The Geophysical Structure of the Sea 309 



5. The Dynamical Method of Preparation of Oceanographic Data 



The oceanographic measurements made at a station give the thermo-haline structure 

 of the sea at this place in terms of temperature and salinity at definite depths. The 

 dynamic evaluation of this data includes the determination of the density and the 

 specific volume in situ at definite standard depths, and, in addition, the calculation 

 of the pressure for given depths and the dynamic depths at given pressures, respectively. 

 The starting point for this is the integrals of the two equations (IX. 9) which for 

 practical calculation are expanded into sums of small intervals 



and i) = ^^' JA + ^'^ft + ... (IX.13) 



For this it can be assumed as a first approximation that the dynamic depths and the 

 pressures are expressed by the same values as valid for the geometric depths. This 

 first approximation already gives sufficient accuracy in most cases. The most detailed 

 tables for the calculation of these values are those given by Bjerknes and co-workers 

 (1910). In these tables it is assumed 



Ps, t, D = Pzb, 0, i> + ^s + ft + ^s, t + ^s. D + ((,D 



and in addition to the basic values for the homogeneous oceans (Table 1 1 0) six tables are 

 also given for the numerical determination of the six terms on the right-hand side. 

 One term, e^, ;, />, is usually so small that it does not have to be taken into consideration. 

 Hesselberg and Sverdrup (1914-15) have simplified the calculation of the density 

 in situ by introducing the value of ot, which is known from 



Ps,uo=l -}- 10-=^ a,. 

 Putting 



P35, 0,D= P35. 0. + ^ D 



gives 



Ps./.o= 1 + 10-^c7,.fl, (IX. 14) 



where 



(^t,D 10-^ = (Tt \0-^ -f ej) -i- €,,D + et,D. 



If Gt is known then only three tables are required instead of six for the calculation of 

 the density in situ. 



The calculation of the specific volume and especially the specific volume anomaly 

 can be simplified in the same way (Sverdrup, 19336): 



««, /. p = a35. 0. p + S. where S = 8, + 8^ + 8,, < + 8,, p + 8^, ^ 



Putting 



S. + 8, + 8„, =A,,t 

 gives 



8 = J„, + S„p+ 8,.^. (IX.15) 



The first term can be readily found from ct^ and then 



a. X 10-3 



A..,= \ 



I + Gt X 10- 



