Munk Boundary Layer

The Munk boundary layer is the western boundary current produced when lateral (horizontal eddy) friction, rather than bottom friction, balances the planetary vorticity advection in Munk’s 1950 model of the wind-driven gyre. Its width scales as (A_h / beta)^(1/3), where A_h is the lateral eddy viscosity and beta the meridional gradient of the Coriolis parameter, giving order 50 to 100 kilometers. Like Stommel’s earlier bottom-friction model it explains westward intensification: the return flow that balances the Sverdrup interior can close only on the western boundary, forming currents like the Gulf Stream and Kuroshio.