A global view on bimodal wave spectra and crossing seas from ERA-interim

The paper aims at providing a global view of the wave climate, with specific focus on separation of the wave components and the analysis of crossing seas. The knowledge about complex sea-states may, in fact, have a great influence in the prediction of ship responses. The occurrence of bimodal wave spectra is assessed by analysing the ERA-interim wave database and in particular the parameters describing the different spectral components for wind-sea and swell. A brief description of the global wave climate is provided, with a discussion on the significance of the average conditions as representative for the actual scenarios that can be expected, and the consistency of the results with previous studies is verified. The contribution of the two regimes in different areas is then investigated, as well as the probability of crossing seas, separating the stormy conditions by the highly swell dominated periods, highlighting those regions where a traditional single peak representation could lead to inaccuracies in the representation of the actual sea-state. A qualitative analysis is then supported by some examples in which two different spectral models are compared in a number selected locations.