116 Nonlinear Theories — Inertial 



theory which also takes account of the earth's rotation. However, it does 

 seem likely that the efiFect of the earth's rotation will not radically alter the 

 internal Froude criterion: the real Gulf Stream approaches critical internal 

 Froude flow, and it is quite conceivable that as a result there are internal 

 hydraulic jumps and other interesting smaU-scale phenomena, such as 

 obUque shock fronts, along the left-hand, inshore, edge of the Stream. 



THE BOUNDARY-LAYER TECHNIQUE 



Although Munk's first theoretical treatment of the wind-driven ocean 

 currents involved complete analytical solutions for the entire ocean, he 

 quickly reahzed that, since the viscous terms (the highest-order derivatives) 

 were important only near the coasts, the problem could have been solved 

 more simply by using Sverdrup's (1947) simple first-order (in transport 

 function) equations for the central parts of the ocean, and fitting a viscous 

 boundary layer to the solution for the central regions at those places near 

 the coasts where higher-order terms become significant. In the more com- 

 pUcated cases of triangular ocean basins this alternative procedure was 

 adopted (Munk and Carrier, 1950). The ocean is thus divided into two 

 regions : one, which we shall call the interior region, which includes all central 

 regions of the ocean, and which is determined by the form of the wind stress; 

 the other, the boundary -layer region, in which the higher-order terms 

 are important. Actually, so far as the boundary layer is concerned, it does 

 not matter what physical process produces the interior current regime. As 

 long as some interior solution exists, be it uind-driven or thermodynamicaUy 

 produced, a linear viscous boundary layer can be fitted to it on the western 

 coast. 



We shall take advantage of this natural separation of the problem into 

 two parts in our formulation of the Gulf Stream as an inertial boundary 

 layer. Furthermore, we shall Hmit the application of the theory to the 

 region bounded by latitudes 10 and 35° N. , the region of formation or growth 

 of the Gulf Stream. North of 35° N. latitude the Stream breaks away from 

 the coast, and we enter the region of decay. This region is not dealt with in 

 either the Morgan theory or the Charney theory, both of which are dis- 

 cussed in the next section. 



THE INERTIAL THEORIES OF MORGAN 

 AND CHARNEY 



In the latter half of 1954 1 made several futile attempts to construct a theory 

 of an inertially governed Gulf Stream that would provide a more complete 

 solution than the partial solutions described above. I confided my troubles 



