The Chukchi Sea is completely covered in ice from mid-December to mid-May. The condition of the ice in this sea changes rapidly, with 80% of the winter ice disappearing in the summer. Factors contributing to this rapid change are temperature, winds, ocean currents and morphological effect of the Wrangel Island and the ocean floor. The multi-year ice carried in from the north is seen in Long Strait, which separates the Wrangel Island from the Siberian mainland. These factors will have a strong impact on the selection of an optimum route for the NSR.
3.3.4 Precipitation and Snow Cover
The snow cover on sea ice is a major controlling factor in its growth and melting, and significantly affects the propulsion and steering performance of icebreaking vessels. Most of the Arctic Ocean lies under weak high-pressure system throughout the year. Except for the occasional effect of the Iceland low-pressure, which encompasses the Barents Sea and at times the Kara Sea, storms are quite rare. As the table of monthly average precipitation shows below, precipitation in all regions is highest in the summer - though even then, no more than 40mm - and annual precipitation is a rather low 180-250mm a year.
The depth of snow cover on level ice varies widely from place to place. An overview of the snow cover in the Arctic Ocean is as follows: On the continental shelf of the NSR, particularly on the relatively flat first-year ice, areas of snow cover with 5-10cm are twice as common as those with only 0-5cm. In the Alaskan and Canadian Arctic, on the other hand, areas of snow cover with 0-5cm are slightly more common than those with 5-10cm. A histogram calculated from observation data of depth of snow cover on multi-year ice from over 100 locations shows that the most common range of snow depth is 12-18cm on flat sea ice but as much as 60-100cm on pressure ridges. This is because blowing snow tends to pile up around pressure ridges. In April, when snow cover on the ridges is at its peak, snow cover of 200cm is found in Greenland and 140cm in the NSR region.
Maximum snow cover in the vicinity of pressure ridges in April (cm) (Romanov, 1995)
Average monthly precipitation in each region of the Arctic Ocean (mm) (Radionov, 1997)