OGO 3 observations of ELF noise in the magnetosphere: 2. The nature of the equatorial noise

Abstract

An examination of the noise present between 1 and 1000 Hz at the magnetic equator with the OGO 3 search coil magnetometer has revealed a previously unobserved class of signals existing only in the outer plasmasphere. These waves are propagating nearly perpendicular to the magnetic field, probably within less than 1° of perpendicular to it; they exist only between about twice the proton gyrofrequency and half the lower hybrid resonant frequency. The waves are confined to a region within about 2° of the equator and therefore have a large amplitude gradient along the magnetic field lines. They are resonant with harmonics of the electron bounce frequency and have sufficient amplitude (∼10 mγ rms) to cause the observed pitch-angle diffusion of electrons mirroring near the equator.