Summary

Solar activity is primarily driven by the coronal solar magnetism, while measurements of the magnetic field in the corona is very rare and still in their infancy. Instead, the magnetic field is routinely measured in solar photosphere and, more seldom, chromosphere. The coronal magnetic field is typically evaluated using modeling constrained by the photospheric (more seldom, chromospheric) magnetograms. The accuracy of this models depends on accuracy and completeness of those constraints. The team activity was focused on (i) casting active regions (ARs) on the Sun and selection of an AR subset with extraordinarily complete observational data permitting to firmly constrain their 3D magnetic structure; (ii) assessment of these different heterogeneous data sets for their compatibility and complementarity; (iii) creation of the improved 3D magnetic data cubes with the use of all available constraints; and (iv) assessment of the validity of the data cubes by comparison synthetic radiation patterns with the observables in microwave, X-ray, and EUV domains. The improved AR magnetic models have a tremendous relevance to understand accumulation of free magnetic energy driving solar flares and eruptions and to pinpoint locations, where magnetic reconnection is likely to happen. Such improved models are also needed to initiate time-dependent dynamic models of ARs hosting flares and eruptions. Within the team activity we identified several ARs suitable for our analysis of which we focused on AR12723 for which we have high-resolution spectro-polarimetric measurements simultaneously in several magnetic-sensitive spectral lines forming in various heights of the solar atmosphere. We also employed photospheric magnetograms provided by SDO/HMI and EUV data provided by SDO/AIA to create a sequence of static and time-dependent (data-driven) models of this AR. We developed new model validation and data-to-model comparison tools and assessed the model fidelity by direct data-to-model comparison. We identified several bottle necks and shortcomings of currently available magnetic field data and 3D modeling techniques and formulated a roadmap to substantially improve them in the future.