Analysis of Extreme Negative Arctic Oscillation Values and their Relationship to Southeast U.S. Cold Air Outbreaks

The Arctic Oscillation (AO) is a large-scale climate pattern characterized by sea level pressure variability in the polar region. The AO consists of a positive and negative phase, both having impacts on global climate. Its variability is greatest during the cold season, and negative AO values are believed to be associated with below normal temperatures in the Eastern United States. The purpose of this study is to determine whether extreme negative AO values are associated with significant cold air outbreaks in the Southeastern United States. Daily AO index data has been recorded since 1950. From this data, 23,100 AO index values were sorted from negative to positive. Within the lowest 100 daily AO index values (lowest 0.43%), there are eleven distinct time periods of four or more consecutive days. All eleven periods were analyzed. Minimum temperatures and departures from normal were examined for Atlanta, GA, Columbia, SC and Raleigh, NC. The events turned out to be either a record minimum temperature event, a prolonged cold air outbreak lasting for up to a week, or in some cases, both. It was noted that minimum temperatures tended to lag the AO by one to three days.