Stability of a coastal upwelling front over topography
Barth, John A.
MetadataShow full item record
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.
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
Suggested CitationThesis: Barth, John A., "Stability of a coastal upwelling front over topography", 1987-10, DOI:10.1575/1912/4955, https://hdl.handle.net/1912/4955
Showing items related by title, author, creator and subject.
Dell, Rebecca Walsh (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2013-02)Physical oceanographers have known for several decades the total amount of abyssal mixing and upwelling required to balance the deep-water formation, but are still working to understand the mechanisms and locations—how ...
Austin, Jay A. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1998-08)Data from the Coastal Ocean Processes Inner Shelf Study are analyzed to determine atmospheric forcing characteristics and the heat balance of the inner shelf, and are used as motivation for a numerical study of inner ...
Osychny, Vladimir I. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1997-09)A series of numerical experiments is conducted in order to examine the role of topographic irregularities in generation of subinertial cross-channel barotropic currents and to obtain quantitative estimates of the offshore ...