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Coupled Boundary Layers and Air-Sea Transfer (CBLAST) Program
Al Plueddemann, Gene Terray, John Trowbridge, and Bob Weller, Sandy Williams
The interaction between the atmosphere and ocean is of tremendous interest to both meteorologists and oceanographers since the exchange of energy across their coupled surfaces drives both atmospheric and oceanic circulation. Therefore, investigating the nature of this exchange is required to improve our understanding of marine weather, our changing climate, the generation of ocean waves and currents and related issues such as coastal erosion and sediment transport. To improve our understanding of air-sea exchange, a number of scientists at WHOI are participating in the Coupled Boundary Layers and Air-Sea Transfer (CBLAST) program in the Atlantic Ocean south of Martha's Vineyard. The main objective of the CBLAST program is to improve our understanding of processes that drive ocean-atmosphere interactions in low to moderate winds. The CBLAST main experiment will take place in the summer of 2003, and will also involve an offshore tower, buoys, moorings, soundings, aircraft, and research vessels.
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Figure 1
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At present, a major factor limiting understanding air-sea interactions is the lack of direct measurements of the energy and momentum exchange. Near-interface measurements of vertical fluxes are rare and incomplete in the marine atmospheric boundary layer, and they are virtually nonexistent in the oceanic surface layer. To overcome this problem, a team of scientists in AOP&E has constructed the Air-Sea Interaction Tower (ASIT) off the south shore of Martha's Vineyard (Figure 1). The ASIT is located 3 km due south of Edgartown Great Pond in 15 m of water and extends approximately 22 m into the marine. The ASIT is directly connected to the Martha's Vineyard Coastal Observatory (MVCO) to provide data transmission and power directly from shore. It is specifically designed to make turbulent flux measurements in the ocean and atmosphere and allows us to deploy sensors capable of directly measuring the heat, mass, momentum, and radiative fluxes across the coupled boundary layers. A major focus will be determination of the relative roles of shear-generated turbulence, buoyancy-generated turbulence, surface waves, and Langmuir circulations in controlling vertical fluxes and energetics (Figure 2). We will also use the measurements for a critical examination of the parameterizations used to simulate this exchange in numerical models to improve their marine weather forecasts and ocean circulation models.
Data from the ASIT is being integrated with the MVCO data and made directly available to all users via the MVCO web site at http://www.whoi.edu/mvco. The data will include wind speed and direction, air and sea temperature, waves height and direction, and currents. For life beyond this experiment, the ASIT is designed to survive the extreme conditions encountered offshore for at least 10 years. We expect the ASIT to find wide use in future investigations of coastal processes that include gas exchange, bio-optics, shallow water acoustics, sediment transport, and ocean mixing (Figure 3).
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Figure 3
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