Abstract

Satellite-derived mean sea level anomalies were blended with mean dynamic topography to obtain seasonal climatologies of the eastern South Pacific Ocean's surface circulation with an emphasis on the Humboldt Current. The Humboldt Current is confined to a narrow northward flowing jet-like stream of about 350 km associated with maximum geostrophic velocities of more than 15 cm s -1 from 35° to 23°S. The current streams closer to the coast in the south (within 500 km), but is found 500 km offshore in its northern section. A bifurcation takes place at 23°S, with a more coastal branch heading toward the coast of southern Peru (15°S) and an oceanic branch continuing in a north-northwesterly direction. The Humboldt Current intensifies by 3 cm s -1 in austral summer as compared to winter. In contrast, the Humboldt, Current's coastal branch is stronger in austral winter by the same order of magnitude. We attribute these distinct seasonal flow fields to the meridional movement of the South Pacific Anticyclone, which includes a seasonal relocation of a strong wind stress curl nucleus from offshore central-southern (austral summer) to central-northern Chile (austral winter), thus driving the Humboldt Current by means of seasonal Sverdrup dynamics. The geostrophic flow field in the eastern South Pacific communicates colder and fresher Sub-Antarctic Surface Water toward the tropics along the eastern rim of the subtropical gyre. Copyright 2008 by the American Geophysical Union.