Low Frequency Radio Emission from Extensive Air Showers


RADIO pulses associated with extensive air showers have been observed over a frequency range of 2 MHz (refs 1 and 2) to 550 MHz (ref 3). Up to now measurements over the range of 20 MHz to 100 MHz have proved to be those most easily made4. At the highest frequencies a decrease in the lateral extent of the radiation, a decrease in its amplitude and increasing receiver noise have limited observations. At the lowest frequencies the overriding experimental problem is background noise. Only the use of highly directional antennas2 or the reduction in daytime noise due to ionospheric D-layer absorption1 have enabled measurements to be made down to 2 MHz. But the lowest frequencies hold particular interest since the large amplitudes reported seem to be in gross disagreement with theory5. Also, long wavelength radiation might prove to have a large lateral spread which could be exploited in the form of a large air shower detecting array.

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GREGORY, A., CLAY, R. & PRESCOTT, J. Low Frequency Radio Emission from Extensive Air Showers. Nature 245, 86–87 (1973). https://doi.org/10.1038/245086a0

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