A modern solver interface to manage solution algorithms in the Community Earth System Model

Global Earth System Models (ESMs) can now produce simulations that resolve ∼50 km features and include finer scale, interacting physical processes. However, the current explicit algorithms that dominate production ESMs require ever-decreasing time steps in order to achieve these fine-resolution solutions, which limits time to solution even when efficiently exploiting the spatial parallelism. Solution methods that overcome these bottlenecks can be quite intricate, and there is no single set of algorithms that perform well across the range of problems of interest. This creates significant implementation challenges, which is further compounded by the complexity of ESMs. Therefore, prototyping and evaluating new algorithms in these models requires a software interface that is flexible, extensible, and easily introduced into the existing software. We describe our efforts to create a parallel solver interface that links the Trilinos collection of solver libraries to the Glimmer Community Ice Sheet Model (Glimmer-CISM), a continental ice-sheet model used in the Community Earth System Model (CESM). We demonstrate this interface within both current and developmental versions of Glimmer-CISM and provide strategies for its integration into the rest of the CESM.