SLOPE IN DEGREES 



5° DOWN 



+ 10 -10 



DEPTH CHANGE (FT.) 



Figure 8. Frequency distribution of differences in depth between half- minute 

 or 304 ft spaced readings of 9°C isotherm, leg one, cruise 2. 



The vertical depth and slope changes of the two chosen iso- 

 therms on the shoreward leg are shown in figure 10. The fre- 

 quency distribution for the 16 °C isotherm is sharply peaked and 

 narrower than for any other record. The 9°C isotherm also has a 

 narrower slope distribution than in the two previous directions of 

 tow, with 50 per cent of observations falling within 15 minutes. 



The distribution of isothermal slopes may be useful in de- 

 termining the propagation direction of the dominant internal waves. 

 When the ship is running counter to the waves the slopes should be 

 steeper, and when the waves are running in other directions the 

 slopes should be less. The diagrams show that the slopes were 

 more gentle on the last two legs of the cruise (figs. 9B and 10B) 

 than on the first leg, for similar isotherms (9°C). Thus, it may 

 be inferred that the waves were moving more in the shoreward 

 direction than the other two directions sampled (see later discus- 

 sion under Direction of Propagation). However, it must again be 

 pointed out that not all the isotherm depth readings were simul- 

 taneous. The depths are actually depths of encounter and thus 

 these slopes may not necessarily be the true ones. 



20 



