Timothy H. Ruppel
Code 7173, Naval Res. Lab., Stennis Space Center, MS 39529-5004
The accuracy of the adiabatic approximation is known to be suspect when applied to certain environments, particularly areas along the continental shelf. An issue in these environments is the degree to which the adiabatic assumption is valid. Transmission loss calculations using both parabolic equation and coupled mode models show that for steep slopes much more energy reaches the shelf from deep water than predicted by the adiabatic approximation. It has been shown that rapid variations in the energy flux as calculated from a parabolic equation model often indicate a breakdown of the adiabatic approximation and, therefore, significant mode coupling. This study connects these observations to the propagation physics and the standard coupled mode equations. The limits and strengths of using variations in the energy flux as an indicator of mode coupling are outlined. It is shown that this method of determining the degree of validity of the adiabatic assumption is valid in a large class of environments.