Abstract
We consider the observation and analysis of oceanic rogue waves collected within spatio-temporal (ST) records of 3D wave fields. This class of records, allowing a sea surface region to be retrieved, is appropriate for the observation of rogue waves, which come up as a random phenomenon that can occur at any time and location of the sea surface. To verify this aspect, we used three stereo wave imaging systems to gather ST records of the sea surface elevation, which were collected in different sea conditions. The wave with the ST maximum elevation (happening to be larger than the rogue threshold 1.25Hs) was then isolated within each record, along with its temporal profile. The rogue waves show similar profiles, in agreement with the theory of extreme wave groups. We analyze the rogue wave probability of occurrence, also in the context of ST extreme value distributions, and we conclude that rogue waves are more likely than previously reported; the key point is coming across them, in space as well as in time. The dependence of the rogue wave profile and likelihood on the sea state conditions is also investigated. Results may prove useful in predicting extreme wave occurrence probability and strength during oceanic storms.
Highlights
There is increasing consensus[1,2,3] that a likely physical mechanism explaining the formation of oceanic rogue waves in stormy conditions is the spatio-temporal focusing due to the dispersive nature of water waves in intermediate-deep waters[4,5,6], further enhanced by second-order non-resonant nonlinearities[7,8,9]
We interpret rogue waves as space-time (ST) maxima, and we use five ST records of sea surface elevations collected with different stereo wave imaging systems to reveal key aspects of the rogue waves behavior, in particular their temporal profile and probability of occurrence, in connection, with the sea state conditions
We investigate five ST wave records collected using three different stereo wave imaging systems deployed at stations in the Pacific Ocean, Adriatic Sea (Acqua Alta platform), and Black Sea (Katsiveli platform) during active wind conditions
Summary
There is increasing consensus[1,2,3] that a likely physical mechanism explaining the formation of oceanic rogue waves in stormy conditions is the spatio-temporal focusing due to the dispersive nature of water waves in intermediate-deep waters[4,5,6], further enhanced by second-order non-resonant nonlinearities[7,8,9]. Point-like instruments provide only a “tunnel vision” of rogue waves, as the occasional presence of those waves as outliers within a time series is due to the dynamical effects of a coherent and large 3D wave group that focuses nearby the specific observational point[19, 20] In this respect, with reference to the iconic Draupner rogue wave event[21], Cavaleri et al.[22] argue that rogue waves are relatively common and part of the realm of stormy 3D waves: the key point is coming across them. We interpret rogue waves as space-time (ST) maxima, and we use five ST records of sea surface elevations collected with different stereo wave imaging systems to reveal key aspects of the rogue waves behavior, in particular their temporal profile and probability of occurrence, in connection, with the sea state conditions. We conclude discussing the consequence of our analysis in the framework of rogue wave studies
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