Ocean Currents in a Non-homogeneous Ocean 505 



At the present time this dynamic method of computation is used extensively every- 

 where. It is used particularly for the dynamic evaluation of widely varying vertical 

 profiles and gives information on the water displacements at right angles to the profile, 

 The scientific treatment of observational data carmot be considered complete if it 

 does not include dynamic methods. Few complete evaluations exist at present of the 

 relative and absolute topographies of the isobaric surfaces for larger oceanic regions. 

 The available data is in most cases insufficient for this, since it requires a reasonably 

 uniform network of stations over a rather extensive area. Of surveys of this type which 

 have been made may be mentioned : the regular series observations of the International 

 Ice Patrol Service near the Newfoundland Banks; those made by the "Marion" and 

 "General Green" expeditions in Davis Strait and the Labrador Sea by Smith, Soule 

 and Mosby; in the eastern North Atlantic by Helland-Hansen and Nansen; in the 

 Caribbean Sea and the Cayman Sea by Parr; in the Antarctic Ocean by Deacon; in the 

 Gulf Stream area by Iselin and Dietrich; in the area off the Californian coast by the 

 Scripps Oceanographic Institution La Jolla and in the area east of Japan. A complete 

 dynamic evaluation of the observational material accumulated for the whole of the 

 Atlantic is given in the "Meteor" report. The results of these surveys will be discussed 

 later in connection with the flow conditions in individual oceans. 



The observational data for investigations of this type must satisfy certain demands. 

 In the first place they must be as homogeneous as possible and this can only be achieved 

 by a collection of the data according to uniform principles, and by a critical dynamic 

 evaluation using standard methods. Strictly speaking, the data should be collected 

 synoptically, but this cannot be done by expeditions using only a single vessel. For 

 larger oceanic areas it is customary, if there are no pronounced seasonal variations in 

 the current conditions, to combine all the available series observations and consciously 

 abandon the ideal of simultaneous observations. It lies in the nature of such a pro- 

 cedure that a representation of the phenomena in this way cannot, of course, show 

 individual details and the resulting charts only contain the main features. Repetition of 

 such surveys in the same area shows to what extent the topography remains stationary. 

 More importance will certainly be attached in the future to the need for simultaneous 

 synoptic observations. This, however, will require a greater number of oceanographic 

 vessels doing survey work in groups at the same time, or simultaneous recording 

 instruments put out into the open ocean to form a synoptic network to be collected 

 later. 



Observational data, as well as being homogeneous and synoptic should satisfy a 

 further requirement which is equally not easy to fulfil. This is the density in the station 

 network necessary for each oceanographic survey. If only the major features of the 

 phenomena are required, then the interval between stations customary for oceano- 

 graphic expeditions (50-150 nautical miles) seems to be sufficient. Data collected on 

 this basis will not give refined details — neither in the distribution of the oceanographic 

 factors nor in topographic charts. It also will give no idea of differences between small 

 oceanic areas. It is, however, difficult to specify just how dense the network of stations 

 should be in order to obtain a representative picture of oceanographic conditions. 

 These questions are closely connected with changes in the oceanographic factors with 

 time and it is obvious that these variations cannot be studied by a single oceanographic 

 vessel alone. These essential questions of oceanography were dealt with in detail by 



