The effect of vertical coordinates on the accuracy of a shelf sea model

The vertical coordinates (VC) are one of the most important set configuration options an ocean model. Optimisation is, however, a non-trivial exercise. We compare nine configurations to investigate different VC and contrast Vanishing Quasi-Sigma (VQS), partial step z-level, s-z hybrid Multi-Envelope (MEs) approaches. Using NEMO model simulations, hierarchy experiments conducted, including: unforced multi-year climatological simulations with comparisons against tracer profile observations, tide-only simulations. Hydrostatic pressure gradient errors on continental slope in VQS found be consistent reduced domain-averaged accuracy both realistic Reduced shelf is associated larger advective transports at shelfbreak. Accuracy improved by using separate definitions computational surfaces MEs hybridisation employing steepness parameter, r m x , 0.04–0.07, perform comparably configurations. Restrictions tilt upper appear less important. In contrast, without stratification show that tidal simulation quality linked accurately representing bathymetry, which favours terrain-following systems. support transitioning across shelfbreak either or approach as flexible route improving regional global models. • Sigma-coordinate error degrades sea accuracy. Pressure drives on-shelf field inaccuracy. Tide determined coordinate setup shelf. case study supports Multi-envelope s-coordinates comparably.