Enhancement of the Jovian Magnetospheric Plasma Circulation Caused by the Change in Plasma Supply From the Satellite Io

Abstract

The innermost Galilean satellite, Io, supplies a large amount of volcanic gasses to the Jovian magnetosphere. The fast rotation of Jupiter and the outward transport of ionized gasses are responsible for forming a huge and rotationally dominant magnetosphere. The plasma supply from the satellite has a key role in the characterization of the Jovian magnetosphere. In fact, significant variations of the plasma population in the inner magnetosphere caused by the volcanic eruptions in Io were found in early 2015, using a continuous data set of the Io plasma torus obtained from an extreme ultraviolet spectroscope onboard the Hisaki satellite. The time evolution of the Io plasma torus radial distribution showed that the outward transport of plasma through 8 RJ from Jupiter was enhanced for approximately 2 months (from the end of January to the beginning of April 2015). Intense short‐lived auroral brightenings––which represent transient energy releases in the outer part of the magnetosphere—occurred frequently during this period. The short‐lived auroral brightenings accompanied well‐defined sporadic enhancements of the ion brightness in the plasma torus, indicating a rapid inward transport of energy from the outer part of the magnetosphere and the resultant enhancement of hot electron population in the inner magnetosphere. This evidently shows that the change in a plasma source in the inner magnetosphere affects a large‐scale radial circulation of mass and energy in a rotationally dominant magnetosphere.

Azimuthal Variation in the Io Plasma Torus Observed by the Hisaki Satellite From 2013 to 2016

“…In the dawnside, for example, the intensities of SII 76.5 nm and SIV 65.7 nm were almost the same (~50 R) until the middle of January (~day of year 19). After day of year 19, the SII intensity increased to ~120 R while the SIV intensity slightly decreased to ~40 R (Tsuchiya et al, ; Yoshikawa et al, ). Then, the ratio of SIV to SII decreased.…”

“…Ground‐based observations of iogenic sodium emissions showed that the brightness was almost constant with only some small enhancements detected in seasons A and C but increased significantly in season B from the middle of January to March 2015 (Yoneda et al, ; Figure S3), suggesting that there was an increase in volcanic activity. Infrared (IR) monitoring of Io during season B was sparse (de Pater et al, ; de Kleer & de Pater, ), but it is suggested that Pillan Patera and Kurdalagon Patera could be candidate sources of the active plumes during this period (Tsuchiya et al, ). de Kleer and de Pater () showed that the brightness of Loki Patera increased around January and April 2016 (in season C), although the sodium emission did not show significant variation.…”

“…In this paper, the data set of the Io plasma torus emissions obtained by the extreme ultraviolet spectrograph EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics), onboard the Hisaki satellite, is used (section ). Hisaki has conducted long‐term monitoring of the Io plasma torus since December 2013 and captured responses of the Jovian magnetosphere to the increase in neutrals from Io in early 2015 (Kimura et al, ; Koga et al, ; Tao et al, ; Tsuchiya et al, ; Yoshikawa et al, ; Yoshioka et al, ). The purpose of this study is to survey azimuthal variations in the torus using the large Hisaki data set obtained from December 2013 to August 2016.…”

The Space Environment of Io and Europa

“…The Japanese space agency (JAXA) put the Hisaki satellite into orbit around Earth in September 2013 (Kimura et al, 2019; Yoshikawa et al, 2014, 2016; Yoshioka et al, 2013). Hisaki 's UV spectrometer has been observing emissions from the Io plasma torus, determining composition (Hikida et al, 2018; Yoshioka et al, 2014, 2017), mapping the oxygen neutral cloud (Koga et al, 2018a, 2018b), and measuring temporal variations (Hikida et al, 2020; Kimura et al, 2018; Koga et al, 2019; Tsuchiya et al, 2015, 2018, 2019; Yoshikawa et al, 2017).…”

Transient Change of Io's Neutral Oxygen Cloud and Plasma Torus Observed by Hisaki

“…The figure shows that the OI 130.4 nm emission increased from DOY 17 to 108 (called high density period hereafter). Yoneda et al (2015) observed the evolution of Na emissions via ground-based telescope, and Tsuchiya et al (2018) compared time variations of OI, Na (neutral emissions), OII, SII, SIII, and SIV (IPT emissions) during the same period in 2015. Kimura et al (2018), Tao et al (2018), Tsuchiya et al (2019), Yoshikawa et al (2017), and Yoshioka et al (2018) also showed the change of IPT in 2015.…”