The growth of convective plumes at seafloor hot springs

The growth of buoyant plumes in the presence of stratification (N) and rotation (f) is studied and illustrated with a number of numerical experiments of convection induced by a localized source of buoyancy at the lower boundary of a linearly stratified fluid. The presence of stratification constrains the convection in the vertical giving rise to an equilibrium-spreading layer which receives the rising mass of plume fluid ; the plume can be divided into an upper, mass-source driven anticyclone and a lower, buoyancy-source (F) driven cyclone. With N/f large, the plume's rise-height is set by the classical non-rotating scaling l N = (F/N 3 ) 1/4 . Physically motivated scaling laws invoke angular momentum constraints and indicate the fundamental role played by rotation, which sets the scale l f = (F/f 3 ) 1/4 . The lateral spread of the upper-level anticyclone is constrained by rotation : for times greater than f -1 the anticyclone grows laterally at a rate which is essentially independent ofN, and given by l f (ft) 1/3 ; the ratio of the lateral scale of the anticyclone to its vertical scale (aspect ratio) is proportional to N/f. The cyclone's lateral scale is l f , and the strong cyclonic flow scales like fl f . An enhanced lateral mixing is suggested to occur in the cyclone along slanted angular momentum and isopycnal surfaces, which become closely aligned. On a much longer time scale, the scaling suggests that the lateral growth of the upper level anticyclone is arrested by its interaction with the lower level cyclone ; a baroclinic instability is expected to detach the anticyclone from the source after a time of order ft ∼100N/f.