40"^ 



30' 



20"^ 



\ 



0^2 



^10 9 





1 







7 



/diurnal 





""1 



^4i>J 



(TIDES 



/SEMIDIURNAL 











% 





■^ 



\"^- 







\ SAN FRANCISCO 











\ 



\ 



^i>4^ 





5^_ 



— \ SAN DIEGO 



\ 



"2 







\\ 



w 





"~^4- 



^^_ 





% 





^ 



V\ ' 





\ 



^\, 



\ 







160° 



150° 



140° 



130° 



120"= 



110^ 



Figure IT. Cofidal lines of the semidiurnal tides (after Dietrich, ref. 13) and 

 direction of progress of the infernal semidiurnal and diurnal tidal waves on 

 the cruise from San Diego to Hawaii. 



were computed for each isotherm up to the 40th harmonic. The con-esponding 

 periods are 72/n hours. 



4. To check the influence of the mean inclination of the isotherms on 

 the spectra, the depth change of the isotherms was computed by taking the 

 difference of the mean values of the first and last 10 hours of each 72-hour record. 



5. Mean values, A , for all isotherms of each combined set were computed 

 from the A^ . 



As is well known from hydrographic sections, ^^ the stationary isotherms 

 are inclined in the upper 1000 meters, increasing in depth toward the west. If the 

 linear depth change of an isotherm over a length L is denoted by A and the 

 Fourier amplitudes of this interval are denoted by a„ ^^ and b„gf, then 

 Fourier analysis leads to the amplitude spectrum 



— , where A„ ^, 



[a 



fc„ ,j2] l/2anda„ = 0, 6„ 



^-ith n = 1,2, 



Any Fourier analysis of the chain records considered here is therefore strongly 

 influenced in the long-period range by this stationary inclination. The amplitudes, 

 A^ , of the periodic changes are superimposed on this hyberbolic spectrum of the 

 stationary component of the isotherm. _ 



Table 6 gives the mean deptji change, A , of the isotherms for each com- 

 bined set, the expected amplitude, Aq g^= -^ due to these change_s, A , and the 

 analyzed amplitudes, A , from the record. The numbers show that A results 

 mainly from the stationary inclination of the isotherms. 



39 



