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.