THE ADIABATIC MODE PARABOLIC EQUATION

An efficient method is developed for solving problems involving three-dimensional acoustic propagation in a thin spherical shell. The method is based on the adiabatic mode approximation, which assumes that energy coupling between modes is negligible, and the parabolic equation (PE) method, which efficiently handles spatial variations in the acoustic properties. The PE method is used to solve two-dimensional wave equations for the adiabatic mode coefficients over latitude and longitude. Due to this reduction in dimension, the adiabatic mode PE should be practical for solving global-scale ocean acoustics problems. These types of problems, which are currently of great interest [Heaney et al., J. Acoust. Soc. Am. 90, 2586-2594 (1991); Baggeroer and Munk, Phys. Today 45(9), 22-30 (1992)], are too large to solve with other existing three-dimensional models.