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Lightning Return-Stroke Current Waveforms Aloft, From Measured Field Change, Current, and Channel GeometryDirect current measurements are available near the attachment point from both natural cloud-to-ground lightning and rocket-triggered lightning, but little is known about the rise time and peak amplitude of return-stroke currents aloft. We present, as functions of height, current amplitudes, rise times, and effective propagation velocities that have been estimated with a novel remote-sensing technique from data on 24 subsequent return strokes in six different lightning flashes that were triggering at the NASA Kennedy Space Center, FL, during 1987. The unique feature of this data set is the stereo pairs of still photographs, from which three-dimensional channel geometries were determined previously. This has permitted us to calculate the fine structure of the electric-field-change (E) waveforms produced by these strokes, using the current waveforms measured at the channel base together with physically reasonable assumptions about the current distributions aloft. The computed waveforms have been compared with observed E waveforms from the same strokes, and our assumptions have been adjusted to maximize agreement. In spite of the non-uniqueness of solutions derived by this technique, several conclusions seem inescapable: 1) The effective propagation speed of the current up the channel is usually significantly (but not unreasonably) faster than the two-dimensional velocity measured by a streak camera for 14 of these strokes. 2) Given the deduced propagation speed, the peak amplitude of the current waveform often must decrease dramatically with height to prevent the electric field from being over-predicted. 3) The rise time of the current wave front must always increase rapidly with height in order to keep the fine structure of the calculated field consistent with the observations.
Document ID
20030033856
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Willett, J. C.
(Willett (J. C.) Garrett Park, MD, United States)
LeVine, D. M.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
September 8, 2013
Publication Date
January 1, 2002
Subject Category
Meteorology And Climatology
Meeting Information
Meeting: AGU Meeting
Location: San Francisco, CA
Country: United States
Start Date: December 7, 2002
End Date: December 10, 2002
Sponsors: American Geophysical Union
Distribution Limits
Public
Copyright
Other

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