The far-ultraviolet main auroral emission at Jupiter – Part 1: Dawn–dusk brightness asymmetries

Bonfond, Bertrand; Gustin, Jacques; Gérard, Jean‐Claude; Grodent, Denis; Radioti, Aikaterini; Palmaerts, Benjamin; Khurana, K. K.; Tao, Chihiro

doi:10.5194/angeo-33-1203-2015

Cited by 25 publications

(34 citation statements)

References 29 publications

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“…In our simulations, the main oval is also slightly brighter at dusk than at dawn. This dusk‐dawn asymmetry of the brightness of the main oval has been observed by Bonfond et al [].…”

Section: How Does the Solar Wind Density Influence The Ionospheric Cusupporting

confidence: 77%

How is the Jovian main auroral emission affected by the solar wind?

et al. 2017

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The influence of the solar wind on Jupiter's magnetosphere is studied via three‐dimensional global MHD simulations. We especially examine how solar wind density variations affect the main auroral emission. Our simulations show that a density increase in the solar wind has strong effects on the Jovian magnetosphere: the size of the magnetosphere decreases, the field lines are compressed on the dayside and elongated on the nightside (this effect can be seen even deep inside the magnetosphere), and dawn‐dusk asymmetries are enhanced. Our results also show that the main oval becomes brighter when the solar wind is denser. But the precise response of the main oval to such a density enhancement in the solar wind depends on the local time: on the nightside the main oval becomes brighter, while on the dayside it first turns slightly darker for a few hours and then also becomes brighter. Once the density increase in the solar wind reaches the magnetosphere, the magnetopause moves inward, and in less than 5 h, a new approximate equilibrium position is obtained. But the magnetosphere as a whole needs much longer to adapt to the new solar wind conditions. For instance, the total electrical current closing in the ionosphere slowly increases during the simulation and it takes about 60 h to reach a new equilibrium. By then the currents have increased by as much as 45%.

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“…In our simulations, the main oval is also slightly brighter at dusk than at dawn. This dusk‐dawn asymmetry of the brightness of the main oval has been observed by Bonfond et al [].…”

Section: How Does the Solar Wind Density Influence The Ionospheric Cusupporting

confidence: 77%

How is the Jovian main auroral emission affected by the solar wind?

et al. 2017

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“…These have been shown to occur near-constantly and manifest as spikes in the dusk power (Figure 1e), but they do not fully account for the underlying steady asymmetry between dawn and dusk which we observe here. At Jupiter, a similar asymmetry was observed and suggested to be related to a partial ring current in the nightside magnetosphere (Bonfond et al, 2015), but it is unclear whether a similar process could be important in Saturn's magnetosphere. The case study presented in Figure 1 is not the only quiet sequence observed.…”

Section: Saturn's Quiet Main Aurora: Subcorotational and Ppo Systemscontrasting

confidence: 75%

The Dynamics of Saturn's Main Aurorae

Bader

Cowley

Yao

et al. 2019

Geophysical Research Letters

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Saturn's main aurorae are thought to be generated by plasma flow shears associated with a gradient in angular plasma velocity in the outer magnetosphere. Dungey cycle convection across the polar cap, in combination with rotational flow, may maximize (minimize) this flow shear at dawn (dusk) under strong solar wind driving. Using imagery from Cassini's Ultraviolet Imaging Spectrograph, we surprisingly find no related asymmetry in auroral power but demonstrate that the previously observed “dawn arc” is a signature of quasiperiodic auroral plasma injections commencing near dawn, which seem to be transient signatures of magnetotail reconnection and not part of the static main aurorae. We conclude that direct Dungey cycle driving in Saturn's magnetosphere is small compared to internal driving under usual conditions. Saturn's large‐scale auroral dynamics hence seem predominantly controlled by internal plasma loading, with plasma release in the magnetotail being triggered both internally through planetary period oscillation effects and externally through solar wind compressions.

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“…Since Jupiter's magnetic axis is tilted by only ~10° with respect to the spin axis, Earth‐orbiting observatories can only capture one portion of Jupiter's aurora at the time. Therefore, we follow the methodology described by Bonfond et al () in which the closure of the contour is achieved with a Fourier series. This effect was also accounted for in Figure and Table , where the emitted power is corrected for the viewing geometry by a time‐dependent factor equal to the ratio between the total area of the subregion of interest and the area of its portion visible from Earth (Nichols, Clarke, Gérard, Grodent, & Hansen, ).…”

Section: Auroral Power and Subregionsmentioning

confidence: 99%

Jupiter's Aurora Observed With HST During Juno Orbits 3 to 7

et al. 2018

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A large set of observations of Jupiter's ultraviolet aurora was collected with the Hubble Space Telescope concurrently with the NASA‐Juno mission, during an eight‐month period, from 30 November 2016 to 18 July 2017. These Hubble observations cover Juno orbits 3 to 7 during which Juno in situ and remote sensing instruments, as well as other observatories, obtained a wealth of unprecedented information on Jupiter's magnetosphere and the connection with its auroral ionosphere. Jupiter's ultraviolet aurora is known to vary rapidly, with timescales ranging from seconds to one Jovian rotation. The main objective of the present study is to provide a simplified description of the global ultraviolet auroral morphology that can be used for comparison with other quantities, such as those obtained with Juno. This represents an entirely new approach from which logical connections between different morphologies may be inferred. For that purpose, we define three auroral subregions in which we evaluate the auroral emitted power as a function of time. In parallel, we define six auroral morphology families that allow us to quantify the variations of the spatial distribution of the auroral emission. These variations are associated with changes in the state of the Jovian magnetosphere, possibly influenced by Io and the Io plasma torus and by the conditions prevailing in the upstream interplanetary medium. This study shows that the auroral morphology evolved differently during the five ~2 week periods bracketing the times of Juno perijove (PJ03 to PJ07), suggesting that during these periods, the Jovian magnetosphere adopted various states.

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The far-ultraviolet main auroral emission at Jupiter – Part 1: Dawn–dusk brightness asymmetries

Cited by 25 publications

References 29 publications

How is the Jovian main auroral emission affected by the solar wind?

How is the Jovian main auroral emission affected by the solar wind?

The Dynamics of Saturn's Main Aurorae

Jupiter's Aurora Observed With HST During Juno Orbits 3 to 7

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