What is the Equatorial countercurrent?

The North and South Equatorial currents move westward. The Equatorial countercurrent moves eastward, driven by wind (inspite of the mean westward wind stresses in the tropics.  It is also called the North Equatorial countercurrent.

The change in direction of flow is explained by the Sverdrup theory which shows that the east-west transport is governed by the north-south change in the curl of the wind stress.

This flows at a depth of 10-15m. There is also an Equatorial undercurrent that flows at a greater depth and it is not to be confused with the Equatorial countercurrent.

The South Equatorial Countercurrent is geostrophic in nature. A geostrophic current is an oceanic flow in which the pressure gradient force is balanced by the Coriolis effect.

The Equatorial current also flows due to the low lying nature of the Pacific as compared to the Atlantic.