During the geomagnetic storm of March 20--21, 1990, substorm activity is clearly evident in magnetometer data collected during the night at the middle- and low-latitude stations Fredericksburg (38.2 ¿N, 282.6 ¿E) and San Juan (18.1 ¿N, 293.8 ¿E). At the same time, incoherent scatter radars at Millstone Hill (42.6 ¿N, 288.5 ¿E) and Arecibo (18.3 ¿N, 293.25 ¿E) observed ionospheric storm effects, which included the penetration of magnetospheric electric fields and disturbance neutral winds to the latitude of Arecibo. The eastward electric fields associated with the substorm disturbances result in increases in the F2 peak height (hmF2) at Arecibo. Decreases in hmF2 follow as a result of increased downward diffusion and/or the effects of an ion drag induced poleward wind. During the intervals between the electric field penetration events, equatorward surges in the neutral wind result in westward electric fields by the disturbance dynamo mechanism. At these times the horizontal ionization 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 components of the ion drift parallel (V∥) and perpendicular to the magnetic field in the northward direction (V⊥N) results in approximately horizontal (constant altitude) ion drift motion throughout the interval. Calculations of spatial gradients in the electron 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 continuity equation, with both advection of spatial gradients and divergence of the ion flow important at times. ¿ American Geophysical Union 1993