The effects of double diffusion and background turbulence on the persistence of submarine wakes

Abstract

A numerical study has been performed to investigate the feasibility of hydro-dynamically based detection of propagating submersibles. Of particular concern is the possibility of utilizing microstructure measurements as a means of wake identification. The simulations are based on the Massachusetts Institute of Technology General Circulation Model (MITgcm), which has been modified for wake analysis. The dissipation of a turbulent wake produced by a sphere uniformly propagating in a doubly stratified environment is examined for three scenarios: (i) quiescent regime, (ii) double-diffusive regime, and (iii) a flow with pre-existing turbulence. The analysis of the numerical models was based on two quantities, the dissipation of turbulent kinetic energy (ε), and the dissipation of thermal variance (χ). This analysis indicates that wake signatures generated by a 1-meter wide object are detectable for 0.4 and 1.2 hours, depending on regime, and the detection interval is not strongly sensitive to the density ratio. Double-diffusive convection plays a significant role in the duration of submarine wakes. The extrapolation of the simulations to objects of ~10m propagating with speeds ~10m/s suggests that microstructure-based detection is feasible for at least two hours after the passage of a submersible and significantly longer outside the double-diffusive regime. These results indicate that microstructure-based observations of stratified wakes offer a viable method for the non-acoustic detection of submerged objects.