Detailed study of FUV Jovian auroral features with the post‐COSTAR HST faint object camera

Prangé, Renée; Rego, D.; Pallier, Laurent; Connerney, J. E. P.; Zarka, Philippe; Queinnec, Julien

doi:10.1029/98je01128

Cited by 108 publications

(100 citation statements)

References 28 publications

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“…The calculations of Cowley and Bunce (2001) and Cowley et al (2002Cowley et al ( , 2003 yielded field-aligned voltages of ∼25-100 kV for typical parameters, sufficient to produce precipitating electron energy fluxes of up to several tens of mW m −2 , thus leading to 'main oval' auroras of up to several hundred kR in brightness, comparable to observed intensities (e.g. Satoh et al, 1996;Prangé et al, 1998;Clarke et al, 1998;Vasavada et al, 1999;Pallier and Prangé, 2001;Grodent et al, 2003). Most recently, Nichols and Cowley (2004) have also self-consistently included the effect of precipitation-induced enhancement of the ionospheric Pedersen conductivity.…”

Section: Introductionmentioning

confidence: 88%

Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: effect of magnetosphere-ionosphere decoupling by field-aligned auroral voltages

Nichols

Cowley

2005

Ann. Geophys.

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Abstract.We consider the effect of field-aligned voltages on the magnetosphere-ionosphere coupling current system associated with the breakdown of rigid corotation of equatorial plasma in Jupiter's middle magnetosphere. Previous analyses have assumed perfect mapping of the electric field and flow along equipotential field lines between the equatorial plane and the ionosphere, whereas it has been shown that substantial field-aligned voltages must exist to drive the field-aligned currents associated with the main auroral oval. The effect of these field-aligned voltages is to decouple the flow of the equatorial and ionospheric plasma, such that their angular velocities are in general different from each other. In this paper we self-consistently include the field-aligned voltages in computing the plasma flows and currents in the system. A third order differential equation is derived for the ionospheric plasma angular velocity, and a power series solution obtained which reduces to previous solutions in the limit that the field-aligned voltage is small. Results are obtained to second order in the power series, and are compared to the original zeroth order results with no parallel voltage. We find that for system parameters appropriate to Jupiter the effect of the field-aligned voltages on the solutions is small, thus validating the results of previously-published analyses.

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Section: Introductionmentioning

confidence: 88%

Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: effect of magnetosphere-ionosphere decoupling by field-aligned auroral voltages

Nichols

Cowley

2005

Ann. Geophys.

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“…Satoh et al, 1996;Prangé et al, 1998;Clarke et al, 1998;Vasavada et al, 1999), though in this case they appear to be considerably less variable in both UT and local time (Grodent et al, 2003). However, these emissions, located at ∼15 • magnetic colatitude, map magnetically to middle magnetosphere field lines at equatorial distances beyond ∼20 R J (Gérard et al, 1994;Prangé et al, 1998;Clarke et al, 1998), and have been suggested to be associated with the field-aligned currents of a current system which enforces partial corotation of plasma moving outward from the Io torus Hill, 2001;Southwood and Kivelson, 2001). Cowley and have set up a quantitative empirical model of this current system, and have shown using Knight's (1973) kinetic theory that the precipitated energy flux of downward-accelerated auroral electrons associated with the region of upward current is sufficient to produce the ∼100 kR to ∼1 MR auroras observed.…”

Section: Introductionmentioning

confidence: 99%

Corotation-driven magnetosphere-ionosphere coupling currents in Saturn’s magnetosphere and their relation to the auroras

2003

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Abstract.We calculate the latitude profile of the equatorward-directed ionospheric Pedersen currents that are driven in Saturn's ionosphere by partial corotation of the magnetospheric plasma. The calculation incorporates the flattened figure of the planet, a model of Saturn's magnetic field derived from spacecraft flyby data, and angular velocity models derived from Voyager plasma data. We also employ an effective height-integrated ionospheric Pedersen conductivity of 1 mho, suggested by a related analysis of Voyager magnetic field data. The Voyager plasma data suggest that on the largest spatial scales, the plasma angular velocity declines from near-rigid corotation with the planet in the inner magnetosphere, to values of about half of rigid corotation at the outer boundary of the region considered. The latter extends to ∼15-20 Saturn radii (R S ) in the equatorial plane, mapping along magnetic field lines to ∼15 • co-latitude in the ionosphere. We find in this case that the ionospheric Pedersen current peaks near the poleward (outer) boundary of this region, and falls toward zero over ∼5 • -10 • equatorward of the boundary as the plasma approaches rigid corotation. The peak current near the poleward boundary, integrated in azimuth, is ∼ 6 MA. The field-aligned current required for continuity is directed out of the ionosphere into the magnetosphere essentially throughout the region, with the current density peaking at ∼10 nA m −2 at ∼20 • co-latitude. We estimate that such current densities are well below the limit requiring field-aligned acceleration of magnetospheric electrons in Saturn's environment (∼70 nA m −2 ), so that no significant auroral features associated with this ring of upward current is anticipated. The observed ultraviolet auroras at Saturn are also found to occur significantly closer to the pole (at ∼10 • -15 • co-latitude), and show considerable temporal and local time variability, contrary to expectations for corotation-related currents. We thus conclude that Saturn's 'main oval' auroras are not associated with corotationenforcing currents as they are at Jupiter, but instead are most probably associated with coupling to the solar wind as at Correspondence to: S. W. H. Cowley (swhc1@ion.le.ac.uk) Earth. At the same time, the Voyager flow observations also suggest the presence of radially localized 'dips' in the plasma angular velocity associated with the moons Dione and Rhea, which are ∼1-2 R S in radial extent in the equatorial plane. The presence of such small-scale flow features, assumed to be azimuthally extended, results in localized several-MA enhancements in the ionospheric Pedersen current, and narrow bi-polar signatures in the field-aligned currents which peak at values an order of magnitude larger than those associated with the large-scale currents. Narrow auroral rings (or partial rings) ∼0.25 • co-latitude wide with intensities ∼1 kiloRayleigh may be formed in the regions of upward field-aligned current under favourable circumstances, located at co-latitudes between ∼17 • and ∼20...

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“…The recent discovery of Earth-like charged particle injections within Jupiter's magnetosphere 14,15 is surprising because Jupiter's magnetosphere is powered mostly from the inside by the rapid but steady planetary rotation rather than from the outside by the variable solar wind. The role of injections in generating auroral emissions at Jupiter has been heretofore unknown, to our knowledge.…”

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confidence: 99%

A pulsating auroral X-ray hot spot on Jupiter

Gladstone

Waite

Grodent

et al. 2002

Nature

203

272

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Detailed study of FUV Jovian auroral features with the post‐COSTAR HST faint object camera

Cited by 108 publications

References 28 publications

Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: effect of magnetosphere-ionosphere decoupling by field-aligned auroral voltages

Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: effect of magnetosphere-ionosphere decoupling by field-aligned auroral voltages

Corotation-driven magnetosphere-ionosphere coupling currents in Saturn’s magnetosphere and their relation to the auroras

A pulsating auroral X-ray hot spot on Jupiter

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