09/22/2014
Initializing Ice Sheet Models in Earth System Models
Summary
Studies of ice-sheet interactions with the climate system are needed to project sea level changes. For such studies, models of ice sheets must be integrated into a coupled climate model system. A challenge is to determine the “initial conditions,” or what values of ice flow and other conditions to give the system when the model starts. Department of Energy scientists at Los Alamos National Laboratory recently addressed complications in the coupling of a dynamic ice sheet model (ISM) and an Earth System Model (ESM). Such complications arise because of the unknown ISM initial conditions. Unless explicitly accounted for during ISM initialization, the ice sheet is far from equilibrium with the surface conditions from the ESM. When coupled to the ESM conditions, the result is a shock and unphysical and undesirable transitions in ice geometry and state. To solve the problem, the team assumed equilibrium between the ice and the climate system, and the researchers derived an approach for finding ISM initial conditions. The approach involves a statistical optimization of the solution of slippage and topography on the bedrock, given what is observed and is physically reasonable. The method was first applied to a synthetic test problem, and then to a simulation of the Greenland ice sheet. The results show that, in the presence of uncertainties in the basal topography, ice thickness also should be treated as an optimization variable. While the focus here is on the coupling between an ISM and ESM surface, the method could be extended to include optimal coupling to an ocean model as well.
References
Perego, M., S. F. Price, and G. Stadler. 2014. “Optimal Initial Conditions for Coupling Ice Sheet Models to Earth System Models,” Journal of Geophysical Research: Earth Surface, DOI:10.1002/2014JF003181.