Magnetic Field in the Martian Magnetosheath and the Application as an IMF Clock Angle Proxy

We present a study of the magnetic field in the Martian magnetosheath using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission and provide a proxy for the upstream interplanetary magnetic field (IMF) clock angles based on the sheath field directions. The magnetic field data from MAVEN taken in the sheath region are organized in the Mars Solar Electric field coordinate system and sorted by the IMF polarity. The sheath magnetic field distributions clearly illustrate the morphology of draped IMF around the planetary obstacle and show strong asymmetries between the quasi‐perpendicular and quasi‐parallel bow shock quadrants as well as a slight asymmetry between the +Eand –Equadrants. We have also studied the effects of different drivers on the strengths and clock angles of the sheath magnetic field and find that the sheath field is strongly affected by upstream IMF and solar wind and that Martian crustal fields also have small contributions to the sheath magnetic field strength. Based on the morphology of the draped field in the sheath, we developed a simple IMF clock angle proxy as the clock angle of the orbital‐averaged sheath magnetic field, which works well under steady IMF conditions. This proxy has an error <44° for 75% of all instances. The uncertainty of the proxy depends on upstream conditions and spacecraft orbit geometry. We also provide estimates of the proxy uncertainty based on sheath magnetic field variability and proxy clock angle. The magnetic field in the Martian magnetosheath shows asymmetric features with respect to the upstream electric field and IMF directionsThe sheath magnetic field is mainly controlled by IMF and solar wind conditions and slightly modified by Martian crustal fieldsThe sheath magnetic field can be used as an IMF clock angle proxy with an error <45 degrees for 75% of all instances