Shock sub-structure in partially-ionised plasma.

The partially-ionised nature of the lower solar atmosphere introduces new and exciting complexities to shock solutions. Here we study numerically the slow-mode shock triggered via a magnetic discontinuity, mimicking the slow-mode shocks that can form as a result of magnetic reconnection. In single-fluid ideal MHD, the slow-mode shock occurs as a discontinuous jump in parameters. However, in the two-fluid partially-ionised plasma, the shock occupies a finite width due to the coupling and decoupling of plasma and neutral species across the shock. It is found that this finite width region allows for shock sub-structure that can affect the overall dynamics of the system. In particular, we find that an intermediate shock can exist where the plasma velocity transitions from super to sub Alfvenic velocities. A key feature of this type of shock is that the magnetic field is reversed across the interface. We present numerical results analysing the formation and evolution of intermediate shocks as sub-structure within slow-mode shocks, commenting on the potential consequences of such shocks occurring in the lower solar atmosphere.