intensively. Naturally, under such circumstances a thick and very light layer of water forms along 

 the shore, and in this layer a circulation occurs counter to the wind and keeps the floating ice away 

 for a long period of time. Such a situation is not very probable in winter, because in winter the 

 waters are less stratified. 



However, during onshore winds in coastal waters a circulation is created with horizontal axes 

 approximately parallel to the shoreline. These circulations, thanks to friction along the bottom, 

 raise the sea level at the shoreline. The resistance to friction increases in proportion to the square 

 of the velocity, and therefore the velocity of the onshore current does not increase in proportion to 

 the wind speed, as in the case of currents in the open sea. Furthermore, the speed of the actual 

 wind drift of ice is not a function of nearness to the shore and thus the drift of ice toward the shore 

 is not decelerated by the shore as much as the movement of the coastal waters, and continues even 

 after the movement of the coastal waters in this direction has ceased. 



In the case of offshore (dispersive) winds, the ice becomes scattered or leads form which 

 stretch along the coast or the edge of the immobile ice. 



IJTERATURE: 62, 77. 



Section 143. Wind Leads and Polynyas 



Wind and polynyas form along the shore, or at the edge of shore ice and may be temporary (in 

 the case of temporary offshore winds occurring during the passage of pressure systems) or constant 

 (in the case of prevailing offshore wdnds) . 



The temporary wind and polynyas are sometimes highly important for navigation in long 

 straits. 



Figures 146 a and b show the ice situation in Vilkitski Strait according to aerial reconnais- 

 sance data for 8 and 24 July 1943. 



We know that in Vilkitski Strait there is a stream of ice carried out from the Kara Sea by a 

 steady current into the Laptev Sea. This flow of ice increases with favorable westerly winds and 

 decreases with easterly counter vidnds. Furthermore, winds cause this stream to shift sometimes 

 to the north and sometimes to the south. 



During the natural synoptic period from 1 through 7 July 1943, the isobars in Vilkitski Strait 

 stretched northwest- southeast, and the center of the pressure high was situated above the southwest 

 part of the Kara Sea, while the low-pressure center was located over the New Siberian Islands. The 

 reconnaissance of 8 July shows that an enormous polynya formed off the south coast of Bolshevik 

 Island as a result of north-northwest winds and the ice drift southeast. 



From 8 through 13 July, the isobars in the region of Vilkitski Strait stretched almost from 

 north to south, the high pressure region was situated above the northern part of the Laptev Sea. In 

 the synoptic period which began 21 July, the isobars were situated approximately as they had been 

 in the period from 8 through 13 July. Corresponding to this position of the isobars, the ice pressed 

 against Bolshevik Island. From 14 through 21 July, the isobars in Vilkitski Strait stretched from 

 northeast to southwest, the high pressure center was situated in the southwest part of the Kara Sea 

 and the ice correspondingly pressed against the continental coastline . 



393 



