Decadal Climate Fluctuations in the Arctic

L. A. Mysak (Department of Atmospheric and Oceanic Sciences and Centre for Climate and Global Change Research, McGill University, Montreal, QC, Canada; phone (514) 398-3768; fax (514) 398-6115; Internet: mysak@zephyr.meteo.mcgill.ca); S. A. Venegas (Department of Atmospheric and Oceanic Sciences and Centre for Climate and Global Change Research, McGill University, Montreal, QC, Canada; phone (514) 398-7448; fax (514) 398-6115; Internet: silvia@arctic.meteo.mcgill.ca)

During the past two decades there has been considerable research on identifying the nature and causes of interannual and interdecadal climate variability in the Arctic through the analysis of various atmospheric, oceanic, sea ice and hydrological data sets. Due to the limited duration of the earlier records, especially those for sea ice concentration, many of these investigations focussed on interannual variability in the Arctic. However, with the availability of longer records it has become clear that the dominant signal of variability in the Arctic and subarctic has a decadal timescale. For example, the time expansion coefficients of the first empirical orthogonal function modes for sea ice concentration (SIC), sea level pressure (SLP), 500-hPa height and 850-hPa temperature each exhibit an oscillatory pattern since the 1960s, with a period of around 10 years.

In this talk we shall further elucidate the nature of this decadal-scale climate oscillation by presenting a combined complex empirical orthogonal function (CCEOF) analysis of 40 years of SIC and SLP data which span the Arctic poleward of 45 N. The analysis indicates that over most of the duration of this climate cycle, the ice cover anomalies are created by the atmosphere ( ie, are wind generated), and change through ocean advection. However, we suggest that during relatively short intervals the atmosphere rapidly responds to the changing sea ice conditions, which results in reversals of the sign of the North Atlantic Oscillation (NAO) index. The evolving patterns of the SIC and SLP anomalies over the 10-year climate cycle can be succinctly described in terms of a feedback loop, which has remnants of, but is quite distinct from that proposed some time ago by Mysak and his collaborators.