that the deeper isotherms undergo greater vertical oscillations 

 per unit distance. 



Since the distribution of values is not skewed, the oscilla- 

 tions can be approximated by a sine curve of the form 

 Z= Z + A sin ( kx+wt ). The second term for the shallower iso- 

 therm is approximately equal to 1/119 sin (kx + wb), whereas the 

 deep isotherm is 1/84 sin (kx+wt). The total of the 65,000 

 observations (fig. 17) is about 1/100 sin (kx+wt). 



DIRECTION OF SLOPE 



If there is a dominant direction to internal-wave propagation 

 in the thermocline, the absolute -value 50th percentile of slope 

 should be greater when (1) the tow is opposite to the direction of 

 propagation, or (2) in the same direction as the waves if the ship 

 speed is much greater than that of the waves. The slope values 

 would be expected to be relatively small when the ship is running 

 parallel with the crests or troughs. 



Although the data samplings are not distributed equally in 

 all directions of tow, there is considerable spread around the 

 compass and in different areas. The steepness of the thermocline 

 may be related to the direction of tow. To show this relationship, 

 the computed absolute-value 50th percentile of slope for each sec- 

 tion of isotherm depth is plotted with reference to the direction of 

 tow (fig. 19, open points). The individual values are marked A to 

 AA corresponding to the sections shown (fig. 15). A wide fluctua- 

 tion of median slopes is present in all directions of tow. The 

 absolute -value median slopes range from less than 10 minutes 

 (0.9 foot change per 304 feet of travel) to over 52 minutes (4. 7foot 

 change per 304 feet of travel). The average slope value of all data 

 was 25 minutes, which is higher than the average of 16 minutes 

 measured on a previous cruise between San Diego and Honolulu. 3 



A similar presentation of the absolute -value 70th percentile 

 slope values for the shallow isotherm of each section is also given 

 (fig. 19, solid points). The results show that this percentile angle 

 varies from 0°17' to 1°37'. 



To smooth the values and demonstrate any dependence on the 

 towing direction, data were averaged by 45 -degree increments of 

 direction of tow and the averages were connected by a solid line for 



41 



