| Summary: | In the ocean, the interplay between heat diffusion and salt diffusion can drive double diffusive instability and lead to the formation of spatially periodic density profiles. These periodic structures, called thermohaline staircases, can persist over large regions and have also been suggested to exist in astrophysical bodies, such as in giant planet interiors. In this talk, we show that such periodically stratified fluids can host internal gravity waves with properties reminiscent of photonic crystal and topological insulator physics. Combining experimental, numerical and analytical modeling, we show the formation of band gaps and surface states that are exponentially localized near interfaces and controlled by boundary conditions. We also find that these internal wave states are robust to perturbations and can be observed in numerical simulations performed with geophysical stratification profiles from the Arctic Region. Our results suggest that energy transport by internal waves could be profoundly altered by the presence of periodic stratifications naturally occurring in the ocean, and could therefore influence large-scale circulation patterns.
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