Comparisons are made between surface wind stress measurements obtained by the inertial-dissipation anddirect 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 inertialdissipationand direct covariance values, to within 62% in the mean and with a 10% or lower rms scatter. Theinertial-dissipation determinations also exhibited less scatter than the tower direct covariance measurements. Adetailed error analysis indicates that shipboard inertial-dissipation wind stress values can have an accuracy ofbetter 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 measurementsfrom a tower. Errors in inertial-dissipation wind stress values are most likely due primarily to deviationsfrom the assumed balance between turbulent kinetic energy production and dissipation and to errors in determiningthe wind speed variance spectra. Errors in direct covariance measurements are most likely due primarily to finitetime 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-knowndifficulties in shipboard direct covariance measurements due to platform motion and flow distortion, demonstratethat the inertial-dissipation method is the best option at present for determining the wind stress from a ship.
展开▼
