit digitizer sampling at 100 MHz, and an integrated waveform, Eint, was computed by numerically integrating dE/dt and comparing the result with an analog E waveform digitized at 10 MHz. All signals were recorded under conditions where the lightning locations were known and there was minimal distortion in the fields due to the effects of ground-wave propagation. The dE/dt waveforms radiated by leader steps tend to fall into three categories: (1) "simple" - an isolated negative peak that is immediately followed by a positive overshoot (where negative polarity follows the normal physics convention), (2) "double" - two simple waveforms that occur at almost the same time, and (3) "burst" - a complex cluster of pulses with a total duration of about one microsecond. In this paper, we will give examples of each of these waveform types, and we will summarize their characteristics on a submicrosecond time-scale. For example, in an interval starting 9 $\mu$s before to 4 $\mu$s before the largest, negative (dominant) peak in dE/dt peak in the return stroke, 131 first strokes produced a total of 296 impulses with a peak amplitude greater than 10% of the dominant peak, and the average amplitude of these pulses was 0.21 of the dominant peak. The last leader step in a 12 $\mu$s interval before the dominant peak was a simple waveform in 51 first strokes, and in these cases, the average time-interval between the peak dE/dt of the step and the dominant peak of the stroke was 5.8 $\pm$ 1.7 $\mu$s, a value that is in good agreement with prior measurements. The median full-width-at-half-maximum (FWHM) of 274 simple Eint signatures was 141 ns, and the associated mean and standard deviation were 187 $\pm$ 131 ns.
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting