the 12-second interval scan falls on all wave phases. If one scan 

 falls on the wave crest and the next off it, 120 feet away, an abrupt 

 change in the normally smooth isotherm is recorded. Other wave 

 phases are also recorded on successive scans, and thus a rough 

 appearance is created when short waves are encountered. 



Since the isotherms in the northern part of the section are 

 more irregular and reflect higher-frequency internal waves than 

 those in the southern part, the ship may have been alternately 

 moving in the same and opposite direction as the internal wave 

 propagation, thus producing a Doppler effect. 



The ridge may be considered a front, or boundary, with a 

 sloping density structure rising toward the crest. Small internal 

 waves propagating at an angle with the boundary may be refracted 

 as they are on the continental slope and be propagated toward the 

 crest from both sides. A Doppler effect can therefore be experi- 

 enced when towing toward and away from the crest (left to right, 

 fig. 9). Waves propagating toward each other can create mixing 

 and result in isothermal water near the surface, as was measured 

 over the crest. This may cause the large difference in wavelength 

 measured on either side of the rise, and the mixed structure over 

 the crest. 



Other causes for differences in thermocline roughness are 

 the variability and patchiness of the ocean. Since wave frequency 

 on the thermocline may vary widely over a short distance, addi- 

 tional examples are presented in order to demonstrate the types of 

 thermocline and their distribution. 



THERMOCLINE CLASSIFICATION 



Thermoclines may be categorized either by their oceanog- 

 raphic processes or (somewhat subjectively) by the wavelengths 

 of their smaller oscillations. To identify types of thermoclines, 

 a total of 30 2-hour (12-mile) two-dimensional data sections were 

 selected from the ship's track (fig. 10) and classified in four 

 categories: smooth, normal, rough, and irregular (Appendix A). 

 The variability of oceanic thermal structure is confirmed by the 

 fact that each type of thermocline is found near the other. 



16 



