Analysis of Internal Tides from a Cross -Like Section 



To obtain preliminaiy information on the direction of progress of the 

 internal tides, the thermistor chain was towed in a cross-shaped pattern moving, 

 consecutively, from west to east, east to west, north to south, and south to 

 north. The end points of the cross were 31°54'N, 119°25'W;3r54'N, 117° 10 'W; 

 32° 50 'N, 118° 16 'W; and 30° 52 'N, 118° 16 'W. The duration of each leg was about 

 20 hours. Mean water depth was about 1600 meters. As shown by the spectra at 

 the drift stations, the energy is peaked in the tidal range; therefore, even with 

 these short records, dominant energy shift over frequency came mainly from the 

 tidal peaks. 



Figures 9 and 10 show the amplitude spectra for the four legs. Because 

 the records are short, high confidence cannot be expected. The spectra were 

 obtained at trial periods lasting from 2 hours to 38 hours. The amplitudes in 

 the periods longer than 12 hours are generally larger in the case of the west- 

 east and the south-north legs than in the other two legs. If their spectral 

 densities are compared at common frequencies, they would imply that the 

 semidiurnal, as well as the diurnal internal tidal waves run in a northeasterly 

 direction. This supports the results obtained by H.Sunrners and K.O. Emery. ^ 

 The additional maximum in the east-west and north-south directions in periods 

 near 8 hours might be a reflected wave traveling in a southwesterly direction 

 and having a smaller amplitude than the waves traveling to the northeast. 

 Because the amplitudes are different, we cannot expect standing internal tidal 

 waves in the Gulf of Santa Catalina. In agreement with the results presented on 

 pages 15 — 20, the energy level is higher in the towed records than in the records 

 from the drift stations. 



20 



f^ 15 



^ 10 

 o 



1 



1 1 1 1 1 1 1 





WEST- EAST /^ / 





^^ / 





^^-^ .^ 





^^^ ^ 





^^-^ • 





^ — ^ 





















/ — -•^'^ 



- 



/ ^^ EAST-WEST 





/ / 





/ y 





1 / 





A / / 





/\ J"^ 





/ \ // 



~ 



/ \y/ 





L^ X/ 



1 



— 1 — 1 — 1 — 1 — 1 — [ 1 



12 



16 20 

 HOURS 



24 28 32 36 



Figure 9. Amplitude specfr 

 and wesf-easf. 



for the legs east-west 



37. 



