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SOFAR Float Trajectories from an Experiment to Measure the Atlantic Cross Equatorial Flow (1989-1990)

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Technical rept.

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Neutrally buoyant SOFAR floats at nominal depths of 800, 1800, and 3300 m were tracked for 21 months in the vicinity of western boundary currents near 6N and at several sites in the Atlantic near 11N and along the equator. Trajectories at 1800 m show a swift 50 cm.sec, narrow 100 km wide southward-flowing deep western boundary current DWBC extending from 7N to the equator. At times February-March 1989 DWBC water turned eastward and flowed along the equator and at other times August-September 1990 the DWBC crossed the equator and continued southward. The mean velocity near the equator was eastward from February 1989 to February 1990 and westward from March 1990 to November 1990. Thus the cross-equatorial flow in the DWBC appeared to be linked to the direction of equatorial currents which varied over periods of more than a year. No obvious DWBC nor swift equatorial current was observed by 3300 m floats. Eight-hundred-meter floats revealed a northwestward intermediate level western boundary current although flow patterns were complicated. Three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cmsec. Six 800 m floats drifted eastward along the equator between 5S and 6N at a mean velocity of 11 cmsec one reached 5W in the Gulf of Guinea, suggesting that the equatorial current extended at least 35-40 deg along the equator. Three of these floats reversed direction near the end of the tracking period, implying low frequency fluctuations.

Subject Categories:

  • Physical and Dynamic Oceanography
  • Marine Engineering

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