SOME CHARACTERISTICS OF SEA WATER STRUCTURE 651 



It is not necessary to calculate a at every observation, rather the 

 mean values of temperature and salinity may be evaluated similarly to 

 Equation 5, and the mean value of a computed from them in the usual 

 way. Having evaluated a in each zone, these may be treated in the 

 usual manner to discover the dynamic height. 



This procedure reduces the number of calculations and is probably 

 more accurate than the usual computations based on linear interpola- 

 tion between observations. 



Deductions Regarding Mechanism and Structure 



Origin and Behaviour of Water Masses 



It has long been recognized that sea water occurs as masses, each 

 having characteristic values of temperature, salinity or other properties. 

 Usually these water masses are generated in some locality such as the 

 Arctic, the Tropics, estuaries, etc. As they move out from the sources 

 they over-ride the more dense, or under-run the lighter waters that are 

 encountered enroute. 



It is supposed that a water mass must be subject to internal turbu- 

 lence if it is moving at an appreciable rate, since the Reynold's Num- 

 ber in all natural flows far exceeds the threshold of turbulence. Each 

 water mass tends to pursue its own course and speed and so is inde- 

 pendent to some extent. Consequently, there is a region of boundary 

 turbulence resulting from the shear between water masses. 



Turbulence, regardless of its course or location, may be regarded 

 as the random exchange of fluid elements normal to the plane of mo- 

 tion. In the vertical direction it is statistically similar to diffusion, and 

 results in exchange of properties through a zone. 



This is indicated by the derivatives of the observed relation (Equa- 

 tion 1) 



-^ = ^ (6) 



dz z ^ ' 



where z refers to the total depth from the surface. This implies that 

 the limit of every zone is virtually at the sea surface. 



The slope constant (k), as shown in Equation 2, depends only on 

 the thickness of a zone, and the difference of the values of the properties 

 at the upper and lower limits. It describes the physical character of 

 the zony at the instant of observation, and is not, by itself, indicative 

 of the mechanism by which the zone is created. It is possible to ima- 

 gine a situation where there were two water masses with identical turbu- 

 lence (energy) characteristics. An upper, boundary, and lower zone 

 would be formed, each having a different gradient of properties. '1 he 

 mechanism of mixing is revealed by the form of the relation, and the 

 source of the exchange is truly at the surface. 



