Improving global barotropic tides with sub-grid scale topography

In recent years, efforts have been made to include tides in both operational ocean models as well as climate and earth system models. The accuracy of the barotropic tides is often limited by the model topography, which is in turn limited by model horizontal resolution. In this work, we explore the reduction of barotropic tidal errors in an ocean general circulation model (Modular Ocean Model version 6; MOM6) using sub-grid scale topography representation. We follow the methodology from Adcroft (2013, ), which utilizes statistics from finer resolution topographic data sets to represent sub-grid scale features with a light computational cost in a structured finite volume formulation. The geometric effect from sub-grid scale topography can be introduced to the model with only a few parameters at each grid cell. The porous barriers, which are implemented at the walls of the grid cells, are used to modify transport between grid cells. Our results show that the globally averaged tidal error in lower-resolution simulations is significantly reduced with the use of porous barriers. We argue this method is a potentially useful tool to improve simulations of tides (and other flows) in low-resolution simulations.