EFFECTS OF MAGNETOSPHERIC ELECTRIC-FIELDS AND NEUTRAL WINDS ON THE LOW-MIDDLE LATITUDE IONOSPHERE DURING THE MARCH 20-21, 1990, STORM

During the geomagnetic storm of March 20-21, 1990, substorm activity i s clearly evident in magnetometer data collected during the night at t he middle- and low-latitude stations Fredericksburg (38.2-degrees-N, 2 82.6-degrees-E) and San Juan (18.1-degrees-N, 293.8-degrees-E). At the same time, incoherent scatter radars at Millstone Hill (42.6-degrees- N, 288.5-degrees-E) and Arecibo (18.3-degrees-N, 293.25-degrees-E) obs erved ionospheric storm effects, which included the penetration of mag netospheric electric fields and disturbance neutral winds to the latit ude of Arecibo. The eastward electric fields associated with the subst orm disturbances result in increases in the F2 peak height (hmF2) at A recibo. Decreases in hmF2 follow as a result of increased downward dif fusion and/or the effects of an ion drag induced poleward wind. During the intervals between the electric field penetration events, equatorw ard surges in the neutral wind result in westward electric fields by t he disturbance dynamo mechanism. At these times the horizontal ionizat ion drifts are not as strong as the neutral winds, apparently because of a partial shorting out of the dynamo electric fields as a result of some E region conductivity. The anticorrelation between the component s of the ion drift parallel (V(parallel-to)) and perpendicular to the magnetic field in the northward direction (V(perpendicular-to N)) resu lts in approximately horizontal (constant altitude) ion drift motion t hroughout the interval. Calculations of spatial gradients in the elect ron density and in the components of the ion velocity are carried out using the multi-directional incoherent scatter observations at Arecibo . The results show that the variations in electron density during this disturbed interval follow closely the motion term in the F2 region co ntinuity equation, with both advection of spatial gradients and diverg ence of the ion flow important at times.