Local time asymmetry of Saturn's magnetosheath flows

Burkholder, Brandon; Delamere, P. A.; Ma, Xuanye; Thomsen, M. F.; Wilson, R.; Bagenal, F.

doi:10.1002/2017gl073031

Cited by 24 publications

(41 citation statements)

References 44 publications

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“…Overall, compared to dusk events, the dawn magnetospheric compression events occur more frequently, are more likely to include a gradual growth phase, are more likely to be associated with a reconnection signature, and are more likely to feature a change to a more dipolar, more swept back field. The change in bendback angle is consistent with the expected effects of momentum transfer from the solar wind to the magnetosphere via a viscous‐like process (e.g., Burkholder et al, ): The bendback angle would decrease (become more swept back) on the dawnside, but experience the opposite at dusk. During reconnection events, these changes are consistent with mass loss due to plasmoid release (e.g., Vogt et al, ), though increasing sweep back of the magnetic field can also indicate increased mass loading.…”

Section: Discussionsupporting

confidence: 81%

Solar Wind Interaction With Jupiter's Magnetosphere: A Statistical Study of Galileo In Situ Data and Modeled Upstream Solar Wind Conditions

et al. 2019

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Jupiter's magnetosphere is often said to be rotationally driven, with strong centrifugal stresses due to large spatial scales and a rapid planetary rotation period. While the solar wind is therefore expected to have a relatively small influence on Jupiter's magnetosphere and aurora, there is considerable observational evidence that the solar wind does affect the magnetopause standoff distance, auroral radio emissions, and the ultraviolet auroral position and brightness. We report on the results of a comprehensive, quantitative study of the influence of the solar wind dynamic pressure on magnetospheric data sets measured by the Galileo mission (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003). Using model predictions of the solar wind conditions near Jupiter calculated by propagating measurements made near the Earth, we have established how predicted changes in the solar wind affect the magnitude and direction of the magnetic field in the magnetosphere, the hectometric auroral radio emissions, and energetic particles in Jupiter's magnetosphere. We find that increases in the solar wind dynamic pressure are statistically associated with magnetospheric compression events but that tail reconnection and plasmoid release is most likely driven internally by the Vasyliunas cycle. We find no link between solar wind conditions and the occurrence of quasiperiodic modulations in the magnetosphere. Overall, we conclude that activity in Jupiter's magnetosphere is both internally and solar wind driven. Finally, we examine the effects of solar wind-induced magnetospheric compressions on Jupiter's auroral brightness and mapping, finding that a solar wind compression could shift the auroral mapping of a given point in the magnetosphere by~3°on average.

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Section: Discussionsupporting

confidence: 81%

Solar Wind Interaction With Jupiter's Magnetosphere: A Statistical Study of Galileo In Situ Data and Modeled Upstream Solar Wind Conditions

et al. 2019

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“…In contrast, the Maxwell stress reaches its peak value of 0.015 T 0 in the early nonlinear stage (i.e., t ≈90) and becomes saturated at a relatively large value of 0.008 T 0 . This result suggests that the magnetic field lines, which cross the magnetosheath‐magnetospheric boundary (i.e., x = 0), play the dominant role in dragging the solar wind and transport momentum from the solar wind into the magnetosphere (i.e., “viscous‐interaction”) (Burkholder et al, ).…”

Section: Resultsmentioning

confidence: 99%

Plasma Transport Driven by the Three‐Dimensional Kelvin‐Helmholtz Instability

et al. 2017

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It has been well demonstrated that the nonlinear Kelvin‐Helmholtz (KH) instability plays a critical role for the solar wind interaction with the Earth's magnetosphere. Although the two‐dimensional KH instability has been fully explored during the past decades, more and more studies show the fundamental difference between the two‐ and three‐dimensional KH instability. For northward interplanetary magnetic field (IMF) conditions, the nonlinear KH wave that is localized in the vicinity of the equatorial plane can dramatically bend the magnetic field line, generating strong antiparallel magnetic field components at high latitudes in both North and South Hemispheres, which satisfy the onset condition for magnetic reconnection. This high‐latitude double reconnection process can exchange the portion of magnetosheath and magnetospheric flux tubes between those two reconnection sites. This study used a high‐resolution 3‐D magnetohydrodynamic simulation to demonstrate that nonlinear KH waves can generate a large amount of double‐reconnected flux during the northward IMF condition, which can efficiently transport the plasma with a high diffusion coefficient of 1 × 1010 m2 s−1 for typical magnetopause conditions at the Earth. The presence of the magnetic field component along the shear flow direction not only decreases the KH growth rate but also causes north‐south asymmetry, which generates more open flux and reduces the efficiency of the plasma transport process.

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“…On the other hand, in the prenoon sector, flows were accepted as valid only if the flag indicates that corotation is not in the FOV. Burkholder et al () presented persuasive evidence that this procedure satisfactorily identified valid magnetosheath flow speeds. They used the resulting data set to demonstrate a prenoon/postnoon asymmetry in flow speed, which was interpreted as evidence for momentum coupling across the magnetopause.…”

Section: Introductionmentioning

confidence: 93%

Survey of Magnetosheath Plasma Properties at Saturn and Inference of Upstream Flow Conditions

et al. 2018

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A new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416 s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties of various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach‐number bow shock is ~4% of the dissipated flow energy. The data set is available as supporting information to this paper.

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Local time asymmetry of Saturn's magnetosheath flows

Cited by 24 publications

References 44 publications

Solar Wind Interaction With Jupiter's Magnetosphere: A Statistical Study of Galileo In Situ Data and Modeled Upstream Solar Wind Conditions

Solar Wind Interaction With Jupiter's Magnetosphere: A Statistical Study of Galileo In Situ Data and Modeled Upstream Solar Wind Conditions

Plasma Transport Driven by the Three‐Dimensional Kelvin‐Helmholtz Instability

Survey of Magnetosheath Plasma Properties at Saturn and Inference of Upstream Flow Conditions

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