T(0 = S (^-Q, ^1 = - / ^ fa,2 - f'^iy)]^, c.2^/2 (y^) 



(85) 



^ 

 Therefore, equation 84 can be solved: 



y^^i^ 



y ($ = Y(0) cos H + sin fe^ + sin k(^ - ^J (86) 



k k 



This solution shows that at ^=<fi , given by w = f , a reflected wave is 



Y(0 

 created which travels back into the area co>f , having the amplitude — r — , the 



wave number k , and the phase k^^ . Because of G = ioj^ - f^)Y , the vertical 



component w = G{y) W{z) of the wave vanishes at co = f . In the following 



section it is shown that the spectra of the chain reccrds do not indicate any 



significant decrease of the amplitudes of the diurnal internal tidal wave at 



cf) = 30° or north of it. Therefore, it is believed that the observed internal 



tidal waves are forced waves. 



ANALYSIS AND INTERPRETATION OF THERMISTOR CHAIN 

 DATA RECORDED AT A DRIFT STATION 



As pointed out previously, an advantage of anchor stations is that their 

 data can be interpreted directly by the theory of internal waves. They permit the 

 easiest computation of the amplitudes of the modes. 



Drift Station 1 



At Drift Station 1, a continous temperature-depth recording was made 

 with the NEL thermistor chain by USS MARYSVILLE from 2135 hours on 10 

 October to 2135 hours on 11 October 1963 at the central position 31'^0'N, 

 121°00 'W. The ship was drifting approximately 1 knot to the southeast, which 

 might have caused a doppler shift in the higher modes. Numerical computations 

 of density are based on a hydrographic station in the nearby area. These data 

 are given in table 1. 



A Fourier analysis has been made on the depth fluctuations of the isotherms. 

 The spectrum of the mean value for all isotherms is shown in figure 5- Both the 

 diurnal and semidiurnal internal tidal waves have amplitudes of about 6 meters 

 (mean value for the upper 200 meters). They are, therefore, equally important. 



In order to analyze the contributions of each mode to the resultant amp - 

 litudes, the vertical change of the amplitudes must be decomposed into the 

 modes. This was npt done because the chain is only 900 feet long and therefore, 

 the observations did not extend to the bottom. 



28 



