Variability of Jupiter's main auroral emission and satellite footprints
observed with HST during the Galileo era
Abstract
Hubble Space Telescope images of Jupiter’s UV aurora show that the main
emission occasionally contracts or expands, shifting toward or away from
the magnetic pole by several degrees in response to changes in the solar
wind dynamic pressure and Io’s volcanic activity. When the auroral
footprints of the Galilean satellites move with the main emission this
indicates a change in the stretched field line configuration that shifts
the ionospheric mapping of a given radial distance at the equator.
However, in some cases, the main emission shifts independently from the
satellite footprints, indicating that the variability stems from some
other part of the corotation enforcement current system that produces
Jupiter’s main auroral emissions. Here we analyze HST images from the
Galileo era (1996-2003) and compare latitudinal shifts of the Ganymede
footprint and the main auroral emission. We focus on images with
overlapping Galileo measurements because concurrent measurements are
available of the current sheet strength, which indicates the amount of
field line stretching and can influence both the main emission and
satellite footprints. We show that the Ganymede footprint and main
auroral emission typically, but do not always, move together.
Additionally, we find that the auroral shifts are only weakly linked to
changes in the current sheet strength measured by Galileo. We discuss
implications of the observed auroral shifts in terms of the
magnetospheric mapping. Finally, we establish how the statistical
reference main emission contours vary with CML and show that the
dependence results from magnetospheric local time asymmetries.