D. SOlffi CHARACTERISTICS OF THE POLAR PACK 



The geographical center of the Arctic polar pack is approximately 

 SS'N ISCWo The pack covers an area roughly rectangular in shape, be- 

 tween Novaya Zemlya, Svalbard, Banks Island, and Ostrov Vrangelya, plus 

 some projections out from the rectangular shape, especially on the 

 Siberian side. The Canadian Archipelago acts as a shield preventing 

 the pack from extending further into the IVestem Hemisphere, Each day 

 the Ptarmigan weather reconnaissance flights reach close to the center 

 of the packo 



Ice at the geographical center of the pack does not move much. 

 Thus the concentrations in that area are observed to remain more or less 

 constant from day to day, making allowance for the varying areas of the 

 surface that are visible from the planes' altitude. The center of 

 gravity of the pack moves back and forth due to temporary packing and 

 thinning near the edges caused by wind movement and other factors. If 

 the edge moves, for example, 50 miles, the center of gravity is changed, 

 even though the ice at the geographical center may be stationary *. How- 

 ever, in order to move the edge a distance of 50 miles, a wind movement 

 of 2500 to 3000 miles is necessary, or thp< equivalent of a 25-knot wind 

 blowing for 100 to 120 hours. Such wind movement in the Arctic is known, 

 but it is rare in the summer months at which time pressure gradients are 

 usually Weak except near the center of the occasional LOMS which move 

 through the basin. 



Therp are large-scale differences from one year to the next in the 

 ice boundary locations along Alaska's north coast, the boundary varying 

 from a few miles offshore to 100 or I50 miles offshore. From the wind 

 movement specified above, which vjould necessarily have to be southerly 

 or southeasterly in opposition to the prevailing northeasterly wind, it 

 seems unlikely that wind stress is the primary factor causing this year- 

 to-year changeo Other possible factors are water temperature changes, 

 variations in the continpntal warming, and changes in currents. 



Variations in the temperature and strength of the current coming 

 through the Bering Strait may be responsible for the differences in 

 pack boiindary locations. If the amount of warm water entering the 

 Bering Sea is subject to variations from year to year, the heat pnergy 

 available for m.elting the pack would vary correspondingly. Thus, vari- 

 ations in the Kuroshio may account for the year-to-year changes in the 

 pack boundary in the Alaskan area. No data to test this theory in the 

 Alaskan sector have been collected, 



Anothf>r differential factor may be variations in the warming effect 

 of the continents This is not likely, since thp over-all cloud coverage 

 and h°nce potential in?olation and outgoing radiation are quite constant 

 from year to y^-ar, v/hen averaged over a ppriod of months. Solar radiation 

 data from Barrcw and Aklavik tend to support this last statement. 



Still another factor may be a breakup at thp edge of the pack due 

 to temporary strong winds, with subsequent rapid malting of the ice and 



