### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 2pUW21. A method for computing adiabatic modal wavefronts.

**Evan K. Westwood
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*Appl. Res. Lab., P.O. Box 8029, The Univ. of Texas at Austin, Austin, TX
78713-8029
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An approach has been developed for determining the modal wavefronts that
allow normal modes to be propagated adiabatically in smoothly range-dependent
ocean waveguides. The method is motivated by the fact that propagation in an
isospeed penetrable wedge is accurately modeled by ``adiabatic wedge modes,''
which are identical to the usual ``vertical modes'' except that the wavefront
curvature induced by the sloping bottom is taken into account. For the wedge,
the wavefronts are assumed to be circular arcs centered on the wedge apex. In
order to generalize the notion of wedge modes to other types of range
dependence, wavefronts are constructed numerically such that the derivative of
each mode in the direction normal to its wavefront, (cursive
beta)(phi)/(cursive beta)s, is zero. The result is that the first-order modal
coupling coefficients, which involve (cursive beta)(phi)/(cursive beta)s
integrated over depth, are zero, and the adiabatic algorithm can be used. The
quantities (cursive beta)(phi)/(cursive beta)z and (cursive beta)(phi)/(cursive
beta)r versus depth are used to obtain the directions normal to the wavefront.
For the isospeed penetrable wedge, wavefronts computed in this manner do indeed
correspond closely to the expected circular arcs. [Work supported by the ARL
Internal Research and Development Program.]