Michael D. Collins
K. D. Heaney
W. A. Kuperman
B. E. McDonald
Naval Res. Lab., Washington, DC 20375
Arthur B. Baggeroer
MIT, Cambridge, MA 02139
Peter N. Mikhalevsky
Sci. Applications Internatl. Corp., McLean, VA 22217
An adiabatic normal-mode model was previously applied to explain the arrival structure of signals propagating between nearly antipodal points [Heaney et al., J. Acoust. Soc. Am. 90, 2586--2594 (1991)]. To investigate the role of mode coupling, an approximate full-wave version of this solution has been implemented based on solving a two-dimensional parabolic equation (PE) along modal ray paths. For 57-Hz propagation from Heard Island to California, a finite-difference solution of the energy-conserving PE is obtained with an Iris workstation in nearly real time (i.e., the computation time is comparable to the propagation time). This solution agrees with data received on a vertical array at a site off California during the Heard Island Feasibility Test (HIFT) [Munk et al., J. Acoust. Soc. Am. 90, 2328--2331 (1991)]. In particular, the PE predicts the experimental result that the received energy is concentrated near mode five. Energy migrates in depth with the sound channel starting near the ocean surface at Heard Island, reaching a maximum depth near the equator, and moving back toward the ocean surface approaching California. Significant mode coupling occurs off the southeast coast of New Zealand due to interaction with the seafloor and the Antarctic Circumpolar Current (ACC). Mode coupling due to the ACC was previously predicted for a shorter HIFT path by Shang et al. [J. Acoust. Soc. Am. 90, 2348 (1991)]. [sup a)]Permanent address: Planning Systems, Inc., McLean, VA 22101.