Ionospheric origin of magnetospheric O+ ions

Flows of thermal atomic oxygen (O+) ions are deduced from topside ionospheric plasma density profiles. The mean flux within most of the polar cap is of the order of 10^12 m^{−2} s^{−1}, a figure which is consistent with both theoretical and experimental estimates of the light ion polar wind at greater altitudes. Larger flows (up to 6 × 10^12 m^{−2} s^{−1}) are observed near the poleward edge of the night-side statistical auroral oval, a feature not reproduced in the light ion flux. The implication is one of a low altitude acceleration mechanism, acting upon the O+ ions at these latitudes and at heights above that at which the fluxes are observed. Such a process would enable ions to escape from the ionosphere because they do not exchange charge with neutral hydrogen. The observations are in general agreement with energetic O+ ions as previously observed in various parts of the magnetosphere.

The bottomside mid-latitude ionospheric trough

The measured power losses and Doppler shifts of h.f. radio waves propagated over a long, west-east, sub-auroral path are found to exhibit features which cannot be explained by simple predictions and models. Both theory and the limited available data indicate that a bottomside F2-layer depletion should be present below the topside mid-latitude trough. Introducing this into the models (using the mean statistical positions of the trough deduced from Alouette I and II soundings) is shown to explain many of these features. From the Doppler shifts and a simple ray-tracing model the height of the depleted F2-peak inside the trough is deduced to be greater than its value outside the trough by an amount of the order of only 30–80 km.