Flux Tube Entropy and Specific Entropy in Saturn's Magnetosphere

Ma, Xuanye; Delamere, P. A.; Thomsen, M. F.; Otto, A.; Neupane, B. R.; Burkholder, Brandon; Nykyri, K.

doi:10.1029/2018ja026150

Cited by 9 publications

(17 citation statements)

References 84 publications

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“…After this region, the radial transport rates increase significantly. However, the flux tube entropy increases with radial distance due to an ever increasing flux tube volume and increasing plasma pressure in the middle and outer magnetosphere (Ma et al., 2019). In general, if ∂S / ∂L > 0, then the magnetodisc should be stable to centrifugal interchange motion.…”

Section: Introductionmentioning

confidence: 99%

On The Nature of Turbulent Heating and Radial Transport in Saturn's Magnetosphere

Neupane

Delamere

et al. 2021

JGR Space Physics

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Based on magnetic field fluctuations, Saturn's magnetosphere can be divided into quiet (little or not much fluctuation) and disturbed periods (large fluctuation of the magnetic field). Kaminker et al. (2017, https://doi.org/10.1002/2016JA023834) showed that the average heating rate density of entire magnetosphere of Saturn is ∼10−17 W m−3 based on magnetic field fluctuations. Here, we categorize the magnetosphere of Saturn on the basis of magnetic field fluctuation. Using the eigenvalues of the variance analysis of the magnetic field, it has been found that the magnetodisc is in a disturbed state almost 6%–7% of the time. Dwell time normalization of the disturbed events suggests that most of the events happen at all latitudes between −5° and +30° and mostly on the dayside. Kinetic turbulent heating due to magnetic field fluctuation (δB) could potentially provide a significant amount of the required power.

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Section: Introductionmentioning

confidence: 99%

On The Nature of Turbulent Heating and Radial Transport in Saturn's Magnetosphere

Neupane

Delamere

et al. 2021

JGR Space Physics

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“…The numerous calculations from this study add another piece to the puzzle of resolving the relative importance of the various reconnective processes that affect the transport of plasma (Dialynas, ) in Saturn's magnetosphere. It is increasingly evident that reconnection is a fundamentally important process that allows for the outward transport of plasma while conserving magnetic flux in the magnetosphere (Ma et al, ).…”

Section: Introductionmentioning

confidence: 99%

Convection in the Magnetosphere of Saturn During the Cassini Mission Derived From MIMI INCA and CHEMS Measurements

et al. 2020

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An extensive analysis of Cassini Ion and Neutral Camera (INCA) and Charge Energy Mass Spectrometer (CHEMS) measurements of ~6–231 keV ion anisotropies acquired during selected spin and stare periods for nearly all mission orbits has been completed. Based on this analysis, we find that the computed azimuthal speed of Saturn's magnetodisk plasma increases within the inner and middle magnetosphere. Beyond the orbit of Titan, in the magnetotail, the calculated rotation speed remains roughly constant with increasing distance from Saturn. The component of convection parallel to Saturn's spin axis is smaller and on average nearly zero. The radial speed of plasma shows distinct local time dependence and increases outward with increasing distance down the magnetotail. The magnetodisk flow remains primarily azimuthal to large distances, indicating the plasma is still under the influence of Saturn as it transits across the nightside. Tailward flows have been observed in the region near the dawn and dusk magnetotail flanks. The plasma flow in the predawn quadrant is much more disorganized than that in the premidnight quadrant. The hydrogen and oxygen hot ion temperatures increase with decreasing distance to Saturn. Some plasma evidently escapes into a dusk boundary layer at the dusk magnetotail flank, while the remaining plasma primarily moves across the magnetotail and is entrained into the flow of a boundary layer at the dawn flank of the magnetotail. When scaled to the magnetopause standoff distance and corotation fraction, the convection speed of plasma in the magnetospheres of Jupiter and Saturn is similarly organized.

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“…We summarize our results as follows: The outward radial plasma mass transport rate is roughly ∼55 kg/s. There is a dawn‐dusk asymmetry in the flows. The dusk region is dominated by the inward flows, while dawn is dominated by outward flows, which could indicate that mass loss in the dusk flank is important. The nonzero magnetic flux transport rate indicates that the transport process at Saturn could be dominated by small‐scale, patchy reconnection where plasma mass is transported outward without changing magnetic flux significantly (Ma et al, ). …”

Section: Resultsmentioning

confidence: 99%

“…Flux tube entropy must increase with the radial distance as a result of the required stability condition; otherwise, the magnetodisc would be convectivly unstable (Southwood & Kivelson, ). Reconnection of the magnetic field lines changes the flux tube entropy leading to radial transport (Ma et al, ; Otto et al, ; Vasyliuǹas, ).…”

Section: Introductionmentioning

confidence: 99%

“…This type of reconnection transports the plasma radially outward without involving large magnetic flux circulation. This double reconnection helps to maintain the stability in the magnetodisc because partial flux tube interchange preserves the flux tube entropy profile (Ma et al, ) . Wave‐induced (diffusive) transport can be significant in high beta plasma where kinetic Alfvèn waves produce stochastic ion motion (Johnson & Cheng, ).…”

Section: Introductionmentioning

confidence: 99%

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Quantifying Mass and Magnetic Flux Transport in Saturn's Magnetosphere

et al. 2019

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Radial transport is an important dynamical process in Saturn's internally driven magnetosphere. Radial transport is presumed to occur by a centrifugally driven interchange instability, determined by the gradient of flux tube content and flux tube entropy. Plasma produced in the inner magnetosphere must be transported radially outward. The outward motion of the plasma stretches the magnetic field lines, leading to magnetic reconnection. Reconnection allows the mass to be transported radially while allowing the flux to circulate back to the inner magnetosphere. Both radial transport of mass and magnetic flux in Saturn's magnetosphere have been estimated based on Cassani Plasma Spectrometer data provided by Wilson et al. (2017, https://doi.org/10.1002/2017JA024117) and suggesting the radial transport rate of plasma of around 55 kg/s. The net magnetic flux transport should be 0, but the data suggest a net outward magnetic flux transport indicating the existence of different possible transport mechanisms in Saturn's magnetodisc.

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Flux Tube Entropy and Specific Entropy in Saturn's Magnetosphere

Abstract: The motivation of this paper is to discuss the dynamical processes

Cited by 9 publications

References 84 publications

On The Nature of Turbulent Heating and Radial Transport in Saturn's Magnetosphere

On The Nature of Turbulent Heating and Radial Transport in Saturn's Magnetosphere

Convection in the Magnetosphere of Saturn During the Cassini Mission Derived From MIMI INCA and CHEMS Measurements

Quantifying Mass and Magnetic Flux Transport in Saturn's Magnetosphere

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