high-performance computing
Large changes in flow have been observed in outlet glaciers
first factor is the substantial improvement in scientific knowledge of subglacial topography, particularly in deep channel- feeding outlet glaciers. Tis knowledge was slowly built up over
several different projects such as the NASA airborne mission Operation IceBridge (OIB) which began in 2009. OIB deciphered several 1,000 km radar-derived ice thickness profiles. Te remaining gaps were covered by mass-conserving interpolation methods which were used to derive flow-compatible, high-resolution maps of ice thickness and subglacial topography. Tis knowledge, combined with
advances in HPC performance and code parallelisation, have made high-resolution ice sheet modelling feasible. Te research notes that combining these
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advances allows the researchers develop a set of numerical experiments to investigate whether spatially complex flow patterns in outlet glaciers can be captured in whole-ice- sheet simulations using only ice-sheet-wide (spatially uniform) parameters, without local ‘tuning’ applied to individual grid cells. Te study used the PISM model, coupled
with models of subglacial hydrology and basal sliding, to simulate the velocity field of the Greenland ice sheet at a resolution of <1 km. Te paper states: ‘We demonstrate that
outlet glacier flow can be captured with high fidelity if ice thickness is well constrained and vertical shearing, as well as membrane stresses, are included in the model (without solving the full-stress configuration).’ However, the study also reports that
computing flow from vertical shearing alone or using low-resolution ice thickness leads to poor agreement with previous observations. ‘Overall root mean squared (RMS)
velocity differences decrease with increasing model resolution. Tis indicates that ongoing improvements in the mapping of subglacial topography, together with improvements in modelling resolution, go a long ways towards improved whole-ice-sheet numerical simulations’ the research notes.
Providing the
computational muscle Te computational muscle behind this research project comes from the UAF’s Geophysical Institute which houses two HPC systems ‘Chinook’, an Intel based cluster from Penguin Computing and ‘Fish’
AUGUST/SEPTEMBER 2017 5
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Henri Vandelanotte/
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