标题： 在高性能计算机上驱动太阳日冕 magnetohydrodynamics 模拟 显示英文标题

标题： Driving solar coronal MHD simulations on high-performance computers

摘要： 当今的研究质量往往受到可用计算能力和代码扩展到多个处理器的能力的严格限制。 例如，解决加热太阳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。 在当前高性能计算（HPC）硬件上数值求解太阳小活动区（AR）的磁流体力学（MHD）描述需要数百万的计算小时。 本工作的目的是描述用于高效并行化边界条件和数据输入/输出（IO）策略的方法，这些方法可以更好地扩展到数千个处理器（CPU）。 在优化之前和之后测试了Pencil代码，以比较AR上方的日冕MHD模型的性能和可扩展性。 我们提出了一种新的非垂直磁场的边界条件，在光球层中，我们接近光球层下的实际压力增加。 通过这种方式，随着深度增加，磁通束变窄，磁通密度相应增加。 通过HPC友好的边界条件和IO策略，可扩展性提高了两个数量级以上。 这项工作还描述了将来自太阳光球的观测磁场驱动MHD模型所需的调整方法。 此外，我们展示了上下大气边界条件（光球层和外日冕），包括减少扰动的沼泽层。 总之，这些方法使关于AR上方日冕加热问题的3D MHD模拟比以前的模型更现实——仅仅是因为能够有效地在并行处理中使用大量CPU。 显示英文摘要

摘要： 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 parallelization 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 optimization 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.