Scaling and anisotropy in magnetohydrodynamic turbulence in a strong mean magnetic field

We present an analysis of the anisotropic spectral energy distribution in incompressible magnetohydrodynamic turbulence permeated by a strong mean magnetic field. The turbulent flow is generated by high-resolution pseudospectral direct numerical simulations with large-scale isotropic forcing. Examining the radial energy distribution for various angles theta with respect to B-0 reveals a specific structure which remains hidden when not taking axial symmetry with respect to B-0 into account. For each direction, starting at the forced large scales, the spectrum first exhibits an amplitude drop around a wave number k(0) which marks the start of a scaling range and goes on up to a dissipative wave number k(d)(theta). The three-dimensional spectrum for k >= k(0) is described by a single theta-independent functional form F(k/k(d)), with the scaling law being the same in every direction. The previous properties still hold when increasing the mean field from B-0 = 5 up to B-0 = 10b(rms), as well as when passing from resistive to ideal flows. We conjecture that at fixed B-0 the direction-independent scaling regime is reached when increasing the Reynolds number above a threshold which raises with increasing B-0. Below that threshold critically balanced turbulence is expected.