Dynamic Martian Magnetosphere: Transient Twist Induced by a Rotation of the IMF

International audienceSimulation studies of the Martian environment are usually restricted to stationary situations under various static conditions of the solar wind and solar radiation. Dynamic transients and their implications have so far attracted little attention although global simulation models can provide valuable insights to understand disagreements between simulations and in situ observations. We make use for the first time of the three dimensional multispecies hybrid simulation model that we have developed (Modolo et al., Ann. Geophys., 23, 433, 2005) to investigate the response of the Martian plasma environment to a sudden rotation of the IMF. The simulation model couples charged and neutral species via three ionisation mechanisms: the absorption of solar extreme ultraviolet radiation, the impacts of solar wind electrons, and the charge exchanges between ions and neutral atoms or molecules. When a rotational discontinuity conveyed by the solar wind reaches the Martian environment the bow shock adapts quickly to the new solar wind conditions in contrast to the induced magnetosphere, especially the magnetic lobes in the wake. Timescales necessary to recover a stationary state can be estimated from such simulations, and implications for space observations will be discussed, especially the use of magnetic field proxies for ordering particle measurements made by a spacecraft like Mars Express without an onboard magnetometer. Moreover the spatial distribution of escaping ion fluxes being significantly modified by time dependant solar wind conditions, a reassessment of simulated escape is worth the effort in order to improve the comparison with fluxes derived from observations