29 



a vertical meridional plane for a temperature difference of l8°c g^id k 

 equal to 5 car/s is kO million tons/s . This is about l/2 the observed 

 transport of the Gulf Stream (Stommel, 1958)' The average circuit time for 

 water to sink to great depth and rise to the surface again is obtained by 

 dividing the strength of the circulation into the volume of a basin 5 km 

 deep. The right hand ordinate of Figure k indicates that the circuit time 

 is of the order of centuries for the particular case under discussion. 



Further calculations are in progress to test the effect of much larger 

 variations in the Rossby number, and the modifications introduced by the 

 effect of wind acting at the surface . It is hoped that such calculations 

 will bridge the gap between theories of the thermocline and theories of 

 purely wind-driven circulations . In principle there are no difficulties in 

 including salinity in the model which will allow a much more realistic 

 formulation of the boundary conditions. Robinson and Stommel (1959) have 

 emphasized the importance of the vertical diffusion, <, and have pointed 

 out how little is known about the forced convection represented by this 

 parameter. Based on the simplified density- driven model of this study, < 

 is shown to be the principal factor in determining the partitioning of 

 poleward heat flux between the hydrosphere and the atmosphere. 



