Possible evidence of flux transfer events in the polar ionosphere.

We present magnetic field data from the cusp-latitude South Pole station that exhibit, under appropriate local time and interplanetary magnetic field conditions, the signature predicted by recent models of a flux transfer event (FTE) at the magnetopause. In particular, these models of multiple X-line reconnection at the magnetopause predict field-aligned currents in helical flux tubes, with transverse magnetic fields propagating as Alfven waves toward the ionosphere. The signatures of FTE's at a polar cap magnetic station can be used to infer the signs of the B(y) and B(z) components of the interplanetary magnetic field.