Response of Jupiter's inner magnetosphere to the solar wind derived from extreme ultraviolet monitoring of the Io plasma torus

Murakami, Go; Yoshioka, Kazuo; Yamazaki, Atsushi; Tsuchiya, F.; Kimura, Tomoki; Tao, Chihiro; Kita, Hidetoshi; Kagitani, Masato; Sakanoi, Takeshi; Uemizu, Kazunori; Kasaba, Yasumasa; Yoshikawa, Ichiro; Fujimoto, M.

doi:10.1002/2016gl071675

Cited by 42 publications

(69 citation statements)

References 48 publications

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“…The dependence of the ratio on the electron temperature, shown in Figure b, indicates that this ratio range yields a thermal electron temperature range between 4.2 and 5.7 eV, which is consistent with the thermal electron temperature range in the plasma torus (6–7 R J ) reported previously (e.g., Bagenal, ; Steffl et al, ; Yoshioka et al, ). The mean ratios were larger for the duskside (red) than for the dawnside (black), which is consistent with the difference in the thermal electron temperature that is caused by a large‐scale dawn‐dusk electric field (Barbosa & Kivelson, ; Ip & Goertz, ; Murakami et al, ). Figures c and d show the azimuthal variation of the ratio.…”

Section: Resultssupporting

confidence: 71%

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

et al. 2019

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In the Jovian magnetosphere, sulfur and oxygen ions supplied by the satellite Io are distributed in the so‐called Io plasma torus. The plasma torus is located in the inner area of the magnetosphere and the plasma in the torus corotates with the planet. The density and the temperature of the plasma in the torus have significant azimuthal variations. In this study, data from three‐year observations obtained by the Hisaki satellite, from December 2013 to August 2016, were used to investigate statistically the azimuthal variations and to find out whether the variations were influenced by the increase in neutral particles from Io. The azimuthal variation was obtained from a time series of sulfur ion line ratios, which were sensitive to the electron temperature and the sulfur ion mixing ratio S3+/S+. The major characteristics of the azimuthal variation in the plasma parameters were consistent with the dual hot electron model, proposed to explain previous observations. On the other hand, the Hisaki data showed that the peak System III longitude in the S3+/S+ ratio was located not only around 0°–90°, as in previous observations, but also around 180°–270°. The rotation period, the System IV periodicity, was sometimes close to the Jovian rotation period. Persistent input of energy to electrons in a limited longitude range of the torus is associated with the shortening of the System IV period.

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Section: Resultssupporting

confidence: 71%

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

et al. 2019

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“…Previous observations from Voyager UVS demonstrated the presence of a LT asymmetry in the brightness of the Io torus (Sandel & Broadfoot, ). This was later interpreted as the existence of a dawn‐dusk electric field either caused by plasma motion flowing down the magnetotail (Barbosa & Kivelson, ; Ip & Goertz, ), or required by the horizontal closure of field‐aligned Birkeland currents (Goertz & Ip, ; Murakami et al, ). This electric field forces ions to be pushed further away on the dawnside and further in on the duskside.…”

Section: Observation Of the Io Footprintmentioning

confidence: 99%

Juno‐UVS Observation of the Io Footprint During Solar Eclipse

et al. 2019

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The two main ultraviolet‐signatures resulting from the Io‐magnetosphere interaction are the local auroras on Io's atmosphere, and the Io footprints on Jupiter. We study here how Io's daily eclipses affect the footprint. Previous observations showed that its atmosphere collapses in eclipse. While remote observers can observe Io's local auroras briefly when Io disappears behind Jupiter, Juno is able to follow the Io footprint in the unlit hemisphere. Theoretical models of the variability of the energy flux fed into the Alfvén wings, ultimately powering the footprints, are not sufficiently constrained by observations. For the first time, we use observations of Io's footprint from the Ultraviolet Spectrograph (UVS) on Juno recorded as Io went into eclipse. We benchmark the trend of the footprint brightness using observations by UVS taken over Io's complete orbit and find that the footprint emitted power variation with Jupiter's rotation shows fairly consistent trends with previous observations. Two exploitable data sets provided measurements when Io was simultaneously in eclipse. No statistically significant changes were recorded as Io left and moved into eclipse, respectively, suggesting either that (i) Io's atmospheric densities within and outside eclipse are large enough to produce a saturated plasma interaction, that is, in the saturated state, changes in Io's atmospheric properties to first order do not control the total Alfvénic energy flux, (ii) the atmospheric collapse during the Juno observations was less than previously observed, or (iii) additional processes of the Alfvén wings in addition to the Poynting flux generated at Io control the footprint luminosity.

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“…The 2-week periodicity identified in the prenoon sector's L b values ( Figure 2b) hints that the strength of convection is modulated by the interaction of Saturn's magnetosphere with the solar wind. By comparison, convection in Jupiter's inner magnetosphere is also regulated by solar wind transients (Murakami et al, 2016). Evidence that Saturn was almost continuously exposed to CIRs during the proximal orbits is provided in .…”

Section: The Origin Of the Inner Electron Radiation Belt Boundarymentioning

confidence: 99%

Sources, Sinks, and Transport of Energetic Electrons Near Saturn's Main Rings

Roussos

Kollmann

Krupp

et al. 2019

Geophysical Research Letters

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The inner boundary of Saturn's electron radiation belts, near the planet's A ring (∼2.27 Rs), is studied using Cassini's proximal orbit measurements. We find that variable convective flows transport energetic electrons to the A ring, which absorbs them instantaneously, forming the inner belt boundary. These flows are also responsible for a variable and longitudinally asymmetric boundary configuration. Prenoon, the boundary oscillates toward and away from the A ring with a 2‐week period. Postnoon, it maps persistently near the F ring (∼2.32 Rs) and coexists with localized MeV electron intensity enhancements (microbelts). We propose that the microbelts contain electrons in drift resonance with corotation, trapped in local time‐confined trajectories, which result from the aforementioned convective flows. The microbelts' collocation with the F ring implies either a local, secondary electron production due to galactic cosmic ray collisions with F ring dust or an enhanced resonant electron trapping due to an electrodynamic interaction between the F ring and Saturn's magnetosphere.

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Response of Jupiter's inner magnetosphere to the solar wind derived from extreme ultraviolet monitoring of the Io plasma torus

Cited by 42 publications

References 48 publications

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

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

Juno‐UVS Observation of the Io Footprint During Solar Eclipse

Sources, Sinks, and Transport of Energetic Electrons Near Saturn's Main Rings

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