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Comparison of Equatorial Winds as Measured by Cup and Propeller Anemometers

H. Paul FreitagPacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington

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Michael J. McPhadenPacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington

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Andrew J. ShepherdPacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington

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Abstract

This study compares the performance of cup vs. propeller anemometers from surface-following taut-line moorings in the equatorial Pacific. Vector wind components at 4 m above the sea surface were measured from a mooring instrumented with a cup anemometer and concurrently from a nearby mooring instrumented with a propeller anemometer. Mean wind conditions over the 115-day comparison period were typical of the southeast trade winds with a mean speed of 6.7 m s−1 and a steadiness factor of 0.96. Differences between the time series measured by the two wind sensors were small. Mean speed differed by 0.02 m s−1 and mean direction by 1.4°. Correlation coefficients for 2-hour vector-averaged zonal component, meridional component, speed and direction were 0.97 or above. The small differences in measurements imply that the two systems are equally suited for near-surface wind observations under typical tradewind conditions.

Abstract

This study compares the performance of cup vs. propeller anemometers from surface-following taut-line moorings in the equatorial Pacific. Vector wind components at 4 m above the sea surface were measured from a mooring instrumented with a cup anemometer and concurrently from a nearby mooring instrumented with a propeller anemometer. Mean wind conditions over the 115-day comparison period were typical of the southeast trade winds with a mean speed of 6.7 m s−1 and a steadiness factor of 0.96. Differences between the time series measured by the two wind sensors were small. Mean speed differed by 0.02 m s−1 and mean direction by 1.4°. Correlation coefficients for 2-hour vector-averaged zonal component, meridional component, speed and direction were 0.97 or above. The small differences in measurements imply that the two systems are equally suited for near-surface wind observations under typical tradewind conditions.

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