Analysis of Dangerous Sea States in the Northwestern Mediterranean Area

Abstract

Extreme sea waves, although rare, can be notably dangerous when associated with energetic sea states and can generate risks for the navigation. In the last few years, they have been the object of extensive research from the scientific community that helped with understanding the main physical aspects; however, the estimate of extreme waves probability in operational forecasts is still debated. In this study, we analyzed a number of sea-states that occurred in a precise area of the Mediterranean sea, near the location of a reported accident, with the objective of relating the probability of extreme events with different sea state conditions. For this purpose, we performed phase-resolving simulations of wave spectra obtained from a WaveWatch III hindcast, using a Higher Order Spectral Method. We produced statistics of the sea-surface elevation field, calculating crest distributions and the probability of extreme events from the analysis of a long time-series of the surface elevation. We found a good matching between the distributions of the numerically simulated field and theory, namely Tayfun second- and third- order ones, in contrast with a significant underestimate given by the Rayleigh distribution. We then related spectral quantities like angular spreading and wave steepness to the probability of occurrence of extreme events finding an enhanced probability for high mean steepness seas and narrow spectra, in accordance with literature results, finding also that the case study of the reported accident was not amongst the most dangerous. Finally, we related the skewness and kurtosis of the surface elevation to the wave steepness to explain the discrepancy between theoretical and numerical distributions.

Wave Height Distributions and Rogue Waves in the Eastern Mediterranean

“…The crest-to-trough symmetry found in almost all waves identified as rogue by the several commonly used thresholds is not a trivial finding. While comparison with previous reports from the area of the Eastern Mediterranean is currently impossible due to the lack of such reports, which was one of the motivations of this study, our findings are in clear contradiction with the available reports on rogue waves characteristics available from other parts of the world, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The rogue waves are commonly reported as having a high crest-to-trough amplitude ratio, indicating strong nonlinearity.…”

“…The mean third of highest waves at the time of the incident was about 4 m (5 m measured by the nearest buoy, 25 km away), while eyewitnesses reported three waves above 8 m high impacting the ship. This accident laid foundations for several papers involving hindcast modeling by [15] and [16]. The first pointed the possibility of rogue waves due to the coexistence of two meteorological systems traveling at 40-60 degrees angle to one another and having similar peak frequency.…”