Statistics of unidirectional wave groups with and without freak waves observed in the Norwegian Sea.

This article focuses on the statistical properties and morphology of unidirectional ocean wave groups, including extreme wave groups containing freak waves, based on over one million measured wave groups in the deep Norwegian Sea over a decade. It finds that both the non-dimensional group energy and group duration of ordinary wave groups follow Generalized Extreme Value (GEV) distributions, with spectral width significantly influencing these statistics while wave steepness has minimal effect. Extreme wave groups exhibit energies 3.0–4.5 times greater and durations 1.4–1.8 times longer than ordinary groups, with consecutive large waves ("three sisters") being common alongside isolated freak waves. The study also shows that the NewWave theory underestimates the energy and amplitude of extreme wave groups, leading to the proposal of a modified model that more accurately predicts the average shapes and energies of extreme wave groups in this region, providing improved theoretical support for marine structure design.