Key as in Table 5.21a

Key as in Table 5.21a A characterisation of groups and macrotypes of circulation

A knowledge of the thermal characteristics of the 16 circulation types discussed above is both desirable and useful in forecasting the weather and climatic conditions, especially for rather limited areas. In the case of attempts to forecast the climate for the whole Arctic, such a large number of circulation types makes it extremely difficult to accurately assess the influence of circulation on climate. It must be remembered that particular circulation types manifest their influence differently in various regions of the Arctic. Moreover, the nature of the influence also changes in the course of the year. Hence, whenever it is possible, circulation types characterised by a similar distribution of pressure fields are joined together. Using this method, Dydina (1982) singled out 6 groups of synoptic processes: A, B, W, G, D, and K. The thermal characterisation of these 6 groups is presented below, augmented with 3 circulation macrotypes (W, C, and E) according to the Vangengeim-Girs typology, singled out for the Atlantic-European sector of the Northern Hemisphere.

The Atlantic Region

The western sub-region. Taking into consideration monthly anomalies of T., the coldest circulation group in Danmarkshavn in the periods from September to March is group A; in April and May the coldest is group W, and in the summer - group B. From May to July, it is the warmest when the air of group A flows in, whereas in the remaining part of the year various other groups are the warmest in particular months (Figure 5.34a). Taking into consideration mean seasonal anomalies of T. (Tables 5.20a-d) for particular groups of circulation, it can be seen that in the autumn, winter, and spring, it is the coldest during synoptic situations A and W, which are characterised by the development of cyclonic activity over the area examined. Since ATLSRw is more often than not under the influence of western section of lows, cold air inflows there from the northern sector. In the summer, only group B is characterised by negative anomalies of T. (-0.7oC). Other circulation groups bring slight warming relative to mean values.

In the course of the year, the lowest monthly and seasonal anomalies of T (Tables 5.20a-d, Figure 5.34a) are brought by the western circulation (W). The remaining two circulation macrotypes (C and E) are characterised by weak positive anomalies.

In Danmarkshavn the least stable thermal conditions occur in the autumn and spring (CT amounting to 8.7°C and 7.9°C respectively) whereas they are the most stable in the summer (o = 2 . 90C) . In the winter, the greatest differentiation ofT. accompanies circulation groups G and D and the lowest differentiation accompanies A and B. In the summer, group W brings the most variable whereas group B the most stable

The greatest dispersion of T. around the long-term mean value occurs in the autumn (a = 8.0°C) and in the winter (o = 6.9°C) with macrotype E, and in the spring (ct = 9.3°C) and summer (cr = 2.9°C) with macrotype C. In the autumn and winter the most stable thermal conditions accompany circulation macrotype C and in the spring and sum mer they accompany circulation macrotype E.

The southern sub-region. The western, markedly maritime part of the sub-region is represented by the station Jan Mayen whereas the eastern, continental part is represented by the station Naryan-Mar.

The warmest circulation group in Jan Mayen is group G, except for July and the period from November to January, when greater positive anomalies of T. occur with group D. The majority of monthly (Figure 5.34a) and seasonal (Tables 5.20a-d) anomalies of 7] are the smallest with group W. Decidedly the coldest air masses in all months and seasons are brought by the western circulation (exclusively negative anomalies of occur). Macrotype C is accompanied by the highest T in January and in the period from April to October. In the remaining months the warmest is macrotype E (Figure 5.34a).

Jan Mayen is characterised by the most stable thermal conditions of all the meteorological stations analysed (Tables 5.21a and 5.21b). The greatest dispersion of T. around the long-term mean occurs in the winter (ct = 5.2°C) whereas the lowest occurs in the summer (a = 2.3°C). In the winter, the most unstable thermal conditions accompany groups A (ct = 5.6°C) and W (a = 5.2°C) and macrotypes C and E (0 = 5.3 °C). The smallest changes of T. are brought by groups G (ct = 3.5°C) and K (ct = 4.5°C) and macrotype W (ct = 4.9°C).

Figure 5.34a. Mean annual course of T. anomalies at Danmarkshavn and Jan Mayen taken for the days with groups (A, B, W, G, D, and K) and macrotypes (W, C, and E) of circulation chosen over the period 1951-1990.

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