OCEAN CURRENTS RELATED TO THE DISTRIBUTION OF MASS 1 1 5 



increase in the direction of flow, whereas, between two parallel Q lines 

 indicating transport to the south, the transport will decrease in the 

 direction of flow. Taking this fact into account, one can construct 

 curves between which the transport is constant, but these curves will 

 no longer be exactly parallel to the direction of the transport. Within 

 a small area the deviation will be imperceptible, but within a larger 

 area it w^ill be considerable. 



Between two stations A and B (A lying to the right) at distance L 

 the volume transport is 



f-=?/: 



{ADa - ADB)dz. 



(VI, 37) 



Thus, the volume transport between two stations depends only on the 

 geopotential anomalies at the two stations. It is independent of the 

 distance between the stations, 

 and it is also independent of 

 the distribution of mass in the 

 interval between the stations. 



It is not necessary to de- 

 velop corresponding equations 

 for the mass transport, because 

 this can be derived with suffi- 

 cient accuracy from the volume 

 transport by multiplication 

 with an average density. 



A consideration of com- 

 puted transport and of the 

 continuity of the system is 

 helpful under certain condi- 

 tions in separating currents 

 flowing one above the other. 

 The average transport through 

 a vertical section that represents 

 the opening to a basin must 

 be zero, because water cannot 

 accumulate in the basin, nor can it continue to flow out of the basin. 

 Observations at stations at the two sides of such a section may, however, 

 show transport in or out if the velocity along the bottom is assumed to be 

 zero. If such is the case, the assumption is wrong, and a depth of no 

 motion must be determined in such a manner that the transports above 

 and below that depth are equal. This can be done by plotting the differ- 

 ence AD^ — ADb against depth, computing the average value of the 

 difference between the surface and the bottom, and reading from the 

 curve the depth at which that average value is found. This depth is then 



Fig. 28. Determination of the depth above 

 and below which the transport between two 

 stations, A and B, is equal. 



