Low Froude number flow past three-dimensional obstacles. Part I: baroclinically generated lee vortices

The lee vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle; however, this boundary layer is absent (by design) in the present experiments and lee vortices still occur. We argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in response to the flow over the obstacle. This deformation is adequately predicted by linear gravity-wave theory, which allows one to deduce, using the next-order correction to linear theory, the existence of a vortex pair of the proper sense in the lee of the obstacle. Thus, the lee vortices are closely associated with the dynamics of gravity waves. -from Authors