Wolfgang Krauss

Wind-generated internal waves and intertial-period motions

The ocean is subdivided into a homogeneous upper layer (Ekman layer) and a continuously stratified lower layer. Horizontal velocities which in analogy to Fredholms solution contain inertial oscillations, are generated in the upper layer by the tangential stress of the wind field varying both in space and time. The spatial structure of the wave field corresponds to that o the stress field. If the surface remains at rest (ζ=0), vertical motions result from the horizontal oscillations. At the bottom of the Ekman layer the spatial structure of these vertical motions is proportional to divergence and rotation of the wind stress. Internal waves of the lower layer which primarily have periods approaching the inertial-period are generated by the vertical velocity field at the bottom of the Ekman layer (Ekman suction). Their structure is essentially more complicated than near the surface. Beats are a common phenomenon due to the superposition of internal modes.

Intertial waves in an infinite channel of rectangular cross section

Inertial waves in a channel of finite width consist of two different systems. In the surface layer a suddenly imposed wind produces the same system of Ekman currents and inertial waves as in the open ocean. Besides that the wind produces cross oscillations and a permanent deflection of the sea surface and due to this a geostrophic current. The onset of this geostrophic current is accompanied by a second system of inertial waves which is out of phase by 1800. In the vertically integrated equations the two systems cancel each other.

A semi-spectral model for the computation of mesoscale processes in a stratified channel of variable depth

A method is presented which allows to include bottom topography into spectral models, by adding a sum of free waves to the forced solutions in such a way that the sum of all Fourier components fulfills the boundary condition at the bottom. Examplese are given which show the mean currents and the spectra in the frequency range The model allows to resolve inertial, internal and bottom trapped waves.

A semispectral model on the β-plane

The numerical procedures used in solving the linear hydrodynamic equations on the β-plane are being described. The response characteristics of a rectangular ocean basin are discussed and examples of the solution given.