South Equatorial Current in the context of 20th parallel south

The North Equatorial Current (NEC) is a westward wind-driven current mostly located near the equator, but the location varies from different oceans. The NEC in the Pacific and the Atlantic is about 5°-20°N, while the NEC in the Indian Ocean is very close to the equator. It ranges from the sea surface down to 400 m in the western Pacific.

The NEC is driven by the north-hemisphere easterly trade wind. In couple with NEC, there is another current called South Equatorial Current (SEC), generated by the easterly trade wind in the southern hemisphere. Despite the well-coupled name of the two equatorial currents, the distribution of the NEC and the SEC is not in symmetry at the equator, but slightly northward to the equator. This asymmetric distribution is aligned to the location of the Intertropical Convergence Zone (ITCZ), which is the area that the northeast and the southeast trade wind converge.

The Equatorial Counter Current is an eastward flowing, wind-driven current which extends to depths of 100–150 metres (330–490 ft) 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, Indian Ocean 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 along the equator at depths around 200 metres (660 ft) in the western Pacific rising to 100 metres (330 ft) in the eastern Pacific.

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.