2023 Volume 79 Issue 17 Article ID: 23-17053
On the water surface under a wind stress, many surface streaks are formed even in a case of almost no wind waves. In this study, field observations and numerical simulations were conducted in order to investigate features and the formation mechanism of such streaks. Movie data analyses obtained at Yata River revealed that such streaks were stable in time and space. Previous studies by authors showed yet that, beneath similar surface streaks, horizontally-periodic velocity profiles of wind-driven currents were formed, and it revealed the existence of secondary circulations. Numerical results by using LES with the rigidsurface model also indicated the formation of surface streaks and secondary circulations. However, they were more unstable in time and space than observed streaks and circulations. Movie data analyses also indicated low surface elevations at high-speed jets at surface streaks. According to these results, spatially-periodic high-speed jets and low surface elevations in the lateral direction were given as the surface boundary conditions. Numerical results revealed surface streaks and secondary circulations were formed stable in time and space. Its suggested that these surface streaks and circulations with almost no wind waves were formed due to the interaction between wind-driven currents and surface boundary conditions.
