The intensification of the western limb of an oceanic circulation gyre. This is inevitable given a rotating earth, a meridional boundary, and a zonal wind stress pattern that reverses direction at some latitude as was shown using a simple dynamical model in the classic paper of Stommel (1948). Common features of such currents include their flowing as swift narrow streams along the western continental rise of ocean basins, their extension to great depth well below the thermocline, and their separation from the coast at some point and continuation into the open ocean as narrow jets that develop instabilities along their paths. The most well-known western boundary currents are the Gulf Stream and the Kuroshio Current.