Response of the Equatorward Boundary of the Ion Auroral Oval to the Southward turning of the Interplanetary Magnetic Field

The response of the equatorward boundary of the ion aural oval in the dusk-midnight sector to the southward turning of the Interplanetary Magnetic Field (IMF), using ground based SuperDARN radars, is detailed in this paper. The equatorward boundary moves equatorward in response to the southward turning of the IMF. The equatorward motion is always delayed with respect to the southward turning of the IMF. We have estimated the boundary response delay using two methods. In the first method, we have directly used the measurement of the IMF by an upstream solar wind monitor and corrected for the propagation delay of the IMF change from the satellite to the ionosphere and estimated delay of the boundary response. This method yielded an average delay of ~37 minutes. In the second method, in order to avoid the uncertainty in the estimation of the propagation delay from the IMF monitor to the ionosphere, we have used changes in the polar cap convection as a indicator of the arrival of the change in the IMF at the ionosphere and estimated the boundary response delay from the time of the polar cap convection change. This method yielded an average delay of ~28 minutes. This confirms that the boundary response is always delayed with respect to the changes in the IMF and suggests the boundary response is consistent with the progressive propagating scenario of the changes associated with the transitions of the IMF.