Observational Buoy Studies of Coastal Air–Sea Fluxes

Paul A. Frederickson Department of Meteorology, Naval Postgraduate School, Monterey, California

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Kenneth L. Davidson Department of Meteorology, Naval Postgraduate School, Monterey, California

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Abstract

Recent advancements in measurement and analysis techniques have allowed air–sea fluxes to be measured directly from moving platforms at sea relatively easily. These advances should lead to improved surface flux parameterizations, and thus to improved coupled atmosphere–ocean modeling. The Naval Postgraduate School has developed a “flux buoy” (FB) that directly measures air–sea fluxes, mean meteorological parameters, and one-dimensional and directional wave spectra. In this study, the FB instrumentation and data analysis techniques are described, and the data collected during two U.S. east coast buoy deployments are used to examine the impact of atmospheric and surface wave properties on air–sea momentum transfer in coastal ocean regions. Data obtained off Duck, North Carolina, clearly show that, for a given wind speed, neutral drag coefficients in offshore winds are higher than those in onshore winds. Offshore wind drag coefficients observed over the wind speed range from 5 to 21 m s−1 were modeled equally well by a linear regression on wind speed, and a Charnock model with a constant of 0.016. Measurements from an FB deployment off Wallops Island, Virginia, show that neutral drag coefficients in onshore winds increase as the wind–wave direction differences increase, especially beyond ±60°.

Corresponding author address: Paul A. Frederickson, Dept. of Meteorology, Naval Postgraduate School, Code MR/FD, 589 Dyer Rd., Rm. 254, Monterey, CA 93943-5114. Email: pafreder@nps.navy.mil

Abstract

Recent advancements in measurement and analysis techniques have allowed air–sea fluxes to be measured directly from moving platforms at sea relatively easily. These advances should lead to improved surface flux parameterizations, and thus to improved coupled atmosphere–ocean modeling. The Naval Postgraduate School has developed a “flux buoy” (FB) that directly measures air–sea fluxes, mean meteorological parameters, and one-dimensional and directional wave spectra. In this study, the FB instrumentation and data analysis techniques are described, and the data collected during two U.S. east coast buoy deployments are used to examine the impact of atmospheric and surface wave properties on air–sea momentum transfer in coastal ocean regions. Data obtained off Duck, North Carolina, clearly show that, for a given wind speed, neutral drag coefficients in offshore winds are higher than those in onshore winds. Offshore wind drag coefficients observed over the wind speed range from 5 to 21 m s−1 were modeled equally well by a linear regression on wind speed, and a Charnock model with a constant of 0.016. Measurements from an FB deployment off Wallops Island, Virginia, show that neutral drag coefficients in onshore winds increase as the wind–wave direction differences increase, especially beyond ±60°.

Corresponding author address: Paul A. Frederickson, Dept. of Meteorology, Naval Postgraduate School, Code MR/FD, 589 Dyer Rd., Rm. 254, Monterey, CA 93943-5114. Email: pafreder@nps.navy.mil

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