3-LAYERED CIRCULATION IN REVERSE ESTUARIES

Driven by an upper-layer density deficit and lower-layer density surpl us from an adjacent sea, circulation in an estuarine embayment may be three-layered, with top and bottom inflows separated by a mid-layer ou tflow. The characteristics of this type of circulation as functions of density forcing, background stratification and lateral depth variatio n in an embayment are examined using a three-dimensional primitive-equ ation model with a free surface. Among all the details, the dominance of bottom intrusion over the surface one stands out and presents a dep arture from early models that have missed the importance of bottom int rusion in regulating the three-layered circulation. A strong or deeper upper density deficit from the adjacent sea, bottom stress and narrow ing estuary width at depths all produce transients discouraging the de velopment of the bottom intrusion. In time, the bottom inflow invariab ly gains strength and thickness and squeezes up the core of the mid-la yer outflow to above the mid-depth. A heuristic argument follows to ex plain this counter-intuitive result. (C) 1996 Elsevier Science Ltd