A study of wind stress determination methods from a ship and an offshore tower
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Authors
Frederickson, Paul A.
Davidson, Kenneth L.
Edson, James B.
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Date of Issue
1997
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Abstract
Comparisons are made between surface wind stress measurements obtained by the inertial-dissipation and
direct covariance methods on a stable offshore tower and by the inertial-dissipation and bulk methods on a ship.
The shipboard inertial-dissipation friction velocity measurements agreed very well with both the tower inertialdissipation
and direct covariance values, to within 62% in the mean and with a 10% or lower rms scatter. The
inertial-dissipation determinations also exhibited less scatter than the tower direct covariance measurements. A
detailed error analysis indicates that shipboard inertial-dissipation wind stress values can have an accuracy of
better than 15% in near-neutral conditions, as compared to an accuracy of roughly 30% for the bulk method.
The accuracy of shipboard inertial-dissipation values was shown to be equal to that of direct covariance measurements
from a tower. Errors in inertial-dissipation wind stress values are most likely due primarily to deviations
from the assumed balance between turbulent kinetic energy production and dissipation and to errors in determining
the wind speed variance spectra. Errors in direct covariance measurements are most likely due primarily to finite
time averaging and to flow distortion effects, unless great care is taken to minimize or correct for flow distortion.
The high accuracy of inertial-dissipation wind stress values found in this study, combined with the well-known
difficulties in shipboard direct covariance measurements due to platform motion and flow distortion, demonstrate
that the inertial-dissipation method is the best option at present for determining the wind stress from a ship.
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Article
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Meteorology
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Journal of Atmospheric and Oceanic Technology, Volume 14, pp. 822-834.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.