high-performance computing Te results also demonstrate that the


spatial variability can explain spatial variability in flow in ice thickness. Te research paper states: ‘We find


that inversion of surface properties for individual glaciers is not essential to reproduce the overall flow pattern. Using simple parametrisations of basal motion and subglacial hydrology, we find good agreement between simulated and observed spatial flow patterns.’ However, the work is not yet over as the


researchers note that the reproduction of the velocity magnitude requires further improvements, especially in the transitional zone 100 to 300km inland. Te study also lists some areas of possible investigation for future improvements including inadequacies in parameterising basal motion and subglacial hydrology which may account for the disagreement between observed and simulated speeds. Te researchers also list other


➤


a Cray system installed in 2012 based on the Cray XK6m-200 that uses AMD processors. Chinook, the system used for this


project, is known as a Penguin Computing Community Cluster and operates under a ‘community condo model’ that allows principal investigators (PI) to obtain access to computational resources. Tis includes a regulated datacentre, network connectivity, equipment racks, management and technical staff – resources they may not be able to procure, allowing users to focus time and energy on research, rather than owning and operating individual clusters. Participants in the condo service then


share unused portions or elements of the computational resources they add to Chinook with each other and non-invested users – such as students who might not pay a fee for access. A queue management system gives vested PIs top priority to the share they have purchased whenever the PI needs the resource. Te system operates a number of nodes for


the community and then two-tier shareholder nodes, including some nodes dedicated purely to the dedicated use of shareholders. In January 2017, with support from the


M J Murdock Charitable Trust, the Geophysical Institute, UAF vice chancellor of research, UAF International Arctic Research Center, and UAF IDeA Network of Biomedical Research Excellence, UAF Research Computing Systems engineers upgraded their HPC system. Te upgrade doubled the number of


available cores to 1892 and increased interconnect speeds from 40 Gb/s up to 100


6 SCIENTIFIC COMPUTING WORLD


Gb/s by deploying Mellanox InfiniBand technology across multiple racks of their HPC system. ‘Tis community, condo model project


launches a significant change in how high- performance computing resources are offered to the UA community,’ said Gwendolyn Bryson, manager of Research Computing Systems at the UAF Geophysical Institute. ‘Chinook is more capable, more flexible,


OUR SIMULATIONS


HAVE IMPLICATIONS FOR EFFORTS TARGETED AT PROJECTING 21ST- CENTURY SEA LEVEL RISE


and more efficient than our legacy HPC resources.’ Tis increase in performance will allow


researchers to carry out more complex simulations and to process data much faster as the interconnect upgrade has significantly increased the speed of data transfer. Tis may allow future glacial studies at a higher resolution to more accurately model the structure and movement of glacial ice flow.


Finding answers Te research project successfully managed to portray Greenland’s flow structure in unprecedented detail. Te paper reports that most outlet glaciers considered in the study were captured at grid resolutions of less than 1 km.


considerations such as the fact that not all heat sources that affect the viscosity of ice are accounted for in the model. For example, refreezing of surface meltwater (‘cryo- hydrologic warming’) can soſten the ice and enhance flow, which may be relevant in the transitional zone. Ultimately this research will help other


researchers come to a better understanding of the potential for sea level rise as ice flows from glaciers into the sea. While these simulations can go some way towards an understanding of glacial flow in Greenland, they still need to be applied to other glaciers before gaining a complete understanding of the implications. ‘Our simulations have implications for


efforts targeted at projecting 21st-century sea level rise,’ stated the paper. It also reported that the Intergovernmental


Panel on Climate Change (IPCC) Fourth Assessment Report called for the need to resolve the full stress configuration in ice- sheet models to simulate changes in outlet glaciers. Since then, ice sheet models have


seen substantial improvements in their representation of flow physics. ‘We find that models that resolve both


membrane and vertical stress gradients are capable of reproducing the observed flow structure with high fidelity. ‘In regions with large transverse velocity


gradients, such as sheer margins, the mismatch between observed and simulated flow may be further reduced by resolving additional components of the stress balance,’ the researchers noted. l


@scwmagazine l www.scientific-computing.com


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