Abstract

A theory of fronts within the general circulation is discussed. These fronts and their associated jets differ from the more classical picture of boundary jets and their extensions (an example being the Gulf Stream system) in that they occur in the interior of the general circulation. The mechanism at the heart of the frontogenesis is nonlinear beta steepening, which arises from geostrophy in the presence of continuity. Such dynamics have been used in the past in a study of planetary shock waves. It is here argued that these dynamics result in stationary shock fronts in the general circulation. An equation governing the trajectory of the shock front is found. This equation represents a balance between the westward beta-driving of the shock front and the retarding influence of the Sverdrup flow. The fronts are shown to play a number of potentialIy important roles in the circulation. For example, they are capable of resolving conflicting information emanating from the boundaries, can determine subsurface potential vorticity in certain regions and can influence the positioning of outcrop trajectories. An examination of the thermocline structure at the latitude separating the subpolar and subtropical gyres, as a function of the complete range of possible boundary conditions, reveals that arrested front solutions dominate the possible solution types for the general circulation and the complete suite of such solutions is described. Lastly, an attempt to reproduce the thermocline parameters of the mid-ocean jet observed during the Local Dynamics Experiment is discussed.

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