Basic Principles of the General Oceanic Circulation 579 



in the water masses of the stratosphere the boundary separating it from the tropo- 

 sphere will slope in the opposite direction in accordance with the compensation 

 principle mentioned above. At this internal surface there is a stratospheric ridge at the 

 equator and a trough in Ross latitudes. Thus in the Atlantic the boundary is at 300 m 

 depth at the equator and at 700 m depth in Ross latitudes: ^2 = 400 m at 30° latitude. 

 With the observed values pj = 1-0260, pa = 1-0275, equation (XVIII. 1) gives the rise 

 in physical sea level from the equator to 30° latitude as approximately 58 cm; an order 

 of magnitude which agrees with the dynamic computations of the absolute topo- 

 graphy of isobaric surfaces. At 20° latitude where the physical sea level has a rise of 

 35 cm and p^— pi = 25 x 10~^, the decline of the tropospheric transition layer is 

 140 m, also in good agreement with observation. In this circular vortex there is no 

 circumstance which would give rise to an equatorial counter current. 



Winds in the atmospheric West Wind Drift are of rather variable character; but 

 only in the general average westerly winds predominate. In the top layer they produce 

 an oceanic West Wind Drift and a consequent piling up of water cum sole towards 

 the subtropics, which counteracts the accumulation of water associated with the equa- 

 torial currents. There is thus an accumulation of water from both sides in a belt around 

 the earth. On the equatorial side of this belt water flows westward, on the polar side 

 eastward. This is the subtropical convergence region, one of the most important bound- 

 ary lines of the oceanic circulation. Corresponding to the downward slope of the 

 physical sea level towards the poles there is an upward slope in the internal boundary 

 surface between the troposphere and the stratosphere from its deepest position in the 

 subtropics to the surface of the ocean at the polar front {polar convergence). This is the 

 60° N. and S. it must rise 700 m over 30 degrees of latitude. When pi = 1.0265 and 

 P2 = 1.0275 the physical sea level will have a slope of 68 cm according to equation 

 (XVIII. 1). If the physical sea level at the equator is taken as zero, it will have an eleva- 

 tion of 58 cm in the subtropics and a depression of 10 cm at the polar front. The 

 prevailing easterly winds around the polar caps produce a westward drift current 

 (polar currents) and there is a corresponding rise in the sea level from its lowest 

 position at the polar front. 



Although the circulation system shown in Fig. 262 is only schematic, it shows the 

 main features of the surface circulation system clearly, particulary as in the Pacific 

 and in the circumpolar Antarctic waters where it is not strongly disturbed by the 

 presence of continents. With a circular vortex of this type under stationary conditions 

 no vertical movements are to be expected. A deep-sea circulation will therefore not 

 develop and the three horizontal current zones (the Equatorial Currents, the West 

 Wind Drifts and the Polar Currents) can be explained as solely caused by winds. 

 The topography of the physical sea level, of the internal boundary surface between 

 the troposphere and the stratosphere and of the tropospheric transition layer of the 

 tropics and subtropics are coupled with these zones. 



6. The Influence of Meridionally Oriented Coasts on the Oceanic Circulation 



The oceans are bounded everywhere on their western and eastern sides by conti- 

 nents which act as meridional barriers to the oceanic circulation and prevent the 

 formation of a simple circular vortex around the earth. At the meridional barriers 

 the equation of continuity must be satisfied, and in order to allow the conservation of 



