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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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