Nested-discrete global grids for multi-scale ocean features: construction and performance evaluation

The ocean exhibits strongly multi-scale dynamics that require flexible discretization across a wide range of spatial scales. Although Discrete Global Grid System (DGGS) has been introduced to overcome limitations of conventional grids through its unified hierarchical tessellation, existing applications mainly focus on single-level or problem-specific simulations, while its capability for generalized multi-scale ocean modelling has yet to be fully explored. This study develops a DGGS-based global multi-nested grid framework using ISEA4T tessellation. The framework constructs nested meshes across multiple DGGS resolution levels and introduces a resolution-adaptive refinement scheme. By integrating DGGS with oceanographic considerations, it enables systematic grid configuration from coarse global grids to locally refined regions. Global simulations with the FVCOM model are conducted to evaluate the framework and different refinement schemes. Results show that DGGS-based nested grids reproduce major global circulation features while improving regional flow representation through targeted refinement. Rossby-radius-based refinement improves open-ocean mesoscale representation, whereas coastal and topographic refinement enhances nearshore dynamics. These results suggest that DGGS can support multi-scale ocean discretization within a unified hierarchical framework and provide a valuable reference for applying DGGS structures into multi-scale ocean modelling, with the potential to be extended to broader Earth system modelling in the future.