Evidence of electrostatic proton cyclotron harmonic waves from Alouette 2 satellite data

An ELF noise band observed by the Alouette 2 receiver has been analyzed using digital power spectrum techniques. Detailed spectra indicate that for altitudes 500–3000 km and all geomagnetic latitudes sharp lower frequency cutoffs of the noise band occur very near to the calculated proton gyrofrequency. Further spectral characteristics are pointed out. All aspects of the noise band are interpreted in terms of ambient electrostatic proton cyclotron harmonic waves. In particular, this hypothesis explains such features of the noise spectra as the upper and lower cutoffs of the noise band at harmonics of the gyrofrequency and the changing character of cutoffs due to changing accessibility conditions and Doppler shifting.