EQUILIBRIUM SALT-FINGERING CONVECTION

The possible existence of equilibrium salt fingering in a deep fingering domain, equivalent to large Rayleigh number fingering convection, is investigated with a numerical model of a continuously heat and salt stratified fluid system. The growth of fingering heat and salt fluxes in this system is shown to be limited by the instability of fingering cells, and an equilibrium state is achieved when the instability has increased the energy dissipation sufficiently to balance the buoyancy forcing generated by double diffusion. The equilibrium fluxes are shown to vary proportional to the mean vertical T and 5 gradients, in contrast to the inverse relationship that holds for convection across a finite height, or low Rayleigh number, fingering zone. The structure of equilibrium convection is shown to be disorganized and turbulent-like, characterized by incoherently rising and sinking blobs of anomalous density fluid. A model of equilibrium fingering based on the blob structure is presented to interpret the convective processes. Estimates of the finger blob scale and the heat-to-salt flux ratio are also made from the model and are shown to be consistent with those determined from direct numerical simulations. Finally, a critical Rayleigh number is suggested and estimated to delineate the equilibrium fingering regime from the low Rayleigh number fingering regime. © 1995 American Institute of Physics.