Effect of the solar radiation in the topside atmosphere/ionosphere of Mars: Mars Global Surveyor observations

The peak electron density in the ionosphere of Mars and the neutral atmosphere scale height are proportional to the solar radiation flux. The data of the radio occultation experiments on board Mariner 9 and Viking 1 and 2 have already been analyzed to derive the relationship between the peak electron density and neutral atmosphere scale height and F10.7 flux which was used as a proxy of the solar UV radiation. The data points from Mariner 9 and Viking 1 and 2 missions are distributed from −40° to +38° in latitude and rather nonuniformly distributed in longitude. The experiment with the Mars Global Surveyor (MGS) accelerometer has revealed significant diurnal variations and latitudinal and longitudinal variations in the neutral atmosphere density and scale height. The effect of the solar radiation can be more confidently established if the effects of diurnal, latitudinal, and longitudinal variations are minimized. In the northern hemisphere the 732 electron density profiles derived from the data of the MGS radio science experiment, which were collected during the mapping phase of the mission, are located in the narrow latitude interval from +63° to +77°. In the southern hemisphere, 219 profiles are located in the latitude interval from −69° to −64.5°. These profiles were also obtained within narrow intervals of local time and are practically uniformly distributed in longitude. The peak electron density and the effective scale height of the neutral atmosphere density in the vicinity of the ionization peak have been derived for each of the profiles studied. The daily averages of E10.7 index are derived from the solar radiation fluxes measured near Earth. Their values are then recalculated, accounting for the relative positions of Mars and the Earth, and are used as a proxy of the EUV radiation flux at Mars. For the time period November 2000 to January 2001 the calculated daily averages of the adjusted peak electron density and effective scale height have been compared with the daily averages of E10.7 index. Analysis has shown that Te was, on average, slightly larger in the southern hemisphere than it was in the northern hemisphere. The hot electrons could be actually trapped within the latitude interval from −69° to −64.5° and the strong crustal magnetic fields have detectable but modest effect in the southern hemisphere Te might be, on average, 50–60% larger than Te in the northern hemisphere. In the case of density profiles measured in the period 1–31 Janua