Ocean Boundary Layer Dynamics and Air-Sea Interaction

Abstract

The dynamics of the ocean surface boundary layer are examined using theory, high-resolution moored observations from the equatorial Atlantic ocean, and idealized modeling. An approximate solution is found for the ocean response to wind-forcing in the presence of baroclinic pressure gradients, surface wave shear, and spatially varying turbulent mixing. The manner in which these parameters modify the classic physical model of the wind-forced ocean is discussed, and estimates of their spatial distribution are provided. Next, the role of time-varying shear in determining the near-surface eddy viscosity is assessed using velocity observations from the equatorial Atlantic, and the implications for several simple parameterizations are considered. These observations are then utilized to provide a first in situ observational assessment of the diurnal cycle of shear and stratification in the equatorial Atlantic, demonstrating how mixed-layer dynamics modulate the diurnal cycle of sea surface temperature, coupling the dynamic and thermodynamic responses. Further, these results suggest the existence of a deep-cycle turbulence layer in the equatorial Atlantic, providing a complementary perspective on similar recent work from the Pacific. Finally, the effect of time-varying eddy viscosity on the low-frequency wind-driven flow is assessed using theory and idealized modeling, providing a new conceptual tool for understanding the dynamics of the near-surface ocean, and for guiding the interpretation of observations. A particular focus throughout this thesis is the role of ocean dynamics in determining the near-surface ocean response to surface atmospheric fluxes.