Ray-based description of normal modes in a deep ocean acoustic waveguide

Modal structure of the wave field in a deep ocean environment with sound speed fluctuations induced by random internal waves is considered. An approximate analytical description of the modal structure at megameter ranges is derived by combining two known results: (i) relations expressing mode amplitudes through parameters of ray paths and (ii) stochastic ray theory. For a monochromatic wave field, a simple analytical estimate has been obtained for a coarse-grained distribution of acoustic energy between normal modes. Significant attention has been paid to the investigation of the mode pulses, that is, sound pulses carried by individual modes. Analytical estimates for the spread of mode pulse and bias of its mean travel time in the presence of internal waves are derived.