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  • Author or Editor: S. P. Hayes x
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L. J. Mangum
,
S. P. Hayes
, and
L. D. Stratton

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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S. P. Hayes
,
H. B. Milburn
, and
E. F. Ford

Abstract

A free-fall instrument, TOPS, measures vertical profiles of horizontal ocean velocity, conductivity and temperature. Profiling capability extends throughout the full water column (6000 db pressure limitation). Larger vertical wavelength (water depth > λ ≳ 20 m) velocity fluctuations are resolved by acoustically tracking TOPS relative to an array of bottom moored transponders. Shorter vertical wavelength velocity fluctuations (1000 m ≳ λ > 0.2 m) are resolved by an onboard acoustic velocimeter, which measures ocean velocity relative to the profiler. Motions of the profiler are monitored with a two-axis accelerometer and fluxgate compass. The instrument, data acquisition system and processing are described. In order to interpret the onboard velocimeter measurements, a planar, irrotational flow model is developed that describes the response of TOPS to an arbitrary oceanic shear profile. The model is verified using measured velocity and acceleration and by comparing oceanic velocity computed from the onboard velocimeter with that obtained from the acoustic tracking system. The two velocity profiles, smoothed with a 25 m half-width Gaussian filter, had a rms difference over a 1000 m depth interval of only 2 cm s−1. Accelerometer measurements, interpreted through the response model, are also used to obtain ocean velocity over wavelengths longer than 10 m. These estimates agree with those based on the velocimeter to within 1.5 cm s−1. Results of our model are compared with other models that describe similar free-fall dropsondes. In addition, TOPS measured velocities are compared with independent measurements taken with another profiler. The agreement found in these internal and external comparisons gives confidence in the accuracy of the TOPS model and the ability to obtain full water column high-resolution velocity profiles in the manner described.

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