Observed Quasi-steady Flow Patterns in Shallow Seas

Abstract

This final chapter will attempt to connect the simple steady-state models of circulation of Chapters 6 and 7 to observational evidence. Circulation features more persistent than weather related events are sometimes brought to light by averaging fixed-point current meter data for periods of the order of a month or longer, or by Lagrangian tracer studies involving horizontal displacements of drifters or of water masses over similar periods. A mean circulation pattern determined by such methods is not necessarily relatable to simple dynamical models of the kind discussed above, because cumulative effects of transient flow events may swamp those of steady, low-level forcing. In the long-term average equations of motion, in the heat and salt transport equations, and in stress or flux boundary conditions the cumulative effects are manifested by various mean products, akin to Reynolds stresses. Where transient flow events dominate, such mean products are difficult to quantify or to relate to the mean flow. One has to allow for the possibility, therefore, that transient flow events bring about some unexpected redistribution of heat, salt or momentum. A few concrete examples of this have been discussed elsewhere (Csanady, 1975, 1976a). Generally, redistribution effects are localized and do not modify the basic pattern of mean circulation. However, in confronting the mean circulation problem in a shallow sea previously unexplored, one would do well to keep an open mind in this regard.