During the UniSDyn project we developed a new approach to model and understand stellar dynamos with novel simulation and data analysis tools. We also performed extensive work to constrain the models by observations of stellar magnetic fields. Related to the observational work, we, e.g. analysed stellar chromospheric activity data and obtained the strongest confirmation so far of convective turbulence being a required ingredient of stellar dynamos (these results were disseminated in an article in Nature Astronomy by Lehtinen et al., 2020). At the heart of these tools are graphics-processing accelerated algorithms that have enabled simulations with unprecedented resolutions. This work culminated in the release of the full-fledged stencil library Astaroth (disseminated in Pekkilä et al., 2020, in the leading computer science journal Parallel Computing), now used in many other research groups world-wide outside our institution. With the help of these computational tools, we have now been able to reach out to more star-like regimes, such as investigated small magnetic Prandtl number plasmas, closely matching the conditions in the bottom of the solar convection zone. We were able to verify favourable conditions for the excitation of a solar small-scale dynamo in deeper depths of the convection zone, before believed to occur only in the surface regions (disseminated in Nature Astronomy by Warnecke et al., 2023). We also developed data-analysis tools that can interrogate the turbulent flow, enabling us to measure and characterise the turbulent transport in stellar convection zones (disseminated in the Astrophysical Journal, Käpylä et al, 2020, 2022). With the help of these tools we have performed improved convection dynamo simulations to serve as laboratories from which we have measured, investigated, and characterised the turbulent transport coefficients (disseminated in Astronomy and Astrophysics, Warnecke et al., 2023). Finally, global dynamo models incorporating the turbulent effects in full have been constructed based on these results (disseminated e.g. in Astrophysical Journal letters by Warnecke et al., 2021). All the discoveries obtained during the project point to the direction of stellar magnetism being based on two different dynamo instabilities, the large-scale (global) and the small-scale (fluctuating) dynamo mechanism and their interactions. Hence, global-scale magnetism and kinetic and magnetic turbulent fluctuations are intimately coupled. Dynamo models incorporating both these dynamo mechanisms are essential to understand stellar dynamos.
