### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 4aUW12. Nonadiabatic ocean acoustic environments and the flux density
derivative.

**Timothy H. Ruppel
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*Code 7173, Naval Res. Lab., Stennis Space Center, MS 39529-5004
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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.