626 



FIGURE 3. Internal waves in a shear flow with profiles of U and p similar to those of Figure 

 2(b), except that the interface is at z = H/4 and the mean, depth averaged, flow is zero. The 

 waves propagate to the left and in (a) the mean flow in the upper layer is to the right, lower 

 to the left (x'^O) , in (b) there is no mean flow, whilst in (c) the mean flow in the upper layer 

 is to the right and in the lower layer to the left (x ^ 0) . 



(b) 



u> 



p, 



FIGURE 4. Interfacial waves in a two-layer fluid. In 

 (a) the phase speed of the waves, c, is equal to the 

 speed of the lower layer, U2. The wave shape is identi- 

 cal to that of surface waves on a layer of depth hj , 

 but inverted. (This corresponds to x "^ 0) . In (b) , 

 c = Uj , and the wave shape is identical to that of 

 surface waves on a layer of depth h2. 



