594 



The Tropospheric Circulation 



2. The Tropospheric Circulation of the Tropical and Subtropical Oceans 



The tropical and subtropical circulation of the oceanic troposphere is dominated 

 by the enormous water transports of the North and South Equatorial Currents. 

 They determine dynamically the position of the tropical and subtropical discon- 

 tinuity layer. Its depth in the Atlantic between 25° N. and 25° S. is shown in Fig. 269. 

 From a depth of more than 200-300 m in western Ross-latitudes of both hemispheres 



Fig, 



269. Depth (m) of the tropospheric discontinuity (thermocline) in the Atlantic Ocean 

 between 25° N. and 25° S. 



the discontinuity layer rises towards the southeast to a depth of 40 m in the Northern 

 Hemisphere and towards the north-east to a depth of 20 m in the Southern Hemi- 

 sphere. Between the equator and about 6°-10° N. these rising slopes are separated by 

 an east-west depression extending into the Gulf of Guinea. This striking arrangement 

 of the topography of the discontinuity surface is a direct consequence of the equatorial 

 currents on either side of the equator; because of dynamic reasoning these currents 

 also determine the rise of the discontinuity layer towards the equator. Up to about 

 6° to 10° N., the depth of the density transition layer is associated with the Equatorial 

 Counter Current and its further extension (the Guinea Current). For a connection 

 between the state of motion of the water masses above and below the discontinuity 

 and the topography of the discontinuity layer see p. 463 et seq. Further information on 

 the conditions of motion in the individual layers of the oceanic troposphere can be 

 gained by investigation of the striking salinity maxima near the discontinuity layer, 



