Equatorial Counter Current - Pacific North Equatorial Countercurrent

Pacific North Equatorial Countercurrent

The Pacific NECC is the major eastward moving surface current that transports more than 20 Sv from the West Pacific warm pool to the cooler East Pacific. In the western Pacific the countercurrent is centered near 5°N while in the central Pacific it is located near 7°N. The northern boundary of the Pacific NECC is easily defined by the adjacent westward flow found in the North Equatorial Current (NEC). The southern boundary, however, can be more ambiguous. The southern boundary in the central Pacific is clearly defined by the westward South Equatorial Current (SEC) at the surface, but at depth it merges with the North Subsurface Countercurrent (NSCC). In the western basin, the NECC may merge with the Equatorial Undercurrent (EUC) below the surface. Generally, the current weakens to the east in the basin, with estimated flows of 21 Sv, 14.2 Sv, and 12 Sv in the western, central, and eastern Pacific, respectively.

Like the Atlantic NECC, the Pacific NECC undergoes an annual cycle. Unlike the Atlantic however, the eastward Pacific NECC does not generally disappear. During late boreal winter and spring, the current is weaker as the northeasterly trade winds are shifted south, and oppose the current. When the northeasterly trades are shifted north and weaker in the later summer and fall, the NECC is stronger. These seasonal fluctuations are in phase with that of the NEC, but opposite in phase to the SEC.