Small Scales Structure of MHD Turbulence, Tubes or Ribbons? - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2017

Small Scales Structure of MHD Turbulence, Tubes or Ribbons?

Résumé

Observations in the solar wind indicate that turbulent eddies change their anisotropy with scales [1]. At large scales eddies are elongated in direction perpendicular to the mean-field axis. This is the result of solar wind expansion that affects both the anisotropy and single-spacecraft measurments [2,3]. At small scales one recovers the anisotropy expected in strong MHD turbulence and constrained by the so-called critical balance: eddies are elongated along the mean-field axis. However, the actual eddy shape is intermediate between tubes and ribbons, preventing us to discriminate between two concurrent theories that predict 2D axysimmetric anisotropy [4] or full 3D anisotropy [5]. We analyse 10 years of WIND data and apply a numerically-derived criterion to select intervals in which solar wind expansion is expected to be negligible. By computing the anisotropy of structure functions with respect to the local mean field we obtain for the first time scaling relations that are in agreement with full 3D anisotropy, i.e. ribbons-like structures. However, we cannot obtain the expected scaling relations for the alignment angle which, according to the theory, is physically responsible for the departure from axisymmetry. In addition, a further change of anisotropy occurs well above the proton scales. We discuss the implication of our findings and how numerical simulations can help interpreting the observed spectral anisotropy. [1] Chen et al., ApJ, 768:120, 2012 [2] Verdini & Grappin, ApJL, 808:L34, 2015 [3] Vech & Chen, ApJL, 832:L16, 2016 [4] Goldreich & Shridar, ApJ, 438:763, 1995 [5] Boldyrev, ApJL, 626:L37, 2005
Fichier non déposé

Dates et versions

hal-02796754 , version 1 (05-06-2020)

Identifiants

  • HAL Id : hal-02796754 , version 1

Citer

Andrea Verdini, Roland Grappin, O. Alexandrova, S. Lion. Small Scales Structure of MHD Turbulence, Tubes or Ribbons?. American Geophysical Union, Fall Meeting, Dec 2017, New Orleans, Louisiane, United States. pp.SH41D-02. ⟨hal-02796754⟩
13 Consultations
0 Téléchargements

Partager

Gmail Mastodon Facebook X LinkedIn More