Evolution of internal tide scattering hidden below mesoscale eddies

Abstract

The internal tide (IT) is the internal wave with tidal frequency. During propagation, ITs are scattered by topographies such as seamounts and slopes. Mesoscale eddies, which generally consist of anticyclonic eddies (AEs) and cyclonic eddies (CEs), are widely observed in the ocean and can modulate scattering processes. However, whether AEs and CEs affect topographic scattering of IT differently is unknown. In this study, the responses of semidiurnal IT scattering to mesoscale eddies are explored based on LLC4320 data and idealized numerical simulations. The results suggest that mesoscale eddies can both enhance and weaken scattering in topographic regions, causing spatial divergence in the scattering in response to eddies. This modulation can be attributed to the refraction of mode one IT by mesoscale eddies. AEs and CEs refract IT to opposite directions; therefore, they have opposite effects on modulating topographic scattering. Regions that undergo amplification of scattering by an AE would probably experience the weakening of scattering caused by a CE. These findings imply that eddies can actively participate in modulating IT scattering, which contributes to a better understanding of the interaction between internal waves and mesoscale eddies.