Mathematical study of degenerate boundary layers

This paper is concerned with a complete asymptotic analysis as E \to 0 of the Munk equation \partial _x\psi -E \Delta ^2 \psi = \tau in a domain \Omega \subset \mathbf R^2, supplemented with boundary conditions for \psi and \partial _n \psi . This equation is a simple model for the circulation of currents in closed basins, the variables x and y being respectively the longitude and the latitude. A crude analysis shows that as E \to 0, the weak limit of \psi satisfies the so-called Sverdrup transport equation inside the domain, namely \partial _x \psi ^0=\tau , while boundary layers appear in the vicinity of the boundary.