Sensitivity of mixed layer duct propagation to deterministic ocean features.

Here, the problem of mode coupling in a mixed layer (ML) surface duct is considered where the coupling is induced by deterministic upper ocean features such as eddies, filaments, and/or density compensated temperature and salinity anomalies (spice). The single scatter Dyson series solution for mode energy is used to define a non-dimensional mode interaction parameter Γmn that quantifies the strength of coupling between modes m and n as a function of environmental factors and frequency. Direct coupled mode simulations at 400 and 1000 Hz show weak, first order coupling and small ML transmission loss (TL) variability when Γ m n 1, there is strong, higher order coupling with large changes in ML TL. Importantly, there is a frequency dependent resonance condition associated with the range width of the perturbations, Δ, such that Γ m n → 0 as Δ → 0 and ∞.