Hectometric Line Spectra Detected by the Arase (ERG) Satellite

Abstract

AbstractA new type of terrestrial line spectra has been detected by the Arase satellite. These spectra are called hectometric line spectra. They consist primarily of constant frequency narrowband components at frequencies between 525 and 1,700 kHz, which originate and are sometimes amplified from AM broadcasting waves and other generated emissions. These line spectra can be amplified or generated by the odd‐harmonic electrostatic cyclotron instability while in the Z mode. Hectometric line spectra need to be mode‐converted to the L‐O mode to be received at higher altitudes because the Z mode can only exist when its frequency is lower than the local upper hybrid resonance frequency. Wave penetration into the ionosphere and mode conversion are enabled by low‐density regions and steep density gradients in ionospheric irregularities. Note that the broadcasting waves passed through the ionosphere with frequencies lower than the maximum plasma frequency along their paths.