Alfvén Wave Propagation in the Io Plasma Torus

Hinton, P. C.; Bagenal, F.; Bonfond, Bertrand

doi:10.1029/2018gl081472

Cited by 37 publications

(73 citation statements)

References 44 publications

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“…These numbers are within the range of the modeled arcs in the northern hemisphere here. The separation of the Alfvén wave reflections is also larger in the southern hemisphere than in the northern when assuming Io located at 180° of west longitude (Hinton et al, 2019). The equally spaced peaks in the

H_{3}^{+}

on Jupiter's atmosphere observed by Juno (Mura et al, 2018) and from Earth (Connerney & Satoh, 2000) (~5°) also point to the multiple reflections of Alfvén waves within the torus and are indicator of the Io interaction and Jupiter's magnetosphere.…”

Section: Discussionmentioning

confidence: 99%

Juno Reveals New Insights Into Io‐Related Decameter Radio Emissions

et al. 2020

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The Juno mission is providing stunning new information about Jupiter and its environment. A new magnetic field model (JRM09) with much improved accuracy near the planet provides the basis for a better understanding of Io‐related decametric radio emissions (DAM) and implications for auroral processes. Here, we selected Io‐related DAM events observed by the Juno Waves instrument to shed light into the beaming angle, the resonant electron energy, and radio source location by forward modeling. We use the JRM09 model to better constrain the location and observability of DAM and characterize the loss cone‐driven electron cyclotron maser instability. We obtained good agreement between synthetic and observed arcs with calculated beaming angles ranging from 33° to 85° and resonant electron energies up to 23 times higher than previously proposed. In addition, through a quantitative analysis, we provide an explanation regarding the higher likelihood of observing groups of arcs of Io DAM originating in the northern hemisphere relative to those originating in the southern hemisphere. This is primarily a consequence of the asymmetry of the magnetic field geometry, observer location, and pitch angles of the electrons at the equator.

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H_{3}^{+}

Section: Discussionmentioning

confidence: 99%

Juno Reveals New Insights Into Io‐Related Decameter Radio Emissions

et al. 2020

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“…As described in Hinton et al (2019) and references therein, the Alfvén waves reflect at the Jovian ionosphere in this model. The Main Alfvén Waves launched from Io both northward and southward are shown along with the initial portion of their corresponding reflected Alfvén waves.…”

Section: Journal Of Geophysical Research: Space Physicsmentioning

confidence: 92%

“…We first identify the peak DEF energy for each anode averaged over the inner region and assume that each anode is measuring particles with its center PA α, given in Table 2. The timing of the intersection of the MAW and torus Alfvén boundaries is determined by accounting for the travel time of Alfvén waves launched from a range of epochs and propagating to these boundaries (Hinton et al, 2019). Under this assumption, they gyrate on magnetic field lines and experience only the magnetic mirror force F μ = − μ∂B/∂s, where μ = mv 2 sin 2 α/2B is the magnetic moment, m is the proton mass, v is the speed, α is the PA, B is the magnitude of the magnetic field, and s is the distance along the magnetic field line.…”

Section: Shell-like Populationmentioning

confidence: 99%

Proton Acceleration by Io's Alfvénic Interaction

et al. 2020

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The Jovian Auroral Distributions Experiment aboard Juno observed accelerated proton populations connected to Io's footprint tail aurora. While accelerated electron populations have been previously linked with Io's auroral footprint tail aurora, we present new evidence for proton acceleration due to Io's Alfvénic interaction with Jupiter's magnetosphere. Separate populations were accelerated above the Io torus and at high latitudes near Jupiter. The timing suggests the acceleration is due to Alfvén waves associated with Io's Main Alfvén Wing. The inferred high-latitude proton acceleration region spans 0.9-2.5 Jovian radii in altitude, comparable to the expected location for electron acceleration, and suggests the associated Alfvén waves are able to accelerate electrons and protons in similar locations. The proton populations magnetically connected to Io's orbit are recently perturbed, equilibrating with the nominal torus plasma population on a timescale smaller than Io's System III orbital period of~13 h, likely due to wave-particle interactions. The tail populations are split into a wake-like structure with distinct inner and outer regions, where the inner region maps to an equatorial width nearly identical to the diameter of Io. The approximately symmetric surrounding outer regions are each slightly smaller than the central region and may be related to Io's atmospheric extent. The nominal, corotational torus proton population exhibits energization throughout all regions, peaking at the anti-Jovian flank of the inner core region mapping to Io's diameter. These proton observations suggest Alfvén waves are capable of accelerating protons in multiple locations and provide further evidence that Io's Alfvénic interaction is bifurcated. Plain Language SummaryThe interaction between Jupiter's moon Io and Jupiter's rapidly rotating magnetic field produces a persistent aurora in Jupiter's upper atmosphere. The Juno spacecraft's trajectory crossed magnetic field lines connected to this aurora. We found that protons are accelerated in multiple places between Jupiter and Io. The interaction is evidenced in two distinct regions, with the central core region mapping to almost exactly the size of Io in the equatorial plane. We also find the protons that comprise the nominal "background" population are hotter in this central region.

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“…The blue vertical lines indicate the typical timescales over which a change in the electrodynamic interaction would propagate after ingress and egress, based on the Alfvén travel times. The orange vertical lines indicate the typical timescale of 20 min of the collapse of Io's atmosphere (see Figure 3 of Tsang et al, 2016) The Alfvén travel time was calculated using a 3-D plasma torus model, combined with the JRM09 magnetic field model (Hinton et al, 2019). This information provides a typical timescale over which one would expect The PJ3 data set provided the best coverage of the footprint during eclipse, as of PJ15 (7 September 2018).…”

Section: Contribution From the Eclipse On The Footprint Emitted Powermentioning

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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Alfvén Wave Propagation in the Io Plasma Torus

Cited by 37 publications

References 44 publications

Juno Reveals New Insights Into Io‐Related Decameter Radio Emissions

Juno Reveals New Insights Into Io‐Related Decameter Radio Emissions

Proton Acceleration by Io's Alfvénic Interaction

Juno‐UVS Observation of the Io Footprint During Solar Eclipse

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