Effects of bound-wave asymmetry on North Sea rogue waves

Since the 1990s, modulational instability has been proposed as an alternative to the constructive interference of waves to explain the occurrence of rogue waves in the open ocean. This study questions the relevance of this instability for real rogue waves by analyzing a novel dataset of high-frequency laser altimeter wave measurements collected over an 18-year period () at the offshore Ekofisk platform in the central North Sea. A composite statistics of the ensemble of 27505 half-hourly sea states, accounting for data heterogeneity, show that third-order modulational instabilities do not significantly impact large waves; instead, second-order bound nonlinearities, shaping waves with asymmetric sharper crests and shallower troughs, are the primary factor that enhances the linear dispersive focusing, or constructive interference, of extreme waves.