The Variable Rotation Period of the Inner Region of Saturn's Plasma Disk

Gurnett, D. A.; Persoon, A. M.; Kurth, W. S.; Groene, J. B.; Averkamp, T. F.; Dougherty, M. K.; Southwood, D. J.

doi:10.1126/science.1138562

Cited by 228 publications

(362 citation statements)

References 24 publications

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“…Various models have been suggested to explain the properties of the Kronian magnetosphere (Espinosa et al, 2003;Southwood and Kivelson, 2007;Goldreich and Farmer, 2007;Gurnett et al, 2007;Southwood and Kivelson, 2009;Khurana et al, 2009;Carbary and Mitchell, 2013). Recently Jia and Kivelson (2012) proposed a numerical model, which agrees well with most of the experimental results currently known.…”

Section: Introductionsupporting

confidence: 72%

The latitudinal structure of the nightside outer magnetosphere of Saturn as revealed by velocity moments of thermal ions

et al. 2015

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Abstract. In this study we investigate the latitudinal behavior of the azimuthal plasma velocities in the outer magnetosphere of Saturn using the numerical ion moments derived from the measurements of the Cassini Plasma Spectrometer. One of the new results presented is that although these moments display some scatter, a significant positive correlation is found to exist between the azimuthal velocity and the plasma density, such that on average, the higher the density the higher the rotation speed. We also found that both the azimuthal velocity and the density anticorrelate with the magnitude of the radial component of the magnetic field and drop rapidly with increasing distance from the magnetic equator. The azimuthal velocities show periodic behavior with a period near the planetary rotation period, which can also be explained by the strong dependence on magnetic latitude, taking into account the flapping of the magnetodisk. It is thus found that the dense plasma near the magnetic equator rotates around the planet at high speed, while the dilute plasma at higher latitudes in the northern and southern hemispheres rotates significantly slower. The latitudinal gradient observed in the azimuthal speed is suggested to be a direct consequence of the sub-corotation of the plasma in the outer magnetosphere, with highest speeds occurring on field lines at lowest latitudes mapping to the rapidly rotating inner regions of the plasma sheet, and the speed falling as one approaches the lobe, where the field lines are connected to strongly subcorotating plasma.

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Section: Introductionsupporting

confidence: 72%

The latitudinal structure of the nightside outer magnetosphere of Saturn as revealed by velocity moments of thermal ions

et al. 2015

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“…Despite this, however, oscillations with a period near thẽ 11 h planetary period are observed throughout Saturn's magnetosphere. Such modulations are observed in the magnetic field, Saturnian kilometric radiation (SKR), plasma parameters, energetic particle fluxes, and associated neutral atom emissions, as well as auroral ultraviolet, infrared, and radio emissions [e.g., Warwick et al, 1981Warwick et al, , 1982Desch and Kaiser, 1981;Gurnett et al, 1981Gurnett et al, , 2007Gurnett et al, , 2010aSandel and Broadfoot, 1981;Sandel et al, 1982;Carbary and Krimigis, 1982;Espinosa and Dougherty, 2000;Krupp et al, 2005;Cowley et al, 2006;Kurth et al, 2007;Southwood and Kivelson, 2007;Carbary et al, 2007Carbary et al, , 2008aCarbary et al, , 2008bZarka et al, 2007;Andrews et al, 2008;Nichols et al, 2008Nichols et al, , 2010aNichols et al, , 2010bBurch et al, 2009;Provan et al, 2009aProvan et al, , 2009bClarke et al, 2006;Badman et al, 2012;Lamy et al, 2013]. Those oscillations were first observed in Voyager measurements of the SKR emissions, around the time of Saturn's northern hemisphere spring equinox [Kaiser et al, 1980].…”

Section: Introductionmentioning

confidence: 99%

Planetary period oscillations in Saturn's magnetosphere: Examining the relationship between abrupt changes in behavior and solar wind‐induced magnetospheric compressions and expansions

et al. 2015

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We examine planetary period oscillations (PPOs) observed in Saturn's magnetospheric magnetic field data from the time of Saturn's equinox in 2009. In particular, we focus on the time period commencing February 2011, when the oscillations started to display sudden and unexpected changes in behavior at ~100–200 day intervals. These were characterized by large simultaneous changes in the amplitude of the northern and southern PPO systems, together with small changes in period and jumps in phase. Nine significant abrupt changes have been observed in the postequinox interval to date, commencing as the Sun started to emerge from a long extended solar minimum. We perform a statistical study to determine whether these modulations in PPO behavior were associated with changes in the solar and/or upstream solar wind conditions. We report that the upstream solar wind conditions show elevated values of solar wind dynamic pressure and density around the time of PPO behavioral transitions, as opposed to before and after these times. We suggest that abrupt changes in PPO behavior may be related to significant changes in the size of the Saturnian magnetosphere in response to varying solar wind conditions.

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“…[41] Gurnett et al [2007] have earlier suggested on the basis of asymmetries in electron density that there is a rotating circulation system in Saturn's magnetosphere which serves to carry ionized material injected in the inner magnetosphere by Enceladus out into interplanetary space. The sketch of the circulation given by Gurnett et al [2007, Figure 2b] shows a familiar two cell circulation pattern.…”

Section: Relation To Plasma Circulationmentioning

confidence: 99%

Direct evidence of differences in magnetic rotation rate between Saturn's northern and southern polar regions

Southwood

2011

J. Geophys. Res.

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The Variable Rotation Period of the Inner Region of Saturn's Plasma Disk

Cited by 228 publications

References 24 publications

The latitudinal structure of the nightside outer magnetosphere of Saturn as revealed by velocity moments of thermal ions

The latitudinal structure of the nightside outer magnetosphere of Saturn as revealed by velocity moments of thermal ions

Planetary period oscillations in Saturn's magnetosphere: Examining the relationship between abrupt changes in behavior and solar wind‐induced magnetospheric compressions and expansions

Direct evidence of differences in magnetic rotation rate between Saturn's northern and southern polar regions

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