Spectral energy dynamics in magnetohydrodynamic turbulence -: art. no. 114502

Spectral direct numerical simulations of incompressible MHD turbulence at a resolution of up to 1024(3) collocation points are presented for a statistically isotropic system as well as for a setup with an imposed strong mean magnetic field. The spectra of residual energy, E-k(R) = parallel to E-k(M)-E-k(K)parallel to, and total energy, E-k=E-k(K)+E-k(M), are observed to scale self-similarly in the inertial range as E-k(R)similar to k(-7/3), E-k similar to k(-5/3) (isotropic case) and E-k perpendicular to(R)similar to k(perpendicular to)(-2), E-k perpendicular to similar to k(perpendicular to)(-3/2) (anisotropic case, perpendicular to the mean field direction). A model of dynamic equilibrium between kinetic and magnetic energy, based on the corresponding evolution equations of the eddy-damped quasinormal Markovian closure approximation, explains the findings. The assumed interplay of turbulent dynamo and Alfven effect yields E-k(R)similar to kE(k)(2), which is confirmed by the simulations.