Climate change and teleconnection patterns: An analysis of temperature and flow regime trends over North America

Several studies have recently indicated that there has been a significant increase in global temperatures, especially in the Northern Hemisphere, over the past several decades. While this increase in temperature is consistent with predictions of Greenhouse warming, questions remain as to how this warming is/will be manifested. Toward this end, decadal trends in two of the principal teleconnection patterns, the Pacific North American Pattern (PNA) and the North Atlantic Oscillation are examined, and then related to the winter climate over North America. Preliminary results indicate that over the past 40 years, there have been significant upward trends in both the PNA and the NAO. These upward trends in the teleconnection indices is consistent with observed temperature trends over the Pacific Northwest and New England. Evidence of the impact of the changing flow regime on temperature trends is presented through an analysis of thickness trends over North America, with cooling over the past 50 years indicated over parts of northeastern Canada and Greenland. This relatively isolated cooling is located in a region of expected negative temperature anomalies for a positive NAO index. Furthermore, stratification of the NAO into its positive and negative phases reveals that the negative phase of the NAO is a much better predictor of wintertime temperatures over New England than the positive phase. Finally, data are presented indicating that the weather is becoming more extreme for a given NAO pattern, with recent negative phases producing significantly colder weather over New England than those occurring in the 50's and 60's.