Observation of Extreme Sea Waves in a Space–Time Ensemble

Abstract

In this paper, an observational space-time ensemble of sea surface elevations is investigated in search of the highest waves of the sea state. Wave data were gathered by means of a stereo camera system, which was installed on top of a fixed oceanographic platform located in the Adriatic Sea (Italy). Waves were measured during a mature sea state with an average wind speed of 11 m s 21 . By examining the space-time ensemble, the 3D wave groups have been isolated while evolving in the 2D space and grabbed ''when and where'' they have been close to the apex of their development, thus exhibiting large surface displacements. The authors have selected the groups displaying maximal crest height exceeding the threshold adopted to define rogue waves in a time record, that is, 1.25 times the significant wave height (H s ). The records at the spatial positions where such large crests occurred have been analyzed to derive the empirical distributions of crest and wave heights, which have been compared against standard statistical linear and nonlinear models. Here, the maximal observed wave crests have resulted to be outliers of the standard statistics, behaving as isolated members of the sample, apparently uncorrelated with other waves of the record. However, this study has found that these unexpectedly large wave crests are better approximated by a space-time model for extreme crest heights. The space-time model performance has been improved, deriving a second-order approximation of the linear model, which has provided a fair agreement with the empirical maxima. The present investigation suggests that very large waves may be more numerous than generally expected.

Can Rogue Waves Be Predicted Using Characteristic Wave Parameters?

“…Wave buoys provide a single-point time series and therefore only capture rogue waves occurring at that point, but whether or not a wave is breaking cannot be determined from the time series. It is possible that rogue waves could occur nearby but not directly at the buoy's locations, and hence, the likelihood of rogue waves is under represented by buoys (Benetazzo et al, 2015;Fedele et al, 2013). This can be investigated numerically with simulations of high-order spectral calculations of the Euler equations for water waves (Dommermuth & Yue, 1987;Fedele et al, 2016), and experimentally using stereo imagery to form spatiotemporal records of 3-D wavefield s (Benetazzo et al, 2012;Gallego et al, 2011).…”

The close circumstellar environment of Betelgeuse

“…We adopt here the term rogue cell to designate such a statistical outlier, by analogy with the abnormally large rogue waves occasionally present in Earth's oceans (Benetazzo et al 2015). Although the existence of such rogue cells is putative, the detection of a faint but significant magnetic field on Betelgeuse by Aurière et al (2010) indicates the presence of strong convection cells able to generate a local magnetic field through a dynamo effect (Dorch 2004;Tessore et al 2017a).…”

The Draupner wave: A fresh look and the emerging view

“…The second one stems from the theoretical development of space‐time extreme wave statistics due to Fedele [], and applied by Benetazzo et al . [] in a nonlinear context. We first use both theories to derive the Draupner wave probability of occurrence, and then we discuss what we consider the correct view of any similar event.…”