Impact of tidal mixing with different scales of bottom roughness on the general circulation
The current study deals with a parameterization of diapycnal diffusivity in an ocean model. The parameterization estimates the diapycnal diffusivity depending on the location of tidal-related energy dissipation over rough topography. The scheme requires a bottom roughness map that can be chosen depending on the scales of topographic features. Here, we implement the parameterization on an ocean general circulation model, and we examine the sensitivity of the modeled circulations to different spatial scales of the modeled bottom roughness. We compare three simulations that include the tidal mixing scheme using bottom roughness calculated at three different ranges of spatial scales, with the largest scale varying up to 200 km. Three main results are discussed. First, the dependence of the topographic spectra with depth, characterized by an increase in spectral energy over short length scales in the deep ocean, influences the vertical profile of the diffusivity. Second, the changes in diffusivities lead to different equilibrium solutions in the Atlantic meridional overturning circulation and bottom circulation. In particular, the lower cell of the Atlantic overturning and the bottom water transport in the Pacific Ocean are stronger for stronger diffusivities at the corresponding basins and depths, and the strongest when using the small-scale roughness map. Third, a comparison of the density fields of the three simulations with the density field of World Ocean Atlas dataset, from which the models are initialized, shows that among the simulations with three different roughness maps, the one using small-scale bottom roughness map has the smallest density bias.
KeywordsTidal mixing Overturning circulation Bottom roughness
We thank Dr. Steven Jayne for providing the data for the medium-scale roughness. We also thank the two anonymous reviewers for their helpful comments. We are grateful to Suvarchal Kumar Cheedela for providing useful comments and ground for fruitful discussion. This work is partly funded by the DFG through the research project Sonderforschungsbereich 512. The model integration was performed on the Linux-cluster of the German Climate Computing Center in Hamburg. This work is supported by the Max Planck Society and the International Max Planck Research School on Earth System Modelling.
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