Sensitivity of M2 barotropic tide solutions to resolution and a physically based wave drag parameterization

Le résumé fourni par la source

Tides can modify sea surface height by several meters, yet their representation in models remains imperfect, largely owing to errors in simulating tidal energy loss. In the open ocean, barotropic tides lose energy to internal tides; this process is typically parameterized using a wave drag scaled by a scaling factor greater than one to compensate for processes not captured by the parameterization. Here, we implement a novel wave drag parameterization consistent with linear internal tide theory in MOM6 and run a global, barotropic, M 2 -tide-only model to examine the sensitivity of modelled tides to resolution. We apply physics-based, spatially varying tuning to explore the role of missing dissipative processes in simulating M 2 tides. Decreasing grid spacing from 100 km to 4 km reduces the global tidal elevation error from 10.21 cm to 4.37 cm and improves the simulated dissipation. Modelled tidal solutions converge at 4–8 km resolution, with the scaling factor converging to ∼6. The scaling factor remaining larger than one suggests that linear internal tide generation alone cannot explain all open-ocean dissipation. Correcting linear theory for supercritical topography and applying spatially varying tuning reduce tidal elevation error by a further 0.41 cm, but lead to larger regional disagreement in dissipation compared with observations. These results suggest that barotropic tide models should be run with grid spacing of 8 km or less, and that minimising global tidal elevation error may not, by itself, be a sufficient tuning criterion, as it does not always guarantee an improved distribution of tidal energy loss.

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