Fig. 8-11. Top: Winter index of the North Atlantic Oscillation (1895-1983) based on the mean normalized pressure difference between Ponta Delgadas, Azores and Akureyri, Iceland. Bottom: Normalized winter mean pressure anomaly for the region 60-70°N, 30-65°W from 1900 to 1979. Dashed lines represent smoothed data using a 1-4-6-4-1 low-pass filter (from Rogers, 1984).