A case study in support of closure of bow shock current through the
ionosphere utilizing multi-point observations and simulation
On the bow shock in front of Earth flows current due to the curl of
interplanetary magnetic field across the shock. It is uncertain whether
the bow shock current closes on the magnetopause, into the ionosphere
along magnetic field lines, or both. We present simultaneous
observations from MMS, AMPERE, and DMSP during a period of strong
$B_y$, weakly negative $B_z$, and small $B_x$. This IMF
orientation should lead to current flowing mostly south-north on the
shock. AMPERE shows current poleward of the Region 1 currents flowing
into the northern polar cap and out of the south, consistent with bow
shock current closing along open field lines; a DMSP flyover confirms
that this current is poleward of the convection reversal boundary.
Additionally, we investigate bow shock current closure for these
conditions using an MHD simulation. We conclude that the evidence points
to partial closure of bow shock current through the ionosphere.