Norwegian version of this page

Andrius Popovas

Researcher - Rosseland Centre for Solar Physics

Email andriusp@astro.uio.no

Available hours 08:20 - 16:30

Username

Visiting address Svein Rosselands hus Sem Sælands vei 13 0371 OSLO

Press photo Download business card

ReCon²

ReCon‬‭^2‬ aims to‬‭ demonstrate‬‭ that‬‭ the‬‭ long-standing‬‭ mismatch‬‭ between‬‭ simulated‬‭ and‬‭ observed‬‭ solar‬ convection‬‭ is‬‭ not‬‭ a‬‭ fundamental‬‭ problem‬‭ in‬‭ solar‬‭ physics‬ — but‬‭ a‬‭ consequence‬‭ of‬‭ insufficient‬‭ realism‬‭ in‬ existing‬‭ models.‬‭ By‬‭ combining‬‭ surface‬‭ cooling‬‭ driven‬‭ convection,‬‭ compressible‬‭ MHD,‬‭ and‬‭ high-resolution‬ local and global simulations,‬‭ if successfull, this project will finally‬‭ put the‬‭ convective conundrum‬‭ to rest‬‭.‬

Project is funded by the Research Council of Norway via the Researcher Projects for Young Scientists (FRIPRO), project number 359643. I am the PI of the project. More information can be found here

Other projects

I am currently working on resolving the solar convective conundrum. That requires large scale simulations of the entire solar convection zone. We use the publicly available DISPATCH framework and the 'volleyball' mesh decomposition. We were awarded 165 million CPU hours from the EuroHPC Extreme Scale Access to run the simulations on LUMI supercomputer. I continue to work on improving the simulations and hope that soon we will be able to share some fantastic results with the scientific community.

Two sides of the global simulation of the Sun. The left shows the radial velocities, while the right shows the entropy per unit mass at the surface

Academic interests

Solar physics, stellar and planetary atmospheres, magnetohydrodynamics, planet formation, radiative heat transport, plasma physics, statistical quantum mechanics

Background

I have obtained both my M.Sc. (thesis titled "Stellar model atmospheres of late spectral type stars") and Ph.D. (thesis titled "Planet formation. The roles of pebble accretion, radiative and convective energy transport") in the Niels Bohr Institute, University of Copenhagen in Denmark. Apart of computational astrophysics, in my "free time", I like doing observational astronomy, I have participated in the MiNDSTEp collaboration, searching for exoplanets using the gravitational microlensing technique with the Danish 1.54m telescope in La Silla, Chile.

My ORCID

Tags: HPC, Solar Physics, Hydrodynamics, MHD, Computational Astrophysics, Convective Conundrum, Global Simulations

Eitner, Philipp; Bergemann, Maria; Hoppe, Richard; Storm, Nicholas; Lipatova, Veronika & Glover, Simon C. O. [Show all 9 contributors for this article] (2025). M3DIS – A grid of 3D radiation-hydrodynamics stellar atmosphere models for stellar surveys: II. Carbon-enhanced metal-poor stars. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 703. doi: 10.1051/0004-6361/202555406. Full text in Research Archive Show summary
Aims . Understanding the origin and evolution of carbon-enhanced metal-poor (CEMP) stars is key to tracing the early chemical enrichment of the Galaxy. In this work we investigate how physically realistic 3D radiation-hydrodynamic (RHD) carbon-enhanced model atmospheres affect the inferred carbon abundances in CEMP stars, and assess the implications for their classification and for Galactic chemical evolution (GCE). We pay particular attention to the systematic biases introduced by traditional 1D hydrostatic equilibrium (HE) models. Methods . We used the M3DIS code to compute 3D RHD model atmospheres for main-sequence and sub-giant stars spanning a wide range of metallicities and carbon enhancements. Synthetic spectra of the CH G band were calculated using full 3D radiative transfer and compared to spectra from classical 1D HE MARCS models. We derived abundance corrections and applied them to a large literature sample of metal-poor stars from the SAGA database to quantify systematic effects on the carbon abundance distribution and CEMP classification. Results . Our new 3D CEMP models predict significantly cooler upper atmospheric layers than 1D HE models, resulting in stronger CH absorption and lower inferred carbon abundances by up to −0.9 dex at the lowest metallicities. Carbon enhancement in the atmosphere itself increases molecular opacities and leads to radiative re-heating, which partly offsets the adiabatic cooling in 3D models and reduces the magnitude of 3D − 1D abundance corrections. Applying these corrections lowers the CEMP fraction by up to 20% below [Fe/H] = −3, and furthermore alters the relative contribution of CEMP sub-classes. In particular, the fraction of stars classified as CEMP-no increases and that of CEMP-r/s stars decreases, owing to the downward revision of absolute carbon abundances. These changes bring the Galactic carbon abundance distribution into better agreement with GCE models that assume a contribution from faint supernovae of 20%. Physically realistic model atmospheres are thus essential for a reliable reconstruction of the early chemical enrichment history of the Galaxy.
Popovas, Andrius (2025). DISPATCH methods: An approximate, entropy-based Riemann solver for ideal magnetohydrodynamics. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 698. doi: 10.1051/0004-6361/202554028. Full text in Research Archive Show summary
With the advancement of supercomputers, we can now afford simulations with very wide scale ranges. In astrophysical applications – for example simulating solar, stellar and planetary atmospheres, interstellar medium, and so on – physical quantities such as gas pressure, density, temperature, plasma β, and Mach and Reynolds numbers can vary by orders of magnitude. This requires a robust solver, which can deal with a very wide range of conditions and maintain hydrostatic equilibrium where it is applicable. We reformulated a Godunov-type Harten–Lax–van Leer discontinuities (HLLD) approximate Riemann solver that would be suitable for maintaining hydrostatic equilibrium in atmospheric applications in a range of Mach numbers, which represent regimes where kinetic and magnetic energies dominate over thermal energy without any ad hoc corrections. We changed the solver to use entropy instead of total energy as the primary thermodynamic variable in the system of magnetohydrodynamic equations. The entropy is not conserved; it increases when kinetic and magnetic energy are converted to heat, as it should. We propose using an approximate entropy-based Riemann solver as an alternative to already widely used Riemann solver formulations where it might be beneficial. We conducted a series of standard tests with varying conditions and show that the new formulation for the Godunov-type Riemann solver works and is promising.
Kohutova, Petra & Popovas, Andrius (2021). Excitation and evolution of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 647. doi: 10.1051/0004-6361/202039491. Full text in Research Archive Show summary
Context. Solar coronal loops are commonly subject to oscillations. Observations of coronal oscillations are used to infer physical properties of the coronal plasma using coronal seismology. Aims. Excitation and evolution of oscillations in coronal loops is typically studied using highly idealised models of magnetic flux tubes. In order to improve our understanding of coronal oscillations, it is necessary to consider the effect of realistic magnetic field topology and evolution. Methods. We study excitation and evolution of coronal oscillations in three-dimensional (3D) self-consistent simulations of solar atmosphere spanning from the convection zone to the solar corona using the radiation-magnetohydrodynamic (MHD) code Bifrost. We use forward-modelled extreme-ultraviolet emission and 3D tracing of magnetic field to analyse the oscillatory behaviour of individual magnetic loops. We further analyse the evolution of individual plasma velocity components along the loops using wavelet power spectra to capture changes in the oscillation periods. Results. Various types of oscillations commonly observed in the corona are present in the simulation. We detect standing oscillations in both transverse and longitudinal velocity components, including higher-order oscillation harmonics. We also show that self-consistent simulations reproduce the existence of two distinct regimes of transverse coronal oscillations: rapidly decaying oscillations triggered by impulsive events and sustained small-scale oscillations showing no observable damping. No harmonic drivers are detected at the footpoints of oscillating loops. Conclusions. Coronal loop oscillations are abundant in self-consistent 3D MHD simulations of the solar atmosphere. The dynamic evolution and variability of individual magnetic loops suggest that we need to re-evaluate our models of monolithic and static coronal loops with constant lengths in favour of more realistic models.
Kohutova, Petra; Antolin, Patrick; Popovas, Andrius; Szydlarski, Mikolaj Marcin & Hansteen, Viggo (2020). Self-consistent 3D radiative magnetohydrodynamic simulations of coronal rain formation and evolution. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 639. doi: 10.1051/0004-6361/202037899. Full text in Research Archive Show summary
Context. Coronal rain consists of cool and dense plasma condensations formed in coronal loops as a result of thermal instability. Aims. Previous numerical simulations of thermal instability and coronal rain formation have relied on the practice of artificially adding a coronal heating term to the energy equation. To reproduce large-scale characteristics of the corona, the use of more realistic coronal heating prescription is necessary. Methods. We analysed coronal rain formation and evolution in a three-dimensional radiative magnetohydrodynamic simulation spanning from convection zone to corona which is self-consistently heated by magnetic field braiding as a result of convective motions. Results. We investigate the spatial and temporal evolution of energy dissipation along coronal loops which become thermally unstable. Ohmic dissipation in the model leads to the heating events capable of inducing sufficient chromospheric evaporation into the loop to trigger thermal instability and condensation formation. The cooling of the thermally unstable plasma occurs on timescales that are comparable to the duration of the individual impulsive heating events. The impulsive heating has sufficient duration to trigger thermal instability in the loop but does not last long enough to lead to coronal rain limit cycles. We show that condensations can either survive and fall into the chromosphere or be destroyed by strong bursts of Joule heating associated with a magnetic reconnection events. In addition, we find that condensations can also form along open magnetic field lines. Conclusions. We modelled, for the first time, coronal rain formation in a self-consistent 3D radiative magnetohydrodynamic simulation, in which the heating occurs mainly through the braiding and subsequent Ohmic dissipation of the magnetic field. The heating is stratified enough and lasts for long enough along specific field lines to produce the necessary chromospheric evaporation that triggers thermal instability in the corona.
Voort, Luc Rouppe van der; Pontieu, Bart Walter De; Carlsson, Mats; Rodriguez, Jaime de la Cruz; Bose, Souvik & Chintzoglou, Georgios [Show all 33 contributors for this article] (2020). High-resolution observations of the solar photosphere, chromosphere, and transition region: A database of coordinated IRIS and SST observations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 641. doi: 10.1051/0004-6361/202038732. Full text in Research Archive Show summary
NASA’s Interface Region Imaging Spectrograph (IRIS) provides high-resolution observations of the solar atmosphere through ultraviolet spectroscopy and imaging. Since the launch of IRIS in June 2013, we have conducted systematic observation campaigns in coordination with the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides complementary high-resolution observations of the photosphere and chromosphere. The SST observations include spectropolarimetric imaging in photospheric Fe  I lines and spectrally resolved imaging in the chromospheric Ca  II 8542 Å, H α , and Ca  II K lines. We present a database of co-aligned IRIS and SST datasets that is open for analysis to the scientific community. The database covers a variety of targets including active regions, sunspots, plages, the quiet Sun, and coronal holes.
Popovas, Andrius; Nordlund, Åke & Ramsey, Jon P. (2019). Pebble dynamics and accretion on to rocky planets – II. Radiative models. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 482(1), p. L107–L111. doi: 10.1093/mnrasl/sly197. Full text in Research Archive Show summary
We investigate the effects of radiative energy transfer on a series of nested-grid, high-resolution hydrodynamic simulations of gas and particle dynamics in the vicinity of an Earth-mass planetary embryo. We include heating due to the accretion of solids and the subsequent convective motions. Using a constant embryo surface temperature, we show that radiative energy transport results in a tendency to reduce the entropy in the primordial atmosphere, but this tendency is alleviated by an increase in the strength of convective energy transport, triggered by a correspondingly increased superadiabatic temperature gradient. As a consequence, the amplitude of the convective motions increase by roughly an order of magnitude in the vicinity of the embryo. In the cases investigated here, where the optical depth towards the disc surface is larger than unity, the reduction of the temperature in the outer parts of the Hill sphere relative to cases without radiative energy transport is only ∼100 K, while the mass density increase is of the order of a factor of two in the inner parts of the Hill sphere. Our results demonstrate that, unless unrealistically low dust opacities are assumed, radiative cooling in the context of primordial rocky planet atmospheres can only become important after the disc surface density has dropped significantly below minimum-mass-solar-nebula values.
Popovas, Andrius; Nordlund, Åke; Ramsey, Jon P & Ormel, Chris W (2018). Pebble dynamics and accretion on to rocky planets - I. Adiabatic and convective models. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 479(4), p. 5136–5156. doi: 10.1093/mnras/sty1752. Full text in Research Archive Show summary
We present nested-grid, high-resolution hydrodynamic simulations of gas and particle dynamics in the vicinity of Mars- to Earth-mass planetary embryos. The simulations extend from the surface of the embryos to a few vertical disc scale heights, with a spatial dynamic range of ∼1.4 × 105. Our results confirm that ‘pebble’-sized particles are readily accreted, with accretion rates continuing to increase up to metre-size ‘boulders’ for a 10 per cent MMSN surface density model. The gas mass flux in and out of the Hill sphere is consistent with the Hill rate, R2 H = 4 10−3 M⊕ yr−1. While smaller size particles mainly track the gas, a net accretion rate of ≈2 10−5 M⊕ yr−1 is reached for 0.3–1 cm particles, even though a significant fraction leaves the Hill sphere again. Effectively, all pebble-sized particles that cross the Bondi sphere are accreted. The resolution of these simulations is sufficient to resolve accretion-driven convection. Convection driven by a nominal accretion rate of 10−6 M⊕ yr−1 does not significantly alter the pebble accretion rate. We find that, due to cancellation effects, accretion rates of pebble-sized particles are nearly independent of disc surface density. As a result, we can estimate accurate growth times for specified particle sizes. For 0.3–1 cm size particles, the growth time from a small seed is ∼0.15 million years for an Earth-mass planet at 1 au and ∼0.1 million years for a Mars mass planet at 1.5 au.

View all works in NVA

Popovas, Andrius (2026). Whole Sun Simulations: Riding Exascale to the Core. Full text in Research Archive Show summary
In this talk I highlight our global simulations of the entire convection zone of the Sun and point to the outstanding bottleneck that exascale simulations will encounter - data and analysis.
Popovas, Andrius; Nordlund, Åke; Szydlarski, Mikolaj & Zhou, Yixiao (2026). Towards Resolving the Solar Convective Conundrum: A staged approach in progress. doi: 10.5281/ZENODO.20642947. Full text in Research Archive Show summary
The solar convective conundrum — the order-of-magnitude discrepancy between helioseismically inferred deep convective velocities and those predicted by global simulations — has resisted resolution for over a decade. Three suspects have been proposed: missing physics, insufficient resolution, and the way simulations are configured. ReCon² addresses all three together in a single controlled programme, with the third element implemented through a novel staged column-relaxation strategy: solar convection is first developed in a narrow horizontal column, where large-scale unstable modes are geometrically excluded, then progressively expanded to production widths while carrying the equilibrated small-scale physics forward. This poster, presented at Cool Stars 23 (Tokyo, 15–19 June 2026), reports first-stage results from the cz_f25_d100 run: a 25 Mm wide column at Δx = 100 km finest resolution, with fully realistic physics (OPAL/FreeEOS equation of state with ionization, OP opacities and radiative diffusion in the interior, multi-bin short-characteristics radiative transfer at the surface, fully compressible MHD, entropy-based HLLS solver), initialized from rest. Horizontally-averaged entropy perturbation statistics over 300 hours of simulated time show a coherent thermal mixing layer descending ~140 Mm into the convection zone. The active layer is strongly negative-skewed (≤ −2) — the statistical signature of entropy rain (Käpylä 2025), indicating distributions dominated by narrow cold extremes. A compensating positive-skew layer at the leading edge marks warm material displaced by penetrating cold plumes, and discrete late-time arcs at z ≈ 480–540 Mm correspond to individual extreme plumes reaching ~200 Mm depth, exhibiting Käpylä's predicted "tree" morphology. A complementary photospheric kinetic-energy spectrum from an exploratory wider-box run shows that the surface convective physics matches established surface-tracking diagnostics within the box-resolved range.
Popovas, Andrius; Nordlund, Åke & Szydlarski, Mikolaj (2026). Recent updates on global Sun modeling with DISPATCH. Full text in Research Archive Show summary
In this talk i present an update on our global simulations of the solar convection. I demonstrate that we can simulate the entire convection zone from below the tachocline all the way to lower chromosphere with smallest cell size near the surface of 98km. Then I discuss "entropy rain" and it's effects on the convection morphology.
Popovas, Andrius (2025). DISPATCH implementation of solar MHD solver (Entropy based HLLD Riemann solver (Popovas A&A 2025)). Full text in Research Archive
Popovas, Andrius (2025). From Convection Zone to Surface: Bridging the Solar Interior and Photosphere with DISPATCH. Full text in Research Archive
Popovas, Andrius (2025). From Convection Zone to Surface: Bridging the Solar Interior and Photosphere with DISPATCH. Full text in Research Archive Show summary
In this talk I present our simulations of the entire convection zone of the Sun - challenges and results.
Popovas, Andrius (2025). Update on the global MHD simulations of the Sun: where we were and are now. Full text in Research Archive Show summary
In this talk i present an update on our global simulations of the solar convection. I demonstrate that we can simulate the entire convection zone from below the tachocline all the way to lower chromosphere with smallest cell size near the surface of 98km. Then I discuss "entropy rain" and it's effects on the convection morphology.
Popovas, Andrius & Nordlund, Åke (2024). Realistic Simulations of Solar Dynamics. Full text in Research Archive
Popovas, Andrius & Nordlund, Åke (2024). Realistic simulations of solar dynamics from interior to the surface. Full text in Research Archive
Popovas, Andrius & Nordlund, Åke (2024). Realistic simulations of solar dynamics from interior to the surface. Full text in Research Archive
Popovas, Andrius & Nordlund, Åke (2024). Realistic Simulations of Solar Dynamics. Full text in Research Archive
Popovas, Andrius & Nordlund, Åke (2024). Update on the global MHD simulations of the Sun. Full text in Research Archive
Popovas, Andrius; Nordlund, Åke; Szydlarski, Mikolaj; Kohutova, Petra; Hansteen, Viggo Haraldson & Noraz, Quentin Jean Francois Alain [Show all 7 contributors for this article] (2023). Update on global MHD simulations of the solar convective region. Full text in Research Archive
Popovas, Andrius; Nordlund, Åke; Szydlarski, Mikolaj; Kohutova, Petra; Hansteen, Viggo Haraldson & Noraz, Quentin Jean Francois Alain [Show all 7 contributors for this article] (2023). Global MHD simulation of the solar convective region. Full text in Research Archive
Popovas, Andrius; Nordlund, Åke; Szydlarski, Mikolaj; Kohutova, Petra & Noraz, Quentin Jean Francois Alain (2023). Global MHD simulations of the solar convective zone using a volleyball mesh decomposition: Pilot. Full text in Research Archive
Popovas, Andrius; Szydlarski, Mikolaj & Nordlund, Åke (2022). First results from global MHD simulations of Solar convective zone. Full text in Research Archive
Kohutova, Petra; Popovas, Andrius; Antolin, Patrick; Szydlarski, Mikolaj & Carlsson, Mats (2022). Coronal oscillations in the self-consistent 3D MHD simulations of the solar atmosphere. Full text in Research Archive
Kohutova, Petra; Popovas, Andrius; Antolin, Patrick; Szydlarski, Mikolaj & Carlsson, Mats (2022). Coronal oscillations in the self-consistent 3D MHD simulations of the solar atmosphere. Full text in Research Archive
Popovas, Andrius; Szydlarski, Mikolaj & Nordlund, Åke (2022). Multi-scale simulations of the Sun. Full text in Research Archive
Kohutova, Petra; Antolin, Patrick; Popovas, Andrius; Szydlarski, Mikolaj Marcin & Hansteen, Viggo (2019). 3D radiative MHD simulations of coronal rain formation and evolution. Full text in Research Archive
Popovas, Andrius (2018). "What you need to grow your first planet". Full text in Research Archive

View all works in NVA

Published May 16, 2018 10:26 AM - Last modified Sep. 15, 2026 9:53 AM