A new NAO index is presented here using homogenized surface pressure data from Reykjavik and Gibraltar (for November to March) and Reykjavik and Ponta Delgada (for April to October). This index suggests that the positive trend in recent years is not unprecedented, as the early 20th century was also a period of persistently positive NAO values. The relationship between the secular warming trend and the influence of the NAO on near-surface temperatures over the North Atlantic region and surrounding land masses is examined on a seasonal basis using standardized temperature anomalies since 1900. The near-surface temperature field separates into two independent modes, which we designate a “warming” mode and dynamic (“NAO”) mode, with distinct seasonal cycles.
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.