The Age of a Wake

This study attempts to quantify decay rates of stratified wakes in active oceanic environments, characterized by the presence of intermittent turbulence and double-diffusive convection. The investigation is based on a series of direct numerical simulations of wakes produced by a sphere uniformly propagating in stratified two-component fluids. We examine and compare the evolution of wakes in fluid systems that are initially quiescent, double-diffusively unstable, or contain preexisting turbulence. Model diagnostics are focused primarily on dissipation of turbulent kinetic energy ($\varepsilon )$ and thermal variance ($\chi )$. Analysis of decay patterns of $\varepsilon $ and $\chi $ indicates that microstructure generated by an object of D $=$ 0.6 m in diameter moving at the speed of U $=$ 0.02 m/s could be detected, using modern high resolution profiling instruments, for 0.5--0.7 h. Convective overturns are shown to be particularly effective in terms of dispersion of microscale wake signatures. Extrapolation of model results to objects of $\sim $10 m in diameter propagating with speeds of $\sim $10 m/s suggests that this form of detection is feasible for at least 4 h after the object's passage through the monitored areas.