The kinetic ballooning/interchange instability as a source of dipolarization fronts and auroral streamers

The possibility that the dipolarization fronts (DFs) observed in the plasma sheet could be produced by the ballooning/interchange instability is explored using three-dimensional electromagnetic particle-in-cell simulations. The localized interchange heads produced in the nonlinear stage of the instability exhibit the main near-equatorial properties of a DF: the cross-tail extent is on the order of 1 RE, the ramp-ups in Bz and the magnitude of Ey as well as the sharp density decrease all occur on the ion inertial scale, while there is a more gradual increase in the bulk flow. The field-aligned currents associated with the breakup of the head should produce a structuring of the corresponding auroral streamer in the ionosphere, a result that is confirmed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager data. The dissipation associated with the head occurs in electron-scale regions in the center of the plasma sheet. Away from the center, the head is strongly modulated by waves with frequency on the order of the ion gyrofrequency. The strength of the accompanying Ey oscillations is in the range of 30–50 mV/m, and the δE/δB ratio is 3–4 times the local Alfven speed. The waves appear to be produced by the electromagnetic current-driven ion cyclotron instability.