  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.
