Solar Wind Response of the Dawn-Dusk Asymmetry in the Io Plasma Torus Using the Haleakala T60 and HISAKI Satellite Observations

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 angstrom) 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 19-23 February 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.