A study of polar cap/dayside convection response to substorm intervals using Canadian Advanced Digital Ionosondes (CADIs), situated well within the polar cap, and SuperDARN radars during steady and prolonged southward IMF Bz conditions showed three distinct features: (1) gradual prolonged decrease of dayside/polar cap convection speed until the substorm onset; (2) sudden decrease of convection following the onset of the substorm; and (3) increase of convection during the recovery phase of the substorm. We hypothesize that the observed features of the convection are due to the modulation of the Region 1 current system associated with the substorm. The ground magnetic response of magnetometers situated inside the polar cap is at least consistent with our postulate.