Gradient-Tracking Generalized Vertical Coordinate for Ocean Models: Results of Idealized Experiments Using the Regional Oceanic Modeling System (v3.7)

A gradient-tracking generalized vertical coordinate (GT) for ocean models is proposed in the study. The movement of the grid height surfaces is based on a simple Arbitrary Lagrangian–Eulerian (ALE) method ensuring that the discrete representation of the main gradient features of ocean states is uniform and small, optimal for the resolution of gradients in the vertical profile throughout the simulation. We have successfully implemented this algorithm into the Regional Oceanic Modeling System (ROMS v3.7). The numerical experiments used to evaluate the performance of the ALE ROMS include the propagation of linear internal waves, the lock-exchange flow, the gravitational currents over steep topography, and the seamount problem. The results demonstrate that generally, a better solution with significantly less spurious numerical mixing and smaller horizontal pressure gradient force error is produced by the GT coordinate compared to the sigma and s coordinate in ROMS. Further examinations of the GT coordinate are necessary regarding its performance in more realistic scenarios of simulations.