Electric field induced drifts from the French Incoherent Scatter Facility

The Saint-Santin facility has been operating in its quadristatic configuration since October 1973. A set of 8 days and 7 nights (winter and equinox) of F region drift measurements perpendicular to the magnetic field is presented and provides information on the ionospheric electric fields. For quiet magnetic conditions the day-to-day variability is found to be weak, and the corresponding daily variations show the dominance of a 50 m/s diurnal oscillation in east-west drifts and of a 15–20 m/s terdiurnal oscillation in north-south drifts. None of the presently available models of quiet time electric fields have been found to reproduce this data over 24 hours. Comparison with other mid- and low-latitude electric field results shows a rather good agreement with incoherent scatter results south of Saint-Santin but a strong contrast with Millstone Hill results despite comparable geographic latitudes. For disturbed magnetic conditions, perpendicular drift velocities appear displaced from their quiet day values with a tendency to westward deviations. On some occasions those displacements reach large values of 100 m/s (4 mV/m electric field) and more over 1 or 2 hours. An interpretation in terms of penetration of the plasmasphere by electric fields associated with magnetospheric substorms is suggested.