Integration of Higher-Order Physics in the Community Ice Sheet Model: Scientific and Software Concerns

The Community Ice Sheet Model (CISM) is a next-generation land ice model that is designed to answer important questions regarding the response of Earth’s land ice to climate forcing. The program extends Glimmer, an ice sheet model based on the shallow ice approximation. This thesis concerns a project to ready CISM for these questions by integrating an ice velocity diagnostic based on a first-order approximation of the Navier-Stokes equations. I present in detail the derivation of the first-order momentum balance equations for both the interior of an ice sheet and a variety of boundary conditions. I discuss the numerical techniques used to build and solve a finite difference approximation of these equations, as well as the software engineering process and design solutions used to integrate this model with the rest of CISM. I then build a case for the correctness of the integrated model by presenting the results of numerous experiments that compare this model to data, exact solutions, and a collection of similar models. I find that in most cases the integrated model performs favorably in model intercomparisons and in comparisons to exact solutions. I finally present possible future directions for the CISM project with respect to higher-order ice modeling, as well as lessons learned for future maintainers