Observations of Anisotropic Scaling of Solar Wind Turbulence

Luo, Quantian; Wu, D. J.

doi:10.1088/2041-8205/714/1/l138

Cited by 81 publications

(73 citation statements)

References 22 publications

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“…In the inertial range one observes a bifurcation of the two spectra: the perpendicular spectrum follows the Kolmogorov's slope, E(k ⊥ ) ∼ k −5/3 ⊥ , while the parallel spectrum is steeper, E(k ) ∼ k −2 . This result, initially seen in fast wind measured by Ulysses (Horbury et al 2008) has been confirmed by several other studies (Podesta 2009;Luo and Wu 2010;Wicks et al 2010Chen et al 2011a). These magnetic field spectral scaling observations provide an intriguing, if not unequivocal, connection to the Goldreich-Sridhar theory (Higdon 1984;Goldreich and Sridhar 1995).…”

Section: Magnetic Fluctuationssupporting

confidence: 80%

“…However, this interpretation requires substantial turbulent energy at k ρ i ≈ 1, that is in apparent contradiction to the Goldreich-Sridhar model and to the solar wind measurements described in the following section (Horbury et al 2008;Podesta 2009;Luo and Wu 2010;Wicks et al 2010;2011;Chen et al 2011a). This is another puzzle that has important ramifications for the coronal heating problem.…”

Section: The Mhd Scale Cascadementioning

confidence: 91%

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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: Magnetic Fluctuationssupporting

confidence: 80%

Section: The Mhd Scale Cascadementioning

confidence: 91%

Solar Wind Turbulence and the Role of Ion Instabilities

et al. 2013

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“…As has been first shown by Matthaeus et al (1990), followed by many others (see e.g. recent papers by Osman and Horbury (2009), Sahraoui et al (2010), Luo and Wu (2010), and references therein), solar wind turbulence is dominated by large perpendicular wavenumbers k ⊥ k z . In these conditions, satellites measure perpendicular wavenumber spectra, f ∝ k ⊥ , except for rare cases of B 0 V SW , where frequency measures parallel wavenumber, f ∝ k z .…”

mentioning

confidence: 68%

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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“…Moreover, in the inner heliosphere, there is only weak distance or wind speed dependence in the results, at least towards the high-frequency end of the inertial range [45,46]. Slab + 2D-type fits similar to equation (3.1) have been widely used [48][49][50]53,[60][61][62] and these also report high values for the inertial range two-dimensional fraction, e.g. 70-100%.…”

Section: (A) Review Of Observationsmentioning

confidence: 99%

“…In addition, whether B 0 is computed as a global or local mean is an important issue [23,48,60,61,[98][99][100][101][102]; see appendix B. The velocity anisotropy ratio, A v , is defined analogously.…”

Section: Component (Variance) Anisotropymentioning

confidence: 99%

Anisotropy in solar wind plasma turbulence

Oughton

Matthaeus

Wan

et al. 2015

Phil. Trans. R. Soc. A.

123

113

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One contribution of 11 to a theme issue 'Dissipation and heating in solar wind turbulence' . A review of spectral anisotropy and variance anisotropy for solar wind fluctuations is given, with the discussion covering inertial range and dissipation range scales. For the inertial range, theory, simulations and observations are more or less in accord, in that fluctuation energy is found to be primarily in modes with quasi-perpendicular wavevectors (relative to a suitably defined mean magnetic field), and also that most of the fluctuation energy is in the vector components transverse to the mean field. Energy transfer in the parallel direction and the energy levels in the parallel components are both relatively weak. In the dissipation range, observations indicate that variance anisotropy tends to decrease towards isotropic levels as the electron gyroradius is approached; spectral anisotropy results are mixed. Evidence for and against wave interpretations and turbulence interpretations of these features will be discussed. We also present new simulation results concerning evolution of variance anisotropy for different classes of initial conditions, each with typical background solar wind parameters.

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Observations of Anisotropic Scaling of Solar Wind Turbulence

Cited by 81 publications

References 22 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

Anisotropy in solar wind plasma turbulence

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