Open SESAME: status and further plans

The ERC-AdG project Open SESAME (project No 101141362) aims to develop a time-evolving model for the entire solar atmosphere, including the chromosphere and transition region, based on a multifluid description. Currently, models are primarily steady, rely on a single-fluid description and include only the corona due to computational challenges. We plan to use time-evolving ion-neutral and ion-neutral-electron models. The multifluid approach will enable us to describe the intricate physics in the partially ionised chromosphere and quantify the transfer of momentum and energy between the atmospheric layers. The questions of where the solar wind originates and solar flares and coronal mass ejections are driven have fundamental scientific importance and substantial socio-economic impact. Indeed, the solar atmospheric model is the crucial missing link in the Sun-to-Earth model chain to predict the arrival and effects of CMEs on Earth.

This goal is now possible by combining our implicit numerical solver with a high-order flux-reconstruction (FR) method. The implicit solver avoids the numerical instabilities that lead to strict time-step limitations on explicit schemes. The high-order FR method enables high-fidelity simulations on very coarse grids, even in zones of high gradients. We started with this new development and will introduce three critical innovations. First, we will combine high-order FR with physics-based r-adaptive (moving) unstructured grids, redistributing grid points to regions with high gradients. Second, we will implement CPU-GPU algorithms for the new heterogeneous supercomputers advanced by HPC-Europa. Third, we will implement AI-generated magnetograms to make the model respond to the time-varying photospheric magnetic field, which is crucial for understanding important solar plasma properties and processes.

Thus, we will develop a first-in-its-kind high-order GPU-enabled 3D time-accurate solver for multifluid plasmas. If successful, we will implement the most advanced data-driven solar atmosphere model in an operational environment. The project started on 1 September 2024, and we already have interesting results on time-dependent corona modelling and high-order flux-reconstruction simulations.