Equatorward motion of quiet auroral arcs was studied together with the F region ionospheric plasma drift observed by the European Incoherent Scatter radar in Troms¿. Variations in the arc velocity lagged behind corresponding variations in the ionospheric convection velocity by 5--9 min. The same result was obtained from comparison of the arc velocity with variations in the eastward component of ground magnetic field. The variations in the arc and plasma drift velocities followed interplanetary magnetic field Bz variations. The observations indicate that the dawn-dusk electric potential difference arises at the open polar cap magnetic field lines due to the solar wind-magnetosphere interaction and then propagates to the closed magnetotail field lines through the ionosphere. ¿ 2001 American Geophysical Union