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Saturn's Nightside Ring Current During Cassini's Grand Finale.

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Title: Saturn's Nightside Ring Current During Cassini's Grand Finale.
Authors: Provan, G.1 gp31@le.ac.uk, Bradley, T. J.1, Bunce, E. J.1, Cowley, S. W. H.1, Cao, H.2,3, Dougherty, M.4, Hunt, G. J.4, Roussos, E.5, Staniland, N. R.4, Tao, C.6
Source: Journal of Geophysical Research. Space Physics. Mar2021, Vol. 126 Issue 3, p1-33. 33p.
Subject Terms: *Equatorial currents, Magnetotails, Magnetic fields, Solar wind
Company/Entity: Cassini (Spacecraft)
Abstract: During Cassini's Grand Finale proximal orbits, the spacecraft traversed the nightside magnetotail to ∼21 Saturn radii. Clear signatures of Saturn's equatorial current sheet are observed in the magnetic field data. An axisymmetric model of the ring current is fitted to these data, amended to take into account the tilt of the current layer by solar wind forcing, its teardrop-shaped nature and the magnetotail and magnetopause fringing fields. Variations in ring current parameters are examined in relation to external driving of the magnetosphere by the solar wind and internal driving by the two planetary period oscillations (PPOs), and compared with previous dawn and dayside observations. We find that the relative phasing of the PPOs determines the ring current's response to solar wind conditions. During solar wind compressions when the PPOs are in antiphase, a thick partial ring current is formed on the nightside, dominated by hot plasma injected by tail reconnection. This partial ring current should close partly via magnetopause currents and possibly via field-aligned currents into the ionosphere. However, during solar wind compressions when the PPOs are in phase, this partial ring current is not detected. During solar wind rarefactions an equatorial “magnetodisc” configuration is observed in the dayside/dawn/nightside regions, with similar total currents flowing at these local times. During very quiet intervals of prolonged solar wind rarefaction, a thin current sheet with an enhanced current density is formed, indicative of a ring current dominated by cool, dense, Enceladus water group ions. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Saturn's Nightside Ring Current During Cassini's Grand Finale.
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Space+Physics%22">Journal of Geophysical Research. Space Physics</searchLink>. Mar2021, Vol. 126 Issue 3, p1-33. 33p.
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  Data: *<searchLink fieldCode="DE" term="%22Equatorial+currents%22">Equatorial currents</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetotails%22">Magnetotails</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetic+fields%22">Magnetic fields</searchLink><br /><searchLink fieldCode="DE" term="%22Solar+wind%22">Solar wind</searchLink>
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  Data: During Cassini's Grand Finale proximal orbits, the spacecraft traversed the nightside magnetotail to ∼21 Saturn radii. Clear signatures of Saturn's equatorial current sheet are observed in the magnetic field data. An axisymmetric model of the ring current is fitted to these data, amended to take into account the tilt of the current layer by solar wind forcing, its teardrop-shaped nature and the magnetotail and magnetopause fringing fields. Variations in ring current parameters are examined in relation to external driving of the magnetosphere by the solar wind and internal driving by the two planetary period oscillations (PPOs), and compared with previous dawn and dayside observations. We find that the relative phasing of the PPOs determines the ring current's response to solar wind conditions. During solar wind compressions when the PPOs are in antiphase, a thick partial ring current is formed on the nightside, dominated by hot plasma injected by tail reconnection. This partial ring current should close partly via magnetopause currents and possibly via field-aligned currents into the ionosphere. However, during solar wind compressions when the PPOs are in phase, this partial ring current is not detected. During solar wind rarefactions an equatorial “magnetodisc” configuration is observed in the dayside/dawn/nightside regions, with similar total currents flowing at these local times. During very quiet intervals of prolonged solar wind rarefaction, a thin current sheet with an enhanced current density is formed, indicative of a ring current dominated by cool, dense, Enceladus water group ions. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1029/2020JA028605
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        Text: English
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        PageCount: 33
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      – SubjectFull: Equatorial currents
        Type: general
      – SubjectFull: Magnetotails
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      – SubjectFull: Magnetic fields
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      – SubjectFull: Solar wind
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      – SubjectFull: Cassini (Spacecraft)
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      – TitleFull: Saturn's Nightside Ring Current During Cassini's Grand Finale.
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              Text: Mar2021
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