Large nearshore storm waves off the Irish coast

Francesco Fedele,James Herterich,Aziz Tayfun,Frederic Dias

doi:10.1038/s41598-019-51706-8

Francesco Fedele, James Herterich + Show 2 more

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https://doi.org/10.1038/s41598-019-51706-8

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Abstract

We present a statistical analysis of nearshore waves observed during two major North–East Atlantic storms in 2015 and 2017. Surface elevations were measured with a 5-beam acoustic Doppler current profiler (ADCP) at relatively shallow waters off the west coast of Ireland. To compensate for the significant variability of both sea states in time, we consider a novel approach for analyzing the non-stationary surface-elevation series and compare the distributions of crest and wave heights observed with theoretical predictions based on the Forristall, Tayfun and Boccotti models. In particular, the latter two models have been largely applied to and validated for deep-water waves. We show here that they also describe well the characteristics of waves observed in relatively shallow waters. The largest nearshore waves observed during the two storms do not exceed the rogue thresholds as the Draupner, Andrea, Killard or El Faro rogue waves do in intermediate or deep-water depths. Nevertheless, our analysis reveals that modulational instabilities are ineffective, third-order resonances negligible and the largest waves observed here have characteristics quite similar to those displayed by rogue waves for which second order bound nonlinearities are the principal factor that enhances the linear dispersive focusing of extreme waves.

Highlights

We present a statistical analysis of nearshore waves observed during two major North–East Atlantic storms in 2015 and 2017
We will show that the Tayfun and Boccotti[9,10] models for wave heights, previously validated for both simple[4,10] and mixed seas[11,12,13] in deep water, describe the statistics of large waves in intermediate to relatively shallow waters reasonably well
We explore the occurrence frequency of rogue waves observed at a fixed point at sea

Summary

Introduction

We present a statistical analysis of nearshore waves observed during two major North–East Atlantic storms in 2015 and 2017. To compensate for the significant variability of both sea states in time, we consider a novel approach for analyzing the nonstationary surface-elevation series and compare the distributions of crest and wave heights observed with theoretical predictions based on the Forristall, Tayfun and Boccotti models The latter two models have been largely applied to and validated for deep-water waves. Several cases of extreme wave occurrences of practical and theoretical interest such as the Andrea, Draupner and Killard waves[1] and the sinking of El Faro[2] have been studied in detail by way of higher order spectral wave simulations and validated with probabilistic wave models These studies have shown that second-order statistical distributions of crests, in particular those often referred to as Tayfun[3,4,6,7] and Forristall[8] models, both describe rogue statistics reasonably well in intermediate to deep waters. We propose novel probability models appropriate to non-stationary processes so as to be able to analyze the surface-elevation time series gathered during the two storms

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