Observation of an ionospheric acceleration mechanism producing energetic (keV) ions primarily normal to the geomagnetic field direction

0+ ions with energies of approximately 1 keV have been observed flowing upward out of the ionosphere with a pitch angle distribution having a minimum along the magnetic field direction and maxima in about the 130°–140° range. The measurements were obtained with an energetic ion mass spectrometer experiment on the satellite 1976-65B at an altitude of about 7600 km in the northern dayside polar cusp. The data are interpreted as resulting from a mechanism which accelerates ambient ionospheric ions in a direction perpendicular to the geomagnetic field.