Oliver Rice | Searcharxiv

arXiv2026

Global Coronal Equilibria with Solar Wind Outflow II -- Optimizing the Outflow Model

We expand upon our paper (Rice and Yeates, 2021) which introduced `Outflow Fields': alternatives to the widely-used potential field source surface (PFSS) extrapolations of the Sun's coronal magnetic field which take into account the effect of the solar Wind. We showed that our fields have several advantages over PFSS, namely more accurate measurements of the Open Solar Flux (OSF) relative to observations, more realistic streamer shapes and less dependence on the arbitrary source-surface height. In this paper we seek to quantify these improvements. This includes comparison of magnetic field line angles with eclipse photography, an improved solar wind solution model and the introduction of data from a wider range of observations. We use these comparisons to determine the optimum parameters for our model using an evolutionary algorithm, in addition to the creation of synthetic eclipse images. We find that our Outflow Fields can accurately capture the overall topology of the magnetic field, and reduce the well-known discrepancy with in-situ magnetic field measurements by a significant margin relative to PFSS. Specifically, over the period between 2000 and 2022 for a typical source-surface height we find that optimized Outflow fields reduce this discrepancy from around 45% to 24% while also matching the field line topology seen during eclipse photography. Our model is presented for wider use by the community as a new python package "outflowpy".

astro-ph.SR↗

arXiv2025

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

Understanding the evolution of the complex magnetic fields found in solar active regions is an active area of research. There are numerous models for such fields which range in their complexity due to the number of known physical effects included in them, the one common factor being 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 hard 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 eruption 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 capture the effect the chromospheric stratification well.

astro-ph.SR↗