Eddy analysis in the subtropical zonal band of the North Pacific Ocean

There are two zonal bands of eminently high eddy kinetic energy (EKE) in the North Pacific Ocean. The highest one is located in the Kuroshio Extension and the second one is in the subtropical area. This paper focuses on the latter. An eddy detection scheme based on velocity vector geometry is applied to the SSHA-derived geostrophic currents to identify and track eddies, and to generate an eddy dataset which includes spatial and temporal information on eddy generation, evolution and termination. Analysis of this dataset allowed the investigation of a broad range of eddy parameters. From 1993 to 2010, about six thousand eddies with lifetime longer than eight weeks were generated within the band. All eddies moved westward, and both cyclonic and anticyclonic eddies deflected northward south of 21 degrees N and southward north of 21 degrees N, respectively. Statistically, three different stages of an eddy's lifetime can be identified: the first one-fifth of its lifetime corresponds to the growing period; the successive three-fifths after that to its stable stage; the last one-fifth to its decaying period. Observed Argo vertical profiles collected within the detected eddy areas are used to investigate the eddy-induced vertical displacement of the thermocline and the halocline. Frontal intensity derived from the SST data is used to explain the mechanism modulating temporal and spatial eddy variations within the zonal band. (c) 2012 Elsevier Ltd. All rights reserved.