Variation of Jupiter’s Aurora Observed by Hisaki/EXCEED: 4.
Quasi-Periodic Variation
Abstract
Quasi-periodic variations of a few to several days are observed in the
energetic plasma and magnetic dipolarization in Jupiter’s magnetosphere.
Variation in the plasma mass flux related to Io’s volcanic activity is
proposed as a candidate of the variety of the period. Using a long-term
monitoring of Jupiter by the Earth-orbiting space telescope Hisaki, we
analyzed the quasi-periodic variation seen in the auroral power
integrated over the northern pole for 2014–2016, which included
monitoring Io’s volcanically active period in 2015 and the solar wind
near Jupiter during Juno’s approach in 2016. Quasi-periodic variation
with periods of 0.8–8 days was detected. The difference between the
periodicities during volcanically active and quiet periods is not
significant. Our dataset suggests that a difference of period between
this volcanically active and quiet conditions is below 1.25 days. This
is consistent with the expected difference estimated from a proposed
relationship based on a theoretical model applied to the plasma
variation of this volcanic event. The periodicity does not show a clear
correlation with the auroral power, central meridional longitude, or Io
phase angle. The periodic variation is continuously observed in addition
to the auroral modulation due to solar wind variation. Furthermore,
Hisaki auroral data sometimes shows particularly intense auroral bursts
of emissions lasting <10h. We find that these bursts coincide
with peaks of the periodic variations. Moreover, the occurrence of these
bursts increases during the volcanically active period. This auroral
observation links parts of previous observations to give a global view
of Jupiter’s magnetospheric dynamics.