Modeling of Fine Structures in the Near-Surface Layer of the Ocean

High-resolution in-situ measurements in the near-surface layer of the ocean occasionally reveal fine-scale horizontal structures. These structures are usually associated with re-stratification of the upper ocean mixed layer due to diurnal warming, rain, or fronts. Narrow lines or sharp interfaces are also observed on synthetic aperture radar (SAR) images of the ocean surface. In areas of intense navigation, surface ships leave turbulent wakes, which may have comparable features on SAR images to naturally occurring fine structures. The sharp interfaces are presumably related to convergence zones on the sea's surface and may also contain increased concentration of surfactants. Numerical modeling is complicated by non-hydrostatic conditions in these hydrodynamic systems. In this work, a non-hydrostatic computational fluid dynamics (CFD) technique Fluent with 3-D Hybrid LES turbulence model has been applied for modeling the hydrodynamics of fine structures in the near-surface layer of the ocean including rain-formed plumes and far wakes of ships. A striking feature of simulation results was an asymmetry within both rain-formed plumes and ship wakes with respect to wind stress direction. Sharp boundaries formed on downwind sides and more diffuse boundaries on upwind sides of plumes and wakes. The results of numeric simulations are discussed in the context of the field data obtained during high-resolution measurements in TOGA COARE and a year- long ship-wake experiment on the University of Miami volunteer observing ship Explorer of the Seas.