Observations of ocean spice and isopycnal tilt sound-speed structures in the mixed layer and upper ocean and their impacts on acoustic propagation

Edward L Richards; John A Colosi

doi:10.1121/10.0021311

Observations of ocean spice and isopycnal tilt sound-speed structures in the mixed layer and upper ocean and their impacts on acoustic propagation

J Acoust Soc Am. 2023 Oct 1;154(4):2154-2167. doi: 10.1121/10.0021311.

Authors

Edward L Richards¹, John A Colosi²

Affiliations

¹ Ocean Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA.
² Department of Oceanography, Naval Postgraduate School, Monterey, California 93943, USA.

PMID: 37800989
DOI: 10.1121/10.0021311

Abstract

A 400-m deep and 970 km long conductivity, temperature, depth section in the Northeast Pacific Ocean is decomposed into sound-speed variations associated with tilting isopycnals and ocean spice. The vertical distribution of sound-speed variance from these two processes shows significant fluctuations in the mixed layer (ML) and transition layer (TRL) below. Acoustic simulations at 400 and 1000 Hz are conducted with the decomposed fields to quantify their relative impact on upper ocean propagation for source locations in the ML and TRL. The low frequency simulations show that localized scattering processes dominate the propagation while higher frequencies experience more diffuse scattering. For propagation in the ML, spice generates the most loss while tilt can reduce loss when combined with spice. Statistics further show that energy can couple into and out of the ML duct depending on source depth and frequency.