where 17 is referenced to the undisturbed level of the density discon- 

 tinuity. From Equation (3), it is seen that when the discontinuity is 

 at mid-depth the phase speed is independent of internal wave amplitude. 



Since the above equations apply to a free surface, the internal wave 

 crest or trough must be accompanied by a solitary surface wave trough 

 or crest, respectively. In practically all observed cases near TT4, 

 signature passage was indicated by positive humps or crests in 

 temperature measured at a fixed level. Under normal conditions of a 

 negative temperature gradient and positive salinity or isohaline profile, 

 this would correspond to an internal wave trough accompanied by an 

 imperceptible crest on the water surface. 



A precise comparison of individually observed signature speeds to 

 Keulegan's theory is not possible since salinity was neither measured 

 continuously nor at the same depths as temperature. Water samples 

 for salinity analysis were taken at several depths daily from 13 May 

 to 3 June I960 to provide a gross picture of the mean salinity structure. 

 These data are tabulated in Appendix IV from which the average 

 salinity is found to vary from 31.4%o at the surface to about 32.5%o 

 at and below a depth of 90 feet. For purposes of two-layer calculation 

 of wave speeds during the spring period, values of 31.5%o for salinity 

 in the upper layer (Si ) and 32.5%© for salinity in the lower layer (S2) 

 have been assumed. Salinity is assumed to be 32.0%o in both layers 

 for calculated speeds during the data period in the fall of 1959. 



The average speed given in Appendix II for the signatures shown in 

 Figure 7 is 0.95 knot. Replacement of the mean thermal structure in 

 Figure 7 with a sharp discontinuity at 70 feet, temperatures of 20°C 

 in the upper layer and 10°C in the lower layer, and a constant salinity 

 of 32%o result in density values of p, = 1.0225 and p? = 1.0247. The 

 mean temperature gradient at 65 feet as shown in Figure 7 is about 

 0.25°C per foot. The observed temperature changes at that level were 

 approximately 7°C indicating an internal wave height, 77 , of 28 feet. 

 Substitution of these values in Equations (2) and (3) gives an average 

 speed of 0.96 knot as compared to the 0.95 knot observed. 



A second direct comparison may be made for the wave shown in 

 Figure 8. The discontinuity level at 60 feet is chosen and average 

 temperatures and salinities are taken as follows: Ti = 10°C, S, = 

 31.5%o, T^ = 4°C, and S2 = 32.5%o. The mean temperature gradient 

 from 40 to 100 feet was approximately 0.1 °C per foot and the tempera- 

 ture range at 70 feet was about 2.5°C inferring an internal wave height 



