The solar wind (SW) mainly interacts with the Martian ionosphere/atmosphere. However, the intense crustal magnetization creates localized minimagnetospheres above the surface. The interplanetary magnetic field (IMF) can reconnect with these crustal fields and this allows SW and more energetic particles to precipitate into and heat the neutral atmosphere in localized regions, especially in the southern hemisphere. A study of 907 electron density profiles obtained by the MGS Radio Science (RS) experiment at latitudes from +63¿ to +77¿ and 219 profiles at latitudes -69¿ to -64.5¿ has been conducted. The role of the magnetic field as a driving force of the cross-terminator convection is discussed. Longitudinal variations of neutral atmosphere scale height Hpeak derived from the MGS RS data have been analyzed. Ionospheric parameters are found to be more variable in the southern than in the northern hemisphere. This correlates well with the variability of the magnetic field direction from local zenith. The scale height of neutral atmosphere density HACC derived from the MGS accelerometer data is also found to be more variable in the southern than in the northern hemisphere.