Ekman-type solutions for shallow-water flows on a rotating sphere: A new perspective on a classical problem

An asymptotic analysis, based solely on a small shallow-water parameter, produces a generalisation of the classical Ekman spiral which combines all the relevant physical processes, including nonlinearity, in a balance of terms at leading order. This new approach is applicable both at mid-latitudes (where linearity prevails) and near the Equator (where classical Ekman fails so that nonlinear effects have to be included).