Variation of Jupiter's aurora observed by Hisaki/EXCEED: 2. Estimations of auroral parameters and magnetospheric dynamics

Chihiro Tao (1) , Tomoki Kimura , Sarah V. Badman , Nicolas André (1) , Fuminori Tsuchiya , Go Murakami , Kazuo Yoshioka , Ichiro Yoshikawa , Atsushi Yamazaki , Masaki Fujimoto

1 IRAP - Institut de recherche en astrophysique et planétologie

Jupiter's auroral parameters are estimated from observations by a spectrometer EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) on board Japanese Aerospace Exploration Agency's Earth-orbiting planetary space telescope Hisaki. EXCEED provides continuous auroral spectra covering the wavelength range over 80-148 nm from the whole northern polar region. The auroral electron energy is estimated using a hydrocarbon color ratio adopted for the wavelength range of EXCEED, and the emission power in the long wavelength range 138.5-144.8 nm is used as an indicator of total emitted power before hydrocarbon absorption and auroral electron energy flux. The quasi-continuous observations by Hisaki provide the auroral electron parameters and their relation under different auroral activity levels. Short- (within < one planetary rotation) and long-term (> one planetary rotation) enhancements of auroral power accompany increases of the electron number flux rather than the electron energy variations. The relationships between the auroral electron energy (~70-400 keV) and flux (10²⁶-10²⁷/s, 0.08-0.9 μA/m²) estimated from the observations over a 40 day interval are in agreement with field-aligned acceleration theory when incorporating probable magnetospheric parameters. Applying the electron acceleration theory to each observation point, we explore the magnetospheric source plasma variation during these power-enhanced events. Possible scenarios to explain the derived variations are (i) an adiabatic variation of the magnetospheric plasma under a magnetospheric compression and/or plasma injection, and (ii) a change of the dominant auroral component from the main emission (main aurora) to the emission at the open-closed boundary.

Keywords: Jupiter; aurora; Hisaki; EXCEED; Hubble Space Telescope

Domains: Sciences of the Universe [physics]

Chihiro Tao, Tomoki Kimura, Sarah V. Badman, Nicolas André, Fuminori Tsuchiya, et al.. Variation of Jupiter's aurora observed by Hisaki/EXCEED: 2. Estimations of auroral parameters and magnetospheric dynamics. Journal of Geophysical Research: Space Physics, 2016, 121, pp.4055-4071. ⟨10.1002/2015JA021272⟩. ⟨insu-03670234⟩