On the acceleration of positive ions by high‐latitude, large‐amplitude electric field fluctuations

The effect on cold ions of ionospheric origin of the low‐frequency, large‐amplitude electric field fluctuations (LEF) observed by Viking on auroral latitude magnetic field lines is calculated directly with the use of an observed time series of the electric field. The perpendicular acceleration of O+ ions is found to be more effective than that of protons. Energies in keV and tens of keV ranges are reached within a few tens of seconds by both O+ and H+ ions, but O+ ions obtain higher energies. Outflow velocities along the field line of hundreds of kilometers per second are generally acquired. Similar results can be found with a completely random variation of the electric field, but with less favoring of O+ ions over protons. The amplitude dependence of the perpendicular acceleration is roughly quadratic. The efficiency of LEF in bringing ionospheric ions of all kinds, but particularly heavier ions, into the magnetosphere is very high.