702 Main Features of General Oceanic Circulation and their Physical Exploration 



Fig. 336. (a) Diagram of circulation induced in a rotating sector by a source ® and a 

 sink positioned as shown, (b) Sketch of flow pattern expected with source @ at apex of 

 sector, surface of fluid rising uniformly, (c) Sketch of flow pattern expected with source © 

 at western edge of rim, surface of fluid rising uniformly (according to Stommel, Arons and 



Faller, 1958). 



There a narrow intense western boundary current develops always, and in (a) after 

 reaching the outer rim the water returns in another zonal geostrophic current to the 

 sink 0. In (h) there develops a narrow intense western boundary current and in a 

 surprising way the basin fills up from the rim although water is added at the apex. 

 Even more surprising is case (c). The sector is allowed to fill up from the isolated source 

 at the western edge of the rim. The interior geostrophic flow is again directed towards 

 the centre, but the interior radial transport is so large that it feeds at the apex a narrow 

 western boundary current which flows back towards the source ©. 



The theory of these processes explains convincingly the nature of the water transports 

 and explains the formation of the western boundary current which governs the process, 

 though without, however, giving any detailed dynamic explanation. To check and to 

 illustrate the principles of the theory and quantitative ideas concerning the flow in the 

 rotating sector, Stommel, Arons and Faller have made rotational experiments in a 

 tank with the form of a truncated sector of 60° width. In Fig. 337 are shown the 

 experiments corresponding to those of Figures 336a and c; these confirm clearly the 

 qualitative and theoretical argument. 



The application of the results of such experiments to phenomena which can be 

 observed in the ocean, is readily understood and their further development with the 

 guidance of carefully chosen theoretical models should contribute much to an under- 

 standing of the phenomena occurring in ocean currents. 



4. The Transient Response of an Ocean to a Variable Wind Stress 



In all theoretical investigations of the ocean circulation induced by zonal winds it 

 has been assumed that the effect of the wind does not change with time (is constant 

 with time). It is known, however, that this is true only for a first approximation and 

 attempts have occasionally been made to study the effect of a wind that changes with 

 time on vertical structure and circulation of an ocean. A study of the time-dependent 

 wind-driven circulation in a homogeneous, rectangular ocean has been given by 

 Veronis and Morgan (1955). Already somewhat earlier the problem has also been 

 considered by Ichye (1951). They start essentially from the same equations of motion 



