696 Main Features of General Oceanic Circulation and their Physical Exploration 



the opposite direction in the lower branch. The meridional density sections show that 

 this condition is satisfied and the dynamic evaluation of the observational data has 

 given proof of the internal forces acting in the pressure field and resulting from the 

 three-dimensional mass structure. 



In the troposphere the thermo-haline circulation in a meridional direction is less 

 important as compared with the effects of the wind. The air currents therefore set the 

 characteristic pattern for the circulation here and determine its more zonal direction. 

 The western and eastern boundaries set by the continents to the oceans, due to the 

 surface accumulation of water (piling up; Anstau), give rise to gradient currents which 

 besides the wind drift determine the character of the tropospheric oceanic circulation. 



WUst chose a different type of representation to show the oceanic circulation. The 

 surface currents and the deep-sea circulation of the Atlantic were shown in form of a 

 block-diagram in order to arrive at a three-dimensional representation and to elucidate 

 thereby the internal completeness of the circulations (Fig. 332). This survey of the 

 oceanic circulation teaches that the basic causes of the entire oceanic circulation lie 

 in the atmosphere. They are due partly to the vv/>7^ which transfers energy to the water, 

 and partly due to climatic effects on the water masses, especially in polar and subpolar 

 oceanic regions. These then give rise in the first place to the water movements in the 

 deep layers. 



2. Summary of Present Individual Theories and the Prospects of a Comprehensive 

 Theory of the General Circulation Including the Deep Layers 



The existing theory of the wind-driven circulation in closed oceanic basins has been 

 found applicable to individual parts of the ocean, but a comprehensive theory of the 

 wind-driven circulation covering all oceanic parts is so far still missing. It has already 

 been pointed out (p. 583 et seq.) that the highest advanced theory of Munk and 

 Carrier (1950, led at least qualitatively to very reasonable results. Criticism has 

 been expressed primarily on account of the high value of the coefficient of lateral eddy 

 viscosity required in order to explain the intense currents along western coasts. 

 Morgan (1956) in attempts to overcome this drawback has examined the necessity 

 of the inclusion of the lateral eddy viscosity for balancing the wind torque on the 

 water surface. 



The ocean can be represented on a different model from those used previously. 

 In this it is divided into a northern and a southern part, and attention is paid only to 

 the southern one which in itself is subdivided into an interior region and a boundary 

 region adjacent to the western shore. Figure 333 shows these three oceanic subdivisions 

 and the boundaries between them. The figure contains a typical stream line of the 

 circulation, most of which or perhaps all of the stream lines can be expected to pass 

 through all three regions. The equations of motion given for spherical co-ordinates 

 are formally integrated over the depth both for a homogeneous ocean and for a two- 

 layered ocean. From these the approximate equations are derived applicable to the 

 interior region /^ of the currents, that is, to a region sufficiently remote from any 

 coast. They show that all terms which are non-linear in the velocity components as 

 well as the terms giving the contributions of the lateral eddy viscosity are negligibly 

 small there. This is the same result as obtained from the Sverdrup solution. Wind 

 and Coriolis forces are the principal forces in this region. For the boundary region /,, 



