title: Enhanced acoustic mode coupling resulting from an internal solitary wave approaching the shelfbreak in the South China Sea.
abstract: Internal waves and bathymetric variation create time- and space-dependent alterations in the ocean acoustic waveguide, and cause subsequent coupling of acoustic energy between propagating normal modes. In this paper, the criterion for adiabatic invariance is extended to the case of an internal solitary wave (ISW) encountering a sloping bathymetry (i.e., continental shelfbreak). Predictions based on the extended criterion for adiabatic invariance are compared to experimental observations from the Asian Seas International Acoustics Experiment. Using a mode 1 starter field, results demonstrate time-dependent coupling of mode 1 energy to higher adjacent modes, followed by abrupt coupling of mode 5-7 energy to nonadjacent modes 8-20, produces enhanced mode coupling and higher received levels downrange of the oceanographic and bathymetric features. Numerical simulations demonstrate that increasing ISW amplitude and seafloor slope enhance the coupling of energy to adjacent and nonadjacent modes. This enhanced coupling is the direct result of the simultaneous influence of the ISW and its proximity to the shelfbreak, and, compared to the individual effect of the ISW or shelfbreak, has the capacity to scatter 2-4 times the amount of acoustic energy from below the thermocline into the upper water column beyond the shelfbreak in realistic environments.
authors: Institution of Applied Marine Physics and Undersea Technology, National Sun Yat-sen University, No. 70, Lienhai Road, Kaohsiung 80424, Taiwan. linus@mail.nsysu.edu.tw
authors: Linus Y S
authors: LY
authors: Chiu
authors: D Benjamin
authors: DB
authors: Reeder
authors: Yuan-Ying
authors: YY
authors: Chang
authors: Chi-Fang
authors: CF
authors: Chen
authors: Ching-Sang
authors: CS
authors: Chiu
authors: James F
authors: JF
authors: Lynch
mesh_terms: D000162:Acoustics; D003198:Computer Simulation; D008962:Models, Theoretical; D009038:Motion; D009716:Numerical Analysis, Computer-Assisted; D009792:Oceans and Seas; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D013018:Sound Spectrography; D013997:Time Factors; D014867:Water; D014872:Water Movements
chemical_list: D014867:Water