MHD turbulence generated by time-varying field-aligned currents

The MHD turbulence driven by time-varying field-aligned currents is calculated. It is shown that a current pulse with a parallel velocity of the order of or smaller than the Alfven velocity can generate kinetic Alfven waves. These results are applied to the interpretation of magnetic pulses observed in the auroral zone by low-altitude polar satellites. They provide a challenge to the usual interpretation in terms of a crossing by the spacecraft of static structures of thin parallel-current sheets. It must be stressed that the field-aligned current densities necessary to explain the observed magnitude of the magnetic turbulence are smaller for a time-dependent than for a static model.