Multiple time scales in anisotropic magnetohydrodynamics

Abstract

The consequences of a multiple time-scale resonance theory of magnetohydrodynamics with a strong (vertical) background field are examined and compared with direct numerical solutions at high Reynolds number. The background field defines a characteristic wavenumber kL. Modes with vertical wavenumber above kL are passively driven by the k=0 mode, even when the majority of the energy is contained in the passive wavenumbers. The passive modes do not cascade to higher vertical wavenumbers, so the vertical wavenumber spectrum is not a power law and does not extend to dissipation scales. The k=0 mode evolves with two-dimensional dynamics, forming coherent current structures which are mirrored by the passive modes.