@article{fdi:010086411,
  title = {{I}mproved {G}ulf {S}tream separation through {B}rinkman penalization},
  author = {{D}ebreu, {L}. and {K}evlahan, {N}. {K}. {R}. and {M}archesiello, {P}atrick},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he advantage of a smooth representation of bathymetry in terrain-following a-coordinate ocean models is compromised by the need to avoid numerical errors on steep slopes associated with pressure gradient discretization or spurious diapycnal diffusion. {G}eopotential z-coordinate models avoid these errors, but greatly underrepresent the interaction of flow with a topographic slope, especially when the bathymetry is underresolved. {H}ybrid coordinate models are also deficient because it is difficult to find a satisfactory compromise between z and sigma coordinates. {M}ore general vertical coordinates (not just combinations of z and sigma) can also be used, in particular for ocean interior, but without solving the problems associated with the representation of bathymetry. {W}ith volume penalization, we do not seek a compromise, but rather a correction to the usual coordinate systems that realistically recovers continuous and steep bathymetry. {T}he {B}rinkman volume penalization method studied here is a modified version of the one introduced in {D}ebreu et al. (2020) that simplifies the numerical implementation of the penalization, increases robustness and improves its computational performance for realistic long-term simulations, while preserving accuracy. {W}e apply this penalization method to the {G}ulf {S}tream separation problem that has puzzled modelers for decades. {T}he method improves the representation of the flow-topography interaction and achieves realistic separation of the {G}ulf {S}tream at resolutions as coarse as 1/8 degrees. {I}n addition, it provides a tool to separate the effect of eddy activity and topographic slope when changing grid resolution. {T}his has never before been possible because at coarse resolution none of the usual coordinate systems can properly represent a steep continental slope. {O}ur results show that realistic bathymetry is more important than eddy activity in ensuring realistic {G}ulf {S}tream separation, even though many recent studies tend to focus on the eddy activity. {A} steep slope can exert a stabilizing influence that promotes a strong mean slope current with strong inertia that helps it separate from the coast at the topographic curvature of {C}ape {H}atteras. {W}e anticipate that a successful topographic slope correction will be very valuable for climate models, as their current resolution is far from sufficient to represent western boundary currents ({WBC}s) using traditional coordinate systems. {O}ur results suggest that a climate model with a 1/4 degrees resolution using volume penalization - and perhaps also some parameterization of the eddy-mean flow interaction to energize the {WBC}s - could represent ocean circulation much more realistically than a model at the same resolution, but without volume penalization.},
  keywords = {{A}lgorithms ; {P}enalization ; {B}athymetry ; {G}ulf {S}tream ; {O}cean modeling ; {ATLANTIQUE}},
  booktitle = {},
  journal = {{O}cean {M}odelling},
  volume = {179},
  numero = {},
  pages = {102121 [13 p.]},
  ISSN = {1463-5003},
  year = {2022},
  DOI = {10.1016/j.ocemod.2022.102121},
  URL = {https://www.documentation.ird.fr/hor/fdi:010086411},
}