Auroral vortex street formed by the magnetosphere-ionosphere coupling instability

By performing three-dimensional nonlinear MHD simulations including Alfven eigenmode perturbations most unstable to the ionospheric feedback effects, we reproduced the auroral vortex street that often appears just before substorm onset. We found that an initially placed arc splits, intensifies, and rapidly deforms into a vortex street. We also found that there is a critical convection electric field for growth of the Alfven eigenmodes. The vortex street is shown to be a consequence of coupling between the magnetospheric Alfven waves carrying field-aligned currents and the ionospheric density waves driven by Pedersen/Hall currents.