Investigating the Effects of Atmospheric Stratification on Coronal Active Region Field Modeling

Abstract Understanding the evolution of the complex magnetic fields found in solar active regions is an active area of research. There exist many different models for such fields, which range in their complexity due to the number of physical effects included in them—one common factor being that they all extrapolate the field up from the photosphere. In this study, we focus on the fact that above the photosphere and below the corona lies the relatively cool and dense chromosphere—which is often neglected in coronal models, due to it being comparatively thin and difficult to model. We isolate and examine the effect including this boundary layer has on a 2.5D class of driven MHD models of an active region eruption. We find that it can result in significant changes to the dynamics of an erupting field far higher in the atmosphere than the chromosphere itself, generally delaying eruptions and increasing the magnetic energy released in each eruption. We also test whether these effects can be approximated using a variation of the more computationally efficient magnetofrictional model, finding a number of simple adaptations of the standard magnetofrictional model, which capture the effect of the chromospheric stratification well.