Improved Gulf Stream separation through Brinkman penalization

The advantage of a smooth representation bathymetry in terrain-following σ-coordinate ocean models is compromised by the need to avoid numerical errors on steep slopes associated with pressure gradient discretization or spurious diapycnal diffusion. Geopotential z-coordinate these errors, but greatly underrepresent interaction flow topographic slope, especially when underresolved. Hybrid coordinate are also deficient because it difficult find satisfactory compromise between z and σ coordinates. More general vertical coordinates (not just combinations σ) can be used, particular for interior, without solving problems bathymetry. With volume penalization, we do not seek compromise, rather correction usual systems that realistically recovers continuous Brinkman penalization method studied here modified version one introduced Debreu et al.(2020) simplifies implementation increases robustness improves its computational performance realistic long-term simulations, while preserving accuracy. We apply this Gulf Stream separation problem has puzzled modelers decades. flow-topography achieves at resolutions as coarse 1/8°. In addition, provides tool separate effect eddy activity slope changing grid resolution. This never before been possible resolution none properly represent continental slope. Our results show more important than ensuring separation, even though many recent studies tend focus activity. A exert stabilizing influence promotes strong mean current inertia helps from coast curvature Cape Hatteras. anticipate successful will very valuable climate models, their far sufficient western boundary currents (WBCs) using traditional systems. suggest model 1/4° — perhaps some parameterization eddy-mean energize WBCs could circulation much same resolution, penalization.