X ray pulsations with a period of ~150 s were observed in the predawn hours during a balloon flight from S¿ndre Str¿mfjord, Greenland (L=14.5). Simultaneous riometer observations of auroral absorption at the south pole showed absorption pulsations with a period of ~300 s. These results suggest surface wave instabilities with different temporal features on portions of the magnetopause above and below the magnetic equator.