Earth's magnetosheath: a comparison of plasma flow direction between models and observations
The solar atmosphere is expanding and flows supersonically through the interplanetary space. This flow is called the solar wind. Earth's magnetic field creates an obstacle for it. The solar wind compresses it and deflects. The region with Earth's magnetic field outside the atmosphere is called the magnetosphere. A bow shock is created upstream of it. The space between the bow shock and the magnetosphere is called the magnetosheath. In the article we compare in detail three models of magnetic field and flow direction in the magnetosheath with spacecraft measurements. It is found that the models yield very similar results and mostly satisfactorily agree with observations. They even describe quite well large changes of the compared quantities in the magnetosheath, caused by changes in the upstream solar wind.

M. Vandas, et al. 2026, Ann. Geophys., 44, 137

Ion non-gyrotropy and effective dissipation of weakly collisional plasma turbulence

We investigated properties of the ion pressure-strain interaction at ion scales using three-dimensional hybrid simulations in the context of the weakly collisional solar wind. While the pressure-strain interaction is in principle reversible it may work as an effective dissipation of turbulent fluctuations. The reversibility of this interaction is seen in numerical simulations as the substantial temporal oscillations of the average pressure-strain term which takes both positive and negative values and only when time-averaged it leads to a one-way transfer of energy to the ion internal energy. We analyzed different way how to separate the time-oscillating part and found that the oscillatory part is mostly included in the gyrotropic part of the coupling. The remaining non-gyrotropic contribution is almost non-oscillatory and significantly contributes to ion heating.

P. Hellinger , et al. 2025, A&A, 704, A131

Apparent motion of penumbral grains in a sunspot simulation
The bright heads of penumbral filaments, penumbral grains (PGs), are manifestations of hot plasma flows rising to the surface. They are observed to move horizontally towards the sunspot umbra or away from it. Recent analyses of observations indicate that the direction of this motion is related to the inclination of the surrounding magnetic field. We analysed the penumbra of a sunspot simulated by the radiative magnetohydrodynamic code MURaM to obtain typical physical conditions in PGs, compare them with those in the surroundings, describe their spatial distribution, and study their evolution. The statistical analysis of the simulation results provides average values of temperature, magnetic field strength and inclination, vertical velocity, and their changes with radial distance from the spot centre. We find a subtle difference between simulated PGs with opposite directions of motion when comparing the magnetic field inclinations inside and outside the PGs. The case studies, documented by movies, show that the differences in inclinations and the direction of motion may change during the lifetime of some PGs and that the turbulence in the surface layers introduces some randomness in the apparent motions of PGs.

M. Sobotka, et al. 2025, A&A, 699, A211

Quasi-Separatrix Layers and Three-Dimensional Magnetic Reconnection: Theory and Observations of Solar Flares
This review paper describes 30 years of research focusing on the currently best available theory of solar flares - quasi-separatrix layers (QSLs). The QSLs are locations within the magnetic field, where the magnetic connectivity experiences drastic, but still continuous, changes. These are unambiguously locations where solar flares are observed. The paper summarizes the QSL theory, its development along with predictions of numerical simulations, as well as observational evidence. This includes several modes of three-dimensional magnetic reconnection, many of which were discovered here at ASU. 

J. Dudík, et al. 2025, Solar Physics, 300, 139

Deconvolution of SDO/HMI intensity and the vector magnetic field to achieve Hinode/SOT-SP data quality
The Sun is constantly changing, with magnetic features such as sunspots, pores, and smaller magnetic elements appearing and evolving over time. Two key space-based instruments observe the Sun: NASA’s Solar Dynamics Observatory (SDO), which provides continuous full-disk images with high time resolution, and Japan’s Hinode satellite, which offers much sharper images but only from small regions and less frequently. This trade-off between coverage and detail has long posed a challenge to solar physicists. In this study, we developed a deep learning model—a type of artificial intelligence—that can enhance SDO observations by making them as sharp as Hinode’s. The resulting deconvolution technique improves both the continuum intensity and the full vector magnetic field measured by SDO. This enables scientists to obtain clear and detailed magnetic maps of the entire Sun, at all times, and to follow the complete life cycle of active regions—including the birth, evolution, and decay of sunspots and pores—in very high detail.

D. Korda, et al. 2025, A&A, 697, A28

Physics of solar flares and prominences

The group focuses on research of bright and energetic phenomena, including solar filaments and prominences, flares/CME, their mutual relationships, but also on physics of the solar corona and transition region. The primary goals include understanding of the magnetic flux ropes, and also mechanisms of solar eruptions and coronal heating. To this end, our researchers use a variety of numerical models and/or multiwavelength observations (from X-rays to radio) performed by space-borne and ground-based instruments. Group members also participate in proposing new instrumentation and observing campaigns.

Part of this working group is also the Solar Patrol Service, which provides a daily overview of solar activity in the form of drawings of the solar photosphere and synoptic images. Another task of the Solar Patrol is to issue weekly and daily forecasts of solar activity.

Head: Jaroslav Dudík
Scientists: Arkadiusz Berlicki, Elena Dzifčáková, František Fárník, Vlastislav Feik, Stanislav Gunár, Petr Heinzel, Jana Kašparová, Dieter Nickeler, Martina Pavelková, Maciej Zapiór, Alena Zemanová

Structure and physics of the solar atmosphere

The research goal of the group is to understand the physical conditions and processes in the solar atmosphere. It focuses on both active and quiescent regions of the atmosphere and particularly on sunspots. Using numerical models and analysis of spectroscopic and spectro-polarimetric observations of number of spectral lines that form at different layers of the solar atmosphere, members of the group aim to advance our understanding of the processes that shape the Sun's atmosphere. The group is involved in the development of the large European solar telescopes in the Canary Islands. In particular, it is currently involved in the realisation of the European Solar Telescope (EST). 

Head: Jiří Štěpán
Scientists: Jose Iván Campos Rozo, Marta García Rivas, Jan Jurčák, David Korda, Michal Sobotka, Michal Švanda

Physics of the Heliosphere

The group studies physical processes in the solar wind using in situ spacecraft observations, numerical simulations and theoretical analyses. It concentrates on properties of solar wind particles (electrons & ions) and their interactions with waves, turbulence, and nonlinear structures. Furthermore, it investigates interactions between the solar wind and solar system planets and moons as well analogic interactions between moons and planetary magnetosperes. 

Head: Petr Hellinger
Scientists: Štěpán Štverák, Marek Vandas, Leoš Pohl

Group of solar radioastronomy

The working group studies physical properties of the solar atmosphere and processes there through analysis of solar radio data obtained in the wide range of wavelengths from decimeters to millimeters. At the Ondrejov observatory the group operates several solar radio telescopes running at decimetric wavelengths. The group includes members of the Atacama Large Millimeter/submillimeter Array Regional Centre (ALMA ARC-CZ) Czech node, which runs since 2016 and supports the ALMA user community of Central and Eastern Europe. The Czech ARC node provides scientific and technical support in the field of solar and (extra) galactic research with ALMA.

Head: Artem Koval
Scientists: Miroslav Bárta, Yi Chai, Marian Karlický, Wenjuan Liu