The Effect of Wind and Surface Currents on Drifters

A. D. Kirwan Jr.
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G. McNally
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M-S. Chang
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R. Molinari
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Abstract

The problem analysed here is the motion of a drifter acted on by wind, surface and subsurface currents. From the condition of static equilibrium of all drag forces acting on the drifter, the effects of wind and surface current of arbitrary direction and magnitude and drogue characteristics are examined parametrically. Specific application is made to a recently developed drifter with 9.2 and 11.85 m parachute drogues and a window shade drogue. The calculations show that for some environmental conditions the deviation between the magnitudes of the drifter velocity and the water parcel velocity may exceed 500%. Furthermore, the direction of velocity vectors may differ by as much as 45°. Drifter data from an experiment conducted by the Atlantic Oceanographic and Meteorological Laboratories and the NOAA Data Buoy Office in the Gulf of Mexico Loop Current are examined in light of the theoretical results. The wind effects predicted by the theory were observed in the field. Thus wind corrections to the drifter velocity records which are based on the theory can significantly improve the velocity records.

Abstract

The problem analysed here is the motion of a drifter acted on by wind, surface and subsurface currents. From the condition of static equilibrium of all drag forces acting on the drifter, the effects of wind and surface current of arbitrary direction and magnitude and drogue characteristics are examined parametrically. Specific application is made to a recently developed drifter with 9.2 and 11.85 m parachute drogues and a window shade drogue. The calculations show that for some environmental conditions the deviation between the magnitudes of the drifter velocity and the water parcel velocity may exceed 500%. Furthermore, the direction of velocity vectors may differ by as much as 45°. Drifter data from an experiment conducted by the Atlantic Oceanographic and Meteorological Laboratories and the NOAA Data Buoy Office in the Gulf of Mexico Loop Current are examined in light of the theoretical results. The wind effects predicted by the theory were observed in the field. Thus wind corrections to the drifter velocity records which are based on the theory can significantly improve the velocity records.

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