Chromospheric extension of the MURaM code

Context . Detailed numerical models of the chromosphere and corona are required to understand heating solar atmosphere. An accurate treatment is complicated by effects arising from non-local thermodynamic equilibrium (NLTE) radiative transfer. A small number strong, highly scattering lines dominate cooling in chromosphere. Additionally, recombination times ionised hydrogen longer than dynamical timescales, requiring a non-equilibrium (NE) ionisation. Aims. We describe set necessary additions MURaM code that allow it handle some important NLTE effects. investigate impact on caused NE radiation magnetohydrodynamic simulations Methods. The was extended include physical process for an simulation chromosphere, as implemented Bifrost code. This includes time-dependent ionisation, multi-group transfer scheme, approximations cooling. Results. inclusion physics has large structure chromosphere; ionisation leads higher fraction enhanced populations first excited state throughout cold inter-shock regions this prevents buffering energy fluctuations, leading hotter shocks cooler regions. ground 10 2 –10 3 upper up 9 near transition region. Conclusions. Including significant differences chromospheric dynamics. thermodynamics calculated using version consistent with previous simulations. electron temperature accurately synthesise spectral lines.