On a generation of bottom currents by a fluid pulse distortion on the surface of the ocean

A model of propagation of a pulse of a surface horizontal water distortion (caused by a non-stationary wind field) from the surface to the bottom in a stratified medium is considered in the frameworks of linear theory of internal waves in a long-wave approximation; In the model, a there-layer fluid is presented as two-step structure of the density profile with alteration of density discontinuities and homogeneous fluid layers. Rather simple equations for velocities for the first three modes (the barotropic and two baroclinic modes) are derived. The results of calculation show that the presence of sharp discontinuities in density leads to interrelation between the surface and bottom current fields. In this care transfer of the surface pulse into deep water is performed by internal wave. The model of the propagation was tested using experimental moored & cast data and time distribution of the surface wind stresses during storms in winter of 1992 at the shelf and slope off the Sakhara coast. Well developed surface and bottom boundary layers were approximately of the same thickness. High frequency maxima were revealed in energy spectra of the near bottom velocities. Whereas the peak at a period of about 24 min corresponded to the typical buoyancy frequency at the site, the model of the pulse propagation from the surface to the bottom allowed us to explain the peaks at periods 60-70 min. It shows that the model discussed describes one of mechanisms of the increase of current velocities in near-bottom layers.