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  • Author or Editor: L. A. Regier x
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R. T. Pollard and L. A. Regier

Abstract

Density and velocity data with 4-km horizontal resolution from a survey of a front during FASINEX (Frontal Air-Sea Interaction Experiment) are combined to describe the structure of the top 300 m of the ocean.

The geostrophic velocity field is derived and is used to examine the relative importance of stratification, relative vorticity, and twisting terms in Ertel's potential vorticity Q. Tenfold isopycnic changes in Q are found across a horizontal scale of only 10 km. These changes are confined to isopycnals that outcrop from the seasonal thermocline into the mixed layer. The ageostrophic velocity field is quantified by solution of the omega equation, and vertical velocities of up to 40 m day−1 are found. Small (40 km) surface-trapped (top 200 m) eddies are found to play a crucial role in the transport and effective diffusion of properties across the thermocline out of the mixed layer.

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T. K. Chereskin, D. Halpern, and L. A. Regier

Abstract

Depth-averaged current shears computed from shipboard acoustic Doppler current profiler (ADCP) and moored Savonius rotor and vane vector-averaging current meter (VACM) measurements are compared at 35, 62.5, 100 and 140 m depths within 7 km of each other near 0°, 140°W during a 12-day interval in November 1984. The agreement between the VACM and ADCP shears was excellent. The average root-mean-square difference of hourly shear values was small, approximately 0.21 × 10−2 s−1, and the average correlation coefficient was 0.90. Spectral estimates were equivalent to within 95% significance level and the VACM and ADCP shears were 95% statistically coherent with zero phase difference for frequencies below 0.2 cycles per hour.

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J. N. Moum, D. R. Caldwell, C. A. Paulson, T. V. Chereskin, and L. A. Regier

Abstract

A 3°N to 3°S transect of the equator at 140°15'W was made in November 1984. Vertical profiles of temperature, conductivity and turbulent dissipation were obtained at approximately 1 km intervals. Contrary to previous results, we found no obvious peak in dissipation either at the equator or clearly associated with the Equatorial Undercurrent. A thermistor chain towed behind the ship indicated the rich (and previously unseen) variability of the hydrophysical field of the equatorial ocean. Some of this variability (especially, internal waves) is intimately linked to mixing processes.

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R. E. Davis, L. A. Regier, J. Dufour, and D. C. Webb

Abstract

The autonomous Lagrangian circulation explorer (ALACE) is a subsurface float that cycles vertically from a depth where it is neutrally buoyant to the surface where it is located by, and relays data to, System Argos satellites. ALACEs are intended to permit exploration of large-scale low-frequency currents and to provide repeated vertical profiles of mean variables. ALACEs periodically change their buoyancy by pumping hydraulic fluid from an internal reservoir to an external bladder, thereby increasing float volume and buoyancy. Because positioning and data relay are accomplished by satellite, ALACEs are autonomous of acoustic tracking networks and are suitable for global deployment in arrays of any size. While providing only a sequence of displacements between surfacing intervals, ALACEs are efficient in gathering the widely spaced long-term observations needed to map large-scale average flow.

The primary technical challenges met in the ALACE design are maximizing energy efficiency to achieve a lifetime of 50 surfacing cycles over several year., achieving reliable satellite communication with minimal surface buoyancy, and developing overall system reliability in an instrument that cannot be recovered or diagnosed after most failures. This paper describes the ALACE system, design specifications, and some field experiences. The singular failure of a simple dynamical model to predict the surface following behavior of scale models in laboratory tests serves as a cautionary note in using simple models to infer the dynamics of surface floats in various oceanographic applications. The limitations of interpreting the sequence of net displacements between surface positions, including errors caused by surface drift, are also discussed.

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