Shortperiod Variability Of Arctic Seas Ice Extent

Although the short-period (2-3-year and 6-7-year) cyclic variability of ice extent of the Siberian shelf seas is typically considered "noise" in comparison to long-period climatic variability, this obscures some significant changes in Arctic climate. The

Figure 2.10. Periodograms of the variability of ice extent in the Arctic Seas, smoothed by a five-year running mean procedure for 1933-2003: a) and b) show the Greenland and Barents Seas, respectively, in April; for August, c) shows the Greenland Sea, d) the Barents Sea, e) the Kara Sea, /) the Laptev Sea, g) the East Siberian Sea, and h) the Chukchi Sea.

Figure 2.10. Periodograms of the variability of ice extent in the Arctic Seas, smoothed by a five-year running mean procedure for 1933-2003: a) and b) show the Greenland and Barents Seas, respectively, in April; for August, c) shows the Greenland Sea, d) the Barents Sea, e) the Kara Sea, /) the Laptev Sea, g) the East Siberian Sea, and h) the Chukchi Sea.

Table 2.6. Statistical characteristics of "20-year" and "10-year" components of ice extent variation

Seas

Month

A20 103km2

^10, 103 km2

^20/^10

a20' 106 km4

106 km4

^20 (%)

^10 (%)

Greenland

IV

68.6

31.8

2.16

2353

506

12.2

2.6

Barents

IV

71.1

39.5

1.80

2528

780

10.6

3.3

Greenland

VIII

30.9

19.3

1.60

477

186

6.9

2.7

Barents

VIII

59.9

24.2

2.48

1794

293

10.3

1.7

Kara

VIII

60.9

37.0

1.65

1854

684

7.8

2.9

Laptev

VIII

19.2

26.0

0.74

184

338

1.9

3.4

East-Siberian

VIII

54.2

38.4

1.41

1469

737

12.6

6.3

Chukchi

VIII

12.4

18.8

0.66

77

177

3.6

8.3

Greenland + Barents + Kara

VIII

113.5

80.0

1.42

6435

3200

13.0

6.5

Laptev + East-Siberian + Chukchi

VIII

80.0

74.5

1.07

3200

2775

7.2

6.3

Note: rçio and ^20 indicate contribution to the total "20-year" and "10-year" variability, respectively.

Note: rçio and ^20 indicate contribution to the total "20-year" and "10-year" variability, respectively.

contribution of these cycles to the interannual variability of ice conditions in these seas and their areas (Gudkovich et al, 1972) is comparatively large; therefore, in the 1970s, a great deal of attention was devoted to their study in connection with development of ice forecasting methods. Studies by Volkov and Sleptsov-Shevlevich (1970, 1971) revealed the spatial-temporal structure of a "two-year" standing wave, whose loop was located in the Severozemelsky region, and its node in the vicinity of the New Siberian Islands. The variability of quasi-two-year anomalies in ice extent of the Siberian shelf seas was analyzed by Karklin (1977), and an assessment of the contribution to total ice extent variance, which changes from 20-50%, was carried out.

The publications of Maksimov (1960), Kovalev (1960), Volkov and Sleptsov-Shevlevich (1971), Gudkovich et al. (1970), and Karklin (1977, 1987) are devoted to investigation of a "7-year" cycle of ice extent changes. It was revealed that this variability is maximal in the eastern Laptev Sea (east of 125°E), where its range is 30-40% of the region's area. It was also observed that a "7-year" wave is gradually displaced from east to west traveling over 4-5 years from the Chukchi Sea to the Kara Sea, which partially explains the existence of opposite ice extent conditions between the seas of the western and eastern sectors of Eurasian Arctic.

The results obtained in these studies do not provide a complete understanding of the spatial and temporal effects of this cycle on the ice extent of the Arctic Seas. We analyzed this variability using the ice extent series of the Arctic Seas in August for the period 1933-1999. The filtration (weight) function proposed by Leith and Holloway (1958) was used to isolate 6-7-year variability (the cycle duration varies within 5-8 years; see Table 2.7), and to exclude 2-3-year variability as well as variability of 11

Table 2.7. Duration of short cycles and the number of cases of their occurrence during the period 1933-1999

Region

Cycle duration, years

4

5

6

7

8

Southwestern Kara Sea

-

2

4

1

-

Northeastern Kara Sea

1

2

3

1

-

Western Laptev Sea

-

1

4

2

-

Eastern Laptev Sea

-

3

1

3

-

Western East Siberian Sea

1

-

3

2

-

Eastern East Siberian Sea

1

2

-

2

1

Chukchi Sea

-

1

2

1

2

years or more from multiyear variability of ice extent. Table 2.7 shows that the cycle most often occurs for 5-6 years in the western regions of the Arctic Seas (from the Kara Sea to the western Laptev Sea), while in the eastern regions, the number of cycles lasting 6-7 years increases. In the total ice extent of the Arctic Seas, the 7-8-year cycles prevail.

The amplitude of the cycle is unstable and can change several times in each of the regions (Table 2.8). The maximum amplitudes are observed in the Laptev Sea. In the

Table 2.8. Amplitudes of 6-7-year cycles and their effects on multiyear variability of the Arctic Seas ice extent

Region

Amplitudes (thousand km2)

Contribution to dispersion (%)

Average

Maximum

Minimum

Southwestern Kara Sea

35.5

50.9

17.4

29

Northeastern Kara Sea

32.7

56.9

9.9

14

Western Laptev Sea

27.4

57.3

8.7

26

Eastern Laptev Sea

42.5

80.4

10.0

41

Western East-Siberian Sea

41.0

69.7

11.3

31

Eastern East-Siberian Sea

25.6

45.2

10.2

18

Chukchi Sea

27.5

39.1

10.4

31

Total sea-ice extent

145.5

243.3

65.2

32

course of a 6-7-year cycle, the ice extent in this sea can change by more than 50%. To the west and east of the Laptev Sea, the cycle amplitudes decrease.

The contribution of 6-7-year variability is significant and ranges from 14 to 41% (Table 2.8). The largest effect of a 6-7-year cycle is apparent in the ice extent variability of the New Siberian region (from the eastern Laptev Sea to the western East Siberian Sea) and of the Chukchi Sea. The cross-spectral analysis of ice extent for various regions at the frequency corresponding to a 6-7-year cycle showed this variability in the west and east of the Arctic Seas to occur in opposite phase, i.e., their character is close to a standing wave. Unlike this wave, the distribution of the phase difference at the frequency corresponding to a 2-3-year cycle testifies that this variability is manifested in the form of a two-nodal standing wave, with nodal zones passing across the eastern Laptev Sea and along the boundary between the Barents and the Kara Seas.

Was this article helpful?

0 0

Post a comment