Winter NAO in 6 GCMs. December 2010. Leading EOF of Surface Pressure. NAO is defined here as the leading EOF of surface pressure 20 o N-90 o N,120 o W-60 o E for Dec.,Jan., and Feb. NAO PDF. Control DJF09/10 NCEP-R1. Observed NAO DJF09/10: Dec. -2.19 Jan. -1.30 Feb. -3.03.