SOLARNET Conference: The Many Scales of the Magnetic Sun

Explosive phenomena are known to trigger a wealth of shocks in warm plasma environments, such as the solar chromosphere and molecular clouds, where the medium consists of both ionised and neutral species. Partial ionisation is critical in determining the behaviour of shocks, since the ions and neutrals locally decouple, allowing for substructure to exist within the shock. We study a switch-off slow-mode shock using a multi-level hydrogen model with both collisional and radiative ionisation and recombination rates implemented into the two-fluid (PIP) code, with physical parameters that are typical of the solar chromosphere.

The multi-level hydrogen model differs significantly from MHD solutions due to the macroscopic thermal energy loss during collisional ionisation. In particular, the post-shock temperature is significantly reduced and the compression is enhanced when compared to the MHD results. Furthermore, the maximum temperature within the finite-width of the shock is significantly cooler than the MHD case.

The decreased temperature and increased compression reveal the importance of non-equilibrium ionised in the thermal evolution of shocks in partially ionised media. Since partially ionised shocks are not accurately described by the Rankine-Hugoniot shock jump conditions, it may be incorrect to use these to infer properties of shocks in the lower solar atmosphere.