Evidence for topographic effects on the Martian ionosphere

The Radio occultation experiment on board Mariner 9 has been used to demonstrate that the altitude of the main electron density peak in the Martian ionosphere is closely related to the height of Mars’ surface at the occultation point. This is direct evidence for topographic effects on the Martian ionosphere. Modeling indicates that topographic-induced modulations of the neutral density in the upper atmosphere can account for the observed ionospheric effects. The neutral density modulation is likely to be caused by nonmigrating tides in the Martian thermosphere.