The salinity gradient is apparently of little importance in areas north 

 of the North Atlantic Current. The gradient "be comes important to the south 

 of this current, especially in major currents. Figure 27 shows the fre- 

 quency distribution of At ' based on random observations in the area between 

 the North Atlantic and the North Equatorial Currents. The range of At ' is 

 -3° to + 3° F; more than hair of the salinity gradients were negative. In 

 this area actual stability may be considerably different from that indi- 

 cated by At, especially with negative salinity gradients. Since k(?7) curves 

 correspond to 1 F higher stability indexes, the correction C = -At'-1° must 

 be applied in case of negative salinity gradients. For example, if 

 T -T],qq = 10° F, and the salinity difference in the thermocline corresponds 



to At 1 = -2°, the correction would be C=-2 -1 =-3 , and the actual stability 

 index would be 7° F. This would correspond to stability produced by 

 T -T^qq = 7° F at constant salinity. If salinity increases with depth the 



correction is C sAt'-l ; that is, no correction applies when At 1 = 1°, a 

 1° correction applies when At ' =2 F, etc. 



-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.5 10 1.5 2.0 2.5 3.0 at' 



At = -0.44°F 31 OBS 



A. RANDOM OBSERVATIONS SOUTH OF THE NORTH ATLANTIC CURRENT 



i,,,:,,,::,t„ , ,;, , , , .^L 



II ZTTV - 



r~~ 



B. RANDOM OBSERVATIONS IN THE NORTH EQUATORIAL CURRENT 

 GULF STREAM, AND NORTH ATLANTIC CURRENT 



FIGURE 27. FREQUENCY DISTRIBUTIONS OF DENSITY CHANGES IN THE 

 THERMOCLINE DUE TO SALINITY DIFFERENCES EXPRESSED 

 AS TEMPERATURE DIFFERENCES At' IN °F 



55 



