For this study four months of nearly continuous thermocline depth 

 data were collected using isotherm followers (LaFond 1961), instruments 

 which follow and record the depth of an isotherm as it moves with the 

 thermocline. Three such devices, suspended from booms on the tower, 

 were operated throughout the May-August period (l96l), when the gradient 

 was the strongest. Supplemental wind* and tide** data taken nearby 

 during the same period were used to determine the influence of these 

 forces on the thermal structure. 



Data 



The nearly continuous recording of the depth of an isotherm in 

 the middle of the thermocline showed that the thermocline undergoes 

 high-amplitude vertical oscillations. In addition to the short-period 

 internal waves, these. are predominantly of diurnal and semidiurnal 

 periods. Figure 2 shows a typical example of 3 days of recorded 

 isotherm depth together with the corresponding period of wind and tide 

 data. These thermocline oscillations are about 30 feet high, but during 

 other periods they may measure as much as 50 feet in height at the 

 Mission Beach Site. 



The normal summer wind off Mission Beach is an onshore sea breeze 

 that develops in the morning, becomes strongest in the afternoon, and 

 recedes in the evening. There is usually a weak, offshore breeze in 

 the early morning. Thus the dominant wind cycle is diurnal. 



The tide has a semidiurnal cycle with a mean range of 3.6 feet. 



DATA ANALYSIS 



According to the wind transport theory formulated in 1902 by 

 V. W. Ekman (1905), the total mass transport by the wind, in the open 



*The wind was recorded at the U. S. Weather Bureau Station at Lindbergh 

 Field, 4 l/2 miles from the tower. 



**The tide was measured at the Scripps Institution of Oceanography pier 

 near La Jolla, 6 miles from the tower. 



115 



