Mid‐altitude modeling of cusp ion injection under steady and varying conditions

A cusp ion injection model incorporating mutually consistent electric and magnetic fields is developed. We have simulated cusp ion energy‐latitude spectrograms for paths similar to certain orbits of DE‐1 and Viking. Both the large‐scale energy‐latitude dispersion and the embedded small‐scale energy‐pitch‐angle V signatures are clearly evident in these simulated spectrograms. Our results show that a much narrower V microsignature is obtained when the ion injection source is restricted to a small region. However, the cutoff of the plasma injection at the magnetosheath sonic line alone also yields relatively narrow V‧s, without restricting the injection region. This effect is most noticeable in winter conditions. By introducing a time‐dependent magnetosheath plasma density variation along the magnetopause to our cusp model, we are also able to reproduce a well observed meso‐scale ion injection pattern which can appear to be the overlap of multiple injections, even with assuming steady interconnection.