1
|
Lamy L, Zarka P, Cecconi B, Prangé R, Kurth WS, Hospodarsky G, Persoon A, Morooka M, Wahlund JE, Hunt GJ. The low-frequency source of Saturn’s kilometric radiation. Science 2018; 362:362/6410/eaat2027. [DOI: 10.1126/science.aat2027] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Accepted: 09/04/2018] [Indexed: 11/02/2022]
Abstract
Understanding how auroral radio emissions are produced by magnetized bodies requires in situ measurements within their source region. Saturn’s kilometric radiation (SKR) has been widely used as a remote proxy of Saturn’s magnetosphere. We present wave and plasma measurements from the Cassini spacecraft during its ring-grazing high-inclination orbits, which passed three times through the high-altitude SKR emission region. Northern dawn-side, narrow-banded radio sources were encountered at frequencies of 10 to 20 kilohertz, within regions of upward currents mapping to the ultraviolet auroral oval. The kilometric waves were produced on the extraordinary mode by the cyclotron maser instability from 6– to 12–kilo–electron volt electron beams and radiated quasi-perpendicularly to the auroral magnetic field lines. The SKR low-frequency sources appear to be strongly controlled by time-variable magnetospheric electron densities.
Collapse
|
2
|
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.
Collapse
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
| |
Collapse
|