Modelling temperature and salinity in Liverpool Bay and the Irish Sea: sensitivity to model type and surface forcing

Three shelf sea models are compared against observed surface temperature and salinity in Liverpool Bay and the Irish Sea: a 7 km NEMO (Nucleus for European Modelling of the Ocean) model, and 12 km and 1.8 km POLCOMS (Proudman Oceanographic Laboratory Coastal Ocean Modelling System) models. Each model is run with two different surface forcing datasets of different resolutions. Comparisons with a variety of observations from the Liverpool Bay Coastal Observatory show that increasing the surface forcing resolution improves the modelled surface temperature in all the models, in particular reducing the summer warm bias and winter cool bias. The response of surface salinity is more varied with improvements in some areas and deterioration in others. The 7 km NEMO model performs as well as the 1.8 km POLCOMS model when measured by overall skill scores, although the sources of error in the models are different. NEMO is too weakly stratified in Liverpool Bay, whereas POLCOMS is too strongly stratified. The horizontal salinity gradient, which is too strong in POLCOMS, is better reproduced by NEMO which uses a more diffusive horizontal advection scheme. This leads to improved semi-diurnal variability in salinity in NEMO at a mooring site located in the Liverpool Bay ROFI (region of freshwater influence) area.