Eddy characteristics in the eastern South pacific

The main eddy characteristics ( length scales, rotation period, swirl and translation velocities) are determined in the eastern South Pacific region ( 10 degrees-35 degrees S and 70 degrees-100 degrees W) based on surface drifter measurements, satellite altimetry, and hydrographic data from the WOCE-P19 section. The "Chile-Peru Current eddies'' have a typical diameter of order of 30 km, smaller than the typical Rossby radii observed in the region. They are principally formed near the South American coast and propagate seaward with a translation velocity varying from 3 cm s(-1) in the southern part of the study domain to 6 cm s(-1) north of 15 degrees S. Long-lived anticyclonic eddies propagate northwestward with a mean angle of around 333 degrees T, whereas cyclonic vortices propagate westward, consistent with the vortices propagation theory on a beta plane. The radial distribution of the swirl velocity shows that the Chile-Peru Current eddies have a maximum diameter of order 200 km with a swirl velocity of around 14 cm s(-1) and a rotation period of 50 days. Hydrographic data reveal a vertical extent down to around 2000 m for energetic eddies. No significant difference is observed between the tangential velocities of cyclonic and anticyclonic eddies. Geostrophic balance can be considered for large radii, whereas ageostrophic dynamics may play an important role near the eddy centers.