Steady waves and wake dynamics in pycnoclines*

Pycnoclines with nonlinear stratification occur commonly in the oceanic environment. In this study, we present the results of one of the first body-inclusive LES simulations of wakes in a pycnocline. A circular disk at diameter-based Reynolds number of 5000 is considered with three types of stratification profiles, two of which are pycnoclines and one has linear stratification. The minimum background Froude number is 1 for all the cases. The characteristics of steady lee waves are compared with the analytical results obtained from linear theory. A Kelvin ship wave pattern (absent for the linear case) is observed and is analysed by solving the Taylor-Goldstein Equation. The wakes in nonlinear stratification show an increase in fluctuation levels during the non-equilibrium regime. Simulation based diagnostics attribute the increased turbulence to enhanced lateral production and internal wave flux. Wakes evolving in pycnoclines also show diferent decay characteristics of mean defect velocity and turbulent kinetic energy compared to the linear stratification case.