Upper ocean dynamics

Research on upper ocean dynamics has contributed steady progress towards a more complete and useful understanding of the ocean's role in air/sea interaction and climate. High resolution models of the upper ocean thermal structure are now quite realistic, and in some applications are limited as much by uncertainties in the surface heat flux as by uncertainties in model physics. Low resolution upper ocean thermal models are routinely included in most climate models, and have been shown to give far better simulations than do simple slab or heat conduction models. Some of these climate models have provided important new insights into the mechanisms by which the ocean may respond to a future greenhouse-imposed surface heating anomaly. In contrast, the structure of the upper ocean wind-driven velocity is not so well understood. Some models and high quality field data show significant sustained vertical shears within the temperature mixed-layer, while other data sets show organized, energetic, three-dimensional flow structures. Still other field data appear to reveal a velocity mixed-layer very much like the thermal mixed-layer. Thus the structure of the upper ocean velocity is an important and still open issue for dynamics and models, and also for the interpretation of the large and rapidly growing drifting buoy data base. The role of surface waves in generating and maintaining this current structure also remains poorly understood. Waves certainly play a central role in the mechanics of momentum transfer across the air-sea interface, both through surface roughness and more directly as a consequence of breaking. The combined system of waves and wind-driven currents is also known to be unstable, and their interaction may be an important mechanism for producing certain types of organized convection in the mixed-layer.