It is proposed that the westward traveling surge is formed as a result of a partial blockage of the substorm-enhanced Hall current from closure in the magnetosphere. The partial blockage of the enhanced Hall current leads to a buildup of ''excess'' charge in the ionosphere that in turn produces a polarization electric field. We show that the resulting ionospheric electric field exhibits the characteristic distortion of the convection pattern associated with substorms. The distortion of the convection streamlines intrudes westward: the westward traveling surge is an optical manifestation of this intrusion. The speed of the westward traveling surge is identified with the speed of the charge spread, which depends on the time rate of change of the Hall current blockage and the propagation of charges across field lines via electrostatic ion acoustic waves in the ionosphere.