Jupiter's ultraviolet auroral bridge: the influence of the solar wind on polar auroral morphology

Jupiters ultraviolet aurora frequently shows a number of arcs between the
dusk-side polar region and the main emission, which are denoted as bridges.
This work presents a largely automated detection and statistical analysis of
bridges over 248 Hubble-Space-Telescope observations, alongside a
multi-instrument study of crossings of magnetic field lines connected to
bridges by the Juno spacecraft during its first 30 perijoves. Bridges are
observed to arise on timescales of around 2 hours, can persist over a full
Jupiter rotation, and are conjugate between hemispheres. The appearance of
bridges is associated with compression of the magnetosphere, likely by the
solar wind. Low-altitude bridge crossings are associated with upward-dominated,
broadband electron distributions, consistent with Zone-II aurorae, as well as
with plasma-wave emission observed by Juno-Waves, in agreement with existing
theoretical models for the generation of polar-region aurorae. Main-emission
crossings where no bridges are visible also show characteristics associated
with bridges (more upward electron flux, plasma-wave emission), which is not
the case for main-emission crossings with visible bridges, as though bridges
remain present but spatially indistinguishable from the main emission in the
former case. In all, compression of the magnetosphere may work to spatially
separate the Zone-I and Zone-II regions of the main emission, in the form of
Zone-II bridges.