Sampling Requirements for the Surface Wind Field over the Tropical Pacific Ocean

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  • 1 Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington
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Abstract

Moored wind measurements at near-equatorial locations along 110°W, 125°W, 140°W, 170°W, and 165°E are used to investigate the space-time variability of the tropical Pacific wind field. These measurements complement previous studies that relied on island winds in the central Pacific or a few moored measurements in the eastern Pacific. Results indicate that the energetic portion of the zonal and meridional wind is significantly coherent over meridional scales of about 200 km and zonal scales of 1500 km. Even at these separations the estimated coherence often accounts for less than 50% of the variance. Temporal subsampling indicated (in agreement with previous studies) that at least ten samples per month were required to resolve monthly wind speed to within 1 m s−1 in the eastern equatorial Pacific. West of the date line and in the intertropical convergence zone (ITCZ), nearly daily sampling was required. Investigation showed that little error in the daily average of derived quantities such as wind speed and stress was associated with computing these variables from daily vector averages of the wind components rather than from hourly values of the components that were subsequently averaged.

Abstract

Moored wind measurements at near-equatorial locations along 110°W, 125°W, 140°W, 170°W, and 165°E are used to investigate the space-time variability of the tropical Pacific wind field. These measurements complement previous studies that relied on island winds in the central Pacific or a few moored measurements in the eastern Pacific. Results indicate that the energetic portion of the zonal and meridional wind is significantly coherent over meridional scales of about 200 km and zonal scales of 1500 km. Even at these separations the estimated coherence often accounts for less than 50% of the variance. Temporal subsampling indicated (in agreement with previous studies) that at least ten samples per month were required to resolve monthly wind speed to within 1 m s−1 in the eastern equatorial Pacific. West of the date line and in the intertropical convergence zone (ITCZ), nearly daily sampling was required. Investigation showed that little error in the daily average of derived quantities such as wind speed and stress was associated with computing these variables from daily vector averages of the wind components rather than from hourly values of the components that were subsequently averaged.

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