BUOYANCY-DRIVEN PLUMES IN ROTATING, STRATIFIED CROSS-FLOWS - PLUME DEPENDENCE ON ROTATION, TURBULENT MIXING, AND CROSS-FLOW STRENGTH

A three-dimensional time-dependent convection model is used to describ e circulation and property fields in rotating, stratified, and moving fluids near a point source of heat. The study context and, consequentl y, model scales are those of chronically discharging hydrothermal vent fields found at submarine ridge crests. Hydrothermal plumes having di stinctive thermal and chemical anomalies have been observed to rise se veral hundreds of meters above the deep-sea floor before being advecte d away by background cross flows typically of magnitude 1-4 cm s(-1). The model is used to study effects of rotation and indicate difference s in plumes with respect to variation of subgrid-scale turbulence inte nsity and cross-flow strength. Counterrotating vorticity (zeta) couple ts in all three coordinate directions develop in the lower plume stem at startup and follow the plume to the level of neutral buoyancy; for a nonrotational case (Omega = 0), zeta patterns resemble those previou sly found for jets injected into homogenous cross flow. Ambient fluid entrainment into the convecting column is primarily from the upstream side, but deflection of background flow around both sides of the risin g column is the root of the relative vorticity (zeta(z)) couplet in th e lower plume. Turbulence intensity within the buoyant region of the p lume and/or globally controls smoothness and temporal variability of d istal nonbuoyant plume distributions, allowing or preventing oscillati ons of potential temperature, theta, for example, at background buoyan cy frequency, N. Over the range of turbulent mixing studied, rise heig ht of plumes did not change appreciably, but breadth of plumes, counte rintuitively, increased for decreasing turbulent mixing strength. Incr easing cross-flow strength, U-0, bends model plumes such that rise hei ght proportional to U-0(-0.4). For the two largest values of cross flo w, for which R, the ratio of maximum vertical velocity to U-0, took va lues of 2.8 and 1.0, plumes showed evidence of bifurcation.