Soliton groups as the reason for extreme statistics of unidirectional sea waves

The results of the probabilistic analysis of the direct numerical simulations of irregular unidirectional deep-water waves are discussed. It is shown that an occurrence of large-amplitude soliton-like groups represents an extraordinary case, which is able to increase noticeably the probability of high waves even in moderately rough sea conditions. The ensemble of wave realizations should be large enough to take these rare events into account. Hence we provide a striking example when long-living coherent structures make the water wave statistics extreme.