SECT. 5] 



INTERNAL WAVES 



739 



smaller than at 700 ft. The decrease in the magnitude of temperature variations 

 below 700 ft indicated that the effect of internal waves on the vertical mass 

 field was greatest at depths of less than 700 ft. 



From such closely spaced observations, currents were computed by a simpli- 

 fied procedure. By use of a temperature-salinity relation, the specific volume 

 anomaly 8, was converted from a function of temperature, salinity and depth 

 to a function of temperature and depth only. The numerical values of lO^S over 

 the temperature-depth range experienced were computed. 



H L H L H L H 



JULt 8 : i JULIf 9 iJULY 10 



j lZOO 1600 i 2000 0000 0400 i 0600 1200 1600 : 2000 0000 0^ 



Fig. 10. Fluctuations of sea temperatvires at 100-ft intervals from 400 to 900 ft, derived 

 through repeated bathythermograph observations over a period of 40 h near Bikini 

 Atoll. 



Then, by a simple numerical integration over the depth of the water column, 

 the dynamic-height anomaly, 10^ AD, was found. The resulting values presented 

 an irregular pattern that can be attributed largely to internal waves. 



To show the effect of internal waves upon 10^ AD, and in turn on current 

 calculations, the dynamic-height anomalies from one day of repeated bathy- 

 thermograph observations were obtained. The data were averaged and plotted 

 (Fig. 11). The resulting fluctuations in dynamic height anaomalies amount to 

 as much as 0.08 dynamic meters in a few hours. 



Seiwell (1937) showed that internal waves will change the distribution of 

 mass along any vertical structure, and will, therefore, cause the geopotential 

 height of the free surface, relative to a given isobaric surface, to vary periodi- 

 cally. For the Atlantis Station 2639, Seiwell found that, because of internal 

 waves, the Variation of geopotential height of the free surface, relative to the 



