Centro de Geofísica (Geophysics Center) Departamento de Física (Department of Physics)

• Main Authors: António R. Tomé, Pedro M. A. Miranda, Campo Gr, Ed. C
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: NAO; variability; climate trends; Iceland; North Atlantic; North Atlantic oscillation
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.690.3651; http://www.dfisica.ubi.pt/%7Eartome/TomeEtalWRR2004.pdf

The North Atlantic Oscillation (NAO) is a major feature of the Northern Hemisphere climate system. The unprecedented trends it exhibited after the early 60’s led some authors to propose human induced climate forcing as a possible cause. The various NAO indices are not able to distinguish the variability associated to the magnitude strengthening/weakening of the action centers and the variability associated with the movement of these centers. Using the NCEP/NCAR reanalysis for the years 1958 till 1998 the positions of the Iceland low-pressure and of the Azores high-pressure systems were tracked down. With the geographic position of these two action centers and the corresponding pressure values, an