Implementation and performance of adaptive mesh refinement in the Ice Sheet System Model (ISSM v4.14)

Abstract

Abstract. Accurate projections of the evolution of ice sheets in a changing climate require a fine mesh/grid resolution in ice sheet models to correctly capture fundamental physical processes, such as the evolution of the grounding line, the region where grounded ice starts to float. The evolution of the grounding line indeed plays a major role in ice sheet dynamics, as it is a fundamental control on marine ice sheet stability. Numerical modeling of a grounding line requires significant computational resources since the accuracy of its position depends on grid or mesh resolution. A technique that improves accuracy with reduced computational cost is the adaptive mesh refinement (AMR) approach. We present here the implementation of the AMR technique in the finite element Ice Sheet System Model (ISSM) to simulate grounding line dynamics under two different benchmarks: MISMIP3d and MISMIP+. We test different refinement criteria: (a) distance around the grounding line, (b) a posteriori error estimator, the Zienkiewicz–Zhu (ZZ) error estimator, and (c) different combinations of (a) and (b). In both benchmarks, the ZZ error estimator presents high values around the grounding line. In the MISMIP+ setup, this estimator also presents high values in the grounded part of the ice sheet, following the complex shape of the bedrock geometry. The ZZ estimator helps guide the refinement procedure such that AMR performance is improved. Our results show that computational time with AMR depends on the required accuracy, but in all cases, it is significantly shorter than for uniformly refined meshes. We conclude that AMR without an associated error estimator should be avoided, especially for real glaciers that have a complex bed geometry.

Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the AWI contribution to ISMIP6-Greenland using ISSM

“…This may be a reason for under-representing glacier velocities inside the main trunk and over-estimate velocities outside the main flow as apparent in G750. This effect shall be addressed in further studies, in which ideally error estimators as presented by dos Santos et al (2019) are engaged.…”

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

“…Both employ the shallow-shelf approximation to describe englacial stresses, discretized according to the finite-element method, on a uniform mesh with 1 km horizontal resolution. Thickness transport is effected with an incremental remappping scheme (Dukowicz and Baumgardner, 2000): ice thickness and velocity data are stored at staggered locations. The difference between submissions is the choice of basal friction rule: one submission uses the Schoof (2005) scheme and the other uses the Weertman (1957) scheme.…”

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

“…and TDI_ISSM_SSA_Weertman_500m, differ from the others in their use of an evolving adaptive mesh (Santos et al, 2019), which is updated throughout the simulations to maintain 500 m resolutions close to the grounding line and coarser resolution elsewhere.…”