EXOS D observations of enhanced electric fields during the Giant Magnetic Storm in March 1989

We study spatial and temporal variations of the intense electric field that is observed in middle latitudes in the evening sector. The observations were made by the EXOS D (AKEBONO) satellite at altitudes of 2000‐6000 km during and after the great storm event of March 13‐14, 1989. During the main phase of the storm a sharp peak was observed in the poleward electric field. The strength of this field was ∼100 mV/m when projected to the ionosphere, and this corresponds to the plasma drift speed of 1.8 km/s. The position of the peak moved toward higher latitudes during the recovery phase. Comparison with the electron density profile deduced from the wave measurements (Oya et al., 1990) shows that the peak was located in the low‐density region outside the plasmapause. An intense electric field of the same kind was observed also on March 15‐17 when the geomagnetic field was only moderately disturbed.