Stratification and convection produced by multiple turbulent plumes

A study of convection in a finite box is presented, in which two or more bu oyancy sources produce well-separated, turbulent plumes. In the "filling-bo x" problem, where turbulent plumes "fill'' a finite box, the source with th e largest buoyancy flux produces the plume that descends to the bottom to g ive rise to the "bottom waters". Each of the sources having smaller buoyanc y fluxes produces water that spreads at an intermediate depth. We study the "filling-box" convection from two or more well-separated turbulent plumes and present numerical solutions and for large times, analytical approximati ons. These show that the spreading depth of a weaker plume is dependent on the 2/3 power of the ratio of its buoyancy flux to the flux of the stronges t plume, a result which is verified by experiments. The experiments also sh ow that the circulation pattern formed consists of a number of counterflowi ng shear layers. This pattern is primarily forced by the bottom outflow fro m the source with the largest buoyancy flux, but is modified by the volume flux injected at shallower depths by the weaker plume. The pattern is suppo rted by the stable density stratification produced collectively by all the sources. Because the horizontal velocities in the shear layers dominate ove r all other horizontal motions, they influence the spreading of each interm ediate-depth outflow. The results may be of significance to the thermohalin e circulation of the oceans, where there are a number of intermediate and d eep water sources. (C) 1999 Elsevier Science B.V. All rights reserved.