The climate of the eastern Pacific exhibits a pronounced equatorial asymmetry. Boundary layer air originating in the Southern Hemisphere trades crosses the equator and flows into the intertropical convergence zone (ITCZ), whose southern limit is nearly always located at least 4° to the north of the equator. The sea-surface temperature (SST) distribution is characterized by a prominent “cold tongue” centered ∼ 1°S, a strong frontal zone centered ∼ 2°N, and a warm eastward current centered near 5°N. The surface wind field exhibits a pronounced horizontal divergence as the air flows northward across the oceanic frontal zone. These features vary in strength in response to the annual cycle and the El Niño/Southern Oscillation phenomenon. The northward cross-equatorial surface winds, the cold tongue and the frontal zone all tend to be strongest during the cold season (July through November). During the cold season of the coldest years, when the cold tongue is most prominent, the cross-equatorial flow t... Abstract The climate of the eastern Pacific exhibits a pronounced equatorial asymmetry. Boundary layer air originating in the Southern Hemisphere trades crosses the equator and flows into the intertropical convergence zone (ITCZ), whose southern limit is nearly always located at least 4° to the north of the equator. The sea-surface temperature (SST) distribution is characterized by a prominent “cold tongue” centered ∼ 1°S, a strong frontal zone centered ∼ 2°N, and a warm eastward current centered near 5°N. The surface wind field exhibits a pronounced horizontal divergence as the air flows northward across the oceanic frontal zone. These features vary in strength in response to the annual cycle and the El Niño/Southern Oscillation phenomenon. The northward cross-equatorial surface winds, the cold tongue and the frontal zone all tend to be strongest during the cold season (July through November). During the cold season of the coldest years, when the cold tongue is most prominent, the cross-equatorial flow t...