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Lamy L, Cecconi B, Prangé R, Zarka P, Nichols JD, Clarke JT. An auroral oval at the footprint of Saturn's kilometric radio sources, colocated with the UV aurorae. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2009ja014401] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- L. Lamy
- LESIA, Observatoire de Paris, UPMC, CNRS; Université Paris Diderot; Meudon France
- Space and Atmospheric Physics Group, Blackett Laboratory; Imperial College London; London UK
| | - B. Cecconi
- LESIA, Observatoire de Paris, UPMC, CNRS; Université Paris Diderot; Meudon France
| | - R. Prangé
- LESIA, Observatoire de Paris, UPMC, CNRS; Université Paris Diderot; Meudon France
| | - P. Zarka
- LESIA, Observatoire de Paris, UPMC, CNRS; Université Paris Diderot; Meudon France
| | - J. D. Nichols
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - J. T. Clarke
- Center for Space Physics; Boston University; Boston Massachusetts USA
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Nichols JD, Clarke JT, Cowley SWH, Duval J, Farmer AJ, Gérard JC, Grodent D, Wannawichian S. Oscillation of Saturn's southern auroral oval. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008ja013444] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- J. D. Nichols
- Center for Space Physics; Boston University; Boston Massachusetts USA
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - J. T. Clarke
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - J. Duval
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - A. J. Farmer
- Harvard-Smithsonian Center for Astrophysics; Harvard University; Cambridge Massachusetts USA
| | - J.-C. Gérard
- Institut d'Astrophysique et de Géophysique; Université de Liège; Liege Belgium
| | - D. Grodent
- Institut d'Astrophysique et de Géophysique; Université de Liège; Liege Belgium
| | - S. Wannawichian
- Center for Space Physics; Boston University; Boston Massachusetts USA
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Gérard JC, Grodent D, Cowley SWH, Mitchell DG, Kurth WS, Clarke JT, Bunce EJ, Nichols JD, Dougherty MK, Crary FJ, Coates AJ. Saturn's auroral morphology and activity during quiet magnetospheric conditions. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2006ja011965] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Clarke JT, Gérard JC, Grodent D, Wannawichian S, Gustin J, Connerney J, Crary F, Dougherty M, Kurth W, Cowley SWH, Bunce EJ, Hill T, Kim J. Morphological differences between Saturn's ultraviolet aurorae and those of Earth and Jupiter. Nature 2005; 433:717-9. [PMID: 15716945 DOI: 10.1038/nature03331] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2004] [Accepted: 12/22/2004] [Indexed: 11/10/2022]
Abstract
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, and those of Jupiter, where processes are driven by a large source of internal plasma. 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 and Saturn kilometric radio emission, 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 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.
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Affiliation(s)
- J T Clarke
- Boston University, 725 Commonwealth Avenue, Boston, Massachusetts 02215, USA.
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Badman SV, Bunce EJ, Clarke JT, Cowley SWH, Gérard JC, Grodent D, Milan SE. Open flux estimates in Saturn's magnetosphere during the January 2004 Cassini-HST campaign, and implications for reconnection rates. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2005ja011240] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Gérard JC, Bunce EJ, Grodent D, Cowley SWH, Clarke JT, Badman SV. Signature of Saturn's auroral cusp: Simultaneous Hubble Space Telescope FUV observations and upstream solar wind monitoring. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2005ja011094] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Gérard JC. Characteristics of Saturn's FUV aurora observed with the Space Telescope Imaging Spectrograph. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2004ja010513] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Jackman CM. Interplanetary magnetic field at ∼9 AU during the declining phase of the solar cycle and its implications for Saturn's magnetospheric dynamics. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2004ja010614] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Cowley SWH. A simple quantitative model of plasma flows and currents in Saturn's polar ionosphere. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003ja010375] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Trauger JT, Clarke JT, Ballester GE, Evans RW, Burrows CJ, Crisp D, Gallagher JS, Griffiths RE, Hester JJ, Hoessel JG, Holtzman JA, Krist JE, Mould JR, Sahai R, Scowen PA, Stapelfeldt KR, Watson AM. Saturn's hydrogen aurora: Wide field and planetary camera 2 imaging from the Hubble Space Telescope. ACTA ACUST UNITED AC 1998. [DOI: 10.1029/98je01324] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Shemansky DE, Hall DT. The distribution of atomic hydrogen in the magnetosphere of Saturn. ACTA ACUST UNITED AC 1992. [DOI: 10.1029/91ja02805] [Citation(s) in RCA: 92] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Clarke JT, Hudson MK, Yung YL. The excitation of the far ultraviolet electroglow emissions on Uranus, Saturn, and Jupiter. JOURNAL OF GEOPHYSICAL RESEARCH 1987; 92:15139-47. [PMID: 11542130 DOI: 10.1029/ja092ia13p15139] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We propose that the diffuse FUV emissions of H and H2 in excess of photoelectron excitation observed from the sunlit atmospheres of Uranus, Saturn, and Jupiter are produced by electric field acceleration of photoelectrons and ions locally in the upper atmospheres. This in situ acceleration is required to satisfy the many observational constraints on the altitude distribution, exciting particle energy, and total input energy requirements of the electroglow mechanism. We further suggest that a primary mechanism leading to this acceleration is an ionospheric dynamo, which is created in the same manner as the Earth's dynamo. The calculated altitude of charge separation by the neutral wind drag on ions across magnetic field lines is consistent with the observed peaks in electroglow emissions from the Voyager ultraviolet spectrometer limb scan data on both Saturn (near the homopause) and Uranus (just above the homopause). This dynamo action therefore appears to initiate the acceleration process, which must have the form of field-aligned potentials to accelerate the magnetized electrons. We propose that these field-aligned potentials are due to anomalous resistivity, which results from sufficiently high field-aligned currents in the ionosphere to generate plasma instabilities and therefore runaway electrons and ions above some critical lower initial energy. There are multiple candidate processes for inducing these currents, including polarization in the equivalent F regions and inner magnetospheric convection, and each of these processes should exhibit latitudinal structure. The acceleration of low-energy electrons in an H2 atmosphere preferentially results in FUV radiation and further ionization, whereas electron acceleration in a nitrogen/oxygen atmosphere such as the Earth's is dominated by elastic scattering and thus results in electric currents. Individual electron and proton collisions with H2 molecules will result in excitation, ionization, and heating, so that considerable enhancement of the ionospheric density and heating of the upper atmosphere will accompany the FUV emission.
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Affiliation(s)
- J T Clarke
- Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
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Clarke J, Durrance S, Atreya S, Barnes A, Belcher J, Festou M, Imhoff C, Mihalov J, Moos W, Murthy J, Pradhan A, Skinner T. Continued observations of the H Ly α emission from Uranus. ACTA ACUST UNITED AC 1986. [DOI: 10.1029/ja091ia08p08771] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Cheng AF, Lanzerotti LJ, Pirronello V. Charged particle sputtering of ice surfaces in Saturn's magnetosphere. ACTA ACUST UNITED AC 1982. [DOI: 10.1029/ja087ia06p04567] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Gérard JC, Singh V. A model of energy deposition of energetic electrons and EUV emission in the Jovian and Saturnian atmospheres and implications. ACTA ACUST UNITED AC 1982. [DOI: 10.1029/ja087ia06p04525] [Citation(s) in RCA: 69] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Broadfoot AL, Sandel BR, Shemansky DE, Holberg JB, Smith GR, Strobel DF, McConnell JC, Kumar S, Hunten DM, Atreya SK, Donahue TM, Moos HW, Bertaux JL, Blamont JE, Pomphrey RB, Linick S. Extreme Ultraviolet Observations from Voyager 1 Encounter with Saturn. Science 1981; 212:206-11. [PMID: 17783831 DOI: 10.1126/science.212.4491.206] [Citation(s) in RCA: 319] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The global hydrogen Lyman alpha, helium (584 angstroms), and molecular hydrogen band emissions from Saturn are qualitatively similar to those of Jupiter, but the Saturn observations emphasize that the H(2) band excitation mechanism is closely related to the solar flux. Auroras occur near 80 degrees latitude, suggesting Earth-like magnetotail activity, quite different from the dominant Io plasma torus mechanism at Jupiter. No ion emissions have been detected from the magnetosphere of Saturn, but the rings have a hydrogen atmosphere; atomic hydrogen is also present in a torus between 8 and 25 Saturn radii. Nitrogen emission excited by particles has been detected in the Titan dayglow and bright limb scans. Enhancement of the nitrogen emission is observed in the region of interaction between Titan's atmosphere and the corotating plasma in Saturn's plasmasphere. No particle-excited emission has been detected from the dark atmosphere of Titan. The absorption profile of the atmosphere determined by the solar occultation experiment, combined with constraints from the dayglow observations and temperature information, indicate that N(2) is the dominant species. A double layer structure has been detected above Titan's limb. One of the layers may be related to visible layers in the images of Titan.
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