Numerical simulation through complex computer codes has been a fundamental tool in physics and technology research for decades. The rapid growth of computing capabilities, coupled with significant advances in numerical mathematics, has made this branch of research accessible to medium-sized research centers, bridging the gap between theoretical and experimental physics. Astrophysics is no exception to this trend. Since the late 1970s, a specialized field known as computational astrophysics has emerged, allowing us to understand a wide range of phenomena that were previously inaccessible to pure theoretical research and to account for previously unexplained observations.
In recent decades, its primary areas of application have included (magneto)hydrodynamic phenomena and gas dynamics in various cosmic environments. For example, this includes the interiors and atmospheres of stars and planets, the interstellar medium, including magnetohydrodynamics and dynamos, accretion disks, the evolution of planetary nebulae, supernova explosions and remnants, and more. The incorporation of radiative transport equations into numerical simulations, which occurred in past decades, has added greater realism to the study of hydrodynamic processes in stellar photospheres and chromospheres.
The current project aims to support the development of astrophysical research at the IAC based on the use of large numerical codes that require massively parallel computers and their connection with observational results. The general objective of this project is to perform calculations related to cosmic fluid dynamics and radiative transport. The topics of these calculations will focus on:
1. Magnetized gas dynamics in the interiors and atmospheres of stars.
2. Radiation transport and polarization signals in spectral lines based on realistic atomic and molecular models, including Hanle and Zeeman effects.
3. Comparing theoretical/numerical results with observational data.
This project is particularly relevant given the increasing involvement of the IAC in national and European supercomputing networks and, more generally, in large-scale supercomputer installation initiatives.
In the following, we highlight the results of our annual year-end summary.
Throughout the year 2022, partial ionization effects, nonequilibrium ionization effects, and multi-fluids have been one the main blocks of development both from the theoretical and numerical perspective. For instance, a generalization of the the Braginskii 1965 equations has been achieved for a general multi-species plasmas with arbitrary masses and temperatures, and where all of the viscosities and heat fluxes in the model are described by their own evolution equations. This new approach has a crucial advantage that the parallel components along the magnetic field lines do not become unbounded (infinitely large) in regimes of low-collisionallity of interest for this group as, for example, the solar corona (Hunana et al. 2022). In this thematic block, 2D and 3D simulations, using a two-fluid model that treats the neutral and ionized species as two separate components, have also been performed to analyze the effect that the collisional interaction between both components has on the dynamics of coronal rain, the evolution of the instability of Kelvin-Helmholtz, the propagation of magneto-acoustic waves through the solar chromosphere or the heating of the plasma (Martínez-Gómez et al. 2022a). Another example of the theoretical development with potential numerical applications has been the pursuit of the effects of the ambipolar diffusion in the chromosphere from a more fundamental perspective by means of analytical solutions. The obtained solutions for cases with cylindrical symmetry are shown to constitute a demanding, but nonetheless viable, test for magnetohydrodynamic (MHD) codes that incorporate ambipolar diffusion. In addition, detailed tabulated runs of the solutions have been made available public for the community (Moreno-Insertis et al. 2022). Lastly, nonequilibrium ionization effects of the Hydrogen atom together with the study of the Lyman α effects have been started to study in simple configurations to be applied later in realistic simulations that include the chromosphere.
Improving and testing the capabilities of the available MHD codes in the solar group has been another of the major key developments carried out in 2022. For example, the results obtained by Moreno-Insertis et al. 2022 were used to check that the MHD Bifrost code is able to reproduce the theoretical solutions with sufficient accuracy up to very advanced diffusive times, as well as to explore the asymptotic properties of these theoretical solutions. In addition to that, several changes have been performed in the MANCHA code whose aim was to increase the efficiency and to add new features that will allow the researchers to perform more realistic experiments as well as exploring new research areas. For instance, MANCHA code has been extended to be able to simulate solar simulations up to the corona, adding a new module that efficiently calculates one of the key ingredients in the corona: the thermal conduction (Navarro et al. 2022). The preparation of the MANCHA code for its multi-fluid extension with radiation has also been another working branch concerning the numerical development in 2022. In addition, new equation-of-state and opacity routines have been developed that allow separating the equilibrium background contributions from those treated out of the equilibrium. Besides facing different challenges in solar physics, the huge development brought about in MANCHA is useful to study main sequence cool stars (G,K,M), which contributes to the better understanding of the stellar physics. To accomplish all these tasks, it was necessary not only to carry out numerous scaling tests and numerical experiments in local machines at the IAC, as well as on Supercomputers such as LaPalma, PICASSO, PizDaint, and MareNostrum4; but also to work together with external collaborators.
During 2022, in this project there has also been a focus on different solar atmosphere phenomena and the corresponding comparison with observations. As an illustrative example, Coronal Bright Points (CBPs) have been modeled for the first time with enough realism to unravel the mechanisms that generate them and provide them with energy, being also able to explain different characteristics observed from space satellites. The comparison with observations is through synthetic SDO/AIA, Solar Orbiter EUI-HRI, and IRIS images that have been computed from the numerical experiment performed with the Bifrost code (Nóbrega-Siverio and Moreno-Insertis, 2022). Another example is the combination of 3D numerical experiments with the MoLMH code and forward modelling using Hα line to study transverse kink oscillations in prominence threads. The results contain relevant implications for the field of prominence seismology, showing that the Hα emission can be used to detect the fundamental mode of the oscillations (Martínez-Gómez et al. 2022b). In addition, ground high-resolution observations of ejective phenomena such as surges in the solar atmosphere have been analyzed, finding striking similarities with results obtained from numerical experiments. On top of that, there have also been significant contributions from the members of this project to the further advance of the observations and construction of new telescopes (Quintero et al. 2022) and satellites (De Pontieu et al. 2022, Cheung et al. 2022), using the earned knowledge from the theoretical-numerical experiments. Finally, an exploratory first attempt at understanding the physics of coronal holes and active regions from a global point of view through 2D magnetohydrostatic solutions was performed (Terradas et al. 2022), which will need of further development in the incoming years for comparisons with observations.
Last but not least, state-of-the-art tools such as the ones provided by Machine Learning and Bayesian statistics have been applied to solar atmosphere problems. In this vein, a project to characterize the limits of the k-means methods and its application to solar observations was launched. In addition, new development in radiative transfer codes have being started to use in a preliminary study of machine learning approach to the computations of radiative terms. Development of the application of Bayesian techniques to the comparison of models in seismology of the solar atmosphere continued in 2022, with a review article published that accounts for the main results obtained in the last decade (Arregui 2022a). Moreover, the Bayesian formalism has been successfully applied to the prediction of the amplitude of the solar activity cycle, proposing a new methodology to quantify the goodness of both the prediction and the underlying model (Arregui 2022b).
A comparative study of resistivity models for simulations of magnetic reconnection in the solar atmosphere
Context. Magnetic reconnection is a fundamental mechanism in astrophysics. A common challenge in mimicking this process numerically in particular for the Sun is that the solar electrical resistivity is small compared to the diffusive effects caused by the discrete nature of codes. Aims: We aim to study different anomalous resistivity models andFærder, Ø. H. et al.
Large Ion-neutral Drift Velocities and Plasma Heating in Partially Ionized Coronal Rain Blobs
In this paper we present a numerical study of the dynamics of partially ionized coronal rain blobs. We use a two-fluid model to perform a high-resolution 2D simulation that takes into account the collisional interaction between the charged and neutral particles contained in the plasma. We follow the evolution of a cold plasma condensation as itMartínez-Gómez, David et al.
Observational and numerical characterization of a recurrent arc-shaped front propagating along a coronal fan
Context. Recurrent, arc-shaped intensity disturbances were detected by extreme-ultraviolet channels in an active region. The fronts were observed to propagate along a coronal loop bundle rooted in a small area within a sunspot umbra. Previous works have linked these intensity disturbances to slow magnetoacoustic waves that propagate from the lowerSieyra, M. V. et al.
Ambipolar Diffusion in the Lower Solar Atmosphere: Magnetohydrodynamic Simulations of a Sunspot
Magnetohydrodynamic (MHD) simulations of the solar atmosphere are often performed under the assumption that the plasma is fully ionized. However, in the lower solar atmosphere a reduced temperature often results in only the partial ionization of the plasma. The interaction between the decoupled neutral and ionized components of such a partiallyMacBride, Conor D. et al.
The European Solar Telescope
The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopesQuintero Noda, C. et al.
A 2D Model for Coronal Bright Points: Association with Spicules, UV Bursts, Surges, and EUV Coronal Jets
Coronal bright points (CBPs) are ubiquitous structures in the solar atmosphere composed of hot small-scale loops observed in extreme-ultraviolet (EUV) or X-rays in the quiet Sun and coronal holes. They are key elements to understanding the heating of the corona; nonetheless, basic questions regarding their heating mechanisms, the chromosphereNóbrega-Siverio, D. et al.
Doppler-velocity Drifts Detected in a Solar Prominence
We analyzed multiline observations of a quiescent prominence from the slit spectrograph located at the Ondřejov Observatory. Dopplergrams and integrated intensity maps of the whole prominence were obtained from observations in six spectral lines: Ca II H, Hϵ, Hβ, He I D3, Hα, and Ca II IR. By combining integrated intensity maps with non-LTEZapiór, Maciej et al.
Modeling the thermal conduction in the solar atmosphere with the code MANCHA3D
Context. Thermal conductivity is one of the important mechanisms of heat transfer in the solar corona. In the limit of strongly magnetized plasma, it is typically modeled by Spitzer's expression where the heat flux is aligned with the magnetic field. Aims: This paper describes the implementation of the heat conduction into the code MANCHA3D with anNavarro, A. et al.
Generalized Fluid Models of the Braginskii Type
Several generalizations of the well-known fluid model of Braginskii (1965) are considered. We use the Landau collisional operator and the moment method of Grad. We focus on the 21-moment model that is analogous to the Braginskii model, and we also consider a 22-moment model. Both models are formulated for general multispecies plasmas with arbitraryHunana, P. et al.
Ambipolar diffusion: Self-similar solutions and MHD code testing. Cylindrical symmetry
Context. Ambipolar diffusion is a process occurring in partially ionised astrophysical systems that imparts a complicated mathematical and physical nature to Ohm's law. The numerical codes that solve the magnetohydrodynamic (MHD) equations have to be able to deal with the singularities that are naturally created in the system by the ambipolarMoreno-Insertis, F. et al.
Construction of coronal hole and active region magnetohydrostatic solutions in two dimensions: Force and energy balance
Coronal holes and active regions are typical magnetic structures found in the solar atmosphere. We propose several magnetohydrostatic equilibrium solutions that are representative of these structures in two dimensions. Our models include the effect of a finite plasma-β and gravity, but the distinctive feature is that we incorporate a thermalTerradas, J. et al.
Recent Applications of Bayesian Methods to the Solar Corona
Solar coronal seismology is based on the remote diagnostics of physical conditions in the corona of the Sun by comparison between model predictions and observations of magnetohydrodynamic wave activity. Our lack of direct access to the physical systems of interest makes information incomplete and uncertain so our conclusions are at bestArregui, I.
Methodology for Predicting the Probability Distribution of the Amplitude of Solar Cycle 25
A number of precursor-type methods for solar-cycle prediction are based on the use of regression models and confidence-level estimates. A drawback of these methods is that they do not permit one to make probability statements, nor do they offer straightforward ways to propagate the uncertainty from observations to the quantities of interest. WeArregui, Iñigo
Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE). I. Coronal Heating
The Multi-slit Solar Explorer (MUSE) is a proposed mission composed of a multislit extreme ultraviolet (EUV) spectrograph (in three spectral bands around 171 Å, 284 Å, and 108 Å) and an EUV context imager (in two passbands around 195 Å and 304 Å). MUSE will provide unprecedented spectral and imaging diagnostics of the solar corona at high spatial (De Pontieu, Bart et al.
Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE). II. Flares and Eruptions
Current state-of-the-art spectrographs cannot resolve the fundamental spatial (subarcseconds) and temporal (less than a few tens of seconds) scales of the coronal dynamics of solar flares and eruptive phenomena. The highest-resolution coronal data to date are based on imaging, which is blind to many of the processes that drive coronal energeticsCheung, Mark C. M. et al.
Transverse kink oscillations of inhomogeneous prominence threads: Numerical analysis and Hα forward modelling
Context. Prominence threads are very long and thin flux tubes that are partially filled with cold plasma. Observations have shown that transverse oscillations are frequent in these solar structures. The observations are usually interpreted as the fundamental kink mode, while the detection of the first harmonic remains elusive. Aims: The propertiesMartínez-Gómez, David et al.
Editorial AppreciationArregui, Iñigo et al.
Solar surges related to UV bursts. Characterization through k-means, inversions, and density diagnostics
Context. Surges are cool and dense ejections typically observed in chromospheric lines and closely related to other solar phenomena such as UV bursts or coronal jets. Even though surges have been observed for decades now, questions regarding their fundamental physical properties such as temperature and density, as well as their impact on upperNóbrega-Siverio, D. et al.
Large-amplitude longitudinal oscillations in solar prominences simulated with different resolutions
Context. Large-amplitude longitudinal oscillations (LALOs) in solar prominences have been widely studied in recent decades. However, their damping and amplification mechanisms are not well understood. Aims: In this study, we investigate the attenuation and amplification of LALOs using high-resolution numerical simulations with progressivelyLiakh, V. et al.
Effect of momentum and heat losses on the hydrodynamic instability of a premixed equidiffusive flame in a Hele-Shaw cell
The linear stage of hydrodynamic instability of a laminar premixed flame propagating in a Hele-Shaw cell is investigated. Our theoretical model takes into account momentum and heat losses, temperature-dependent transport coefficients, and the continuous internal structure of the flame front. The dispersion relation is obtained numerically as aHan, Yifan et al.