Published online by Cambridge University Press: 20 April 2006
Grimshaw (1979) discussed the mean flow induced by an internal gravity-wave packet propagating in a shear flow. The present paper analyses the effect of dissipative processes on this problem. In a manner similar to that described by Longuet-Higgins (1953) for water waves, frictional effects in the Stokes boundary layers modify the mean-flow field just outside the boundary layers. Just outside the bottom boundary layer there is a wave-induced mean Lagrangian velocity, whose magnitude is proportional to the square of the wave amplitude, while just below the free-surface boundary layer there is a wave-induced mean-velocity gradient. In the interior of the fluid the presence of dissipation in the wave field will induce a significant mean-flow field whenever the group velocity of the wave packet exceeds the phase speed of a longwave mode. Ultimately, this interior mean flow will be modified by diffusion from the boundaries of effects induced in the aforementioned Stokes layers.