Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence

We measure the local anisotropy of numerically simulated strong Alfvénic turbulence with respect to two local, physically relevant directions: along the local mean magnetic field and along the local direction of one of the fluctuating Elsasser fields. We find significant scaling anisotropy with resp...

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Váldodahkkit: Mallet, A, Schekochihin, A, Chandran, B, Chen, C, Horbury, T, Wicks, R, Greenan, C
Materiálatiipa: Journal article
Almmustuhtton: Oxford University Press 2016
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author Mallet, A
Schekochihin, A
Chandran, B
Chen, C
Horbury, T
Wicks, R
Greenan, C
author_facet Mallet, A
Schekochihin, A
Chandran, B
Chen, C
Horbury, T
Wicks, R
Greenan, C
author_sort Mallet, A
collection OXFORD
description We measure the local anisotropy of numerically simulated strong Alfvénic turbulence with respect to two local, physically relevant directions: along the local mean magnetic field and along the local direction of one of the fluctuating Elsasser fields. We find significant scaling anisotropy with respect to both these directions: the fluctuations are ‘ribbon-like’ – statistically, they are elongated along both the mean magnetic field and the fluctuating field. The latter form of anisotropy is due to scale-dependent alignment of the fluctuating fields. The intermittent scalings of thenth-order conditional structure functions in the direction perpendicular to both the local mean field and the fluctuations agree well with the theory of Chandran, Schekochihin & Mallet, while the parallel scalings are consistent with those implied by the critical-balance conjecture. We quantify the relationship between the perpendicular scalings and those in the fluctuation and parallel directions, and find that the scaling exponent of the perpendicular anisotropy (i.e. of the aspect ratio of the Alfvénic structures in the plane perpendicular to the mean magnetic field) depends on the amplitude of the fluctuations. This is shown to be equivalent to the anticorrelation of fluctuation amplitude and alignment at each scale. The dependence of the anisotropy on amplitude is shown to be more significant for the anisotropy between the perpendicular and fluctuation-direction scales than it is between the perpendicular and parallel scales.
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spelling oxford-uuid:b2ca956c-85a7-4c53-ab4e-933b40eddaf72022-03-27T04:14:12ZMeasures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulenceJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:b2ca956c-85a7-4c53-ab4e-933b40eddaf7Symplectic Elements at OxfordOxford University Press2016Mallet, ASchekochihin, AChandran, BChen, CHorbury, TWicks, RGreenan, CWe measure the local anisotropy of numerically simulated strong Alfvénic turbulence with respect to two local, physically relevant directions: along the local mean magnetic field and along the local direction of one of the fluctuating Elsasser fields. We find significant scaling anisotropy with respect to both these directions: the fluctuations are ‘ribbon-like’ – statistically, they are elongated along both the mean magnetic field and the fluctuating field. The latter form of anisotropy is due to scale-dependent alignment of the fluctuating fields. The intermittent scalings of thenth-order conditional structure functions in the direction perpendicular to both the local mean field and the fluctuations agree well with the theory of Chandran, Schekochihin & Mallet, while the parallel scalings are consistent with those implied by the critical-balance conjecture. We quantify the relationship between the perpendicular scalings and those in the fluctuation and parallel directions, and find that the scaling exponent of the perpendicular anisotropy (i.e. of the aspect ratio of the Alfvénic structures in the plane perpendicular to the mean magnetic field) depends on the amplitude of the fluctuations. This is shown to be equivalent to the anticorrelation of fluctuation amplitude and alignment at each scale. The dependence of the anisotropy on amplitude is shown to be more significant for the anisotropy between the perpendicular and fluctuation-direction scales than it is between the perpendicular and parallel scales.
spellingShingle Mallet, A
Schekochihin, A
Chandran, B
Chen, C
Horbury, T
Wicks, R
Greenan, C
Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence
title Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence
title_full Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence
title_fullStr Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence
title_full_unstemmed Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence
title_short Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence
title_sort measures of three dimensional anisotropy and intermittency in strong alfvenic turbulence
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AT schekochihina measuresofthreedimensionalanisotropyandintermittencyinstrongalfvenicturbulence
AT chandranb measuresofthreedimensionalanisotropyandintermittencyinstrongalfvenicturbulence
AT chenc measuresofthreedimensionalanisotropyandintermittencyinstrongalfvenicturbulence
AT horburyt measuresofthreedimensionalanisotropyandintermittencyinstrongalfvenicturbulence
AT wicksr measuresofthreedimensionalanisotropyandintermittencyinstrongalfvenicturbulence
AT greenanc measuresofthreedimensionalanisotropyandintermittencyinstrongalfvenicturbulence