CHAPTER XI 

 WIND AND THE DRIFT OF ICE 



Section 132. The Wind Drift of Ice 



All observers are struck by the speed with which ice, both close ice and scattered ice, reacts 

 to any change in the wind speed and direction. 



For example, it takes but a few hours of fresh wind of the proper direction to change the 

 entire ice situation in a given region beyond recognition. Of course, this change is determined by 

 the geographic conditions, the contour of the coast line, the bottom relief, the system of steady 

 currents, the distribution of temperature and the salinity of the water in the given region, etc. 



Despite the great complexity of the wind movement of ice, one may distinguish three 

 characteristic cases: 



1. The wind drift of close ice. 



2. The wind drift of an isolated floe. 



3. The wind drift of scattered ice. 



In the first case, the wind, exerting pressure on the ice cover, causes the ice cover to drift. 

 In turn, the drift of the ice cover causes a current in the water masses beneath it and this current 

 is subject to the same laws of vertical distribution of velocity and direction as the current caused 

 by the direct action of the wind. In this connection, a very complex resistance arises, the resis- 

 tance offered by the water to the wind drift of ice. 



In the second case, the wind causes a wind current with which the ice flow moves. However, 

 since the action of the wind on the floe is stronger than on the equivalent water surface, the flow 

 acquires its own wind motion. 



The third case, the wind motion of scattered ice, is intermediate between the first and second 

 cases and depends on the concentration of the ice. Furthermore, this type of drift exhibits features 

 which appear because floes of different form and size drift at different speeds and in different 

 directions , depending on the force and direction of the wind . 



In addition, one must distinguish wind drift during the freezing period and during the thaw 

 period. In the first case, when there is hummocking in connection with drift, the new expanses of 

 open water which appear are rapidly covered over with ice and thus the total amount of ice in- 

 creases. In the second case, expanses of open water also appear, but the heat from solar radiation 

 accumulates rapidly in these spaces and this results in a decrease in the total amount of ice. 



Theoretical investigations of the wind motion of ice are seriously hampered by lack of know- 

 ledge of the vertical distribution of wind velocity and direction over the open sea as well as over 

 ice fields and also by the lack of knowledge of the vertical distribution of water velocities immedi- 

 ately below the lower surface of the ice. 



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