Leveling of MHD turbulence imbalance in shear flows

We investigate magnetohydrodynamic (MHD) turbulence in plane shear flows with a streamwise background magnetic field in the super-Alfvénic regime. We show that the large-scale velocity shear suppresses turbulence imbalance, driving the system toward a balanced state – the energies of counter-propagating Alfvén waves become essentially equal, even at initially perfectly imbalanced Alfvénic turbulence. This balancing is due to the shear-induced linear non-modal dynamics of Alfvén waves, including their transient growth and over-reflection. This linear route to balancing turbulence is new – fundamentally different from nonlinear ones operative in shearless MHD turbulence – and have direct implications for understanding balanced/imbalanced MHD turbulence in the solar wind, which is modeled as a shear flow in a thermodynamically complex plasma.