The use of the equivalent overhead current approximation for geomagnetic perturbations is critically examined by using the height-integrated ionospheric current density deduced by the Chatanika incoherent scatter radar and the simultaneous ground magnetic variations from the Alaska meridian. It is found that time variations of H on the earth's surface are in good agreement with those of the observed east-west ionospheric current density if variations in width and location of the electroject with respect to a ground-based observatory are carefully examined. However, by using the conventional infinite overhead current approximation the height-integrated current density in the ionosphere is, on the average, underestimated by a factor of 2 or more.