Real world ocean rogue waves explained without the modulational instability

Abstract

Since the 1990s, the modulational instability has commonly been used to explain the occurrence of rogue waves that appear from nowhere in the open ocean. However, the importance of this instability in the context of ocean waves is not well established. This mechanism has been successfully studied in laboratory experiments and in mathematical studies, but there is no consensus on what actually takes place in the ocean. In this work, we question the oceanic relevance of this paradigm. In particular, we analyze several sets of field data in various European locations with various tools, and find that the main generation mechanism for rogue waves is the constructive interference of elementary waves enhanced by second-order bound nonlinearities and not the modulational instability. This implies that rogue waves are likely to be rare occurrences of weakly nonlinear random seas.

Spontaneous emergence of rogue waves in partially coherent waves: A quantitative experimental comparison between hydrodynamics and optics

“…Therefore, the statistical properties of the surface elevation may change and rogue waves may appear more often than predicted by the linear theory. The origin of such waves is very much debated and different explanation may be found in the literature [3][4][5][6][7][8][9]. In the limit of weakly nonlinear one dimensional waves, simplified forms of the primitive equation of motion may offer some insights on the problem.…”

Extreme wave events in Ireland: 2012–2016

“…Presumably it is a combination of wind and waves that alters the dunes here. A rogue wave was observed by a Waverider buoy near Killard deployed by the ESB, on the 28th January 2014 with a maximum trough-to-crest (upcrossing) value of 26.45m (Fedele et al, 2016). Analysis of the raw data shows that a rogue wave with a crest-to-trough/downcrossing value of 33.96 m was possibly recorded on 26th January 2014 at 22:30.…”

“…Once thought to be folklore of seafarers, they are now accepted as an important class of wave. This is due to recent scientific investigations motivated by account of huge waves hitting ships (Kharif and Pelinovsky, 2003;Didenkulova et al, 2006) and measurements of 30 unusually large waves from oil-platforms (Olagnon and Prevosto, 2004;Magnusson and Donelan, 2013; Christou and Ewans, 2014; Fedele et al, 2016;Cavaleri et al, 2016;Donelan and Magnusson, 2017). Rogue waves are random in nature, occur in both deep and shallow waters, and may act as a single wave or a group of waves.…”

“…However, Fedele et al (2016) recently investigated real world ocean rogue waves and showed that their observed results could be explained by directional focussing. A discussion of linear and nonlinear rogue wave mechanisms is given in Dudley et al…”

The set-down and set-up of directionally spread and crossing surface gravity wave groups

“…This finding is supported by a high-resolution hindcast model of the Draupner storm performed by Cavaleri et al (2016), which highlighted the presence of two large crossing wave systems. In addition to Draupner, Fedele et al (2016) examined set-up in the wave-averaged surface elevation of two other very large wave Directionally spread and crossing surface gravity wave groups 133 events, concluding that crossing directional spectra were the likely cause. The set-up of the wave-averaged free surface in crossing seas can thus be seen as an important contribution to the crest height of freak waves (see Kharif & Pelinovsky (2003), Dysthe, Müller & Krogstad (2008), Onorato et al (2013) and Adcock & Taylor (2014) for reviews of the mechanisms behind freak waves).…”