Multi-year investigation of flux ropes in the Martian ionosphere

A magnetic flux rope is a collection of twisted magnetic field lines capable of transporting plasma from one region to another. Several studies report the occurrence of magnetic flux ropes in the Martian ionosphere [Cloutier et al., 1999; Vignes et al., 2004; Eastwood et al., 2008; Brain et al., 2010; Morgan et al., 2011]. Observations of a flux rope transporting ionospheric plasma away from Mars indicate that flux ropes could be an important means of atmospheric loss. Interestingly, there are at least three suggested flux rope formation mechanisms at Mars; the first is similar to Venus type events where the flux rope is formed via a shear related instability that occurs by interaction with the solar wind [Cloutier et al., 1999; Vignes et al., 2004]. The second mechanism is similar to plasmoid creation in the Earth's magnetotail, where the flux rope is created when the crustal fields stretch and shear due to interaction with the solar wind [Brain et al., 2010; Morgan et al., 2011]. The third flux rope formation mechanism is based on the identification of flux ropes near current sheets on the night side of Mars and likely created via collisionless magnetic reconnection [Eastwood et al., 2008]. Previous statistical surveys suggest that all three of these formation mechanisms are continuously active at Mars, but have had difficulty differentiating the three populations of flux ropes due to the spacecraft orbit or lack of events. We conducted a larger statistical study of the Martian flux ropes using two years of the MGS magnetic field and suprathermal electron datasets in the circular mapping orbit at ~400km. The purpose of this study is to collect a large dataset of events to characterize the flux rope formation mechanisms and study the relationship to solar cycle.