ABSTRACT The quality of today's research is often tightly limited to the available computing power and scalability of codes to many processors. For example, tackling the problem of heating the solar corona requires a most realistic description of the plasma dynamics and the magnetic field. Numerically solving such a magneto-hydrodynamical (MHD) description of a small active region (AR) on the Sun requires millions of computation hours on current high-performance computing (HPC) hardware. The aim of this work is to describe methods for an efficient parallelisation of boundary conditions and data input/output (IO) strategies that allow for a better scaling towards thousands of processors (CPUs). The Pencil Code is tested before and after optimisation to compare the performance and scalability of a coronal MHD model above an AR. We present a novel boundary condition for non-vertical magnetic fields in the photosphere, where we approach the realistic pressure increase below the photosphere. With that, magnetic flux bundles become narrower with depth and the flux density increases accordingly. The scalability is improved by more than one order of magnitude through the HPC-friendly boundary conditions and IO strategies. This work describes also the necessary nudging methods to drive the MHD model with observed magnetic fields from the Sun's photosphere. In addition, we present the upper and lower atmospheric boundary conditions (photospheric and towards the outer corona), including swamp layers to diminish perturbations before they reach the boundaries. Altogether, these methods enable more realistic 3D MHD simulations than previous models regarding the coronal heating problem above an AR – simply because of the ability to use a large amount of CPUs efficiently in parallel.

中文翻译：

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在高性能计算机上驱动日冕 MHD 模拟

摘要 当今研究的质量通常严格受限于许多处理器的可用计算能力和代码的可扩展性。例如，解决加热日冕的问题需要对等离子体动力学和磁场进行最真实的描述。在当前的高性能计算 (HPC) 硬件上，对太阳上小活动区 (AR) 的这种磁流体动力学 (MHD) 描述进行数值求解需要数百万个计算小时。这项工作的目的是描述有效并行化边界条件和数据输入/输出 (IO) 策略的方法，以便更好地扩展到数千个处理器 (CPU)。Pencil Code 在优化前后进行测试，以比较 AR 之上的冠状 MHD 模型的性能和可扩展性。我们为光球层中的非垂直磁场提出了一种新的边界条件，我们在其中接近光球层下方的真实压力增加。这样，磁通束随着深度变窄，磁通密度相应增加。通过对 HPC 友好的边界条件和 IO 策略，可扩展性提高了一个数量级以上。这项工作还描述了使用来自太阳光球层的观测磁场驱动 MHD 模型的必要微调方法。此外，我们展示了大气上下边界条件（光球层和朝向外日冕），包括沼泽层以在扰动到达边界之前减少扰动。共，