Interaction of substorm injections with the subauroral geospace: 1. Multispacecraft observations of SAID

Subauroral ion drifts (SAID) are the prominent feature of the active subauroral geospace, just earthward of the electron plasma sheet (PS) boundary in the premidnight sector. We explore magnetically conjugate satellite observations of substorm SAID near the magnetic equator and in the topside ionosphere confirming and expanding on our previous results. The SAID channels reside between the hot electron (PS/auroral) boundary at the plasmapause and the drop in the hot ion flux inside the plasmasphere. The overall features are inconsistent with the paradigm of voltage and current generators. Rather, they are explained in terms of a short circuiting of substorm‒injected hot plasma jets over the plasmapause and formation of a turbulent plasmaspheric boundary layer. The short circuiting occurs when the cold plasma density exceeds a critical value of 5–10 cm −3 . As the polarization field at the front of the hot plasma jet is shorted out, the hot electrons are arrested, while the hot ions yet move inward. This provides a natural explanation of the long‒known dispersionless auroral precipitation boundary. Enhanced plasma turbulence within the SAID channel provides anomalous circuit resistivity and magnetic diffusion, as with the well‒documented plasmoid‒magnetic barrier problem.