Principles of Magnetospheric Ion Composition

摘要

Ion composition provides an important diagnostic tool for identifying and quantifying source, loss, energization, and transport processes applicable to magnetospheric charged particles. However, the situation is not as simple as had been envisioned a decade ago. Ring-current and radiation-belt ions are believed to come from either the sun or the earth's ionosphere or both. Entry is not direct in either case. Solar-wind velocity and ion composition vary considerably with time. Ion-velocity distributions are partially thermalized in the magnetosheath after crossing the bow shock. Entry of solar-wind ions into the magnetosphere is modulated in part by reconnection efficiency, i.e., by the ratio of cross-tail electric field to asymptotic interplanetary electric field. Non-adiabatic motion in the plasma sheet may enable the crosstail electric field to heat the various ion species by different amounts. Entry of ionospheric ions into the plasma sheet seems to occur primarily through afternoon- and evening-sector auroral arcs, rather than through the polar wind as has previously been postulated. Energization occurs through interaction with the auroral potential structure (which varies with magnetic activity) and through plasma-sheet processes cited above.