VERTICAL MOTION IN THE GULF-STREAM NEAR 68-DEGREES-W

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 degrees N, 68 degrees W, and show that vertical motions infer red from all three independent data sources and different analysis met hods give similar results. The time derivatives of RAFOS float pressur es on isopycnal surfaces are used to determine directly observed verti cal motion w(RAF). Second, vertical motions are inferred from the heat equation using measured temperature changes and the backing and veeri ng of currents observed by a stack of current meters to produce w(CM). Third, vertical motions are calculated from the quasigeostrophic vort icity equation using geostrophic streamfunctions from inverted echo so under measurements to produce w(IES) w(CM) agrees well with w(RAF) fro m all floats that pass within 10 km of a current meter mooring. Daily fields of w(IES) show very good coherence with time series of w(CM) fo r periods longer than 16 d, but noise domination for periods shorter t han 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 nea r the center of the Gulf Stream. The characteristic spatial and tempor al scales of upwelling or downwelling features are clearly defined fro m the horizontal maps and time series of w, and the location of these vertical motions relative to Gulf Stream mesoscale features is discern ed.