Figure 144. A sector of compressive and 



dispersive winds with respect to 

 the shoreline or to moving ice. 



Figure 145 shows the relationship between the wind direction, the wind drift of ice and the ice 

 concentration. The sketch was made by Shestiperov on the basis of 580 series of observations made 

 by him at Mys Schmidt in the Chuckchee Sea with a theodolite. From this sketch, in which the thick 

 arrows indicate direction and force of the wind at the time of observation and the thin arrows indi- 

 cate the direction and speed of the wind drift of the ice, we can see that generally the drift angle in- 

 creases as the concentration of the ice decreases (greater freedom of motion of the floes) and 

 second that the wind drift of the ice is deflected to the left of the wind direction in the case of north- 

 erly and northwesterly winds, and by the orientation of the coastline in this region (compass 

 direction 130-310°). 



The configuration of the coast along the Chuckchee Sea where Shestiperov conducted his obser- 

 vations is very straight, hence the winds can be separated into compressive and dispersive com- 

 ponents very simply on the basis of logical judgments. In other regions, where the coastline is 

 sinuous, only observations can reveal whether a wind is compressive or dispersive and such obser- 

 vations must be made for various amounts of ice in the adjacent regions of the sea and under various 

 synoptic conditions. 



There are characteristic phenomena associated with compressive and dispersive winds rela- 

 tive to the edge of floating ice. 



During compressive winds, the ice edge is highly consolidated and stretches in a relatively 

 even and stable line for a great distance. Usually, the ice is close packed at the very edge while at 

 some distance from the edge it is less compact. Thus, the edge of the pack acts somewhat as a 

 breeik-water. In the case of dispersive winds, the edge becomes scattered. On the seaward side of 

 this type of ice edge, one finds small floes greatly eroded by the wind and waves and on passing 

 farther into the ice the number of floes and the size of the floes gradually increase. 



During dispersive winds, very often whole strips of ice consisting of floes of various size and 

 form detach from the edge. In these strips, which stretch in a direction approximately perpendicu- 

 lar to the wind direction, the floes usually group as indicated above; i.e., the larger floes are found 

 on the leeward . 



391 



