Solar rotation effects on the Martian ionosphere

We present a detailed investigation of the solar rotation effects on the Martian high-latitude (~63°N–81°N) ionosphere using the electron density (Ne) data measured by Mars Global Surveyor and solar XUV and EUV fluxes measured by SOHO under high (2000–2001), medium (2003), and low (2005) solar activity conditions. A fast Fourier transform spectral analysis method is used to estimate the amplitude of the rotation period in these parameters. This method clearly reveals the presence of solar rotation effects in the Martian ionospheric Ne at all altitudes (90–220 km), peak electron density (NmM2), and total electron content under the three solar activity conditions. These effects are in phase with the solar UV fluxes (corrected for the Martian orbit). The period of rotation effect (~26 days) is the same at all altitudes, though its amplitude is strongest at the ionospheric M2 peak (~135–140 km, ~3.5–6% of the mean values) and has a secondary enhancement at the M1 peak (~110–115 km). The effect of solar rotation on the M2 peak is larger during medium solar activity (2003) than during high solar activity (2000–2001). The effect, however, is absent in the ionospheric peak height (hmM2). The rotation effects on Mars are also compared with those on the Earth. Unlike at Mars, the Earth's high-latitude ionosphere shows no clear solar rotation effect, though the effect is observed clearly at lower latitudes.