Abstract
An explicit expression is derived for the speed of equatorial upwelling by filtering out the inertial oscillations from the wind-forced, Lagrangian, dynamics north and south of the equator. The derivation focuses on the poleward motion of the steady states of the meridional dynamics of water columns of unit zonal length forced by a uniform, westward directed, wind stress. A significant advance is achieved by substituting the pseudo angular momentum for the zonal velocity in all equations. The derived expression for the speed is independent of the Ekman layer's depth and varies linearly with the wind stress. Its only free parameter is the initial meridional extent of the water column that straddles the equator. The theoretical speed matches available observations of the upwelling speed when the column's meridional extent is 350–400 km on each side of the equator.