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Abstract :
[en] The jovian main auroral emission (ME) is known to be of variable size and morphology, though it is
presently not fully understood in what way these properties depend on the state of the magnetosphere. A
study of the variability in morphology of the jovian UV ME is presented, based on images from Juno-UVS
from perijoves 1 through 54. Novel arc-detection techniques have been developed to automatically detect
the ME in these images. The northern and southern ME are observed to expand and contract together,
as are the day-side and night-side ME in both hemispheres, which indicates that the processes responsible
for the variable expansion/contraction of the ME affect the magnetosphere globally and have timescales
longer than 4 hours. The auroral footprint of Ganymede is observed to move poleward when the ME is
contracted, which is not the case for the footprint of Io, which indicates that the expansion of the ME is
predominantly caused by a stretching of magnetic field lines in the middle magnetosphere. This conclusion
is supported by the correlation between increased magnetodisc current constant and the expansion of the
ME. Finally, during periods of known compression of the magnetosphere, the ME is observed to be both
contracted and brighter than average on the day side, as viewed by HST. These findings are then placed
into the context of an Alfv ́enic generation of the ME.
