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

Abstract

[1] We report on plasma observations along Jupiter's dusk magnetospheric flank from ∼1625 to 2550 R J using measurements from the Solar Wind Around Pluto instrument onboard New Horizons (NH). NH observed 16 magnetopause crossings between 1654 and 2429 R J 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.Citation: Ebert, R. W., D. J. McComas, F. Bagenal, and H. A. Elliott (2010), Location, structure, and motion of Jupiter's dusk magnetospheric boundary from ∼1625 to 2550 R J ,

Jupiter's deep magnetotail boundary layer

“…The flow direction of the plasma in this region implied that flapping of the magnetotail occurred in both the meridional and equatorial planes deflecting the magnetopause by roughly 5°. This observation supported the interpretation of Ebert et al (2010a).…”

“…The ratio of secondary to primary counts can be used to determine whether the measured particles are light or heavy ions Ebert et al, 2010b). Ebert et al (2010a) showed that the boundary layer plasma observed by SWAP is composed primarily of light ions. They did so by calculating the secondary to primary counts ratio in that region.…”

“…In this study, we extend this technique to derive the ion fluid properties of the deep jovian boundary layer. The time periods that NH spent in the boundary layer ( $ 65 h in total) around the 16 MP crossings were identified by Ebert et al (2010a) (for more information see their Figure 4). …”

“…These crossings were identified as transitions between regions of significantly different plasma flux. Ebert et al (2010a) studied the 16 magnetopause crossings and compared the observed magnetopause locations with those predicted by semiempirical models. They suggested that these multiple crossings resulted from the deflection and contraction/expansion of the magnetotail during the passage of co-rotating interaction regions (CIRs) and high-speed streams in the near Jupiter solar wind.…”

“…After the Jupiter flyby, NH crossed the distant jovian magnetopause $ 16 times Ebert et al, 2010a). The first crossing of the distant magnetopause occurred on DOY 132, 2007 with NH entering Jupiter's magnetosheath at $ 1654R j along the dusk flank.…”