A theoretical explanation of intensity of low latitude ELF emissions and identification of their generation mechanism

Abstract

The intensities of low latitude ELF hiss emissions are calculated for known plasma parameters by considering incoherent Cerenkov emission mechanism and electron cyclotron resonance instability mechanism. The equatorial intensities calculated in incoherent Cerenkov emission mechanism at <i>L </i>= 1.30-5.50, being several orders of magnitude lower than the observed intensities, rule out the possibility of generation of low latitude ELF hiss emissions in this mechanism.Unlike this, the intensities calculated by electron cyclotron resonance instability mechanism at the equatorial locations above <i>L </i>= 4 are found to be consistent with the intensities observed in the low latitude ground stations. Therefore, it is opined that

these emissions originate in the electron cyclotron resonance instability mechanism above <i>L </i>= 4 in the equatorial plane. However, it has been shown that the ELF hiss band below 1 kHz propagates from the generation region in the vicinity of the plasma pause to low latitudes after several successive magnetospheric reflections there, confirming the suggestion of

Hayakawa <i>et al. </i>[J <i>Atmos & Terr Phys, </i>37 (1975) 517; <i>Planet & Space Sci</i>, 25 (1977) 35].