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The Velocity Field in the Northeast Atlantic from Satellite-Tracked Drifting Buoys

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Master's thesis

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Data from 36 surface drifters Holey Socks were collected for a period of 23 months from July 1991 to May 1993 in the Northeast Atlantic Ocean between the Azores Islands and the Canary Islands as a part of the SUBDUCTION experiment. The position information from those drifters is analyzed in this study to obtain horizontal velocity statistics at the drogue level 15m. Mean currents in the area are found to be less than 2 cmsec except in the vicinity of the Azores Front where the 2-year mean eastward currents measure 3.9-1.7 cm.sec. Zonally-averaged northward currents are divergent over most of the area in contrast to the convergent surface currents expected in the region due to convergence of the climatological Ekman transport. It is shown, however, that array bias due to the nonuniform distribution of particles in the presence of an eddy field can account for this result. The mean eddy kinetic energy level is 103sq cmsq sec and the mean diffusivity is 5.0 x 10exp 7sq cmsec. These values are in line with results from previous drifter studies. Mean Lagrangian integral time and length scales are 5.7 days and 48 km, respectively and, in all cases, east-west scales are greater than north-south scales. In general, this long data set is still dominated by the effects of mesoscale eddies. An objective method to select eddy portions of drifter trajectories is presented that may help to characterize the eddy field in future studies.

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  • Physical and Dynamic Oceanography
  • Marine Engineering

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