Wave-current interaction in tidal fronts

Burkard Baschek

Woods Hole Oceanographic Institution, MA, USA

14th Aha Hulikoa Winter Workshop: Rogue Waves, Honolulu, Hawaii, January 2005

Tidal fronts are a common feature of the coastal ocean. They are formed by the interaction of tidal currents with topography and are characterized by surface convergence areas with strong gradients in density and current speed. Waves -- or even small disturbances formed at low wind speed -- that travel into these areas are slowed down by the currents and tend to steepen and break. Because the location of wave breaking is therefore highly predictable, tidal fronts form an ideal and easily accessible natural laboratory for studying wave-current and wave-wave interactions. The conditions in the fronts favor the formation of statistically extreme waves, i.e. waves with heights of up to twice the significant wave height. Due to the small spatial scales of tidal fronts, it is possible to observe the history of these waves in space and time simultaneously. In spite of the different scales of the waves, the principal physics of the formation mechanisms may be applicable to the open ocean case where rogue waves represent a significant threat to ship traffic and offshore structures.