PROCESSING PROCEDURES 



17 



74- 



25.00-- 



T=4.55 



26.00 



3 



^ 3- 



27.00-- 



0-, = 27.27 



28.00- 



32 00-- 



33 00-- 



z 

 . < 



34.00-- 



S=34.40-- 



35.00 - - 



Figure 19. — Nomogram for determining "Sigma-T," a,, from temperature and salinity. 



insignificant error in AZ> introduced by this 

 substitution is negligible, amounting to 1 per- 

 cent or less. 



Procedure in computing AD at each station is 

 as follows. The specific volume anomaly, S, at 

 each depth is calculated by one of the methods 

 previously outlined. The mean specific volume 

 anomaly, d, for each depth interval may be 

 determined by averaging the two bounding 

 values. Multiplying this mean value, 6, by the 

 depth interval (which corresponds essentially 

 to the pressure interval between depths) gives 

 the anomaly of dynamic height, AD, for each 

 small depth (or pressure) layer. The required 

 total AD for each station is obtained by adding 

 the anomalies of dynamic height, AD, from the 

 selected reference level of no motion to the level 

 at which relative currents are to be computed. 



The final step in computing the current pass- 



ing between two stations is to equate the forces 

 acting along the sloping isobaric surface be- 

 tween stations, and solve for the velocity. The 

 force of gravity acting downslope is expressed 

 by the difference in the anomalies of dynamic 

 height at the two stations divided by the dis- 

 tance between stations. Since the computation 

 of AD was based upon pressure in decibars, 

 rather than the standard unit centibars, a factor 

 of 10 is necessary to convert the expression to 

 meter-ton-second units. Equating this force to 

 the expression for the Coriolis force acting up- 

 lO{AD^-ADs)_ 



slope gives 



= T'2w sin (p (Sand- 



stromand Helland-Hansen, 1903) (£2) where, 



AZ>A — AZ>fl= difference in the anomalies of 

 dynamic height at stations 

 A and B, in dynamic meters, 



