The anomalous tracks of North Pacific drifting buoys 1981 to 1983

Abstract

Satellite tracked drogued buoys, initially deployed in August 1981 along 160°W south of the Aleutians, rather than recirculate in the Alaskan Gyre, slowly moved eastward to cross the North Pacific. Their trajectories contrast sharply with earlier buoy tracks in the region which all turned north into the Gulf of Alaska consistent with the pattern of mean annual 0/500 db dynamic topography. This marked difference in buoy trajectories is shown to be related to anomalies in the large-scale atmospheric pressure distribution rather than to anomalies in the oceanic geostrophic current. Comparisons between buoy and wind velocities reveal that the buoys respond to the wind-driven Ekman current. The anomalous buoy tracks and sea-level pressure patterns occurred in late 1981 and early 1982 just prior to the El Niño Southern Oscillation event of 1982 to 1983. During their anomalous eastward transit, the two southernmost buoys deployed almost 200 km apart in latitude behaved similarly with cross correlations of about 0.9 in their latitude, longitude displacements over a year. A third buoy crossing the same region three months later followed a path similar to the earlier two buoys, suggesting a stationary flow pattern over this period. The first two buoys finally turned north near the west coast of North America in late 1982 and rapidly continued northward near the coast in early 1983 with maximum velocities > 100 cm s −1. At the same time the third buoy shifted north and moved equally rapidly westward across the northern border of the Gulf of Alaska. Trajectories of buoys deployed in the autumn of 1982 suggest a return to the traditionally accepted circulation pattern of northward flow into the Gulf of Alaska at the eastern end of the North Pacific Current between 140° and 150°W.