[1] Trends and interannual variations of the Canadian High Arctic aerosol record at Alert, Canada (82.5°N), from 1981 to 2007 are investigated and attributed to the influences of anthropogenic emissions and long-range transports. Sulfate and black carbon (BC) atmospheric mass concentrations declined from the mid 1980s to the late 1990s but have been relatively steady since. These tendencies are closely associated with those of the anthropogenic emissions of Eurasia (Europe and the Asian part of the former Soviet Union) and North America (United States and Canada). Interannual variations correlate with two indices derived from the 700 hPa geopotential heights. Variations in the emissions and the geopotential height indices can be used to reproduce up to 75% of the variations of the observed Arctic sulfate and BC mass concentrations. Over the 27 years of observational record, the relative contribution to sulfate and BC at Alert from Eurasia has decreased from more than 90% to about 75%. During the same time, the contributions from North American emissions has increased from less than 10% to about 25%. The increasing influence from North America was due to the faster reductions of sulfur and black carbon emissions in Eurasia during the period of these observations.
The decadal covariability of northern wintertime land surface temperature and 500-hPa geopotential anomalies is examined using the National Centers for Environmental Prediction–National Center for Atmospheric Research and the Twentieth-Century Reanalyses over the twentieth century and a 996-yr preindustrial climate simulation from the Canadian Earth System Model. Based on the reanalysis data, the covariability is dominated by two leading maximum covariance analysis (MCA) modes. MCA1 is characterized by temperature anomalies over most of Canada, the eastern United States, Mexico, and Eurasian mid- to high latitudes, accompanied by anomalies of opposite sign elsewhere over northern landmasses. MCA2 features temperature anomalies over most of North America, Eurasia, and Greenland with opposite anomalies elsewhere. In the upper troposphere the synoptic vorticity fluxes reinforce the anomalous circulation, while in the lower troposphere advection by the anomalous mean flow offsets the eddy forcing and maintains the decadal temperature perturbation. The MCA1-associated variability has a broad spectrum over decadal–interdecadal time scales, while the MCA2-related variability has a significant power peak around 20 yr. The change of temperature and geopotential trends around 1990 tends to be a decadal-scale shift in winter and has significant features of the leading mode of the decadal covariability. The climate model has broadly similar decadal covariability, including the leading MCA patterns as well as the temporal evolution of the patterns. The decadal temperature and geopotential anomalies primarily covary with the North Atlantic Oscillation but also with the variability of the North Pacific index, while the Southern Oscillation index variability tends to be the least important predictor for the northern decadal temperature and geopotential anomalies.
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