Rossby adjustment over canyons

• Main Author: Chen, Xiaoyang
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/6289

The influence of submarine canyons on currents is studied using the Rossby adjustment method for an inviscid fluid on an /-plane. Two geometric models are used: (1) a flat bottom, uniform width, vertical edged and infinitely long canyon which cuts through a flat infinite ocean (F canyon model), and (2) a sloping bottom, uniform width, vertical edged and finite long canyon which extends from the shelf break into a semi-infinitely long strait (S canyon model). The waves which exist around an F canyon are composed of both superinertial waves (Poincare waves) and subinertial waves ("canyon waves"). The canyon waves are more important than Poincare waves in the determination of the steady state. The dispersion relation of the canyon waves is obtained. The canyon waves are dispersive and propagate in both directions along the canyon. While both the geostrophic and the transient solutions of Rossby adjustment over the F and the S canyons are studied, the emphasis of this thesis is to study the geostrophic state. For a homogeneous fluid in the northern hemisphere: (1) when a shelf flow approaches an F canyon, a net transport along the canyon is generated to the left (looking downstream) of the approaching shelf flow; (2) when a shelf flow approaches an S canyon, if the flow is left-bound (with the coast to its left looking downstream), a net in-canyon flux is generated, while if the flow is right-bound (with the coast to its right looking downstream), a net out-canyon flux is generated. For a two-layer stratified fluid (regardless of the shear) in the northern hemisphere: (3) over an F canyon in which the interface is above the shelf, the lower layer adjusts over the canyon in a similar way as in a homogeneous fluid but over the length scale of the baroclinic Rossby radius, while the upper layer adjusts in a way to accommodate the changes at the interface; (4) over an S canyon in which the interface is below the shelf, a left/right-bound shelf flow leads to an in/outcanyon flow throughout the water column. The time scale for adjustment is 1/f for both a homogeneous and a stratified fluid. A parameter, σ ε {0, 1}, which is denoted as the Canyon Number, is found to control the geostrophic state over a canyon. The Canyon Number, which is calculated from the geometric parameters of the shelf-canyon system, determines the interactive strength of one canyon edge on the circulation induced by the other edge. The parameter cr can be used to unify theories over canyons, steps, ridges and straits. The research has demonstrated that a canyon can have an important influence on cross-shelf circulation and has gone beyond earlier work in explaining the details of flow patterns around canyons.