Resolving a fjord tidal jet with AGRIF two-way nesting: NEMO simulations of Quatsino sound, British Columbia, Canada

Abstract Structured-grid ocean models facilitate downscaling in the northeast Pacific, particularly for operational regional modelling and ocean forecasting in coastal British Columbia (BC), Canada. However, the complex oceanography and rugged coastal geography of BC pose well-known challenges for such models. In this study, we apply Adaptive Grid Refinement in Fortran (AGRIF) two-way nesting within the Nucleus for European Modelling of the Ocean (NEMO) framework to simulate a fjord system on northwestern Vancouver Island as a case study. The nested child domain is configured for Quatsino Narrows, a narrow, shallow channel that forms a T-shaped junction with the deeper Holberg–Rupert Inlets and the nearby Marble River. The AGRIF two-way nested model demonstrates improved skill in representing tidal mixing, as indicated by temperature and salinity profiles collected recently within the junction area. Examination of child-domain outputs saved at 15-minute intervals shows that near-surface and subsurface internal waves are generated sequentially during each flood phase along the tidal-jet section slope. Tidal analysis was conducted to quantify barotropic-to-baroclinic energy conversion and baroclinic tidal energy flux, as well as their seasonal variability. Barotropic-to-baroclinic energy conversion for M2 tides is found along the tidal-jet slope and in the shallow waters west of Hankin Point. Estimates of the spatially integrated baroclinic tidal energy terms and fluxes through boundaries suggest that the T-shaped junction region acts as a sink for M2 and a source for M4 baroclinic tidal energy.