Field Measurements of Rogue Water Waves

Abstract

This paper concerns the collation, quality control, and analysis of single-point field measurements from fixed sensors mounted on offshore platforms. In total, the quality-controlled database contains 122 million individual waves, of which 3649 are rogue waves. Geographically, the majority of the field measurements were recorded in the North Sea, with supplementary data from the Gulf of Mexico, the South China Sea, and the North West shelf of Australia. The significant wave height ranged from 0.12 to 15.4 m, the peak period ranged from 1 to 24.7 s, the maximum crest height was 18.5 m, and the maximum recorded wave height was 25.5 m. This paper will describe the offshore installations, instrumentation, and the strict quality control procedure employed to ensure a reliable dataset. An examination of sea state parameters, environmental conditions, and local characteristics is performed to gain an insight into the behavior of rogue waves. Evidence is provided to demonstrate that rogue waves are not governed by sea state parameters. Rather, the results are consistent with rogue waves being merely extraordinary and rare events of the normal population caused by dispersive focusing.

Real world ocean rogue waves explained without the modulational instability

“…Further, the surface statistics follow the Tayfun32 distribution32 in agreement with observations9103133. This is confirmed by a recent data quality control and statistical analysis of single-point measurements from fixed sensors mounted on offshore platforms, the majority of which were recorded in the North Sea34. The analysis of an ensemble of 122 million individual waves revealed 3649 rogue events, concluding that rogue waves observed at a point in time are merely rare events induced by dispersive focusing.…”

“…Further, oceanic evidence available so far313334 seems to suggest that the statistics of large oceanic wind waves are not affected in any discernible way by third-order nonlinearities, including NLS-type modulational instabilities that attenuate as the wave spectrum broadens24. Indeed, extensive analyses of storm-generated extreme waves do not display any data trend even remotely similar to the systematic breather-type patterns observed in 1D wave flumes10313334. However, third-order bound nonlinearities may affect both skewness and kurtosis as they shape the wave surface with sharper crests and shallower troughs.…”

“…Oceanic rogue wave measurements34 indicate that the rogue threshold for crest heights is exceeded on average once every N r  ~ 10 4 waves. Similarly, recent measurements off the west coast of Ireland35 yield N r  ~ 6 · 10 4 .…”

The Making of the Andrea Wave and other Rogues

“…Rogue waves have been shown to be due primarily to frequency focusing (constructive interference) with a higher order contribution from the non-resonant interaction of fundamental and bound harmonics4. For ocean waves, the crest enhancement due to modulational instability has been shown – theoretically8, numerically9 and observationally10 – to be minor. This is to be expected since the dispersive nature of gravity waves, at the root of frequency focusing, operates on a time scale of order T, the spectral peak period; whereas the modulational instability, due to quasi-resonant third order interactions, evolves much more slowly as order T/mean square slope of interacting waves11.…”

On the discrimination of extreme waves and outliers measured by in Situ wave gauges: first approaches and results

“…Another potential advantage is, that presumably rogue, freak or freague waves are a subset of extreme waves. Christou and Ewans have noted the inconveniences of rogue wave measurements [3]: "... obtaining a large sample of rogue waves is inherently difficult because they are such rare events and field measurements are generally only recorded at single points in the vast oceans. ... To address this, it is necessary to accumulate a very large database of field measurements and hope that it will capture some rogue wave events.…”