Currents in Haida Eddies

Measurements by a variety of sensors provided details of flow in Haida Eddies, which are anticyclonic, mesoscale features that move slowly westward through the eastern Gulf of Alaska. These measurements provided the best comparison and analysis to date of mesoscale eddy currents by various ship- and satellite-based sensors. The relative contribution of barotropic currents to the total eddy orbital motion at ocean surface was found to be up to 16%, based on comparison of total sea-surface height anomalies measured by satellite altimetry, and baroclinic elevation of the ocean surface detected by ship-based measurements of density through the eddies. Acoustic Doppler current meters on a ship transiting two Haida Eddies found that the observed currents were considerably different from the expected orbital motion, perhaps due to inertial currents or to previously undetected barotropic structure. Lagrangian drifters drogued near the ocean surface in two eddies revealed that inertial currents in late spring and summer were similar in magnitude to eddy orbital motion and larger than eddy currents following periods of strong winds. Drifter tracks also provided evidence that the eddy rotated as a solid body (constant vorticity) within 30-40 km of the eddy center, and that material could remain in these central waters for at least 2 months in summer. For most of the 2-month period during which the drifters were tracked, they steadily moved away from the center of the eddy, implying a gradual uplift of the pycnocline within the eddy core due to slow decay of the eddy, or to its uplift as it moved westward into denser ambient waters.