Large-Scale Magnetic Field Convection and Flux Ropes in the Ionospheres of Mars and Venus

The pattern of the magnetic field/plasma convection can be, to some extent, recovered from the magnetic field measurements by employing either theoretical or numerical models. Pioneer-Venus Orbiter magnetic field measurements have been used to study large-scale convection-diffusion of the interplanetary magnetic fields in the Venusian day-side ionosphere and formation of flux ropes. For the sake of comparison, we use the MAG/ER day-time measurements of the magnetic field at the altitudes from 90 to 180 km during the elliptical orbits of MGS. Analysis of the altitude variation of the characteristics of the large-scale magnetic fields, which were measured away from the crustal magnetic anomalies, is summarized. The low density of the Martian atmosphere together with the crustal magnetization results in remarkable differences of the magnetic field features within the ionosphere of Venus and Mars (even in its Venus-like northern hemisphere where the crustal magnetization is, on average, low). Various scenarios of flux ropes formation and evolution are discussed in order to explain why only a few flux ropes were observed deep inside the subsolar ionosphere of Mars.