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

Provan, G.; Cowley, S. W. H.; Bunce, E. J.; Milan, S. E.; Persoon, A. M.; Gurnett, D. A.

doi:10.1029/2021ja029332

“…Otherwise, the differential rotation of the northern and southern parts of the same L-shell would stretch its field lines indefinitely in the azimuthal direction in the vicinity of the plasma sheet. Observations reporting slightly different periodicities in the two lobes for various magnetospheric phenomena (Andrews et al 2008(Andrews et al , 2010(Andrews et al , 2012Provan et al 2012Provan et al , 2019Provan et al , 2021Szego et al 2012Szego et al , 2013 suggest that the flow patterns in the two lobes are independent. Another important aspect to be considered about these planetary period oscillations (PPOs) is that the vortex model decouples the observed periodicity and the plasma speed.…”

Section: Theorymentioning

confidence: 99%

Closed field line vortices in planetary magnetospheres

Nemeth

2023

Preprint

0

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In a rotation-dominated magnetosphere, there is a region where closed field lines rotate around the planet, and also a region where the open field lines stretch away from the planet, forming the lobes of the magnetotail. This paper shows that there could be a third, significantly different region, where the closed field lines form twisted vortex structures anchored in the magnetotail. Such patterns form when there are significant plasma sources inside the magnetosphere and the time scale of the plasmoid formation process is substantially larger than the planetary rotation period. In the presence of vortices, the Dungey and Vasyliunas cycles act differently. The Dungey flow does not penetrate the central region of the polar cap. Tail reconnection events are rare, thus leaving the plasma time enough to participate in the essentially 3-dimensional vortex-forming plasma motion. The above conditions are fulfilled for Saturn. We discovered vortex-like patterns in the plasma and magnetic field data measured by the Cassini spacecraft in the nightside magnetosphere of Saturn. The plasma whirling around in these vortices never reaches the dayside, instead, it performs a retrograde motion in the high latitude regions of the magnetotail. Low-energy plasma data suggest that the observed patterns correspond to the closed field line vortices.

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Phase locking among Saturn radio emissions revealed byCassiniobservations

Wu,

Ye,

Fischer

et al. 2023

A&A

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Context.Rotational modulation has been observed in different magnetospheric phenomena at Saturn, including radio emissions, which reflect the fundamental plasma processes in key regions. Though previous studies have shown Saturn’s kilometric radiation, 5 kHz narrowband emissions, and auroral hiss to be rotationally modulated, the modulation features of its 20 kHz narrowband emissions are still unknown.Aims.This work complements previous modulation analysis of Saturn radio emissions by undertaking the analysis of 20 kHz narrowband emissions and comprehensively comparing the phases among the regularly observed radio components.Methods.We carried out a least-squares analysis using the time series of narrowband emissions, which we derived from an event list based on a previous statistical study on Saturn narrowband emissions.Results.We reveal a “phase-lock” relation between the 5 and 20 kHz narrowband emissions and Saturn’s kilometric radiation, which suggests these strongly clock-like modulated emissions are connected to the rotating field-aligned current system, with local time preferences for the generation of the radio emissions. This local time preference cannot be well explained by existing theoretical frameworks. Although the phase-lock relation is relatively stable, it may be disrupted during solar wind compression. Therefore, the phase lock between these radio emissions may become a fundamental phenomenon that could help in establishing a global picture of the large-scale dynamics of Saturn’s magnetosphere.

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Closed field line vortices in planetary magnetospheres

Németh

¹

2023

Monthly Notices of the Royal Astronomical Society

0

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In a rotation-dominated magnetosphere, there is a region where closed field lines rotate around the planet, and also a region where the open field lines stretch away from the planet, forming the lobes of the magnetotail. This paper shows that there could be a third, significantly different region, where the closed field lines form twisted vortex structures anchored in the magnetotail. Such patterns form when there are significant plasma sources inside the magnetosphere and the time scale of the plasmoid formation process is substantially larger than the planetary rotation period. In the presence of vortices, the Dungey and Vasyliunas cycles act differently. The Dungey flow does not penetrate the central region of the polar cap. Tail reconnection events are rare, thus leaving the plasma time enough to participate in the essentially 3-dimensional vortex-forming plasma motion. The above conditions are fulfilled for Saturn. We discovered vortex-like patterns in the plasma and magnetic field data measured by the Cassini spacecraft in the nightside magnetosphere of Saturn. The plasma whirling around in these vortices never reaches the dayside, instead, it performs a retrograde motion in the high latitude regions of the magnetotail. Low-energy plasma data suggest that the observed patterns correspond to the closed field line vortices.

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

Abstract: 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

Cited by 4 publications

References 45 publications

Closed field line vortices in planetary magnetospheres

Closed field line vortices in planetary magnetospheres

Phase locking among Saturn radio emissions revealed byCassiniobservations

Closed field line vortices in planetary magnetospheres

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