The modulation of plasma and waves by background electron density irregularities in the inner magnetosphere

The background electron density decreases away from the Earth with a sharp boundary in the density profile which is defined as the plasmapause. Density irregularities are frequently observed near the plasmapause and these density structures are believed to play an important role in the generation and propagation of plasma waves. In this letter, we report an event with clear modulation of particle fluxes and EMIC, MS as well as the electrostatic waves by the background plasma density structure at a plasmapause crossing near the post-dusk magnetic equator based on Van Allen Probe B observation on 9^th October, 2013. It is shown that the energies of peak fluxes for proton and helium supra-thermal populations are well correlated with the background electron density variations. In addition, EMIC and MS waves are simultaneously observed in high plasma density regions but vanish in low density regions. Furthermore, the broadband electrostatic waves occur in the density depletion regions. Our simulations indicate that the variations of electromagnetic waves are caused by the wave generation conditions in association with the density irregularities.