FIGURE A2.1. (a) Daily amplitudes of the Arctic Oscillation (AO)
the North Atlantic Oscillation (NAO), and the Pacific-North
American (PNA) pattern. The pattern amplitudes for the AO, (NAO,
PNA) are calculated by projecting the daily 1000-hPa (500-hPa)
height anomaly field onto the leading EOF obtained from
standardized time- series of daily 1000-hPa (500-hPa) height for
all months of the year. The base period is 1979–2000. (b-d)
Northern Hemisphere mean and anomalous 500-hPa geopotential
height (CDAS/Reanalysis) for selected periods during the month
are shown in the remaining 3 panels. Mean heights are denoted by
solid contours drawn at an interval of 8 dam. Dark (light)
shading corresponds to anomalies greater than 50 m (less than
-50 m). Anomalies are calculated as departures from the 1979–95
base period daily means.