An ELF noise band observed by the Alouette II satellite has been studied. A digital power spectrum program was set up in order to investigate in detail the noise band spectra. Primary results from this analysis are that: a) for altitudes 500-3000 Km. and all geomagnetic latitudes, sharp lower cutoffs of the noise band occur within ~30Hz of the calculated gyrofrequency, b) upper cutoffs to the noise band occur frequently near harmonics of the gyrofrequency, and c) the noise appears to be Doppler shifted when the angle between the velocity vector of the satellite and the geomagnetic field is near 90°. The occurrence pattern of the noise band has been investigated using available Rayspan analyzed data for epoch 1966. This analysis indicated a pronounced daytime maximum of occurrence. It is shown that almost all aspects of the noise band may be interpreted in terms of the hypothesis of ambient electrostatic proton cyclotron harmonic waves in the ionosphere, and the concomitant accessibility conditions in the spatially varying geomagnetic field. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate