Turbulent mixing due to surface waves indicated by remote sensing of suspended particulate matter and its implementation into coupled modeling of waves, turbulence and circulation

Kurzfassung

This paper studies the impact of the surface waves on the turbulent mixing. The satellite observations of Suspended Particulate Matter (SPM) at ocean surface as an indicator of turbulent quantities of the flow are used. In a water column, SPM builds a vertical profile depending on settling velocities of the particles and on vertical mixing processes, thus SPM is a perfect marker to study the turbulent quantities of the flow. Satellite observations in the North Sea show that surface SPM concentrations, in locations of its deposition, grow rapidly and build plume-shaped, long (many km) uninterrupted and consistent structures during a storm. Also, satellites reveal that SPM rapidly sinks to the seabed after the storm peak has passed and wave height decreases, i.e. with absence of strong turbulence. The non-breaking wave-induced turbulence has been discussed, parameterized and implemented into an equation of evolution of turbulent kinetic energy (TKE) in the frame of mean-flow concept, which can be used in existing circulation models. The ratio between dissipated and total wave energy is used to describe the influence of wave dumping on the mean flow. Our numerical tests reproduce experiments in a wave tank very well and are supported by observations of SPM in the North Sea. Our results show that the motion of an individual non-breaking wave includes turbulent fluctuations if the critical Reynolds number for wave motion is exceeded, independent from presence of currents due to wind or tides. These fluctuations can produce high diffusivity and strongly influences mixing in the upper water layer of the ocean.