It is shown that oscillations of ionospheric Doppler velocity are associated with Pc3 geomagnetic pulsations recorded at ground level. Two mechanisms are proposed to account for this association, namely, variations in the refractive index of the ionosphere due to the oscillating b↘, and vertical E↘¿B↘ drift of the ionosphere as a whole. The latter is used to determine the east-west component of pulsation electric field in the ionosphere.