Computer Cluster for Numerical Modelling and Simulation

气候地理学工作组的重点是在区域和全球范围内对山区冰川进行数值模拟，以重建过去的冰川动态，进行预测，并对冰川-气候--相互作用进行概念研究。这些结果用于调查冰川对季节性水供应的贡献，并用来量化冰川对区域海平面变化的贡献。我们还调查了这些冰川变化影响的社会后果。我们的工作是基于开放式全球冰川模型(OGGM，http://oggm.org)，)，该模型是由该组织开发的，国际社会的贡献越来越大。我们进一步应用大气的统计和动力降尺度来研究冰-空气边界的相互作用，这是由山区的复杂地形决定的。由于OGGM模拟的冰川不是动态耦合的，因此该模型的全球运行由大量独立的过程组成，导致该模型具有很好的可扩展性。因此，原则上，OGGM非常适合部署在像HLRN这样的地区/国家高性能计算中心。在实践中，这是不可能的，因为OGGM依赖于大量的外部数据源，这些数据源经常更新，并从互联网上动态加载。出于安全考虑，这在HLRN是不可能的。或者，数据可以打包并上传，这是不可行的，因为需要的数据量(每次全球模型运行大约1TB)。此外，由于OGGM正在非常活跃的开发中，它需要一个最新的Python环境和频繁的更新。这一要求与计算中心(如HLRN)对稳定性的需求不兼容，这阻止了用户直接控制已安装的包。测试表明，OGGM对最新软件包的依赖阻碍了其在HLRN资源上的部署。由于模型开发是正在进行的工作的一个重要方面，因此需要能够灵活分配和配置的当地资源。最后，除了模拟大量单个冰川的(可伸缩性很好的)任务外，还有某些“全局”任务(主要涉及模型验证和优化)不能并行化，因此需要很高的最大挂钟时间。此处请求的计算集群是确保工作组所需计算资源安全所必需的。

The working group Climate Geography focusses on numerical modeling of mountain glaciers on the regional and global scale, both for reconstructing past glacier dynamics, for producing projections and for conceptual studies of glacier-climate-interactions. The results are used for investigating the contribution of glaciers to seasonal water availability and for quantifying the contribution of glaciers to regional sea-level change. We also investigate societal consequences of these impacts of glacier change. Our work is based on the Open Global Glacier Model (OGGM, http://oggm.org), which is developed by the group with growing contributions from the international community. We further apply statistical and dynamical downscaling of the atmosphere to investigate interactions at the ice-air boundary, which are governed by the complex topography of mountain regions. Since the glaciers simulated by OGGM are not dynamically coupled, a global run of the model consists of a great number of independent processes, leading to very good scalability of the model. In principle, OGGM is therefore well suited to be deployed at regional/national high performance computation centers like HLRN. In practice, this is made impossible by the dependency of OGGM on a great number of external data sources, which are updated frequently and dynamically loaded from the internet. This is impossible at HLRN because of security considerations. Alternatively, data could be packaged and uploaded, which is impracticable because of the required amount of data (ca. 1 TB per global model run). Moreover, since OGGM is in very active development, it needs an up-to-date Python environment and frequent updates. This demand is incompatible with the compute centers’ (like HLRN) need for stability, which prevents users from getting direct control of the installed packages. Tests have shown that the dependence of OGGM on up-to-date software packages prevents its deployments at HLRN resources. Since model development is an important aspect of the ongoing work, local resources that can allocated and configured flexibly are needed. Finally, apart from the (well scalable) tasks of modeling a great number of individual glaciers, there are certain “global” tasks (mostly concerning model validation and optimization) that cannot be parallelized and thus need high maximum wall clock times. The compute cluster requested here is needed to secure the computational resources needed by the working group.