PORTA: A three-dimensional multilevel radiative transfer code for modeling the intensity and polarization of spectral lines with massively parallel computers

Abstract

The interpretation of the intensity and polarization of the spectral line radiation produced in the atmosphere of the Sun and of other stars requires solving a radiative transfer problem that can be very complex, especially when the main interest lies in modeling the spectral line polarization produced by scattering processes and the Hanle and Zeeman effects. One of the difficulties is that the plasma of a stellar atmosphere can be highly inhomogeneous and dynamic, which implies the need to solve the non-equilibrium problem of the generation and transfer of polarized radiation in realistic three-dimensional (3D) stellar atmospheric models. Here we present PORTA, an efficient multilevel radiative transfer code we have developed for the simulation of the spectral line polarization caused by scattering processes and the Hanle and Zeeman effects in 3D models of stellar atmospheres. The numerical method of solution is based on the non-linear multigrid iterative method and on a novel short-characteristics formal solver of the Stokes-vector transfer equation which uses monotonic Bézier interpolation. Therefore, with PORTA the computing time needed to obtain at each spatial grid point the self-consistent values of the atomic density matrix (which quantifies the excitation state of the atomic system) scales linearly with the total number of grid points. Another crucial feature of PORTA is its parallelization strategy, which allows us to speed up the numerical solution of complicated 3D problems by several orders of magnitude with respect to sequential radiative transfer approaches, given its excellent linear scaling with the number of available processors. The PORTA code can also be conveniently applied to solve the simpler 3D radiative transfer problem of unpolarized radiation in multilevel systems.

15 pages, 15 figures, to appear in Astronomy and Astrophysics

References in corpus (3)

• Center-to-Limb Variation of Solar 3-D Hydrodynamical Simulations
• Scattering Polarization of Hydrogen Lines in Weakly Magnetized Stellar Atmospheres I. Formulation and Application to Isothermal Models
• On the Sensitivity of Partial Redistribution Scattering Polarization Profiles to Various Atmospheric Parameters

Cited by in corpus (51)

• An Open Source, Massively Parallel Code for Non-LTE Synthesis and Inversion of Spectral Lines and Zeeman-induced Stokes Profiles
• RH 1.5D: a massively parallel code for multi-level radiative transfer with partial frequency redistribution and Zeeman polarisation
• Radiative diagnostics in the solar photosphere and chromosphere
• A novel investigation of the small-scale magnetic activity of the quiet Sun via the Hanle effect in the Sr I 4607 Å line
• Three-dimensional radiative transfer simulations of the scattering polarization of the hydrogen Ly$\alpha$ line in a MHD model of the chromosphere-corona transition region
• The Hanle and Zeeman polarization signals of the solar Ca II 8542 Å line
• Radiation hydrodynamics in simulations of the solar atmosphere
• The Lightweaver Framework for NLTE Radiative Transfer in Python
• The transfer of resonance line polarization with partial frequency redistribution and J-state interference
• CLASP Constraints on the Magnetization and Geometrical Complexity of the Chromosphere-Corona Transition Region
• Formal Solutions for Polarized Radiative Transfer. I. The DELO Family
• Chromospheric diagnosis with Ca II lines: forward modeling in forward scattering (I)
• The effects of three-dimensional radiative transfer on the resonance polarization of the Ca I 4227 $\mathring{\mathrm{A}}$ line
• Quiet-Sun hydrogen Lyman-alpha line profile derived from SOHO/SUMER solar-disk observations
• Flare Kernels May be Smaller than You Think: Modelling the Radiative Response of Chromospheric Plasma Adjacent to a Solar Flare
• Formal solutions for polarized radiative transfer. III. Stiffness and instability
• Novel framework for the three-dimensional NLTE inverse problem
• Numerical non-LTE 3D radiative transfer using a multigrid method
• Near optimal angular quadratures for polarised radiative transfer
• Formal Solutions for Polarized Radiative Transfer. IV. Numerical Performances in Practical Problems
• Comparison of theoretical and observed Ca~{\sc ii}~8542 Stokes profiles in quiet regions at the centre of the solar disc
• The dynamic chromosphere: pushing the boundaries of observations and models
• Radiance Cascades: A Novel High-Resolution Formal Solution for Multidimensional Non-LTE Radiative Transfer
• SunnyNet: A neural network approach to 3D non-LTE radiative transfer
• Scattering polarization in solar flares
• Improved near optimal angular quadratures for polarised radiative transfer in 3D MHD models
• Discontinuities in numerical radiative transfer
• Formation of the Mg II h and k polarization profiles in a solar plage model and their suitability to infer magnetic fields
• The impact of limited time resolution on the forward-scattering polarization in the solar Sr I 4607 Å line
• Designing wavelength sampling for Fabry-Pérot observations. Information-based spectral sampling
• Chromospheric Polarization in the Photospheric Solar Oxygen Infrared Triplet
• A new nonlocal thermodynamical equilibrium radiative transfer method for cool stars
• An Assessment of and Solution to the Intensity Diffusion Error Intrinsic to Short-Characteristic Radiative Transfer Methods
• Long characteristics vs. short characteristics in 3D radiative transfer simulations of polarized radiation
• Scattering line polarization in rotating, optically thick disks
• A numerical approach for modelling the polarisation signals of strong resonance lines with partial frequency redistribution. Numerical applications to two-term atoms and plane-parallel atmospheres
• Magnetic field diagnostics of prominences with the Mg II k line: 3D Stokes inversions versus traditional methods
• Progress towards a 3D Monte Carlo radiative transfer code for outflow wind modelling
• Diagnostic potential of wavelength-integrated scattering polarisation signals of the solar He II Ly-alpha line
• Three-dimensional simulations of scattering polarization and the Hanle effect in MHD chromospheric models
• The He I 10830 A line: Radiative transfer and differential illumination effects
• The potential of the wavelength-integrated scattering polarization of the hydrogen Ly-alpha line for probing the solar chromosphere
• Evaluating the reliability of a simple method to map the magnetic field azimuth in the solar chromosphere
• Magnetic Imaging of the Outer Solar Atmosphere (MImOSA): Unlocking the driver of the dynamics in the upper solar atmosphere
• The uncertainty of magnetic fields in 3D non-local thermodynamic equilibrium inversions
• On the formation of Lyman $\beta$ and the O I 1027 and 1028 Å spectral lines
• Accelerating 3D Non-LTE Synthesis with Graph Neural Networks
• Irregular grids for 3D NLTE radiative transfer in stellar atmospheres
• Current status of NLTE analysis of stellar atmospheres
• The effect of horizontal plasma inhomogeneities in 3D NLTE radiation transfer in stellar atmospheres
• A single frequency approach to nonequilibrium modeling of the chromosphere