Williams, G. P., 1971: Baroclinic annulus waves. Journal of Fluid Mechanics, 49 (3), 417-449.
Abstract: The thermally driven motion of water contained in a rotating annulus of
square cross-section and having a free surface is investigated by numerical
integration of the three-dimensional non-linear Navier-Stokes equations.
The nature of steady wave flow is examined in detail and a comparison made
with the corresponding axisymmetric solution in parameter space. # The steady
wave solution proves to be consistent kinematically, dynamically and energetically
with Lorenz's hypothesis that the wave can be attributed to the baroclinic
instability mechanism. The deviatoric* wave possesses some of the characteristics
of the theoretical Eady wave and it is possible to define the complete deviatoric
wave structure by means of two-dimensional quasi-phase, amplitude diagrams.
These diagrams may also typify the nature of certain solutions to the non-separable
baroclinic instability problem.
The wave motion is almost completely independent of the side boundary layers
which make little contribution to the characteristics and energetics of
the deviatoric flow. These side layers are approximately axisymmetric and
appear qualitatively indistinguishable from their counterparts in the axisymmetric
solution. However, significant Ekman layer features appear in the deviatoric
wave structure. # Away from the boundaries the dynamical balance of terms
is hydrostatic and quasi-geostrophic with changes of vertical vorticity
influenced by stretching and viscous diffusion. Heat conduction is completely
unimportant except in the side boundary layers.
The angular momentum transport by the deviatoric motion is largest at the
free surface and is mainly against the angular momentum gradient. A strong
outward deviatoric flux of momentum is found in the Ekman layer.
The dissipation of deviatoric kinetic energy occurs in the Ekman layer
and jet whilst most of the dissipation of the mean kinetic energy occurs
in the boundary layer of the inner wall.
The large differences between the axisymmetric and zonal mean states is
not strictly relevant to an understanding of the wave formation. The character
of the wave suggests that the mean environment with which the deviatoric
wave interacts is the wave-present zonal mean state. Only a non-linear finite
amplitude baroclinic instability analysis (as yet undeveloped) could possibly
explain the wave formation.
*The deviation from the zonal mean.