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1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
Figure 10: Upper panel: Winter (December through March) index of the North Atlantic
Oscillation (NAO) based on the normalized difference between normalized sea-level pressure time series at Lisbon, Portugal and Stykkisholmur, Iceland. Lower panel: difference
in sea-level pressure between "high" and "low index" winters, as defined by +1.0 and
-1.0 standard deviations of the same NAO Index, respectively, based on data from 1900
onward. Contour interval 2 mb. From Hurrell (1995).