Nature of Kinetic Scale Turbulence in the Earth's Magnetosheath

Chen, C. H. K.; Boldyrev, Stanislav

doi:10.3847/1538-4357/aa74e0

Cited by 148 publications

(212 citation statements)

References 83 publications

(93 reference statements)

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“…It should be stressed that both phenomenological arguments and numerical simulations predict a transition at d e , while observational spectra in the terrestrial magnetosheath only display a transition at ρ e (Huang et al 2014), associated with electron demagnetization. In fact, a transition at d e is more clearly observed at the level of the magnetic compressibility (Chen & Boldyrev 2017). This does exclude that additional effects such as other kind of waves or structures could play a role.…”

Section: Resultsmentioning

confidence: 79%

“…Capturing the saturation observed in data from the Magnetospheric Multiscale (MMS) mission, near the electron Larmor radius (Chen & Boldyrev 2017) nevertheless requires a suitable descriptions of the FLR effects at this scale, which is beyond the scope of the present model. It is of interest to compare the predictions of the present reduced fluid models with those of the kinetic theory obtained using the WHAMP software (Rönnmark 1982).…”

Section: Isothermal Regimementioning

confidence: 99%

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Electron-scale reduced fluid models with gyroviscous effects

2017

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Reduced fluid models for collisionless plasmas including electron inertia and finite Larmor radius corrections are derived for scales ranging from the ion to the electron gyroradii. Based either on pressure balance or on the incompressibility of the electron fluid, they respectively capture kinetic Alfvén waves (KAWs) or whistler waves (WWs), and can provide suitable tools for reconnection and turbulence studies. Both isothermal regimes and Landau fluid closures permitting anisotropic pressure fluctuations are considered. For small values of the electron beta parameter β e , a perturbative computation of the gyroviscous force valid at scales comparable to the electron inertial length is performed at order O(β e ), which requires second-order contributions in a scale expansion. Comparisons with kinetic theory are performed in the linear regime. The spectrum of transverse magnetic fluctuations for strong and weak turbulence energy cascades is also phenomenologically predicted for both types of waves. In the case of moderate ion to electron temperature ratio, a new regime of KAW turbulence at scales smaller than the electron inertial length is obtained, where the magnetic energy spectrum decays like k −13/3 ⊥ , thus faster than the k −11/3 ⊥ spectrum of WW turbulence.

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Section: Resultsmentioning

confidence: 79%

Section: Isothermal Regimementioning

confidence: 99%

Electron-scale reduced fluid models with gyroviscous effects

2017

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“…Figure b shows the normalized ratio of electron density

\overset{n_{e}}{true}

and magnetic field fluctuations

\overset{B}{true}

, defined as

\overset{n_{e}}{true} = {((), 1 + \frac{T_{i}}{T_{e}})}^{1 false/ 2} \frac{v_{s}}{v_{A}} {([], 1 + {((), \frac{v_{s}}{v_{A}})}^{2} ((), 1 + \frac{T_{i}}{T_{e}}))}^{1 false/ 2} \frac{n_{e}}{n_{0}},

\overset{B}{true} = \frac{B}{false| boldB false|} .

where v s is the sound speed (Boldyrev et al, ; Chen & Boldyrev, ; Chen, Boldyrev, et al, ; O. W. Roberts, Narita, Li, et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…Recently, kinetic Alfvén waves (KAWs) have been invoked to explain the morphology of the spectrum at ion kinetic scales in the solar wind (e.g., He et al, ; Podesta, ; Sahraoui et al, ; Salem et al, ; Telloni et al, ) and in the magnetosheath (Chen & Boldyrev, ). Multispacecraft observations of solar wind plasma at ion scales often reveal slowly propagating fluctuations in the plasma frame with low intrinsic frequencies ω pla ∼0 (e.g., Perrone et al, ; O. W. Roberts et al, , ).…”

Section: Introductionmentioning

confidence: 99%

Ion‐Scale Kinetic Alfvén Turbulence: MMS Measurements of the Alfvén Ratio in the Magnetosheath

Roberts

Toledo‐Redondo

Perrone

et al. 2018

Geophysical Research Letters

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Turbulence in the Earth's magnetosheath at ion kinetic scales is investigated with the magnetospheric multiscale spacecraft. Several possibilities in the wave paradigm have been invoked to explain plasma turbulence at ion kinetic scales such as kinetic Alfvén, slow, or magnetosonic waves. To differentiate between these different plasma waves is a challenging task, especially since some waves, in particular, kinetic slow waves and kinetic Alfvén waves, share some properties making the possibility to distinguishing between them very difficult. Using the excellent time resolution data set provided from both the fluxgate magnetometer and the Fast Plasma Instrument, the ratio of trace velocity fluctuations to the magnetic fluctuations (in Alfvén units), which is termed the Alfvén ratio, can be calculated down to ion kinetic scales. Comparison of the measured Alfvén ratio is performed with respect to the expectation from two‐fluid magnetohydrodynamic theory for the kinetic slow wave and kinetic Alfvén wave. Moreover, the plasma data also allow normalized fluctuation amplitudes of density and magnetic field to be compared differentiating between magnetosonic‐like and kinetic Alfvén‐like turbulence. Using these two different ratios, we can rule out that the fluctuations at ion scales are dominated by magnetosonic‐like fluctuations or kinetic slow‐like fluctuations and show that they are consistent with kinetic Alfvén‐like fluctuations. This suggests that in the wave paradigm, heating in the direction of the parallel magnetic field is predominantly by the Landau damping of the kinetic Alfvén wave.

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“…Such a regime may be relevant for the solar corona (e.g., Chandran et al 2011), hot accretion flows (e.g., Quataert 1998), collisionless shocks (e.g., Treumann 2009;Ghavamian et al 2013;Chen & Boldyrev 2017), etc. The tearing mode calculation proceeds in the usual way; it is not hard to see that the most unstable tearing mode is such that Δ′δ∼1 and δ∼d e .…”

Section: Reconnection In the Kinetic Turbulence Rangementioning

confidence: 99%

Collisionless Reconnection in Magnetohydrodynamic and Kinetic Turbulence

Loureiro

Boldyrev

2017

ApJ

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It has recently been proposed that the inertial interval in magnetohydrodynamic (MHD) turbulence is terminated at small scales not by a Kolmogorov-like dissipation region, but rather by a new sub-inertial interval mediated by tearing instability. However, many astrophysical plasmas are nearly collisionless so the MHD approximation is not applicable to turbulence at small scales. In this paper, we propose an extension of the theory of reconnectionmediated turbulence to plasmas which are so weakly collisional that the reconnection occurring in the turbulent eddies is caused by electron inertia rather than by resistivity. We find that the transition scale to reconnectionmediated turbulence depends on the plasma beta and on the assumptions of the plasma turbulence model. However, in all of the cases analyzed, the energy spectra in the reconnection-mediated interval range from μ^-(

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Nature of Kinetic Scale Turbulence in the Earth's Magnetosheath

Cited by 148 publications

References 83 publications

Electron-scale reduced fluid models with gyroviscous effects

Electron-scale reduced fluid models with gyroviscous effects

Ion‐Scale Kinetic Alfvén Turbulence: MMS Measurements of the Alfvén Ratio in the Magnetosheath

Collisionless Reconnection in Magnetohydrodynamic and Kinetic Turbulence

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