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James A. Van Allen journal, October 1955-March 1958
Page 36
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Electromagnetic pulses from lightening discharges (impulsive atmospherics) are apparently propagated out through the ionosphere along magnetic lines of force and are so guided back into the opposite hemisphere. Some are then reflected and retrace their paths back to general vicinity of source. Are picked up as audio-frequency radio signals. Due to dispersion in the atmosphere, (there is a "Fourier spread of frequencies of the original pulse) the frequency starts high and diminishes with time. [graph/sketch/picture] graph of [~frequency versus time?] (f exponent -(1/2)) versus time comparing short whistler and long whistler for time from 1 to 3 seconds
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Electromagnetic pulses from lightening discharges (impulsive atmospherics) are apparently propagated out through the ionosphere along magnetic lines of force and are so guided back into the opposite hemisphere. Some are then reflected and retrace their paths back to general vicinity of source. Are picked up as audio-frequency radio signals. Due to dispersion in the atmosphere, (there is a "Fourier spread of frequencies of the original pulse) the frequency starts high and diminishes with time. [graph/sketch/picture] graph of [~frequency versus time?] (f exponent -(1/2)) versus time comparing short whistler and long whistler for time from 1 to 3 seconds
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