Understanding Spacecraft Trajectories through Detached Magnetotail
Interchange Heads
Abstract
The kinetic ballooning/interchange instability (BICI) was recently found
to produce azimutally narrow interchange heads extending into the dipole
region from a reversed radial gradient of B$_Z$ in the near-Earth
magnetotail. In their nonlinear evolution individual heads were
predicted to detach from the reversed B$_Z$ 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 k$_y$ structure of the BICI modes. Simultaneous
conjugate observations of DFs by THEMIS probes at 11 Earth’s radii
(R$_E$) 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]. 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 THEMIS 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.