Gyrokinetic Simulations of Solar Wind Turbulence from Ion to Electron Scales

Howes, G. G.; TenBarge, Jason; Dorland, W.; Quataert, Eliot; Schekochihin, A. A.; Numata, Ryusuke; Tatsuno, T.

doi:10.1103/physrevlett.107.035004

Cited by 243 publications

(292 citation statements)

References 27 publications

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“…Several explanations have been proposed to explain the steeper scaling. For example, Howes et al (2011) also observed a k −2.8 ⊥ magnetic spectrum in their gyrokinetic simulations, interpreting the steeper-than-k −7/3 ⊥ result as due to the presence of electron Landau damping. The steeper spectrum, however, has also been observed in simulations that do not contain such damping Franci et al 2015).…”

Section: Phenomenological Models Of Kinetic Range Turbulencementioning

confidence: 99%

Recent progress in astrophysical plasma turbulence from solar wind observations

2016

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This paper summarises some of the recent progress that has been made in understanding astrophysical plasma turbulence in the solar wind, from in situ spacecraft observations. At large scales, where the turbulence is predominantly Alfvénic, measurements of critical balance, residual energy and three-dimensional structure are discussed, along with comparison to recent models of strong Alfvénic turbulence. At these scales, a few per cent of the energy is also in compressive fluctuations, and their nature, anisotropy and relation to the Alfvénic component is described. In the small-scale kinetic range, below the ion gyroscale, the turbulence becomes predominantly kinetic Alfvén in nature, and measurements of the spectra, anisotropy and intermittency of this turbulence are discussed with respect to recent cascade models. One of the major remaining questions is how the turbulent energy is dissipated, and some recent work on this question, in addition to future space missions which will help to answer it, are briefly discussed.

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Section: Phenomenological Models Of Kinetic Range Turbulencementioning

confidence: 99%

Recent progress in astrophysical plasma turbulence from solar wind observations

2016

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“…More recent theories of strong KAW turbulence also predict a -7/3 spectrum for both density and magnetic field (Schekochihin et al 2009). The fact that the observed spectra are typically steeper than this has been explained in several ways, including electron Landau damping (Howes et al 2011b), compressibility effect (Alexandrova et al 2007) and an intermittency correction resulting in a spectral index of -8/3 . The same spectral index of −8/3 can (Chen et al 2010a).…”

Section: Ion Scale Instabilities Driven By Solar Wind Expansion and Cmentioning

confidence: 99%

“…There is a range of terminology used to describe this range, including "dissipation range", "dispersion range" and "scattering range". The possible physics taking place here includes dissipation of turbulent energy (Leamon et al 1998(Leamon et al , 1999(Leamon et al , 2000Smith et al 2006;Schekochihin et al 2009;Howes et al 2011b), a further small scale turbulent cascade (Biskamp et al 1996;Ghosh et al 1996;Galtier 2006;Alexandrova et al 2007Schekochihin et al 2009;Howes et al 2011b;Rudakov et al 2011; or a combination of both.…”

Section: Turbulence At Kinetic Scalesmentioning

confidence: 99%

Solar Wind Turbulence and the Role of Ion Instabilities

et al. 2013

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Solar wind is probably the best laboratory to study turbulence in astrophysical plasmas. In addition to the presence of magnetic field, the differences with neutral fluid isotropic turbulence are: (i) weakness of collisional dissipation and (ii) presence of several characteristic space and time scales. In this paper we discuss observational properties of solar wind turbulence in a large range from the MHD to the electron scales. At MHD scales, within the inertial range, turbulence cascade of magnetic fluctuations develops mostly in the plane perpendicular to the mean field, with the Kolmogorov scaling k −5/3 ⊥ for the perpendicular cascade and k −2 for the parallel one. Solar wind turbulence is compressible in nature: density fluctuations at MHD scales have the Kolmogorov spectrum. Velocity fluctuations do not follow magnetic field ones: their spectrum is a power-law with a −3/2 spectral index. Probability distribution functions of different plasma parameters are not Gaussian, indicating presence of intermittency. At the moment there is no global model taking into account all these observed properties of the inertial range. At ion scales, turbulent spectra have a break, compressibility increases and the density fluctuation spectrum has a local flattening. Around ion scales, magnetic spectra are variable and ion instabilities occur as a function of the local plasma parameters. Between ion and electron scales, a small scale turbulent cascade seems to be established. It is characterized by a well defined power-law spectrum in magnetic and density fluctuations with a spectral index close to −2.8. Approaching electron scales, the fluctuations are no more self-similar: an exponential cut-off is usually observed (for time intervals without quasi-parallel whistlers) indicating an onset of dissipation. The small scale inertial range between ion and electron scales and the electron dissipation range can be together described by ∼ k −α ⊥ exp(−k ⊥ d ), with α 8/3 and the dissipation scale d close to the electron Larmor radius d ρ e . The nature of this small scale cascade and a possible dissipation mechanism are still under debate.

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“…This formalism captures the large-scale fluctuations, compared to the proton thermal gyroradius. Although a kinetic approach is needed for the treatment of scales smaller than the proton gyroradius [1,2], where the interaction of kinetic Alfvén waves [3] and electron heating of the solar wind [4] become important, the self-organization of turbulent structures remains predominantly a large-scale effect, determined by fluidlike dynamics.In MHD turbulence, the conservation of cross helicity for the ideal systems represents a dynamical constraint of interest, as it is the quantity that leads to a balanced or imbalanced state of MHD turbulence. While the scaling of the energy spectra for these states has received a lot of attention in recent years [5][6][7], less effort was given to understand the impact on particle acceleration and heating due to the different arrangement of structures.…”

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confidence: 99%

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

et al. 2014

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The present work investigates the acceleration of test particles, relevant to the solar-wind problem, in balanced and imbalanced magnetohydrodynamic turbulence (terms referring here to turbulent states possessing zero and nonzero cross helicity, respectively). These turbulent states, obtained numerically by prescribing the injection rates for the ideal invariants, are evolved dynamically with the particles. While the energy spectrum for balanced and imbalanced states is known, the impact made on particle heating is a matter of debate, with different considerations giving different results. By performing direct numerical simulations, resonant and nonresonant particle accelerations are automatically considered and the correct turbulent phases are taken into account. For imbalanced turbulence, it is found that the acceleration rate of charged particles is reduced and the heating rate diminished. This behavior is independent of the particle gyroradius, although particles that have a stronger adiabatic motion (smaller gyroradius) tend to experience a larger heating. Introduction. The slow and fast streams in the solar wind represent good examples of balanced and imbalanced states (differing by the level of cross helicity; to be defined below) of magnetohydrodynamic (MHD) turbulence, respectively. This formalism captures the large-scale fluctuations, compared to the proton thermal gyroradius. Although a kinetic approach is needed for the treatment of scales smaller than the proton gyroradius [1,2], where the interaction of kinetic Alfvén waves [3] and electron heating of the solar wind [4] become important, the self-organization of turbulent structures remains predominantly a large-scale effect, determined by fluidlike dynamics.In MHD turbulence, the conservation of cross helicity for the ideal systems represents a dynamical constraint of interest, as it is the quantity that leads to a balanced or imbalanced state of MHD turbulence. While the scaling of the energy spectra for these states has received a lot of attention in recent years [5][6][7], less effort was given to understand the impact on particle acceleration and heating due to the different arrangement of structures. Although it is commonly accepted that the energy transfer rate is reduced in imbalanced MHD turbulence (for which the cross helicity is nonzero) compared to balanced turbulence [8][9][10], the issue of whether particle heating is similarly dependent on the degree of imbalance has been answered differently by different authors. Quasilinear theory, in which the diffusion of particle position and momentum in MHD turbulence is quantified via Fokker-Planck coefficients [11,12], predicts a strong dependence [13,14], although it was recently suggested that the perpendicular heating rate of ions in the solar wind may not be significantly affected by imbalance [15].In this context, two general questions arise: How do dynamical constraints on a macroscopic level, responsible for the self-organization process of turbulent structures, affect the acceleration...

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Gyrokinetic Simulations of Solar Wind Turbulence from Ion to Electron Scales

Cited by 243 publications

References 27 publications

Recent progress in astrophysical plasma turbulence from solar wind observations

Recent progress in astrophysical plasma turbulence from solar wind observations

Solar Wind Turbulence and the Role of Ion Instabilities

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

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