Magnetic Field Line Twisting by Photospheric Vortices: Energy Storage and Release

We investigate the dynamics of a closed-corona Cartesian reduced magnetohydrodynamic model where photospheric vortices twist the coronal magnetic field lines. We consider two corotating or counterrotating vortices localized at the center of the photospheric plate and, additionally, more corotating vortices that fill the plate entirely. Our investigation is specifically devoted to studying the fully nonlinear stage, after the linear stage during which the vortices create laminar and smoothly twisting flux tubes. Our main goal is to understand the dynamics of the photospheric vortices twisting the field lines of a coronal magnetic configuration permeated by finite-amplitude broadband fluctuations. We find that, depending on the system parameters and the arrangement and handedness of the photospheric vortices, an inverse cascade storing a significant amount of magnetic energy may or may not occur. In the first case, a reservoir of magnetic energy available to large events, such as destabilization of a pre–coronal mass ejection (CME) configuration, develops, while in the second case, the outcome is a turbulent heated corona. Although our geometry is simplified, our simulations are shown to have relevant implications for coronal dynamics and CME initiation.