Vertical Motion in the Gulf Stream Near 68°W

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  • 1 University of Rhode Island, Graduate School of Oceanography, Narragansett Bay Campus, Narragansett, Rhode Island
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Abstract

The authors compute and compare vertical motions from three different data sources within a 300-km square domain centered in the Gulf Stream near 38°N, 68°W, and show that vertical motions inferred from all three independent data sources and different analysis methods give similar results. The time derivatives of RAFOS float pressures on isopycnal surfaces are used to determine directly observed vertical motion wRAF. Second, vertical motions are inferred from the heat equation using measured temperature changes and the backing and veering of currents observed by a stack of current meters to produce wcm. Third, vertical motions are calculated from the quasigeostrophic vorticity equation using geostrophic streamfunctions from inverted echo sounder measurements to produce wIES. wCM agrees well with WRAF from all floats that pass within 10 km of a current meter mooring. Daily fields of wCM show very good coherence with time series of wCM for periods longer than 16 d, but noise domination for periods shorter than 12 d. Typical magnitudes during strong “events” as estimated by all three data sources are on the order of 1–2 mm s−1 in regions near the center of the Gulf Stream. The characteristic spatial and temporal scales of upwelling or downwelling features are clearly defined from the horizontal maps and time series of w, and the location of these vertical motions relative to Gulf Stream mesoscale features is discerned.

Abstract

The authors compute and compare vertical motions from three different data sources within a 300-km square domain centered in the Gulf Stream near 38°N, 68°W, and show that vertical motions inferred from all three independent data sources and different analysis methods give similar results. The time derivatives of RAFOS float pressures on isopycnal surfaces are used to determine directly observed vertical motion wRAF. Second, vertical motions are inferred from the heat equation using measured temperature changes and the backing and veering of currents observed by a stack of current meters to produce wcm. Third, vertical motions are calculated from the quasigeostrophic vorticity equation using geostrophic streamfunctions from inverted echo sounder measurements to produce wIES. wCM agrees well with WRAF from all floats that pass within 10 km of a current meter mooring. Daily fields of wCM show very good coherence with time series of wCM for periods longer than 16 d, but noise domination for periods shorter than 12 d. Typical magnitudes during strong “events” as estimated by all three data sources are on the order of 1–2 mm s−1 in regions near the center of the Gulf Stream. The characteristic spatial and temporal scales of upwelling or downwelling features are clearly defined from the horizontal maps and time series of w, and the location of these vertical motions relative to Gulf Stream mesoscale features is discerned.

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