Global Characteristics of Magnetic Flux Ropes in Mars Atmosphere

We report observations of magnetic fields amplitude, which consist of a series of individual spike in the Martian atmosphere. A minimum variance analysis shows that these spikes form twisted cylindrical filaments. These small diameter magnetic filaments are commonly called magnetic flux ropes. We examine the global characteristics of these magnetic flux ropes, which are observed on 3% of the elliptical orbits of Mars Global Surveyor. Flux ropes are more often observed on Venus atmosphere (70% of the orbits). No flux ropes were observed on the southern hemisphere of Mars. Most of them occur at high solar zenith angle and at high latitude, close to the terminator, with altitudes below 400 km. As the Martian ionosphere is quite often magnetized by the high magnetic components of the crustal field, this crustal magnetic field seems to avoid the flux ropes formation in the southern hemisphere. However, some orbits without crustal magnetic field were observed without flux ropes. So, another factor seems to suppress the flux ropes formation process, like the solar wind dynamic pressure as for Venus. Then, the magnetization of the ionosphere by both, the crustal magnetic field and the high solar wind dynamic pressure doesn't seem favorable for flux ropes formation.