The North Atlantic Oscillation: Past, present, and future

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Visbeck, Martin, Hurrel, J. W., Polvani, L., Cullen, H. M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: National Academy of Sciences 2001
• Subjects: Arctic; Greenland; Iceland; North Atlantic; North Atlantic oscillation
• Online Access: https://oceanrep.geomar.de/id/eprint/5880/; https://oceanrep.geomar.de/id/eprint/5880/1/12876.full.pdf; https://doi.org/10.1073/pnas.231391598

The climate of the Atlantic sector exhibits considerable variability on a wide range of time scales. A substantial portion is associated with the North Atlantic Oscillation (NAO), a hemispheric meridional oscillation in atmospheric mass with centers of action near Iceland and over the subtropical Atlantic. NAO-related impacts on winter climate extend from Florida to Greenland and from northwestern Africa over Europe far into northern Asia. Over the last 3 decades, the phase of the NAO has been shifting from mostly negative to mostly positive index values. Much remains to be learned about the mechanisms that produce such low frequency changes in the North Atlantic climate, but it seems increasingly likely that human activities are playing a significant role. When the North Atlantic Oscillation (NAO) is in its positive phase, low-pressure anomalies over the Icelandic region and throughout the Arctic combine with high-pressure anomalies across the subtropical Atlantic to produce stronger-than-average westerlies across the midlatitudes. During a positive NAO, conditions are colder and drier than average over the northwestern Atlantic and Mediterranean regions, whereas conditions are warmer and wetter than average in northern Europe, the eastern United States, and parts of Scandinavia (Fig. 1 top). Walker and Bliss (1) were among the first to recognize and study this pattern of climate anomalies, which is most pronounced during boreal winter (December through March).