PROPAGATION CHARACTERISTICS OF LINEAR INTERNAL WAVES IN A CONTINUOUSLY STRATIFIED FLUID.

In investigating the fields of linear internal gravity waves generated by localized sources in the arbitrarily stratified fluid extensive use is made of the dispersion relations and the eigenfunctions of the basic boundary-value problem. The most powerful wave trains (Airy waves) can occur in the neighborhood of local group velocity maxima. Long internal waves have a maximum group velocity and at the fronts of each mode the asymptotic form of the fields of linear internal gravity waves is expressed in terms of the Airy function and its square in the case of moving and non-moving sources, respectively. This paper shows that nonmonotonicity of the group velocity is also observed for single-extremum vertical distributions N(z), if there exists at least one waveguide interval with a Brunt-Vaisala frequency that differs from the maximum and from zero and varies slowly at the wavelength of the corresponding natural vertical standing oscillations. For the commonest oceanic distribution N(z), when there is an upper homogeneous layer and seasonal and permanent thermocline layers, the regions of the parameters for which the group velocity of mode number n is nonmonotonic are determined.