Lens eddies in rotating two-fluid systems

Abstract

Laboratory experiments are conducted on the instantaneous release of a constant volume of intermediate density fluid along the interface of a two-layer fluid system in rigid body rotation about a vertical axis. Such a system leads to the development of a thin lens of fluid with anticyclonic motion which grows in radial extent to reach an equilibrium radius as the radial motion is captured by Coriolis effects, becomes unstable to non-symmetric dusturbances, and finally decays due to the action of fluid viscosity. Scaling and dimensional analysis arguments are advanced for the growth, equilibrium and decay phases of the motion. The scaling analysis for the initial growth and equilibrium phases are shown to be in good agreement with the experimental observations. The lens decay data do not collapse under the assumption of a simple Ekman spindown model assuming immiscible fluids. An empirical fit of the data for the decay phase is presented.