General Theory of Ocean Currents in a Homogeneous Sea 44 1 



This also was shown as at least partly dependent on the turbulent state of the air 

 above the ice. 



The ice drift thus to a large extent follows regular laws; it is dependent on three 

 forces : the effect of the wind on the ice, the frictional resistance between different ice 

 masses and the dei!ecting force of the Earth rotation. The much greater wind factor 

 over the Weddell Sea than over the open ocean (see p. 449) is due to the fact that the ex- 

 posed surface of the ice is more favourable to the action of the wind than that of the 

 freely moving open sea. Over the Siberian Shelf, on the other hand, the wind factor ob- 

 served was smaller than over the Weddell Sea; this may be due to the thickness and 

 compactness of the Arctic ice cover which must offer a much greater resistance to 

 movement than the ice of the Weddell Sea. 



6. Inertia Currents 



In the preceding sections ocean currents in a homogeneous sea have everywhere 

 been considered as stationary phenomena. Observations show that in most cases this 

 assumption corresponds more or less closely with actual conditions. However, it 

 can hardly be assumed that the forces involved will always be in equilibrium. Any 

 disturbance of the equilibrium must, however, alter the state of motion of the water 

 masses and in this the inertia of the water will play a major role. It is only in more 

 recent times that one has started to draw attention to such phenomena, 



{a) Inertia Currents as Disturbances of a Steady Current 



A water mass moving frictionless in a horizontal direction under the action of a 

 gradient force will, speaking completely in general, be subject to the equations of 

 motion (X.16). If the .v-axis is taken in the direction of the pressure gradient 

 (dpjdy = 0), and this pressure gradient corresponds to a steady current (geostrophic 

 current), then 



1 cp 

 Fo = ^ V- and U^ = 

 fp ex 



and one obtains (disregarding frictional forces) 



'i/=^^^-^»^ '"^ it = -^"' 



A periodic solution for an observer moving with current is 



u = t'o sin// -f Uo cos ft, 

 V = Vq cos ft -f "o sin/r + Fq, 

 or 



u = Co sm {ft -f ip), 

 V = Co cos (ft + 0) + Vo, 

 where 



^0 = Vi^l + '") ar'<i t^n ^ = — 



^0 



