The propagation speed of a positive lightning return stroke
Abstract
The first direct determination of the propagation speed of a lightning return stroke lowering positive charge to ground has been made. This stroke was the third of eight otherwise negative strokes in a triggered lightning flash initiated at the Kennedy Space Center, Florida. Two independent optical systems, one photographic and the other photoelectric, yielded common recordings for the third and fourth strokes; the respective two-dimensional return stroke propagation speeds were 1.0 vs. 0.93 ×108 m/s for the positive (third) stroke and 1.0 vs. 1.0 ×108 m/s for the fourth stroke. Using fast electric-field data, we estimated the positive stroke peak current to be 21 kA. Photoelectric data only yielded propagation speeds of 1.4, 1.6, 1.2, 1.3, 1.0 and 0.90 × 108 m/s for the first, second and fifth through eighth return strokes, respectively. All propagation speeds were evaluated over 850 m of channel near ground and have an error estimate of 10-15%. For this positive stroke, we found a return stroke propagation speed typical of negative strokes. Whether positive return strokes, in general, travel at typical negative return stroke speeds must await future measurements.
- Publication:
-
Geophysical Research Letters
- Pub Date:
- November 1987
- DOI:
- 10.1029/GL014i011p01150
- Bibcode:
- 1987GeoRL..14.1150I
- Keywords:
-
- Meteorology and Atmospheric Dynamics: Atmospheric electricity;
- Meteorology and Atmospheric Dynamics: Lightning