Plasma originating from the satellite Io forms a dense plasma region known as the Io plasma torus (IPT) in the Jovian inner magnetosphere. Slightly inside the Io-orbit is a distinct structure called the “ribbon,” where the plasma spreads along the magnetic field lines. The ribbon moved dawnward owing to the dawn-to-dusk electric field. Extreme ultraviolet (EUV) observations of the IPT showed that the electric field was enhanced under compressed conditions of the magnetosphere caused by solar wind. However, no reports have been published on the influence of solar wind on the radial position of the ribbon. Here, we show the correlation between the temporal variation in the ribbon’s position and solar wind. We analyzed the visible ([SII] 6716, 6731 Å) IPT images observed by the Tohoku 60-cm telescope (T60) and the EUV emissions observed by the Hisaki satellite. We found that the position of the ribbon shifted dawnward when the solar wind dynamic pressure was enhanced. The dawnward shift was more significant on the dawn side than on the dusk side, indicating that the change in the electric field was inhomogeneous. The simultaneous observations of T60 and the Hisaki satellite on February 19–23, 2016 indicated that the averaged intensity of the electric field derived from T60 was 3.9±0.9 mV/m, consistent with that of 2.8±1.2 mV/m derived from the Hisaki satellite. Our results demonstrate how solar wind affects the nonuniformity of the electric field in the inner magnetosphere.

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.