In the case of Fig. 1b, the multiple enhancements of the ionospheric electric field were well correlated with the multiple reorientations of the IMF/IEF. Kelley et al. (2003) analyzed a similar case and performed a cross-correlation to determine the solar wind propagation delay. In the cases studied in our paper, the solar wind propagation delay is determined by matching the minimum electric fields, as discussed in the previous section, and no crosscorrelation is performed.