During the tow some temperature sensors in the string of 34 

 developed electrical shorts and did not operate properly. This is 

 shown by flat lines in the data. The shorts nullified detection of 

 any isotherm passing through the depth of the faulty sensor. This 

 did not, however, affect the recording of isotherms at other depths. 

 It was feasible to choose and analyze the characteristics of iso- 

 therms at other valid depths. In the example of raw data (fig. 3), 

 the 18- and 23-degree isotherms were chosen for analysis. 



The data samples used were from an 8- or 12-hour continu- 

 ous section each day for 16 consecutive days. Shown in figure 2 is 

 the location of the sections used and in table 1 the specific times, 

 positions, and sample size. 



Nature of Vertical Oscillations 



The nature of the detailed vertical changes in the isotherms 

 has not been investigated in an open sea area before nor has the 

 cause of vertical oscillations been established. It seems fairly 

 certain that the density boundaries in the sea should have certain 

 frequencies of oscillation and modes thereof. Eckart, referring 

 to Vaisala,® points out that a given density boundary may have its 

 own normal oscillating frequency, the Vaisala frequency . Still 

 another possibility is that strong winds may create convection 

 cells and eddies in the upper layers of the sea, the circulation of 

 which will cause the thermocline to be lowered more in one area 

 than another. Tidal forces causing water movement around land 

 boundaries and topographic features can start oscillation in the 

 thermal structure. There is, however, reason to believe that the 

 vertical variations observed with distance in the isotherms are in- 

 ternal waves moving in one or more directions. The progressive 

 nature of these oscillations in shallow water has been determined 

 by studies conducted from anchored ships and from the NEL 

 Oceanographic Research Tower. 



The detailed recording of isotherm depths indicates the com- 

 plicated character of oceanic thermal structure and emphasizes 

 the exceedingly complex nature of the sea, not only in temperature, 

 but in chemical, biological, and other aspects. 



