Glider observations of kinematics in a Gulf of Alaska eddy

Abstract

The depth‐radial structure of a Gulf of Alaska (GoA) eddy is investigated using observations from an autonomous winged buoyancy‐driven glider, drifters, and satellite altimeters. The eddy formed when Sitka and Yakutat eddies merged in June 2005. Sitka and Yakutat eddies form in the northeastern GoA and travel westward carrying anomalous energy, temperature, and chemical properties. The glider crossed the eddy seven times from mid‐August to late October 2005. A temperature maximum, at 130 m depth near the eddy's center, is indicative of coastal water. The strongest azimuthal current is 0.35 m s−1, occurring at 270 m depth and 17.5 km radius. The eddy's Rossby (Burger) number is 0.16 (0.47). Using a model with nonzero constant potential vorticity anomaly only within each depth's radius of strongest current, a function is fit to azimuthal current. The fit explains a large percentage of the current's radial variance, with a squared correlation coefficient of ≥0.9 at the depths of strongest current (270 m) and weakest stratification (360 m). Temporal trends in azimuthal volume transport rate and depth mean potential vorticity are not observed during the glider survey.