Solar corona MHD models driven by observations

The corona is the outer atmosphere of the Sun and features strange and fascinating bright loops that are invisible to our bare eyes. The dynamic structure of the corona can be observed in extreme ultra-violet light with modern space telescopes. Typically, bright loops appear above regions with complex magnetic activity on the visible surface of our host star. While historic works revealed the corona is millions of degrees Celsius hot, this fact gives riddles for solar physics during the past 70 years, because it is still unknown what exactly heats those structures in the corona and how the corona may sustain its high temperature that is way higher than the surface of the Sun that reaches only thousands of degrees Celsius. Going away from a heat source, one would expect it gets cooler and not hotter... From the theoretical side, one can classify the existing hypotheses on the heating in the corona into groups where either magnetic waves or electric currents provide the energy. Only recently, we could simulate a realistic loops system in the corona with a computer model that was driven with an actually observed magnetic state of the solar surface. From that data, we compare the loops with the observed ones and find a fundamental match in their 3D structure. This first step hints towards a transport mechanism of magnetic energy through the horizontal motions on the solar surface that perturb the magnetic field and these perturbations are then traveling into the corona to ultimately heat the plasma there. With this project we aim to verify if this mechanism holds true also for other magnetic activity levels, like in quiet Sun regions that cover much more of the solar surface. Also we may now test another hypothesis on the formation of borders around dark sunspots near strong magnetic fields. With most modern high-performance computers such models now become feasible and may be checked directly against real observations of the Sun.

Detailed simulations of magnetically active regions and sunspots on the Sun were carried out. Certain theories about heating in the corona - the Sun's atmosphere - were tested. Realistic simulations provide images of hot loops in the corona that closely match the actually observed phenomena. Flows of plasma matter with temperatures of a million degrees were also simulated and observed. We conclude that our models of coronal heating are realistic and physically complete enough to correctly describe and understand hot and UV-emitting loops in the corona. Further studies are necessary to better assess the stability of these magnetically active regions, because eruptions on the Sun can lead to strong solar storms, which can also influence the Earth's magnetic field. Such solar storm events were observed several times in Austria, especially in 2024.