The Lightweaver Framework for Nonlocal Thermal Equilibrium Radiative Transfer in Python

Osborne, Christopher; Milić, Ivan

doi:10.3847/1538-4357/ac02be

Cited by 22 publications

(17 citation statements)

References 41 publications

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“…In Jenkins & Keppens (2021, 2022, we used the MPI-AMRVAC 2.0 toolkit (Xia et al 2018;Keppens et al 2021) to construct realistic 2.5 & 3 dimensional representations of solar prominences and filaments (see also, Kaneko & Yokoyama 2018). This was corroborated through a direct comparison between simulations and observations.…”

Section: Methodsmentioning

confidence: 99%

“…The recently developed Lightweaver framework (Osborne & Milić 2021) is used to solve the radiative transfer equation and statistical equilibrium equations for a given stratification of atmospheric parameters. Lightweaver determines the non LTE populations of the species in the plasma by iteratively computing the associated radiation field (using the cubic Bézier short characteristic formal solver of de la Cruz Rodríguez & Piskunov (2013)) and then updating the atomic level populations taking into account the updated radiative and collisional rates (using the fully preconditioned Multilevel Accelerated Lambda Iteration (MALI) method (Rybicki & Hummer 1992;Uitenbroek 2001)).…”

Section: The Lightweaver Frameworkmentioning

confidence: 99%

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1.5D non-LTE spectral synthesis of a 3D filament and prominence simulation

Jenkins

Osborne

Keppens

2023

A&A

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Context. Overly idealised representations of solar filaments and prominences in numerical simulations have long limited their morphological comparison against observations. Moreover, it is intrinsically difficult to convert simulation quantities into emergent intensity of characteristic, optically thick line cores and/or spectra that are commonly selected for observational study. Aims. In this paper, we demonstrate how the recently developed Lightweaver framework makes non-'local thermodynamic equilibrium' (NLTE) spectral synthesis feasible on a new 3D ab initio magnetohydrodynamic (MHD) filament-prominence simulation, in a post-processing step. Methods. We clarify the need to introduce filament-and prominent-specific Lightweaver boundary conditions that accurately model incident chromospheric radiation, and include a self-consistent and smoothly varying limb-darkening function.Results. Progressing from isothermal and isobaric models to the self-consistently generated stratifications within a fully 3D MHD filament-prominence simulation, we find excellent agreement between our 1.5D NLTE Lightweaver synthesis and a popular Hydrogen Hα proxy. We computed additional lines including Ca ii 8542 alongside the more optically thick Ca ii H&K & Mg ii h&k lines, for which no comparable proxy exists, and we explore their formation properties within filament and prominence atmospheres. Conclusions. The versatility of the Lightweaver framework is demonstrated with this extension to 1.5D filament and prominence models, where each vertical column of the instantaneous 3D MHD state is spectrally analysed separately, without accounting for (important) multi-dimensional radiative effects. The general agreement found in the line core contrast of both observations and the Lightweaver-synthesised simulation further validates the current generation of solar filament and prominence models constructed numerically with MPI-AMRVAC.

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Section: Methodsmentioning

confidence: 99%

Section: The Lightweaver Frameworkmentioning

confidence: 99%

1.5D non-LTE spectral synthesis of a 3D filament and prominence simulation

Jenkins

Osborne

Keppens

2023

A&A

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“…Note that a new radiation transfer code capable of including time-dependent effects (if sufficiently high-cadence snapshots are available) and processes such as PRD and overlapping transitions has recently been developed: Lightweaver (Osborne and Milić, 2021). This exciting new resource has not yet been used to study IRIS observables (to my knowledge!)…”

Section: Forward Modelling Iris Observablesmentioning

confidence: 99%

Interrogating solar flare loop models with IRIS observations 1: Overview of the models, and mass flows

Kerr

2022

Front. Astron. Space Sci.

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Solar flares are transient yet dramatic events in the atmosphere of the Sun, during which a vast amount of magnetic energy is liberated. This energy is subsequently transported through the solar atmosphere or into the heliosphere, and together with coronal mass ejections flares comprise a fundamental component of space weather. Thus, understanding the physical processes at play in flares is vital. That understanding often requires the use of forward modelling in order to predict the hydrodynamic and radiative response of the solar atmosphere. Those predictions must then be critiqued by observations to show us where our models are missing ingredients. While flares are of course 3D phenomenon, simulating the flaring atmosphere including an accurate chromosphere with the required spatial scales in 3D is largely beyond current computational capabilities, and certainly performing parameter studies of energy transport mechanisms is not yet tractable in 3D. Therefore, field-aligned 1D loop models that can resolve the relevant scales have a crucial role to play in advancing our knowledge of flares. In recent years, driven in part by the spectacular observations from the Interface Region Imaging Spectrograph (IRIS), flare loop models have revealed many interesting features of flares. For this review I highlight some important results that illustrate the utility of attacking the problem of solar flares with a combination of high quality observations, and state-of-the-art flare loop models, demonstrating: 1) how models help to interpret flare observations from IRIS, 2) how those observations show us where we are missing physics from our models, and 3) how the ever increasing quality of solar observations drives model improvements. Here in Paper one of this two part review I provide an overview of modern flare loop models, and of electron-beam driven mass flows during solar flares.

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“…The atomic level populations start from statistical equilibrium, then at each timestep as the radiation from the boundary condition changes, the populations are updated in a time-dependent fashion, and the outgoing intensity is computed. All of the models shown here are simulated using the Lightweaver framework (Osborne & Milić 2021), with boundary conditions treated as coupled radiative transfer models using RA-DYN's thermodynamics where necessary, thanks to the flexibility of Lightweaver. In the two-dimensional slab, the BESSER formal solver of Štěpán & Trujillo Bueno (2013) is used, along with linear interpolation of atmospheric parameters to grid-ray intersections where needed.…”

Section: Two-dimensional Slabmentioning

confidence: 99%

“…The shape of Ca 854.2 nm is very sensitive to the electron density in the line core formation region (e.g. see the example in Osborne & Milić 2021;Bjørgen et al 2019), and it is likely that this is the primary origin of the differences, as the statistical equilibrium with fixed electron density (central panel), agrees well with the full time-dependent results, with slight discrepancies in line core depth over the first 100 km of 𝑥. This agrees well with the results found in time-dependent plane-parallel models presented in Section 5.5 of Osborne (2021).…”

Section: Statistical Equilibrium Comparisonmentioning

confidence: 99%

Flare Kernels May be Smaller than You Think: Modelling the Radiative Response of Chromospheric Plasma Adjacent to a Solar Flare

Osborne¹,

Fletcher²

2022

Preprint

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Numerical models of solar flares typically focus on the behaviour of directly-heated flare models, adopting magnetic fieldaligned, plane-parallel methodologies. With high spatial-and spectral-resolution ground-based optical observations of flares, it is essential also to understand the response of the plasma surrounding these strongly heated volumes. We investigate the effects of the extreme radiation field produced by a heated column of flare plasma on an adjacent slab of chromospheric plasma, using a two-dimensional radiative transfer model and considering the time-dependent solution to the atomic level populations and electron density throughout this model. The outgoing spectra of H𝛼 and Ca 854.2 nm synthesised from our slab show significant spatial-, time-, and wavelength-dependent variations (both enhancements and reductions) in the line cores, extending on order 1 Mm into the non-flaring slab due to the incident transverse radiation field from the flaring boundary. This may lead to significant overestimates of the sizes of directly-heated flare kernels, if line-core observations are used. However, the radiation field alone is insufficient to drive any significant changes in continuum intensity, due to the typical photospheric depths at which they forms, so continuum sources will not have an apparent increase in size. We show that the line formation regions near the flaring boundary can be driven upwards in altitude by over 1 Mm despite the primary thermodynamic parameters (other than electron density) being held horizontally uniform. This work shows that in simple models these effects are significant and should be considered further in future flare modelling and interpretation.

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The Lightweaver Framework for Nonlocal Thermal Equilibrium Radiative Transfer in Python

Cited by 22 publications

References 41 publications

1.5D non-LTE spectral synthesis of a 3D filament and prominence simulation

1.5D non-LTE spectral synthesis of a 3D filament and prominence simulation

Interrogating solar flare loop models with IRIS observations 1: Overview of the models, and mass flows

Flare Kernels May be Smaller than You Think: Modelling the Radiative Response of Chromospheric Plasma Adjacent to a Solar Flare

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