626 



The Tropospheric Circulation 



in this way a decline of the physical sea level along the eastern and western sides. This 

 would be the geodetically determined rise between Florida and Nova Scotia. 



All cross-sections through the Gulf Stream show a strong stratification in the upper 

 layers but beneath this where the current is weak it is less pronounced. It is to be 

 expected that there will be a layer of no motion just beneath this layer. Figure 294 given 

 by Neumann (1956) shows the position of the zero level d in an "Atlantic" cross- 

 section through the Gulf Stream. The latter one indicates clearly the form given in 

 Fig. 292 with shallow depth along the left-hand edge of the current, a strong down- 

 ward slope below the maximum transverse density change and uniform larger values 

 at the right-hand edge. Tliis distribution is characteristic of all sections through free 

 jet currents in the ocean. Neumann has also shown that over the whole of the moving 

 layer from the surface down to the depth of no motion d there are only slight changes 

 in the mean density distribution. There exists thus in a first approximation no trans- 

 verse density gradient. This means that the entire current system is an equivalent to 

 that of a two-layered model in which there are two water bodies, one on top of the 

 other with an internal boundary surface between. Thus as a first approximation the 

 Gulf Stream can be regarded as an equivalent-barotropic system in which the boundary 

 layer slopes downward from the left-hand to the right-hand edge. Figure 295 shows the 



1231 1230 1229 1228 1227 



1226 



500 



1000 



1500 



2000 



50km 



Fig. 295. Velocity distribution in the "Atlantis", section Chesapeake Bay-Bermuda, April 

 1932 {d, lower limit of the current system). 



velocity distribution calculated from the mass field (Fig. 295) for a cross-section at the 

 lower limit of the current system d. For the vertical shear under equivalent-barotropic 

 conditions as a first approximation one obtains 



(XIX. 16) 



dv g dp 



dz f p 8x' 



where p is the mean density of the current layer. If as on p. 608 t, denotes the surface 



