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Why we assembled this International ISSI Team of experts? 

Magnetic fields govern all aspects of solar activity, from the 11-year solar cycle to the most energetic events in the solar system, namely solar flares and Coronal Mass Ejections (CMEs), which threaten our modern technological civilization. As seen on the surface of the Sun, this activity emanates from localized concentrations of magnetic fields, which emerge sporadically from the solar interior. These locations are called solar Active Regions (ARs). During the period from AR birth to maturity, and depending on their magnetic complexity as seen at the surface, a varying degree of flaring and explosive activity may be observed due to rapid magnetic energy release by magnetic reconnection in the solar corona.

 

Over the last decades we have seen great progress in our understanding of how solar ARs form from first principles thanks to advanced 3D magnetohydrodynamic (MHD) simulations covering the solar interior up to the solar corona. However, such simulations are extremely computationally expensive and they are not able to model the birth and evolution of real, observed ARs, because they are not explicitly constrained by the observations. We call such models “data-inspired”, as in “inspired from observations”.

 

A separate class of 3D models has been developed, known as “data-constrained” because real observations of the magnetic field of the Sun at the photosphere are used to reconstruct the magnetic field in the solar atmosphere. However, they rely on simplifications, e.g., assuming the absence of plasma in the corona and that the magnetic field there is “force-free” (i.e., electric currents are aligned with the magnetic field) and static.

Despite the strong assumptions and limitations, “data-constrained” models are still widely used by the scientific community. A new class of 3D models called “data-driven” are also based on the data available from observations but are able to simulate evolving ARs. Hence, they have advantages over the previous approaches. Several models have been developed by different teams around the world. However, each of them use different methods for data-driving and/or make different assumptions for the coronal environment, e.g., whether it is plasma-free (nonlinear “force-free” modeling) or not (e.g., “data-driven” 3D MHD models). Consequently, it has not been straightforward to assess how successful such models are in modeling evolving solar ARs; such assessment requires careful design of tests to compare and contrast the different modeling techniques with each other.

Our International ISSI Team brings together world experts in solar observations and theoretical modeling. The goal of our Team will be to develop, test, and assess the next generation of “data-driven” models of evolving solar Active Regions. Our results will improve our understanding of the physical evolution of the solar corona, bringing our field closer to the ultimate goal of accurate prediction of solar explosive events.