The Stratosphere Circulation 693 



the Mediterranean waters flow with considerable velocity and due to the influence of 

 the Coriolis force keep especially in the Spanish Bay to the northern side. Finally, 

 they pass around Cape San Vincent while steadily sinking and still keeping close to 

 the Portuguese coast past Cape Finisterre as far as the Bay of Biscay. Observations 

 show that this is the first stage of spreading; and the whole process of spread behaves 

 exactly in the way described on p. 524 et seq. and in Fig. 251a. The second stage of 

 spreading starts from this tongue of Mediterranean Water off the Portuguese coast. 

 Due to the much lower velocities the Coriolis force is no longer effective and the 

 influence of lateral and vertical mixing becomes dominant. The picture presented 

 in Fig. 330 is thus an effect of mixing processes and Defant (1957) has shown that 

 a lateral eddy viscosity coefficient of about 5-5 x 10'' cm^ sec~^ is quite sufficient to 

 explain the lateral spread. A precise account of the whole process, however, requires 

 systematic series observations and current measurements along suitable sections. 



The Indian Ocean also shows in all meridional salinity sections, starting from the 

 Gulf of Aden in the north-west, an unmistakable effect of the highly saline waters 

 spreading out from the Red Sea through the Gulf of Aden into the Indian Ocean. In 

 this case also the effect of this outflow is of decisive importance for the stratospheric 

 circulation. 



It is only to be expected that there will be seasonal variations in the extent of the 

 spread of the water from the subtropical adjacent seas, since the outflow in itself is 

 known to be subject to rather strong variations of this period (p. 503). The observa- 

 tional data available at the present time do not allow to show the influence of such 

 seasonal fluctuations in the open ocean. 



Investigations of the extent of spread of the Mediterranean Water show the great 

 importance of the subtropical adjacent seas for the deep-sea circulation. Due to the 

 high density of the water masses flowing with the deeper currents into the open ocean 

 the layers of the stratosphere will have a sinking tendency and form a source for the 

 onset of large-scale circulations. This source is at least as important as the convection 

 acting from the sea surface downward in polar and subpolar seas. These inflows are 

 also important because of another reason. Mixing of the water masses transported 

 by these currents with tropospheric water masses above causes an interaction between 

 the oceanic troposphere and stratosphere, and direct exchange between the two main 

 layers of the ocean is probably restricted to these places. While the Atlantic and Indian 

 Oceans are affected by subtropical adjacent seas, the outflow from which considerably 

 intensifies the circulation in the uppermost part of the oceanic stratosphere, there are 

 no adjacent seas of this type connected with the Pacific. Consequently, the Pacific 

 lacks the large meridional contrast in salinity of the deeper layers which provides the 

 driving force for a stronger circulation. 



