Dynamic Alignment in Driven Magnetohydrodynamic Turbulence

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 λ approximately as θ_λ∝λ^1/4. This can naturally lead to a weakening of the nonlinear interactions and provide an explanation for the energy spectrum E(k)∝k^-3/2 that is observed in numerical experiments of strongly magnetized turbulence.