Evolution of Internal Gravity Waves in a Mesoscale Eddy Simulated Using a Novel Model.

We investigate the effect of wave–eddy interaction and dissipation of internal gravity waves propagating in a coherent mesoscale eddy simulated using a novel numerical model called the Internal Wave Energy Model based on the six-dimensional radiative transfer equation. We use an idealized mean flow structure and stratification, motivated by observations of a coherent eddy in the Canary Current System. In a spindown simulation using the Garret–Munk model spectrum as initial conditions, we find that wave energy decreases at the eddy rim. Lateral shear leads to wave energy gain due to a developing horizontal anisotropy outside the eddy and at the rim, while vertical shear leads to wave energy loss which is enhanced at the eddy rim. Wave energy loss by wave dissipation due to vertical shear dominates over horizontal shear. Our results show similar behavior of the internal gravity wave in a cyclonic as well as an anticyclonic eddy. Wave dissipation by vertical wave refraction occurs predominantly at the eddy rim near the surface, where related vertical diffusivities range from O ( 10 − 7 ) to O ( 10 − 5 )   m 2   s − 1 . Significance Statement: Using a novel model and observations from the Canary Current System of a coherent eddy of 100-km diameter, we explore the interaction between a realistic internal gravity wave field and this eddy. We study wave refraction and energy transfers between the waves and the eddy induced by the eddy's lateral and vertical shear. Waves lose energy at the eddy rim by vertical shear and gain outside of the eddy rim by horizontal shear. We find large vertical wave refraction by vertical shear at the eddy rim, where waves break and mix density, which can have wide ranging effects on the ocean's circulation. These results are important for understanding the ocean's mixing and energy cycle and to develop eddy and wave parameterizations. [ABSTRACT FROM AUTHOR]