Dynamic Alignment and Exact Scaling Laws in MHD Turbulence

Abstract

Magnetohydrodynamic (MHD) turbulence is pervasive in astrophysical systems. Recent high-resolution numerical simulations suggest that the energy spectrum of strong incompressible MHD turbulence is $E(k_{\perp })\propto k_{\perp }^{-3/2}$. 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 & 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 relations are reconciled by the phenomenon of scale-dependent dynamic alignment that was recently discovered in MHD turbulence.

Published version

References in corpus (3)

• Dynamic Alignment in Driven Magnetohydrodynamic Turbulence
• Role of cross helicity in magnetohydrodynamic turbulence
• Numerical Measurements of the Spectrum in Magnetohydrodynamic Turbulence

Cited by in corpus (1)

• Simulations of Supersonic Turbulence in Molecular Clouds: Evidence for a New Universality