INTERNAL WAVES 



Bathythermo grams obtained from the USS CACOPAN on 

 Operation HIGHJUMP in the antarctic were used to study 

 internal waves. The first series (fig. 19A) was taken at a 

 stationary location (68°l6'S, 174°53'W) which was occupied 

 on 28 and 29 January 1947. Repeated lowerings at this location 

 were made every 10 minutes for the five-hour period, 2135Z 

 to 0230Z. Another series (fig. 19B) was made in the area 

 67°47'S, 176°54'W to 67°40'S, 176°10*W. Measurements 

 here were made for 2 hours and 20 minutes at five-minute 

 intervals from 0045Z to 0305Z on 28 January 1947. 



Whenever repeated bathythermograph observations are 

 made in one locality, the vertical fluctuations of any isotherm 

 is considered to result from internal waves. In order to 

 study them in the antarctic, depths of isotherms were plotted 

 against time. An examination of the bathythermograms 

 revealed that the most suitable temperature was the 30-degree 

 F. (1.1-degree C.) isotherm because it was continuously in 

 the thermocline. 



Many of the bathythermograms showed a double trace 

 in the thermocline. This double trace may be due to hysteresis 

 of the instrument or to the presence of internal waves of very 

 short periods. Only the shoaler trace is used here. 



Figure 19A shows variation in the depth of the 30-degree F. 

 isotherm at each observation made at 10-minute intervals. 

 The maximum variation in any 10 minutes was 15 feet. In 

 this 5-hour period, the maximum difference between crest 

 and trough for the series was 40 feet. 



Figure 19B (the second series of repeated lowerings) 

 shows similar fluctuations due to internal waves for the first 

 80 minutes at an average depth of 50 feet. Then there is a 

 very sharp drop in the depth of the isotherm to about 140 feet. 

 However, these observations were made while the ship was 

 moving at about 3 knots so it is likely that a boundary between 

 two water masses was crossed. Thus, this increase in the 

 depth of the isotherm is probably not related to internal waves. 



Because each station was occupied for only a short time, 

 it is impossible to make any analysis involving the long-period 

 waves such as those related to tidal periods. For the same 

 reason, it would not be profitable to perform a harmonic 

 analysis to determine the dominant periods. 



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