Atmosphere

• Main Authors: J. Richter-menge, J. Overl, E. Hanna, M. J. J. E. Loonen, A. Proshutinsky, V. Romanovsky, D. Russell, Van Bogaert, R. Armstrong, L. Bengtsson, J. Box, T. V. Callaghan, B. Ebbinge, O. Grau, R. Przybylak, J. Walsh
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: Arctic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.630.2403; http://www.maartenloonen.nl/literatuur/arcticreportcard2007.pdf

The annually averaged Arctic Oscillation index (AO, a measure of the strength of circumpolar winds) was slightly positive in 2006, continuing the trend of a relatively low and fluctuating index which began in the mid-1990s (Figure A1). This follows a strong, persistent positive pattern from 1989 to 1995. The current characteristics of the AO are more consistent with the characteristics of the period from the 1950s to the 1980s, when the AO switched frequently between positive and negative phases. Initial data from 2007 shows a positive AO pattern. Figure A1. Time series of the annually-averaged Arctic Oscillation Index (AO) for the period 1950- 2006 based on data from the website www.cpc.ncep.noaa.gov. (Courtesy of I. Rigor) Surface Temperatures and Atmospheric Circulation In 2006 the annual surface temperature over land areas north of 60 ° N was 1.0°C above the mean value for the 20th century (Figure A2). The surface temperature in this region has been consistently above the mean since the early 1990s. Figure A2 also shows warm temperatures in the 1930s and early 1940s, possibly suggesting a longer-term oscillation in climate. However, a detailed analysis shows different proximate causes for the 1930s compared to recent maxima. The early warm and cold periods are associated with internal variability in high-latitude circulation patterns, while the recent warm temperatures have an anthropogenic component