Researchers present a comparison of the numerics and simulation results for two “full” Stokes ice sheet models, FELIX-S and Elmer/Ice. The models are applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d). 

For the diagnostic experiment (P75D) the two models give similar results (<2% difference with respect to along-flow velocities) when using identical geometries and computational meshes, which researchers interpret as an indication of inherent consistencies and similarities between the two models. 

For the standard (Stnd), P75S, and P75R prognostic experiments, researchers find that FELIX-S (Elmer/Ice) grounding lines are relatively more retreated (advanced), results that are consistent with minor differences observed in the diagnostic experiment results and that they show to be due to different choices in the implementation of basal boundary conditions in the two models. 

While researchers are not able to argue for the relative favorability of either implementation, they do show that these differences decrease with increasing horizontal grid resolution and that those grounding-line positions for FELIX-S and Elmer/Ice converge to within the estimated truncation error for Elmer/Ice. Stokes model solutions are often treated as an accuracy metric in model intercomparison experiments, but computational cost may not always allow for the use of model resolution within the regime of asymptotic convergence. 

In this case, researchers propose that an alternative estimate for the uncertainty in the grounding-line position is the span of grounding-line positions predicted by multiple Stokes models. 

This research results have been published in the journal The Cryosphere in an article entitled A Comparison of Two Stokes Ice Sheet Models Applied to the Marine Ice Sheet Model Intercomparison Project for Plan View Models (MISMIP3d). 

 A schematic of the different basal boundary masking schemes used by FELIX-S and Elmer/Ice and their impact on the definition of the MISMIP3d basal friction coefficient (C(x, y) is assumed uniform beneath grounded ice for illustrative purposes. (Image by Tong ZHANG)