Articles | Volume 12, issue 3
https://doi.org/10.5194/os-12-781-2016
https://doi.org/10.5194/os-12-781-2016
Technical note
 | 
09 Jun 2016
Technical note |  | 09 Jun 2016

Technical note: Common characteristics of directional spreading–steepness joint distribution in freak wave events

Shouhua Liu, Yizhen Li, and Xinyang Yue

Abstract. Seven freak wave incidents previously documented in the real ocean in combination with model hindcast simulations are used to study the variations associated with freak-wave-related parameters, such as wave steepness, directional spreading, and frequency bandwidth. Unlike the strong correlations between the freak wave parameters and freak waves' occurrence which were obtained in experimental and physical research, the correlations are not clear in the freak waves occurring in the real ocean. Wave directional spreading–steepness joint distribution is introduced and common visual features were found in the joint distribution when freak waves occur among seven “freakish” sea states. The visual features show that freak wave incidents occur when the steepness is large and directional spreading is small. Besides large steepness and small directional spreading, a long-duration, relatively rough sea state is also necessary for the freak wave generation. The joint distribution is more informative than any single statistical wave parameter. The continuous sea states of local large steepness and small directional spreading are supposed to generate freak waves, and two-dimensional distribution visualization is found to be a useful tool for freak waves' forecast. The common visual features of joint distributions supply an important cue for the theoretical and experimental research.

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Short summary
Common visual features were found in the joint distribution of directional spreading--steepness when freak waves occurred among seven “freakish” sea states. It's interesting that the visual features look similar. The common visual features supply an important cue for the theoretical and experimental research of freak waves.