Ultraviolet auroral bridge of Jupiter: The effect of the solar wind on the morphology of the polar aurora

The ultraviolet aurora of Jupiter frequently shows a number of arcs between the dusk-side polar region and the main emission. These arcs are called bridges. We present a largely automated detection and statistical analysis of the bridges in over 248 Hubble-Space-Telescope observations. We also performed a multi-instrument study of the magnetic field line crossings that are connected to bridges by the Juno spacecraft during its first 30 perijoves. The bridges are observed to arise on timescales of ~2 hours, they can persist over a full Jupiter rotation, and they are conjugate between hemispheres. The appearance of the bridges is associated with the 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, and also with plasma-wave emission observed by Juno-Waves. This agrees with existing theoretical models for the generation of aurorae in the polar regions. Main-emission crossings in which no bridges are visible also show characteristics that are associated with bridges (a stronger upward electron flux and plasma wave emission), which is not the case for main-emission crossings with visible bridges, as though bridges remain present, but are spatially indistinguishable from the main emission in the former case. In all, the 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.