The effect of salt-fingering structure on sound propagation in the Strait of Hormuz

Abstract

Structures caused by temperature and salinity gradients and their resulting mixing have a significant effect on sound propagation in shallow and deep waters. One of the vertical structures is salt-fingering (SF), which is formed by the vertical gradient of temperature and salinity, when warm and salty water is located above cold and fresh water. Quantification of double diffusion (DD) structures is done by the Turner (Tu) angle theory. Warm surface water from the Oman Sea, evaporation and salty surface water of the Persian Gulf provides the initial conditions for the formation of SF in the Strait of Hormuz. In depth less than 5 m, weak SF (45 < Tu ≤ 67.5) are formed and by dominating water buoyancy, salt fingers gradually grow and strong SF (67.5≤Tu < 90) extend from the surface to 25 m deep. This process causes mixing and changing the depth of the boundary layer. The diffusion structure in the SF plays a significant role in the deflection and energy loss of the sound signal. By passing through the SF structure on the surface, the sound signal is scattered, and its transmission is lost up to 80 dB (TLS), and the propagation of the sound along the channel is weakened. With increasing frequency and propagation angle, the deflection occurs from the location of the SF towards the cold and fresh water. But by passing through the place of the strong SF, the sound signal is propagated with a delay and 10–20 dB increase in TLS.