N. E. Turner, D. N. Baker, T. I. Pulkkinen, H. J. Singer, N. Maynard, F. Mozer, R. P. Lepping, K. Ogilvie, T. A. Fritz, T. Mukai

We have made use of several ISTP spacecraft to analyze the magnetospheric response to sudden southward turnings of the interplanetary magnetic field. Specifically, we have looked at the timing and efficiency of electric field penetration from the solar wind into the polar cap region using solar wind data from WIND, GEOTAIL, and IMP-8 and magnetospheric data from POLAR. Magnetic field data from the WIND MFI experiment were combined with solar wind velocities from the SWE experiment to calculate the interplanetary electric field. Events were then selected which exhibited a sudden change from $E_y > 0$ to $E_y < 0$ after an hour or more of relatively stable conditions. We further narrowed our event choices by requiring that POLAR be in the polar cap. We used EFI data to find responses in the magnetospheric electric field, and analyzed CEPPAD and CAMMICE data to help identify magnetospheric regions and also to look for particle energizations and flux enhancements. We found a range of responses in our events. One common signature in the EFI data was a sudden change from rapidly varying field to steady field minutes after the predicted arrival of the solar wind discontinuity. Analysis of approximately 40 events will be presented.