Ballooning/Interchange Heads in the Earth’s Magnetotail and Their Ionospheric Manifestations

Abstract:

We review recent progress by the authors on the appearance of the ballooning/interchange instability in the Earth’s magnetotail. Based on the multi-point in situ THEMIS observations we show that the instability signatures are observed at the tailwardside of the local Bz minimum region between the Earth’s dipolar field lines and the stretched field liens of the magnetotail, and that the ballooning/interchange heads may propagate also dawnward. We find that the electromagnetic ion-cyclotron waves presumably driven by the differential electron-ion drift ripple the heads. We further use conjugate remote ionospheric observations to show auroral beads and rays presence near the heads’ footprints during quieter periods of the instability development. Some of the heads appeared to experience a process of detachment from the reversed Bz gradient, growing in pronounced dipolarization fronts, which manifest themselves as suddenly lighted up former beads or rays. Finally, we compare THEMIS crossings with virtual spacecraft observations from instability simulations to highlight in situ signatures of the heads at different stages of development.