IPCC Fourth Assessment Report: Climate Change 2007 Climate
Change 2007: Working Group I: The Physical Science Basis  3.6.4
The North Atlantic Oscillation and Northern Annular Mode  The
only teleconnection pattern prominent throughout the year in the
NH is the NAO (Barnston and Livezey, 1987). It is primarily a
north-south dipole in sea level pressure characterised by
simultaneous out-of-phase pressure and height anomalies between
temperate and high latitudes over the Atlantic sector, and
therefore corresponds to changes in the westerlies across the
North Atlantic into Europe (Figure 3.30). The NAO has the
strongest signature in the winter months (December to March)
when its positive (negative) phase exhibits an enhanced
(diminished) Iceland Low and Azores High (Hurrell et al., 2003).
The NAO is the dominant pattern of near-surface atmospheric
circulation variability over the North Atlantic, accounting for
one third of the total variance in monthly MSLP in winter. It is
closely related to the NAM, which has si