Clark and Yarnall 



a) A slight temperature decrease in the near- 

 surface layer, 



b) A deepening of the mixed layer. 



c) A general westward drift of surface water 

 (Ekman transport) . 



The westward surface current is the phenomenon that ap- 

 parently controls the H3 phase in the data of LCT-1. In this regard, 

 we note immediately that a westward transport of surface water in the 

 Straits will bring relatively warmer water into the path of the H3 

 hydrophone. This is an indirect consequence of the geostrophic bal- 

 ance associated with the northerly flow of the Florida Current, A 

 cross-stream surface temperature rise is an observable feature in the 

 Straits. A value for this rise, about 1°C, can be obtained from the 

 Institute of Marine Science hydrographic data,'^ A recent overflight 

 with an airborne infrared thermometer yielded a surface temperature 

 rise of 1.3°C,* 



The strong control which Ekman currents can exercise over 

 the temperature of the medium near coastlines has been discussed by 

 several authors. 22,23 ,24 in general we may expect a north wind par- 

 allel to the Florida coast to set up a surface current convergence 

 at the coastline. This will force the cold water of the local thermo- 

 cline away from the coast; creating a body of water near the coast 

 which, spatially averaged, may have a higher temperature. Given the 

 weather pattern of the Florida coast, one can predict that this process 

 will take place in a series of steps coincident with the southward 

 progression of polar fronts. Available data, in fact, indicate that 

 the step function changes in signal phase at H3 are the signatures of 

 "impulse" surface current convergences associated with polar front 

 passage. 



The experimental evidence for this hypothesis is contained 

 in Figures 24, 25 and 26. Figure 25 emphasizes the correlation which 

 exists between these step signatures in the H3 phase, T5 temperature, 

 and the northerly component of the local wind; Figure 26 lends sup- 

 port to the assumed cross- stream transport of warmer water. 



Because of the failure of the Fowey Rocks anemometer (Fig, 2, 

 Table I) it was necessary to derive the north- south and east-west 

 wind components (Fig. 24) from 3 hourly readings measured at the 

 Miami International Airport, 25 Both wind components have been 

 smoothed with a 24 hour running average. The thermistor string data 

 in Figure 24 are repeated from Figure 13. Also in Figure 24 is the 



Special flight conducted on 22 March 1967 by R.B. Stone and 

 T.R. Azarovitz of the Sandy Hook Marine Laboratory, U.S. 

 Bureau of Sport Fisheries and Wildlife. 



330 



