Two years of satellite-derived maps of sea surface temperature are used to evaluate their oceanographic applications and to study advection in the eastern part of the subtropical gyre of the South Pacific Ocean. The advance and retreat of a tongue of cool water stretching from the coast of Chile to the northwest under the southeast trade winds are analyzed and explained as advection. The time history of the development of this cool tongue is described, and its different behavior during the two years is related to the 1976 El Ni¿o event. During 1976, advection in the subtropical gyre was much weaker than during the year before. It is concluded that satellite-derived surface temperature maps form an important new tool in the analysis and monitoring of the time changes of large-scale thermal features at the surface of the ocean.