Eddy Dynamics Near Sharp Interfaces and in Straining Flows

Summary

Idealised models of eddy motion near sharp interfaces, such as shear layers and density interface, are examined. Strong shear layers can block the vertical motion of eddies with part of their impulse permanently transferred to the shear layer. Eddies which pass through the shear layer communicate a fraction of their impulse to the shear layer. Throughout these processes, the far field dipole moment (and total impulse) is conserved. For sharp density interfaces, vertical impulse is not globally conserved and the kinetic energy of the vortex goes towards generating waves. Here, both blocking and sheltering occurs, since the eddy vertical motion is constrained and the dipole moment is reduced. In straining flows, we show that the rotation and rapid amplification/suppression of the vortex impulse leads to an upscale transport in impulse, but the energy of the vortex hardly changes. Vorticity annihilation caused by diffusion can partially or completely destroy the colliding vortex patches causing the energy to decrease. The general relevance of these results is discussed.