Lightning electromagnetic radiation field spectra in the interval from 0. 2 to 20 MHz
- Air Force Geophysics Lab., Hanscom AFB, MA (USA)
- Univ. of Alabama, Huntsville (USA)
- Inst. de Physique et Chimie des Materiaux (France)
- Univ. of Arizona, Tucson (USA)
Average energy spectral densities are presented for the fast transitions in most of the components that produce large radiation field impulses from cloud-to-ground lightning; first and subsequent return strokes; stepped, dart-stepped, and 'chaotic' leaders; and 'characteristic' cloud pulses. A disagreement in the previous literature about the spectral energy radiated by return strokes at high frequencies is noted and explained. The authors show that the spectral amplitudes are not seriously distorted by propagation over less than 35 km of seawater, although as much as 45 km of such propagation does appear to produce significant attenuation above about 10 MHz. First and subsequent return strokes produce identical spectra between 0.2 and 20 MHz. The spectra of stepped and dart-stepped leader steps are nearly identical and are very similar to that of characteristic pulses. The spectra of leader steps also match return stroke spectra above 2-3 MHz after the former are increased by about 7 dB. The shapes of individual spectra do not depend on their amplitude, so the shapes of the average spectra are probably not distorted by the trigger thresholds used in the data acquisition. Return strokes are the strongest sources of radiation from cloud-to-ground lightning in the 0.2- to 20-MHz frequency range, although certain intracloud processes are stronger radiators above 8 MHz.
- OSTI ID:
- 5270594
- Journal Information:
- Journal of Geophysical Research; (United States), Vol. 95:D12; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
LIGHTNING
ENERGY SPECTRA
AMPLITUDES
CLOUDS
ELECTRIC GROUNDS
ELECTROMAGNETIC RADIATION
FREQUENCY DEPENDENCE
MHZ RANGE
SEAWATER
SPECTRAL DENSITY
ELECTRIC DISCHARGES
FREQUENCY RANGE
FUNCTIONS
HYDROGEN COMPOUNDS
OXYGEN COMPOUNDS
RADIATIONS
SPECTRA
SPECTRAL FUNCTIONS
WATER
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