Variation of Jupiter's aurora observed by Hisaki/EXCEED: 1. Observed characteristics of the auroral electron energies compared with observations performed using HST/STIS

In early 2014, continuous monitoring with the Hisaki satellite discovered transient auroral emission at Jupiter during a period when the solar wind was relatively quiet for a few days. Simultaneous imaging made by the Hubble Space Telescope (HST) suggested that the transient aurora is associated with a global magnetospheric disturbance that spans from the inner to outer magnetosphere. However, the temporal and spatial evolutions of the magnetospheric disturbance were not resolved because of the lack of continuous monitoring of the transient aurora simultaneously with the imaging. Here we report the coordinated observation of the aurora and plasma torus made by Hisaki and HST during the approach phase of the Juno spacecraft in mid‐2016. On day 142, Hisaki detected a transient aurora with a maximum total H2 emission power of ~8.5 TW. The simultaneous HST imaging was indicative of a large “dawn storm,” which is associated with tail reconnection, at the onset of the transient aurora. The outer emission, which is associated with hot plasma injection in the inner magnetosphere, followed the dawn storm within less than two Jupiter rotations. The monitoring of the torus with Hisaki indicated that the hot plasma population increased in the torus during the transient aurora. These results imply that the magnetospheric disturbance is initiated via the tail reconnection and rapidly expands toward the inner magnetosphere, followed by the hot plasma injection reaching the plasma torus. This corresponds to the radially inward transport of the plasma and/or energy from the outer to the inner magnetosphere.

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“…The unabsorbed power estimation for the Hisaki data is established by Tao et al . [, ]. See these references for the details for the estimation.…”

Section: Resultsmentioning

confidence: 99%

Transient brightening of Jupiter's aurora observed by the Hisaki satellite and Hubble Space Telescope during approach phase of the Juno spacecraft

Kimura

Nichols

Gray

et al. 2017

Geophysical Research Letters

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“…We used the model developed by Tao et al (, ) to convert the emission power in the 900–1,480 Å range to the corresponding unabsorbed total emission power from the northern hemisphere in the 700–1,800 Å UV range. This removes the effects of Jupiter's atmospheric absorption and rotational modulation from the data (see Tao et al, , , for details). Based on the unabsorbed power, we found that the identified 23 transient auroral events emitted energy of ~10 15 to 10 17 J/event, which corresponds to total electron energy of ~10 16 to 10 18 J/event precipitating into the auroral region.…”

Section: Discussionmentioning

confidence: 99%

“…The transient aurora with a peak power of ~2 TW, which is the strongest auroral power in the present analysis period, occurs during the interplanetary shock arrival at Jupiter on DOY 87. The unabsorbed emission power of the peak is estimated to be ~10 TW by the Tao et al (, ) model. The temporal intervals between the strongest event and adjacent transient auroras are ~10 days, which are longer than the most frequent interval of 2–6 days.…”

Section: Discussionmentioning

confidence: 99%

“…Uncertainty in the arrival time of the solar wind shock structures, the Corotating Interaction Region and Coronal Mass Ejections, at Jupiter is dependent on the Earth‐Sun‐Jupiter angle, which was 82°–180° for the present analysis period. The arrival time uncertainty is estimated to be approximately a few days or more, as discussed in Kimura et al (, ), Kita et al (), and Tao et al (, ).…”

Section: Data Setmentioning

confidence: 97%

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Response of Jupiter's Aurora to Plasma Mass Loading Rate Monitored by the Hisaki Satellite During Volcanic Eruptions at Io

et al. 2018

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The production and transport of plasma mass are essential processes in the dynamics of planetary magnetospheres. At Jupiter, it is hypothesized that Io's volcanic plasma carried out of the plasma torus is transported radially outward in the rotating magnetosphere and is recurrently ejected as plasmoid via tail reconnection. The plasmoid ejection is likely associated with particle energization, radial plasma flow, and transient auroral emissions. However, it has not been demonstrated that plasmoid ejection is sensitive to mass loading because of the lack of simultaneous observations of both processes. We report the response of plasmoid ejection to mass loading during large volcanic eruptions at Io in 2015. Response of the transient aurora to the mass loading rate was investigated based on a combination of Hisaki satellite monitoring and a newly developed analytic model. We found that the transient aurora frequently recurred at a 2–6 day period in response to a mass loading increase from 0.3 to 0.5 t/s. In general, the recurrence of the transient aurora was not significantly correlated with the solar wind, although there was an exceptional event with a maximum emission power of ~10 TW after the solar wind shock arrival. The recurrence of plasmoid ejection requires the precondition that an amount comparable to the total mass of magnetosphere, ~1.5 Mt, is accumulated in the magnetosphere. A plasmoid mass of more than 0.1 Mt is necessary in case that the plasmoid ejection is the only process for mass release.

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“…The difference of the power by a factor of ~8 is contributed by different estimation methods. The different wavelength range (Hisaki EXCEED: 900–1,480 Å, Juno UVS: 700–1,190 Å, and 1,230–1,620 Å) and exclusion of the auroral emission at the geocoronal emission lines for Hisaki EXCEED contributed to the difference by a factor of 3 when the color ratio of Hisaki EXCEED (Tao et al, ; Tao et al, ; Tao et al, ) was 1.5–2 corresponding to the time interval of our interest. In addition, the longitudinal modulation correction causes the difference by a factor of 2, since Juno UVS refers to the maximum intensity of the total power, whereas Hisaki EXCEED refers to the average of the total power.…”

Section: Instruments and Data Analysismentioning

confidence: 91%

Jovian UV Aurora's Response to the Solar Wind: Hisaki EXCEED and Juno Observations

et al. 2019

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We summarize Jupiter's ultraviolet (UV) auroral response to solar wind dynamic pressure variations during Juno's approach to Jupiter in 2016. The response time of Jupiter's aurora to external drivers has thus far been unknown owing to a sparsity of upstream in situ solar wind measurements. Combining the Juno solar wind observations with continuous UV aurora data obtained by Hisaki EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) and Juno UV spectrograph, the UV aurora brightenings in response to three major shock arrivals showed time lags of 10-15 hr. These time lags are longer than the time required for ballistic propagation of the shocks by the solar wind. In addition to that puzzle, while an enhancement in the UV auroral power was observed with an increase in dynamic pressure to~0.03 nPa, no associated brightening was observed with a dynamic pressure elevation of >0.1 nPa. These imply that internal magnetospheric aspects need to be taken into consideration to fully resolve the issue. Plain Language Summary Jovian ultraviolet aurora are emitted from hydrogen molecules inJupiter's atmosphere when energetic electrons precipitate from the magnetosphere to excite the atmospheric molecules. The Jovian magnetosphere is always under the influence of the solar wind. Variation in the solar wind affects magnetospheric dynamics and thus the Jovian aurora intensity. The solar wind-magnetosphere interaction is well studied for Earth, and the issue of aurora response to the solar wind is also well studied for Earth, but the issue remains open for Jupiter. Here we obtain the response time of aurora brightening upon intensification of the solar wind, which is a very fundamental quantity, to find it to be too long to be explained by a simple propagating model that assumes the solar wind as the dominant driver. Furthermore, some small variations in solar wind shocks led to aurora brightenings, while larger variations did not trigger other events. The characteristics discussed in this paper provide good case studies to validate theories or numerical simulations of how Jovian aurora may respond to changes in the solar wind.

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Variation of Jupiter's aurora observed by Hisaki/EXCEED: 1. Observed characteristics of the auroral electron energies compared with observations performed using HST/STIS

Cited by 16 publications

References 35 publications

Transient brightening of Jupiter's aurora observed by the Hisaki satellite and Hubble Space Telescope during approach phase of the Juno spacecraft

Transient brightening of Jupiter's aurora observed by the Hisaki satellite and Hubble Space Telescope during approach phase of the Juno spacecraft

Response of Jupiter's Aurora to Plasma Mass Loading Rate Monitored by the Hisaki Satellite During Volcanic Eruptions at Io

Jovian UV Aurora's Response to the Solar Wind: Hisaki EXCEED and Juno Observations

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