Elastic Interaction Between a Mesoscale Eddy-Pair and an Axisymmetrical Eddy

We investigate numerically the elastic interaction between an eddy-pair and an axisymmetrical eddy in inviscid isochoric two-dimensional (2D) flows, as well as in three-dimensional (3D) flows under the quasi-geostrophic (QG) approximation. The eddy-pair is a straight moving Lamb-Chaplygin dipole where the absolute value of either its positive or negative amount of vorticity equals the vorticity of the axisymmetrical eddy. The results for the 2D and 3D cases show that interactions with almost no vorticity exchange, or vorticity loss to the background field between ocean eddies, but causing changes in their displacement velocity, are possible. When the eddy-pair approaches the axisymmetrical eddy, their respective potential flows interact, the eddy-pair's trajectory acquires curvature and their vorticity poles separate. In the QG dynamics, the eddies suffer little vertical deformation, being the barotropic effects dominant. At the moment of highest interaction, the anticyclonic eddy of the pair elongates, simultaneously the cyclonic eddy of the pair evolves toward spherical geometry, and the axisymmetrical eddy acquires prolate ellipsoidal geometry in the vertically stretched QG space. Once the eddy-pair moves away from the axisymmetrical eddy, its poles close, returning to their original geometry, and the anticyclonic and cyclonic eddies continue as an eddy-pair with a straight trajectory but along a new direction. The interaction is sensitive to the initial conditions and, depending on the initial position of the eddy-pair, as well as on small changes in the vorticity distribution of the axisymmetrical eddy, inelastic interactions may instead occur.

Automated summary

This study numerically investigates the elastic interaction between an eddy-pair and an axisymmetrical eddy in inviscid isochoric 2D flows and quasi-geostrophic 3D flows. The results show that interactions with almost no vorticity exchange or vorticity loss to the background field are possible, but changes in displacement velocity occur. The interaction is sensitive to initial conditions, and inelastic interactions may occur depending on the initial position of the eddy-pair and small changes in the vorticity distribution of the axisymmetrical eddy.