Particle measurements at 3 RE in the auroral zone revealed the existence of simultaneous upgoing hydrogen and oxygen beams on auroral field lines. The observed beam distributions were broad, indicating that significant heating took place near or below the satellite. The most interesting features that were noted in the distribution functions included extended parallel O+ high energy and H+ low energy tails, and a perpendicular broadening of the O+ distribution. The purpose of the present work was to carry out an analysis of the mechanism that could produce such heating, and to base this analysis as fully as possible on plasma and wave parameters measured by the Dynamics Explorer 1 (DE 1) satellite. An analysis of Maxwellian fits to the observed distribution functions showed that an oblique slow hydrogen acoustic mode was weakly unstable at frequencies between the oxygen and hydrogen gyrofrequencies. The location of wave-particle resonant and nonresonant regions in velocity space suggested qualitatively that H+ undergoes weak parallel heating on the low velocity side of the beam and that O+ is heated in the perpendicular direction on the high velocity side of the beam at satellite altitude. Energy is transferred from parallel motion of H+ to perpendicular motion of O+ during this process.

Calculations of diffusion time scales for both H+ and O+ showed quantitatively that resonant diffusion within 1 RE of the satellite is sufficiently fast to explain the perpendicular O+ heating and a substantial portion of the parallel H+ heating. Some additional parallel diffusion of both species must have taken place below the satellite. Nonresonant diffusion and interactions of ions with a parallel H+ acoustic wave, which may be unstable below the satellite, could be responsible for this additional heating. These processes transfer energy from parallel motion of H+ to parallel motion of O+. The presence of a third ion species also could have modified the parallel heating rate. These latter possibilities could not be studied in detail with the available data. ¿ American Geophysical Union 1989