IGOR POLYAKOV

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Arctic decadal and interdecadal variability

I. Polyakov, U. Bhatt, R. Colony, A. Makshtas, D. Walsh (all IARC/UAF)
G. Alekseev, R. Bekryaev, V. Karklin, A. Yulin (all AARI)
M. Johnson (IMS/UAF)

[Details of this research may be found in our papers
click on links below to download pdfs:
Polyakov and Johnson, 2000;
Polyakov et al., 2002, 2003a, b
Vinje et al., 2002, and on our web pages]

Two distinct warming periods from 1920 to 1945, and 1975 to present stand out for the arctic region north of 62N (Figure 1). Compared with global and hemispheric temperature rise, the high-latitude temperature increase was stronger in the late 1930s-early 1940s than in recent decades. A wavelet transform displays strong low-frequency variability on the decadal and multi-decadal time scales with the strongest signal at low-frequency oscillation (LFO) periods (Figure 1). The enhanced warming observed in the 1930-40s and in recent decades, and the strong cooling in the Arctic in the 1960-70s and prior to the 1920s may be associated, at least partly, with the positive (warm) and negative (cold) phases of the LFO superimposed on the background warming trend. The surface-air pressure time series shows fluctuations similar to what one might expect from adding decadal variability to the multi-decadal LFO signal with higher values prior to the 1900s and in the 1940s - mid-1980s (negative LFO phases) and lower values in the 1900-30s and mid-1980s - present (positive LFO phases) [Polyakov et al., 2002, 2003a].

This variability resembles a machine ''pushing'' alternating pulses of warm and cold air from the North Atlantic into the Arctic every 25-40 years (similar ``mechanical'' terminology has been widely used in Russian climate studies). Indeed, in the 1990s associated with a positive (warm) LFO phase, the number of cyclones penetrating into the Arctic from the North Atlantic has increased carrying heat from lower latitudes poleward. Propagation of the LFO signal may be clearly seen in the correlation map between air temperature from arctic coastal stations and the North Atlantic Oscillation (NAO) index which is characterized by a north-to-south oriented dipole air pressure structure over the Atlantic, with maximum correlations in the near-Atlantic region, decaying toward the North Pacific (Figure 2).

The Arctic responds to the low-frequency intrusions of the Atlantic warm/cold air mass anomalies with alternating regimes of weakened/strengthened anticyclonic Beaufort Gyre circulation, and intensified/suppressed cyclonic circulation in the eastern Arctic. In this dipole-like structure, a zero vorticity contour separates two large-scale centers of atmospheric circulation. Calculated for the last 50 years, atmospheric vorticity for the eastern Arctic is presented in Figure 2).

The rapid reduction of arctic ice thickness observed in the 1990s in the central Arctic where Scientific Ice Expeditions (SCICEX) data were released [Rothrock et al., 1999] may be one manifestation of the intense atmosphere and ice cyclonic circulation regime. A coupled ice-ocean model captures the substantial ice reduction in the 1990s over the SCICEX area (compare 1.0 m from the model with 1.30 m from observations, Figure 3c) [Polyakov and Johnson, 2000]. However, the simulated ice thickness averaged over the whole Arctic Ocean including the Greenland and Barents seas does not exhibit a quasi-linear decline like in the SCICEX area, but is rather a complex superposition of decadal and multi-decadal modes of variability and a slight downtrend (Figure 3b). The resemblance between variability of the ice thickness (Figure 3b) and the vortivity index ( Figure 3a) is striking, attesting to a close connection between large-scale atmospheric circulation pattern and arctic ice conditions.

The Arctic Ocean has an important role in the global thermohaline circulation. Following the inverse barometer rule, sea level is elevated during positive (cyclonic) LFO phases and depressed during negative (anticyclonic) phases with possible sequences for the water exchange between the Arctic Ocean and North Atlantic. The correlation between the NAO index and PC1 (time series associated with EOF1) of sea level variations ([Dvorkin et al., 2000]) is consistent with the correlation pattern of air temperature and NAO index, with maximum correlations in the near-Atlantic region (Figure 2). Bottom water formed in the Greenland Sea is an important water mass for the the global ocean, and it's formation rate has slowed considerably in the recent decades [Dickson et al., 1996]. This decrease may be explained in the context of the shift from negative to positive phases of these multi-decadal fluctuations (see for details our web page: http://www.frontier.iarc.uaf.edu/~igor/convec/index.php).

References

Delworth, T. L., and M. E. Mann, Observed and simulated multidecadal variability in the Northern Hemisphere, Climate Dynamics, submitted.

Dickson, R., J. Lazier, J. Meincke, P. Rhines, and J. Swift, Long-term coordinated changes in the convective activity of the North Atlantic, Prog. Oceanogr., 38, 241-295, 1996.

Dvorkin, E. N., S. Yu. Kochanov, and N. P. Smirnov, The North Atlantic Oscillation and long-term changes in the level of the Arctic Ocean, Russian Meteorology and Hydrology, 3, 59-64, 2000.

Polyakov, I., and M. A. Johnson, Arctic decadal and inter-decadal variability, Geophys. Res. Lett., 27, 4097-4100, 2000. [download PDF file]

Polyakov, I. V., G. V. Alekseev, R. V. Bekryaev, U. Bhatt, R. L. Colony, M. A. Johnson, V. P. Karklin, A. P. Makshtas, D. Walsh, and A. V. Yulin, Observationally based assessment of polar amplification of global warming, Geophys. Res. Lett., 29, 1878, doi:1029/2001GL011111, 2002.

Polyakov, I. V., R. V. Bekryaev, G. V. Alekseev, U. Bhatt, R. L. Colony, M. A. Johnson, A. P. Makshtas, and D. Walsh, Variability and trends of air temperature and pressuremin the maritime Arctic, 1875-2000, J. Climate, 16(12), 2067-2077, 2003a. [download PDF file]

Polyakov, I.V., G. V. Alekseev, R. V. Bekryaev, U. Bhatt, R. L. Colony, M. A. Johnson, V.P. Karklin, D. Walsh, and A. V. Yulin, Long-term ice variability in Arctic marginal seas. J. Climate, 16(12), 2078-2085, 2003b. [download PDF file]

Proshutinsky, A. Yu., and M. A. Johnson, Two circulation regimes of the wind-driven Arctic Ocean, J. Geophys. Res., 102, 12493-12514, 1997.

Rothrock, D. A., Y. Yu, and G. A. Maykut, Thinning of the arctic sea-ice cover, Geophys. Res. Lett., 26, 3469-3472, 1999.

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Last modified: May 06, 2004. 14:57:34 pm