NARROW SPECTRAL PEAKS IN ELECTRONS PRECIPITATING FROM THE SLOT REGION

Narrow L-dependent peaks commonly occur in the energy spectra of electrons precipitating from the inner radiation belt at L approximately equals 1. 5-1. 85, and the cause of the peaks has been attributed to cyclotron resonance interactions with waves generated by VLF transmitters. In the slot region, L-dependent peaks have also been reported at L approximately equals 2-3. 5, but these have been predominately wide and consistent with their origin being cyclotron resonance ineractions involving naturally occurring hiss. Here the infrequent occurrence of narrow peaks in electrons precipitating at L greater than equivalent to 2 is investigated. From coordinated wave and plasma density measurements it is found that if the narrow peaks are formed by first-order cyclotron resonant interactions occurring close to the magnetic equator between narrow band waves and the trapped electron population, then the equatorial plasma density gradients ae unusually steep. This finding is consistent with the evidence previously obtained by other techniques for structured plasma density profiles in that L shell region of space.