Simulations of Magnetohydrodynamic Turbulence in a Strongly Magnetized Medium

We analyze 3D numerical simulations of driven incompressiblemagnetohydrodynamic (MHD) turbulence in a periodic box threaded by a moderatelystrong external magnetic field. We sum over nonlinear interactions withinFourier wavebands and find that the time scale for the energy cascade isconsistent with the Goldreich-Sridhar model of strong MHD turbulence. Usinghigher order longitudinal structure functions we show that the turbulentmotions in the plane perpendicular to the local mean magnetic field are similarto ordinary hydrodynamic turbulence while motions parallel to the field areconsistent with a scaling correction which arises from the eddy anisotropy. Wepresent the structure tensor describing velocity statistics of Alfvenic andpseudo-Alfvenic turbulence. Finally, we confirm that an imbalance of energymoving up and down magnetic field lines leads to a slow decay of turbulentmotions and speculate that this imbalance is common in the interstellar mediumwhere injection of energy is intermittent both in time and space.Comment: ApJ accepted, 29 pages, 10 figures; some revisions, new figure