Equatorial Counter Current
Equatorial counter current is a current phenomenon noted near the equator, an eastward flow of oceanic water in opposition to and flanked by the westward equatorial currents of the Atlantic, Pacific, and Indian oceans. It is also called as North Equatorial Countercurrent. It flows from west to east at a about 3-10°N in the Atlantic and Pacific basins, between the South Equatorial Current (SEC)and North Equatorial Current (NEC). Note that it is different from Equatorial Undercurrent which flows in east direction from the equator but at some depth.
In the Indian Ocean, circulation is dominated by impact of Asian monsoon winds.
NECC has a cycle in Atlantic and Pacific which reaches its peak in later summers and fall and nadir in late winter and spring. Pacific NECC is stronger during El Nino Southern Oscillations (ENSO).
There is a South Equatorial Counter current (SECC) as well but is season is not as properly defined as that of NECC.
Pacific North Equatorial Current – It is the major eastward moving surface current which transports more than 20 Sv from the West Pacific warm pool towards the cooler East Pacific pool. In the western Pacific the counter current is centred near 5°N while in the central Pacific it is located near 7°N. The northern boundary of the Pacific NECC can be easily defined by adjacent westward flow found in the North Equatorial Current (NEC). The southern boundary, however, is difficult to define. The southern boundary of the central Pacific is again clearly defined by the westward South Equatorial Current (SEC) at the surface, but not at the depth as it merges with the North Subsurface Counter current (NSCC). In the western basin, the NECC may also merge with the Equatorial Undercurrent (EUC) under the surface. Generally, the current weakens to the east of the basin. The Pacific NECC undergoes and annual cycle. During late boreal winter and spring, the current is weaker because the north easterly trade winds shift south and oppose the current. When these north easterly trade winds shift north and are weaker in the later summer and fall, the NECC becomes stronger. Pacific NECC cycle depends highly upon North Easterly Trade Winds.
Atlantic North Equatorial Current – Atlantic NECC is unique owing to its extreme seasonality. The Atlantic NECC is the eastward zonal transport of water between 3°N and 9°N, with widths of the order of 300 km. Maximum eastward flow is attained in late summers and it falls in late winter and spring. The magnitude greatly east of 38°W because of the westward equatorial current. Following the El Nino, Atlantic NECC is stronger than usual with 1983 and 1987 being notable examples.
Sv (Svedrup) – Is a unit of measure of volume transport. Used exclusively to measure volumetric rate of transport of oceanic currents. It is named in the honour of the great Oceanographer Harald Svedrup.