Bremsstrählung as a Possible Source of UHF Emissions from Lightning

Abstract

FEW ultra high frequency (UHF) studies from lightning discharges have been made. Takagi and Takeuti¹ reported measurements at 500 MHz; these were later extended by Brook and Kitagawa² who, with the help of a ‘Polard type R’ microwave receiver, scanned the frequency range of 400 MHz to 1 GHz. They showed that most high frequency radiation was associated with the stepped and dart leaders and with the k-changes. By contrast, the return stroke radiated poorly. Kosarev et al.^3,4 have reported measurements in the range 100 MHz to 1.3 GHz which indicated that at a distance of 1 km from the foot of the channel, the power received was independent of frequency and was in the order of 10⁻¹⁵ W/m²/Hz. Kosarev et al.⁴ suspected that the electron synchrotron process might be responsible for the observed high frequency emissions. Considering the highest channel temperatures so far measured (of the order of 10⁴ K), it does not seem possible to associate relativistic velocities to the electrons present in the channel, and the possibility of synchrotron radiation from lightning seems remote.