Figure 5.14. Year-to-year course of the seasonal and annual mean anomalies of Arctic T and their trends over the period 1936-1990 (27 stations since 1951).
(a) year-to-year course
(b) running 10-year mean
(c) linear trend over the whole period of observation
(d) linear trend over the period 1961-1990.
to those annually, occurred in all seasons except for the spring, for which they were positive in the area of the Barents Sea and surrounding islands. In the period between 1936 and 1990 the nature of trends is similar to that presented above in the area of ATLR, SIBR, the eastern part of CANR, and BAFR. However, in PACR and, in all likelihood, in the western part of CANR, weak positive trends were noted in all seasons except for the autumn. The data in Table 5.10 demonstrate that stronger trends were calculated for the period between 1936 and 1990 because in this case the starting point for the calculation falls within the period of the maximum warming of the Arctic. TA according to data published by Alekseev and Svyashchennikov (1991) almost fully confirms the above results (Table 5.10) except for the summer T.trends, which are positive here. This discrepancy results probably from the fact that the calculations by these authors concern the 65-85°N zone; as a result, this series takes into consideration many areas lying to the south of the area discussed in the present work. It is also worth noting that it is only in the large part of ATLR and BAFR that negative winter trends are greater than those of autumn. In the remaining area it is the autumn that was affected by the greatest cooling. As Table 5.10 shows, this affected the whole Northern Hemisphere, trends for other seasons and for the year as a whole were most often positive; most of them, however, are statistically insignificant. The temperature of water in the Barents Sea, similar to the temperature of the air, is characterised by a statistically significant downward tendency (-0.10°C/10 years in 1936-1990), and the mean annual surface of sea-ice cover was growing at that time at the rate of 1.16% /10 years.
As follows from the data in Table 5.11 and Figures 5.20-5.23, in the period 1951-1990 negative T. trends still prevailed in the Arctic. On average, they amounted to -0.10°C and -0.04°C/10 years for the annual values of TAl and respectively. Cooling occurred in all regions of the Arctic, to the exclusion of PACR, which was characterised by a positive trend (0.15°C/10 years) for mean annual T.. SIBR also underwent a slight cooling at that time (Table 5.11). The statistically significant downward tendency of T. was calculated only for BAFR (-0.32°C/10 years). The trends of mean T. in all climatic regions of the Arctic had the same sign (±) only in the autumn (Table 5.11). A detailed spatial distribution of the magnitudes of seasonal and annual trends olT. is shown in Figures 5.20 and 5.21. In the period under discussion, the greatest downward tendency of mean annual T. occurred in ATLSRn, in the eastern part of CANSRs and in BAFR (< -0.2°C/10 years). Negative trends prevailed in ca. 80% of the Arctic. Positive trends occurred mostly in the southernmost part of SIBR, in PACR and in the south-western part of CANSRn; they did not, however, exceed 0.2°C/10 years in most cases (Table 5.11, Figure 5.20). Jones et al. (1988, see their Figure 2) presented a similar course of isolines of the trend of 0°C/10 years in the Arctic in the 40-year period be tween 1947 and 1986. Results similar to those presented above were also obtained by Ye et al. (1995) through the analysis of the frequency of occurrence of cold and warm air-masses and their physical properties in the past 40 years in the Canadian and Russian Arctic. This research method is commonly used in synoptic climatology and has also been adopted in the present work (cf. sub-chapter 5.3). Taking into consideration particular seasons, it can be clearly seen that, similar to the longer periods discussed above, the strongest cooling in the 40-year period between 1951-1990 was evident in autumn (on average -0.18°C and -0.17°C/10 years for TM and TA2 respectively). This phenomenon affected all regions of the Arctic (Table 5.11). Very slight positive trends occurred in this season only in some areas of the southern parts of the Russian and Canadian Arctic (the area of Hudson Bay) (cf. Figure 5.21).
Gfst E n n
Was this article helpful?