A new global high resolution wave model for the tropical ocean

Abstract. Climate change is driving sea-level rise and potentially intensifying extreme events in the tropical belt, thereby increasing coastal hazards. In tropical islands, extreme sea levels and subsequent marine flooding can be triggered by cyclones but also distant-source swells. The knowledge of sea states in the tropical ocean is thus of key importance and their study is usually based on spectral wave models. However, existing global wave models typically employ regular grids with a coarse resolution, which fail to accurately represent volcanic archipelago, a problem usually circumvented by the use of obstruction grids but typically resulting in large negative biases. To overcome this problem, this study presents a new global wave model with a focus on distant-source swells, which received less attention than waves generated by cyclones. To accurately simulate sea-states in tropical areas, we have implemented the spectral wave model WAVEWATCH III© (WW3) over a global unstructured grid with a spatial resolution ranging from 50 km to 100 m. The model is forced by ERA5 wind fields, corrected for negative biases through a quantile-quantile approach based on satellite radiometer data. The wind input source terms adjusted accordingly and the explicit representation of tropical islands result in improved predictive skills in the tropical ocean. Moreover, this new simulation allows for the first time direct comparisons with in-situ data collected close to shore by water depths ranging from 30 m to 10 m.