PREDICTION OF SUMMER THERMOCLINE DEPTH OFF MISSION BEACH 



by 



James L. Cairns and E. C. LaPond 

 U. S. Navy Electronics Laboratory, San Diego, California 92152 



INTRODUCTION 



A strong thermocline occurs, during the summer, in the ocean off 

 Southern California. Vertical oscillations of the thermocline, as high 

 as 50 feet, have been measured. It is important to the Navy to acquire 

 more knowledge of this phenomenon in view of its importance to naval 

 operations. This is due to the facts that the depth, strength, and 

 general nature of the thermocline influence the propagation and trans- 

 mission of underwater sound; the refraction properties of the gradient 

 layer differ from those of the surrounding ocean; and the water, above 

 and below the thermocline, may move in opposite directions or at 

 varying speeds. 



Within this thermocline is normally a high plankton content, which 

 hampers visual or optical observation. Therefore a prediction of the 

 thermocline depth in this region is valuable to the Navy. This study 

 presents a new insight into the vertical motion of the water layers 

 associated with the Southern California offshore summer thermocline, 

 and provides a procedure for predicting its depth within usable limits. 



DATA COLLECTION 



The thermal structure data for this study were obtained from the 

 USNEL Oceanographic Research Tower located about a mile off Mission 

 Beach, California (Fig l). Daily bathythermograph records have in- 

 dicated that a thermocline becomes established along the Southern 

 California coast by the end of March, reaches a well-developed state by 

 mid-May, and remains strong until late September. During the May-August 

 period, the vertical thermal gradient within the layer is on the order 

 of 0.5°F per foot. 



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