Oleg A. Godin
NOAA/Atlantic Oceanogr. and Meteorol. Lab., 4301 Rickenbacker Cswy., Miami, FL 33149
Sound propagation in a multicomponent fluid, parameters of which including flow velocity as well as shape of boundaries are smooth and slowly varying functions of time and two horizontal coordinates, is considered. No limitations are imposed on the Mach number and the fluid parameters dependence on the vertical coordinate other than the assumption that sound/flow synchronism points are absent. All the processes in the fluid are assumed to be adiabatic. The method of two-scale expansions is used to construct asymptotic development of solutions of the set of hydrodynamic equations linearized with respect to the wave's amplitude. The well-known ``vertical modes-horizontal rays'' approach is generalized to cover acoustic waves in nonstationary moving media. An adiabatic invariant is found that governs the amplitude variation of a normal mode along the corresponding space-time horizontal ray. Physical meaning of the adiabatic invariant is analyzed. Results are compared to those of recent studies of guided propagation in moving time-independent [O. A. Godin, DAN SSSR 320, 204--208 (1991)] and unstationary motionless fluid [A. V. Aref'ev and V. S. Buldyrev, Akust. Zh. 40, 205--211 (1994)]. The importance of a consistent account of medium's motion and its time dependence is demonstrated. [Work supported by RBRF and NRC.]