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Acoustic Doppler current profilers (ADCPs) were used in two modes. A hull-mounted system continuously measured the upper ocean currents, typically over the depth range 20-400 m, with a horizontal resolution of about 2 km. In addition, a lowered ADCP (LADCP) mounted to the rosette provided full ocean depth profiles of horizontal currents at hydrographic stations. Our Pacific field work includes hull-mounted ADCP observations on P14N, P15S, P16 south of Hawaii, P17, P17A, P17E, P18, P19 and P31. Initially, our LADCP observations focused on the equatorial currents (P13, P16, P17). As the technique became more routine, LADCP observations encompassed higher-latitude stations as well as the equatorial (P10, P14N, P15S, P18, P19, P31). Our observations document the upper ocean current structure along the cruise tracks, describe the complex system of zonal currents found throughout the water column near the equator, and provide some description of the full-depth current structure in selective higher-latitude regions at the time of the various WOCE lines.
In the near equatorial region, the LADCP observations document the vertical and horizontal structure of the intermediate and deep circulation features, and show that several features extend across the entire Pacific basin. In the Kuroshio just southeast of Japan (P10), the LADCP measurements illustrate the detailed structure of the current, as well as the large depth-averaged component of the current and adjacent recirculation features. In the Kuroshio Extension (P14N), the shipboard and lowered ADCPs measured currents exceeding 1 m/s to the south near the surface at 33°N (along the track and invisible to geostrophic calculations from this section); the flow weakens with depth and extends to the bottom. Near the South Pacific eastern boundary at 53°S (P19), the LADCP provides estimates of a massive barotropic flow component to the south and just offshore of the continental slope with estimated southward transport exceeding 25 Sv. The Southern Ocean lines reveal what seems to be a characteristic feature of the velocity field south of the subpolar front: strongly barotropic motion, with little change in current direction from top to bottom. At these latitudes the flow is often dominated by highly barotropic eddies that are poorly resolved by the station spacing. An "Amazing Feature" appears in one profile at 62°S (P18): a 30-cm/s westward jet at 3000 m embedded in a westward barotropic flow. Most of the above features, as well as many others, would have been missed, or badly misrepresented, without the shipboard and lowered ADCP data.
Areas of active research include: a basic description of the pattern of currents with regional focus on the equatorial band, western and eastern boundary currents, the Southern Ocean and the gyre interior; optimization of the geostrophic referencing using both ADCP and LADCP data; quantification of the ageostrophic component of the circulation; and a statistical characterization of the eddy and inertial fields. Future research efforts, in cooperation with other investigators, will include the horizontal transports of heat, freshwater and other properties; the forcing of upper ocean circulation by air-sea fluxes; the use of detailed velocity information to evaluate numerical models; and the use of the data on the vertical shear of horizontal velocity to help characterize mixing in the deep ocean.
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