A note on a boundary-layer collision on a rotating sphere

A recent study of the unsteady boundary layer near the equator of a spinning sphere provided strong numerical evidence that the solution develops a singularity a finite time after the motion is initiated. In this paper we reformulate and complete the asymptotic structure proposed to describe this singularity. It is then self-consistent and provides convincing evidence of the accuracy of the computations and of the existence of the singularity.