North Equatorial Current

The North Equatorial Current (NEC) is a strong ocean flow pushed westward by winds, mostly found close to the equator in different parts of the world’s seas. In the Pacific and the Atlantic Oceans, it sits between about 5° to 20° north of the equator, while in the Indian Ocean, it runs very near the equator itself. This current stretches from the surface down to around 400 meters deep in places like the western Pacific.

The NEC is driven by steady winds in the northern hemisphere called the easterly trade winds. It works together with another current, the South Equatorial Current or SEC, which is pushed by similar winds in the southern hemisphere. Even though they have matching names, these two currents aren’t evenly split around the equator. Instead, the NEC tends to sit slightly north of the equator, matching the position of a special weather zone called the Intertropical Convergence Zone (ITCZ), where winds from the north and south meet.

Related processes

The Equatorial Counter Current

The North Equatorial Current (NEC) and the South Equatorial Current (SEC) create something called the Equatorial Counter Current (ECC). In the Pacific and Atlantic oceans, this is named the North Equatorial Counter Current (NECC), and in the Indian Ocean, it is called the South Equatorial Counter Current (SECC).

Even though the NEC and SEC flow westward, the water doesn’t just build up at the western side of the ocean. Some of the water moves north or south to join other currents, and some flows back east as part of the Equatorial Counter Current.

The Ekman transport

The Ekman transport is a movement of water caused by winds and the Earth’s rotation. In the northern hemisphere, this movement happens to the right of the water flow, and in the southern hemisphere, it happens to the left. In the areas where the NEC and SEC flow westward, the Ekman transport moves north for the NEC and south for the SEC. This movement helps shape the currents but is smaller compared to the main flow of the currents.

Another effect of the Ekman transport is upwelling, where water rises to the surface between the NEC and the SEC.

Interaction with climate

The NEC, SEC, and ECC are important for Earth’s climate. They influence patterns like the El Niño–Southern Oscillation (ENSO), the Atlantic Meridional Mode (AMM), the Atlantic Multidecadal Oscillation (AMO), and seasonal rains in the Indian Ocean. In turn, climate changes can also affect how these currents behave.

In different oceans

Pacific NEC

a) and b) show the mean zonal surface velocity in Pacific during El Niño (1997) and La Niña years (1998). Positive values (red) represent eastward flow, negative values (blue) for westward flow. All the data plotted in this article is obtained from the GODAS dataset.

The North Equatorial Current (NEC) can be seen around 10° to 18° north in the Pacific Ocean, stretching from the Philippines to Nicaragua. It usually moves at a speed of about 30 centimeters every second. This current doesn't change much with the seasons but can vary from year to year, especially during events like El Niño and La Niña.

When the NEC reaches the Philippines, it splits into two parts. One part flows northward, feeding the Kuroshio Current, while the other flows southward, feeding the Mindanao Current.

a) shows the mean zonal surface currents within the Atlantic in the first half-year (Jan-Jun) of 1997. b) shows the second half (Jul-Dec). These two figures show a strong seasonality, with NECC stronger during July to December. Positive values (red) represent eastward flow, negative values (blue) for westward flow.

Atlantic NEC

In the Atlantic Ocean, the NEC is found around 10° to 20° north, from 16° to 60° west of the prime meridian. It usually moves at about 10 centimeters every second, slower than in the Pacific. The NEC changes more with the seasons than with years. It is stronger from July to December and weaker from January to June.

This figure shows the mean zonal surface current of different periods in the Indian Ocean. a), b) and c) are currents during January and February, during July and August, and in May, respectively. Positive values (red) represent eastward flow, negative values (blue) for westward flow.

When the NEC reaches the northern part of South America, it splits and joins the North Brazil Current (NBC).

The Indian Ocean NEC

In the Indian Ocean, the NEC is affected by the land to the north. It sits very close to the equator, between 45° and 100° east. In winter, it can reach speeds of up to 50 centimeters every second because of winds from the northeast.

The NEC changes a lot with the seasons. In winter, it flows all the way to the east coast of Somalia and joins the Somali Current. In summer, the NEC moves southward, and the Somali Current changes direction. During these changes in May and November, the NEC becomes very weak, and a different current called the Wyrtki jets appears near the equator.