Spectrum of Magnetohydrodynamic Turbulence

Boldyrev, Stanislav

doi:10.1103/physrevlett.96.115002

Cited by 556 publications

(698 citation statements)

References 19 publications

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“…The rate of occurrence of the linear scaling in the solar wind time series, and the corresponding energy transfer rate, have been related to several solar wind parameters. For example, the energy transfer rate has been shown to anti-correlate with the cross-helicity level Stawarz et al 2010;Marino et al 2011Marino et al , 2012Podesta 2011), confirming that alignment between velocity and magnetic field reduces the turbulent cascade, as expected for Alfvénic turbulence (Dobrowolny et al 1980;Boldyrev 2006). Relationships with heliocentric distance and solar activity have also been pointed out, with controversial results (Marino et al 2011(Marino et al , 2012Coburn et al 2012).…”

Section: Energy Transfer Ratementioning

confidence: 89%

“…Beyond the anisotropy of the fluctuations with respect to the magnetic field direction, (Boldyrev 2006) also suggested that the turbulence can be anisotropic with respect to the local fluctuation direction -and that this anisotropy will be scale dependent. Remarkably, in the solar wind observations there is some recent evidence for the scale-dependent alignment predicted by this theory at large scales (Podesta et al 2009b) and for the local 3D anisotropy small scales .…”

Section: Magnetic Fluctuationsmentioning

confidence: 99%

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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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Section: Energy Transfer Ratementioning

confidence: 89%

Section: Magnetic Fluctuationsmentioning

confidence: 99%

Solar Wind Turbulence and the Role of Ion Instabilities

et al. 2013

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“…The transition wavenumber for the γ GS k = γ NL k↑↑ transition is practically the same, k ⊥1 ρ p 0.6. However, the above estimations did not take into account the weakening of the MHD nonlinear interactions by the dynamic alignment between velocity and magnetic perturbations (Boldyrev, 2005) and/or by the nonlocal decorrelation mechanism proposed by Gogoberidze (2007). In general, the interaction rate can be written as a reduced GS rate (RGS)…”

Section: Spectral Kinksmentioning

confidence: 99%

Turbulent spectra and spectral kinks in the transition range from MHD to kinetic Alfvén turbulence

Voitenko

Keyser

2011

Nonlin. Processes Geophys.

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Abstract.A weakly dispersive range (WDR) of kinetic Alfvén turbulence is identified and investigated for the first time in the context of the MHD/kinetic turbulence transition. We find perpendicular wavenumber spectra ∝ k −3 ⊥ and ∝ k −4 ⊥ formed in WDR by strong and weak turbulence of kinetic Alfvén waves (KAWs), respectively. These steep WDR spectra connect shallower spectra in the MHD and strongly dispersive KAW ranges, which results in a specific doublekink (2-k) pattern often seen in observed turbulent spectra. The first kink occurs where MHD turbulence transforms into weakly dispersive KAW turbulence; the second one is between weakly and strongly dispersive KAW ranges. Our analysis suggests that partial turbulence dissipation due to amplitude-dependent non-adiabatic ion heating may occur in the vicinity of the first spectral kink. The threshold-like nature of this process results in a conditional selective dissipation that affects only the largest over-threshold amplitudes and that decreases the intermittency in the range below the first spectral kink. Several recent counter-intuitive observational findings can be explained by the coupling between such a selective dissipation and the nonlinear interaction among weakly dispersive KAWs.

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“…This symmetric case where the fluxes of oppositely directed Alfvén waves are equal does not however strictly apply to the solar wind (Goldreich and Sridhar, 1997), where the fluxes are observed to be asymmetric. Recent numerical simulations (Müller and Grappin, 2005), and analysis (Boldyrev, 2006 hereafter SB) obtain a ∼k −3/2 ⊥ spectrum for the case of a strong local background magnetic field. This −3/2 exponent, combined with the anisotropy of the fluctuations, is in contradiction with WI (either isotropic, −3/2 exponent or anisotropic, −2 exponent) and SA (anisotropic, −5/3 exponent) phenomenologies.…”

Section: Scaling Exponents Mhd Turbulence Models and Similarity Analmentioning

confidence: 99%

Solar cycle dependence of scaling in solar wind fluctuations

Chapman

Hnat

Kiyani

2008

Nonlin. Processes Geophys.

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Abstract. In this review we collate recent results for the statistical scaling properties of fluctuations in the solar wind with a view to synthesizing two descriptions: that of evolving MHD turbulence and that of a scaling signature of coronal origin that passively propagates with the solar wind. The scenario that emerges is that of coexistent signatures which map onto the well known "two component" picture of solar wind magnetic fluctuations. This highlights the need to consider quantities which track Alfvénic fluctuations, and energy and momentum flux densities to obtain a complete description of solar wind fluctuations.

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Spectrum of Magnetohydrodynamic Turbulence

Cited by 556 publications

References 19 publications

Solar Wind Turbulence and the Role of Ion Instabilities

Solar Wind Turbulence and the Role of Ion Instabilities

Turbulent spectra and spectral kinks in the transition range from MHD to kinetic Alfvén turbulence

Solar cycle dependence of scaling in solar wind fluctuations

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