Horizontal entrainment and detrainment in large-scale eddies.

Abstract

The evolution of disturbances are computed for a circularly symmetric eddy having uniform vorticity in a central core, in a surrounding annulus, and in the irrotational exterior water mass. This vortex is known to be (Kelvin-Helmholtz) unstable when its annular width is less than the core radius. Calculations for the nonlinear regime show that amplification of azimuthal wave number n = 2 causes the vortex to split into two dipoles, in agreement with previous numerical calculations for a smoothed version of our vorticity field. Attention is paid to the evolution of large amplitude disturbances on the outer edge of a stable and robust eddy. It is shown that lateral wave breaking of vorticity isopleths causes intrusions of the irrotational exterior water mass into the central core of the vortex.