Variability of the Solar Wind Flow Asymmetry in the Martian Magnetosheath observed by MAVEN

Abstract:

The solar wind interaction with Mars starts upstream from the Martian bow shock, partly due to the presence of the extended oxygen atmosphere. A recent study has shown that the coupling between the former and the oxygen planetary ions results in the lateral deflection of the solar wind flow in the Martian magnetosheath, in the direction opposite to the solar wind convective electric field [Dubinin et al., 2017]. In this work, we provide a comprehensive characterization of the resulting solar wind flow asymmetry in the magnetosheath making use of five years of MAVEN Magnetometer and Solar Wind Ion Analyzer data between November 2014 and November 2019. In addition, we quantify effects that several properties of the magnetized solar wind upstream from the Martian bow shock, e.g., solar wind velocity, density, interplanetary magnetic field (IMF), have on such magnetosheath flow deflection at the terminator plane. In particular, we find that the difference between the mean magnetosheath solar wind velocity component along the solar wind convective electric field in the positive and negative hemispheres displays an approximate linear dependence with the ratio between the upstream IMF cross-flow component and the solar wind proton density. Moreover, we also characterize the variability of such linear relationship as a function of the distance along the Sun-Mars line. These results suggest that the observed solar wind deflection and variability with the external conditions can be associated with an electromagnetic force that depends linearly on the differential streaming between solar wind protons and planetary oxygen ions, with boundary conditions partly defined by the pristine solar wind properties.