Description
The Volleyball Sun experiment is based on the DISPATCH code framework, and is the first simulation of the Sun that covers the whole convection zone using no modifications of the physics (fully compressible MHD, realistic equation of state, with no modification of phase speeds). The convection zone is covered by a large number (up to more than 5 million) of small Cartesian "patches" (3D data cubes), with overlapping guard zones. The patches are arranged in a “volleyball geometry”, with 6 identical “faces”, in which patches are lined up in the (locally) longitudinal direction, with constant latitudinal offsets. The patches generated on the first face are duplicated, via permutation and reflection operations, to the remaining 5 faces. Each patch is exactly Cartesian (unigrid, with optional adaptive mesh refinement), with one axis exactly vertical, and the spherical geometry only enters via the guard zone interpolation mechanisms, which also handle the transformation of vector variable between the slightly tilted neighbors of each patch. The HD and MHD solvers can in principle be chosen freely, but to avoid problems in handling the very nearly adiabatic internal layers, we choose to use Riemann solvers with entropy per unit volume as the energy-related conserved variable. We use the FreeEOS equation of state, represented by a fast tabular lookup procedure. The calculations are carried out at the LUMI supercomputing center, under an Extreme Scale Access grant from EuropHPC. I will present first results, and additional details about the experiment, including methods to utilize GPU off-loading to handle radiative energy transfer and charged particle acceleration in the surface layers. On the basis of this first experiment, we plan to continue with a number of “zoom in” simulations, which use the larger scale results as initial and boundary conditions, while extending the computational domain locally into the chromosphere and corona, offering the opportunity to model, for the first time ab initio, the dynamics controlling solar “active regions”.
