Figure 2.31: The High Latitude
Mode (Kidson, 1988) or Antarctic Oscillation (AAO), defined as the first orthogonal
pattern (covariance eigenvector of the Southern Hemisphere monthly surface pressure,
January 1958 to December 1997) (Gong and Wang, 1999c; Kiladis and Mo, 1999). Data
from NCAR/NCEP Reanalysis (Kalnay et al., 1996). Note that Thompson and Wallace
(2000) use 850 hPa height to define their AAO.