Variation of Jupiter's Auroral Energy Input Observed by Hisaki/EXCEED

Abstract:

EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) is an instrument for extreme ultraviolet (EUV) spectroscopy onboard JAXA's Earth-orbiting space planetary telescope, Hisaki. EXCEED observed the Jupiter's northern pole, which is our main interest here, and the Io plasma torus continuously during January and April 2014. EXCEED detects auroral emission covering the H₂ Lyman and Werner bands of Jupiter over 800—1480 Å wavelength range with ~1 Å resolution. The observed spectrum shows H₂ self-absorption (<1150 Å) and hydrocarbon absorption (<1350 Å) as seen in previous observations. Using the latter hydrocarbon absorption, we analyze temporal variations of auroral electron energy and flux using a new hydrocarbon color ratio adopted for EXCEED's wavelength range. The integrated auroral main variability over the pole region can be explained simply by the rotation of Jupiter's main auroral oval with the planet. The auroral color ratio also varies with a lesser dependence on the planetary rotation phase. We found that the short-term enhancements of auroral intensity associated with and without solar wind dynamic pressure enhancements are mainly due to the electron number flux variation. This suggests enhancement of auroral activity connected with the inner magnetosphere as seen in the low-latitude expansion and bright emission seen in the Hubble Space Telescope (HST) images taken simultaneously. We also compare with the HST spectra acquired during January 2014.