The Role of Roughness and Stability on the Momentum Flux in the Marine Atmospheric Surface Layer: A Study on the Southwestern Atlantic Ocean

摘要

For the first time, in situ turbulence measurements collected in the vicinity of the Brazil-Malvinas Confluence are used to determine the influence of the ocean waves and atmospheric stability on the Marine Atmospheric Surface Layer. From the analysis of 187 high-frequency sampled segments of temperature and wind velocity, carefully selected from three ship campaigns of the Air-Sea Interaction at Brazil-Malvinas Confluence project, we found a particular behavior of the drag coefficient, with a negative trend for a calm wind speed up to 10 m/s when the significant wave height was lower than 2.5 m, and a continuous decrease of the drag coefficient with increasing wind speed for significant wave height higher than 2.5 m. The results suggest that waves act as roughness elements during high wave conditions, inducing a zero-plane displacement in the order of 0.1 to 1 m as an indication for a wave-induced roughness layer. In addition, the analysis of the turbulent kinetic energy (TKE) budget indicates the occurrence of upward TKE transport mainly during stable conditions, while the general patterns of transport and dissipation of TKE are similar to observations taken over land surfaces.