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J. Cho (U. Texas; Johns Hopkins U.), E.T. Vishniac (Johns Hopkins U.)
We perform direct 3-dimensional numerical simulations for magnetohydrodynamic (MHD) turbulence threaded by uniform magnetic fields. We analyze the structure of the eddies as a function of scale. (1) When the external fields are strong, equipartition between the kinetic and magnetic energy densities occurs at a scale near the kinetic energy peak. Our results show that anisotropy of eddies depends on the spatial size of the eddies: smaller eddies are more elongated than larger ones along magnetic field lines. These results are consistant with the scaling law k\| ~ kperp2/3 proposed by Goldreich and Sridhar (1995). (2) When the external fields are weak, the equipartition occurs at a scale somewhat smaller than the kinetic energy peak. Above the equipartition scale the velocity structure is,asexpected, nearly isotropic and the magnetic field structure is uncertain. At the equipartition scale the magnetic fields show a moderate degree of anisotropy, so that the typical radius of curvature of field lines is comparable to the typical perpendicular scale for field reversal. We do not see a large number of reversals within individual eddies, suggesting that simple arguments based on flux freezing do not apply to these simulations. At scales below the equipartition scale, both velocity and magnetic structures are anisotropic.
This work was partially supported by National Computational Science Alliance under CTS980010N and utilized the NCSA SGI/CRAY Origin2000.
The author(s) of this abstract have provided an email address for comments about the abstract: cho@pha.jhu.edu