Abstract
We investigate numerically the elastic interaction between an eddy-pair
and an axisymmetrical cyclonic eddy in inviscid isochoric
two-dimensional (2D), 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 changing 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 towards 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 eddy 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.