90° .180° 270° 



RELATIVE DIRECTION OF SHIP AND WAVES 



360° 



Figure 23. Frequency factor of the relative direction of ship and internal wave 

 motion using the speed of 6 knots for ship and 1. 5 knots for waves. 



The records from the four 2-mile-diameter tracks (I, n, 

 III, and IV, fig. 24) are arranged one above the other for compari- 

 son. In each case the record is broken down into four depth in- 

 tervals, going from left to right in the figure. The horizontal 

 scale is the direction of tow in each case. However, the nature of 

 the waves at all directions of tow fails to indicate any wavelength 

 that is specific for a particular direction of tow. 



A similar depth-direction (distance) presentation of iso- 

 therms is used for the 6 -mile-diameter record (fig. 25). 



The significant point is that there are vertical fluctuations 

 in all directions of tow for both the 2- and 6-mile tracks. Visual 

 inspection reveals no dominant wave heights in any direction nor 

 any obvious change in frequency. The duration of tow in any direc- 

 tion by this small circle technique is too small for reliable anal- 

 ysis, but the occurrence of internal waves at any direction of tow 

 demonstrates that waves are not parallel in lines. In fact, they 

 must be in the form of irregular bumps and depressions, so that 

 any direction of traverse will cross a high and low thermal sur- 

 face feature. 



In the sharp parts of the thermocline there is a good corres- 

 pondence in the vertical traverse of adjacent isotherms, but this 

 correlation deteriorates when the vertical gradients become weak. 



38 



