RESPONSE OF THE OUTER IONOSPHERE TO THE MAGNETIC STORM OF 20-22 MARCH1990

Measurements of the thermal plasma parameters in the interval 17-23 Ma rch 1990, made within the scope of the ACTIVE Project,were analysed to study the response of the outer ionosphere to the storm with SSC at 2 2.45 UT on 20 March. These measurements in the morning sector at altit udes around 2000 km clearly reflect the enhanced geomagnetic activity. They allow us to estimate the radial depth to which the plasmasphere has been affected by increased magnetospheric convection and at which a new equatorial plasmapause has formed. They also provide the possibi lity of monitoring the initial phase of recovery. The measurements in the dusk altitudes of 500-1000 km indicate a distinct trough in electr on concentration and also a trough of light ions under relatively quie t, as well as under disturbed, conditions. The position of the equator ial edge of these troughs and the position of electron temperature pea ks enable us to judge whether a plasmaspheric bulge has formed, and wh ether an inner plasmapause exists.