At most stations in winter (Figure 6.8), except for those lying to the south of ATLR (Jan Mayen and Mys Kamenny), P is usually within the 0-25 mm or the 25-50 mm intervals. The probability of the occurrence of the most frequent P is close to or higher than 50%. All winter P sums between 1951 and 1990 at Resolute A station were < 25 mm, and at Barrow station only 10% of P exceeded 25 mm. Most distribution has a clear positive asymmetry. P at Jan Mayen, a station representing ATLSRs, differs from that at the other stations mostly in terms of its frequency distribution. Here it is closest to the normal distribution (Table 6.4). A more even distribution of the frequency of occurrence ofparticu-lar P intervals is also characteristic of this station. The highest frequency fell within the 200-225 mm interval and amounted to a mere 20%. The widest P range (from 50 mm to 300 mm) also occurred here.

In the regions of the Arctic influenced by the lows forming around and over Iceland (ATLSRw, ATLSRs, and the southern part of BAFR), the range of P is significantly smaller in summer than in winter. It is caused by a stronger and a more vigorous cyclonic circulation in winter (Przybylak 1992a; Serreze et al. 1993). However, the situation is different throughout the remaining area of the Arctic. The distribution of summer P differs from that of the winter mainly in the lesser dominance of one interval over the others. In most of the analysed stations, the frequency of the occurrence of the most frequent interval did not exceed 40%. In most parts of the Arctic, except for ATLSRs, ATLSRe, and CANSRs, summer P very rarely exceeds 100 mm (with a probability of < 10% at most stations).

The widest range of the annual totals of P (up to 500 mm) is characteristic of the warmest part of the Arctic, i.e. ATLSRs (Jan Mayen), and the narrowest one (150-200 mm) is characteristic of the coolest, i.e. the northeastern part of CANSRn and the central part of SIBR. P distribution in these areas is symmetric and platykurtic (Table 6.4).

In ATLSRw, the most frequent P lies within the 100-150 mm (30%) interval. It occurs in the neighbouring intervals with only a slightly lower frequency. P of less than 50 mm and greater than 250 mm is extremely rare (2-3 %) (Figure 6.8a).

Figure 6.8a. Relative frequency (in %) of the occurrence of winter, summer, and annual P in selected stations representing particular climatic regions and sub-regions of the Arctic over the

In ATLSRs (Jan Mayen), annual P oscillates from 450 mm to 950 mm, with maximum frequency falling into two intervals: 750-800 mm (20%), and 600-650 mm (27.5%). Between these two intervals, the frequency of P is clearly lower (Figure 6.8a).

In ATLSRn, represented by Ostrov Vize, there is a clear dominance of P fitting into the 150-200 mm interval (42.5%). At this station, P also occurs very frequently in the 200-250 mm interval (25%) and is always higher than 50 mm. However, it very rarely (2.5%) exceeds 250 mm (Figure 6.8a).

When compared to ATLSRn, the range of P in ATLSRe increases considerably as cyclones form over the Kara Sea. Moreover, cyclones forming

Figure 6.8b. Relative frequency (in %) of the occurrence of winter, summer, and annual P in selected stations representing particular climatic regions and sub-regions of the Arctic over the period 1951-1990.

over Iceland also reach this sub-region. At the station representing ATLSRe (Mys Kamenny), P occurs with almost equal frequency (about 20%) in four intervals: 250-300 mm, 300-350 mm, 350-400 mm, and 400-450 mm (Figure 6.8a). Annual P beyond the 250-500 mm interval occurs rarely, with a frequency of around 10%.

Ostrov Kotelny lies in the coolest part of SIBR, where, as has been already mentioned, the range of P is very narrow (50-250 mm). In the 100200 mm interval P occurs with 85% frequency, and in the dominant interval (100-150 mm) the frequency equals 47.5% (Figure 6.8a).

The range of P in PACR is a little wider than in SIBR and oscillates from 0 mm to 250 mm at Barrow station. Similar to SIBR, P occurs here with the greatest frequency in the 100-150 mm interval (47.5%) (Figure 6.8b). Its annual totals often (32.5%) fit into the 50-100 mm interval. Thus, the probability of the occurrence of P beyond the 50-150 mm interval is small and equals 20%.

P is much higher at Coral Harbour A (CANSRs) than at Resolute A (CANSRn). Its range is also much wider here. Nevertheless, the dominance of one interval over the others is quite pronounced at both stations (Figure 6.8b). At Coral Harbour A precipitation falls with the greatest frequency within the 250-300 mm interval (40%), and at Resolute A it falls within the 100-150 mm interval (60%). The northern part of the Canadian Arctic is the coolest region of the Arctic because it is dominated by anticyclone systems which are conducive to the radiation cooling in the greater part of the year. As a result of such conditions, P has its narrowest range in this region of the Arctic (50200 mm).

In BAFR (Clyde A), due to the increased influence of the Icelandic Low on the formation of the weather, the range of annual P increases again, and its distribution becomes bimodal, similar to that at Jan Mayen (Figure 6.8b). None of the intervals occurs here with a frequency exceeding 30%. The greatest frequency of P occurs in the 100-150 mm (27.5%) and the 200-250 mm (22.5%) intervals.

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