Simulating the role of electron and ion precipitation in influencing the ionospheric conductance

Ionospheric conductance, or height-integrated conductivity, plays a crucial role in the highly coupled magnetosphere-ionosphere system. While the solar radiation that provides the energy source of ionizing the upper atmosphere on the dayside, particle precipitation is a primary source in the auroral zone. It is commonly accepted that, compared to ions, the electron precipitation produces the dominant energy deposition down to the upper atmosphere. However, the relative contribution of ion precipitation and how it would impact the ionospheric electrodynamics is not well understood. In this study, we determine the ion precipitation within loss cones caused by two different loss mechanisms in the ring current dynamics: the electromagnetic ion cyclotron (EMIC) waves and field line curvature (FLC) scattering. These two processes are solved in a kinetic ring current model as a diffusion process aided with associated pitch angle diffusion coefficients. Results indicate that the FLC scattering of ions prefers to occur on the nightside where magnetic field lines are stretched and the ion precipitation is mostly effective at L>4-5. In contrast, EMIC wave diffusion produces substantial ion precipitation across wide MLT and L regions, particularly in the dusk-to-night sector. The latter shows much better agreement with the POES data of tens of keV proton precipitation. The incident proton precipitation down to the ionosphere results in largely enhanced ionization and electron density in the E region, in good agreement with Millstone incoherent scattering radar observations. Estimation of ionospheric conductance suggests that the ion precipitation associated with FLC scattering hardly changes the global distribution or intensity of conductance from electrons, but the EMIC wave-induced ion precipitation significantly elevates the conductance in the dusk sector, exceeding the contribution from electrons by a factor of up to 10. Such a large augmentation of conductance subsequently changes the electric potential distribution and leads to a smaller electric field in the dusk-nightside sector, which in turn changes the ring current dynamics, subauroral flows, electron precipitation, and low-altitude conductivity, all as feedback effects.