Three Regimes of Internal Gravity Wave-Stable Vortex Interaction Classified by a Nondimensional Parameter d: Scattering, Wheel-Trapping, and Spiral-Trapping with Vortex Deformation

The internal wave-vortex interaction was investigated for a broad parameter range except near inertial waves, by 1) scaling, 2) numerical experiments, and 3) the estimation of possible occurrences. By scaling, we identified a nondimensional parameter, a = (V/c)[1/(kR)], where V is the vortex flow speed, R is the radius, c is the incident wave phase speed, and k is the horizontal wavenumber. As a appears in all terms related to the interaction, it is important in the classification of the wave-vortex interaction. Numerical experiments were conducted on internal waves incident on a stable barotropic vortex with a parameter range of a = [0.001, 1.7], which is much broader than that used in previous studies (a << 1). We found new phenomena for a > 0.15, in addition to previously known scattering for a <= 0.15 (scattering regime). For 0.15 < a <= 0.4, part of the incident internal wave is trapped in a vortex, forming a wheel-like shape maintaining a superinertial frequency (wheel-trapping regime). When a > 0.4, incident waves are trapped, but with a spiral shape (spiral-trapping regime). Spiral-shaped trapped waves release momentum by wave breaking, which deforms the vortex into a zigzag shape in the vertical direction. Vortex deformation produces vertical shear, which rapidly increases the vertical wavenumber of the incident wave. The distribution of a in the Pacific Ocean was estimated using a high-resolution (1/308) ocean general circulation model output. We found the occurrences of all three regimes. The scattering and wheel-trapping regimes are distributed broadly and varied seasonally, thus affecting mixing variability.