Location, structure, and motion of Jupiter's dusk magnetospheric boundary from ∼1625 to 2550 RJ

Abstract

We report on plasma observations along Jupiter's dusk magnetospheric flank from ∼1625 to 2550 RJ using measurements from the Solar Wind Around Pluto instrument onboard New Horizons (NH). NH observed 16 magnetopause crossings between 1654 and 2429 RJ that were identified by transitions between magnetotail/boundary layer and magnetosheath plasma. These transitions were either sharp, with the magnetopause clearly separating two distinct plasma regimes, or comparatively gradual, where it was difficult to distinguish between different plasma populations. The magnetosheath distributions had high counts, were relatively wide in energy/charge (E/Q), and steadily decreased in speed. Flow speeds in the sheath were always higher (lower) when NH entered (exited) this region. A boundary layer was observed inside of the magnetopause at several crossings. The boundary layer plasma was composed of light ions, and the counts and mean E/Q of these distributions were generally lower than magnetosheath values indicating a lower density and speed. Some of the NH magnetopause crossing locations fell within tail cross‐section estimates from model results/observations closer to the planet, though more than half were outside of the largest tail radius estimate. Estimates of angular displacement of the tail boundary compared favorably with a statistical study of near‐Jupiter solar wind flow cone angle distributions. We propose that the outward crossings resulted from dawnward deflection and contraction of the tail from forward shocks and compression regions in the near‐Jupiter solar wind, and the inward crossings resulted from duskward deflection and tail expansion from the passage of reverse shocks and rarefaction regions.