| description abstract | The effect of internal waves on linear vortices in a homogeneous boundary layer is examined by taking a simple model with a horizontal array of line vortices or vortex cells lying in a layer bounded above by a rigid plane and below by a density interface on which interfacial waves are free to propagate. The interfacial waves stretch, compress, and displace the vortices, so changing their vorticity, orientation, and separation by amounts that are estimated. As a consequence, the instability of an array of vortices of alternating signs is enhanced in regions that depend on the local phase of the interfacial waves. The vortices force secondary disturbances on the wave-perturbed density interface. For parameter values typical of the ocean, the potential energy associated with these disturbances may be comparable with the kinetic energy in the vortices. The energy required to drive the vortices is therefore greater than that in the absence of internal waves, and this may affect the growth and development of the vortices. The presence of a density interface at the foot of the mixed layer, however, increases the primary rate of growth of Langmuir circulation in comparison with that found when the lower boundary is rigid. The subsequent instability is also enhanced. In consequence Langmuir cells in mixed layers overlying stratified water are expected to grow more rapidly and to be more unstable than those developing in a homogeneous layer of the same depth overlying a rigid bottom. The effect of codirectional shear and Stokes drift included in the Craik?Leibovich equations is to reduce the phase speed of internal waves that propagate normal to the mean flow. | |
