Interaction of substorm injections with the plasmasphere: A turbulent plasmaspheric boundary layer

Abstract:

In-situ measurements of plasma, fields, and waves around the plasmasphere's boundary in the evening sector during substorm injection events are presented. The data reveal that the cold plasma short-circuits substorm-injected hot plasma jets when the cold plasma density exceeds a critical value of 5-10 c.c. The substorm-injected hot electrons stop at the pre-substorm plasmapause, thereby providing a natural explanation of the long-known dispersionless auroral precipitation boundary. A turbulent plasmaspheric boundary layer forms initially near the pre-substorm plasmapause due to interactions between the injected and plasmaspheric populations. The main sources of the greatly-enhanced wave activity are the so-called modified two-stream instability driven by the hot electron diamagnetic drift in the entry layer, ion-ring instability driven by the highly-anisotropic hot ion distribution in the central part, and the diamagnetic drift of hot ions near the inner edge. Enhanced plasma turbulence leads to heating of the cold plasma and to acceleration of suprathermal electron tails, thereby enhancing the downward heat transport and concomitant heating of the ionospheric electrons observed by the DMSP satellites.