CEDAR Abstract "The Influence of Solar Variability on the Ionospheres of Earth and Mars" CEDAR Post-doc Interim Report Paul Withers and Michael Mendillo The martian ionosphere and the E-region of the terrestrial ionosphere are both dominated by photochemistry. The source of the ionization for both cases is solar flux at extreme ultraviolet wavelengths. As such, both ionospheres are very responsive to day-to-day variations in solar flux. We shall use simple photochemical theory and more detailed numerical modelling to investigate how ionospheric properties on both planets, such as peak electron densities, vary in response to changes in incident solar flux. Differences in the martian and terrestrial responses will highlight ways in which other processes, such as atmospheric tides, influence these photochemically-dominated ionospheric regions.