General Theory of Ocean Currents in a Homogeneous Sea 



425 



Table 125. South Equatorial Current in the Atlantic Ocean 

 (approx. 14° S., 20° W. to 8° S., 15° W.) 



Table 126. Diagram of forces in the South Equatorial 



Current of the Atlantic Ocean 



(Forces in dyn/cm^) 



Coriolis force 



Pressure force 



Wind stress 



-/or = +1-77 



+fpli= -6-73 



SI5°E 6-95 



gPl^= +1-49 

 gpt\ = +3-28 

 N24°E 3-51 



r„ = -3-26 



Ty = +3-45 



N 43° W 4-74 



in good agreement with the known values. Alternatively, taking h-^ (the frictional depth 

 of the drift current) as about 200 m, the roughness parameter Cq as 0-3 and the surface 

 velocity U as 35 cm/sec, equation (XIII. 37) gives exactly the required value of 4-74. 

 These calculations show in any case that the oceanic current conditions are in good 

 agreement with hydrodynamic concepts about the driving forces. 



The dissipation of the current energy in the ocean. It is probably of some interest to 

 calculate the amounts of energy dissipated in a drift current due to the apparent 

 friction. The energy consumption is of course largest in the uppermost layer and 

 decreases rapidly with increasing depth. If only the /o/a/ energy consumption is required 

 this can be calculated rapidly in the following way. The total work done in the interior 

 of the water must be supplied from the wind at the sea surface. This is, however, 

 given by force x distance. The force is the wind-stress component in the direction of 

 the surface current; the component at right angles does not enter into the calculation. 

 This component is Tcos 45 "" and the distance travelled in unit time is Vq. The energy 

 consumption per second in a vertical water column of 1 cm^ cross-section can then be 

 obtained using equation (XIII.26) (Schmidt, 1919) and is given by 



W = Vq \/{t]pw sin (/«). 



The values of tj given by Thorade give the energy values shown in Table 127. In a 

 vertical water column the total work expended should lie between 2 and 40 erg/sec. 

 There is a considerable increase in these amounts with increasing wind speed and the 

 latitude also has an appreciable effect. 



