Why does equatorial divergent upwelling work only for ocean surface currents traveling from east to west and not west to east?

Clarification might be found at :

http://courses.washington.edu/ocn101/Currents1.pdf

Most land massses are in the N.Hemisphere and here the major surface currents flow in a clockwise direction.

This means that the currents flow down the west coasts of the land masses and are known as Eastern Boundary currents.

The NE trade winds push the currents south and away from shore East to West. Combine this with something known as Ekman transport and this further pushed the waters East to West away from the shore.

The upwelling occurs here because waters being pushed away from shore causes a gradient (sea slope) and water from below is pulled up to replace the surface waters pushed out to sea, so here you have your upwelling.

 

Very briefly put, I know. Further reading can be had from the Open University book entitled Ocean Circulation (Its a banquet, if you are hungry for this type of info)

 

Stephen