Solar wind response of the dawn-dusk asymmetry in the Io plasma torus
using the Haleakala T60 and HISAKI satellite observations
Abstract
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.