Centrifugal Equator in Jupiter’s Plasma Sheet

Abstract

In Jupiter’s magnetosphere, the structure of the plasma sheet depends on the magnetic field geometry and the centrifugal forces on the plasma. We present a simple formulation for the centrifugal equator, the farthest point along a magnetic flux tube from the planetary spin axis, for Jupiter’s torus to plasma sheet region (5–30 jovian radii). The formulation is based on a dipole magnetic field and azimuthally symmetric current sheet, both tilted by 9.5° toward System III west longitude of 201°. We find a good fit to such a model with a hyperbolic tangent function varying sinusoidally with longitude. The latitudinal angle of the derived centrifugal equator relative to the jovigraphic equator changes from the dipolar value (2/3 of the dipole tilt) around 5 jovian radii to close to the full dipole tilt at 25 jovian radii.

Survey of Juno Observations in Jupiter's Plasma Disk: Density

“…The ∼10° tilt of the magnetic dipole causes the spacecraft to oscillate relative to the magnetic equator. We show that for most orbits Juno approaches or crosses the plasma disk, measuring local peaks in the density, controlled by the geometry of the centrifugal equator (as defined by Phipps and Bagenal, 2021). The density profiles through the plasma disk crossings show quite a variation in amplitude and vertical thickness as well as scatter about the equator, the variability increasing beyond ∼35 R J from Jupiter.…”

“…On the right side of the middle and bottom panels of Figures 2 and 3, there is a y ‐axis scale for vertical height of the spacecraft with respect to the Phipps and Bagenal (2021) centrifugal equator at the time of the JADE measurements. The density is expected to peak when the spacecraft crosses the equator so that vertical lines through locations of equator crossings should align with the density peaks.…”

“…Farther out, the effect of the current sheet (aligned with the magnetic equator) is to stretch the field lines and make the centrifugal equator align with the magnetic equator. In this study, we employ a hyperbolic tangent function developed by Phipps and Bagenal (2021) to attain a more accurate centrifugal equator inside 20 R J , smoothly transitioning from a plane with a tilt of 2/3 that of the magnetic dipole to one aligned with the magnetic equator. This function produces a vertical separation between the equators up to a maximum of ∼0.4 R J at 10 R J from Jupiter and aligns the centrifugal equator exactly with the magnetic equator outside 20 R J .…”

“… Each plasma disk crossing in Set 2 (167 total) in which the density could be fit with a Gaussian and the radial component of the magnetic field switched sign within 2 R J of the density peak. The maroon circles indicate Juno 's distance to the centrifugal equator (Phipps & Bagenal, 2021) at the time Br flips, and the green squares indicate the centrifugal distance at the time when Jovian Auroral Distributions Experiment (JADE) measures the peak density. …”

A Comprehensive Set of Juno In Situ and Remote Sensing Observations of the Ganymede Auroral Footprint

“…The Ganymede SIII longitude was 277° at the time of the crossing. This corresponds to a centrifugal latitude of 2°, that is, north of the centrifugal equator, according to the newly derived formulation of the centrifugal equator from Phipps and Bagenal (2021). HST previously observed the multiple spot structure of Ganymede and Europa, consistently with the idea that the physics producing the auroral footprints is common to the Galilean satellites.…”