Direction Symmetry of Wave Field Modulation by Tidal Current

TL;DR

This paper investigates how tidal currents influence wave fields, revealing complex behaviors in broad-banded seas that challenge traditional theoretical predictions based on simpler models.

Contribution

It demonstrates that in broad-banded seas with high directional spread, wave modulation by tidal currents deviates from classical asymmetrical effects predicted by theory.

Findings

Wave behavior in broad-banded seas is highly non-trivial.

Traditional asymmetry predictions do not hold at high tidal current ratios.

Empirical data shows complex wave modulation patterns.

Abstract

Theoretical studies on the modulation of unidimensional regular waves over a flat bottom due to a current typically assign an asymmetry between the effects of opposing/following streams on the evolution of major sea variables, such as significant wave height. The significant wave height is expected to monotonically increase with opposing streams and to decrease with following streams. To some extent, observations on data sets containing a few thousand of waves or over a continuous series of about a day confirm this prediction. Here, based on a multi-year dataset, we show that in very broad-banded seas with high directional spread, the asymptotic behavior of sea variables is highly non-trivial and does not follow the theoretical predictions, especially at high values of the ratio between tidal stream and group speed.