Behavior of Flotsam in the California Current System Utilizing Surface Drift of RAFOS Floats
Gates, Dallas Cody
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The patterns of surface drift of eighty-nine undrogued RAFOS floats in the California Current System have been studied. The floats were launched in the California Undercurrent during 19922010 and were tracked by the ARGOS system when they surfaced at the end of their subsurface mission. The surface drift of these floats was typically equatorward in the California Current. However, some floats moved poleward into the Subpolar Gyre, and others drifted westward into the North Equatorial Current. The duration of surface trajectories varied from as short as 11 days to as long as 280 days. Observations of surface currents typically use drifters which are coupled to the surface layer by drogues which are located at 15 m depth. While drogued observations are useful for studies of circulation of the upper layer of the ocean, a more typical operational problem involves trying to find flotsam that has fallen off the deck of a ship or to predict the path of a floating mine. To better understand the behavior of these surface drifting objects, observations of the surface drift of RAFOS floats in the California Current system were used to compare their motion to wind induced drift and evaluate the drift prediction by three ocean models, Ocean Surface Current Simulator (OSCURS), Global Navy Coastal Model (gNCOM) and Hybrid Coordinate Ocean Model (HYCOM). The results indicate that summer and fall months provided the best correlation between float drift speed and wind speed. Evaluation of the drift prediction by three ocean models was conducted by comparing observed drifter trajectories with model simulated trajectories at 7-day timescales. The model-simulated trajectories were initially collocated with RAFOS positions and restarted every 15 days. These results showed that OSCURS was able to give better short-term prediction of surface drift than gNCOM and HYCOM when OSCURS model parameters were chosen as to minimize separation between modeled and observed trajectories.
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Benson, Kirk R. (Monterey, California. Naval Postgraduate School, 1995-09);This study presents float observations from four RAFOS floats that were deployed off central California for a twenty-three day period as part of a Tomography Demonstration Experiment. These floats, which sampled hourly, ...
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