132 Meanders 



is conceived in the model of the two-layer meander theory. The meanders 

 might conceivably be formed and forced to great amphtudes by the wind 

 without the assistance of any instabihty. In the weather maps for the 

 months of May and June, 1950, there is no marked wind pattern that could 

 be directly forcing the meander pattern observed in the Multiple Ship 

 Survey, and no violent storms over hmited areas are noted. 



If we consider the eddy formation observed in the course of the Multiple 

 Ship Survey of June, 1950, we note that the Stream is continuous and re- 

 latively straight both upstream and downstream of the eddy at 60° W. 

 (fig. 40). One wonders whether there was any marked variation in the 

 component of surface wind stress along the current at 60° W. From the 

 North Atlantic surface vnnd maps made up at La Guardia Field it is possible 

 to obtain the daily ship reports for every 5° along the 40° N. circle of latitude 

 from 70 to 50° W. If we then compute five-day means of the surface wind 

 stress we find that there was a region of low dowTistream stress west of 

 60° W., and a region of fairly high stress east of 60° W. This pattern per- 

 sisted for almost thirty days before the survey of the eddy. The results are 

 given in table 7, the selected coefficient of shear stress being 2 x 10~^. 



TABLE 7 



Mean Component of Daily Wind Stress in Downstream Direction 

 FROM May 15, 1950, to June 19, 1950, on 40° N. Latitude 



Longitude 70° W. 65° W. 60° W. 55° W. 50° W. 45° W. 



Eastward computed wind) _ ^.^^ q,^^ _ ^.^ga + 0-30 + 0-20 + 0-40 



stress (dynes/cm.'') ) 



• Position of eddy. 



It is natural to wonder whether the coincidence of the eddy with the 

 abrupt change in wind stress is simply a chance coincidence, or expresses 

 a cause-and-efFect relationship between the eddy and a monthly mean 

 feature of the wind stress. If the change in wind stress occurs in association 

 with a change in mean current velocity (towed-electrode data on the 

 Multiple Ship Survey of 1950 indicate that east of 60° W. the current 

 velocities fell to about 50 per cent of the velocities to the west), the section 

 of the Stream at 60° W. could act as an important block to passage of 

 meanders. Meanders that were arrested at such a pomt in the Stream might 

 easily grow into eddies. This is all conjecture, of course; other explanations 

 are possible. For example, in Tolstoy's bathymetric chart (see fig. 16) is 

 a series of sea mounts, some as shallow as 1500 m., in the region where the 

 Gulf Stream reaches 65 to 60° W. longitude. It is conceivable that these 

 sea mounts, and other uncharted ones in the region, are the perturbing 

 cause of the breakdown of the Stream in this area. Bottom features are 



