The exchange grid. A mechanism for data exchange between earth system components on independent grids

The chapter presents a mechanism for exchange of quantities among components of a coupled earth system model, where each component is independently discretized. The exchange grid is formed by overlaying two grids such that each exchange grid cell has a unique parent cell on each of its antecedent grids. In earth system models, processes occurring near component surfaces require special surface-boundary-layer physical processes to be represented on the exchange grid. The exchange grid is thus more than just a stage in a sequence of regridding between component grids. The exchange grid is designed not as a sparse matrix among all possible pairs of parent grid cells but as a compact array pointing back to the parents. When parent grids have dynamic tiles, each tile appears as an independent cell on the exchange grid rather than an extra tile dimension. The chapter also presents the design and use of a two-dimensional exchange grid on a horizontal planetary surface in the Geophysical Fluid Dynamics Laboratory (GFDL) flexible modeling system (FMS), highlighting issues of parallelism and performance.