On the ion precipitation due to field line curvature (FLC) and EMIC wave scattering and their subsequent impact on the ionospheric electrodynamics

Abstract:

Both field line curvature (FLC) and electromagnetic ion cyclotron (EMIC) wave scattering are believed to be associated with energetic ion precipitation, which is another important energy source to the ionosphere, in addition to the electron precipitation. But the relative contributions of these two mechanisms on the ionospheric ion precipitation and subsequent effects are still unclear. In this study, by using a global kinetic ring current model that self-consistently treats the electric/magnetic fields with the ring current dynamics, we investigate their impact on the ionosphere from two aspects: the global distribution of ion precipitation and resulting ionospheric conductance. Our results show that the intensity and coverage of ion precipitation due to EMIC waves are larger than that due to the FLC scattering, while the latter mostly contributes to the ion precipitation at outer region (L>4-5). We then examine the subsequent effects on the ionospheric electrodynamics by estimating the conductance with empirical models using simulated ion precipitation energy flux, and compare to that caused by electron precipitation. It is found that when the EMIC associated proton precipitation is included, the conductance is significantly enhanced in the dusk-to-midnight sector and has a wide magnetic latitude (MLAT) range from around 52 ^。 to 62^。. The electric potential is hence altered considerably in the dusk sector, which further influences the particle dynamics in the magnetosphere. On the contrary, the proton precipitation caused by FLC scattering only occurs within a narrow MLAT range close to MLAT = 60^。 and the corresponding conductance is slightly enhanced at midnight. The convective electric potential is hardly influenced. Although the electron precipitation associated conductance is predominant throughout the globe, the proton precipitation can also play an important role to the ionospheric electrodynamics, especially when the EMIC wave scattering is included, as the precipitating proton energy flux can even exceed that of electrons in dusk sector, a region where many subauroral coupling processes take place.