Influence of velocity-magnetic field correlations on decaying magnetohydrodynamic turbulence with neutral X points

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Abstract
Direct numerical simulations at resolutions up to (512)2 of developed turbulence in nondriven two‐dimensional incompressible magnetohydrodynamic (MHD) flows are presented. In all cases, there is no background magnetic field. Nevertheless, periodic exchanges of kinetic and magnetic energies are observed, an effect that is reminiscent of interference of linear Alfvén waves; three‐dimensional runs also display such oscillations. This effect is inhibited by the velocity‐magnetic field correlations. It is also found that the correlations do not sizably affect the characteristic transfer time of energy to the small scales, but significantly reduce the maximum amplitude of velocity and magnetic field gradients. It is shown that velocity‐magnetic field correlation also affects inertial range spectral indices, a result that validates predictions based on two‐point closures [Astron. Astrophys. 1 2 6, 151 (1983)].