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  • Author or Editor: Zachariah R. Hallock x
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Zachariah R. Hallock

Abstract

Changes in round-trip acoustc travel time (τ) measured between a bottom moored inverted echo sounder and the sea surface can be interpreted as changes in dynamic height (D) with suitable calibration information. The τ, D, and isotherm and isopycnal depths (Z) have been calculated using hydrographic (CTD) data from three regions: the Norwegian Current, the Sargasso Sea and the eastern Gulf Stream. Regressions of D and Z on τ were performed. The slope for the Norwegian Current is − 1.70 ± 0.01 [dyn cm (m s)−1], for the Sargasso Sea − 3.89 ± 0.16 [dyn cm (m s)−1] and for the Gulf Stream − 3.13 ± 0.07 [dyn cm (m s)−1]. The quasi-random scatter about regression curves is found to be primarily the result of variability in the seasonal thermocline, where present.

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Zachariah R. Hallock
and
William J. Teague

Abstract

A theoretical model of expendable bathythermograph (XBT) fall rate is reviewed, and a new form of fall-rate equation is proposed to include new-surface transient effects. Comparisons are made of T-7 XBT and CTD (conductivity, temperature, and depth) depths of thermohaline features off Barbados. Fall-rate equation coefficients are derived and compared with the manufacturer-supplied coefficients. As other investigators have found, the Sippican equation consistently underestimates probe depth by as much as 35 m at 760 m. Analysis yields a new equation, Z=6.798t−0.002383t 2−4.01, for depths greater than about 10 m. Considerable probe-to-probe variability is noted and is found to be primarily the result of differences in the linear term or terminal velocity of the probes; variation in effective drag resulting from probe irregularities is the likely cause. Recommendations for additional work are made.

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George O. Marmorino
and
Zachariah R. Hallock

Abstract

A new set of measurements made using an upward-looking broadband acoustic Doppler current profiler (ADCP) is analyzed for “surface velocity,” which previous investigations suggest is related to wind velocity. In the present case, use of a shallow instrument depth and 1-m-depth resolution are shown to yield both a surface return, identified by a maximum in backscatter intensity (similar to previous studies), and a subsequent return that corresponds to a maximum in speed. These returns have speeds (measured relative to the 2-m-depth current) that increase to a peak of 0.7–0.8 m s−1 at a wind speed of 4–5 m s−1 and decrease for higher wind speeds, a behavior similar to that found by Nakajima et al., who made ADCP measurements using the same incidence angle (20°) as in the present study. A new finding is that the return having maximum speed yields a direction that better approximates the wind direction (a mean difference of about 5°) over the range of wind speeds sampled (up to 17 m s−1). Suggestions are made for future investigations.

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George O. Marmorino
,
Clifford L. Trump
, and
Zachariah R. Hallock

Abstract

An experiment was performed to measure the near-surface current by aiming horizontally two of the beams from an acoustic Doppler current profiler (ADCP) deployed at 0.6-m depth from an anchored (but rolling) ship. The results compare favorably with independent current measurements made at 2-m depth but appear to resolve as well a vertical current shear associated with the shallow wind-drift layer. The approach, therefore, has potential for investigating the current profile in the upper meter or two of the water column.

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