New Ground-Truth Solution for Glacier and Ice Sheet Models
Glacier and ice sheet models, like other components of the climate system, require simpler and computationally efficient formulations (parameterizations) when implemented into a full global climate model. For ice sheets, a two-dimensional (2D) solution of simplified (low-order) equations is often used. Furthermore, mountain glaciers, generally located in remote and difficult to access regions, are often hard to simulate due to a lack of necessary model input data, most specifically accurate information on glacier geometry. For this reason, it is often convenient to measure glacier geometry only along a central flowline and to model evolution of those glaciers using a 2D flowline model with parameterizations for capturing across-flow geometric effects.
To test the simpler methods, a computationally slow 3D full set of (Stokes) equations is required. The Department of Energy-sponsored Scientific Discovery through Advanced Computing (SciDAC) project Predicting Ice Sheets and Climate Evolution of Extremes (PISCEES) recently published a full-solution result. Researchers systematically studied the applicability of a 2D, first-order Stokes approximation flowline model, modified by geometric shape factors, for the simulation of land-terminating glaciers by comparing it with a 3D, “full”-Stokes ice-flow model. The researchers then explored the sensitivities of the flowline and Stokes models to ice geometry, temperature, and forward model integration time using steady-state and transient, thermomechanically uncoupled and coupled numerical experiments. Their findings show that the 2D, first-order flowline model may produce inaccurate results for (1) steep glaciers with complex basal topography, (2) polythermal glaciers that contain temperate basal ice and experience basal sliding, and (3) coupled thermomechanical glacier evolution over long time periods (~103 years). They conclude that the 2D first-order flowline model should be applied and interpreted with caution when modeling glacier changes under a warming climate or over long periods of time.
Zhang, T., L. Ju, W. Leng, S. Price, and M. Gunzburger. 2015. “Thermomechanically Coupled Modelling for Land-Terminating Glaciers: A Comparison of Two-Dimensional, First Order and Three-Dimensional, Full-Stokes Approaches,” Journal of Glaciology 61, 702–12. DOI: 10.3189/2015JoG14J220.