Main Features of General Oceanic Circulation and their Physical Exploration 701 



these circulations are now superimposed on each other in Fig. 335f. Particularly 

 noticeable is the absence of the Brazil Current and the intensity of the Gulf Stream, 

 even though the vertical integrated transport is the same for both currents; but 

 according to the interpretation suggested by Stommel the current in the deep layers 

 opposes the Gulf Stream but flows in the same direction as the Brazil Current. The 

 Gulf Stream is reinforced by the thermo-haline component but the Brazil Current is 

 so weakened that it almost disappears. This picture of the circulation of the Atlantic 

 Ocean is undoubtedly interesting and instructive and will stimulate further thinking 

 and conclusions which, however, must be supplemented by corresponding further 

 oceanographic surveys and current measurements in the deeper layers of the oceans. 



3. Model Experiments on Stationary Planetary Flow Patterns 



Thoughts about the physical fundaments of the oceanic circulation lead to an 

 analysis of simple flow patterns in a homogeneous fluid layer: (1) of uniform depth on 

 a rotating sphere and bounded by meridional barriers; (2) of uniform depth on a 

 ^-plane (plane with j8=2a» sim ^ — const, see p. 556) and bounded by barriers running 

 north-south; (3) of radially non-uniform depth on a rotating plane and bounded by 

 radial barriers. Analyses of this type and associated model experiments have been 

 made recently in a very instructive form by Stommel, Arons and Faller (1958). 

 Although these investigations cannot be regarded as concluded they, nevertheless, 

 throw some light on the physical processes operating in the oceanic circulation, so 

 that it seems appropriate to present the main contents of these investigations here. 

 The essential elements which define the simplified regime described above are: 



(a) the flow in the whole layer is steady and geostrophic except and only; 



(b) at the western boundary where a narrow intense western boundary current is 

 permitted to depart markedly from geostrophic conditions, and moreover; 



(c) this system which would otherwise be at rest is driven by a distribution of fluid 

 sources and sinks representing various diff'erent driving agents such as the wind. This 

 is no real restriction. 



Some of these analyses and thoughts were tested by experiments in a pie-shaped 

 sector of a fluid basin rotating counter-clockwise. The free surface was a paraboloid 

 cylinder with vertical axis, concave upwards. The undisturbed depth varied radially 

 from a minimum at the centre to a maximum at the outer rim. The top was covered 

 with a sheet of glass in order to prevent the air in the room exerting any stress on the 

 surface. After rotation for some time the fluid is completely at rest relative to the basin. 

 There will be a component of flow radially outward (or inward) in the interior of the 

 fluid only if there is a local fluid source (or sink). Components of geostrophic flow 

 along circles of constant radius are permissible without divergence except where 

 blocked by radial barriers. Figure 336 shows possible variations in the relative distribu- 

 tion of sources and sinks and the currents that would be expected in each case. The 

 point source @ and sink of equal intensity were placed : 



(a) near to the eastern boundary of the sector at the end of radii of diff'erent length; 



(b) as an isolated source only at the apex of the sector. Since no point sink is pro- 

 vided the free surface will rise uniformly; 



(c ) as an isolated source at the western edge of the rim. 



The current flows along the shortest path to the western boundary of the sector. 



