A similar study was made of the approximate slope of iso- 

 thermal surfaces from the NEL Oceanographic Research Tower 

 off Mission Beach, California. Here, the approximate slope was 

 obtained by means of a continuous depth recording of a single iso- 

 therm in the thermocline made with an isotherm follower. The 

 computation of slopes with the isotherm-follower record, as the 

 internal waves pass the fixed point (tower) in 60 feet of water, is 

 based on an average wave speed of 0. 31 knot. Waves moving 

 faster than 0. 31 knot would give steeper slopes than actually exist, 

 and slower moving waves more gentle slopes. This effect has a 

 tendency to give a little wider distribution of slopes, but the aver- 

 age should be close to the true value. The slopes (accumulative 

 frequencies) detected by this method are shown in figure 11 to- 

 gether with similar curves for the 14° and 16 °C isotherm slopes 



19 



obtained from the data of figures 9A and 10A. 



Although the two methods of obtaining slopes are not the 

 same, nor the results wholly accurate, a comparison of the curves 

 based on large samples (10, 000 at the tower, 3000 in deep water) 



100 



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SLOPE OF ISOTHERM 



Figure 11. Approximate slopes of isothermal surfaces measured in deep and 

 shallow water. 



23 



