Simultaneous observation of upward moving field‐aligned energetic electrons and ions on auroral zone field lines

We present Viking observations of energetic electrons and ions which move upward along the magnetic field lines with energies of the same order of magnitude. The field‐aligned particles are associated with a strong broadband low‐frequency turbulence in the electric field and with downward Birkeland currents. We suggest that both ions and electrons are accelerated by a time‐varying field‐aligned electric field component. The downward field component accelerating the electrons upward is experienced as quasi‐static by the electrons while they remain in the height‐limited acceleration region. For the ions the fluctuating field is a wave field which has only a small translational effect on them.