moving southward and overrode the deep water (arrows, fig. 7). 

 The deep water was either moving at a slower speed or in a 

 northerly direction. The difference in speed was measured to be 

 0. 7-1. 2 knot, and the motion could create a weak shear or tem- 

 perature inversion as shown by the "S" shape of the 11°C and 12°C 

 isotherms (fig. 7). These inversions were 150-200 feet high, 

 fairly weak (about 1°C), and probably transient. The "S" shape 

 implies that the flow in the higher level of the inversion was 

 counter to the ship's motion. 



The main thermocline, between 150 and 300 feet, contained 

 smaller waves. The spectrum of their wave lengths was broad; 

 some were only 600-900-feet long whereas others (upper right) 

 were nearly 4 miles long, and averaged 2-4 per mile. The 12- 

 mile wave on the thermocline was less distinct than in the first 

 example, and the thermocline less sharp. It became weaker with 

 depth, as in the previous section, but was more uniform before 

 transforming abruptly into the large inversions. 



Cold Water Intrusion 



The third example (fig. 8), recorded on a southerly tow 180 

 miles southeast of the second example, featured in its surface 

 layer a 6-mile region about 1°C colder than the adjacent water. 

 Below the surface layer a sharp thermocline changed with in- 

 creasing depth into a more gradual one. The upward bending of 

 the 13°C isotherm indicated an intrusion of colder water that did 

 not extend into the strongest part of the thermocline. The cold 

 area appeared to be an intrusion lying at an angle to the section 

 rather than an up-bending of the thermocline. 



The thermocline was made up of small, wave-like oscilla- 

 tions, particularly between the colder areas, numbering 3 per 

 mile as compared with an average of 2 per mile on either side in 

 the preceding sections. This may be due to a Doppler shift in fre- 

 quency that corresponds to an apparent change in wavelength caused 

 by the relative motion of the ship, current, and wave propagation. 

 If a Doppler effect is assumed, then wave propagation in the cold 

 region would have a more northerly component than waves in the 

 regions on either side. The cold area at a depth of 500 feet where 

 the isotherm curved up appeared to be characteristic of this level. 



12 



