11:15 AM - 11:30 AM
[ACG36-09] Breaking of internal waves parametrically excited by ageostrophic anticyclonic instability
Keywords:rotating stratified fluid, internal gravity waves, elliptic instability, Numerical simulation
A gradient-wind balanced flow with an elliptic streamline parametrically excites internal inertia-gravity waves through ageostrophic anticyclonic instability (AAI). This study numerically investigates the breaking of internal waves and the following turbulence generation resulting from the AAI. In our simulation, we periodically distort the calculation domain following the streamlines of an elliptic vortex and integrate the equations of motion using a Fourier spectral method. This technique enables us to exclude the overall structure of the large-scale vortex from the computation and concentrate on resolving the small-scale waves and turbulence.
From a series of experiments, we identify two different scenarios of wave breaking. First, when the instability growth rate is high, the primary wave amplitude excited by AAI quickly goes far beyond the overturning threshold and directly breaks. The final state is thus strongly nonlinear quasi-isotropic turbulence. Second, if the instability growth rate is relatively low, weak wave-wave interactions begin to redistribute energy across frequency space before the primary wave reaches a breaking limit. Then, after a sufficiently long time, the system approaches a Garrett-Munk-like stationary internal wave spectrum, in which wave breaking occurs at finer vertical scales. In both the experimental conditions, we confirm an evident coincidence of the time scales of linear growth and nonlinear decay in the primary wave energy. This finding facilitates quantification of the energetic linkage between a submesoscale eddy field and much smaller-scale turbulence.
From a series of experiments, we identify two different scenarios of wave breaking. First, when the instability growth rate is high, the primary wave amplitude excited by AAI quickly goes far beyond the overturning threshold and directly breaks. The final state is thus strongly nonlinear quasi-isotropic turbulence. Second, if the instability growth rate is relatively low, weak wave-wave interactions begin to redistribute energy across frequency space before the primary wave reaches a breaking limit. Then, after a sufficiently long time, the system approaches a Garrett-Munk-like stationary internal wave spectrum, in which wave breaking occurs at finer vertical scales. In both the experimental conditions, we confirm an evident coincidence of the time scales of linear growth and nonlinear decay in the primary wave energy. This finding facilitates quantification of the energetic linkage between a submesoscale eddy field and much smaller-scale turbulence.