Effects in the Martian Ionosphere Caused by the Solar Cycle Variation of the EUV Flux and Solar Wind Dynamic Pressure

Solar wind electrons can penetrate the Martian ionosphere outside of the regions of the strong crustal fields. Sometimes, in the northern hemisphere of Mars, the peak electron density does not follow the EUV radiation flux variations, as was found recently. The SW dynamic pressure is assumed to be high in such periods. The SW dynamic pressure reaches its maximum several years after solar activity begins to decline. Thus, following the solar activity maximum, the combination of decreasing EUV flux and increasing SW dynamic pressure may result in conditions such that the peak electron density is not correlated with the EUV radiation flux in that period. For the time period November 2000 - December 2002, electron density profiles have been derived from MGS radio occultation data. We study the correlation between the EUV flux using the E10.7 index and the adjusted peak electron density. Next, we use ACE SWEPAM data (daily averages) to study anti-correlation of the SW dynamic pressure and EUV radiation flux (E10.7 index) in this same time period. Finally, we validate the assumption that the effects of an increasing SW dynamic pressure can reduce any apparent correlation between the peak electron density and EUV radiation flux during the period following solar activity maximum.