Bursts of transverse ion acceleration at rocket altitudes

High-time-resolution ion mass spectrometer distribution function measurements and wave data from a sounding rocket flight over an aurora have revealed the fine structure of the transverse ion acceleration mechanism in the upper ionosphere. The transversely accelerated ion (TAI) events can occur in a volume with a cross-field dimension as small as several tens of meters and thus appear as 50-100 ms ion bursts due to the rocket payload motion. Bulk heating to a characteristic energy of several eV and tail heating in the direction perpendicular to B of a few percent of ambient ions to a characteristic energy the order of 10 eV occur for both hydrogen and oxygen ions. The TAI at 90 deg pitch angle occur in localized regions of intense lower hybrid waves and in regions of density depletion. On close examination of the correlation between the wave bursts and the TAI it is believed that the waves produce the ion acceleration. The TAI occur during periods of field-aligned auroral electron bursts. Finally, near 1000 km altitude they occur about once every second. If the event presented here is considered average, the flux of TAI oxygen ions above 7 eV could account for the ion conic fluxes measured by the ISIS spacecraft.