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The Effect of Inaccuracies in Weather-Ship Data on Bulk-Derived Estimates of Flux, Stability and Sea-Surface Roughness

Theodore V. BlancAtmospheric Physics Branch, Naval Research Laboratory, Washington, DC 20375

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Abstract

An analytical error analysis (or sensitivity study) is performed for the momentum, heat, and humidity flux estimates made from weather-ship observations by using the bulk flux method. Bulk-derived stability and roughness errors are also examined. The analysis is performed with two scenarios for the constituent wind speed, air temperature, water temperature, humidity, barometric pressure, and measurement altitude uncertainties. The error scenarios are constructed from published estimates and used to simulate the typical sensor inaccuracies and ship-induced distortions of meteorological measurements made from weather ships. Four bulk transfer coefficient schemes are tested. The combined influence of the sensor inaccuracies and ship-induced distortions is found to result in a typical uncertainty of about 30% for an average stress of 0.2 N m−2, 50% for an average sensible heat flux of ±25 W m−2, 50% for an average latent heat flux of ±40 W m−2, 80% for an average Monin-Obukhov stability of ±0.06, 40% for an average roughness length of 3 × 10−4, and 60% for an average roughness Reynolds number of 6. Because the analysis generally employed conservative estimates of the measurement uncertainties and left out other sources of error, it is argued that the results of the analysis represent a best case situation.

Abstract

An analytical error analysis (or sensitivity study) is performed for the momentum, heat, and humidity flux estimates made from weather-ship observations by using the bulk flux method. Bulk-derived stability and roughness errors are also examined. The analysis is performed with two scenarios for the constituent wind speed, air temperature, water temperature, humidity, barometric pressure, and measurement altitude uncertainties. The error scenarios are constructed from published estimates and used to simulate the typical sensor inaccuracies and ship-induced distortions of meteorological measurements made from weather ships. Four bulk transfer coefficient schemes are tested. The combined influence of the sensor inaccuracies and ship-induced distortions is found to result in a typical uncertainty of about 30% for an average stress of 0.2 N m−2, 50% for an average sensible heat flux of ±25 W m−2, 50% for an average latent heat flux of ±40 W m−2, 80% for an average Monin-Obukhov stability of ±0.06, 40% for an average roughness length of 3 × 10−4, and 60% for an average roughness Reynolds number of 6. Because the analysis generally employed conservative estimates of the measurement uncertainties and left out other sources of error, it is argued that the results of the analysis represent a best case situation.

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