Subarctic frontal effects on long-range acoustic propagation in the North Pacific Ocean

Acoustic propagation along the Hawaiian-Aleutian path at low frequency (65 Hz) for the acoustic thermometry of ocean climate (ATOC) has been simulated using the implicit finite difference parabolic equation (IFD-PE). This sim ulation is based upon the Semtner-Chervin model with one-half-degree resolu tion. The adiabaticity has been assessed, and it was found that Significant mode coupling takes place at the sub-arctic front area (44.8 degrees N). D ue to the range-dependent double channel, two characteristic ranges were id entified in this area: (i) the modal degeneration range R-m(D) and (ii) the modal scattering range R-m(S). At range R-m(D), mode m and mode n (usually , It = m + 1) are degenerated, the modal wave numbers of mode m and mode n become equal, and mode n then takes the shape of mode m. Therefore, there i s no real repopulation (modal Scattering), but a modal name change takes pl ace at this range. The modal name change can cause a miscalculation of the adiabatic R-m(S),, however, real repopulation does take place. Numerical si mulations travel time. At range R-m(S) illustrate that R-m(D) and R-m(S) ar e separated by about 10 km at lower modes (m < 5) and are merged at higher modes. (C) 1999 Acoustical Society of America. [S0001-4966(99)06603-5].