Superthermal Ions Research Articles

Dynamic variations observed in thermal and superthermal ion distributions in the dayside ionosphere of venus

In-situ measurements of the ion composition and concentration of the ionosphere of Venus are obtained with the Bennett rf ion mass spectrometer (OIMS) on the Pioneer Venus Orbiter (PVO). Dayside ion profiles exhibit considerable variability in the height of the ionopause as well as the scale heights of the ion constituents, which reflect the compression and expansion of the ionosphere in response to solar wind variations. Near the dayside upper boundary of the thermal O + distribution, superthermal (E ⋍ 10–90 ev) ions are detected by the OIMS, presenting a complication for identifying the ion signature of the ionopause. Correlated with the presence of the superthermal ions, the ac electric field detector (OEFD) detects regions of intensified signals, with peak response in the 100 Hz frequency channel. A limited set of comparisons indicates that both the OIMS and the OEFD detect more pronounced enhancements in the superthermal ions and 100 Hz fields, respectively, at midlatitudes (∼ 30°N), relative to low latitudes (∼ 5°N), and that wave like variations are sometimes present. These characteristics of the superthermal ion-plasma wave results suggests that these phenomena are generated in the vicinity of the ionopause, possibly by the turbulent acceleration of planetary ions at the lower boundary of the ionosheath. It is expected that further analysis of the superthermal ion-electric field signatures will contribute to a clearer understanding of the physical processes underlying the formation of the ionopause.

Pre-dawn emission at 6300 Å and super-thermal ions from conjugate points

Analysis of the behaviour of the Doppler temperature and intensity of the red oxygen emission are presented. In winter the maximum of the Doppler temperature occurs about 1.5 h before the maximum of the intensity. A possible hypothesis to explain this phenomenon are discussed.