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Title: Dynamic Alignment in Driven Magnetohydrodynamic Turbulence

Authors:
; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1212014
Resource Type:
Journal Article
Resource Relation:
Journal Name: PHYSICAL REVIEW LETTERS; Journal Volume: 97; Journal Issue: 25
Country of Publication:
United States
Language:
English

Citation Formats

Mason, J, Cattaneo, F, and Boldyrev, S. Dynamic Alignment in Driven Magnetohydrodynamic Turbulence. United States: N. p., 2006. Web. doi:10.1103/PhysRevLett.97.255002.
Mason, J, Cattaneo, F, & Boldyrev, S. Dynamic Alignment in Driven Magnetohydrodynamic Turbulence. United States. doi:10.1103/PhysRevLett.97.255002.
Mason, J, Cattaneo, F, and Boldyrev, S. Wed . "Dynamic Alignment in Driven Magnetohydrodynamic Turbulence". United States. doi:10.1103/PhysRevLett.97.255002.
@article{osti_1212014,
title = {Dynamic Alignment in Driven Magnetohydrodynamic Turbulence},
author = {Mason, J and Cattaneo, F and Boldyrev, S},
abstractNote = {},
doi = {10.1103/PhysRevLett.97.255002},
journal = {PHYSICAL REVIEW LETTERS},
number = 25,
volume = 97,
place = {United States},
year = {Wed Dec 20 00:00:00 EST 2006},
month = {Wed Dec 20 00:00:00 EST 2006}
}
  • Motivated by recent analytic predictions, we report numerical evidence showing that in driven incompressible magnetohydrodynamic turbulence the magnetic- and velocity-field fluctuations locally tend to align the directions of their polarizations. This dynamic alignment is stronger at smaller scales with the angular mismatch between the polarizations decreasing with the scale {lambda} approximately as {theta}{sub {lambda}}{proportional_to}{lambda}{sup 1/4}. This can naturally lead to a weakening of the nonlinear interactions and provide an explanation for the energy spectrum E(k){proportional_to}k{sup -3/2} that is observed in numerical experiments of strongly magnetized turbulence.
  • Magnetohydrodynamic (MHD) turbulence is pervasive in astrophysical systems. Recent high-resolution numerical simulations suggest that the energy spectrum of strong incompressible MHD turbulence is E(k{sub perpendicular}) {proportional_to} k {sup -3/2}{sub perpendicular}. So far, there has been no phenomenological theory that simultaneously explains this spectrum and satisfies the exact analytic relations for MHD turbulence due to Politano and Pouquet. Indeed, the Politano-Pouquet relations are often invoked to suggest that the spectrum of MHD turbulence instead has the Kolmogorov scaling -5/3. Using geometrical arguments and numerical tests, here we analyze this seeming contradiction and demonstrate that the -3/2 scaling and the Politano-Pouquet relationsmore » are reconciled by the phenomenon of scale-dependent dynamic alignment that was recently discovered in MHD turbulence.« less
  • We show that local directional alignment of the velocity and magnetic field fluctuations occurs rapidly in magnetohydrodynamics for a variety of parameters and is seen both in direct numerical simulations and in solar wind data. The phenomenon is due to an alignment between magnetic field and gradients of either pressure or kinetic energy, and is similar to alignment of velocity and vorticity in Navier-Stokes turbulence. This rapid and robust relaxation process leads to a local weakening of nonlinear terms.