Measured Rogue Waves and Their Environment

Mark D Orzech,David Wang

doi:10.3390/jmse8110890

Abstract

We conduct a comprehensive analysis of over 350 years of accumulated ocean surface elevation time series and examine evidence for the effects of nonlinear frequency modulation, wave directional spread, surface current shear, and wind forcing on the likelihood of rogue wave development. Hourly sections of positional time series from 34 surface buoys are examined to identify over 8000 rogue wave events, recording wave sizes, times of occurrence, and geographic locations. The initial dataset is subjected to a quality control process to identify and remove false positives. We investigate the correlation of rogue events with the specified marine environmental factors in an attempt to validate the predictions of earlier theoretical and modeling analyses. The rogue event dataset is contrasted with a control, non-rogue dataset containing a total of nearly 510,000 hourly data segments of surface wave data. The analysis combines the wave records with surface current and wind data from state-of-the-art global coupled models. Statistics of the identified rogue events are summarized, and results of the environmental factor analysis are presented and discussed. This study finds some support for a causal connection between each of the environmental factors and the development of rogue waves. Results also suggest that localized environmental conditions at specific sites, such as seasonal variations in directional spread and/or high surface current vorticity, may provide useful signals of greater rogue wave threat.

Highlights

Rogue waves in the ocean environment are normally defined as surface waves that are anomalously large relative to other waves in the nearby region at a given time
While there is considerable evidence from lab and theory that rogue waves can be produced by frequency modulation in wave spectra for unidirectional waves (e.g., [2,5]), these effects are expected to be reduced in the open ocean
Theoretical and lab studies in three-dimensional (3D) domains have pointed to the importance of the wave directional distribution, showing frequency modulation and rogue wave likelihood to be greater for directionally narrow wave spectra [6,7]

Summary

Introduction

Rogue waves in the ocean environment are normally defined as surface waves that are anomalously large relative to other waves in the nearby region at a given time. Benetazzo et al [22] use a stereo camera system on an oceanic platform in the Adriatic Sea to record surface elevations for a roughly 3000 m2 region over a 15 h period with mature waves (Hs ~ 1–2 m) They identify 16 rogue waves (with heights exceeding 2Hs) in the images during this relatively short time, the largest of which has Hr ≈ 3 m ≈ 2.2Hs. Over 3600 rogues were identified in wave gauge data from oil platforms by [23], who found that these events were uncorrelated with averages of environmental conditions such as sea state, wind forcing, or current direction/magnitude.

Data Sources and Analysis Methods

Findings

Discussion and Conclusions