A simulation study of cross‐basin sound transmission from Heard Island to California Free

An underwater acoustic technique was proposed by Munk and Forbes (1989) for monitoring greenhouse warming. It involves making decadal measurements of cross‐basin acoustic travel‐time variability. A 2‐week global acoustic transmission experiment, led by Munk et al., will be carried out in January 1991 to evaluate the feasibility of this acoustic method. In support of the experimental effort, this modeling work simulates the influence of ocean fronts and eddies on the three‐dimensional acoustic ray paths crossing the Indian and Pacific Oceans to the California coast from Heard Island, the location for the sound source. For the computation of the cross‐basin acoustic paths, a three‐dimensional Hamiltonian acoustic ray‐tracing code developed originally by Jones et al. (1986) is used. The input sound‐speed fields to the acoustic ray model are interpolated from gridded temperature and salinity ouput data from the Semtner‐Chervin eddy‐resolving global general circulation model (1988). Results from tracing rays to the California coast through sound‐speed fields containing mesoscale variability are presented. In particular, the variabilities of the cross‐basin ray paths, travel times, illuminated locations, and azimuthal arrival angles are examined.