Idealized test cases in GFDL's FV3 demonstrating the new Duo-Grid.

The Duo-Grid is a novel algorithm that addresses grid imprinting in generic gnomonic cubed-sphere grids. The algorithm aims to overcome grid discontinuities at the edges and corners by remapping data in a cube’s face halo region from its kinked coordinates to its natural location along extended great circle lines. We recently implemented the Duo-Grid in the Geophysical Fluid Dynamics Laboratory's (GFDL) Finite-Volume Cubed-Sphere Dynamical Core (FV3). We apply the Duo-Grid in idealized tests of 2D shallow water solver and the 3D hydrostatic and non-hydrostatic solvers. Our findings reveal that error norms are greatly reduced and grid imprinting is practically eliminated when employing the Duo-Grid. Most notably we find that a Rossby-Haurwitz wave is maintained significantly longer in the Rossby-Haurwitz tests, from about 80 to beyond 100 days. These results strongly suggest an improvement in FV3's accuracy and robustness.