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Stallard TS, Baines KH, Melin H, Bradley TJ, Moore L, O'Donoghue J, Miller S, Chowdhury MN, Badman SV, Allison HJ, Roussos E. Local-time averaged maps of H 3+ emission, temperature and ion winds. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2019; 377:20180405. [PMID: 31378177 PMCID: PMC6710899 DOI: 10.1098/rsta.2018.0405] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 06/19/2019] [Indexed: 05/20/2023]
Abstract
We present Keck-NIRSPEC observations of Saturn's [Formula: see text] aurora taken over a period of a month, in support of the Cassini mission's 'Grand Finale'. These observations produce two-dimensional maps of Saturn's [Formula: see text] temperature and ion winds for the first time. These maps show surprising complexity, with different morphologies seen in each night. The [Formula: see text] ion winds reveal multiple arcs of 0.5-1 km s-1 ion flows inside the main auroral emission. Although these arcs of flow occur in different locations each night, they show intricate structures, including mirrored flows on the dawn and dusk of the planet. These flows do not match with the predicted flows from models of either axisymmetric currents driven by the Solar Wind or outer magnetosphere, or the planetary periodic currents associated with Saturn's variable rotation rate. The average of the ion wind flows across all the nights reveals a single narrow and focused approximately 0.3 km s-1 flow on the dawn side and broader and more extensive 1-2 km s-1 sub-corotation, spilt into multiple arcs, on the dusk side. The temperature maps reveal sharp gradients in ionospheric temperatures, varying between 300 and 600 K across the auroral region. These temperature changes are localized, resulting in hot and cold spots across the auroral region. These appear to be somewhat stable over several nights, but change significantly over longer periods. The position of these temperature extremes is not well organized by the planetary period and there is no evidence for a thermospheric driver of the planetary period current system. Since no past magnetospheric or thermospheric models explain the rich complexity observed here, these measurements represent a fantastic new resource, revealing the complexity of the interaction between Saturn's thermosphere, ionosphere and magnetosphere. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.
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Affiliation(s)
- Tom S. Stallard
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
- e-mail:
| | - Kevin H. Baines
- Atmospheric Oceanic and Space Science University of Wisconsin-Madison, 1225 W Dayton St, Madison, WI 53706, USA
| | - Henrik Melin
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - Thomas J. Bradley
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - Luke Moore
- Center for Space Physics, Boston University, 725 Commonwealth Avenue, Room 506, Boston, MA 02215, USA
| | - James O'Donoghue
- Institute of Space and Astronautical Science, JAXA, Yoshinodai 3-1-1, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
| | - Steve Miller
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
| | - Mohammad N. Chowdhury
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - Sarah V. Badman
- Department of Physics, Lancaster University, Bailrigg, Lancaster LA1 4YW, UK
| | | | - Elias Roussos
- Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077, Goettingen, Germany
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Jasinski JM, Arridge CS, Lamy L, Leisner JS, Thomsen MF, Mitchell DG, Coates AJ, Radioti A, Jones GH, Roussos E, Krupp N, Grodent D, Dougherty MK, Waite JH. Cusp observation at Saturn's high-latitude magnetosphere by the Cassini spacecraft. GEOPHYSICAL RESEARCH LETTERS 2014; 41:1382-1388. [PMID: 25821276 PMCID: PMC4373149 DOI: 10.1002/2014gl059319] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Accepted: 02/13/2014] [Indexed: 05/24/2023]
Abstract
UNLABELLED We report on the first analysis of magnetospheric cusp observations at Saturn by multiple in situ instruments onboard the Cassini spacecraft. Using this we infer the process of reconnection was occurring at Saturn's magnetopause. This agrees with remote observations that showed the associated auroral signatures of reconnection. Cassini crossed the northern cusp around noon local time along a poleward trajectory. The spacecraft observed ion energy-latitude dispersions-a characteristic signature of the terrestrial cusp. This ion dispersion is "stepped," which shows that the reconnection is pulsed. The ion energy-pitch angle dispersions suggest that the field-aligned distance from the cusp to the reconnection site varies between ∼27 and 51 RS . An intensification of lower frequencies of the Saturn kilometric radiation emissions suggests the prior arrival of a solar wind shock front, compressing the magnetosphere and providing more favorable conditions for magnetopause reconnection. KEY POINTS We observe evidence for reconnection in the cusp plasma at SaturnWe present evidence that the reconnection process can be pulsed at SaturnSaturn's cusp shows similar characteristics to the terrestrial cusp.
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Affiliation(s)
- J M Jasinski
- Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London Dorking, Surrey, UK ; Centre for Planetary Sciences, UCL/Birkbeck London, UK
| | - C S Arridge
- Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London Dorking, Surrey, UK ; Centre for Planetary Sciences, UCL/Birkbeck London, UK
| | - L Lamy
- LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris 6, Université Paris Diderot Meudon, France
| | - J S Leisner
- Blackett Laboratory, Department of Physics, Imperial College London London, UK
| | - M F Thomsen
- Planetary Science Institute Tucson, Arizona, USA
| | - D G Mitchell
- Applied Physics Laboratory, Johns Hopkins University Laurel, Maryland, USA
| | - A J Coates
- Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London Dorking, Surrey, UK ; Centre for Planetary Sciences, UCL/Birkbeck London, UK
| | - A Radioti
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique, Université de Liége Liege, Belgium
| | - G H Jones
- Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London Dorking, Surrey, UK ; Centre for Planetary Sciences, UCL/Birkbeck London, UK
| | - E Roussos
- Max-Planck-Institut für Sonnensystemforschung Göttingen, Germany
| | - N Krupp
- Max-Planck-Institut für Sonnensystemforschung Göttingen, Germany
| | - D Grodent
- Laboratoire de Physique Atmosphérique et Planétaire, Institut d'Astrophysique et de Géophysique, Université de Liége Liege, Belgium
| | | | - J H Waite
- Southwest Research Institute, Space Science and Engineering Division San Antonio, Texas, USA
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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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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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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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