1
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Nichols JD, Badman SV, Baines KH, Brown RH, Bunce EJ, Clarke JT, Cowley SWH, Crary FJ, Dougherty MK, Gérard JC, Grocott A, Grodent D, Kurth WS, Melin H, Mitchell DG, Pryor WR, Stallard TS. Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope. GEOPHYSICAL RESEARCH LETTERS 2014; 41:3323-3330. [PMID: 26074636 PMCID: PMC4459195 DOI: 10.1002/2014gl060186] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 04/28/2014] [Indexed: 05/29/2023]
Abstract
We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ∼330% rigid corotation from near ∼01 h LT toward ∼08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current.
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Affiliation(s)
- J D Nichols
- Department of Physics and Astronomy, University of Leicester Leicester, UK
| | - S V Badman
- Department of Physics and Astronomy, University of Leicester Leicester, UK ; Department of Physics, Lancaster University Lancaster, UK
| | - K H Baines
- Space Science and Engineering Center, University of Wisconsin-Madison Madison, Wisconsin, USA
| | - R H Brown
- Lunar and Planetary Lab, University of Arizona Tucson, Arizona, USA
| | - E J Bunce
- 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
| | - F J Crary
- Laboratory for Atmospheric and Space Physics, University of Colorado Boulder Boulder, Colorado, USA
| | - M K Dougherty
- Blackett Laboratory, Imperial College London London, UK
| | - J-C Gérard
- Laboratoire de Physique Atmospherique et Planetaire, Universite de Liege Liege, Belgium
| | - A Grocott
- Department of Physics and Astronomy, University of Leicester Leicester, UK ; Department of Physics, Lancaster University Lancaster, UK
| | - D Grodent
- Laboratoire de Physique Atmospherique et Planetaire, Universite de Liege Liege, Belgium
| | - W S Kurth
- Department of Physics and Astronomy, University of Iowa Iowa City, Iowa, USA
| | - H Melin
- Department of Physics and Astronomy, University of Leicester Leicester, UK
| | - D G Mitchell
- Applied Physics Laboratory, Johns Hopkins University Laurel, Maryland, USA
| | - W R Pryor
- Department of Science, Central Arizona College Coolidge, Arizona, USA
| | - T S Stallard
- Department of Physics and Astronomy, University of Leicester Leicester, UK
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2
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Meredith CJ, Alexeev II, Badman SV, Belenkaya ES, Cowley SWH, Dougherty MK, Kalegaev VV, Lewis GR, Nichols JD. Saturn's dayside ultraviolet auroras: Evidence for morphological dependence on the direction of the upstream interplanetary magnetic field. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2014; 119:1994-2008. [PMID: 26167441 PMCID: PMC4497471 DOI: 10.1002/2013ja019598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Revised: 02/25/2014] [Accepted: 03/12/2014] [Indexed: 06/04/2023]
Abstract
UNLABELLED We examine a unique data set from seven Hubble Space Telescope (HST) "visits" that imaged Saturn's northern dayside ultraviolet emissions exhibiting usual circumpolar "auroral oval" morphologies, during which Cassini measured the interplanetary magnetic field (IMF) upstream of Saturn's bow shock over intervals of several hours. The auroras generally consist of a dawn arc extending toward noon centered near ∼15° colatitude, together with intermittent patchy forms at ∼10° colatitude and poleward thereof, located between noon and dusk. The dawn arc is a persistent feature, but exhibits variations in position, width, and intensity, which have no clear relationship with the concurrent IMF. However, the patchy postnoon auroras are found to relate to the (suitably lagged and averaged) IMF Bz , being present during all four visits with positive Bz and absent during all three visits with negative Bz . The most continuous such forms occur in the case of strongest positive Bz . These results suggest that the postnoon forms are associated with reconnection and open flux production at Saturn's magnetopause, related to the similarly interpreted bifurcated auroral arc structures previously observed in this local time sector in Cassini Ultraviolet Imaging Spectrograph data, whose details remain unresolved in these HST images. One of the intervals with negative IMF Bz however exhibits a prenoon patch of very high latitude emission extending poleward of the dawn arc to the magnetic/spin pole, suggestive of the occurrence of lobe reconnection. Overall, these data provide evidence of significant IMF dependence in the morphology of Saturn's dayside auroras. KEY POINTS We examine seven cases of joint HST Saturn auroral images and Cassini IMF dataThe persistent but variable dawn arc shows no obvious IMF dependencePatchy postnoon auroras are present for northward IMF but not for southward IMF.
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Affiliation(s)
- C J Meredith
- Department of Physics and Astronomy, University of Leicester Leicester, UK
| | - I I Alexeev
- Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics Moscow, Russian Federation
| | - S V Badman
- Department of Physics and Astronomy, University of Leicester Leicester, UK ; Department of Physics, University of Lancaster Lancaster, UK
| | - E S Belenkaya
- Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics Moscow, Russian Federation
| | - S W H Cowley
- Department of Physics and Astronomy, University of Leicester Leicester, UK
| | - M K Dougherty
- Blackett Laboratory, Imperial College London London, UK
| | - V V Kalegaev
- Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics Moscow, Russian Federation
| | - G R Lewis
- Mullard Space Science Laboratory, University College London Dorking, UK
| | - J D Nichols
- Department of Physics and Astronomy, University of Leicester Leicester, UK
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Stallard TS, Melin H, Miller S, O'Donoghue J, Cowley SWH, Badman SV, Adriani A, Brown RH, Baines KH. Temperature changes and energy inputs in giant planet atmospheres: what we are learning from H3+. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2012; 370:5213-5224. [PMID: 23028167 DOI: 10.1098/rsta.2012.0028] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Since its discovery at Jupiter in 1988, emission from H(3)(+) has been used as a valuable diagnostic tool in our understanding of the upper atmospheres of the giant planets. One of the lasting questions we have about the giant planets is why the measured upper atmosphere temperatures are always consistently hotter than the temperatures expected from solar heating alone. Here, we describe how H(3)(+) forms across each of the planetary disks of Jupiter, Saturn and Uranus, presenting the first observations of equatorial H(3)(+) at Saturn and the first profile of H(3)(+) emission at Uranus not significantly distorted by the effects of the Earth's atmosphere. We also review past observations of variations in temperature measured at Uranus and Jupiter over a wide variety of time scales. To this, we add new observations of temperature changes at Saturn, using observations by Cassini. We conclude that the causes of the significant level of thermal variability observed over all three planets is not only an important question in itself, but that explaining these variations could be the key to answering the more general question of why giant planet upper atmospheres are so hot.
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Affiliation(s)
- Tom S Stallard
- Department of Physics and Astronomy, University of Leicester, Leicester, UK.
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Badman SV, Andrews DJ, Cowley SWH, Lamy L, Provan G, Tao C, Kasahara S, Kimura T, Fujimoto M, Melin H, Stallard T, Brown RH, Baines KH. Rotational modulation and local time dependence of Saturn's infrared H3+auroral intensity. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012ja017990] [Citation(s) in RCA: 30] [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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Badman SV, Achilleos N, Arridge CS, Baines KH, Brown RH, Bunce EJ, Coates AJ, Cowley SWH, Dougherty MK, Fujimoto M, Hospodarsky G, Kasahara S, Kimura T, Melin H, Mitchell DG, Stallard T, Tao C. Cassini observations of ion and electron beams at Saturn and their relationship to infrared auroral arcs. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011ja017222] [Citation(s) in RCA: 44] [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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7
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Radioti A, Grodent D, Gérard JC, Milan SE, Bonfond B, Gustin J, Pryor W. Bifurcations of the main auroral ring at Saturn: ionospheric signatures of consecutive reconnection events at the magnetopause. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011ja016661] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- A. Radioti
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
| | - D. Grodent
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
| | - J.-C. Gérard
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
| | - S. E. Milan
- Department of Physics and Astronomy; University of Leicester; Leicester U. K
| | - B. Bonfond
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
| | - J. Gustin
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
| | - W. Pryor
- Science Department; Central Arizona College; Coolidge Arizona USA
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Grodent D, Gustin J, Gérard JC, Radioti A, Bonfond B, Pryor WR. Small-scale structures in Saturn's ultraviolet aurora. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011ja016818] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- D. Grodent
- Laboratoire de Physique Atmosphérique et Planétaire; Université de Liège; Liège Belgium
| | - J. Gustin
- Laboratoire de Physique Atmosphérique et Planétaire; Université de Liège; Liège Belgium
| | - J.-C. Gérard
- Laboratoire de Physique Atmosphérique et Planétaire; Université de Liège; Liège Belgium
| | - A. Radioti
- Laboratoire de Physique Atmosphérique et Planétaire; Université de Liège; Liège Belgium
| | - B. Bonfond
- Laboratoire de Physique Atmosphérique et Planétaire; Université de Liège; Liège Belgium
| | - W. R. Pryor
- Science Department; Central Arizona College; Coolidge Arizona USA
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9
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Andrews DJ, Cecconi B, Cowley SWH, Dougherty MK, Lamy L, Provan G, Zarka P. Planetary period oscillations in Saturn's magnetosphere: Evidence in magnetic field phase data for rotational modulation of Saturn kilometric radiation emissions. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011ja016636] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- D. J. Andrews
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - B. Cecconi
- LESIA, Observatoire de Paris, CNRS, UPMC; Université Paris VII - Denis Diderot; Meudon France
| | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | | | - L. Lamy
- LESIA, Observatoire de Paris, CNRS, UPMC; Université Paris VII - Denis Diderot; Meudon France
| | - G. Provan
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - P. Zarka
- LESIA, Observatoire de Paris, CNRS, UPMC; Université Paris VII - Denis Diderot; Meudon France
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10
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Galand M, Moore L, Mueller-Wodarg I, Mendillo M, Miller S. Response of Saturn's auroral ionosphere to electron precipitation: Electron density, electron temperature, and electrical conductivity. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja016412] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Marina Galand
- Space and Atmospheric Physics Group, Department of Physics; Imperial College London; London UK
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Luke Moore
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Ingo Mueller-Wodarg
- Space and Atmospheric Physics Group, Department of Physics; Imperial College London; London UK
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Michael Mendillo
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Steve Miller
- Atmospheric Physics Laboratory, Department of Physics and Astronomy; University College London; London UK
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11
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Talboys DL, Bunce EJ, Cowley SWH, Arridge CS, Coates AJ, Dougherty MK. Statistical characteristics of field-aligned currents in Saturn's nightside magnetosphere. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja016102] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- D. L. Talboys
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - E. J. Bunce
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - C. S. Arridge
- Mullard Space Science Laboratory; University College London; London UK
- Centre for Planetary Sciences at UCL/Birkbeck; London UK
| | - A. J. Coates
- Mullard Space Science Laboratory; University College London; London UK
- Centre for Planetary Sciences at UCL/Birkbeck; London UK
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12
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Bunce EJ, Cowley SWH, Talboys DL, Dougherty MK, Lamy L, Kurth WS, Schippers P, Cecconi B, Zarka P, Arridge CS, Coates AJ. Extraordinary field-aligned current signatures in Saturn's high-latitude magnetosphere: Analysis of Cassini data during Revolution 89. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2010ja015612] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- E. J. Bunce
- Department of Physics & Astronomy; University of Leicester; Leicester UK
| | - S. W. H. Cowley
- Department of Physics & Astronomy; University of Leicester; Leicester UK
| | - D. L. Talboys
- Department of Physics & Astronomy; University of Leicester; Leicester UK
| | | | - L. Lamy
- Blackett Laboratory; Imperial College; London UK
| | - W. S. Kurth
- Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA
| | - P. Schippers
- Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA
| | - B. Cecconi
- LESIA, CNRS; Observatoire de Paris; Meudon France
| | - P. Zarka
- LESIA, CNRS; Observatoire de Paris; Meudon France
| | - C. S. Arridge
- Mullard Space Science Laboratory; University College London; Dorking UK
- Centre for Planetary Sciences at UCL/Birkbeck; London UK
| | - A. J. Coates
- Mullard Space Science Laboratory; University College London; Dorking UK
- Centre for Planetary Sciences at UCL/Birkbeck; London UK
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13
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Grodent D, Radioti A, Bonfond B, Gérard JC. On the origin of Saturn's outer auroral emission. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja014901] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Denis Grodent
- LPAP, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
| | - Aikaterini Radioti
- LPAP, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
| | - Bertrand Bonfond
- LPAP, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
| | - Jean-Claude Gérard
- LPAP, Institut d'Astrophysique et de Géophysique; Université de Liège; Liège Belgium
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14
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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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15
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Talboys DL, Arridge CS, Bunce EJ, Coates AJ, Cowley SWH, Dougherty MK. Characterization of auroral current systems in Saturn's magnetosphere: High-latitude Cassini observations. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2008ja013846] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- D. L. Talboys
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - C. S. Arridge
- Mullard Space Science Laboratory; University College London; Dorking UK
- Centre for Planetary Sciences; University College London; London UK
| | - E. J. Bunce
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - A. J. Coates
- Mullard Space Science Laboratory; University College London; Dorking UK
- Centre for Planetary Sciences; University College London; London UK
| | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester UK
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16
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Radioti A, Grodent D, Gérard JC, Roussos E, Paranicas C, Bonfond B, Mitchell DG, Krupp N, Krimigis S, Clarke JT. Transient auroral features at Saturn: Signatures of energetic particle injections in the magnetosphere. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2008ja013632] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- A. Radioti
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liege Belgium
| | - D. Grodent
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liege Belgium
| | - J.-C. Gérard
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liege Belgium
| | - E. Roussos
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - C. Paranicas
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
| | - B. Bonfond
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique; Université de Liège; Liege Belgium
| | - D. G. Mitchell
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
| | - N. Krupp
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - S. Krimigis
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
- Office for Space Research and Applications; Academy of Athens; Athens Greece
| | - J. T. Clarke
- Center for Space Physics; Boston University; Boston Massachusetts USA
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17
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Complex structure within Saturn's infrared aurora. Nature 2008; 456:214-7. [PMID: 19005549 DOI: 10.1038/nature07440] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2008] [Accepted: 09/12/2008] [Indexed: 11/09/2022]
Abstract
The majority of planetary aurorae are produced by electrical currents flowing between the ionosphere and the magnetosphere which accelerate energetic charged particles that hit the upper atmosphere. At Saturn, these processes collisionally excite hydrogen, causing ultraviolet emission, and ionize the hydrogen, leading to H(3)(+) infrared emission. Although the morphology of these aurorae is affected by changes in the solar wind, the source of the currents which produce them is a matter of debate. Recent models predict only weak emission away from the main auroral oval. Here we report images that show emission both poleward and equatorward of the main oval (separated by a region of low emission). The extensive polar emission is highly variable with time, and disappears when the main oval has a spiral morphology; this suggests that although the polar emission may be associated with minor increases in the dynamic pressure from the solar wind, it is not directly linked to strong magnetospheric compressions. This aurora appears to be unique to Saturn and cannot be explained using our current understanding of Saturn's magnetosphere. The equatorward arc of emission exists only on the nightside of the planet, and arises from internal magnetospheric processes that are currently unknown.
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18
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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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19
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Lamy L, Zarka P, Cecconi B, Hess S, Prangé R. Modeling of Saturn kilometric radiation arcs and equatorial shadow zone. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008ja013464] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- L. Lamy
- LESIA, Observatoire de Paris; CNRS, UPMC, Université Paris Diderot; Meudon France
| | - P. Zarka
- LESIA, Observatoire de Paris; CNRS, UPMC, Université Paris Diderot; Meudon France
| | - B. Cecconi
- LESIA, Observatoire de Paris; CNRS, UPMC, Université Paris Diderot; Meudon France
| | - S. Hess
- LESIA, Observatoire de Paris; CNRS, UPMC, Université Paris Diderot; Meudon France
- LUTH, Observatoire de Paris; CNRS, UPMC; Meudon France
| | - R. Prangé
- LESIA, Observatoire de Paris; CNRS, UPMC, Université Paris Diderot; Meudon France
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20
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Bunce EJ, Arridge CS, Clarke JT, Coates AJ, Cowley SWH, Dougherty MK, Gérard JC, Grodent D, Hansen KC, Nichols JD, Southwood DJ, Talboys DL. Origin of Saturn's aurora: Simultaneous observations by Cassini and the Hubble Space Telescope. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008ja013257] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- E. J. Bunce
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - C. S. Arridge
- Mullard Space Science Laboratory; University College London; Dorking UK
| | - J. T. Clarke
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - A. J. Coates
- Mullard Space Science Laboratory; University College London; Dorking UK
| | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | | | - J.-C. Gérard
- Laboratoire de Physique Atmosphérique et Planétaire; Université de Liège; Liège Belgium
| | - D. Grodent
- Laboratoire de Physique Atmosphérique et Planétaire; Université de Liège; Liège Belgium
| | - K. C. Hansen
- Department of Atmospheric, Oceanic, and Space Sciences; University of Michigan; Ann Arbor Michigan USA
| | - J. D. Nichols
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - D. J. Southwood
- Blackett Laboratory; Imperial College; London UK
- European Space Agency, HQ; Paris France
| | - D. L. Talboys
- Department of Physics and Astronomy; University of Leicester; Leicester UK
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Stallard T, Miller S, Melin H, Lystrup M, Cowley SWH, Bunce EJ, Achilleos N, Dougherty M. Jovian-like aurorae on Saturn. Nature 2008; 453:1083-5. [PMID: 18563160 DOI: 10.1038/nature07077] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2007] [Accepted: 04/29/2008] [Indexed: 11/09/2022]
Abstract
Planetary aurorae are formed by energetic charged particles streaming along the planet's magnetic field lines into the upper atmosphere from the surrounding space environment. Earth's main auroral oval is formed through interactions with the solar wind, whereas that at Jupiter is formed through interactions with plasma from the moon Io inside its magnetic field (although other processes form aurorae at both planets). At Saturn, only the main auroral oval has previously been observed and there remains much debate over its origin. Here we report the discovery of a secondary oval at Saturn that is approximately 25 per cent as bright as the main oval, and we show this to be caused by interaction with the middle magnetosphere around the planet. This is a weak equivalent of Jupiter's main oval, its relative dimness being due to the lack of as large a source of ions as Jupiter's volcanic moon Io. This result suggests that differences seen in the auroral emissions from Saturn and Jupiter are due to scaling differences in the conditions at each of these two planets, whereas the underlying formation processes are the same.
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Affiliation(s)
- Tom Stallard
- Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK.
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22
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Wannawichian S, Clarke JT, Pontius DH. Interaction evidence between Enceladus' atmosphere and Saturn's magnetosphere. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007ja012899] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- S. Wannawichian
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - J. T. Clarke
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - D. H. Pontius
- Physics Department; Birmingham-Southern College; Birmingham Alabama USA
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23
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Grodent D, Gérard JC, Radioti A, Bonfond B, Saglam A. Jupiter’s changing auroral location. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007ja012601] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Denis Grodent
- Laboratory for Planetary and Atmospheric Physics; Université de Liège; Belgium
| | - Jean-Claude Gérard
- Laboratory for Planetary and Atmospheric Physics; Université de Liège; Belgium
| | - Aikaterini Radioti
- Laboratory for Planetary and Atmospheric Physics; Université de Liège; Belgium
| | - Bertrand Bonfond
- Laboratory for Planetary and Atmospheric Physics; Université de Liège; Belgium
| | - Adem Saglam
- Laboratory for Planetary and Atmospheric Physics; Université de Liège; Belgium
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24
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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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25
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Saur J, Mauk BH, Mitchell DG, Krupp N, Khurana KK, Livi S, Krimigis SM, Newell PT, Williams DJ, Brandt PC, Lagg A, Roussos E, Dougherty MK. Anti-planetward auroral electron beams at Saturn. Nature 2006; 439:699-702. [PMID: 16467832 DOI: 10.1038/nature04401] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2005] [Accepted: 11/02/2005] [Indexed: 11/10/2022]
Abstract
Strong discrete aurorae on Earth are excited by electrons, which are accelerated along magnetic field lines towards the planet. Surprisingly, electrons accelerated in the opposite direction have been recently observed. The mechanisms and significance of this anti-earthward acceleration are highly uncertain because only earthward acceleration was traditionally considered, and observations remain limited. It is also unclear whether upward acceleration of the electrons is a necessary part of the auroral process or simply a special feature of Earth's complex space environment. Here we report anti-planetward acceleration of electron beams in Saturn's magnetosphere along field lines that statistically map into regions of aurora. The energy spectrum of these beams is qualitatively similar to the ones observed at Earth, and the energy fluxes in the observed beams are comparable with the energies required to excite Saturn's aurora. These beams, along with the observations at Earth and the barely understood electron beams in Jupiter's magnetosphere, demonstrate that anti-planetward acceleration is a universal feature of aurorae. The energy contained in the beams shows that upward acceleration is an essential part of the overall auroral process.
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Affiliation(s)
- J Saur
- Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, Maryland 20723, USA.
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26
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Sittler EC, Blanc MF, Richardson JD. Proposed model for Saturn's auroral response to the solar wind: Centrifugal instability model. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005ja011191] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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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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28
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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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29
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Jackman CM. Interplanetary conditions and magnetospheric dynamics during the Cassini orbit insertion fly-through of Saturn's magnetosphere. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2005ja011054] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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