waves at the interface between the mixed layer and the thermocline. The 

 frequency distribution, mean, and standard deviation were computed for the 

 oscillation ranges of 300 groups. The results are shown in Figure 3. 



X=I7.85 

 S= 10.55 



WWmMMW/MWA 



21 24 27+30 33 36 39 42 45 48 51 54 57 60 63 66 69 

 7.3 X = I7.85 28.4 Miwri_nuuc 



FIGURE 3 AMPLITUDES OF INTERNAL WAVES: FREQUENCY DISTRIBUTION, MEAN, 

 AND STANDARD DEVIATION. (OBS. 300) 



The vertical axis represents the number of observations; the horizontal 

 axis represents 3-foot amplitude classes. The mean value is 17«85 feet, 

 the standard deviation is 10.55 feet, and the highest frequency occurs in 

 the 9- to 12-foot class. Large amplitudes of internal waves were usually 

 found to be associated with the slow passage of strong weather disturbances 

 causing divergent or convergent flow in the upper layers. 



Divergence is produced in the center of a cyclonic low or along a 

 well-defined front where winds with large fetches on both sides of the 

 front change direction quite sharply in the frontal zone. The thermo- 

 cline becomes considerably shallower in the frontal area, and the internal 

 wave propagates with the front. The front may disintegrate or begin to 

 move away rapidly, leaving the original internal wave lagging behind. In 

 either case the divergent wave will probably become a standing wave which 

 will continue to oscillate in the area for several days and become super- 

 imposed on the internal-wave spectrum of tidal and shorter periods. 



Recurring divergence or convergence increases the duration and range 

 of large oscillations. The thermocline depth oscillated between 90 and 

 170 feet on 22 and 23 September 195^ in the area of station CHARLIE. 

 These large amplitudes of internal waves were probably caused by slowly 

 propagating fronts and wind fields passing in succession during these and 

 previous days (Figure h). 



7 



