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tember and January (30-34%), and least frequent in May (15%) and July (21%). The macrotype C is most frequent in May (34%) as well as in June and October (30%), and least frequent in February and August (21%). The most commonly occurring macrotype E is at its maximum in February (57%) and August (55%), and at its minimums in the autumn months: October (36%) and September (40%).

It is worth devoting some attention to the analysis of the frequency of occurrence of types and groups of circulation in the Arctic in the period 19391990 within the macrotypes of circulation. It is similar to the frequency of the occurrence of days with type and group of circulation. In the case of groups of circulation, groups W (26.3%) and D (18.3%) exhibited the highest frequency, while group G (8.2%) exhibited the lowest frequency. The macrotype W is most frequently accompanied by the synoptic processes of groups W (34.2%) and K (20.9%), and least frequently by those of groups G (6.8%) and D (8.4%). As far the macrotype C is concerned, the most frequent are groups D (23.1%) as well as B, A, and W (slightly above 18%), while the least frequent is group G (7.0%). The macrotype E is most frequently accompanied by synoptic processes of the groups W (26.8%) and D (20.9%), and least frequently by those of groups G (9.6%) and K (11.1%). The situation differs in particular seasons.

Table 4.2 shows mean frequencies of the occurrence of groups and macrotypes in particular decades during the period 1939-1990 as well as during C and E+C circulation epochs (1940-1948 and 1949-1990 respectively). Some attention should be devoted to the frequency of occurrence of groups and macrotypes of circulation in the last decade (1981-1990), which was the warmest decade during the period of instrumental observations. According to the annual means there was a decrease in the frequency of occurrence of group B (by 3%) and group K (by 2%), and an increase in the frequency of groups G and D (by 2%). In the same period the frequency of occurrence of the macrotype W increased by 2%, and the macrotype E by 4%, whereas the frequency of macrotype C decreased by as much as 6%.

According to Girs (1977), negative anomalies of the air temperature prevail in the Arctic during the W circulation epoch, and positive during the C circulation epoch. On this basis it can be stated that the circulation factor in the 1980s was conducive to the cooling of the Arctic.

The analysis of 30-year trends (1961-1990) of the frequency of occurrence of 16 types of circulation according to their annual means proved that 5 types (I, VIII, XI, XIII, and XIV) were characterised by a clear ascending trend, while 5 (II, IX, X, XV, and XVI) were characterised by a descending trend.

Table 4.2. Relative frequency (in %) of the occurrence of groups and macrotypes of circulation over the period 1939-1990

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