Abstract :
[en] The ultraviolet aurorae of Jupiter, the brightest in the Solar System, are known to be of variable morphology. It is not entirely understood how this morphology varies with conditions present in Jupiter’s extensive magnetosphere, such as its state of compression. This work presents the first use of automatic detection techniques to analyse the morphology of Jupiter’s UV main auroral emission and link it with the state of the magnetosphere. A new reference oval for the average shape of the main emission is produced for the northern and southern hemisphere, based on images taken by Juno-UVS during its first 54 perijoves. A strong correlation is observed between the expansion/contraction of the main emission compared to these reference ovals in the northern and southern hemispheres, as well as between the main-emission expansion/contraction in the day and night hemispheres of the aurora, which indicates that the processes that work to vary the size of the main emission do so in a global way within the magnetosphere. The equatorward expansion also shows excellent correlation between with the equatorward latitudinal shift of the discrete aurora emission linked to Ganymede and the strength of the current in the magnetospheric current sheet, indicating that it is largely the stretching of the magnetic field of Jupiter that gives rise to the variable size of the main emission. Finally, compression of the magnetosphere is linked to a global main-emission contraction, one that occurs concurrently in both the north, south, day-side, and night-side hemispheres of the aurora, albeit to different extents. In all, these results indicate that the expansion or contraction of the UV main emission can be linked to a number of changes in the state of Jupiter’s magnetosphere and magnetic field.
