The Tropospheric Circulation 659 



stationary. The mathematical basis extended by Haurwitz (1940) affords a relation 

 between the wavelength L, the latitudinal extent D of the stationary disturbance and 

 the velocity of the basic current, U, in the form 



4772^ 1 +L^ID^' 



whereby j8 = 8f/R8<f) = (2aj cos (f>)/R is the change of the Coriolis parameter / with 

 latitude and R the earth radius. 



Analysis of wave disturbances in the South Atlantic convergence region gives an 

 average disturbance length at latitude circle 38° S. of 10-0° or 880 km. The latitudinal 

 extent averages 15° or 1650 km. With these values the velocity of the basic current U 

 is obtained as between 26 and 28 cm/sec. This means that the wave disturbance within 

 the zonal basic current (oceanic West Wind Drift) can be stationary only if such a 

 mean velocity towards East is present. Current charts show an average surface velocity 

 of 25-30 cm/sec. It is thus very probable that the stability of the stationary wave 

 system in the convergence region is due to an equilibrium state between the action of 

 the latitudinal dependence of the Coriolis force and the effect of the curvature of the 

 current trajectories on the horizontal mass transport. The strong solenoidal fields at 

 the boundary between the Brazil and the Falkland Currents may be responsible for 

 the formation of the eastward following series of vortical disturbances inside the general 

 oceanic West Wind Drift. If this is so then the topographical effect of the bottom 

 configuration will be only a supplementary effect which may intensify and probably 

 modify these disturbances. 



Similar phenomena may also develop in the North Atlantic. In the oceanic strip of 

 the North Atlantic Current to the north of the subtropical convergence region there 

 are marked pulsations that also stand out clearly in the charts of the dynamic topo- 

 graphy of the individual isobaric surfaces and in that of the physical sea level. The 

 results of the International Gulf Stream Survey (1938) to the north of the Azores 

 enabled a study to be made of the oscillations in the current system in this particular 

 region. The oceanographic work of the "Armauer Hansen" in 1909, 1925 and 1935-6 

 in the Norwegian Sea off the coast of Norway (Helland-Hansen, 1934, 1939) showed 

 that vortices with vertical axes probably played an important role in the interior of 

 the Atlantic Current. They are also associated with considerable variations in mass 

 transport. It is rather obvious that such variations at fairly long intervals cause reactions 

 in the oceanic phenomena in the Arctic and take influence on climatic conditions in the 

 Scandinavian countries. At present, however, the investigation of these phenomena is 

 only at the very beginning and systematic and synoptic surveys are required in order 

 to obtain a deeper insight into the mechanisms involved. An unusual theory of the 

 variations of the surface circulation in the North Atlantic, especially of the current 

 branches off the coast of Europe, has been given by Le Danois (1934) in his Atlantic 

 Transgressions. He distinguished between three water types in the Atlantic: the 

 tropical, the polar and the continental. The latter has an extremely variable salinity 

 and remains at shallow depths in a relatively narrow band along the coasts. His 

 "transgressions" are periodic movements of variable amplitude carrying Atlantic 

 water of tropical origin, in temporary intrusions into water masses of polar and 

 especially continental origin. The water of the transgressive masses always has a 



