Two‐dimensional structure of the co‐planar and non‐coplanar magnetopause during reconnection

The two‐dimensional (2‐D) magnetopause transition during reconnection is investigated with large‐scale hybrid simulations. Contrary to previous studies, but in agreement with observations, the two discontinuities that form are not an intermediate shock or a slow shock. A 2‐D reconnection configuration develops with jumps that do not satisfy Rankine‐Hugoniot conditions of known discontinuities. All plasma quantities are fairly constant between the discontinuities. This region is characterized by a nearly unchanged sheath density, slight temperature enhancement, and significant magnetic field depression and thus resembles the “Sheath Transition Layer” of Song et al. 1989. For a non‐coplanar magnetic field B zo , the plasma β attains very high values on the outflow side where B zo and the Hall‐generated field cancel, and the jet becomes unstable. In this case, the magnetosheath‐side discontinuity resembles the often‐observed rotational discontinuity.