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Boundary Layer Dynamics
stages in wave growth, and in the land-sea transition.
Since the heat capacity of a few meters of water is equivalent to that of the entire dry atmosphere above, reliable measurements of temperature in the first few meters of the ocean are crucial for improved models of air-sea heat transfer. Simultaneous temperature and turbulence measurements would permit direct measurements of heat flux in the marine boundary layer. Buoys are the primary platform for making such measurements in the open ocean. New techniques and small low-power instruments are needed to accurately measure fluxes near the ocean surface.
Oceanic fluxes are inferred or modeled based on observations of mean fields (velocity, temperature, density, and so on). Improved parameterization of fluxes for use in coupled ocean-atmosphere models is needed for investigations of global change and for climate variability studies.
Accurate measurements of boundary conditions will most probably come from networks of observations of mean conditions. Ultimately, remote sensing will provide, directly or indirectly, data on fluxes over a global scale. Indeed, there have been great advances recently in our ability to monitor ocean properties over large time and space scales.
Questions of current research interest include the following:
How well are fluxes in calm seas understood?
How do ocean surface waves affect marine surface fluxes?
When can the standard Reynolds averaging techniques be applied to define marine surface fluxes?
Do our stability parameterizations, which were determined over land, really work well over the ocean?
How well can energy and momentum budgets be computed at the air-sea interface?
The experimental determination of near-surface fluxes is difficult not only because of the difficulty of working in open ocean conditions, but also because the measurements nearly always disturb the process being measured. Varied solutions to this problem have been tried. Slender towers and masts have been erected that, although they pierce the water surface, cause minimal distortion of the fluxes. Buoys follow the ocean surface, and special care has been taken to remove this motion from the measurements. Other environmental factors may also affect measurements, and new theoretical developments are required to take into account the possibility of such contamination. Aircraft measurements have been attempted, but aircraft have trouble staying in the surface layer and cannot make measurements in the water. Measurements have been made from a blimp using a suspended platform to obtain atmospheric fluxes near the surface, and using towed sensors in the water to measure conditions in the water. Remotely piloted (or operated) vehicles (RPVs or ROVs) are becoming available for making measurements in the atmosphere and under the ocean.
The development of fast-response, stable, dissolved-gas sensors, which can be deployed for periods of months without losing calibration, is making possible field tests of gas transfer models and of their relationship to remotely sensed MABL and OBL properties. The simultaneous measurement of turbulence and dissolved gas will lead to improved models of gas transfer.
At present, the theoretical basis for determining how near-surface stability affects atmospheric fluxes to the ocean rests on the similarity theory developed in the 1950s by Monin and Obukhov. Homogeneity and stationarity are assumed in this theory, so that it may not be adequate in general. Moreover, current theory on surface wave effects on fluxes