Storm-time precipitation of resonant electrons at the lower edge of the inner radiation belt

Abstract

Pitch angle scattering and diffusion of energetic electrons at the lower edge of the inner radiation belt ( L = 1.2) in disturbed magnetic conditions are studied in terms of cyclotron resonance involving naturally occurring ELF/VLF waves and signals radiated from ground-based VLF transmitters. Our results show that the diffusion coefficients are very sensitive to wave magnetic fields. The average lifetimes of energetic electrons at resonant frequencies of 550 Hz and 3.2 kHz ( E R > 1 MeV) are found to be about 2 h and 4 days, respectively, which indicate significant precipitation caused by such waves, whereas the same at resonant frequencies of 9.6 and 16 kHz are found to be about 5 and 28 years indicating that the corresponding resonant electrons are stably trapped. However, the lifetimes of such electrons reduce to hours also if the wave magnetic fields are increased. This may explain L-dependent peaks occurring at higher L values between 1.4 and 1.8. Further, as the calculated energy flux agrees well with the observed energy flux in the low-latitude zone of electron precipitation the results confirm wave-particle interaction involving cyclotron resonance as a source of these electrons.