Ireland's Atlantic nearshore coastal waters experience storms several times every year. Over the last few Winters/Springs, the UCD Wave Group has deployed a Teledyne Sentinel V acoustic Doppler current profiler (ADCP) device into these waters to measure the sea state over a period of months, in the hope of observing these stormy conditions.
In our new paper in Scientific Reports, we present results from two such storms. One was from our 2015 measuring campaign off Killard Point, and the other from the 2017 campaign off the Aran Islands. We analyze 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. Adapting and applying these models in the nearshore, and compensating for the significant variability of both sea states in time, was a novel approach.
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. However, the story does not end here. 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.
Wave measurements and statistics in the nearshore is a challenging topic, with many new and exciting results yet to be discovered!