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 January 2001 in the northern hemisphere Te is likely primarily controlled by the solar wind interaction with the Martian atmosphere/ionosphere.

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[1] We report observations that show the dependence of the altitude of the magnetic pileup boundary (MPB) at Mars on planetary latitude. As seen by the Mars Global Surveyor Magnetometer/Electron Reflectometer instrument, the MPB is further away from Mars on average at southern latitudes than at northern latitudes. The data are consistent with a MPB distance mapped to the terminator plane that does not vary with latitude in the northern hemisphere, but increases with increasing southern latitude in the southern hemisphere. We also report increased variability in the MPB distance within the longitude range 90 -270°E. longitude in the southern hemisphere which is the region that contains the strongest crustal magnetic fields. These trends are most obvious in a planet-fixed coordinate system, indicating a planet-fixed driver of the MPB location. The proposed mechanism is the local diversion of shocked solar wind flow by crustal magnetic fields. INDEX TERMS: 2780 MagnetosphericPhysics: Solar wind interactions with unmagentized bodies; 6225

[1] The magnetic fluxes associated with the Martian crustal remanent magnetization have been studied in order to investigate the global structure of the magnetic field in and above the level of the Martian ionosphere. The intensely and nonuniformly magnetized crustal sources generate an effective large-scale magnetic field. Reconnection with the interplanetary magnetic field can possibly take place in many localized regions. This will permit solar wind (SW) and more energetic particles to precipitate into and heat the neutral atmosphere by impact ionization. This may occur not only in cusp-like field structures above nearly vertical field anomalies but also in halos extending several hundreds of kilometers from these sources. Numerous cusp-like regions may exist above the many crustal anomalies in the southern hemisphere. The large-scale horizontal magnetic fields due to the crustal sources and induced by the SW interaction are responsible for controlling the detailed structure of the Martian ionosphere. Radio occultation observations in the southern hemisphere show relatively constant and low average values of the electron density scale height and zero dependence on zenith angle in contrast to that of nonmagnetic Venus.

[1] Electron density profiles of the ionosphere of Mars derived from radio occultation data obtained by the radio science Mars Global Surveyor (MGS) experiment have been compared with the crustal magnetic fields measured by the MGS Magnetometer/Electron Reflectometer (MAG/ER) experiment. In the northern hemisphere the crustal fields are rather weak and usually do not prevent direct interaction between the solar wind (SW) and the Martian ionosphere/atmosphere. Exceptions do occur in the isolated minimagnetospheres formed by the crustal anomalies. Much stronger crustal fields are located in limited regions in the southern hemisphere and lead to the formation of large-scale mini-magnetospheres. A study of the electron density profiles obtained when the minimagnetosphere regions are near the terminator has been conducted using the magnetic field measurements at altitudes 170-180 km and 400 km. The magnitude of the electron density peak and the effective scale-height of the electron density for two altitude ranges, 145-165 km and 165-185 km, have been derived for each of the 326 selected profiles studied. In each hemisphere, the longitudinal variations of these derived parameters have been studied. A significant difference between the large-scale minimagnetospheres and regions outside of them has been found. The neutral atmosphere is cooler inside the large-scale mini-magnetospheres. The variations of the magnitude of the electron density peak indicate that the electrons are usually ''hotter'' inside a largescale mini-magnetosphere than outside. It appears that the mini-magnetospheres formed by strong crustal magnetic fields prevent additional heating of the neutral atmosphere due to direct interaction of the SW and also confine the hotter electrons created by photo ionization.