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Performance and Accuracy Implications of Parallel Split Physics‐Dynamics Coupling in the Energy Exascale Earth System Atmosphere Model
Journal of Advances in Modeling Earth Systems ( IF 6.8 ) Pub Date : 2020-07-15 , DOI: 10.1029/2020ms002080
Aaron S. Donahue 1 , Peter M. Caldwell 1
Affiliation  

Simultaneous calculation of atmospheric processes is faster than calculating processes one at a time. This type of parallelism is beneficial or perhaps even necessary to provide good performance on modern supercomputers, which achieve faster performance through increased processor count rather than improved clock speed. The scalability of the Energy Exascale Earth System Model (E3SM) Atmosphere Model (EAM) is limited by the fluid dynamics which scales up to the number of mesh cells in the global mesh. In contrast, the suite of physics parameterizations in EAM is scalable up to the total number of physics columns, which is an order of magnitude greater than the number of mesh cells. A proposed solution to unlocking the greater potential performance from the physics suite is to solve the physics and dynamics in parallel. This work represents a first attempt at parallel splitting of the grid‐scale fluid dynamics model and the subgrid‐scale physics parameterizations in a global atmosphere model. We will demonstrate that switching to parallel physics‐dynamics coupling extends the scalability of the EAM to up to 3 times the previous peak scalability limit and is up to 20% faster than the sequentially split coupling at the highest core counts and the same time step. Decadal simulations of both coupling approaches show very little impact to the model climate. This improved performance does not come without drawbacks, however. Parallel splitting requires a shorter time step and other modifications which largely offset performance gains. A mass fixer is required for conservation. Techniques for mitigating these issues are also discussed.

中文翻译:

能量百亿分之一地球系统大气模型中并行分裂物理动力耦合的性能和精度含义

同时计算大气过程比同时计算一个过程要快。在现代超级计算机上提供良好性能时,这种并行性是有益的,甚至可能是必需的,现代超级计算机通过增加处理器数量而不是提高时钟速度来实现更快的性能。亿亿地球系统模型(E3SM)大气模型(EAM)的可伸缩性受到流体动力学的限制,流体动力学可扩展到全局网格中网格单元的数量。相反,EAM中的一组物理参数设置可扩展到最多物理列数,这比网格单元数大一个数量级。提出的从物理套件中释放更大潜力的解决方案是并行解决物理和动力学问题。这项工作代表了在全球大气模型中并行拆分网格规模的流体动力学模型和亚网格规模的物理参数化的首次尝试。我们将证明切换到并行物理-动力学耦合可以将EAM的可扩展性扩展到先前峰值可扩展性极限的三倍,并且比在最大核数和相同时间步长的顺序拆分耦合快20%。两种耦合方法的年代际模拟对模型气候几乎没有影响。但是,这种改进的性能并非没有缺点。并行拆分需要更短的时间步长和其他修改,从而大大抵消了性能提升。需要使用质量固定剂进行保存。还讨论了缓解这些问题的技术。
更新日期:2020-07-15
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