Ion-cyclotron noise excitation in the topside ionosphere according to observations at the Intercosmos-14 satellite

Abstract

A band-limited ELF emission having very distinct upper as well as lower cutoff frequencies, most probably determined by local parameters of the plasma, were discovered by the VLF experiment on board the Intercosmos-14 satellite (apogee height 1707 km, perigee 345 km; inclination 74°). This type of noise was observed in the day-time, at middle and low latitudes, at altitudes 600 km< h < 1400 km. The very clear case observed on March 5, 1976 is discussed in detail and arguments are listed that this ELF emission is locally generated ion-cyclotron noise. Calculations of the growth of the proton cyclotron resonance instability show that the growth may be positive if the loss cone angle of the energetic protons is sufficiently great. This condition is fulfilled at low altitudes near the mirror points. Depending on the width of the distribution function of energetic protons the growth of the Instability may be positive in the whole frequency band of the proton branch of ion-cyclotron waves or only in certain parts of that frequency band.