Ganymede's Auroral Footprint Latitude: Comparison With Magnetodisc Model

Promfu, Tatphicha; Nichols, J. D.; Wannawichian, S.; Clarke, J. T.; Vogt, Marissa F.; Bonfond, Bertrand

doi:10.1029/2022ja030712

Cited by 3 publications

(3 citation statements)

References 67 publications

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“…Understanding and tracking the variability of the plasma sheet current is crucial as they may induce a displacement of the footprint location, especially for Ganymede (Promfu et al, 2022;. The variation in the Ganymede footprint position are large enough to be easily detected and thus is important to track magnetospheric changes.…”

Section: Variability In Magnetospheric Conditions and Lead Anglementioning

confidence: 99%

“…They found that the expected temporal variability obtained from fit of the current sheet results in a 10–20% variability in the magnetic field components, and is longitude‐dependent. Understanding and tracking the variability of the plasma sheet current is crucial as they may induce a displacement of the footprint location, especially for Ganymede (Promfu et al., 2022; Vogt et al., 2022). The variation in the Ganymede footprint position are large enough to be easily detected and thus is important to track magnetospheric changes.…”

Section: Variability In Magnetospheric Conditions and Lead Anglementioning

confidence: 99%

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The Io, Europa, and Ganymede Auroral Footprints at Jupiter in the Ultraviolet: Positions and Equatorial Lead Angles

et al. 2023

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Jupiter's satellite auroral footprints are a consequence of the interaction between the Jovian magnetic field with co‐rotating iogenic plasma and the Galilean moons. The disturbances created near the moons propagate as Alfvén waves along the magnetic field lines. The position of the moons is therefore “Alfvénically” connected to their respective auroral footprint. The angular separation from the instantaneous magnetic footprint can be estimated by the so‐called lead angle. That lead angle varies periodically as a function of orbital longitude, since the time for the Alfvén waves to reach the Jovian ionosphere varies accordingly. Using spectral images of the Main Alfvén Wing auroral spots collected by Juno‐UVS during the first 43 orbits, this work provides the first empirical model of the Io, Europa, and Ganymede equatorial lead angles for the northern and southern hemispheres. Alfvén travel times between the three innermost Galilean moons to Jupiter's northern and southern hemispheres are estimated from the lead angle measurements. We also demonstrate the accuracy of the mapping from the Juno magnetic field reference model (JRM33) at the completion of the prime mission for M‐shells extending to at least 15 RJ. Finally, we shows how the added knowledge of the lead angle can improve the interpretation of the moon‐induced decametric emissions.

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Section: Variability In Magnetospheric Conditions and Lead Anglementioning

confidence: 99%

Section: Variability In Magnetospheric Conditions and Lead Anglementioning

confidence: 99%

The Io, Europa, and Ganymede Auroral Footprints at Jupiter in the Ultraviolet: Positions and Equatorial Lead Angles

et al. 2023

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“…We also looked for a potential day‐night correlation (not shown), but the transversal shift showed no systematic dependency with this criterion. The transversal displacement of the GFP has already been observed by the Hubble Space Telescope (HST; Grodent et al., 2008) and it has been explained by variations in the plasmadisk mass and/or radial transport (Promfu et al., 2022). Although the observations performed during PJ1 and PJ4 suggest local‐time variability, we cannot completely rule out a global variation of the plasmadisk.…”

Section: Discussionmentioning

confidence: 93%

The Infrared Auroral Footprint Tracks of Io, Europa and Ganymede at Jupiter Observed by Juno‐JIRAM

Moirano,

Mura,

Hue

et al. 2024

JGR Planets

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The electromagnetic coupling between the Galilean satellites at Jupiter and the planetary ionosphere generates an auroral footprint, which is detected with high spatial resolution in the infrared L band by the Jovian InfraRed Auroral Mapper (JIRAM) onboard the Juno spacecraft. We report the JIRAM data acquired since 27 August 2016 until 23 May 2022, which are used to compute the average position of the footprint tracks of Io, Europa and Ganymede. The result of the present analysis help to test the reliability of magnetic field models, to calibrate ground‐based observations and to highlight the variability in the footprint positions, which can be used to probe the plasma environment at the orbit of the satellites. The determination of the plasma properties around the moons is particularly relevant to complement the Juno flybys of the moons during its extended mission, and to support the future Juice and Europa Clipper missions. Lastly, we report no clear evidence of the auroral footprint of Callisto, which is likely due to a combination of its low expected brightness and its position very close to the main Jovian aurora.

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Effect of magnetospheric conditions on the morphology of Jupiter’s ultraviolet main auroral emission as observed by Juno-UVS

Head,

Grodent,

Bonfond

et al. 2024

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Auroral emissions are a reflection of magnetospheric processes, and at Jupiter, it is not entirely certain how the morphology of the UV main emission (ME) varies with magnetospheric compression or the strength of the central current sheet. This work leverages the observations from Juno-UVS to link ME variability with particular magnetospheric states. We employed novel arc-detection techniques to determine new reference ovals for the ME from perijoves 1 through 54, in both hemispheres, and analysed how the size and shape of the ME vary compared to this reference oval. The morphology and brightness of the ME vary in local time: the dawn-side ME is typically expanded, while the dusk-side ME is contracted, compared to the reference oval, and the dusk-side ME is twice as bright as the dawn-side ME. Both the northern and southern ME and the day-side and night-side ME expand and contract from their reference ovals synchronously, which indicates that the variable size of the ME is caused by a process occurring throughout the Jovian magnetosphere. The poleward latitudinal shift of the auroral footprint of Ganymede correlates with the poleward motion of the ME, whereas a similar relation is not present for the footprint of Io. Additionally, the expansion of the ME correlates well with an increase in magnetodisc current. These two results suggest that a changing current-sheet magnetic field is partially responsible for the variable size of the ME. Finally, magnetospheric compression is linked to a global ME contraction and brightening, though this brightening occurs predominantly in the day-side ME. This observation, and the observation that the dusk-side ME is typically brighter than the dawn-side ME, stands in contrast to the modelled and observed behaviour of field-aligned currents and thus weakens the theoretical link between field-aligned currents and the generation of the auroral ME.

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Ganymede's Auroral Footprint Latitude: Comparison With Magnetodisc Model

Cited by 3 publications

References 67 publications

The Io, Europa, and Ganymede Auroral Footprints at Jupiter in the Ultraviolet: Positions and Equatorial Lead Angles

The Io, Europa, and Ganymede Auroral Footprints at Jupiter in the Ultraviolet: Positions and Equatorial Lead Angles

The Infrared Auroral Footprint Tracks of Io, Europa and Ganymede at Jupiter Observed by Juno‐JIRAM

Effect of magnetospheric conditions on the morphology of Jupiter’s ultraviolet main auroral emission as observed by Juno-UVS

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