dipolar structure in SAT and sea-ice anomalies in the three (also ENSO) winters (1972/73,1982/83, and 1991/92) can be characterized mainly by the first EOF mode (see Fig. 7 of Wang et al. 1994; Mysak et al. 1996).
The third mode (containing 17.2% of the total variance) may explain the ENSO-induced SAT pattern in the Arctic region. The sea-ice anomalies in Hudson Bay (subregion 3) and Baffin Bay, David Strait and the Labrador Sea (subregion 4) are out of phase with sea-ice anomalies in the Beaufort and Chukchi Seas (subregion 2) and the East Siberian and Laptev Seas (subregion 7), while the other subregion (1, 5, 6, and 8) have no significant difference from the mean (Fig. 1, lower). The spatial pattern is consistent with the SAT anomaly pattern as described in Fig. 9 of Wang et al.
(1994).
To verify the NAO and ENSO modes, the 90-year time series of sea-ice area anomalies for subregions 4 and 5 are shown in Fig. 2 (upper panel). There is some uncertainty in the data before the World War ? (1945). The peak anomalies in the two subregions generally occurred in different timing, or out of phase. This indicates the impact of the NAO (seesaw) effect on these two regions.
Figure 2 (lower panel) also shows the 90-year time series of sea-ice area anomalies for subregions 1, 2, and 4. From 1950s, the peak anomalies in subregions 4 and 2 were generally out of phase: the higher in the Labrador Sea and Hudson Bay, the lower in the Beaufort and Chukchi Seas, indicating the ENSO mode at work, in response to the SAT ENSO mode (Fig. 9 of Wang et al. 1994).
The Monte Carlo simulated correlation coefficients between the first SAT and sea-ice modes (NAO mode) in winter and spring are 0.5 and 0.59, respectively (the significance levels are 0.33 and 0.36, respectively), indicating the sea-ice cover anomaly strength positively relates to the SAT strength. The coefficients between the third SAT and the third sea-ice mode (ENSO mode) are -0.37 in summer (the significance level is 0.34), indicating lower-than-normal sea-ice cover in the Beaufort and Chukchi Seas during the ENSO-induced higher-than-normal SAT in the region. To give a support, the correlation between the Southern Oscillation index (SOI) and the third sea-ice mode is 0.31 which is below the significance level (0.38), but is the highest among the coefficients between the SOI and the first two sea-ice modes.
4. CONCLUSIONS AND DISCUSSION
The results from the analysis of the 90-year sea-ice cover in the Arctic region has been shown only, due to the length limit of this note, although the same analyses were also applied to the SLP and SAT fields. The two physical modes (modes 1 and 3, containing 21% and 17.2% of the total variance, respectively) of the sea-ice anomalies were identified to be related to the corresponding NAO- and ENSO-induced SAT modes.
In the Arctic climate change research program initiated by the Frontier Research Program for Global Change (FRPGC,/ International Arctic Research Center (IARC), the intensive coupled ice-ocean modeling in response to atmospheric forcing should be conducted to reveal the response of sea ice and ocean circulation to the NAO and ENSO modes identified in this study. As the program progresses, more understanding of the Arctic climate system will be achieved.
ACKNOWLEDGEMENTS. This study was supported by FRPGC/IARC and JAMSTEC to JW. JW thanks Ms. A van der Baaren for helping some of the data processing.
REFERENCES
Mysak, L.A., R.G. Ingram, J. Wang and A.van der Baaren, 1996. The anomalous sea-ice extent in Hudson Bay, Baffin Bay and the Labrador Sea during three simultaneous NAO and ENSO episodes. Atmosphere-Ocean, 34: 314-343.
Walsh, J.E. and C.M. Johnson, 1979. An analysis of Arctic sea ice fluctuations, 1953-77. J. Phys. Oceanogr. 9: 580-591.
Wang, J., L.A. Mysak and R.G. Ingram, 1994. Interannual variability of sea-ice cover in Hudson Bay, Baffin Bay and the Labrador Sea. Atmosphere-Ocean 32: 421-447 .
Wang, J., A. van der Baaren, L.A. Mysak, 1995. A principal component analysis of gridded sea-level pressure, surface air temperature, and sea-ice concentration of the Arctic region, 1953-1993. C2GCR Rep. No. 95-4, McGill Univ., 18 pp + figures + Fortran programs.
