Modelling Optically Thick Radiation from Solar Flares with the Lightweaver Framework

Abstract:

Most spectral lines formed in the chromosphere present complex profiles due to their formation in optically thick regions and this is further exacerbated by the rapid variations of this layer during a flare. Whilst these lines carry a wealth of information regarding their formation conditions, this information is difficult to extract. The Lightweaver framework is flexible new software package for synthesising radiation from both plane-parallel and multi-dimensional atmospheres where the atomic populations can be out of local thermodynamic equilibrium. In addition to the more commonly solved statistical equilibrium equations, Lightweaver also provides tools to facilitate solving the problem of time-dependent level populations. This framework is an open source project designed to be used through Python and easily reconfigured to solve new problems. We have applied tools built on Lightweaver to reprocess simulations produced by the RADYN code, allowing further investigation into the effects of partial frequency redistribution, and calculation of response functions in this time dependent context. We expect that these new methods should provide additional diagnostic potential coinciding with observations from next generation telescopes such as DKIST. Lightweaver is also being used to investigate the effect of the radiation emitted from compact flare kernels on surrounding plasma, by extending this reprocessing to multi-dimensional radiative transfer. We will present the Lightweaver framework and discuss how it can easily be adapted to investigate these different phenomena as well as the initial results from these investigations.