Scale‐dependent angle of alignment between velocity and magnetic field fluctuations in solar wind turbulence

Podesta, J. J.; Chandran, Benjamin D. G.; Bhattacharjee, A.; Roberts, D. A.; Goldstein, M. L.

doi:10.1029/2008ja013504

Cited by 58 publications

(98 citation statements)

References 54 publications

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“…In this case, numerics only have to reproduce one or two steps of such cascading to obtain reasonable dissipation rate based on a particular total energy. In this sense, our testing does fairly well, as we mostly consider models of local cascading (LGS07, C08, Perez & Boldyrev 2009;Podesta & Bhattacharjee 2009); at the same time, with 768 3 numerical resolution we reproduce five to six binary steps in k-space.…”

Section: Comparison With Modelsmentioning

confidence: 97%

“…We note parenthetically that measurements of the stationary levels of energies for w + and w − are the most robust and model independent of all other measurements. Another paper, by Podesta & Bhattacharjee (2009) is a modification of Perez & Boldyrev (2009) which tries to resolve a huge discrepancy of the latter. Unfortunately, their theory has an arbitrary parameter that can be tuned to change the prediction for (w + /w − ) 2 and, therefore, cannot be tested numerically.…”

Section: Comparison With Modelsmentioning

confidence: 99%

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Structure of Stationary Strong Imbalanced Turbulence

Beresnyak

Lazarian

2009

ApJ

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In this paper, we systematically study the spectrum and structure of incompressible magnetohydrodynamic turbulence by means of high-resolution direct numerical simulations. We considered both balanced and imbalanced (cross-helical) cases and simulated sub-Alfvénic as well as trans-Alfvénic turbulence. This paper, extends numerics preliminarily reported in Beresnyak & Lazarian. We confirm that driven imbalanced turbulence has a stationary state even for high degrees of imbalance. Our major finding is that the structure of the dominant and subdominant Alfvénic components are notably different. Using the most robust observed quantities, such as the energy ratio, we believe we can reject several existing models of strong imbalanced turbulence.

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Section: Comparison With Modelsmentioning

confidence: 97%

Section: Comparison With Modelsmentioning

confidence: 99%

Structure of Stationary Strong Imbalanced Turbulence

Beresnyak

Lazarian

2009

ApJ

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“…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%

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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“…These aligned domains are the domains where the essential energy of the turbulence is contained, and they are typically well seen in numerical simulations. Solar wind observations also show that globally balanced turbulence is made up of locally imbalanced patches at all scales [36][37][38].…”

Section: Mhd Turbulence Phenomenologymentioning

confidence: 99%

On the Energy Spectrum of Strong Magnetohydrodynamic Turbulence

et al. 2012

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The energy spectrum of magnetohydrodynamic turbulence attracts interest due to its fundamental importance and its relevance for interpreting astrophysical data. Here we present measurements of the energy spectra from a series of high-resolution direct numerical simulations of magnetohydrodynamics turbulence with a strong guide field and for increasing Reynolds number. The presented simulations, with numerical resolutions up to 2048 3 mesh points and statistics accumulated over 30 to 150 eddy turnover times, constitute, to the best of our knowledge, the largest statistical sample of steady state magnetohydrodynamics turbulence to date. We study both the balanced case, where the energies associated with Alfvén modes propagating in opposite directions along the guide field, E þ ðk ? Þ and E À ðk ? Þ, are equal, and the imbalanced case where the energies are different. In the balanced case, we find that the energy spectrum converges to a power law with exponent À3=2 as the Reynolds number is increased, which is consistent with phenomenological models that include scale-dependent dynamic alignment. For the imbalanced case, withfor all Reynolds numbers considered, while E þ has a slightly steeper spectrum at small Re. As the Reynolds number increases, E þ flattens. Since E AE are pinned at the dissipation scale and anchored at the driving scales, we postulate that at sufficiently high Re the spectra will become parallel in the inertial range and scale as E þ / E À / k À3=2 ?. Questions regarding the universality of the spectrum and the value of the ''Kolmogorov constant'' are discussed.

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Scale‐dependent angle of alignment between velocity and magnetic field fluctuations in solar wind turbulence

Cited by 58 publications

References 54 publications

Structure of Stationary Strong Imbalanced Turbulence

Structure of Stationary Strong Imbalanced Turbulence

Solar Wind Turbulence and the Role of Ion Instabilities

On the Energy Spectrum of Strong Magnetohydrodynamic Turbulence

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