Figure 2.30: December to
March North Atlantic Oscillation (NAO) indices, 1864 to 2000, and Arctic Oscillation
(AO) indices, 1900 to 2000, updated from Hurrell (1995) and updated from Thompson
and Wallace (2000) and Thompson et al. (2000b), respectively. The indices were
normalised using the means and standard deviations from their common period, 1900
to 2000, smoothed twice using a 21-point binomial filter where indicated and then
plotted according to the years of their Januarys.
