Abstract:
The response on the continental shelf of a baroclinic ocean to
driving by an alongshore coastal wind stress and by barotropic and
baroclinic wind forced interior motions is studied as a function of
latitude. The relative excitation of continental shelf waves and
internal Kelvin waves is studied.
The response of a rotating stratified ocean with a vertical
boundary, forced at the surface by an alongshore coastal wind stress,
shows vertically propagating subinertial motions. Several examples
which illustrate the basic properties of the response are presented.
Changes in amplitude and frequency with depth are predicted.
Components that decay with depth from the surface and components
that represent coastal internal Kelvin waves with negative vertical
group velocity and upward phase propagation are forced.
The effect of bottom Ekman layer friction and slope topography
on free internal Kelvin waves is examined, using both a steep and
weak slope model. The steep slope represents the low latitude case
while the weak slope represents the mid-latitude case. There are
substantial differences between the results from the two models.
Free waves are frictionally damped and offshore and vertical phase
shifts are induced by friction, as well as an onshore flow. Topography
induces changes to the wave frequency and alongshore phase speed. The
modal amplitude is altered and an onshore flow is induced.
Sea level and current velocity data from the equator to 17°S on
the west coast of South America show that low frequency (0.1-0.2 cpd)
fluctuations propagate poleward with phase speeds similar to those
predicted for first mode baroclinic Kelvin waves. The sea level
and currents are coherent and approximately 1800 out of phase. The
waves do not appear to be the result of local atmospheric forcing.
Empirical orthogonal functions show that the alongshore and vertical
structure of alongshore velocity is consistent with first mode
internal Kelvin waves.
