ANTICYCLONIC CURRENT RINGS IN THE EASTERN TROPICAL PACIFIC-OCEAN

Observations from satellite-tracked drifting buoys, expendable bathythermograph and conductivity-temperature-depth data, and Geosat altimeter data are used to describe anticyclonic eddies that occur in small numbers off the Pacific coast of Central America. These eddies are similar in many respects to the well-known warm-core rings that are observed north of the Gulf Stream off the Atlantic coast of North America, except that they occur in an environment that also is warm, and they contain considerably greater kinetic energy. It is hypothesized that they are formed as a result of conservation of potential vorticity when the North Equatorial Countercurrent (NECC) turns northward upon approaching the eastern boundary during its autumnal maximum. The rings so formed have a strongly nonlinear character which causes them to propagate westward between 9-degrees-N and 14-degrees-N with a speed in excess of that of long Rossby waves. Due to a relatively small available potential energy content, these rings have a dissipation time scale of about 6 months and perhaps end by collision with and reabsorbtion into the NECC. The rings account for the observed enhancement of surface kinetic energy, and probably for the seaward transport of waters enriched in copper.