TRANSMISSION THROUGH A THERMOCMNE 



115 



3900 



3000 



z 2500 



5 2000 



c 1500 

 o 



1000 



500 



X HYDROPHONE 100 FEET OR LESS BELOW TOP OF THERMOCLINE 

 O HYDROPHONE MORE THAN 100 FEET BELOW TOP OF THERMOCLINE 

 -^THEORETICAL CURVE FROM EQUATION 13 -- TOP OF THERMOCLINE 

 ISO FEET BELOW PROJECTOR 



10 



AT IN TOP 30 FEET OF THERMOCLINE IN DEGREES F 



Figure 28. Correlation between Rm and sharpness of thermocline. 



gest that this variation is sufficiently similar to the 

 variation of Rw below the thermocline that Aflio 

 would not be expected to show much predictable 

 change with hydrographic conditions. However, the 

 data analyzed in reference 32 are not sufficiently 

 complete to allow definite conclusions. 



The large scatter of the observed data may also 

 contribute to the failure to find any significant cor- 

 relations in the study of AR4a- Only half the observed 

 values of AR^o at 24 kc lay between 450 and 1,150 yd, 

 corresponding to a quartile deviation of 350 yd. This 

 is about what would be expected from an observa- 

 tional error of 2 db in the measured transmission 

 losses. In the isothermal layer, the value of jRw is 

 changed about 300 yd by a 2-db change in transmis- 

 sion loss. Below the thermocline, the same change in 

 transmission loss produces a change of only 175 yd in 

 Rw] because of the steeper slope of the transmission- 

 loss curve below the thermocline a smaller change of 

 range is required to offset a change of transmission 

 loss than in the isothermal layer. The square root of 

 the sxmi of the squares of these two quantities is about 

 350 yd, in agreement with the observed quartile 

 deviation. This close agreement is somewhat sur- 

 prising since some of the observed scatter is presuma- 

 bly due to variations in hydrographic conditions. In 



any case, since the values of R^q in the isothermal 

 layer introduce so much scattering in the values of 

 ARio, it is reasonable to expect that the analysis of 

 ARia is not an appropriate method for investigating 

 the way in which 7^40 below the thermocline depends 

 on detailed oceanographic conditions. 



Correlation with Depth and Sharpness of 

 Thermocline 



Examination of the values of Rm below the ther- 

 mocline shows that these are in fact correlated with 

 both the sharpness and the depth of the thermocline. 

 First, the data will be presented on the change of i?4o 

 with thermocline sharpness. All the values of ^40 ob- 

 tained by UCDWR when the depth to the top of the 

 thermocline was between 100 and 200 ft and the 

 hydrophone was below the thermocline are plotted 

 in Figure 28 for different intervals of AT, the temper- 

 ature change in the top 30 ft of the layer. The values 

 of AT shown are only approximate, as a result of the 

 grouping of the recorded data into four different 

 groups, as follows: AT less than 0.7 F; AT between 

 0.7 and 1.5 F; AT between 1.6 and 4.0 F; and AT be- 

 tween 4.1 and 12.5 F. 



The crosses represent runs in which the hydro- 

 phone was 100 ft or less below the top of the ther- 



