Sahoo ley 



probes consisting of two closely spaced platinum wires set in epoxy. 

 The conductivity of the solution at the points where each of the probes 

 were located was read from a meter scale. The upper probe was 

 placed one half cm above the interface and the other one half cm 

 below. Standard salt solutions were used to calibrate the conductivity 

 of the probes in order to measure salinity. This calibration was non- 

 linear and temperature corrections were necessary. 



Figure 2 illustrates the technique that was devised to facilitate 

 measuring eddy diffusivity by the use of a series of turbulent pulses 

 of the same amplitude and time. The ordinate of this chart is a 

 record of the temperature difference (0 to 1.67°C/cm) naeasured by 

 the thermopile shown in Fig. 1 vs. time, which progresses from 

 left to right. The record starts at the upper left corner where the 

 temperature difference starts to decrease due to molecular diffusion. 

 At horizontal chart position #5 the mixer shown in Fig. 1 was acti- 

 vated for 15 seconds and then stopped for about 8 minutes. This 

 8 minute pause allows the pulse generated internal waves to damp out 

 so that the temperature difference due to turbulent eddy diffusion 

 can be measured and separated from the relatively slow molecular 

 diffusion. Again at chart positions #6.4 and #7.8 similar 15 second 

 pulsed of turbulence were introduced. The total time of turbulence 

 was thus only 45 seconds, and three successive temperature differ- 

 ences due to eddy diffusion were recorded at three 15 second intervals 

 of turbulence. The effect of eddy diffusion of NaCl was measured 

 by the same technique using the conductivity sensors. 



(.4^ 



Fig. 2. Temperature difference AT vertically vs. time. The 



decay of AT by molecular diffusion is interrupted three 

 times by turbulent pulses lasting 15 sec each. 



314 



