An examination of the substorm onset location inferred from Polar UVI and the location of the equatorward boundary of the proton auroral oval inferred from ground based SuperDARN radars is presented. A study of 96 individual substorm events reveals that the substorms can be initiated either near the equatorward boundary of the proton auroral oval or far poleward of the equatorward boundary of the proton auroral oval depending on the preceding interplanetary conditions. When the Interplanetary Magnetic Field (IMF) is predominantly southward prior to the substorm onset, the onset location is near the equatorward boundary of the proton auoral oval; when the IMF is predominantly northward prior to the onset; the onset location is far poleward of the equatorward boundary of the proton auroral oval. The latitudinal separation (ΔΛ) between the onset location and the equatorward boundary of the proton auroral oval shows a linear dependence on the IMF.