Transient internally driven aurora at Jupiter discovered by Hisaki and the Hubble Space Telescope

Kimura, Tomoki; Badman, S. V.; Tao, Chihiro; Yoshioka, Kazuo; Murakami, Go; Yamazaki, Atsushi; Tsuchiya, F.; Bonfond, Bertrand; Steffl, A. J.; Masters, A.; Kasahara, Satoshi; Hasegawa, Hiroshi; Yoshikawa, Ichiro; Fujimoto, M.; Clarke, J. T.

doi:10.1002/2015gl063272

Cited by 59 publications

(116 citation statements)

References 41 publications

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“…To remove the influence of SW variation and to examine the influence of volcanic activity alone on the IPT, we excluded the dataset obtained when the dynamic SW pressure was higher than 0.1 nPa, as studied by Kimura et al (2015) and Yoshikawa et al (2016). Figure 5 shows enlarged plots of Fig.…”

Section: Discussionmentioning

confidence: 99%

Volcanic activity on Io and its influence on the dynamics of the Jovian magnetosphere observed by EXCEED/Hisaki in 2015

Yoshikawa

Suzuki

Hikida

et al. 2017

Earth Planets Space

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Jupiter's moon Io, which orbits deep inside the magnetosphere, is the most geologically active object in the solar system. Kurdalagon Patera, a volcano on Io, erupted in 2015 and became a substantial source of Jovian magnetospheric plasma. Based on Earth-orbiting spacecraft observations, Io plasma torus (IPT) exhibited the peak intensity (nearly double) of ionic sulfur emissions roughly 2 month later, followed by a decay phase. This environmental change provides a unique opportunity to determine how the more heavily loaded magnetosphere behaves. Indeed, the extreme ultraviolet spectroscope for exospheric dynamics onboard the Earth-orbiting spacecraft Hisaki witnessed the whole interval via aurora and IPT observations. A simple-minded idea would be that the centrifugal force acting on fast co-rotating magnetic flux tubes loaded with heavier contents intensifies their outward transport. At the same time, there must be increased inward convection to conserve the magnetic flux. The latter could be accompanied by (1) increased inward velocity of field lines, (2) increased frequency of inward transport events, (3) increased inward flux carried per event, or (4) combinations of them. The Hisaki observations showed that the densities of major ions in the IPT increased and roughly doubled compared with pre-eruption values. The hot electron fraction, which sustains the EUV radiation from the IPT, gradually increased on a timescale of days. Pairs of intensified aurora and IPT brightening due to the enhanced supply of hot electrons from the mid-magnetosphere to the IPT upon aurora explosions observed during both quiet and active times, enabled the study of the mid-magnetosphere/IPT relationship. Hisaki observations under active Io conditions showed that: (1) the hot electron fraction in the torus gradually increased; (2) brightening pairs were more intense; (3) the energy supplied by the largest event maintained enhanced torus emission for less than a day; (4) the time delay of a torus brightening from a corresponding aurora intensification was roughly 11 h, that is, the same as during quiet times, suggesting that the inward convection speed of high-energy electrons does not change significantly.

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Section: Discussionmentioning

confidence: 99%

Volcanic activity on Io and its influence on the dynamics of the Jovian magnetosphere observed by EXCEED/Hisaki in 2015

Yoshikawa

Suzuki

Hikida

et al. 2017

Earth Planets Space

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“…The length of the slit is 360 arc sec and covers a spatial range of 15 R J at the time of Jupiter opposition. The northern polar region of Jupiter is guided at the center of the slit to measure Jupiter's northern aurora [ Kimura et al ., ; Tao et al ., ]. Solar reflected light that comes from the southern part of Jupiter's disk does not enter the spectrograph but reflects in front of the slit plate and is guided to the FOV guide camera.…”

Section: Data Setmentioning

confidence: 99%

Local electron heating in the Io plasma torus associated with Io from HISAKI satellite observation

et al. 2015

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Io‐correlated brightness change in the Io plasma torus (IPT) was discovered by the Voyager spacecraft, showing evidence of local electron heating around Io. However, its detailed properties and the cause of electron heating are still open issues. The extreme ultraviolet spectrograph on board the HISAKI satellite continuously observed the IPT from the end of December 2013 to the middle of January 2014. The variation in the IPT brightness showed that clear periodicity associated with Io's orbital period (42 h) and that the bright region was located downstream of Io. The amplitude of the periodic variation was larger at short wavelengths than at long wavelengths. From spectral analyses, we found that Io‐correlated brightening is caused by the increase in the hot electron population in the region downstream of Io. We also found that the brightness depends on the system III longitude and found primary and secondary peaks in the longitude ranges of 100–130° and 250–340°, respectively. Io's orbit crosses the center of the IPT around these longitudes. This longitude dependence suggests that the electron heating process is related to the plasma density around Io. The total radiated power from the IPT in January 2014 was estimated to be 1.4 TW in the wavelength range from 60 to 145 nm. The Io‐correlated component produced 10% of this total radiated power. The interaction between Io and the IPT continuously produces a large amount of energy around Io, and 140 GW of that energy is immediately converted to hot electron production in the IPT.

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“…Over ~2 days emission levels decayed down to quiet levels. The UV and infrared (IR) auroral intensities have been reported to vary in response to compression by the solar wind [e.g., Baron et al , ; Pryor et al , ; Nichols et al , , ; Clarke et al , ; Kimura et al , ]. The peaks, followed by the decays, on day 107 and 109 appear to be associated with the adjacent compressional regions arriving on days 105 and 109 in the MHD simulation.…”

Section: Day‐to‐day Variability In Euv and X‐ray Auroramentioning

confidence: 99%

Jupiter's X‐ray and EUV auroras monitored by Chandra, XMM‐Newton, and Hisaki satellite

et al. 2016

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Jupiter's X‐ray auroral emission in the polar cap region results from particles which have undergone strong field‐aligned acceleration into the ionosphere. The origin of precipitating ions and electrons and the time variability in the X‐ray emission are essential to uncover the driving mechanism for the high‐energy acceleration. The magnetospheric location of the source field line where the X‐ray is generated is likely affected by the solar wind variability. However, these essential characteristics are still unknown because the long‐term monitoring of the X‐rays and contemporaneous solar wind variability has not been carried out. In April 2014, the first long‐term multiwavelength monitoring of Jupiter's X‐ray and EUV auroral emissions was made by the Chandra X‐ray Observatory, XMM‐Newton, and Hisaki satellite. We find that the X‐ray count rates are positively correlated with the solar wind velocity and insignificantly with the dynamic pressure. Based on the magnetic field mapping model, a half of the X‐ray auroral region was found to be open to the interplanetary space. The other half of the X‐ray auroral source region is magnetically connected with the prenoon to postdusk sector in the outermost region of the magnetosphere, where the Kelvin‐Helmholtz (KH) instability, magnetopause reconnection, and quasiperiodic particle injection potentially take place. We speculate that the high‐energy auroral acceleration is associated with the KH instability and/or magnetopause reconnection. This association is expected to also occur in many other space plasma environments such as Saturn and other magnetized rotators.

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Transient internally driven aurora at Jupiter discovered by Hisaki and the Hubble Space Telescope

Cited by 59 publications

References 41 publications

Volcanic activity on Io and its influence on the dynamics of the Jovian magnetosphere observed by EXCEED/Hisaki in 2015

Volcanic activity on Io and its influence on the dynamics of the Jovian magnetosphere observed by EXCEED/Hisaki in 2015

Local electron heating in the Io plasma torus associated with Io from HISAKI satellite observation

Jupiter's X‐ray and EUV auroras monitored by Chandra, XMM‐Newton, and Hisaki satellite

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