We investigate the transient response of the Earth's magnetosphere-ionosphere system to a localized density pulse in the solar wind using a magnetohydrodynamic simulation. The simulated ionospheric disturbances exhibit many properties similar to those observed during traveling convection vortices (TCVs). The simulated TCVs are driven by pairs of field-aligned currents. The generation mechanisms of the field-aligned currents in the magnetosphere are evaluated in terms of a wave equation of field-aligned currents. The source current is the inertial current associated with in-out plasma acceleration in the magnetosphere near the impact region. The inertial current is converted into the field-aligned current off from the equatorial region via the curvilinear effect. The inhomogeneous effect also generates the field-aligned current near the inner equatorial region where the sharp gradient of Alfv¿n speed exists.