Clark and Yarnall 



A second factor in the argument concerns the temporal rela- 

 tionships between local tides and the phase fluctuation. If local 

 tides were the dominant influence in controlling the tidally related 

 phase fluctuation, one might expect peaks in the phase fluctuation to 

 be coincident in time with local high or low tide. This is not obser- 

 ved. Figure 21* is not included to specifically illustrate this point, 

 but to show that the filtered H43 time function ("If' hydrophone in this 

 figure) is sufficiently "tide like" to carry out a phase comparison of 

 this kind. (Also note the complex interference patterns formed by 

 signal amplitude on the time scale of this figure.) 



Finally we note that calculations simulating tide height 

 variations in the RBR propagation model predict a maximum phase ex- 

 cursion of about 260° at hydrophone H43 . Experimental maximum values 

 are in the range of 5 to 15 full cycles. Under the assumption that 

 pure SRBR rays dominate the resultant signal at H43, which is con- 

 sidered unlikely, the calculations predict about 3 cycles of phase 

 change. These calculations and the experimental evidence presented 

 above have been taken as sufficient to rule out the possibility that 

 local tides are the dominant direct cause of the tidally related phase 

 fluctuations observed at H43 . 



We pass on to the second possibility--disturbances in the 

 thermal stratification which are spatially coherent over a large por- 

 tion of the acoustic path. Here we have striking experimental evidence 

 favorable to the hypothesis, but we will point out immediately that 

 the evidence is much more convincing for the source to H3 path than 

 for the full propagation path from source to H43 . The evidence con- 

 sists of a direct correlation between H3 phase and motion of the 

 isotherms at the 100 m thermistor string. Figure 22 presents data 

 from several days in August, 1966 which can be used to illustrate this 

 correlation. Figure 22a is a direct comparison of H3 phase and a 

 simultaneous temperature measurement at thermistor T3 (46 m depth) . 

 A certain amount of "eye integration" of the high frequencies in the 

 temperature data is necessary to establish the details of the cor- 

 relation; there is little doubt, however, that the correspondence of 

 the two cuirves is strong on the diurnal time scale. Additional data 

 of this kind confirms the correlation. The data of Figure 22b were 

 taken at a later time in August when no phase information was avail- 

 able. These data are included to illustrate that the diurnal internal 

 disturbance is persistent and is the dominant time varying influence 

 upon the thermocline at the thermistor string. Thermistor T3 is being 

 influenced here by the lower boundary of the mixed layer; T4 (which 

 unfortunately failed prior to LCT-1 and does not appear in Figure 13) 

 illustrates the full range of the motion. The effect appears "damped" 

 at T5 which is located very near the bottom. The motion of isothermal 



* 



This figure appears as No. 4 in Ref. 2. 



327 



