Abstract. An attempt is made to con®rm the generation mechanism of plasmaspheric ELF hiss emissions observed aboard GEOS-1 satellite in the equatorial region both at small and large wave normal angles by calculating their magnetic ®eld intensities in terms of incoherent Cerenkov radiation mechanism and cyclotron resonance instability mechanism, using appropriate and suitable plasma parameters. The ELF intensities calculated by Cerenkov radiation mechanism, being 4 to 5 orders of magnitude lower than the observed intensities, rule out the possibility of their generation by this mechanism. On the other hand, the intensities calculated under electron cyclotron resonance instability mechanism are found to be large enough to account for both the observed intensity and propagation losses and hence to con®rm that plasmaspheric ELF hiss emissions observed aboard GEOS-1 satellite both at small and large wave normal angles were originally generated in the equatorial region by this mechanism just near the inner edge of the plasmapause. The di erence in the observed intensities of two types of the emissions has been attributed to the propagation e ect rather than the generation e fect.

An attempt is made to con®rm the generation mechanism of plasmaspheric ELF hiss emissions observed aboard GEOS-1 satellite in the equatorial region both at small and large wave normal angles by calculating their magnetic ®eld intensities in terms of incoherent Cerenkov radiation mechanism and cyclotron resonance instability mechanism, using appropriate and suitable plasma parameters. The ELF intensities calculated by Cerenkov radiation mechanism, being 4 to 5 orders of magnitude lower than the observed intensities, rule out the possibility of their generation by this mechanism. On the other hand, the intensities calculated under electron cyclotron resonance instability mechanism are found to be large enough to account for both the observed intensity and propagation losses and hence to con®rm that plasmaspheric ELF hiss emissions observed aboard GEOS-1 satellite both at small and large wave normal angles were originally generated in the equatorial region by this mechanism just near the inner edge of the plasmapause. The dierence in the observed intensities of two types of the emissions has been attributed to the propagation eect rather than the generation efect.