Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution October 1987
Description:
A two-layer shallow water equation model is used to investigate the linear
stability of a coastal upwelling front. The model features a surface front near a
coastal boundary and bottom topography which is an arbitrary function of the
cross-shelf coordinate. By combining the various conservation statements for the
global properties of the system, a general stability theorem is established which
allows the a priori determination of the stability of a coastal upwelling front.
Unstable waves are found for the modelled coastal upwelling front. The unstable
wave motions are frontally-trapped and dominant in the upper layer. The wave
propagates phase in the direction of the basic state flow and the primary energy
conversion is via baroclinic instability. The effect of varying the model parameters
is presented. Moving the front closer than ~ 2 Rossby radii to the coastal boundary
results in a decrease in the growth rate of the fastest growing wave. Increasing
the overall vertical shear of the basic state flow, by either decreasing the lower
layer depth or increasing the steepness of the interface, results in an increase in
the growth of the fastest growing wave.
A bottom sloping in the same sense as the interface results in a decrease of
the growth rates and alongfront wavenumbers of the unstable waves in the system.
Linearized bottom friction is included in the stability model and results in a
decrease in the growth rates of the unstable waves by extracting energy from the
system. Since the unstable mode is strongest in the upper layer, bottom friction
will not stabilize the upwelling front.
A comparison between the predictions from the simple two-layer model and
observed alongfront variability for three areas of active upwelling is presented.
Reasonable agreement is found, suggesting that observed alongfront variability
can be interpreted in terms of the instability of a coastal upwelling front.
Description:
This study was supported by the National Science Foundation Grant
OCE 84-08563 and the Office of Naval Research Coastal Ocean Sciences
Program 10/1984.37.
Keywords:
Upwelling
;
Waves
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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