The amplitude spectra of lightning radiation fields in the interval from 1 to 20 MHz

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Abstract
Although the interactions of lightning with aircraft and many other structures are critically dependent on the amplitudes of the electromagnetic fields in the 1 to 20 MHz frequency interval, there are relatively few measurements of these spectra in the lightning literature. In this paper, we present amplitude spectra of the fast‐rising, initial portion of fields that are produced by return strokes, leader steps, and cloud pulses. These data have been derived from ground‐based measurements of dE/dt signatures that were recorded in the time‐domain on a triggered oscilloscope. The spectral amplitudes of first return strokes match previously published data at 1 MHz and decrease with increasing frequency as 1/ƒ between 1 and about 6 MHz and as 1/ƒ2 between 6 and 20 MHz. The spectral amplitudes of leader steps just before return strokes and the fast portion of cloud pulses that triggered the recording system tend to lie 5 to 10 dB below the amplitudes of first return strokes over the entire frequency interval.