DRIFTING BUOY OBSERVATIONS OF A LOOP CURRENT ANTICYCLONIC EDDY

The Loop Current penetrated deep into the Gulf of Mexico in early 1989 . After several eddy formation and reattachment cycles, a southwestwar d propagating anticyclonic eddy was formed during the summer. The Loop Current and subsequent eddy produced strong currents over widespread areas on the Louisiana continental slope, prompting a series of curren t measurement programs. Because of the lack of satellite infrared cove rage in the Gulf of Mexico during the summer, the trajectories of 53 A RGOS tracked drifting buoys deployed in the Gulf of Mexico in 1989 wer e assembled to determine the synoptic history of the Loop Current and anticyclonic eddy during this event. Ten of the most critical summerti me buoy trajectories are discussed here. In addition, the trajectories of three of the buoys simultaneously deployed at different radii in t he eddy were chosen for analysis with a kinematic feature model. The m odel assumes the looping buoy motion is generated by an elliptical orb it around a translating eddy center. The buoy trajectories were used t o determine time series of the feature model parameters, including edd y center, shape and circulation characteristics. The time series resul ts indicate that the eddy actually propagated in a series of short spr ints separated by longer stalls. During the sprints, the eddy propagat ed as an elliptical but otherwise symmetric solid body. During the sta lls, significant asymmetries developed. The asymmetries are consistent with attachment to the Loop Current during the first stall, the effec ts of topographic Rossby wave dispersion during the second, and the ef fects of planetary Rossby wave dispersion during the third. The result s provide both a framework for the interpretation of in situ observati ons and a detailed evolutionary history for numerical modelers.