Kelvin–Helmholtz‐Related Turbulent Heating at Saturn's Magnetopause Boundary

Delamere, P. A.; Ng, C. S.; Damiano, P. A.; Neupane, B. R.; Burkholder, Brandon; Ma, Xuanye; Nykyri, K.

doi:10.1029/2020ja028479

Cited by 15 publications

(11 citation statements)

References 58 publications

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“…Runs (ii) and (iii) respectively correspond to qualitative increases in the helicity and cross-helicity-quantities often described in studies of solar-wind turbulence (Bruno & Carbone, 2016). The gradients of the curves in Figure 4a correspond to heating rates-for the amplitudes in the empirical wave model these rates are consistent with that which may be supplied by cross-scale energy transport when the observed spectrum is interpreted as a non-linear cascade of counterpropagating Alfvén waves (Delamere et al, 2020; see their Equation 13) Comparison of the curves presented in Figure 4a show that increases in the filamentation (Run ii vs. Run i) provide a commensurate increase in heating rate. This enhancement is partially a consequence of the increase of the orthogonal component of  E that the larger filamentation required to retain the same energy density in the 1-D spectrum.…”

Section: Discussionsupporting

confidence: 65%

Ion Scattering and Energization in Filamentary Structures Through Earth's Magnetosheath

Chaston

Trávníček

2021

Geophysical Research Letters

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The action of microphysical processes on shocked solar wind plasmas through the magnetosheath take a variety of forms (e.g., Vörös et al., 2019). Notably, statistical observations (Fuselier et al., 1994;Maruca et al., 2018) have revealed an inverse relationship between the ion temperature anisotropy and value of plasma beta. This relationship has been interpreted in terms of the adiabatic evolution of the distribution, under-going compression or expansion, and the consequent driving of the temperature anisotropy toward threshold conditions of various ion velocity space instabilities (Trávnícek et al., 2007). Diffusion in velocity space, once these thresholds are met, limits the observed anisotropy (Gary & Lee, 1994;Gary et al., 1997).In a system continuously driven by macroscale variations, such as the magnetosheath, the ion distribution may be maintained in a marginally unstable state set by the balance between the driven adiabatic response and diffusion due to wave emission.While the adiabatic response may push the ion distribution toward instability thresholds it is not the only process that may drive ion distribution evolution. The magnetosheath is pervaded by turbulent fluctuations on scales that extend well into the ion kinetic range (e.g., Chaston et al., 2013;Roberts et al., 2018;Sahraoui et al., 2006). These field structures will scatter the ion plasma leading to non-adiabatic changes in the ion distributions (Johnson & Cheng, 2001). Statistical observations suggest that this process may drive heating of magnetosheath ion distributions at a rate of ∼1 eV/s corresponding to significant enhancements in

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Section: Discussionsupporting

confidence: 65%

Ion Scattering and Energization in Filamentary Structures Through Earth's Magnetosheath

Chaston

Trávníček

2021

Geophysical Research Letters

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“…Nevertheless, the KH instability and the associated secondary instabilities are naturally associated with turbulence (Matsumoto and Hoshino, 2006;Stawarz et al, 2016;Nakamura et al, 2017;Nykyri et al, 2017;Dong et al, 2018;Nakamura et al, 2020), which has a long history of studies demonstrating that turbulent heating is a very effective mechanism for ion heating [e.g., Quataert (Quataert, 1998), Johnson and Cheng (Johnson and Cheng, 2001), Chandran et al (Chandran et al, 2010), Told et al (Told et al, 2015), Vasquez (Vasquez, 2015), Grošelj et al (Grošelj et al, 2017), Arzamasskiy et al (Arzamasskiy et al, 2019), Cerri et al (Cerri et al, 2021)]. Delamere et al (Delamere et al, 2021) estimated a turbulent ion heating rate density ≈10 -15 W m −3 during the nonlinear stage of 3-D hybrid KH instability simulations based on the typical Saturn's magnetopause boundary condition, which is consistent with the Cassini data analysis (Burkholder et al, 2020). Such estimations should also apply to investigate Earth's magnetopause boundary both from numerical simulation and observational data analysis, which, however, is out of scope of this paper.…”

Section: Resultsmentioning

confidence: 99%

Ion Dynamics in the Meso-scale 3-D Kelvin–Helmholtz Instability: Perspectives From Test Particle Simulations

Delamere

Nykyri

et al. 2021

Front. Astron. Space Sci.

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Over three decades of in-situ observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath and magnetospheric plasma often occurs on the magnetopause of Earth and other planets under various interplanetary magnetic field (IMF) conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solar-wind-magnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kinetic-scale) physical processes, such as magnetic reconnection, kinetic Alfvén waves, ion-acoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability on the cross-scale process requires a numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, different simulation methods are required to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. Test particle simulation provides such a bridge to connect the MHD scale to the kinetic scale. This study applies different test particle approaches and cross validates the different results against one another to investigate the behavior of different ion species (i.e., H+ and O+), which include particle distributions, mixing and heating. It shows that the ion transport rate is about 1025 particles/s, and mixing diffusion coefficient is about 1010 m2 s−1 regardless of the ion species. Magnetic field lines change their topology via the magnetic reconnection process driven by the three-dimensional KH instability, connecting two flux tubes with different temperature, which eventually causes anisotropic temperature in the newly reconnected flux.

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“…Numerical simulations with hybrid or particle-in-cell models can be a useful tool to better understand the dissipation mechanisms and the associated transport of particles and energy (e.g., Delamere et al, 2021). Future models could focus on more realistic magnetic field geometries with current sheets and inhomogeneous plasma densities along field lines.…”

Section: Discussion: Outstanding Issues and Outlookmentioning

confidence: 99%

Turbulence in the Magnetospheres of the Outer Planets

Saur

2021

Front. Astron. Space Sci.

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The magnetospheres of the outer planets exhibit turbulent phenomena in an environment which is qualitatively different compared to the solar wind or the interstellar medium. The key differences are the finite sizes of the magnetospheres limited by their physical boundaries, the presence of a strong planetary background magnetic field and spatially very inhomogeneous plasma properties within the magnetospheres. Typical turbulent fluctuations possess amplitudes much smaller than the background field and are characterized by Alfvén times, which can be smaller than the non-linear interaction time scales. The magnetospheres of the outer planets are thus interesting laboratories of plasma turbulence. In Jupiter's and Saturn's magnetospheres, turbulence is well-established thanks to the in-situ measurements by several spacecraft, in particular the Galileo and Cassini orbiter. In contrast, the fluctuations in Uranus' and Neptune's magnetospheres are poorly understood due to the lack of sufficient data. Turbulence in the outer planets' magnetospheres have important effects on the systems as a whole. The dissipation of the turbulent fluctuations through wave-particle interaction is a significant heat source, which can explain the large magnetospheric plasma temperatures. Similarly, turbulent wave fluctuations strongly contribute to the acceleration of particles responsible for the planet's auroras.

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Kelvin–Helmholtz‐Related Turbulent Heating at Saturn's Magnetopause Boundary

Cited by 15 publications

References 58 publications

Ion Scattering and Energization in Filamentary Structures Through Earth's Magnetosheath

Ion Scattering and Energization in Filamentary Structures Through Earth's Magnetosheath

Ion Dynamics in the Meso-scale 3-D Kelvin–Helmholtz Instability: Perspectives From Test Particle Simulations

Turbulence in the Magnetospheres of the Outer Planets

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