Cassini UVIS observations of Jupiter's auroral variability

Pryor, W. R.; Stewart, A. I. F.; Esposito, L. W.; McClintock, W. E.; Colwell, Joshua; Jouchoux, A.; Steffl, A. J.; Shemansky, D. E.; Ajello, J. M.; West, Robert A.; Hansen, C. J.; Tsurutani, B. T.; Kurth, W. S.; Hospodarsky, G. B.; Gurnett, D. A.; Hansen, K. C.; Waite, J. H.; Crary, F. J.; Young, D. T.; Krupp, N.; Clarke, J. T.; Grodent, Denis; Dougherty, M. K.

doi:10.1016/j.icarus.2005.05.021

Cited by 39 publications

(42 citation statements)

References 55 publications

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“…A two-zone region of discrete auroral emission will therefore be produced, with emission intensities of order ∼100 kR, and total precipitating powers of ∼1 TW, dominated by the middle magnetosphere. With UV emission efficiencies of ∼10%, the total UV output will thus be ∼100 GW, comparable to typical auroral UV power outputs inferred from both HST and Cassini data (Grodent et al, 2003a, b;Pryor et al, 2005). The power inputs to magnetospheric rotation in each hemisphere are ∼20 TW on open field lines (essentially constant throughout) and ∼200 TW on closed field lines, while that dissipated to atmospheric heating in each hemisphere is ∼200 TW on open field lines (also essentially constant), and ∼100-200 TW on closed field lines, increasing with the extension of the system and consequent sub-corotation of the plasma.…”

Section: Discussionsupporting

confidence: 73%

“…Relevant observations are, however, very sparse. Gurnett et al (2002) and Pryor et al (2005) have reported transient correlated increases in jovian UV and hectometric radio emissions during the Cassini Jupiter fly-by in December 2000-January 2001, that were associated with intervals of high dynamic pressure and field strength in the solar wind, apparently contrary to expectations based on the above discussion. It is notable, however, that the enhanced emissions occur for much shorter intervals than the interplanetary effects, a few hours compared with a few days.…”

Section: Introductionmentioning

confidence: 66%

“…With regard to the issue of which process produces the short-lived intensifications of jovian UV emissions observed in Cassini data e.g. by Gurnett et al (2002) and Pryor et al (2005), our results indicate that in principle these could be due either to a strong rapid compression of the system from an expanded state which induces strong plasma super-corotation with respect to the neutral atmosphere (Fig. 10), or to a strong rapid expansion of the system from a compressed state which induces strong plasma sub-corotation (Fig.…”

Section: Discussionmentioning

confidence: 99%

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Modulation of Jupiter's plasma flow, polar currents, and auroral precipitation by solar wind-induced compressions and expansions of the magnetosphere: a simple theoretical model

2007

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Abstract.We construct a simple model of the plasma flow, magnetosphere-ionosphere coupling currents, and auroral precipitation in Jupiter's magnetosphere, and examine how they respond to compressions and expansions of the system induced by changes in solar wind dynamic pressure. The main simplifying assumption is axi-symmetry, the system being modelled principally to reflect dayside conditions. The model thus describes three magnetospheric regions, namely the middle and outer magnetosphere on closed magnetic field lines bounded by the magnetopause, together with a region of open field lines mapping to the tail. The calculations assume that the system is initially in a state of steady diffusive outflow of iogenic plasma with a particular equatorial magnetopause radius, and that the magnetopause then moves rapidly in or out due to a change in the solar wind dynamic pressure. If the change is sufficiently rapid (∼2-3 h or less) the plasma angular momentum is conserved during the excursion, allowing the modified plasma angular velocity to be calculated from the radial displacement of the field lines, together with the modified magnetosphere-ionosphere coupling currents and auroral precipitation. The properties of these transient states are compared with those of the steady states to which they revert over intervals of ∼1-2 days. Results are shown for rapid compressions of the system from an initially expanded state typical of a solar wind rarefaction region, illustrating the reduction in total precipitating electron power that occurs for modest compressions, followed by partial recovery in the emergent steady state. For major compressions, however, typical of the onset of a solar wind compression region, a brightened transient state occurs in which super-rotation is induced on closed field lines, resulting in a reversal in sense of the usual magnetosphereionosphere coupling current system. Current system reversal results in accelerated auroral electron precipitation occurring Correspondence to: S. W. H. Cowley (swhc1@ion.le.ac.uk) in the outer magnetosphere region rather than in the middle magnetosphere as is usual, with peak energy fluxes occurring just poleward of the boundary between the outer and middle magnetosphere. Plasma sub-corotation is then re-established as steady-state conditions re-emerge, together with the usual sense of flow of the closed field current system and renewed but weakened accelerated electron precipitation in the middle magnetosphere. Results for rapid expansions of the system from an initially compressed state typical of a solar wind compression region are also shown, illustrating the enhancement in precipitating electron power that occurs in the transient state, followed by partial reduction as steady conditions re-emerge.

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Section: Discussionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 99%

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Modulation of Jupiter's plasma flow, polar currents, and auroral precipitation by solar wind-induced compressions and expansions of the magnetosphere: a simple theoretical model

2007

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“…Multidata analysis results showed evidence of correlations between Jupiter's radio emissions at decametric wavelengths and auroral activity and the solar wind structures on timescales of days to a week for that period of time (e.g., Gurnett et al 2002;Prangé et al 2004;Pryor et al 2005;Nichols et al 2007).…”

Section: Discussionmentioning

confidence: 99%

Multifrequency analysis of the Jovian electron-belt radiation during theCassiniflyby of Jupiter

Santos-Costa

Pater

Sault

et al. 2014

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Aims. We examine Very Large Array (VLA) observations of Jupiter to present evidence of fluctuations in the emission produced by the electron belt in January 2001. Investigating the source of fluctuations will provide new opportunities to discuss the scenarios of temporal changes in Jupiter's synchrotron radiation (i.e., the electron belt) in future data analysis and modeling work. Methods. To discuss the electron belt dynamics during the Cassini flyby of Jupiter, we compare the radio measurements from 2−3 January 2001 with VLA observations obtained on 20−21 December 1988, when viewing geometry and array configuration are comparable. All data are scaled to a standard Earth-Jupiter distance of 4.04 AU for comparison purposes. Brightness distribution maps with identical spatial resolutions and cartography of the equatorial radiation are constructed and examined at the wavelengths of ∼21 cm and ∼90 cm. Results. Rotation-averaged maps show that the emission from the equatorial zones of maximum intensity is weaker by ∼5−40%, but the brightness distribution is spatially more extended on 2−3 January 2001, resulting in a total emission at both wavelengths stronger by ∼35%. Between observation periods, the brightness distributions are observed to evolve differently during the planet rotation. Tomographic reconstructions of the equatorial radiation support our conclusion that the electron-belt population was differently distributed around the planet in December 1988 and January 2001. Conclusions. Our analysis of VLA data sets suggests that the spatial distribution of the electron belt on 2−3 January 2001 is different from that usually observed. Our knowledge of solar activity at the time of the Cassini flyby of Jupiter suggests that the emission from the electron radiation belt was responding to external influences, most likely to solar wind structures rather than to solar radio flux, on a timescale of days to a couple of weeks. Combined results from a multisource data analysis -including spacecraft and radio observations -are needed to confirm this relationship.

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“…More detailed understanding was obtained during the Cassini Jupiter flyby in late 2000-early 2001. A combination of Cassini and Galileo spacecraft in situ measurements and remote sensing, along with a program of Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) observations near to closest approach revealed in detail the response of the auroral emissions to changing conditions in the interplanetary medium (Gurnett et al 2002;Pryor et al 2005;). The solar wind during the interval of the encounter, which occurred at solar maximum, was dominated by coronal mass ejections (CMEs), corotating interaction regions (CIRs) and large amplitude stream interactions resulting in deep several-day solar wind rarefaction regions punctuated by strong compressions as highlighted by the interplanetary magnetic field (IMF) magnitude shown in Fig.…”

Section: Jupitermentioning

confidence: 99%

Solar Wind and Internally Driven Dynamics: Influences on Magnetodiscs and Auroral Responses

et al. 2014

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The dynamics of the giant planet magnetodiscs are strongly influenced by planetary rotation. Yet the solar wind must ultimately remove plasma from these rapidly rotating magnetodiscs at the same rate that plasma is transported radially outward from the source regions: the Io and Enceladus plasma tori. It is not clear how the solar wind influences magnetospheric dynamics when the dynamics are dominated by rotation. However, auroral observations provide important clues. We review magnetodisc sources and radial transport and the solar wind interaction with the giant magnetospheres of Jupiter and Saturn in an attempt to connect auroral features with specific drivers. We provide a discussion of auroral signatures that are related to the solar wind interaction and summarize with a discussion of global magnetospheric dynamics as illustrated by global MHD simulations. Many questions remain and it is the intent of this review to highlight several of the most compelling questions for future research.

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Cassini UVIS observations of Jupiter's auroral variability

Cited by 39 publications

References 55 publications

Modulation of Jupiter's plasma flow, polar currents, and auroral precipitation by solar wind-induced compressions and expansions of the magnetosphere: a simple theoretical model

Modulation of Jupiter's plasma flow, polar currents, and auroral precipitation by solar wind-induced compressions and expansions of the magnetosphere: a simple theoretical model

Multifrequency analysis of the Jovian electron-belt radiation during theCassiniflyby of Jupiter

Solar Wind and Internally Driven Dynamics: Influences on Magnetodiscs and Auroral Responses

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