Why are western boundary currents stronger than eastern boundary currents?

Western boundary currents are significantly stronger than eastern boundary currents due to a phenomenon known as westward intensification.1

This process occurs because the Coriolis force increases with latitude. As explained by oceanographer Henry M. Stommel, this latitudinal variation in the Coriolis effect causes the centers of subtropical gyres to shift toward the west.1

Consequently, the poleward-flowing currents on the western side of these gyres are compressed into narrow, jetlike flows that can reach speeds of 2 to 4 meters per second. In contrast, the equatorward-flowing currents on the eastern side of the gyres are broad, slow-moving drifts that typically do not exceed 10 centimeters per second. While western boundary currents like the Gulf Stream and the Kuroshio current are characterized by high-velocity transport, eastern boundary currents are often associated with coastal upwelling, which brings cooler, nutrient-rich water to the surface.12