INTERACTIONS BETWEEN INTERNAL WAVES AND BOUNDARY-LAYER VORTICES

Authors
Citation
Sa. Thorpe, INTERACTIONS BETWEEN INTERNAL WAVES AND BOUNDARY-LAYER VORTICES, Journal of physical oceanography, 27(1), 1997, pp. 62-71
Citations number
27
Categorie Soggetti
Oceanografhy
ISSN journal
00223670
Volume
27
Issue
1
Year of publication
1997
Pages
62 - 71
Database
ISI
SICI code
0022-3670(1997)27:1<62:IBIWAB>2.0.ZU;2-N
Abstract
The effect of internal waveson linear vortices in a homogeneous bounda ry 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 r igid plane and below by a density interface on which interfacial waves are free to propagate. The interfacial waves stretch, compress, and d isplace the vortices, so changing their vorticity, orientation, and se paration by amounts that are estimated. As a consequence, the instabil ity of an array oi vortices of alternating signs is enhanced in region s that depend on the local phase of the interfacial waves. The vortice s force secondary disturbances on the wave-perturbed density interface . For parameter values typical of the ocean, the potential energy asso ciated with these disturbances may be comparable with the kinetic ener gy in the vortices. The energy required to drive the vortices is there fore greater than that in the absence oi internal waves, and this may affect the growth and development of the vortices. The presence of a d ensity interface at the loot of the mixed layer however, increases the primary rate of growth of Langmuir circulation in comparison with tha t found when the lower boundary is rigid. The subsequent instability i s also enhanced. In consequence Langmuir cells in mixed layers overlyi ng stratified water are expected to grow more rapidly and to be more u nstable than those developing in a homogeneous layer of the same depth overlying a rigid bottom. The effect of codirectional shear and Stoke s drift included in the Craik-Leibovich equations is to reduce the pha se speed of internal waves that propagate normal to the mean flow.