19 



INTRODUCTION 



An essential factor in determining the climate of the temperate zone 

 of the Northern Hemisphere is a strong transfer of heat from the ocean to 

 the atmosphere during the autumn and winter. Part of this heat (roughly- 

 half in the North Atlantic) has been received by the ocean during the 

 previous spring and summer. The remainder is supplied by the lateral 

 transfer of heat by ocean currents from other areas which receive a net 

 surplus of heat on an annual basis. Detailed studies of the heat balance 

 of the ocean offer one means of making a quantitative estimate of heat 

 transfer. In Figure 1 estimates of the poleward transport of heat based 

 on heat balance maps of Sverdrup (1957) > Budyko (1956), and Albrecht (1960) 

 are compared with direct measurements of energy transport in the atmosphere 

 made by Starr and White (195*+)' Many features of the estimates in Figure 1 

 differ, but there is general agreement that a significant poleward transport 

 of heat does occur in the Northern Hemisphere, the greater part of which 

 takes place in the North Atlantic. A discussion of these estimates is 

 given in an earlier paper (Bryan, 1962). 



Most of the present-day knowledge of ocean circulation is based on 

 detailed measurements of temjjerature and chemical properties. While this 

 data is very important in tracing the origin and movement of water masses, 

 it is difficult to use it directly in studying heat transfer by ocean 

 currents. Mathematical models are needed to relate ideas gained from 

 water mass analysis to the heat balance of the ocean and large-scale inter- 

 action with the atmosphere. 



Recently, considerable attention has been devoted to the problem of 

 the maintenance of the oceanic thermocline (Robinson and Storamel, 1959, 

 Welander, 1959, Stommel and Webster, 1962, Blandford, 1965). These studies 

 are directly relevant, since they deal principally with the manner in which 

 heat is transferred from the surface to lower levels in the ocean. The 

 steady- state solutions of the thermocline theories are intended to apply 

 to the subtropical region of ocean basins, away from strong boundary 

 currents. A disadvantage of these solutions is that they cannot easily 

 be extended to include subarctic gyres and boundary regions . In particular, 

 difficulties exist in treating regions in which the stratification is 

 unstable, or nearly so. 



These thennocline investigations form the point of departure for the 

 present study. Solutions for an entire closed basin are obtained by 

 numerical methods. To include regions in which convection may ocur, the 

 vertical heat diffusion coefficient is a constant as in the model of 

 Robinson and Stommel (1959)- For unstable stratification this coefficient 

 is effectively infinite. Since small, but significant departures from 

 geostrophy exist in strong currents near lateral boundaries, the model 

 includes the momentum equations in nearly complete form, without the 

 geos trophic approximation. 



