Ice distribution in the Beaufort Sea varies con- 

 siderably from year to year as well as seasonally. 

 The following description, summarized from 

 H.O. 705 (U.S. Navy Hydrographic Office, 

 1968), represents mean conditions, but is of 

 value since no major deviations where observed 

 during 1971 and 1972. 



The Beaufort Sea is covered with 7 to 8 oktas of 

 ice for about 9 months of the year. There is 

 usually some open water along the entire northern 

 coast of Alaska in August and September. How- 

 ever, the heavy polar pack is never far off the 

 coast and can advance onto the shore at any time. 

 Northerly and westerly winds will force the pack 

 against the shore while southerly and easterly 

 winds hold the pack off the coast. During typical 

 years, freezing starts in early October. By mid- 

 October shore-fast ice extends along the length of 

 the northern Alaskan coast with new ice formed or 

 forming throughout the open water areas. By early 

 November, 7 to 8 oktas of ice covers the entire 

 Beaufort Sea. The new ice continues to grow and 

 will reach a first year thickness of 1 to 2 meters by 

 late spring. Breakup and melt begins in June near 

 the mouths of rivers where warm river runoff flows 

 over the sea ice. There is, in addition, some 

 breakup in the Point Banow region due to the 

 intrusion of warmer water up through the Bering 

 Straits. 



Climate 



The climate of the Beaufort Sea region and the 

 Arctic in general is controlled by the heat budget. 

 In the Arctic, the net annual radiation exchange 

 is small since the summer gain is approximately 

 balanced by the winter loss. However, heat re- 

 radiated from ice and open water areas combines 

 with a far greater flux of heat which enters the area 

 as a net annual northward horizontal transport by 

 the atmosphere of excess heat received at the 

 equatorial regions. This energy is radiated into 

 space from the top of the atmosphere resulting in a 

 net annual loss for the region. 



Most of the year the surface of the Beaufort Sea 

 is covered with ice reaching a thickness of 1 to 2 

 meters. This sea ice is sandwiched between two 

 moving fluids (i.e., air and sea water) and is 

 continually fracturing. The air over these frac- 

 tures in winter may be as much as 50 C colder 

 ihan the surface, resulting in the transport of large 

 2 



amounts of heat and water vapor into the atmos- 

 phere. With the exception of these fractures, 

 little heat exchange occurs due to the insulating 

 effect of ice and snow cover. 



Sea level pressure gradients are weakest dur- 

 ing the summer months in the Arctic, and circula- 

 tion is usually poorly defined. The Beaufort Sea, 

 however, is generally under the influence of a 

 weak high pressure ridge. Circulation around this 

 high results in winds from the east or northeast 

 50% of the time, and is usually of low velocity 

 (<20 kts). 



The character of the surface and distribution of 

 the ice pack are more influential in determining 

 the variation and extent of cloudiness than is the 

 behavior of storm cells and frontal zones. In 

 summer, the melting ice pack and associated low 

 level temperature inversion cause the develop- 

 ment of persistent stratus clouds and fog. The 

 mean cloud cover is in excess of 80%. Absence of 

 snow cover on land results in less stable lapse 

 rates and diminishing cloudiness in near shore 

 areas. 



In summer the surface of the pack ice is essen- 

 tially 0°C although melt pools reach slightly 

 higher temperatures. In the Beaufort Sea there- 

 fore, above freezing air temperatures are found 

 only over open water. But even here the air must 

 remain near 0°C since the sea surface tempera- 

 ture does not rise much above the freezing point, 

 and air temperature seldom differs greatly 

 from that of the water. Warm air from inland is 

 often transported considerable distances from the 

 coast, but is cooled so effectively in the lower 

 levels by contact with cold water or ice that a 

 strong inversion forms. Near the immediate coast 

 however, relatively high temperatures (17°C max- 

 imum) may be observed for short periods of time. 



Precipitation on the North Slope and adjacent 

 Beaufort Sea areas is scant (<12 cm/yr) and pre- 

 dominately in the form of snow. Defant (1961) 

 estimates that 33% of the precipitation in the 

 Arctic evaporates. The remaining 67% or 8 cm/yr 

 when multiplied by the area in question would 

 contribute 1 X lO^^'m^ of fresh water per year to the 

 Beaufort Sea assuming no percolation due to per- 

 mafrost. The maximum precipitation occurs in 

 autumn and the minimum in winter, a cycle which 

 is determined by the capacity of air to hold water 

 vapor. 



