The map above shows the sea-surface temperature pattern on May 31, 1988, when the equatorial Pacific was cold. The warmest water is indicated by the dark red and progressively cooler water by yellow and green. Note the "tongue" of recently upwelled water extending westward along the equator from the South American coast. (Image courtesy of Otis Brown, University of Miami and Gene Carl Feldman, NASA, Goddard Space Flight Center.)

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