Understanding Spacecraft Trajectories Through Detached Magnetotail Interchange Heads

The kinetic ballooning/interchange instability (BICI) was recently found to produce azimuthally narrow interchange heads extending into the dipole region from a reversed radial gradient of BZ in the near‐Earth magnetotail. In their nonlinear evolution individual heads were predicted to detach from the reversed BZ gradient and grow into transient earthward moving northward magnetic field intensifications (dipolarization fronts; DFs). The distinguished signatures of such fronts would be their oblique propagation and cross‐tail localization due to the finite ky structure of the BICI modes. Simultaneous conjugate observations of DFs by the Time History of Events and Macroscale Interactions during Substorms probes at 11 Earth's radii (RE) downtail and of sudden brightening and growth of individual auroral beads by the all‐sky imagers on the ground have been suggested to be ionospheric signature of detached magnetotail interchange heads (Panov et al., 2019, https://doi.org/10.1029/2019GL083070). Here we compare such DFs with a simulated interchange head during later(detachment)‐stage BICI head development. The comparison reveals similarly structured leading edges and trailing tails in both the observed DFs and the simulated BICI head. We further identify Time History of Events and Macroscale Interactions during Substorms trajectories through the DFs and find that the trajectories were due to oblique (earthward and dawnward) DF propagation. This analysis further supports the idea that BICI indeed releases obliquely propagating azimuthally localized dipolarization fronts in the Earth's magnetotail. Plain Language Summary The terrestrial magnetic field lines on the antisunwardside of the Earth forming an elongated structure (the magnetotail) are periodically disrupted by magnetic reconnection. Which processes and at which distance from Earth onset magnetotail reconnection? An instability was recently found to produce azimuthally narrow heads that intrude into the dipole region from the near‐Earth magnetotail. At their later stages of development individual heads were predicted to grow into transient earthward moving northward magnetic field intensifications (dipolarization fronts), which under the right conditions may lead to a full‐scale magnetotail disruption. By combining sophisticated high‐performance computing plasma simulations with multipoint in situ observations by the National Aeronautics and Space Administration's Time History of Events and Macroscale Int