Snow Cover

The snow cover becomes established earliest in the ccntral part of the Arctic in late August (Figure 7.12). According to Radionov et al. (1997), stable snow cover at the geographic Pole forms on 20 August. At the height of the Arctic islands (Zemlya Frantsa Josifa, Severnaya Zemlya, Novosi-birskiye Ostrova) the autumn formation of snow cover occurs on around 11 September. Ten days later it becomes established near the north of the Svatbard islands, Taymyr Peninsula, and in the Laptev and New Siberian seas. On 1 October snow cover is present over the entire Arctic, excluding the southern part of the Baffin Bay region, and the western and southern parts of ihc Atlantic region. In the Canadian Arctic, according to the map published by Maxwell (1980), the snow covcr forms in the northern part (on 1 Sep.), in the central part (on 15 Sep.), and in the southern part (on 1 Oct.). The decay of the snow cover begins in the south. At the Eurasian Arctic coast melting starts during the first ten days of June (Figure 7.12). In the Canadian Arctic the decay begins about half a month later (on 15 June). In July snow cover still exists only above 80°N. This is also true of the Canadian Arctic. In the central Arctic the decay of snow cover is delayed until the mid-July. At the North Pole, on average, the snow cover decays around 18 July (Radionov el al, 1997).

From this information it may be concluded that the number of days with snow cover is greatest in the vicinity of the Pole (more than 350 days) (Figure 7.13). A period of more than 300 days occurs northward from the Arctic islands (above 77°N in the Russian and Canadian Arctic and above 83°N in the Atlantic region). The coastal part of the Russian Arctic has about 260 -280 days with snow cover, while in the north-eastern part of the Canadian Arctic the period is longer by about 20 days (280-300 days). In the Atlanlic region the number of days with snow cover is lowest and varies from 200 -240 days. Of course, this characteristic concerns the formation of snow cover on the coastal parts of land and on the sea ice. Mountainous areas have a longer period of snow cover. For example, in the Canadian Arctic the duration of snow cover can reach 320 days (Maxwell 1980).

Figure 7.12, Average dales of stable snow-cover formation (a) and its decay (b) in the Arctic, 1954-199! (after Radionov ei at. 1997).

Figure 7.12, Average dales of stable snow-cover formation (a) and its decay (b) in the Arctic, 1954-199! (after Radionov ei at. 1997).

Figure 7.13. Mean annual number of days with the snow cover in the Arctic, 1954-1991 (after Radionov et al. 1997).

Besides the duration of the snow cover, a very important characteristic is also its thickness. The maximum snow cover thickness is generally observed from April to May, except in the Canadian Arctic, where it is observed most often about one month earlier (Maxwell 1980). The highest rates of snow accumulation in autumn are observed in the Siberian region (Radionov et al. 1997), where from September to November the snow-cover thickness increases, on average, by 14-16 cm. In the central Arctic Ocean and in its part from the Pacific side, the monthly increase in snow cover thickness is smaller and oscillates on average by about 5 cm. During the following months, the rates of snow accumulation over the entire Arctic mostly decrease. The long-term (1954-1991) mean monthly snow cover thickness for May, when the snow accumulation is maximal, is greatest in the central part of the Arctic Ocean (about 40 cm) (Figure 7.14). According to more recent calculations (Warren et al. 1999, their Figure 9), this maximum is located rather in the area between the North Pole and the northern parts of Greenland and the Canadian Arctic Archipelago, Moreover, in this area the mean snow depth is greatest in June (40-46 cm). In the Arctic islands the mean snow cover thickness in May is equal to about 30 cm. On the coastal parts of the Russian Arctic, the northern and western parts of the Canadian Arctic, and Alaska, it varies from 20 to 35 cm. In the eastern part of the Canadian Arctic (the eastern coast of Baffin Island and Ellesmere islands), the snow cover is higher than it is near the North Pole and, according to the data presented by Maxwell (1980, his Figure 3.136), oscillates from 50 to 70 cm on April 30 (mean from 1955-1972). Similar values also occur in Spitsbergen (Pereyma 1983, Lcszkiewicz and Pulina 1996). Thus, probably here, particularly in the southeastern part of Baffin Island, southern Spitsbergen or somewhere in the southern part of Greenland (there is no data), the snow cover reaches the highest thickness in the Arctic. Very frequent cyclonic activity bringing warm and humid air masses from the Icclandic low and favourable orographic conditions (mountainous ridges and slopes well exposed to the main air streamlines) are the most important factors responsible for this situation. The snow cover thickness described above concerns only the accumulation of snow on the areas covered by sea ice and tundra. In the mountainous regions the snow cover thickness is significantly greater (up to 2-3 times and more) (see e.g. Pereyma 1983; Grzes and Sobota 1999).

The least studied characteristic of the snow cover, but one that is also very important, particularly for the computation of the water budget, is its density. Throughout the year, the snow density increases significantly from September to December (from about 0.2 g/cm3 to 0.3 g/cm3), then from December to April the rate of increase is significantly lower. The second largest increase occurs from May to the end of June (from 0.3 g/cm1 to 0.4 g/cm3) due to snow melting (Loshchilov 1964; Radionov et al. 1997; see also Fig-

lire 7.15). The long-term mean snow density for the whole accumulation period changed little across the Arctic Basin, from 0.31 to 0.33 g/cm3. The spatial distribution of the mean snow density for the month of May presented recently by Warren et al. (1999) confirms entirely the correctness of earlier investigations (Figure 7.16). Non-average densities of snow cover show a significantly greater change from only 0.05-0.09 g/cm1 for fresh snow to 0.50-0.55 g/cmJ for melting snow.

Figure 7.14. Distribution of the mean snow-cover depth (in cm) in the Arctic during May, 1954-1991 (after Radionov et al. 1997).

Figure 7.1}. Long-term (1954-1991) mean snow density in the Arctic for each month (large solid dots). All available density measurements for each month are used, irrespective of year and geographical location. Error bars indicate one standard deviation. Values of Loshchilov (1964) based on measurements at stations NP.-2 through NP.-9 arc shown for comparison as dashed line (after Warren et al. 1999).

Figure 7.1}. Long-term (1954-1991) mean snow density in the Arctic for each month (large solid dots). All available density measurements for each month are used, irrespective of year and geographical location. Error bars indicate one standard deviation. Values of Loshchilov (1964) based on measurements at stations NP.-2 through NP.-9 arc shown for comparison as dashed line (after Warren et al. 1999).

Figure 7.16. Mean snow density for the month of May (in g cm J) in the Arctic. A two-dimensional quadratic function was fitted to all the available data tor May, irrespective of year (1954 1991) (after Warren et al. 1999).

Chapter 8

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