Triangular-prism framework for the study of hydrodynamics in semienclosed basins

A framework is presented for the study of hydrodynamics in semienclosed basins. The framework is anchored on a generalized momentum balance in which the drivers of momentum are tides, density gradients and winds. The drivers are balanced by friction and Earth’s rotation. The relative influence of either drivers or balancing agents may be cast in terms of their ratio, represented by nondimensional numbers. Thus, the relative influence between three different pairs of forcings is expressed as follows. Comparisons between tidal forcing and density gradients are cast in terms of a densimetric tidal Froude number. Similarly, the effect of wind forcing versus density gradients is contained in a Wedderburn number, and the impact of wind forcing compared to tidal forcing is described by a ‘Stress number’. Comparisons of balancing agents are contained in the Ekman number, representing the dynamic depth of a semienclosed basin – high Ekman numbers indicate dynamically shallow basins. The hydrodynamic interplay among drivers and balancing agents can thus be drawn on a triangular prism. Each face of the prism represents a parametric space that characterizes the relative dominance of any pair of forcing agents. The height of the prism denotes the dynamic depth. Every semienclosed basin, except any dominated by wind-wave forcing, can be represented on a face of this triangular prism or inside the prism, depending on the dominant hydrodynamics. Thus, any semienclosed basin can be described by a cloud of points inside and on the prism faces, representing the basin’s temporal and spatial variability in its hydrodynamics.