Current interaction in large-scale wave models with an application to Ireland

Abstract

A nested large-scale wave model that covers most of the Atlantic Ocean and focuses on generating accurate swell conditions for Ireland is presented and validated over the two years 2016−2017. A sensitivity analysis for the βmax parameter appearing in the wind input formulation is carried out, optimising the extreme significant wave heights from the model against altimetry data in the North-East Atlantic region around Ireland. An optimal value of 1.75 is found using the ERA5 reanalysis corrected beforehand for a well-known negative bias for the high wind speed values. The impact of currents is studied using the surface currents from the GLORYS12 product. Currents slightly reduce by 1% the root-mean-square and bias errors for significant wave height compared to altimetry data. However, they explain most of the wave energy at scales less than 50m. The variability induced by currents is found to be more noticeable when looking at the satellite tracks. Track following observations indicate that wave refraction and advection induced by mesoscale eddies are correctly captured by the model, inducing a spatial variability reaching up to 0.5m. However, this modulation is of the same order as a shorter-scale variability appearing in the altimetry data. An averaging operator is used to smooth the data and remove those high-frequency variations. The main finding is that a spatial shift seems to appear between the model and the observations, attributed to the relatively poor resolution of the current product used for the scales observed.