736 



[chap. 22 



a. Wave height 



The depth of a single isotherm in the thermocHne was observed to fluctuate 

 widely during one week in water only 60 ft deep (Fig. 5). Superimposed on the 



30" 



40- 



50- 



12 3 4 5 6 7 8 9% 



Fig. 5. Distribution of minute readings, over 7 consecutive days, of the depth of an iso- 

 therm in the thermocUne off Mission Beach, CaUfornia, in 60-ft deep water. 



longer-period oscillations in the thermocline were shorter-period vertical 

 oscillations. Generally, the magnitude of these vertical fluctuations was in- 

 versely proportional to the gradients in which they were found. Smaller 

 fluctuations were nearly always present. 



Fig. 6. Examples of iarge-amphtude internal waves near sea surface. 



During the periods of investigation the maximum, daily vertical migration 

 of an isotherm in the middle of the thermocline, and in the upper 35 ft, was 

 22 ft in August, 1958 (Fig. 6). A day's record for 23-24 September, 1959, is 

 shown in Fig. 7. 



The frequency distribution of shallow internal wave heights at this location 

 for parts of 12 days throughout the summer of 1958, and 7 consecutive days in 

 1959, is shown in Fig. 8. Only waves higher than 2 ft were considered, since 



