Short-term Variation in the Dawn–Dusk Asymmetry of the Jovian Radiation Belt Obtained from GMRT and Hisaki EXCEED Observations

In order to reveal variations of days to weeks in the brightness distribution of Jovian Synchrotron Radiation (JSR), we made simultaneous radio and ultraviolet observations using the Giant Metrewave Radio Telescope (GMRT) and the Hisaki EXtreme ultraviolet spectrosCope for ExosphEric Dynamics (EXCEED). It is known from visible and ultraviolet observations that Io plasma torus (IPT) has dawn–dusk asymmetry, and that this asymmetry is believed to be due to the dawn-dusk electric field. Continuous ultraviolet observation by Hisaki reveals that dawn–dusk asymmetry of IPT changes in days to weeks, therefore, if this global electric field around Io's orbit (5.9 Jovian radii) could penetrate the radiation belt region (<2 Jovian radii), the variations in brightness distribution of JSR and IPT are expected to be correlated. The GMRT observations were made from 2013 December 31 to 2014 January 16 at 610 MHz and 2016 March 14–June 23 at 1390 MHz, while Hisaki continuously monitored IPT. The statistical analysis indicates that JSR and IPT do not have a significant correlation. Although these results do not support our hypothesis, we cannot rule out the possibility that the dawn-dusk electric field was masked by some other process, including the conductivity variation and/or the time-variable longitudinal asymmetry of JSR.