In previous bulletins of this series the position of the outer 

 boundary of the North Atlantic Current water in the Grand Banks 

 region has been reported and related to factors assumed to be asso- 

 ciated with the relative strengths of the North Atlantic Current 

 and the Labrador Current. The boundary has been taken as 

 the horizontal projection of the line of intersection of the isothermal 

 surface of 6° and the isohaline surface of 34.95o/qo. As the boun- 

 dary is characteristically sinuous, its position has been described 

 by the area between it and reference rhumb lines made up of the 

 45th parallel from the boundary to 49° W., the 49th meridian 

 thence to 43° N., and a line from 43° N., 49° W., through 42° N., 

 47° W., extended to the boundary. To compensate for the effect 

 of the Labrador Current on the position of the boundary, the area 

 was adjusted by the subtraction of 10,000 square kilometers for 

 each million cubic meters per second volume of flow of the Labrador 

 Current past section U. The adjusted area was assumed to repre- 

 sent effects on the position of the boundary the causes of which 

 were associated with the North Atlantic eddy. A further assump- 

 tion was made that changes in the streng-th of the Gulf Stream 

 were proportional to changes in the difference in sea level between 

 Bermuda and Charleston, S. C. Monthly mean sea levels at each 

 of these stations, corrected to normal barometric pressure for the 

 station, were used to derive a value for the change in difference in 

 sea level by taking sea level at Charleston minus the departure 

 from average at Bermuda. Over the period from 1934 to 1941 a 

 good correlation was found to exist between the sea level difference, 

 Charleston, minus the Bermuda departure, and the adjusted area 

 in the Grand Banks region 13 1/2 months later. During this period 

 27 surveys gave the relation 



A = 6.8 (i:^- 5.07) +1.34 

 where A is the adjusted area in units of 10,000 square kilometers 

 and H is the sea level difference Charleston minus the Bermuda 

 departure, in feet. 



Since resumption of the oceanographic program of the Interna- 

 tional Ice Patrol after World War II eight surveys of the Grand 

 Banks region have been made, one in 1948, two in 1949, three in 

 1950, and two in 1951. These surveys show a poorer correlation, 

 with three of the eight cases showing a discrepancy as to sign. 

 The differences between the post-war series and the earlier series 

 are large enough to suggest a revision of the above expression for 

 the relationship between the adjusted area and the sea level dif- 

 ference. 



Before deriving a new expression for A, consideration was given 

 to the changes in conditions and to their physical significance. If 

 a true relationship exists, it should apply to both series of observa- 

 tions. The fact that the relationship depends on the departure 



44 



