No abstract

We investigate the anisotropy of Alfvénic turbulence in the inertial range of slow solar wind and in both driven and decaying reduced magnetohydrodynamic simulations. A direct comparison is made by measuring the anisotropic second‐order structure functions in both data sets. In the solar wind, the perpendicular spectral index of the magnetic field is close to −5/3. In the forced simulation, it is close to −5/3 for the velocity and −3/2 for the magnetic field. In the decaying simulation, it is −5/3 for both fields. The spectral index becomes steeper at small angles to the local magnetic field direction in all cases. We also show that when using the global rather than local mean field, the anisotropic scaling of the simulations cannot always be properly measured.

The feasibility of a mean-field dynamo in nonhelical turbulence with a superimposed linear shear is studied numerically in elongated shearing boxes. Exponential growth of the magnetic field at scales much larger than the outer scale of the turbulence is found. The characteristic scale of the field is lB proportional S(-1/2) and the growth rate is gamma proportional S, where S is the shearing rate. This newly discovered shear dynamo effect potentially represents a very generic mechanism for generating large-scale magnetic fields in a broad class of astrophysical systems with spatially coherent mean flows.

Two-dimensional numerical simulations of the effect of background turbulence on twodimensional resistive magnetic reconnection are presented. For sufficiently small values of the resistivity (η) and moderate values of the turbulent power ( ), the reconnection rate is found to have a much weaker dependence on η than the Sweet-Parker scaling of η 1/2 and is even consistent with an η independent value. For a given value of η, the dependence of the reconnection rate on the turbulent power exhibits a critical threshold in above which the reconnection rate is significantly enhanced.