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Detection of Equatorial Plasma Velocity Modulations Associated With Planetary Period Oscillations in Saturn's Magnetosphere.

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Title: Detection of Equatorial Plasma Velocity Modulations Associated With Planetary Period Oscillations in Saturn's Magnetosphere.
Authors: Bradley, T. J.1 (AUTHOR), Provan, G.1 (AUTHOR), Cowley, S. W. H.1 (AUTHOR) swhc1@ion.le.ac.uk, Wilson, R. J.2 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. May2022, Vol. 127 Issue 5, p1-18. 18p.
Subject Terms: Saturn (Planet), Oscillations, Magnetosphere, Phase oscillations, Ion migration & velocity, Quasi-biennial oscillation (Meteorology)
Abstract: We analyze a database of 8920 measurements of thermal ion vector velocities obtained by the Cassini CAPS/IMS instrument in the near‐equatorial (±10° latitude) region of Saturn's magnetosphere in the radial range of 5.5–21.5 Saturn radii (RS) for the presence of modulations due to planetary period oscillations (PPOs). The data span 2004–2012, from Saturn late southern summer to early northern spring, and are analyzed using PPO phases derived previously from Cassini magnetic field data. For the near‐equinox and northern spring data 2008–2012 we show that both northern and southern PPO modulations are present in the azimuthal velocity component with similar amplitudes, typically ∼3 ± 1.5 km s−1 in the inner part of the system inside ∼10–12 RS, rising to typically ∼9 ± 3.5 km s−1 in the outer part of the system to ∼20 RS. Oscillation phases are overall consistent with expectations for PPO modulations driven from the corresponding polar ionospheres in both cases. For the late southern summer data 2004–2007, southern PPO modulations are also present with similar properties, but no clear northern modulations were detected, indicating weaker amplitudes in this case. These findings mirror similar properties in the amplitudes of magnetic field PPO oscillations observed in previous studies. Our results constitute the first direct detection of PPO‐related velocity modulations in Saturn's magnetospheric plasma. However, no clear PPO effects were found in either the radial or colatitudinal velocities, indicating weaker modulations, if any, in these components. Key Points: We analyze a database of Cassini Saturn equatorial ion velocities 2004–2012 spanning 5.5–21.5 RS for planetary period oscillations (PPOs)Northern and southern PPOs are detected at amplitudes few to ∼10 km s–1 in the azimuthal but not in the radial or colatitudinal componentsAzimuthal flow phases are consistent with expectations for oscillations driven outward from the corresponding polar ionospheres [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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  Label: Title
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  Data: Detection of Equatorial Plasma Velocity Modulations Associated With Planetary Period Oscillations in Saturn's Magnetosphere.
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  Data: <searchLink fieldCode="AR" term="%22Bradley%2C+T%2E+J%2E%22">Bradley, T. J.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Provan%2C+G%2E%22">Provan, G.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Cowley%2C+S%2E+W%2E+H%2E%22">Cowley, S. W. H.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> swhc1@ion.le.ac.uk</i><br /><searchLink fieldCode="AR" term="%22Wilson%2C+R%2E+J%2E%22">Wilson, R. J.</searchLink><relatesTo>2</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Space+Physics%22">Journal of Geophysical Research. Space Physics</searchLink>. May2022, Vol. 127 Issue 5, p1-18. 18p.
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  Data: <searchLink fieldCode="DE" term="%22Saturn+%28Planet%29%22">Saturn (Planet)</searchLink><br /><searchLink fieldCode="DE" term="%22Oscillations%22">Oscillations</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetosphere%22">Magnetosphere</searchLink><br /><searchLink fieldCode="DE" term="%22Phase+oscillations%22">Phase oscillations</searchLink><br /><searchLink fieldCode="DE" term="%22Ion+migration+%26+velocity%22">Ion migration & velocity</searchLink><br /><searchLink fieldCode="DE" term="%22Quasi-biennial+oscillation+%28Meteorology%29%22">Quasi-biennial oscillation (Meteorology)</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: We analyze a database of 8920 measurements of thermal ion vector velocities obtained by the Cassini CAPS/IMS instrument in the near‐equatorial (±10° latitude) region of Saturn's magnetosphere in the radial range of 5.5–21.5 Saturn radii (RS) for the presence of modulations due to planetary period oscillations (PPOs). The data span 2004–2012, from Saturn late southern summer to early northern spring, and are analyzed using PPO phases derived previously from Cassini magnetic field data. For the near‐equinox and northern spring data 2008–2012 we show that both northern and southern PPO modulations are present in the azimuthal velocity component with similar amplitudes, typically ∼3 ± 1.5 km s−1 in the inner part of the system inside ∼10–12 RS, rising to typically ∼9 ± 3.5 km s−1 in the outer part of the system to ∼20 RS. Oscillation phases are overall consistent with expectations for PPO modulations driven from the corresponding polar ionospheres in both cases. For the late southern summer data 2004–2007, southern PPO modulations are also present with similar properties, but no clear northern modulations were detected, indicating weaker amplitudes in this case. These findings mirror similar properties in the amplitudes of magnetic field PPO oscillations observed in previous studies. Our results constitute the first direct detection of PPO‐related velocity modulations in Saturn's magnetospheric plasma. However, no clear PPO effects were found in either the radial or colatitudinal velocities, indicating weaker modulations, if any, in these components. Key Points: We analyze a database of Cassini Saturn equatorial ion velocities 2004–2012 spanning 5.5–21.5 RS for planetary period oscillations (PPOs)Northern and southern PPOs are detected at amplitudes few to ∼10 km s–1 in the azimuthal but not in the radial or colatitudinal componentsAzimuthal flow phases are consistent with expectations for oscillations driven outward from the corresponding polar ionospheres [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  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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      – Type: doi
        Value: 10.1029/2021JA030198
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      – Code: eng
        Text: English
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        PageCount: 18
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      – SubjectFull: Saturn (Planet)
        Type: general
      – SubjectFull: Oscillations
        Type: general
      – SubjectFull: Magnetosphere
        Type: general
      – SubjectFull: Phase oscillations
        Type: general
      – SubjectFull: Ion migration & velocity
        Type: general
      – SubjectFull: Quasi-biennial oscillation (Meteorology)
        Type: general
    Titles:
      – TitleFull: Detection of Equatorial Plasma Velocity Modulations Associated With Planetary Period Oscillations in Saturn's Magnetosphere.
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            NameFull: Provan, G.
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            NameFull: Cowley, S. W. H.
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              M: 05
              Text: May2022
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              Y: 2022
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