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Planetary Period Oscillations of Saturn's Dayside Equatorial Ionospheric Electron Density Observed on Cassini's Proximal Passes.

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Title: Planetary Period Oscillations of Saturn's Dayside Equatorial Ionospheric Electron Density Observed on Cassini's Proximal Passes.
Authors: Provan, G.1 gp31@le.ac.uk, Cowley, S. W. H.1, Bunce, E. J.1, Milan, S. E.1, Persoon, A. M.2, Gurnett, D. A.2
Source: Journal of Geophysical Research. Space Physics. Sep2021, Vol. 126 Issue 9, p1-25. 25p.
Subject Terms: Electron density, Magnetosphere, Solar magnetism, Atmospheric ion precipitation, Magnetic reconnection
Abstract: We examine electron density data obtained in Saturn's dayside equatorial ionosphere during Cassini's proximal periapsis passes, specifically data derived from wave spectra, for evidence of modulation with the planetary period oscillations (PPOs) observed ubiquitously throughout Saturn's magnetosphere. Clear evidence is found on northern hemisphere inbound passes where northern system modulations occur in the ionospheric diffusive layer peaking at a factor of ∼7 at ∼3,200 km altitude, extending at lesser factors to ∼7,000 km altitude in the transport region. Simultaneous southern system modulations by factors ∼1.5–2.5 are also found above ∼3,400 km. Factor of ∼4–10 northern system modulations are also detected in the diffusive layer and transport regions to ∼6,000 km in the outbound pass data, though southern system modulations were not clearly discerned within the data scatter. Modulations were not detected in the photochemical equilibrium layer at altitudes ∼1,600–2,200 km. Where clear modulations were observed, their phases in the diffusive layer were close to those of the principal PPO meridians (determined previously from near‐apoapsis nightside magnetic data) for both systems, moving to somewhat earlier PPO phases by a few tens of degrees in the transport region. Comparison with magnetic oscillation phases determined directly from proximal pass data shows that electron density maxima occur ∼30°–50° earlier than azimuthal field maxima for both systems, ∼140°–160° earlier than colatitudinal field maxima for the northern system, nearer to antiphase than to leading quadrature, and ∼50°–70° later than colatitudinal field maxima for the southern system, somewhat less than lagging quadrature. Key Points: Saturn's equatorial ionospheric electron density data from Cassini's proximal orbits are examined for planetary period oscillations (PPOs)Northern and weaker southern PPO modulations occur in the diffusive layer and transport region (∼2,500–10,000 km) but not at lower altitudesDensity maxima occur near the rotating principal meridians for both PPO systems, ΨN,S ≈ 0°, with typical max/min ratios in the range ∼2–10 [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: Planetary Period Oscillations of Saturn's Dayside Equatorial Ionospheric Electron Density Observed on Cassini's Proximal Passes.
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  Data: <searchLink fieldCode="AR" term="%22Provan%2C+G%2E%22">Provan, G.</searchLink><relatesTo>1</relatesTo><i> gp31@le.ac.uk</i><br /><searchLink fieldCode="AR" term="%22Cowley%2C+S%2E+W%2E+H%2E%22">Cowley, S. W. H.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Bunce%2C+E%2E+J%2E%22">Bunce, E. J.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Milan%2C+S%2E+E%2E%22">Milan, S. E.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Persoon%2C+A%2E+M%2E%22">Persoon, A. M.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Gurnett%2C+D%2E+A%2E%22">Gurnett, D. A.</searchLink><relatesTo>2</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Space+Physics%22">Journal of Geophysical Research. Space Physics</searchLink>. Sep2021, Vol. 126 Issue 9, p1-25. 25p.
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  Data: <searchLink fieldCode="DE" term="%22Electron+density%22">Electron density</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetosphere%22">Magnetosphere</searchLink><br /><searchLink fieldCode="DE" term="%22Solar+magnetism%22">Solar magnetism</searchLink><br /><searchLink fieldCode="DE" term="%22Atmospheric+ion+precipitation%22">Atmospheric ion precipitation</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetic+reconnection%22">Magnetic reconnection</searchLink>
– Name: Abstract
  Label: Abstract
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  Data: We examine electron density data obtained in Saturn's dayside equatorial ionosphere during Cassini's proximal periapsis passes, specifically data derived from wave spectra, for evidence of modulation with the planetary period oscillations (PPOs) observed ubiquitously throughout Saturn's magnetosphere. Clear evidence is found on northern hemisphere inbound passes where northern system modulations occur in the ionospheric diffusive layer peaking at a factor of ∼7 at ∼3,200 km altitude, extending at lesser factors to ∼7,000 km altitude in the transport region. Simultaneous southern system modulations by factors ∼1.5–2.5 are also found above ∼3,400 km. Factor of ∼4–10 northern system modulations are also detected in the diffusive layer and transport regions to ∼6,000 km in the outbound pass data, though southern system modulations were not clearly discerned within the data scatter. Modulations were not detected in the photochemical equilibrium layer at altitudes ∼1,600–2,200 km. Where clear modulations were observed, their phases in the diffusive layer were close to those of the principal PPO meridians (determined previously from near‐apoapsis nightside magnetic data) for both systems, moving to somewhat earlier PPO phases by a few tens of degrees in the transport region. Comparison with magnetic oscillation phases determined directly from proximal pass data shows that electron density maxima occur ∼30°–50° earlier than azimuthal field maxima for both systems, ∼140°–160° earlier than colatitudinal field maxima for the northern system, nearer to antiphase than to leading quadrature, and ∼50°–70° later than colatitudinal field maxima for the southern system, somewhat less than lagging quadrature. Key Points: Saturn's equatorial ionospheric electron density data from Cassini's proximal orbits are examined for planetary period oscillations (PPOs)Northern and weaker southern PPO modulations occur in the diffusive layer and transport region (∼2,500–10,000 km) but not at lower altitudesDensity maxima occur near the rotating principal meridians for both PPO systems, ΨN,S ≈ 0°, with typical max/min ratios in the range ∼2–10 [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  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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        Value: 10.1029/2021JA029332
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      – Code: eng
        Text: English
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      Pagination:
        PageCount: 25
        StartPage: 1
    Subjects:
      – SubjectFull: Electron density
        Type: general
      – SubjectFull: Magnetosphere
        Type: general
      – SubjectFull: Solar magnetism
        Type: general
      – SubjectFull: Atmospheric ion precipitation
        Type: general
      – SubjectFull: Magnetic reconnection
        Type: general
    Titles:
      – TitleFull: Planetary Period Oscillations of Saturn's Dayside Equatorial Ionospheric Electron Density Observed on Cassini's Proximal Passes.
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            NameFull: Provan, G.
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            – D: 01
              M: 09
              Text: Sep2021
              Type: published
              Y: 2021
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              Value: 126
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