References of "Bunce, EJ"
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See detailMagnetospheric Science Objectives of the Juno Mission
Bagenal, Fran; Adriani, A.; Allegrini, F. et al

in Space Science Reviews (2014)

In July 2016, NASA’s Juno mission becomes the first spacecraft to enter polar orbit of Jupiter and enture deep into unexplored polar territories of the magnetosphere. Focusing on these polar regions, we ... [more ▼]

In July 2016, NASA’s Juno mission becomes the first spacecraft to enter polar orbit of Jupiter and enture deep into unexplored polar territories of the magnetosphere. Focusing on these polar regions, we review current understanding of the structure and dynamics of the magnetosphere and summarize the outstanding issues. The Juno mission profile involves (a) a several-week approach from the dawn side of Jupiter’s magnetosphere, with an orbit-insertion maneuver on July 6, 2016; (b) a 107-day capture orbit, also on the dawn flank; and (c) a series of thirty 11-day science orbits with the spacecraft flying over Jupiter’s poles and ducking under the radiation belts. We show how Juno’s view of the magnetosphere evolves over the year of science orbits. The Juno spacecraft carries a range of instruments that take particles and fields measurements, remote sensing observations of auroral emissions at UV, visible, IR and radio wavelengths, and detect microwave emission from Jupiter’s radiation belts. We summarize how these Juno measurements address issues of auroral processes, microphysical plasma physics, ionosphere-magnetosphere and satellite-magnetosphere coupling, sources and sinks of plasma, the radiation belts, and the dynamics of the outer magnetosphere. To reach Jupiter, the Juno spacecraft passed close to the Earth on October 9, 2013, gaining the necessary energy to get to Jupiter. The Earth flyby provided an opportunity to test Juno’s instrumentation as well as take scientific data in the terrestrial magnetosphere, in conjunction with ground-based and Earth-orbiting assets. [less ▲]

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See detailAuroral counterpart of magnetic field dipolarizations in Saturn’s tail
Jackman, C.M.; Achilleos, N.; Cowley, S.W.H. et al

in Planetary and Space Science (2013)

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See detailEvidence of upward filed-aligned currents at the open-closed field line boundary in Saturn's noon magnetosphere: observations and theory
Bunce, E. J.; Cowley, S. W. H.; Talboys, D. L. et al

Conference (2007, June 26)

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See detailResponse of Jupiter's UV auroras to interplanetary conditions as observed by the Hubble Space Telescope during the Cassini flyby campaign
Nichols, J. D.; Bunce, E. J.; Clarke, John T. et al

in Journal of Geophysical Research. Space Physics (2007), 112(A2),

We provide a first detailed discussion of the relation between the set of Jovian UV auroral images observed by the Hubble Space Telescope ( HST) in December 2000 to January 2001 and simultaneous ... [more ▼]

We provide a first detailed discussion of the relation between the set of Jovian UV auroral images observed by the Hubble Space Telescope ( HST) in December 2000 to January 2001 and simultaneous interplanetary data obtained by Cassini during its Jupiter flyby. Examination of the interplanetary data surrounding all seven HST observation intervals shows that by chance six of them correspond to solar wind rarefaction regions, which follow compressions by periods of similar to 2 to similar to 6 days. Only one imaging interval, on 13 January 2001, corresponds to a compression region of generally elevated, but highly variable, solar wind dynamic pressure and interplanetary field strength. We have thus first examined the images corresponding to rarefaction regions in order to establish the range of behaviors that occur under these known conditions, which then act as a benchmark against which the compression region images can be compared. The rarefaction region images show relatively consistent properties of the main oval auroras, though differing in detail from interval to interval. The polar auroras show more variability, with the patchy ("swirl") auroras in the central region sometimes forming a diffuse ring structure and at other times being more uniformly distributed, while the "active region" auroras at dusk vary markedly from weak emissions to bright arc-like forms, the latter possibly being associated with intervals within similar to 2 - 3 days of a previous solar wind compression. The two images obtained in the compression region on 13 January 2001 then show remarkably different properties in all the auroral components. The main oval is found to be brighter over its whole length by factors of two to three compared with the rarefaction region images, while its position remains essentially unchanged, close to the usual reference oval. However, bright contiguous "active region" auroras in the postnoon and dusk sector then widen the overall auroral distribution in that sector by up to similar to 5 degrees in the poleward direction. The region of patchy polar auroras is also found to expand to cover essentially the whole of the remaining area of the polar cap, with a much-narrowed darker zone just poleward of the main oval in the dawn and prenoon sector. We discuss whether these enhanced emissions are characteristic of the few-day compression region as a whole or of more localized conditions occurring within the compression region and conclude that the latter is more likely. Examination of the relevant interplanetary data then shows that the brightened images are associated with an interval of significant magnetospheric dynamics, involving a modest compression of the magnetosphere followed by an extended major expansion. [less ▲]

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See detailOpen flux estimates in Saturn's magnetosphere during the January 2004 Cassini-HST campaign, and implications for reconnection rates
Badman, S. V.; Bunce, E. J.; Clarke, J. T. et al

in Journal of Geophysical Research. Space Physics (2005), 110(A11),

During 8-30 January 2004, a sequence of 68 UV images of Saturn's southern aurora was obtained by the Hubble Space Telescope (HST), coordinated for the first time with measurements of the upstream ... [more ▼]

During 8-30 January 2004, a sequence of 68 UV images of Saturn's southern aurora was obtained by the Hubble Space Telescope (HST), coordinated for the first time with measurements of the upstream interplanetary conditions made by the Cassini spacecraft. Using the poleward edge of the observed aurora as a proxy for the open-closed field line boundary, the open flux content of the southern polar region has been estimated. It is found to range from similar to 15 to similar to 50 GWb during the interval, such a large variation providing evidence of a significant magnetospheric interaction with the solar wind, in particular with the interplanetary structures associated with corotating interaction regions (CIRs). The open flux is found to decline slowly during a rarefaction region in which the interplanetary magnetic field remained very weak, while decreasing sharply in association with the onset of CIR-related solar wind compressions. Such decreases are indicative of the dominating role of open flux closure in Saturn's tail during these intervals. Increases in open flux are found to occur in the higher-field compression regions after the onsets, and in a following rarefaction region of intermediate field strength. These increases are indicative of the dominating role of open flux production at Saturn's magnetopause during these intervals. The rate of open flux production has been estimated from the upstream interplanetary data using an empirical formula based on experience at Earth, with typical values varying from similar to 10 kV during the weak-field rarefaction region, to similar to 200 kV during the strong-field compression. These values have been integrated over time between individual HST image sets to estimate the total open flux produced during these intervals. Comparison with the changes in open flux obtained from the auroral images then allows us to estimate the amount of open flux closed during these intervals, and hence the averaged tail reconnection rates. Intermittent intervals of tail reconnection at rates of similar to 30-60 kV are inferred in rarefaction regions, while compression regions are characterised by rates of similar to 100-200 kV, these values representing averages over the similar to 2-day intervals between HST image sequences. [less ▲]

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See detailVariable morphology of Saturn's southern ultraviolet aurora
Grodent, Denis ULg; Gérard, Jean-Claude ULg; Cowley, S. W. H. et al

in Journal of Geophysical Research. Space Physics (2005), 110(A7),

The Space Telescope Imaging Spectrograph camera on board Hubble Space Telescope obtained 68 FUV images of Saturn's southern auroral emission between 8 and 30 January 2004, during Cassini's approach to ... [more ▼]

The Space Telescope Imaging Spectrograph camera on board Hubble Space Telescope obtained 68 FUV images of Saturn's southern auroral emission between 8 and 30 January 2004, during Cassini's approach to Saturn's magnetosphere. The HST observations took place in four different solar wind regimes with a low-field rarefaction region from 8 to 16 January, a minor compression event on 17 January, a rarefaction region with intermediate field strengths from 19 to 25 January, and a major compression region from 26 to 30 January. The images have been projected onto polar maps in order to characterize and compare the general morphology of the auroral emission. The first 20 images were obtained during a period covering about 70% of one full rotation of Saturn. They show that the bright ring of auroral emission actually consists of several arcs of different width and brightness and forming along different parallels. Overall, the auroral region is shown to rotate at similar to 65% of the full planetary rotation, although the angular velocity of some isolated auroral structures constantly decrease with time, down to 20%. The strongest auroral precipitations are observed in the morning sector. The polar projections of the 48 remaining images confirm dramatic changes in morphology, characterized by different average zones. During the campaign, short intervals during which the auroral region is significantly contracted and clearly forms a spiral were followed by intervals of reinflation of the auroral region. It is suggested that the two major auroral contraction events corresponded to the arrival of the solar wind shocks observed by Cassini on 17 January and 25 January. The present analysis indicates that Saturn's auroral morphology responds to the solar wind conditions at Saturn. [less ▲]

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See detailMorphological differences between Saturn's ultraviolet aurorae and those of Earth and Jupiter
Clarke, J. T.; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

in Nature (2005), 433(7027), 717-719

It has often been stated that Saturn's magnetosphere and aurorae are intermediate between those of Earth, where the dominant processes are solar wind driven(1), and those of Jupiter, where processes are ... [more ▼]

It has often been stated that Saturn's magnetosphere and aurorae are intermediate between those of Earth, where the dominant processes are solar wind driven(1), and those of Jupiter, where processes are driven by a large source of internal plasma(2-4). But this view is based on information about Saturn that is far inferior to what is now available. Here we report ultraviolet images of Saturn, which, when combined with simultaneous Cassini measurements of the solar wind(5) and Saturn kilometric radio emission(6), demonstrate that its aurorae differ morphologically from those of both Earth and Jupiter. Saturn's auroral emissions vary slowly; some features appear in partial corotation whereas others are fixed to the solar wind direction; the auroral oval shifts quickly in latitude; and the aurora is often not centred on the magnetic pole nor closed on itself. In response to a large increase in solar wind dynamic pressure(5) Saturn's aurora brightened dramatically, the brightest auroral emissions moved to higher latitudes, and the dawn side polar regions were filled with intense emissions. The brightening is reminiscent of terrestrial aurorae, but the other two variations are not. Rather than being intermediate between the Earth and Jupiter, Saturn's auroral emissions behave fundamentally differently from those at the other planets. [less ▲]

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See detailReconnection in a rotation-dominated magnetosphere and its relation to Saturn's auroral dynamics
Cowley, S. W. H.; Badman, S. V.; Bunce, E. J. et al

in Journal of Geophysical Research. Space Physics (2005), 110(A2),

[1] The first extended series of observations of Saturn's auroral emissions, undertaken by the Hubble Space Telescope in January 2004 in conjunction with measurements of the upstream solar wind and ... [more ▼]

[1] The first extended series of observations of Saturn's auroral emissions, undertaken by the Hubble Space Telescope in January 2004 in conjunction with measurements of the upstream solar wind and interplanetary magnetic field ( IMF) by the Cassini spacecraft, have revealed a strong auroral response to the interplanetary medium. Following the arrival of the forward shock of a corotating interaction region compression, bright auroras were first observed to expand significantly poleward in the dawn sector such that the area of the polar cap was much reduced, following which the auroral morphology evolved into a spiral structure around the pole. We propose that these auroral effects are produced by compression- induced reconnection of a significant fraction of the open flux present in Saturn's open tail lobes, as has also been observed to occur at Earth, followed by subcorotation of the newly closed flux tubes in the outer magnetosphere region due to the action of the ionospheric torque. We show that the combined action of reconnection and rotation naturally gives rise to spiral structures on newly opened and newly closed field lines, the latter being in the same sense as observed in the auroral images. The magnetospheric corollary of the dynamic scenario outlined here is that corotating interaction region- induced magnetospheric compressions and tail collapses should be accompanied by hot plasma injection into the outer magnetosphere, first in the midnight and dawn sector, and second at increasing local times via noon and dusk. We discuss how this scenario leads to a strong correlation of auroral and related disturbances at Saturn with the dynamic pressure of the solar wind, rather than to a correlation with the northsouth component of the IMF as observed at Earth, even though the underlying physics is similar, related to the transport of magnetic flux to and from the tail in the Dungey cycle. [less ▲]

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