The Tropospheric Circulation 615 



circulation over the southern part of the North Atlantic. In winter the strong anti- 

 cyclonic circulation over the ocean increases the inflow into the Gulf Stream and in the 

 summer there are more frequent southerly winds and a greater part of the water masses 

 of the North Equatorial Current is blown directly into the Gulf Stream without passing 

 through the Carribean and the Florida Strait. Both of these effects intensify the Gulf 

 Stream. It is not improbable that the aperiodic variations from year to year wil 

 provide an extremely good indicator of the variations in the intensity of the atmos- 

 pheric circulation over the Atlantic. 



The most recent investigations of the Gulf Stream have the main goal to obtain 

 accurate detailed surveys of the current at short successive intervals, that is, to obtain 

 quasi-synoptic surveys of an extended part of the current. Such methods of investiga- 

 tion need in the first place the rapid gain of the structure of the water masses down to 

 great depths, while the survey vessel is under way whereby the position of each station 

 has to be fixed with accuracy. Both of these conditions can be satisfied by the more 

 recent methods used on board of the oceanographic survey vessels. Quasi-synoptic 

 surveys of this type have been made for the Gulf Stream down to 275 m depth between 

 Cape Hatteras and the Newfoundland Banks but at the present time only few of them 

 exist. They give a very clear picture of the complicated course of the current and show 

 particularly the very considerable local variations in form of meandering wave patterns 

 of large amplitude at both sides of the current. Occasionally a water mass in one of the 

 amplified troughs and ridges is cut off from the main current to form finally a large 

 vortex which will be cyclonic on the southern side and anticyclonic on the northern 

 side. These vortices are different from the smaller size eddies in the shearing zones of a 

 turbulent current that also occur in the Gulf Stream (Spilhaus, 1940). Furthermore, 

 the synoptic surveys have shown that the current velocity in the core may be intensified 

 up to about 4-5 knots over a relatively narrow band (about 10-15 miles wide) a little 

 inside the left-hand boundary of the current; in the counter current the velocity reaches 

 3-4 knots. It is not surprising that the approximate and mean values obtained by the 

 previous methods of investigation gave only low velocities. 



The first multiple ship survey of the Gulf Stream area between Cape Hatteras and 

 the Newfoundland Banks was made during 6-23 June 1950. Six oceanographic survey 

 vessels took part in this "Operation Cabot" and they obtained an almost synoptic 

 survey of the Gulf Stream down to 275 m which gave a clear picture of the compli- 

 cated nature of the current. Figure 287 presents the course of the current as character- 

 ized by the mean temperature of the upper 200 m layer. According to this survey the 

 Gulf Stream is a remarkably narrow band about 40-60 km wide and sharply separated 

 at the edges from the surrounding water masses. The early view of Franklin of the Gulf 

 Stream structure was confirmed, and certainly in the sector between Cape Hatteras 

 and the Newfoundland Banks the Gulf Stream resembles a "river in the ocean" 

 rather than a broad diffuse ocean current. The current does not, however, follow a 

 straight line, but instead flows in long waves which are usually of small amplitude but 

 take occasionally quite a large amplitude. Successive surveys have shown that these 

 long lateral waves move slowly eastwards with increasing amplitude. Figure 288 shows 

 the position of the Gulf Stream at the beginning (8 June) and the end of the operation 

 21 and 22 June). The current core therefore tends towards a meandering behaviour 

 of a pronounced character. The amplitude of these meanders may increase so much 



