Crucial role of ring current H+in electromagnetic ion cyclotron wave dispersion relation: Results from global simulations

Abstract

[1] The effect of ring current (RC) H+ in the real part of electromagnetic ion cyclotron (EMIC) wave dispersion relation is studied on the global magnetospheric scale. The simulations of the 2–3 May 1998 storm are done using our model of the He+-mode EMIC waves self-consistently interacting with RC ions. The wave model describes EMIC waves bouncing between the off-equatorial magnetic latitudes, which correspond to the bi-ion hybrid frequencies in conjugate hemispheres, along with tunneling across the reflection zones and subsequent strong absorption in the ionosphere. This model explicitly includes the EMIC wave growth/damping, propagation, refraction, reflection, and tunneling in a multi-ion magnetospheric plasma. An analysis of the wave observations is presented and strongly supports our wave model. The main findings from our simulations can be summarized as follows: First, RC H+ only contributes a few percent to the total plasma density near the inner edge of the plasmasphere boundary layer, but it can dominate outside the plasmapause. About 90% of the RC H+ density in the dawn MLT sector is formed by the suprathermal ions (≲2 keV), while a major contribution in dusk comes from the 10–100 keV ions, allowing not more than 10-20% for the suprathermal ions. Second, RC H+ in the real part of the wave dispersion relation increases local growth rate leading to a dramatic change in the wave global patterns. The “new” EMIC waves are generated not only on the plasmapause, as expected from previous global simulations, but also inside and outside the plasmapause consistent with the observations.