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.