Michelle L'Heureux et al., GRL 37 (2010), Unusual extremes in the negative phase of the Arctic Oscillation during 2009

Geophysical Research Letters, 37 (2010) L10704; doi: 10.1029/2010GL043338

Unusual extremes in the negative phase of the Arctic Oscillation during 2009

Unusual extremes in the negative phase of the Arctic Oscillation during 2009

Michelle L'Heureux¹, Amy Butler¹, Bhaskar Jha², Arun Kumar¹ and Wanqiu Wang¹

Abstract

During 2009, the Arctic Oscillation (AO) index was exceptionally negative during four months, which was unprecedented in a 60-year record extending back to 1950. The negative phase of the AO corresponded to a nearly zonally symmetric anomaly of temperature and pressure over the middle-to-high latitudes of the Northern Hemisphere. Consistent with the strong negative phase of the AO, below-average temperatures were also observed over North America and parts of Eurasia during June, July, October, and December 2009. Although the impact of the AO on 2-meter temperatures was near zero when averaged over the entire hemisphere (20°–90°N), positive anomalies were evident in the residual pattern of observed temperature. The residual, along with observed below-average stratospheric temperatures, are consistent with anthropogenic climate projections. The possible implication of the recent negative values on the long-term AO trend is also discussed. 

Received 24 March 2010; accepted 20 April 2010; published 21 May 2010. 

¹Climate Prediction Center, NCEP, NWS, NOAA, Camp Springs, MD, U.S.A.

²WYLE Information Systems, Camp Springs, MD, U.S.A.

Link:  http://www.agu.org/pubs/crossref/2010/2010GL043338.shtml