La Contra-Corriente Ecuatorial es una significativa corriente oceánica en los océanos Pacífico e Índico que fluye de Oeste a Este a aproximadamente 5 grados norte. Las Contra-Corrientes son el resultado de equilibrarse el flujo de agua hacia el Oeste en cada océano por las corrientes Ecuatorial del Norte y Ecuatorial del Sur. En los años en que se produce el fenómeno de El Niño, esta corriente se intensifica en el océano Pacífico.

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The Equatorial Counter Current is an eastward moving, wind-driven current flowing 10-15m deep found in the Atlantic, Indian, and Pacific Oceans. More often called the North Equatorial Countercurrent (NECC), this current flows west-to-east at about 3-10°N in the Atlantic and Pacific basins, between the North Equatorial Current (NEC) and the South Equatorial Current (SEC). The NECC is not to be confused with the Equatorial Undercurrent (EUC) that flows eastward at the equator but at some depth. In the Indian Ocean, circulation is dominated by the impact of the reversing Asian monsoon winds. As such, the current tends to reverse hemispheres seasonally in that basin. The NECC has a pronounced seasonal cycle in the Atlantic and Pacific, reaching maximum strength in late boreal summer and fall and minimum strength in late boreal winter and spring. Furthermore, the NECC in the Atlantic disappears in late winter and early spring. The NECC is an interesting case because while it results from wind-driven circulation, it transports water against the mean westward wind stress in the tropics. This apparent paradox is concisely explained by Sverdrup theory, which shows that the east-west transport is governed by the north-south change in the curl of the wind stress. The Pacific NECC is also known to be stronger during warm episodes of the El Niño-Southern Oscillation (ENSO). In fact, an early hypothesis of well-known physical oceanographer Klaus Wyrtki suggested that a stronger NECC led to a buildup of warm water in the East Pacific that is eventually observed as El Niño. There is also a South Equatorial Countercurrent (SECC) that transports water from west to east in the Pacific and Atlantic basins between 2°S and 5°S in the western basin and farther south toward the east. While the SECC is geostrophic in nature, the physical mechanism for its appearance is less clear than with the NECC; that is, Sverdrup theory does not obviously explain its existence. Additionally, the seasonal cycle of the SECC is not as defined as that of the NECC.

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