Stereo Video Observations of Breaking Waves in Storm Conditions
Mika Malila, University of Washington Seattle Campus, Civil and Environmental Engineering, Seattle, United States; University of North Carolina at Chapel Hill, Institute of Marine Sciences, Morehead City, United States, Jim Thomson, University of Washington, Seattle, United States, Oyvind Breivik, Norwegian Meteorological Institute, Bergen, Norway, Brian Scanlon, National University of Ireland, Galway, Ireland, Brian Ward, National University of Ireland, Galway (NUIG), School of Physics, Galway, Ireland, Alvise Benetazzo, CNR-ISMAR, Italy and Filippo Bergamasco, DAIS, Università Ca’ Foscari, Venice, Italy
Abstract:
Deep water wave breaking (whitecapping) is a key process affecting the exchange of mass and energy across the air-sea interface. Due to the practical challenges of collecting field measurements in an open ocean environment, high-resolution, phase-resolved observations of breaking waves are rare, and thus little is known of the three-dimensional (i.e. space-time) structure of whitecaps or the effects of nonlinear wave group dynamics on individual breaking waves. In recent years, however, stereo video imagery has emerged as a promising method for studying such small-scale processes of the surface wave field in fine detail. Offshore stereo video wave measurements, both platform- and ship-based, are also increasingly applied to validate theories of the space-time variability of the surface wave field. This can be used to infer critical engineering information, such as realistic extreme/rogue wave exceedance probabilities over sea-surface areas comparable to offshore oil platforms or wind farms.
We analyze the three-dimensional structure of breaking waves using stereo video field measurements from three sources: an offshore platform located in the central North Sea, and ship-based stereo video imagery collected during two research cruises in the North Pacific in December-January 2015 and December 2019. The North Sea stereo video system was recently installed on the Ekofisk offshore platform complex at 56.5N, 3.2E. With unobstructed exposure to northerly weather systems, the Ekofisk stereo video system is one of a small number of open-ocean in situ stereo video wave observing systems worldwide. The datasets from the 2015 and 2019 cruises, onboard R/V Thomas G. Thompson and R/V Sikuliaq, respectively, were and will be collected in the vicinity of Ocean Station Papa (50N, 145W) with stereo video systems mounted on the port and starboard sides of the vessels. We use stereo video measurements from the aforementioned sources to evaluate the statistics of wave breaking with regard to wave group structures and extreme waves. We will also explore the space-time intermittence of breaking events and the relation to the directionality of the wave field.
