Mean Seasonal and Annual Diurnal Temperature Ranges

The highest mean annual Diurnal Temperature Ranges (DTRs) above 8°C occur over the continental parts of the Canadian and Russian Arctic which are located far from Atlantic and Pacific oceans (Figure 4.10). The lowest DTRs (< 5°C) are noted in the Norwegian Arctic, particularly in those areas which are not covered by sea ice. The region spreading from the Norwegian Arctic to Alaska which encompasses almost all islands lying here (from Spitsbergen to Ostrov Vrangciya) has a slightly higher DTR (5-6°C).

Meaning Spatial Figures
Figure 4.10. Spatial distribution of the mean annual diurnal temperature ranges (DTR, in °C) in the Arctic over the period 1951-1990 (after Przybylak 2000b). Key - dashed lines denote probable course of the isolines.

Probably one of the main factors causing this is the very strong and changeable cyclonic activity occurring here which brings high cloudiness. Its influence in lowering the DTR is noted mainly in the warm half-year. The opposite is true for the cold half-year. As a result, in those regions mentioned, and some others which are also strongly influenced by the atmospheric circulation (the western and northern parts of the Russian Arctic and the western coastal parts of Greenland), the highest DTRs occur in winter (Figure 4.11).

Figure 4.11. Same as Figure 4.10, but for winter (D.!F), spring (MAM), summer (JJA) and autumn (SON) (after Przybylak 2000b).

In winter the highest DTRs are noted in the southern continental parts of the Arctic (> 8°C) and the lowest in the southern Norwegian Arctic as well as on the western coast of Greenland (Figure 4.11). In the central Arctic the DTR is equal to about 7°C.

In spring the differentiation of the DTR is significantly higher than in winter and reaches more than 7°C (in winter only 4°C). The highest values (> 9°C) occur in the centre of the southernmost parts of the Canadian and Russian Arctic (characterised by the greatest degree of continentality of cli mate in the Arctic; see Figure 4.2) and the lowest, similar to those of winter, in the Norwegian Arctic and on the western coast of Greenland (< 6°C).

In summer the mean DTRs are lower than in spring but the differences between the highest (> 10°C) and lowest (< 3°C) values are the same. In this season an exceptionally low DTR is present in the Norwegian Arctic and the north-west-crn part of the Russian Arctic (Figure 4.11) where it drops below 3^l0C.

In autumn the differentiation of the mean DTR in the Arctic decreases (4-5°C). Again, as in other seasons, the highest DTRs are in the centre of the southernmost parts of the Canadian (> 8°C) and Russian (> 6°C) Arctic and the lowest are in the Norwegian Arctic (< 4°C) (Figure 4.11).

Figure 4.12. Annual courses of the DTR in the Arctic based on their seasonal means from the period 1951-1990 (after Przybylak 2000b).

Key: I - maximum of the DTR in winter and minimum in summer, 2 - maximum of the DTR in spring and minimum in autumn, 3 - maximum of the DTR in winter and minimum in autumn, 4 - maximum of the DTR in summer and minimum in autumn.

Figure 4.12. Annual courses of the DTR in the Arctic based on their seasonal means from the period 1951-1990 (after Przybylak 2000b).

Key: I - maximum of the DTR in winter and minimum in summer, 2 - maximum of the DTR in spring and minimum in autumn, 3 - maximum of the DTR in winter and minimum in autumn, 4 - maximum of the DTR in summer and minimum in autumn.

The annual course of the DTR is particularly interesting. Based on the seasonal means it is possible to distinguish four types of the annual course of this variable in the Arctic (Figure 4,12):

i) maximum DTR in winter and minimum in summer, ii) maximum DTR in spring and minimum in autumn, iii) maximum DTR in winter and minimum in autumn, iv) maximum DTR in summer and minimum in autumn.

The first two types clearly dominate in the Arctic. Out of 33 analysed stations, the first type occurred in 14 stations (42.4%) and the second in 11 stations (33.3%). The third and fourth types were present in four (12.1%) and three (9.1%) stations, respectively. Only the DTR in the station Eureka has another pattern. The maximum DTR in winter and minimum in summer occur mostly in the Norwegian Arctic as well as in the western and northern parts of Russian Arctic, and the northern part of the Canadian Arctic. This pattern is probably also present in the central Arctic. It is worth mentioning that these areas are either under the very intense influence of the atmospheric circulation (great frequency of cyclones) or are situated around the North Pole, where the daily contrast of the incoming radiation is the lowest in the Arctic and cyclonic activity, although weaker, is however still present (see Serreze and Barry 1988 or Serreze et al. 1993). The second type in the annual course of the DTR (the highest values in spring and the lowest in autumn), which is almost as frequent as the first, occurs in the parts of the Arctic where cyclonic activity is weak and the daily contrast of the solar forcing is the highest (southern parts of the Canadian and Russian Arctic, northern Alaska and in some parts of Greenland). Ohmura (1984) presents a more detailed explanation of the causes of this kind of annual course of the DTR based on investigations of heat balance conducted on Axe! Heiberg Island (Canadian Arctic) in the summers of 1969 and 1970. This type in scientific literature is known as the 'Fram' type. The occurrence of the third and fourth types in stations located in different isolated parts of the Arctic can be related to the specific local conditions (radiation and atmospheric circulation).

According to the monthly means of the DTR, the highest values most often occurred in April (63.6% of the stations) or February (18.2%) and the lowest in September (62.1%) or October (16.7%) (Przybylak 2000b).

Was this article helpful?

0 0

Post a comment