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We find and investigate via numerical simulations self-sustainedtwo-dimensional turbulence in a magnetohydrodynamic flow with a maximallysimple configuration: plane, noninflectional (with a constant shear ofvelocity) and threaded by a parallel uniform background magnetic field. Thisflow is spectrally stable, so the turbulence is subcritical by nature and henceit can be energetically supported just by transient growth mechanism due toshear flow nonnormality. This mechanism appears to be essentially anisotropicin spectral (wavenumber) plane and operates mainly for spatial Fourierharmonics with streamwise wavenumbers less than a ratio of flow shear to theAlfv\'{e}n speed, $k_y < S/u_A$ (i.e., the Alfv\'{e}n frequency is lower thanthe shear rate). We focused on the analysis of the character of nonlinearprocesses and underlying self-sustaining scheme of the turbulence, i.e., on theinterplay between linear transient growth and nonlinear processes, in spectralplane. Our study, being concerned with a new type of the energy-injectingprocess for turbulence -- the transient growth, represents an alternative tothe main trends of MHD turbulence research. We find similarity of the nonlineardynamics to the related dynamics in hydrodynamic flows -- to the \emph{bypass}concept of subcritical turbulence. The essence of the analyzed nonlinear MHDprocesses appears to be a transverse redistribution of kinetic and magneticspectral energies in wavenumber plane [as occurs in the related hydrodynamicflow, see Horton et al., Phys. Rev. E {\bf 81}, 066304 (2010)] and differsfundamentally from the existing concepts of (anisotropic direct and inverse)cascade processes in MHD shear flows.

Nonlinear transverse cascade and two-dimensional magnetohydrodynamic subcritical turbulence in plane shear flows