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Particle and magnetic field properties of the Saturnian magnetosheath: Presence and upstream escape of hot magnetospheric plasma

Particle and magnetic field properties of the Saturnian magnetosheath: Presence and upstream escape of hot magnetospheric plasma
Particle and magnetic field properties of the Saturnian magnetosheath: Presence and upstream escape of hot magnetospheric plasma

We analyze plasma, energetic particle, and magnetic field data from all available Cassini passes through the Saturnian magnetosheath between July 2004 and July 2011 and provide a statistical overview of particle and field properties. The results show that magnetosheath plasma has an average number density of ∼0.1 cm-3 and a temperature of ∼300 eV. The measured magnetic field strength is ∼1 nT, and the plasma beta is in the range of 10 to 100. The prevailing flow and magnetic field configuration is close to that theoretically expected, with flow speed values of ∼200 km/s. Compositional data reveal that although at low energies (<few keV) the magnetosheath is comprised by shocked solar wind plasma, at high energies (>few keV) there is a strong presence of water group ions (W+) forming localized structures we refer to as W+ "islands" that travel downstream convected in the plasma flow. Under average magnetic field conditions in the Saturnian magnetosheath, the kinetic properties of these hot W+ ions can enable escape upstream from the bow shock. Based on the measured particle and field distributions and the modeled bow shock and magnetopause positions, we describe the energetic ion escape as a function of energy and pitch angle and successfully predict the energy distribution of the escaping W+ ions. Comparison with the ion spectra measured in the nearby solar wind confirms that the suggested escape mechanism due to large ion gyroradii is sufficient to explain the observed leakage of heavy energetic ions upstream from the Saturnian bow shock.

magnetosheath, particles, Saturn
2169-9380
1620-1634
Sergis, N.
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Jackman, C. M.
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Masters, A.
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Krimigis, S. M.
6fc8b68e-aee4-4088-b506-1c36004c78a0
Thomsen, M. F.
710c64ce-779f-4088-8e50-f9e450232f5f
Hamilton, D. C.
86f1fe89-bd97-43bf-bb02-f8758ae56dad
Mitchell, D. G.
a4b6d58b-a70b-48f3-8ebe-e7fa3fcff274
Dougherty, M. K.
aa297043-7e86-4501-952b-a6363edaaba8
Coates, A. J.
61022799-2e2b-46da-a964-23d9aaebe455
Sergis, N.
3b07fcbf-eb7f-496c-9b8d-c4f21fc9f87b
Jackman, C. M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Masters, A.
06e899bb-991d-4fde-9b11-3690af8839d0
Krimigis, S. M.
6fc8b68e-aee4-4088-b506-1c36004c78a0
Thomsen, M. F.
710c64ce-779f-4088-8e50-f9e450232f5f
Hamilton, D. C.
86f1fe89-bd97-43bf-bb02-f8758ae56dad
Mitchell, D. G.
a4b6d58b-a70b-48f3-8ebe-e7fa3fcff274
Dougherty, M. K.
aa297043-7e86-4501-952b-a6363edaaba8
Coates, A. J.
61022799-2e2b-46da-a964-23d9aaebe455

Sergis, N., Jackman, C. M., Masters, A., Krimigis, S. M., Thomsen, M. F., Hamilton, D. C., Mitchell, D. G., Dougherty, M. K. and Coates, A. J. (2013) Particle and magnetic field properties of the Saturnian magnetosheath: Presence and upstream escape of hot magnetospheric plasma. Journal of Geophysical Research: Space Physics, 118 (4), 1620-1634. (doi:10.1002/jgra.50164).

Record type: Article

Abstract

We analyze plasma, energetic particle, and magnetic field data from all available Cassini passes through the Saturnian magnetosheath between July 2004 and July 2011 and provide a statistical overview of particle and field properties. The results show that magnetosheath plasma has an average number density of ∼0.1 cm-3 and a temperature of ∼300 eV. The measured magnetic field strength is ∼1 nT, and the plasma beta is in the range of 10 to 100. The prevailing flow and magnetic field configuration is close to that theoretically expected, with flow speed values of ∼200 km/s. Compositional data reveal that although at low energies (<few keV) the magnetosheath is comprised by shocked solar wind plasma, at high energies (>few keV) there is a strong presence of water group ions (W+) forming localized structures we refer to as W+ "islands" that travel downstream convected in the plasma flow. Under average magnetic field conditions in the Saturnian magnetosheath, the kinetic properties of these hot W+ ions can enable escape upstream from the bow shock. Based on the measured particle and field distributions and the modeled bow shock and magnetopause positions, we describe the energetic ion escape as a function of energy and pitch angle and successfully predict the energy distribution of the escaping W+ ions. Comparison with the ion spectra measured in the nearby solar wind confirms that the suggested escape mechanism due to large ion gyroradii is sufficient to explain the observed leakage of heavy energetic ions upstream from the Saturnian bow shock.

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More information

e-pub ahead of print date: 12 February 2013
Published date: April 2013
Keywords: magnetosheath, particles, Saturn

Identifiers

Local EPrints ID: 436564
URI: http://eprints.soton.ac.uk/id/eprint/436564
ISSN: 2169-9380
PURE UUID: d423cedb-d1b4-41fc-94a2-f7e0d9806668
ORCID for C. M. Jackman: ORCID iD orcid.org/0000-0003-0635-7361

Catalogue record

Date deposited: 13 Dec 2019 17:30
Last modified: 10 Nov 2021 03:35

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Contributors

Author: N. Sergis
Author: C. M. Jackman ORCID iD
Author: A. Masters
Author: S. M. Krimigis
Author: M. F. Thomsen
Author: D. C. Hamilton
Author: D. G. Mitchell
Author: M. K. Dougherty
Author: A. J. Coates

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