THERMAL-STRUCTURE CYCLES 



Of interest were the various time cycles in the depth 

 of the thermocline. Considerable study has been made of 

 the short-period vertical oscillations in the thermocline 

 caused by internal waves. Internal waves are instrumental 

 in changing the level of the thermocline as much as 30 feet 

 in a few minutes. In addition, it is known that the thermo- 

 cline fluctuates with the tide but not necessarily in phase 

 with it. There is, however, a diurnal movement of surface 

 water onshore and offshore in accordance with the diurnal 

 wind system. The WNW component of the usual daily sea 

 breeze, in accordance with the Ekman effect, lowers the 

 thermocline at the tower. This component reaches its 

 maximum in the early evening and terminates at night. The 

 night termination, with an occasional weak reversal, creates 

 an offshore displacement and a rise in thermocline with a 

 minimum depth early in the morning. Thus, sampling every 

 4 hours allows the longer periods of thermocline oscillation 

 to be considered, even though they are greatly influenced 

 by short-period internal waves (Cairns and LaFond, 1965).''"® 



REVERSE SIDE BLANK 63 



