0057 hr. 



0336 hr. 



Figure 15. — The temperature profile from BT pass no. 3 across front 5 (21 April 1961). Cross-hatching shows water that 

 is practically isothermal vertically. The five main bodies of such water (1 - V) are discussed in the text, c = cool side; 

 w = warm side. 



distribution is maintained. There is also a 

 stable density distribution for the E series, 



T-S-8t relationships .-- The complicated 

 form of the interface points to a difficulty in 

 studying such fronts. One cast was made on the 

 warm side, one in the middle, and one on the 

 cool side. Without prior information or the 

 capacity to make a wider hydrocast survey, 

 we supposed that the cast on either side would 

 sample water of only one kind, either warm 

 (Gulf) or cool (California Current) water, 

 whereas the cast in the middle would sample 

 a mixture of both. That this supposition was 

 false is indicated in figures 23 and 24, which 

 show T-S curves (on a 8x field) for the three 

 casts of the B and E series hydrocasts, re- 

 spectively. 



In figure 23, only the curve for the cool side 

 (5B3) clearly fits into one of the three main 

 families given in figures 5 and 6; it corre- 

 sponds to California Current water. If one dis- 

 regards the salinity minima between 15 and 

 35 m. and between 60 and 100 m., the curve 



for the warm side corresponds to a typical 

 curve for Gulf water (fig. 8). The nature 

 of these minima, caused by the California 

 Current water, is evident in the salinity pro- 

 files in figures 19 and 20. The middle curve 

 is similar to that of the cool water in the upper 

 25 m. and to that of the warm water below 

 about 35 m. The zone between 2 5 and 35 m. is 

 the interface between the two kinds of water 

 which apparently are not well mixed, because 

 the curve for the middle station does not lie 

 between the other two. A similar argument 

 holds for the E series curves (fig. 24). 



Cromwell and Reid (1956) stated that a 

 front was an abrupt density change; however, 

 their observations were on temperature only. 

 Knauss (1957) showed a density change of 

 about 0.7 (for ci t:) or 70 cl. ton" 1 (for 8 -p) over 

 about 300 ft. How much of a change, if indeed 

 any, is necessary for a front to be maintained 

 apparently has not been established. Taking 

 Uda's (1959) definition of a temperature front 

 as being between 0.5° C./lO miles and 5.0° 

 C./lO miles (p. 2) and assuming no salinity 



22 



