We use Mars Atmosphere and Volatile EvolutioN observations of the upstream solar wind , and Mars Express observations of ionospheric electron densities and magnetic fields , to study how the topside ionosphere ( > 320 km ) of Mars is affected by variations in solar wind dynamic pressure .
We find that high solar wind dynamic pressures result in the topside ionosphere being depleted of plasma at all solar zenith angles , coincident with increased induced magnetic field strengths .
The depletion of topside plasma in response to high solar wind dynamic pressures is observed in both weak and strong crustal magnetic field regions .
Taken together , our results suggest that high solar wind dynamic pressures lead to ionospheric compression , increased ion escape , and reduced day-to-night plasma transport in the high-altitude nightside ionosphere .