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Ground-based ionosonde and magnetic-field observations on the equatorial station Huancayo, ESRO4 neutral-composition measurements, and theoretical model calculations were used to analyze disturbed <strong>E</strong>×<strong>B</strong> vertical plasma drift during the phase of solar minimum in 1973. Vertical drifts calculated for disturbed days do not show the systematic decrease often mentioned in publications, and demonstrate strong dependence on IMF-<i>B_z</i> changes. It is confirmed with the help of our drift calculations that <i>B_z</i> turnings to a northward direction result in a decrease (up to reversal) of normal Sq (eastward during daytime and westward at nighttime) in the zonal component of electric field. Southward <i>B_z</i> excursions enhance normal <i>E_y</i> both in daytime and nighttime hours. Model predictions of <i>E_y</i>\'s reaction to IMF-<i>B_z</i> changes are discussed.