title: Two-dimensional state in driven magnetohydrodynamic turbulence.
abstract: The dynamics of the two-dimensional (2D) state in driven three-dimensional (3D) incompressible magnetohydrodynamic turbulence is investigated through high-resolution direct numerical simulations and in the presence of an external magnetic field at various intensities. For such a flow the 2D state (or slow mode) and the 3D modes correspond, respectively, to spectral fluctuations in the plane k(∥)=0 and in the area k(∥)>0. It is shown that if initially the 2D state is set to zero it becomes nonnegligible in few turnover times, particularly when the external magnetic field is strong. The maintenance of a large-scale driving leads to a break for the energy spectra of 3D modes; when the driving is stopped, the previous break is removed and a decay phase emerges with Alfvénic fluctuations. For a strong external magnetic field the energy at large perpendicular scales lies mainly in the 2D state, and in all situations a pinning effect is observed at small scales.
authors.affiliation: Space Science Center, University of New Hampshire, Durham, New Hampshire 03824, USA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Bigot
authors.forename: Sébastien
authors.initials: S
authors.lastname: Galtier