Wave-Particle Interactions at the Turbulent Plasmaspheric Boundary

Satellite observations in the near-equatorial magnetosphere across the plasmaspheric boundary (plasmapause) soon after the onsets of individual substorms are reviewed. During the passes, narrow channels of westward-drifting plasma due to 10-30 mV/m outward electric fields in the evening MLT sector have been observed. In magnetically conjugate ionosphere, these SAID (subauroral ion drifts) events have been detected by the DMSP satellites. The fast appearance of SAID is consistent with the fast propagation of substorm-injected plasma jets (plasmoids). The SAID channel is just interior to the inner boundary of the electron plasma sheet that appears as dispersionless cutoff of the substorm-injected electrons. The injected ions penetrate into the plasmasphere where the cold plasma upholds charge neutrality, thereby short-circuiting the injected plasmoid. Nonlinear wave-particle interactions provide fast magnetic diffusion at the leading front and define the circuit's anomalous resistivity. As a result, a turbulent boundary layer is formed over the plasmapause. As in laboratory and active space experiments, gradient-drift and current-driven instabilities shape the boundary layer. Anisotropic ion-driven processes dominate near the SAID inner boundary and next to the channel where hiss-like VLF emissions are enhanced. These emissions appear to constitute a distinctive subset of substorm/storm-related VLF activity excited by freshly injected energetic ions inward of the electron plasma sheet responsible for the alteration of the outer radiation belt boundary during (sub)storms.Plasmapause, plasma sheet inner boundary, and SAID from Cluster, Polar and DMSP.